| Author |
Year |
Title |
Source |
Sort |
Language |
Abstract |
Descriptors |
Remarks |
Alla, N.;
Bérest, P. et al. |
1993 |
In situ tests in brine-filled caverns |
Proc. 3rd. Conf. Mechanical Behavior of Salt,
Palaiseau, 14.-16.09.93, pp.445-454 |
Paper |
|
Mechanical properties of the rock mass surrounding
an underground salt cavern can be measured through different
tests performed in brine filled caverns. Dynamic and static
tests are discussed and a nine years long static test is fully
described. |
In-situ
tests |
- |
Allemandou, X.;
Dusseault, M. B. |
1993 |
Procedures for cyclic creep testing of salt
rock, results and discussions |
Proc. 3rd. Conf. Mechanical Behavior of Salt,
Palaiseau, 14.-16.09.93, pp.193-204 |
Paper |
|
In the experimental research we present here,
we demonstrate that sampling damage causes opening of grain
boundaries and generation of sufficient microfractures as
to significantly affect mechanical properties. We show through
CAT-scan experiments that sampling damage can be healed and
annealed under a hydrostatic stresses. We demonstrate that
unconfined and confined compressive strength of salt rock
are strongly influenced by this healing process. Finally,
we validate a test procedure, and we prove that transient
creep of salt rock can be evaluated using a series of compressional
and extensional cycles. Experiments were conducted under various
stress deviator and mean stress levels from one cycle to another;
the results obtained are consistent with our interpretation
of annealing, and have led to the development of a phenomenological
model for salt rock. |
Creep behavior |
- |
Allison, H. G.;
Ford, E. C. |
1988 |
The first plug is the key to a good plug and
abandonment or liner job |
SMRI Spring Meeting, Mobile, 25.04.88 |
Paper |
|
The plugging and abandonment of caverns and
the cementing of a liner into a leaking wellbore have the
same critical first step: how to establish the first plug
to work against. This paper will discuss five methods that
are being used, these are:
1) Inflatable Packer
2) Umbrellas or oversized cement baskets
3) Section Milling and inflatable packers
4) Lightweight Cement using perlite additives
5) Foamed Lightweight Cements
The success and the cost effectiveness of each method is dependent
upon the borehole geometry, and these considerations will
also be discussed. |
Borehole
seal |
- |
Anthony, T. R.;
Cline, H. E. |
1974 |
Thermomigration of liquid droplets in salt |
Proc. 4th. Symp. on Salt, Vol. 1, pp.313-320 |
Paper |
|
The salt mine burial of fission waste products
resulting from the reprocessing of spent fuel elements is
now planned as a permanent means of disposal of these highly
radioactive wastes. Although salt mine burial is apparently
the best method of disposal the vigorous self-heating of these
waste products leads to some potential problems. Natural salt
formations regularly contain small brine inclusions which
will migrate up the thermal gradients generated by the self-heating
of the waste products. The resulting inflow of water into
the nuclear waste crypts is undesirable because water vapor
may accelerate waste container corrosion and/or lead to fission
product contamination of currently unused sections of the
salt mine. In addition, contaminated vapor-liquid biphase
droplets generated on the walls of the nuclear waste crypt
are capable of dispersing fission products throughout the
salt formation since these unusual inclusions migrate down
thermal gradients, in contrast to the normal thermomigration
of simple gas or liquid droplets up thermal gradients in salt.
By considering viscous gas flow, vapor diffusion, liquid diffusion,
evaporation and condensation, and liquid currents driven by
surface tension gradients, the odd thermomigration behavior
of the vapor-liquid droplets observed in the present investigation
is explained. It is concluded that a modest dispersal of radioactive
wastes may occur in the salt formation. However, because of
droplet trapping by the grain boundaries in the salt, the
escape of radioactivity to the outside environment is unlikely
even on a geological time scale. |
Permeability of rock salt |
- |
| Arnold, W.; Förster, S. et al. |
1974 |
In situ investigations of fracturing in salt
cavities for determining stress components |
9th World Oil Congress, Tokyo, 1974, PD21 (3),
pp.89-96 |
Paper |
|
Knowledge of the state of stress in salt rocks
plays an important role in dimensioning the size of cavities
and the pressure load in underground storage. By laboratory
tests the questions and problems occurring in them cannot
be solved clearly. Therefore, in situ tests are necessary
in different depths. Field tests are reported. wherein salt
rock boreholes gas pressure was produced up to fracturing
of the originally impermeable rocks. Connections appear in
outline between the mechanical strength of the salt rocks,
the presence of so-called etching pits, the strain behavior
and the pressures necessary for the formation of fracturing
in salt rocks in situ. |
Hydrofracturing |
- |
Aubertin, M.;
Gill, D. E. et al. |
1991 |
An internal variable model for the creep of
rock salt |
Rock Mech. Rock Eng. 24 (1991), pp. 81-97 |
Journal Article |
|
The creep strain rate e of rock salt, like
that of other ductile crystalline materials, can be described
by a power law equation of the type ea(oa)n where the active
stress oa is the difference between the total deviatoric applied
stress o and an internal stress oi. In this paper, the origin
and the nature of this internal stress, which develops during
inelastic deformation of the material, are discussed. It is
shown that this internal stress can serve as an internal (or
state) variable in the constitutive model of rock salt, which
reflects the microstructure evolution of the material under
the competitive action of hardening and recovery mechanisms.
An analysis of experimental data, both our own and those taken
from the literature, demonstrates that such a law is able
to correctly reproduce rock salt creep test results in the
steady-state domain. The proposed model is in accordance with
the macroscopic and microscopic behavior of salt, and with
direct measurements of the internal stresses made by others
on this material. |
Creep behavior |
- |
Aufricht, W. R.;
Howard, K. C. |
1961 |
Salt characteristics as they affect storage
of hydrocarbons |
J. Petrol. Technol. (1961) 8,. pp.733-738 |
Journal Article |
|
Results of laboratory tests, field tests and
field observation of salt characteristics pertinent to either
the storage of hydrocarbons or the disposal of industrial
wastes are given. Of particular significance is the indication
that under many conditions dry salt may be sufficiently permeable
to allow appreciable flow of non-aqueous fluids. This flow
appears to occur along crystal boundaries and cleavage planes
and through bands of impurities, including dehydrated shales
or mudstones. Present data indicate that water, even in very
small quantities, materially affects these characteristics.
The variation and the presence or absence of permeability
appear to be a function of (1) the type and amount of impurities
(including shale), (2) the crystalline structure and cleavage
planes, (c) the confining or overburden pressure and (4) water
content. Additional study of these properties will be required
before an accurate evaluation of the feasibility of storage
or disposal under various conditions can be made. The amount
and effect of moisture content are particularly important,
and additional study of both the amount and effect of in situ
moisture is needed. |
Permeability of rock salt |
- |
Baes, C. F.;
Gilpatrick, L. O. et al. |
1983 |
The effect of water in salt repositories, final
report |
Oak Ridge : Oak Ridge National Laboratory,
ORNL-5950 |
Report |
|
Additional results confirm that during most
of the consolidation of polycrystalline salt in brine, the
previously proposed rate expression applies. The final consolidation,
however, proceeds at a lower rate than predicted. The presence
of clay hastens the consolidation process but does not greatly
affect the previously observed relationship between permeability
and void fraction. Studies of the migration of brine within
polycrystalline salt specimens under stress indicate that
the principal effect is the exclusion of brine as a result
of consolidation, a process that evidently can proceed to
completion. No clear effect of a temperature gradient could
be identified. A previously reported linear increase with
time of the reciprocal permeability of salt-crystal interfaces
to brine was confirmed, though the rate of increase appears
more nearly proportional to the product of dDP rather than
dDP² (d is the uniaxial stress normal to the interface
and DP is the hydraulic pressure drop). The new results suggest
that a limiting permeability may be reached. A model for the
permeability of salt-crystal interfaces to brine is developed
that is reasonably consistent with the present results and
may be used to predict the permeability of bedded salt. More
measurements are needed, however, to choose between two limiting
forms of the model. |
Inter-
dependence
rock stresses – permeability |
- |
| Battelle Ingenieurtechnik GmbH et al. |
1995 |
Bestimmung des Diffusions- und Permeabilitätsverhaltens
von Wasserstoff in Steinsalz und kompaktiertem Salzgrus
[Determining diffusion and permeability behavior of hydrogen
in rock salt and compacted salt fines] |
Battelle Ingenieurtechn. GmbH, BMBF-Förderkennzeichen
02 E 8492/3 u. 02 E 8462/9 |
Report (Abstract) |
|
It must be expected that repositories for radioactive
wastes situated in salt rock formations will, in certain zones,
generate and release hydrogen. It must therefore be guaranteed
to ensure long term integrity of the repository that this
does not represent a hazard. In order to be in the position
to make reliable statements concerning the location or transport
of the hydrogen, it is necessary to acquire data on the permeation
and diffusion behavior of salt rock. To achieve this, a number
of model salt cores were prepared using salt fines during
which the following parameters were varied: compaction density
(porosity), compaction time, compaction pressure, mineralogical/chemical
composition, grain size, moisture and temperature. These cores
were then tested for hydrogen permeability and diffusion.
In order to allow comparisons with natural salt rock, a number
of salt cores were also investigated.
In order to prepare the test cores and to perform the comprehensive
permeability and diffusion measurements under various parameters,
a number of suitable test apparatus were constructed.
The tests were carried out using salt fines from the former
Asse salt mine taken at various depths (Staßfurt and
Leine series) and from the Bernburg pit (Leine salt rock).
The cores tested were for the most part recovered from the
Asse salt mine (Staßfurt series).
In order to quantify the various influential parameters, the
salt specimens were analyzed for chemical and mineralogical
composition, grain distribution and their water content and
absorption isotherms were determined.
In preparatory tests a number of different techniques were
reviewed in connection with achieving diffusion-tight clamping
of the salt specimens and the influence of the specimen diameter
and the salt aggregate size on the permeability behavior.
The results were used to perform the main tests using both
original cuttings (recovered from a partial road header) as
well as strained original material (< 10 mm) with in-part
modification of anhydrite content.
The permeability tests on the salt fines samples were performed
while varying type of salt, porosity (compaction density),
mineralogical composition and time. Insodoing the permeability
was found to be in a range of 10-12 m² and 10-23 m².
It was found that the salt dampness, the anhydrite and polyhalite
contents, and the size of the grains had the most influence
on reducing permeability over time (with appropriate overburden
pressure) as well as with falling porosity.
Similarly the temperature of the compaction had a greater
than negligible influence on the permeability behavior of
the specimens over time. In particular, the specimens compacted
hot had a major difference in their pore structure (smaller
pore radii, larger access porosity) than did those compacted
cold. Also the diffusion behavior of the hot compacted specimens
was considerably different to the cold compacted, even with
the same permeability.
The experimentally proven connection between porosity and
permeability allows two ranges to be identified. In the total
porosity range between 7% and 1.5% the permeability drops
exponentially from approx. 1·10 to the power of 13
m² to approx. 5·10 to the power of 17 m².
The influence of the type of salt as well as salt dampness
and mode of preparation (cold or hot compacted) has a virtually
negligible effect in this range. Only those samples prepared
with hygroscopic salt drawn from 490 m and 700 m depths were
found to have a temporal permeability drop of up to four powers
of ten down to the lower permeability detection level within
only a few days in the porosity range between 1.5% and 5%.
The specimen porosity after the measurement was found to be
still in the order of 2%.
In the case of all salt types in the porosity range of <
1.5% the influence of all the above named parameters was found
to be greater than negligible. Below this porosity the permeability
of the salts with low anhydrite content fell dramatically
down to the lower detection limit of k = 8·10-23 m2.
The decisive factor determining the permeability of the porous
material is the accessible porosity of the flow medium. In
order to determine the accessible porosity a number of methods
were investigated. Determining the accessible porosity and
comparing this with the overall porosity shows that the period
of compaction and the pressure of compaction have a decisive
influence on the ratio on these two pore factors in compacted
salt fines. In the case of samples prepared with low compaction
pressure and long compaction time the difference between total
and accessible porosity is a great deal lower than those specimens
compacted at high pressure.
Long term tests and an overburden pressure of 200 bar (creep
compaction) allows a differentiation between samples with
larger k <10-15 m2) and lower initial permeability. In
the case of higher initial permeability (e.g. low compaction
density, large porosity) the influence on the overburden pressure
on the temporal permeability reduction is low - depending
upon type of salt. However, the lower the initial permeability
the larger the temporal permeability falls whereby this also
depends on type of salt and salt moisture. In the case of
intensively dried salt cores the influence on the overburden
pressure on the temporal permeability drop is minor even for
lower values of initial permeability.
Within the permeability measurements the influences resulting
from the method of evaluation (Darcy equation) such as slip
flow, turbulent effects and pore structure, were investigated
as was their influence on the accuracy of the permeability
measurement. The deviations resulting from the evaluation
method between the measured "apparent" and the "true" permeability
are identifiable by suitable tests yet play only a subordinate
role compared with the influential factors referred to above.
During the overall project over 400 salt core samples were
subjected to permeability testing.
The testing of diffusion was undertaken on an apparatus with
open, semi-open and closed systems using nitrogen and hydrogen
as measurement gases. The system differences refer to the
degree of freedom of the gas located on both sides of the
salt specimen core in the hydrogen and nitrogen circuits.
The test conditions were adapted to the conditions found in
the salt mine.
The objectives of the diffusion tests were to arrive at statements
concerning the value of hydrogen diffusion currents and to
quantify the dependence of diffusion on permeability.
The transport of material as a result of a concentration gradient
is predominantly by Fick's diffusion. The influence of molecular
motion after Knudsen is negligible. This is apparent if one
considers the differences between the effective binary diffusion
coefficient D12 and the Knudsen coefficient Dkn,1. At a gas
pressure of only 1 bar the binary diffusion coefficient is
already smaller than the Knudsen coefficient by a factor of
10. As gas pressure rises the effective binary diffusion coefficient
falls hyperbolically. Diffusion is always dependent upon the
larger resistance (lower coefficient of transport).
The results of the diffusion test show that the diffusion
behavior of the salt samples can vary greatly despite having
the same permeability. In the case of samples with a large
Klinkenberg factor (small pore diameters), a larger effective
binary diffusion coefficient was measured than on samples
with a smaller Klingenberg factor but with the same permeability.
Furthermore, tests were made to determine which transport
mechanism was dominant and from which pressure gradients upwards
the material transport by permeation dominated material transport
by diffusion. In practice it can be assumed that from a pressure
gradient pe - pa > 1 bar onwards for permeabilities of > 10-18
m2 the diffusive fraction on the overall transportation of
material is negligible.
The diffusion current and the product of the diffusion coefficient
and gas pressure De·p is only slightly dependent upon
the gas pressure in a pressure range of 1.2 to 10 bar in the
case of the salt specimens tested. In the case of the salt
samples with the same permeability the different diffusion
coefficients result from the different pore structure.
Effective binary diffusion coefficient of between 1·10-7
and 6·10-12 m²·s-1 (at a pressure level
of 1.2 bar) were determined for the measured permeability
of 1.7·10-17 m² to 7·10-21 m².
The results of the diffusion measurements are based on the
testing of approx. 150 salt specimens. |
Permeability of rock salt;
Reservoir |
only abstract; German original at KBB |
Bazargan, W.;
Telandro, S. et al. |
1994 |
In situ gas and brine permeability test in
salt: design and deployment of experimental device |
Proc. 4th Progress Meeting PEGASUS, Exeter,
26.-27.06.94, EUR 16001, pp.171-183 |
Paper |
|
The in situ test conducted in the Potash Mines
of Alsace is designed to measure the permeability of a salt
formation to gas and brine for purposes of long-term safety
assessment of a radioactive waste repository. This paper describes
work relating to the design and deployment of the experimental
device, which is comprised of seals, a resin sealant, a fluid
injection system, data acquisition systems for temperature
and pressure and a heat regulating device for the test. |
Permeability of rock salt |
- |
Beauheim, R. L.;
Saulnier, G. J. et al. |
1991 |
Interpretation of brine-permeability tests
of the Salado formation at the Waste Isolation Pilot Plant
site: First interim report |
Albuquerque : Sandia Nat. Lab., SAND90-0083 |
Report |
|
Pressure-pulse tests have been performed in
bedded evaporites of the Salado Formation at the Waste Isolation
Pilot Plant (WIPP) site to evaluate the hydraulic properties
controlling brine flow through the Salado. Hydraulic conductivities
ranging from about 10-14 to 10-11 m/s (permeabilities of about
10-21 to 10-18 m²) have been interpreted from nine tests
conducted on five stratigraphic intervals within eleven meters
of the WIPP underground excavations. Tests of a pure halite
layer showed no measurable permeability. Pore pressures in
the stratigraphic intervals range from about 0.5 to 9.3 MPa.
An anhydrite interbed (Marker Bed 139) appears to be one or
more orders of magnitude more permeable than the surrounding
halite. Hydraulic conductivities appear to increase, and pore
pressures decrease, with increasing proximity to the excavations.
These effects are particularly evident within two to three
meters of the excavations. Two tests indicated the presence
of apparent zero-flow boundaries about two to three meters
from the boreholes. The other tests revealed no apparent boundaries
within the radii of influence of the tests, which were calculated
to range from about four to thirty-five meters from the test
holes. The data are insufficient to determine 9 brine flow
through evaporites results from Darcy-like flow driven by
pressure gradients within naturally interconnected porosity
or from shear deformation around excavations connecting previously
isolated pores, thereby providing pathways for fluids at or
near lithostatic pressure to be driven towards the low-pressure
excavations. Future testing will be performed at greater distances
from the excavations to evaluate hydraulic properties and
processes-beyond the range of excavation effects. |
Pore pressure
in permeable
salt / high deviatoric
stress;
Reservoir Mechanics |
- |
Bérest, P.;
Bergues, J. et al. |
1996 |
A tentative evaluation of the MIT |
SMRI Spring Meeting, Houston, 14.-17.04.96 |
Paper |
|
In order to check the validity of the nitrogen-leak
MIT, a gas-brine interface was lowered to half-height of a
cavern well in order to minimize the risk of (real) gas leak.
The cavern, which had been leached out 14 years ago, has stabilized;
creep, percolation or thermal effects can be considered negligible.
Mock leaks were then provoked by injecting or withdrawing
known quantities of nitrogen or brine through the well-head.
The test gives clear evidence of the so-called barometric
effect; measured and calculated values of the gas-brine interface
displacement and leaks were found to be in good agreement. |
In-situ tests |
- |
Bérest, P.;
Blum, P. A. |
1993 |
In situ tests in salt caverns |
Proc. 7th. Symp. on Salt, Kyoto, 1993, Vol.
1, pp. 353-362 |
Paper |
|
Three original in situ tests performed on salt
caverns are described and discussed. The first is the measurement
of the natural vibrations of the brine mass contained in the
cavern and tubing. It is proved that their period is of the
order of one minute and is related only to the cavern volume,
therefore the estimation of cavern volume is a very simple
procedure. The second test consists of measuring the dips
induced at ground level by a sudden pressure variation in
a deep salt cavern. The average elastic properties of the
ground at a very large scale can be deduced from these measurements,
which are recorded by a high resolution tiltmeter.
The last test is the measurement of the volume rate of brine
naturally expelled from a salt cavern. The interpretation
is difficult, for many phenomena play a role in the expulsion
of brine. Slowly-varying phenomena are brine heating, cavern
creep and brine percolation. These three phenomena can be
quantified; their relative importance is variable during the
whole test, which lasted nine years. Atmospheric pressure
and temperature at ground level vary widely even during one
day. When these phenomena are taken into account, the effects
of the daily earth tides, in spite of being extremely small,
can easily be observed. |
In-situ tests;
Thermo-
dynamics |
- |
Bérest, P.;
Brouard, B. |
1996 |
Behavior of sealed solution-mined caverns |
Proc. ISRM Int. Symp., Eurock '96, pp.1127-1131 |
Paper |
|
When solution-mined caverns are sealed, rock-salt
creep and brine heating generate a brine pressure build-up
which in many cases leads to fracture. Brine seepage through
the rock-mass mitigates pressure build-up and can prevent
fracturing. |
Cavern abandonment;
Thermo-
dynamics |
- |
Bérest, P.;
Brouard, B. et al. |
1995 |
Behavior of sealed solution-mined caverns |
SMRI Spring Meeting, New Orleans, 1995 |
Paper |
|
Solution-mined caverns will be one day sealed
and abandoned. Due to an increasing concern in environmental
and safety issues, the long term behavior of brine bubble
initially enclosed in the cavern has been analyzed by several
authors, who lay emphasis on the fracturation risk due to
the progressive pressure build up in the cavern caused by
brine heating and cavern creep. In this paper we suggest to
take into account the rock salt permeability : even if small,
it allows some pressure release and leads to a final equilibrium
pressure which is substantially lower, in many cases, than
the lithostatic pressure. |
Cavern abandonment;
Thermo-
dynamics |
- |
Bérest, P.;
Brouard, B. et al. |
1995 |
Some comments on the MIT test |
SMRI Fall Meeting, San Antonio, 22.-25.10.95 |
Paper |
|
We discuss several aspects of the so-called
MIT test which is performed by lowering a nitrogen/brine interface
in the annular space of a salt cavern hole.
1. In case of a gas leak, the leak rate is underestimated
by a factor comprised between 1 and 2 when multiplying the
annular cross section by the interface rise rate.
2. The interface level, as measured by a logging equipment,
can be checked by:
i. Comparing the brine and gas pressures as measured at the
well head.
ii. Measuring the cavern compressibility and brine pre-pressure.
iii. Measuring the nitrogen injected mass.
3. Several factors, like thermal expansion, steady state and
transient creep, brine percolation can modify the interface
rate even in the case of absence of leak. The effect of some
of those factors can be precisely estimated.
4. A thorough examination of brine and gas pressure at ground
level allow for estimating the gas leak. |
In-situ tests; Thermo-dynamics; Rock Mechanics |
- |
Biggers, J. V.;
Dayton, G. O. |
1982 |
Brine migration in hot-pressed polycrystalline
sodium chloride |
ONWI-415 |
Report |
|
This report describes experiments designed
to provide data on brine migration in polycrystalline salt.
Polycrystalline samples of various grain sizes, density, and
purity were prepared from several commercial grade salts by
hotpressing. Three distinct experimental set-ups were used
to place salt billets in an induced thermal gradient in contact
with a brine source. The test designs varied primarily in
the way in the thermal gradient was applied and monitored
and the way in which brine migration was determined. All migration
was in enclosed vessels which precluded visual observation
of brine movement through the microstructure.
Migration velocities were estimated either by the timed appearance
of brine at the hot face of the sample, or by determination
of the penetration distance of migration artifacts in the
microstructure after tests of fixed duration. For various
reasons both of these methods were subject to a large degree
of error. Our results suggest, however, that the migration
velocity in dense polycrystalline salt may be at least an
order of magnitude greater than that suggested by single crystal
experiments.
Microstructural analysis shows that brine prefers to migrate
along paths of high crystalline activity such as grain and
subgrain boundaries and is dispersed rather quickly in the
microstructure. A series of tests were performed using various
types of tracers in brine in order to flag migration paths
and locate brine in the microstructure more decisively. These
attempts failed and it appears that only the aqueous portion
of the brine moves through the microstructure with the dissolved
ions being lost and replaced rather quickly. This suggests
the use of deuterium as a tracer in future work. |
Permeability of rock salt |
- |
| Borgmeier, M. |
1992 |
Untersuchungen zum belastungsabhängigen
Durchlässigkeitsverhalten von Salzgestein unter besonderer
Berücksichtigung der Porenraumbeladung
[Investigations on the load-dependent permeability behavior
of saliferous rock focusing on pore space loading] |
Clausthal-Zellerfeld : Techn. Univ., Fak. f.
Bergbau, Hüttenwesen u. Maschinenwesen |
Thesis (Abstract) |
German |
The shallow north German salt domes appear
to be ideal locations for natural gas storage caverns or as
repositories for nuclear and hazardous waste. One of the most
important conditions to be met for the safe operation of cavern
storages is the impermeability of the enclosing salt layers.
The stress field around cavities created by mining is considerably
disturbed for long periods of time as a result of this activity.
This can lead to changes in the permeability and porosity
in the area proximal to the emplacement chambers.
This work was carried out with the objective of investigating
the effect of various factors on permeability, and primarily
the influence of external loading and the internal pore pressure,
as well as fluid loading and temperature. The investigations
were carried out in a triaxial permeameter on natural salt
cores from cavern wells, as well as on model salt cores made
out of salt granulate.
The following parameters were varied systematically as part
of the test programme: the isostatic and anisotropic external
loads were varied between 5 - 60 MPa, and the gas injection
pressures were varied from 1 to 20 MPa. The tests revealed
that permeability decreases exponentially with increasing
isostatic and radial loading. No significant change occurs
by increasing axial load.
A considerable increase in permeability was determined for
each different load with a gas injection pressure/relocation
pressure ratio of 0.9 - 0.95 under isostatic stress conditions.
This increase can be attributed to the formation of microfractures
as well as a reduction in capillary saturation where a capillary
bound water is present in the pore space. The humidity level
of the fluid is a significant influencing factor on the permeability
behavior. Even minute levels of humidity in pore spaces at
an isostatic load of 20 MPa lead to a strong decrease in permeability
over time. In contrast, no change in permeability over time
can be measured if the humidity is removed from the core by
drying. A continuous temperature increase from 25°C to
80°C led to a linear decrease in permeability. Irreversible
permeability changes were determined during the investigations
looking at the influence of the relocation pressure as well
as temperature. Analogous trends were revealed between natural
salt cores and model salt cores with respect to most of the
factors influencing permeability. |
Interdependence rock stresses - permeability;
High deviatoric stress;
Pore pressure in permeable salt |
only abstract; German original at KBB |
Borgmeier, M.;
Weber, J. R. |
1992 |
Gaspermeabilitätsmessungen an homogenen
Modellsalzkernen
[Permeability investigations of homogenous model salt cores] |
Erdöl Erdgas Kohle 108 (1992) 10, pp.
412-414 |
Journal Article |
German |
In this paper permeability investigations of
homogeneous model salt cores using a triaxialpermeameter are
introduced and discussed. Of major interest was the influence
of stress on the gas flow through the core under different
water saturation conditions. In experiments outer stress was
varied between 5 MPa and 100 MPa while pressure at the entrance
of the pores was differed between 0.5 MPa and 15 MPa. The
results showed a clear dependence of gas permeability on the
inner and outer stress. Furthermore it could be proved that
the permeability behavior. is to a great extent subject to
loads on the pore space. |
Interdependence rock stresses - permeability;
High deviatoric stress |
- |
| Borns, D. J. |
1983 |
Petrographic study of evaporite deformation
near the Waste Isolation Pilot Plant (WIPP) |
Albuquerque : Sandia Nat. Lab., SAND83-0166 |
Report |
|
The Delaware Basin of southeastern New Mexico
contains ~ 1000 m of layered evaporates. Areas in the northern
Delaware Basin, bordering the Capitan reef, have anomalous
seismic reflection characteristics, such as loss in reflector
continuity. Core from holes within this zone exhibits complex
mesoscopic folds and extension structures. On a larger scale,
anticlines and synclines are indicated by structure contours
based on boreholes. The deformation is probably gravity-driven.
Such a process is initiated by basin tilting during either
a Mesozoic or Cenozoic period of uplift. The age of deformation
is equivocal, ranging from Permian to Recent small-scale structures
suggest that deformation was episodic with an early, syndepositional
stage of isoclinal folding. Later, open-to-tight asymmetric
folding is more penetrative and exhibits a sense of asymmetry
opposite to that of the earlier isoclinal folding. The younger
folds are associated with development of zonal crenulation
cleavage and microboudinage of more competent carbonate layers.
At the same time, halite beds developed dimensional fabrics
and convolute folds in anhydrite stringers. Late-stage, near-vertical
fractures formed in competent anhydrite layers. Microscopic
textures exhibit rotated anhydrite porphyroblasts, stress
shadow growth, and microboudinage. Except during late-stage
deformation, anhydrite and halite recrystallized synkinematically.
Drastic strength reduction in anhydrites through dynamic recrystallization
occurs experimentally near 200°C. However, evaporates
of the WIPP site never experienced temperatures >40°C.
Microscopic fabrics and P, T history of the evaporates suggest
that pressure solution was the active mechanism during deformation
of evaporates at the WIPP site. This conclusion stresses the
importance of fluid in facilitating deformation in low-temperature
evaporate sequences. The formation of pressurized brine pockets
is empirically associated with deformation. The development
of high-angle fractures in the uppermost anhydrite unit of
the Castile in response to folding provides the reservoir
for the brines. Brine fluids may have emanated from deforming
halite and anhydrite units through pressure-solution-induced
reduction of porosity. |
Creep behavior - phenomenological approach |
- |
| Borns, D. J. |
1987 |
Rates of evaporite deformation: The role of
pressure solution |
Albuquerque : Sandia Nat. Lab., SAND85-1599 |
Report |
|
Evaporite sequences have been intensely studied
for hazardous waste disposal and hydrocarbon development:
and storage. Rates of deformation are important in evaluating
the long-term performance of different evaporites. Reported
naturally occurring strain rates (x) are: 5 x 10-11 s-1 for
a salt glacier; 10-11 for mine closure; 3 x 10-14, 10-15,
and 10-16 for salt domes; 3 x 10-16 for bedded salt. Rates
are controlled by temperature, differential stress, and active
mechanism of deformation for each specific type of evaporate
and setting.
Strain rates are estimated through in-situ measurements and
the integration of geometric strain analysis and stratlgraphic
arguments for the time required for the observed deformation
to occur. An inherent problem in such calculations is the
large extrapolation of rates through time. Another approach
for rate estimation is to calculate x directly, using the
constitutive models for different deformation mechanisms that
may be dominant. Specific mechanisms can be determined from
petrofabric study, as at the WIPP site, SE New Mexico, where
textures indicating that pressure solution was active are
observed. Calculations based on experimental data are limited
by the relatively poor data on diffusion in intergranular
fluids. A variety of grain boundary diffusion models have
been used. Some models (e.g., cubic approximation of the grain
shape) leave gradients undefined at the grain edge.
For gravity-driven deformation near the WIPP site, geometric-stratigraphic
integration predicts a x of 10-14 s-1 to 10-16 s-l. Strain
rates of 10-15 to 10-16 s-1 are predicted using models for
dislocation creep and pressure solution. The rates using two
approaches, geometric-stratigraphic and constitutive, are
basically in agreement. These rates for the gravitydriven
flow structures near WIPP reflect lower temperatures and stresses
than salt domes. At the temperatures and stresses estimated
for the WIPP flow structures, pressure solution is probably
the dominant mechanism, rather than dislocation creep. It
remains to be determined where in the transition from transient
to steady-state response to an underground excavation in rock-salt
pressure solution becomes a major mechanism. |
Creep behavior - phenomenological approach |
- |
Borns, D. J.;
Stormont, J. C. |
1989 |
The delineation of the disturbed rock zone
surrounding excavations in salt |
Proc. 30th. U.S. Symp. Rock Mechanics, Morgantown,
19.-22.06.89, pp. 353-360 |
Paper |
|
At the Waste Isolation Pilot Plant (WIPP) in
southeastern New Mexico, the Disturbed Rock Zone (DRZ, the
zone of rock in which the -mechanical and hydrologic properties
have changed in response to excavation) has been characterized
with visual observations, geophysical methods, and gas-flow
measurements. The visual observations, geophysics, and gas-flow
tests have defined a DRZ at the WIPP mending laterally throughout
the excavation and varying in depth from 1 to 5 m. Desaturation
and microfracturing has occurred to some degree within the
zone. The dilation that results from the microfracturing in
the DRZ provides a component of the observed closure. |
Permeability of rock salt |
- |
| Bosworth, W. |
1981 |
Strain-induced preferential dissolution of
halite |
Tectonophys. 78 (1981), pp. 509-525 |
Journal Article |
|
Previous experiments on the effect of a fluid
phase in deforming rock and rock analogue systems have failed
to differentiate between the relative roles of stress and
permanent strain in controlling preferential dissolution at
fluid-grain boundary interfaces. Experiments are described
here in which halite single crystals were loaded under dry
conditions, followed by removal of load and immersion of the
crystals in brine. A correlation between net dissolution rate
and plastic strain of the adjacent crystalline material was
then observed at free crystal surfaces. Calculation of the
increase in free energy of the solid phase due to deformation
indicates that plastic strain should play a greater part in
controlling dissolution than elastic strain in the experimental
design reported here.
Although pressure gradients or differences in normal stress
may dominate over strain energy terms in producing solution
transfer or diffusion through disordered phases in natural
rock systems, these halite-water experiments demonstrate that
caution must be used in interpreting mechanisms from petrographic
and other observations of the phenomena now commonly referred
to as "pressure solution". |
Interdependence rock stress - permeability |
- |
Boulanger, A.;
Rousseau, A. J. |
1991 |
Method of rapidly abandoning large cavities
washed-out in rock salt |
US 5 004 298 |
Patent |
|
After they have been washed out, cavities (4)
in rock salt contain a large quantity of brine (8) at a temperature
which is lower than the temperature of the surrounding formation
(2). This means that the cavity cannot be sealed quickly because
the brine will expand progressively as it heats up. The method
of the invention serves to shorten the time period between
the end of working the cavity for salt and being able to abandon
the cavity finally from about 30 years to about 2 years. The
method consists in injecting quantities of a mixture (12)
into the cavity (4), the mixture being of greater density
than brine (8) and being capable of setting, with equivalent
quantities of brine (8) being returned to the surface, and
then in keeping the cavity (4) open after it has been completely
filled with mixture (12) for as long as it takes the rock
salt (2) to creep and fill up the shrinkage voids which appear
during setting of the mixture (12), after which the cavity
(4) can be sealed. To do this, it is advantageous to make
use of waste material for constituting the mixture (12). |
Cavern abandonment |
- |
| Bredehoeft, J. D. |
1988 |
Will salt repositories be dry ? |
EOS Transact., Am. Geophys. Union 69 (1988)
9, pp.121 + 131 |
Journal Article |
|
Data from the Waste Isolation Pilot Plant (WIPP)
site in southeastern New Mexico suggest an alternative hypothesis
to the widely held view that salt in a geologic environment
below the water table is "dry" and impermeable. The alternative
is that the salt section, which for the most part is of low
permeability and low porosity, is saturated with brine. The
implication of this hypothesis is that a repository in salt
will fill with brine once the ventilation of the facility
ceases to remove moisture. The rate of inflow to the facility
will depend on the permeability of the salt. Data from the
WIPP facility suggest an undisturbed salt permeability of
»10 nanodarcies (10-12 cm/s). Given such a low permeability,
the rate of brine inflow to an underground facility will be
quite low, of the order 0.01 L/day/m of tunnel. |
Permeability of rock salt |
- |
Bredehoeft, J. D.;
Papadopulos, S. S. |
1980 |
A method for determining the hydraulic properties
of tight formations |
Water Res. Res. 16 (1980) 1, pp. 233-238 |
Journal Article |
|
A method for testing formations of very low
permeability is presented. The method is based on an analytical
solution that describes the decay of a head change caused
by pressurizing the volume of water stored in a shut-in well.
Type curves prepared from this solution are matched with observed
data to determine the hydraulic properties of the formation
tested. The test is similar to the conventional slug test;
however, its much shorter duration makes the testing of extremely
tight formations feasible. |
Permeability of rock salt |
- |
Bush, D. D.;
Barton, N. |
1989 |
Application of small scale hydraulic fracturing
for stress measurements in bedded salt |
Int. J. Rock Mech. Min. Sci. & Geomech.
Abstr. 26 (1989) 6, pp.629-635 |
Journal Article |
|
In situ rock stress measurements by small-scale
hydraulic fracturing were performed in two salt beds in the
Texas Panhandle, approximately 60km (36 miles) south of Amarillo,
Texas. Data analysis indicates that small-scale hydraulic
fracturing is applicable for determining the magnitude of
the minimum principal stress and the direction of the maximum
stress in salt. However, when hydraulic fracturing equations
based on elasticity are applied to salt (a non-elastic medium),
anomalously high in situ maximum stress and tensile strength
values are calculated. Due to the non-elastic properties of
salt and it's solubility, neither the derived maximum stress
nor the tensile strength values are considered valid using
the elastic hydraulic fracturing stress equations. |
Hydrofracturing |
- |
Cauberg, J.;
Walters, J. V. et al. |
1986 |
Rock mechanical behavior. and sealing aspects
of a closed-in salt cavity filled with brine (SMRI) |
SMRI Fall Meeting, Amsterdam, 21.-24.09.86 |
Paper |
|
Magnesium and potassium salts are being solution-mined
from carnallite/bischofite layers in the north-east of The
Netherlands, near Veendam. It is planned that, at the end
of the mining process, the brine-filled cavities will be abandoned.
The paper presents some rock mechanical considerations with
respect to cavity behavior. after abandonment, assuming perfect
cavity sealing. A finite element analysis of the cavity response
after shut-in, and the design requirements for a suitable
sealing plug for the borehole, are discussed.
The finite element calculations indicate a rise in brine pressure
after shut-in, followed by a gradual pressure increase towards
an asymptotic value. This change in pressure is accompanied
by adjustments in the cavity roof, wall and floor stresses.
Different sealing principles and plug designs are considered.
Cavity response after abandonment, long-term reliability,
and general compatibility with in-situ conditions are the
major criteria in the selection of a suitable sealing plug
material. |
Cavern abandonment;
Borehole seal;
Rock mechanics |
- |
Chan, K. S.;
DeVries, K. L. et al. |
1995 |
A damage mechanics approach to life prediction
for a salt structure |
Computational Mechanics '95, Proc. Int. Conf.
Comp. Eng. Sci., Hawaii, 30.07.-03.08.95, Vol.1, pp.1140-1145 |
Paper |
|
Excavated rooms in natural bedded salt formations
are being considered for use as repositories for nuclear waste.
It is presumed that deformation of the rooms by creep will
lead to loss of structural integrity and affect room life
history and seal efficiency. At projected repository temperatures,
two possible fracture mechanisms in salt are creep-induced
microcracking in triaxial compression and cleavage in tension.
Thus, an accurate prediction of the time of room life and
seal degradation requires a reliable description of the creep
and damage processes.
While several constitutive models that treat either creep
or fracture in salt are available in the literature [1-4],
very few models have considered creep and damage in a coupled
manner. Previously, Munson and Dawson [1] formulated a set
of creep equations for salt based on the consideration of
dislocation mechanisms in the creep process. This set of creep
equations has been generalized to include continuum, isotropic
damage [5] as a fully coupled variable in the response equation
[6]. The extended model has been referred to as the Multimechanism
Deformation Coupled Fracture (MDCF) model. A set of material
constants for the creep and damage terms was deduced based
on test data for both clean and argillaceous salt [7-9].
In this paper, the use of the MDCF model for establishing
the failure criteria and for analysing the creep response
of a salt structure is demonstrated. The paper is divided
into three parts. A summary of the MDCF model is presented
first, which is followed by an evaluation of the MDCF model
against laboratory data. Finally, finite-element calculations
of the creep and damage response of a salt structure are presented
and compared against in-situ field measurements. |
Creep behavior |
- |
Chester, F. M.;
Logan, J. M. |
1990 |
Frictional faulting in polycrystalline halite:
correlation of microstructure, mechanisms of slip, and constitutive
behavior |
American Geophysical Union: Geophysical Monograph
56, pp. 49-65 |
Paper |
|
The relation between friction constitutive
behavior and the mechanisms of shearing in a monomineralic,
polycrystalline material that deforms by combined cataclasis
and crystal-plasticity has been investigated by shearing thin
layers of halite between blocks of quartz sandstone at room
temperature (22°C), constant normal stresses between 20
and 70 MPa, and shear-displacement rates between 300 and 0.030
mm s-1 in a triaxial rock deformation apparatus. Constant
and stepping displacement rate modes of testing were utilized,
and some tests were preceded by a confining pressure (Pc)
reduction load path involving the reduction of Pc after establishing
a differential axial load. Pc-reduction causes the shear stress
to increase as the normal stress approaches zero, and , promotes
compaction and the formation of a slip surface in the halite
at small shear displacements relative to that for constant
normal stress and constant Pc load paths. Discrete changes
in the steady state microstructure and constitutive behavior
of halite with normal stress and displacement rate define
distinct mechanism fields of frictional faulting. Cataclastic
mechanisms dominate at normal stresses less than 40 MPa and
at all displacement rates tested, and the coefficient of friction
varies from 0.6 to 1.0 as a function of displacement rate.
Relatively large magnitude rate-weakening is observed at high
displacement rates and is associated with stick slip sliding
on a discrete surface. Because steady state shear involves
localized slip at these conditions,.the use of Pc-reduction
prior to shearing reduces the magnitude of displacement necessary
to achieve steady state. Small magnitude rate-dependence at
low displacement rates is associated with distributed cataclastic
flow and stable shearing behavior. Both the comminution rates
and stability transition at low normal stresses suggest that
the microstructural state is similarly affected by an increase
in normal stress and a decrease in displacement rate. At normal
stresses greater than 40 MPa and at all displacement rates
tested, halite undergoes nearly homogeneous simple shear by
dislocation mechanisms. However, the frictional behavior displayed
at these conditions implies that stable microfracturing or
some other pressure-sensitive process is operative, and that
flow is semi-brittle. |
Creep behavior |
- |
Clark, J. E.;
Papadeas, P. W. et al. |
1991 |
Gulf Coast borehole closure test well Orangefield,
Texas |
SMRI Fall Meeting, Las Vegas, 27.-19.10.91 |
Paper |
|
A borehole closure protocol for a Gulf Coast
site near Orangefield, Texas was developed by Du Pont. These
procedures were based largely upon recommendations provided
by EPA Region 6 and created a borehole closure test to demonstrate
that, under a worst case scenario, any artificial penetration
will seal naturally. The borehole closure test successfully
demonstrated natural sealing. Within one week of setting the
screen, tubing and pressure transducers in the borehole, testing
confirmed the absence of upward movement of fluid from the
test sand. The documentation for the absence of upward movement
included: 1) Schlumberger Water Flow Log* and 2) the absence
of pressure response on the upper transducer located outside
the tubing and inside the casing. Testing was conducted in
accordance using specified procedures, with pressure testing
conducted at even higher pressures to allow an added margin
of confidence. The borehole closure test provides a significant
additional margin of confidence that there will be no migration
of hazardous constituents from the injection zone for as long
as the waste remains hazardous. |
In-situ tests |
- |
| Cosenza, P. |
1996 |
Sur les couplages entre comportement mécanique
et processus de transfert de masse dans le sel gemme
[Coupled effects between mechanical behavior and mass transfer
phenomena in rock salt] |
Paris : Univ. |
Thesis |
french |
The results of a field experiment carried out
in the Mines de Potasse d'Alsace (MDPA, France) show that
rock salt is permeable to gas and to brine, at least around
underground facilities (four radii far from the gallery wall).
In contrast to gas flow rate, brine flow rate is interpreted
in a satisfactory way using a model based on Darcy's. law.
On the other hand, after brine percolation into the rockmass,
capillarity has a significant effect on the gas injection
flow rate.
During laboratory compressive triaxial tests, under high confining
pressure (up to sixty Mpa) unjacketed samples of MDPA.salt
show a lower damage initiation and a lower compressive strength
than jacketed samples. These effects induced by salt permeability
become more marked when brine is used as confining fluid.
In the theoretical part, a framework is proposed and used
to discuss dissolution/crystallisation phenomenon leading
to a change of transport properties. The "healing process",
associated with viscoplastic strains of grains can explain
the extremely low permeability of rock salt at a geological
time scale.
Results of the calculations on underground structures show
that a very low permeability which may not be measurable using
existing techniques, modifies in a significant way the long
term evolution of an underground storage. |
Rock mechanics;
Permeability - High deviatoric stress;
Interdependence rock stress - permeability;
Reservoir |
French thesis separately;
(1 copy for SMRI) |
Cosenza, P.;
Ghoreychi, M. |
1993 |
Coupling between mechanical behavior and transfer
phenomena in salt |
Proc. 3rd Conf. Mech. Behavior of Salt, Palaiseau,
14.-16.09.93, pp. 271-293 |
Paper |
|
After a review of the basic coupling phenomena
for salt subject to gas and /or brine migration, Thermodynamics
of Open Porous Media is used to set up a model taking into
account Thermal, Hydraulic, Chemical and Mechanical couplings.
The model is simplified and applied to a spherical structure
in salt. The results show that the structure response is very
sensitive to hydro-chemical effects which change the thermo-mechanical
behavior of salt. |
Interdependence rock stress - permeability |
- |
Cosenza, P.;
Ghoreychi, M. |
1997 |
Évolution de la perméabilité
du sel gemme sous sollicitations mécano-chimiques
[Permeability evolution of rock salt under mechano-chemical
stresses] |
Bull. Soc. Géol. France; in Press |
Journal Art.(Abstr.) |
|
The results given in this paper deal with experimental
and theoretical studies performed on rock salt permeability,
in the framework of hydrocarbon or radioactive waste storage.
The results of a field experiment carried out in a salt layer
in the Mines de Potasse d'Alsace is in agreement with those
of the experiments performed in other salt formations : rock
salt is permeable to gas and to brine, at least around underground
facilities. Its permeability is about 10-21 m². This
permeation is due to damage resulting from excavation or tectonics.
Considering rock salt as a porous, permeable and reactive
medium, a theoretical framework is used to discuss two phenomena
playing a role on permeability: (a) dissolution/crystallisation
in microcracks due to brine solubility changes (b) healing
process due to hydrostatic loading. The results of calculations
are in agreement with those of laboratory tests, and show
that a mechano-chemical coupled effect associated with viscoplastic
deformation of grains can explain the extremely low permeability
of rock salt at a geological time scale. |
Rock mechanics;
Permeability - High devitoric stress;
Interdependence rock stress - permeability |
only abstract, in press |
Cosenza, P.;
Ghoreychi, M. et al. |
1997 |
Mesure de la perméabilité in
situ du sel
[In situ permeability measurement in salt] |
Rev. Franc. Géotechn.; in Press |
Journal Art.(Abstr.) |
|
In order to measure rock salt intrinsic permeability
located far from underground facilities, an in situ experiment
was performed in the Amélie mine belonging to the Mines
de Potasse d'Alsace (MDPA, Mulhouse, France). A vertical borehole
was drilled from a niche excavated to access to the S1 bed,
very pure in halite. The selected salt bed is approximately
one meter thick and is located 16 meters away from the gallery
floor. Test fluids were nitrogen and saturated brine. In order
to minimize and to control disturbing phenomena (thermal effects,
solution/crystallization and creep), constant temperature
and constant pressure tests were recommended. As a matter
of fact and because of the geological conditions (low thickness
of the tested halite bed), a special device had to be designed
and its principal components (packers and fluid injection
systens) needed to be tested in the laboratory and in the
field.
The results of the field experiment show that rock salt is
permeable to gas and to brine, even far enough from underground
openings.
The results of the tests with brine are interpreted in a satisfactory
way using a model based on the Darcy's law and characterized
by a permeability value of 2 x 10-21 m2 and an initial pore
pressure value of 1 MPa. Analysis of measured gas flow rate
shows that:
- after a brine percolation, capillary pressure effect
is significant
- fluid migration in salt is not controlled by Darcy diffusion,
Knudsen effect and partial saturation
may play an important role. |
Pore pressure;
Permeability of rock salt;
Reservoir Mechanics |
only abstract, in press |
Cosenza, P.;
Ghoreychi, M. et al. |
1996 |
In situ gas and brine permeability measurements
in salt |
Proc. 4th Conf. Mechanical Behavior of Salt,
Montreal, 1996; in Press |
Paper |
|
The results of a field experiment carried out
in a salt layer in the Mines de Potasse d'Alsace (France)
confirm that rock salt is permeable to gas and to brine, at
least around underground facilities.
A simple analysis of measured gas flow rate shows that (a)
capillary pressure effect is significant (b) fluid migration
in salt is not controlled by Darcy diffusion.
The results of the tests with brine are interpreted in a satisfactory
way using a model based on Darcy's law characterized by a
permeability value of 2 x 10-21 m² and an initial pore
pressure value of 1 MPa. The following non linear effects
are considered : (1) salt damage created by borehole drilling
(2) effective stress changes (3) change in salt concentration
of brine saturation state resulting from pressure changes. |
Pore pressure;
Permeability of rock salt;
Reservoir Mechanics;
Interdependence rock stress - permeability |
in press |
Cosenza, P.;
Ghoreychi, M. et al. |
1995 |
First results and interpretation of in situ
permeability measurement in salt to gas and to brine |
Proc. 5th Progress Meeting PEGASUS, EUR 16746,
pp.167-175 |
Paper |
|
An in situ experiment is being performed in
the Mines de Potasse d'Alsace (M.D.P.A., Mulhouse, France)
in the framework of a C.E.C. contract (coordinator: ANDRA,
contractor: G.3S, technical assistance : COSEREP). The objective
of this test is to measure the permeability of salt to brine
and to gas.
This paper deals with the experimental procedure, the measurements,
and the first interpretation of the results.
Two tests with nitrogen under the pressure levels of 4 and
6 MPa, and three tests with brine under 2, 4 and 6 MPa of
pressure have been performed. The experiments are completed
with three more tests, again with gas under 2,4 and 6 MPa.
These last tests allow to check that a salt formation previously
subjected to brine is not permeable to gas regarding capillary
effects.
The experimental set up is capable to measure very low values
of permeability about 10-21 m². The basic flow mechanism
involved in gas flow is possibly a multiphase flow for which
capillary pressure may play an important role. On going and
further studies will allow the final interpretation of the
experimental results. |
Interdependence rock stress - permeability;
Permeability of rock salt;
Reservoir Mechanics |
- |
Doe, T. W. ;
Boyce, G. |
1989 |
Orientation of hydraulic fractures in salt
under hydrostratic and non hydrostratic stresses |
Int. J. Rock Mech. Min. Sci. & Geomech.
Abstr. 26 (1989) 6, pp. 605-611 |
Journal Article |
|
Laboratory experiments of hydraulic fracturing
in salt have shown that the breakdown pressure does not vary
significantly with the differences between the maximum and
minimum stresses normal to the borehole axis. The presence
of a non-hydrostatic stress in salt may be determinable from
the form of the hydraulic fracture alone. A series of laboratory
experiments were performed to determine the influence of deviatoric
in situ stress on the form and orientation of hydraulic fractures
in salt.
The hydraulic-fracturing tests were run on prismatic blocks
in a polyaxial loading frame over a range of stress ratios
from 1 (hydrostatic) to 1.5. The fracturing oil contained
a fluorescent dye that marked the fracture traces for mapping
after the samples were split.
The results indicate that the form of the hydraulic fracture
reflects whether or not the stresses are nearly hydrostatic.
For large stress ratios (> 1.5), the fractures are straight
and strongly oriented. For stress ratios near one, the fractures
are poorly oriented and exhibit significant branching. Thus,
proximity to hydrostatic conditions can be determined from
the form of the hydraulic fracture alone, regardless of ambiguities
in the interpretation of pressure-time records from the fracturing
experiment. |
Hydrofracturing |
- |
| Durup, J. G. |
1994 |
Long-term tests for tightness evaluations with
brine and gas in salt (Field test n° 2 with gas) |
SMRI Fall Meeting, Hannover, 1994 / SMRI Res.
Proj. Rep. No. 94-0002-S |
Paper + SMRI-Report |
|
Hydraulic fracturing tests were performed at
about 900 meters (2950ft) deep in a bedded salt formation
at ETREZ, eastern France. These tests comprised a "Field Test
N°2 with gas" that followed an initial field test, using
brine as the test fluid, which was performed in the same Well
EZ58.
The principal objectives were to determine hydrofrac gradients
at different pressurization rates, to compare hydrofrac gradients
values obtained with liquid and gas, and to study in such
in-field conditions, self-healing effects and percolation
of fluids in the salt massif. These are believed to be relevant
data for defining maximum operating pressures in salt formations.
With nitrogen as the test fluid, the hydrofrac gradient with
slow pressurization (long-term test over a one-year period)
was 0.237 bar/m (1.05 psi/ft). A value of 0.236 bar/m (1.04
psi/ft) was obtained with relatively, fast pressurization
(short-term test over a one-day period). With brine as test
fluid the values were 0.240 bar/m (1.06 psi/ft) and 0.256
bar/m (1.13 psi/ft) for the long and short-term tests respectively.
The salt massif seems more resistant to hydrofracture (higher
frac gradient) when only one phase (brine) is present in the
crystal interstices.
Testing in Well EZ58 began in 1989 and ended in 1994. For
each test fluid, the short-term test was performed some time
after the end of the long-term test. It was concluded that
under field conditions, recrystalization processes can heal
fractured salt rapidly, in about one month. These tests demonstrate
clearly, that this self-healing process entirely, restores
the mechanical strength of the salt massif.
The test results establish that the test fluids percolated
in the salt massif around the tested openhole before hydrofrac
at all the pressure levels tested. With equivalent conditions,
higher percolation rates were observed for gas than for brine.
With brine, interpretation as Darcy flow gave satisfactory
fitting of calculated and measured flow rates. The estimated
permeability was 6 x 10-20 m² assuming 1 % porosity.
With gas, interpretation was more problematic because of two-phase
flow and pronounced capillary effects. However, the extent
of gas infiltration into the salt massif at close to lithostatic
pressures was estimated as being limited to about one meter
over the one-year testing period. |
In-situ tests;
Permeability - liquid pressure above confining pressure;
Reservoir Mechanics |
- |
| Durup, J. G. |
1994 |
Essais de perméabilité dans un
massif salifère
[Permeability tests in a salt mass] |
Ann. Ass. Franc. Techn. Petrol. Conf. / Pétrol.
Tech. 387, pp.17-20 |
Journal Article |
french |
In this tightness/fracturing test at brine,
the pressure in the free space was gradually raised in steps
of 0.1 MPa. The pressure reached was held constant for a period
of 1 month by precisely controlled injection of fluid. The
results presented here were obtained by applying Darcy's Law
to interpret the development of the fluid injections |
Permeability of rock salt;
Hydrofracturing;
Reservoir Mechanics |
- |
| Dusseault, M. B. |
1989 |
Saltrock behavior as an analogue to the behavior
of rock at great depth |
Maury; Fourmaintraux (Eds.): Rock at great
depth, 1989, pp.11-17 |
Paper |
|
The elastoviscoplastic behavior of saltrocks
may be interpreted in terms of a number of different fundamental
deformation mechanism that act at different rates at different
shear and normal stress levels. The paper presents a new approach
to a constitutive law for these materials, recognising the
complex behavior, and making distinctions between different
types of yield criteria and viscous flow laws. An attempt
is made to develop this behavior as an analogue to the behavior
of rock at high temperatures and stresses, where viscous mechanisms
become possible. It is emphasized that an appreciation of
the dominant deformation mechanisms acting at particular conditions
will guide the form of macroscopic constitutive laws for non-saltrocks. |
Creep behavior |
- |
Ehgartner, B.;
Linn, J. K. |
1994 |
Mechanical behavior of sealed SPR caverns |
SMRI Spring Meeting, Houston, 25.-27.04.94 |
Paper |
|
It is inevitable that sealing and abandonment
will someday occur in a U.S. Strategic Petroleum Reserve (SPR)
cavern or caverns. To gain insight into the long-term behavior
of a typical SPR cavern following sealing and abandonment,
a suite of finite element analyses were performed. The analyses
predict how quickly and to what extent a cavern pressurizes
after it is plugged. The analyses examine the stability of
the cavern as it changes shape due to the increased pressures
generated after plugging. Internal fluid pressures in a brine
filled cavern eventually exceed lithostatic pressure in the
upper portion of the cavern resulting in enlargement and stress
reduction. The buildup of fluid pressure after plugging is
largely determined by salt creep, salt dissolution, and geothermal
heating of brine. Volumetric closure due to creep increases
brine pressure. Salt dissolution and geothermal heating occur
when the brine is unsaturated and cooler than the surrounding
salt at the time of plugging. The individual and coupled effects
of creep, dissolution, and geothermal heating are modeled.
The analyses suggest that the predicted rate and magnitude
of fluid pressurization in SPR caverns is not high enough
to result in fracturing of the salt. However, cavern pressure
can be substantially mitigated by delaying plugging until
the brine has come closer to thermal equilibrium. |
Cavern abandonment;
Thermodynamics;
Creep behavior |
- |
Faske, B.;
Stein-Lausnitz, E.-G.v. et al. |
1987 |
Vorrichtung zum Einbringen eines Dichtmittels
in ein Bohrloch
[Apparatus to inject a sealant into a well] |
DD 262 887 A1 |
Patent |
German |
The apparatus is used for the preservation
and maintenance of wells filled with liquid media, in particular
caverns in evaporites, following termination of usage. Below
the well seal a container is positioned containing the sealant/protective
medium, the walls of which vessel are made either totally
or in part of a single material which is heavily corroded
by the content of the well and which decomposes as a result.
If as a result of geomechanical processes the gas cap is displaced
and the level of the liquid rises up to that of the container
then the corroded metal is perforated and the sealant can
escape from the containers and spread across the surface of
the liquid. |
Borehole seal |
- |
Finley, R. E.;
Zeuch, D. H. et al. |
1994 |
Sealing of boreholes using natural, compatible
materials: granular salt |
Eurock '94, Delft, 29.-31-08.94, pp. 753-760 |
Paper |
|
Granular salt can be used to construct high
performance permanent in boreholes which penetrate rock salt
formations. These seals are described as seal components of
the host rock, the seal material, and the seal rock interface.
The performance of these seal systems is defined by the complex
interactions between these seal system components through
time. The interactions are largely driven by the creep of
the host formation applying boundary stress on the seal forcing
consolidation of the granular salt. The permeability of well
constructed granular salt seal systems is expected to approach
the host rock permeability (<10-21 m² (10-9 Darcy))
with time. The immediate permeability of these seals is dependent
on the emplaced density. Laboratory test results suggest that
careful emplacement techniques could result in immediate seal
system permeability on the order of 10-16 m² to 10-18
m² (10-4 darcy to 10-6 darcy). The visco-plastic behavior
of the host rock coupled with the granular salts ability to
'heal' or consolidate make granular salt an ideal sealing
material for boreholes whose permanent scaling is required. |
Borehole seal |
- |
Fischle, W. R.;
Stöver, W. H. |
1986 |
Construction of a bulkhead and measurement
under brine pressure |
SMRI Fall Meeting, Amsterdam, 21.-24.09.86 |
Paper |
|
The intrusion of water or brine into a final
repository for radioactive waste in salt rock is regarded
as the greatest hypothetical accident scenario.
The intrusion of water or brine into a final repository for
radioactive waste in salt rock is regarded as the greatest
hypothetical accident scenario. The most crucial aspect is
the prevention of dispersal of the dissolved radionuclides
into the biosphere. Special plugs or seals in addition to
the natural barriers of the host rock and caprock play a significant
role in preventing the escape of nuclides through cavities.
The decision to flood the abandoned potash mine at Hope, north
of Hannover, was made in 1982. In addition to geochemical,
geophysical and aeomechanical investigations this provided
the first opportunity for testing the tightness of a bulkhead
in situ at a pressure of 6 MPa at the real scale of 1:1. |
Borehole seal;
In-situ tests |
- |
| Fokker, P. A. |
1995 |
The behavior. of salt and salt caverns |
Delft : Techn. Univ. |
Thesis |
|
Salts are mined for both storage and extraction
purposes, either via dry or solution mining techniques. For
operational, environmental and geological purposes, it is
important to understand and predict the in situ behavior.
of salt, in particular the creep and strength characteristics.
A micro-mechanically based explanation and quantification
of primary (strainhardening) creep in rock salt have not yet
been reported. Creep models for primary creep are still mainly
based on curve fitting. At relatively low temperatures (0-200
C°), as encountered near all excavations, the primary
creep phase is very important, certainly at laboratory time
scales.
Since understanding of the mechanism may be important in extrapolating
relatively short term laboratory tests to long term creep
in situ, an attempt is made in this thesis to explain (and
simulate) both primary and secondary (steady state) creep
via a micro-mechanical approach. Deformation in this model
is governed by dislocation motion, which becomes increasingly
hindered with strain by crystal lattice defects, resulting
in strain hardening. The defects in turn are assumed to be
dislocation dipoles (two mutually trapped dislocations of
opposite sign). Recovery in this model is related to the thermally
activated generation of vacancies and interstitials by the
disintegration of dipoles consisting of very near dislocations.
These vacancies and interstitials in turn precipitate on other
(more rigid) dipoles, allowing them to annihilate by climb.
This model describes the observed measurements very well,
especially in describing transition zones after changing a
strain rate. Unfortunately this model does not result in a
simple constitutive equation, although possible in theory.
Simpler, but for general practice usually sufficiently accurate,
curve-fitting laws have been implemented in the DIANA Finite
Element Code, now capable of simulating salt creep behavior.
Rock salt at greater depth is usually impermeable, thus forming
a good seal against fluid penetration. A combination of high
deviatoric and low confining stresses leads to dilation and
even failure during deformation. Tensile stresses can result
in micro- or macro-fracturing of the salt. These mechanisms
affect the sealing capacity of salt. Contrary to common opinion
so far, it is shown here that fluid pressures (as present
in, for instance, caverns or aquifers) do not increase the
sal'ts bearing capacity. Hence, salt needs to be treated like
a Terzaghi material, subtracting fluid pressures from the
stress field when determining dilation or fracture criteria.
The risk of fracturing or failure implies that care should
be taken with cavern operations. In fluid storage caverns,
fracturing can occur after a period of low cavern pressures
and subsequent filling and pressurizing. The stress field
around the cavern may be relaxed, whereby the salt stress
no longer coincides with the initial stress situation. Fractures
become possible, particularly if the cavern is not embedded
in a large salt mass but is close to a non-creeping overburden,
taking stresses from the salt by arching eventually. Similarly,
such a stress relaxation can lead to a fracture connecting
an aquifer to a cavern or mine, flooding being the result.
Another consequence of the relatively easy fracturing of salts
is that large fluid volumes cannot be sealed permanently by
plugging the cavern entrance (casing). Density differences
between fluid and rock salt will finally lead to an excess
fluid pressure near the top (roof) of the cavern, resulting
in permeation and fracturation of the cavern roof, resulting
in cavern fluid leakage. Although occurring very slowly, the
caverns will vanish in time, resulting in surface subsidence.
Special attention has been paid to the Veendam solution
mines, which have been mined in multicomponent salts (sodium,
magnesium, potassium salts). These offer unique opportunities
to observe creep and fracture related features over a short
period of time (compared to caverns constructed in rock
salt only). |
Creep behavior;
Interdependence rock stress - permeability;
Permeability - liquid pressure above confining p;
Reservoir Mechanics |
- |
Fokker, P. A.;
Kenter, C. J. et al. |
1993 |
The effect of fluid pressures on the mechanical
stability of (rock) salt |
Proc. 7th. Symp. on Salt, Vol. 1, pp.75-82 |
Paper |
|
The effect of fluid pressures on the behavior.
of salt has not been investigated thoroughly until now, since
salt rocks at great depths have been considered impermeable
and non-porous. Recent investigations have shown, however,
that permeability of salts may be significantly increased
both at sub and above lithostatic pressures, which may have
a large influence on the strength. This permeability increase
is believed to be caused by the viscous micro fracturing at
above lithostatic fluid pressures, or by shear dilatancy at
sublithostatic fluid pressures and sufficiently large deviatoric
stresses. The implication of this permeability increase is
that pressure communication between pore fluid and cavern
fluid needs to be taken in account and salt needs to be treated
as a Terzaghi material, splitting total stresses in effective
stresses and pore pressures. Hence conventional cavern analysis
with cavern pressures treated as boundary loads rather than
boundary pore-pressures may not be right for caverns with
sublithostatic pressures at greater depths and for caverns
with above lithostatic pressures in general. Also standard
salt strength determination on jacketed triaxial samples may
not be directly applicable, as for those cavern conditions
fluids will penetrate into salts. The above theory is supported
by laboratory tests and field evidence; for example, unjacketed
triaxial tests have been conducted on halite, which showed
that the strength measured this way does not exceed the UCS
value of approximately 300 bar, regardless of the lateral
pressure applied. From fracture tests on halite it was found
that fracturing occurs at fluid pressures of about 20 bar
in excess of the lowest ambient salt pressure, whilst earlier
tests showed that permeability was significantly increased
at lower excess pressures. Results were further found to be
in agreement with the EZ58 field test of Gaz de France and
lab tests reported in literature. |
Interdependence rock stress - permeability;
Permeability - High deviatoric stress;
Perm. - Liquid pressure above confining pressure |
- |
Fokker, P. A.;
Kenter, C. J.. |
1994 |
The micro mechanical description of rock salt
plasticity |
Proc. Eurock '94, Delft, 29.-31.08.94, pp.705-713 |
Paper |
|
The constitutive behavior. of rock salt is
explained from micro mechanical concepts. Rock salt plasticity
(or primary creep) can be well explained by a dislocation
glide mechanism, where gliding becomes increasingly hindered
by dislocations (in fact dislocation pairs or dipoles), disturbing
the glide paths. Such dipoles are both the main source for
hardening, as well as the main source for time dependent behavior.
From such a description a deformation model can be derived
that relates strain rates to stresses, strains and the temperature.
The resulting creep curve bears great similarity with the
Lemaitre and the Menzel-Schreiner deformation law. However,
different from these curve fitting laws, primary creep here
is based on proper micro-mechanical considerations and moreover
can cope with the transient effects as occurring when load
or strain rate increments are suddenly changed. |
Creep behavior |
- |
| Förster, S. |
1974 |
Durchlässigkeits-und Rißbildungsuntersuchungen
zum Nachweis der Dichtheit von Salzkavernen
[Permeability and fracturing investigations to verify the
tightness of salt caverns] |
Neue Bergbautechn. 4 (1974) 4, pp. 278-283 |
Journal Article |
German |
The main criteria for the construction of storages
or for the use of existing underground cavities for storage
is the tightness of the rock surrounding the cavity. The maximum
working pressures for the cavity must therefore be selected
to ensure that the host rock will not fracture, thereby excluding
possible leakage. The investigations described here focus
on the rock surrounding the salt cavity. |
Permeability of rock salt;
Interdependence rock stress - permeability;
Hydrofracturing |
- |
| Förster, S. |
1985 |
Gasdruckbelastbarkeit und Rißbildung
der für die unterirdische Gasspeicherung in Kavernen
bedeutsamen Salinargesteine des Zechsteins
[Stressability by gas pressure and fracturing of evaporites
of Zechstein-formation relevant to gas cavern storage] |
Freiberger Forsch.-H. A 724 |
Report (Abstract) |
German |
Proceeding from both the theoretical relations
between initial fracturing and fracture propagation in tight
saline rock and the prevailing stress state numerous results
of in-situ investigations gained in several salt deposit areas
are interpreted in a uniform mode. Data are estimated serving
as a basis for the calculation of maximum working pressure
in cavern storage. The results obtained are also important
in designing sealing measures in potash and rock salt mining. |
Hydrofracturing |
only abstract; German original at KBB |
Fuenkajorn, K.;
Daemen, J. J. K. |
1996 |
Sealing of boreholes in rock: an overview |
in: Aubertin et.al.: Rock Mechanics, 1996,
pp.1447-1454 |
Paper |
|
This paper describes the process, criteria,
and considerations for design of borehole seals in rock, with
a main emphasis on the hydraulic and mechanical performance
of the cementitious and bentonitic seals. It is recommended
that design and material selection for borehole seals be site-specific.
Evaluation of sealing effectiveness should be made on the
entire seal system, i.e. seal, seal-rock interface, and the
surrounding rock. |
Borehole seal |
- |
Fuenkajorn, K.;
Serata, S. |
1994 |
Dilation-induced permeability increase around
caverns in salt |
Proc. 1st. North American Rock Mechanics Symp.,
Austin, 01.-03.06.94, pp.649-656 |
Paper |
|
A permeability model is developed from triaxial
flow test data to predict the permeability increase of rock
salt around storage caverns, as affected by excavation, confining
and internal pressures, age and shape. The confining and internal
pressures may increase the surrounding salt permeability from
its in-situ value of 10-22 m² to as high as 10-16 m².
The permeabilities increase with time and reach their ultimate
value at within one year after excavation. Salt permeabilities
around elliptical caverns are several orders of magnitude
higher than those around the spherical cavern. |
Permeability - High deviatoric stress |
- |
Garg, S. K.;
Nur, A. |
1973 |
Effective stress law for fluid-saturated porous
rocks |
J. Geophys. Res. 78 (1973) 26, pp. 5911-5921 |
Journal Article |
|
The functional relationship between various
definitions of effective stress, i.e., conventional, Biot-Willis-Nur-Byerlee,
and theory of interacting continua (Tinc), is explored both
theoretically and experimentally. Stress-strain data on dry
and saturated Weber sandstone demonstrate that the conventional
effective stress law grossly overestimates the pore pressure
effect, whereas Biot-Willis-Nur-Byerlee and Tinc laws somewhat
underestimate this effect. Failure is examined from a microscopic
point of view. It is shown that Tinc-type effective stress
laws cannot account for the effect of pore pressure on failure
in a simple manner. Failure is one aspect of material response
in which the conventional effective stress law is useful.
In summary, it appears necessary to have two effective stress
laws, i.e., one to describe the stress-strain response and
a second to delineate the failure surface. |
Pore pressure in permeable salt;
Reservoir Mechanics |
- |
| Gaz de France |
1990 |
Field tests in well EZ 58 |
SMRI Res. Proj. Rep. No. 90-0002-S |
SMRI Research Report |
|
The matching curves are presented on figures
20 and 21.
It was made clear during the simulation progress that it was
not possible to correctly match the injected volumes over
the whole test, taking into account the assumptions about
pressures initialization and salt petrophysical characteristics
invariance in the vicinity of the well during pressure gradient
increase.
Indeed, if the permeability is chosen so as to adjust the
brine quantities on the first steps (1.6 to 2 gradient), the
volume required for the next steps will be much too high.
If, on the contrary, the matching is made on the last steps
the computed values will be too small for the first steps.
In the first case, we have to assume that the characteristics
of the open hole sail change during the test : the permeability
in the vicinity of the well or, at least the productivity
index would decrease with time.
In the second case, it is possible to think that the uncertainty
on the initial pressures condition prevents to correctly simulate
the flow rate at the beginning of the test, while its influence
becomes less important on the last steps.
This last assumption was eventually retained for the interpretation.
The matching was mainly performed on the permeability as it
is less sensitive to the porosity. It is possible, for instance,
to obtain similar computed flow rates with the following values
:
k = 6 x 10-5 mD = 1 % (mean value)
k = 5.5 x 10-5 mD = 2 % (mean value)
k = 6.5 x 10-5 mD = 0.5 % (mean value)
The influence of other parameters was also examined : if
rock or fluid compressibility is increased, the variation
of the injected volumes from one gradient to another one
stays similar, but it is again necessary to decrease the
permeability to find the same values.
Eventually, the simulations were performed with a permeability
of 6 x 10-5 mD and a porosity of 1 %. |
In-situ tests;
Permeability - liquid pressure above confining pressure;
Reservoir Mechanics |
- |
Gloyna, E. F.;
Reynolds, T. D. |
1961 |
Permeability measurements of rock salt |
J. Geophys. Res. 66 (1961) 11, pp. 3913-3921 |
Journal Article |
|
A method is described for measuring the permeability
of rock salt. Different specimens of salt were studied, and
the technique was checked by use of a solid crystal of sodium
chloride. Both reactive and nonreactive fluids were used in
collecting permeability data. Permeability tests were run
on rock salt from both dome and bedded formations. The dome
salt was found to have a very low permeability, and the bedded
salt was found in general to be impermeable. Where there was
some measurable permeability under the conditions of the test,
it was found that the permeating flow occurred through cracks
or fractures in the salt and not through the crystals themselves.
These fractures were apparently caused by the relaxation of
stress which occurs when underground samples are removed from
a compressed formation. The dome salt was found to have more
fractures than the bedded salt, owing probably to its lower
elastic strength. Such surface fractures, found in both types
of salt, will be localized in the vicinity of a mine and consequently
will not extend throughout a formation. |
Permeability of rock salt |
- |
Gniady, C. T.;
Ehgartner, B. L. |
1993 |
Fracture predictions for over-pressurization
of sealed wellbores |
SMRI Fall Meeting, Lafayette, 24.-28.10.93 |
Paper |
|
The finite element method is used to evaluate
the mechanical response of a wellbore that is internally pressurized
above lithostatic pressure. The uncased wellbore is emplaced
in salt, a rheologic media. Salt creep tends to relax the
stress state in the salt around the wellbore making it possible
to expand the size of the wellbore without fracturing the
surrounding salt. This is a very desirable sealing feature
as plugging and abandoning a cavern typically results in wellbore
pressures that exceed lithostatic pressure. The analyses show
that the rate of pressurization determines the hoop stress
in the salt surrounding the wellbore. Pressurizing the wellbore
above the surrounding lithostatic pressure reduces the hoop
stress and, for very quick pressurization rates, the hoop
stress can become tensile and fracture the salt. For most
cavern fields, the pressurization rates after sealing and
abandonment should be well below that required to mechanically
fracture the salt surrounding a plugged wellbore. In the long-term,
however, other mechanisms may contribute to fracture, or to
increase the permeability in the salt. |
Cavern abandonment;
Rock mechanics |
- |
Hambley, D. F.;
Dusseault, M. B. et al. |
1988 |
Characterization of saltrock creep behavior |
Key questions in rock mechanics: Proc. 29th
U.S. Symp., pp.179-189 |
Paper |
|
Improvement of saltrock creep laws requires
microscopic mechanisms incorporation, adequate tests, appropriate
equation forms, and better use of field data. A low-stress
pressure solution mechanism, affected by grain size, may he
important for field modeling, leading to a stress exponent
of 1.0 in situ for saltrocks with sufficient moisture content. |
Creep behavior |
- |
| Herrmann, A. G. |
1980 |
Geochemische Prozesse in marinen Salzablagerungen:
Bedeutung u. Konsequenzen f. d. Endlagerung..
[Geochemical processes in marine salt deposits: their significance
and their implications in connection with disposal of radioactive
waste within salt domes] |
Z. dt. geol. Ges. 131 (1980), pp.433-459 |
Journal Article |
German |
Attempts to effect permanent disposal of radioactive
wastes in marine evaporates should do nothing to disturb,
either in the short or the long term, the present relative
stability of such bodies of rock. It is necessary to take
account of all of the geochemical and physico-chemical reactions
known to have been involved in the processes which formed
the evaporates before proceeding to an acceptable strategy
for disposal of radionuclides.
These processes can be represented as three kinds of metamorphism:
1. solution metamorphism, 2. thermal metamorphism, 3. dynamic
metamorphism. In all of the evaporate occurrences in Germany
such processes have been influential in altering, on occasion
significantly, the primary mineralogical composition and have
also promoted a considerable degree of transposition of material.
Given similar geochemical and physico-chemical premises, these
metamorphic processes could become effective now or in the
future. It is therefore necessary to discuss the following
criteria when examining salt domes as permanent repositories
of highly radioactive substances:
(1) Temperatures 90° ± 10°C at the contact
between waste containers and rock salt;
(2) Temperatures 75°C within zones of carnallite rocks;
(3) Immobilisation of high-level waste in crystalline forms
whenever possible;
(4) Systems of additional safety barriers around the waste
containers or the unreprocessed spent fuel elements. The
geochemical and physical effectiveness of the barriers within
an evaporate environment must be guaranteed. For example:
Ni-Ti-alloys, corundum, ceramic, anhydrite. |
Permeability of rock salt |
- |
| Hofrichter, E. |
1976 |
Zur Frage der Porosität und Permeabilität
von Salzgesteinen
[Remarks on the porosity and permeability of salt rocks] |
Erdöl-Erdgas-Zs. 92 (1976) 3, pp.77-80 |
Journal Article |
German |
The velocities of elastic waves and the thermal
conductivity of rock salt -measured both in situ as well as
in the laboratory - were compared with the corresponding values
calculated theoretically. The basis of these theoretical values
are the elastic and thermal data of NaCl crystals.
The comparison shows that an undisturbed salt deposit has
the same properties as those of quasiisotropic crystalline
NaCl which is free from voids. Rock salt, in situ around cavities
in the mine and in the form of specimens, must have a looser
structure on account of different elastic and thermal properties.
Experiments with air under high pressure in salt mines have
proven the impermeability of the salt rocks. Bituminous material
in salt formations is usually of syngenetic origin. Its presence
does not indicate a migration into the salt. C02 gas under
high pressure occurs in the salt of the Werra Basin in Germany
as a consequence of Tertiary volcanism. This gas could not
escape since that time because of the impermeability of the
salt. |
Permeability of rock salt;
Pore pressure in permeable salt |
- |
| Horseman, S. T. |
1988 |
Moisture content - a major uncertainty in storage
cavity closure prediction |
Proc. 2nd. Conf. Mechanical Behavior of Salt,
Hannover, 24.-28.09.84, pp. 53-68 |
Paper |
|
This paper examines one of the major uncertainties
in the application of laboratory test results to the design
of solution-mined storage cavities in rock salt The properties
of salt are such that water will, when present, have significant
effects on mechanical behavior., including enhanced ductility,
strength variation, an increased capacity for creep deformation
and possible volume changes associated with the hydration
of secondary minerals. Although these effects are widely recognized,
surprisingly few observations have been recorded and the available
data, discussed here, can only be assessed in a qualitative
manner. The evidence is, however, sufficiently conclusive
to indicate that, unless special measures are taken to reproduce
the in situ condition of the salt in the laboratory, the experimental
results will be grossly incorrect. The uncertainty lies in
the selection of appropriate laboratory test conditions. An
argument is advanced here that, for cavity closure prediction,
salt specimens should be thoroughly dried and tested under
conditions devoid of moisture. |
Creep behavior |
- |
Horseman, S. T.;
Russell, J. E. et al. |
1993 |
Slow experimental deformation of Avery Island
salt |
Proc. 7th. Symp. on Salt, Kyoto, 1993, Vol.
1, pp. 67-74 |
Paper |
|
Two 100 mm diameter by 200 mm long cylinders
of Avery Island (A.I.) rock salt have been subjected to a
constant strain rate 10-9 s-1 at 15 MPa confining pressure
and 50 and 100°C. The experimental conditions have been
virtually constant over a period of about 3.5 years during
which the samples have shortened homogeneously by about 11%.
The specimen deformed at 100°C (Test 47) reached a steady-state
stress of 4.7 MPa at 2% strain whereas that at 50°C (Test
46), still slightly work-hardening, reached a quasi steady-state
stress level of 12.6 MPa. Microstructural analysis reveals
that dislocation glide and cross-slip dominated deformation
at 50°C whereas, at 100°C, subgrain development is
excellent indicating extensive dislocation climb.
These data points from Tests 46 and 47 were combined with
nine earlier constant strain rate steady-state test results
to provide, by nonlinear least squares, the relation
e8 = 6.5 x 10-5 exp (-69.7/RT 10-3)s5.9
When added to 27 A.I. constant stress test data points
of RE/SPEC Inc., ten of the low stress, low strain rate
tests at 100 and 200°C are very well fit by e a s3.4
whereas the remaining high strain rate, high stress quasi
steady-state data are well fit by e a s5.2. This change
in behavior, which must result from a change in dominant,
rate-limiting, mechanism bears importantly on inferences
concerning rates of natural salt deformation. At comparable
temperature and stress, the e a s3.4 relation predicts strain
rates two orders of magnitude higher than does the e a s5.2
equation; the latter is likely to be most pertinent to geotechnical
engineering applications. |
Creep behavior |
- |
Howarth, S. M.;
Peterson, E. W. et al. |
1991 |
Interpretation of in situ pressure and flow
measurements of the Salado formation at the Waste Isolation
Pilot Plant |
SPE Paper 21840 |
Paper |
|
This paper describes preliminary interpretation
of in-situ pressure and flow measurements of the Salado Formation
at the Waste Isolation Pilot Plant (WIPP). The WIPP facility
is located 660 m underground in the Salado, a bedded salt
deposit. Shut-in pressure tests were conducted prior to, and
subsequent to, the mining of a circular drift in order to
evaluate excavation effects on pore pressure, permeability,
and host rock heterogeneity. Borehole deformation was measured
during these tests and used to correct for changes in the
test region volume due to salt creep effects.
Preliminary pre-excavation results indicate that the flow
properties of this layered host rock are heterogeneous. Resulting
pore pressures range from 1 to 14 MPa and permeabilities range
from below measurable to about 1 nanodarcy. Normalized borehole
diameter change rates were between -4 and 63 microstrains/day.
Shut-in pressures and borehole diameters in all test boreholes
were affected by the excavation of Room Q coincident with
the advances of the boring machine. Preliminary results from
post-excavation test results show decreased pore pressures
compared to pre-excavation values. |
In-situ tests;
Permeability of rock salt;
Reservoir Mechanics;
Pore pressure |
- |
Hunsche, U.;
Schulze, O. |
1993 |
Effect of humidity and confining pressure on
creep of rock salt |
Proc. 3rd Conf. Mechan. Behavior of Salt, pp.
223-234 |
Paper |
|
Uniaxial tests with stepwise variation of the
relative humidity f of the surrounding air show that steady
state creep rates are increased by a factor of about 55 between
f = 0 and 75 %RH. Triaxial creep tests with stepwise variation
of the confining pressure p show that steady state creep rates
are increased by a factor of about 30 between p = 3 and 0.1
MPa. This humidity induced creep is explained with moisture
assisted in situ recrystallisation at points with stress concentrations
caused by strain hardening at the contact of grains. This
effect is possible only at low pressures p in the vicinity
of underground openings where the salt is dilatant and thus
permeable for the moisture. An empirical function has been
formulated describing the change of steady state creep rate
as a function of f and p. |
Creep behavior |
- |
Hunsche, U.;
Schulze, O. |
1994 |
Das Kriechverhalten von Steinsalz
[Creep of rock salt] |
Kali u. Steinsalz 11 (1994) 8/9, pp.238-255 |
Journal Article |
German |
This paper provides an overview of the current
level of understanding of the creep behavior. of natural rock
salt on the basis of physical processes and practical experience.
Transient as well as stationary creep were defined on the
basis of the effective deformation mechanisms, and a number
of usable laws discussed for both cases. This revealed that
the reliable prediction of deformation over long periods of
time is only possible on the basis of physical theories.
The correct modelling of the stress sensitivity of the creep
is particularly important. Although this has not yet been
solved satisfactorily, a stress exponent of n = 5 to 7 in
the median stress zone is applicable. The use of a precise
law for the stationary creep of a specific rock salt type
only makes sense if it used together with a law for transient
creep. Transient behavior. can only be adequately modeled
with the help of inner strength variables. In addition, problems
are discussed which arise when extrapolating one dimensional
laws to three dimensional space.
The major differences in creep behavior. of various rock salt
types are presented and attributed to the effect of contamination
- the distribution of which has a geological cause. An example
is the frequently observed difference in behavior. of rock
salt from the Staßfurt series (z2) and the Leine series
(z3). Modern exploration methods allow homogeneous zones with
the same mechanical behavior. to be determined in rock salt
deposits. The increasing effect of humidity on creep in the
vicinity of cavities is quantitatively described on the basis
of laboratory tests. Moreover, the effect of dilation on the
mechanical behavior. of salt is also discussed.
Because the mechanical reaction of a rock salt deposit to
the creation of cavities is so complex, interdisciplinary
collaboration is required for its successful description.
Finally, subjects relating to the deformation behavior. of
rock salt will be presented which require further investigation. |
Creep behavior |
- |
Jäpel, G.;
Fritze, P. et al. |
1991 |
Verfahren zur Endverwahrung von Salzkavernen
[Method for the maintenance of shut in salt caverns] |
DE 41 04 383 C2 |
Patent |
German |
The solution in accordance with the invention
prevents for the most part the transfer into the cavern roof
of substantially higher rock pressures from the lower cavern
section and hence substantially reduces the risk of fracturing.
The invention enables safe abandonment of salt caverns and
secure final disposal of hazardous materials and waste products. |
Borehole seal;
Cavern abandonment |
- |
Jäpel, G.;
Schmidt, T. et al. |
1990 |
Zur Ermittlung der Gasdruckbelastbarkeit des
Werrasteinsalzes und der Ableitung zulässiger maximaler
Betriebsdrücke für die Kavernenspeicheranlage Xanten
[The determination of the maximum gas pressure capacity of
the salt and the deduction ...] |
Erdöl Erdgas Kohle 106 (1990) 4, pp.155-161 |
Journal Article |
German |
An important operational parameter for an underground
gas storage cavern produced in salt by solution mining is
the maximum admissible gas pressure coefficient and the elated
maximum admissible operating pressure for the storage cavern.
In cooperation between the VEB Kombinat Gasanlagen, Mittenwalde
(GDR), the Thyssengas GmbH, Duisburg, and renowned scientists
from the GDR and the Federal Republic of Germany, in-situ
measurements to assess the maximum gas pressure capacity of
the salt were successfully carried out for the first time
in the Federal Republic of Germany employing a testing process
developed in the GDR.
The work carried out has been supported by the competent mining
authority and the results obtained from the basis for the
mining authority's approval of higher maximum internal pressures
at underground gas storage caverns in Xanten. |
Hydrofracturing |
- |
| Jenyon, M. K. |
1986 |
Salt with a pinch of water |
Nature 324 (1986), 11.Dec., pp.515-516 |
Journal Article |
|
The connection between the rheological behavior.
of the mineral halite (NaCl) in the presence of very small
quantities of free water and radioactive waste disposal may
at first seem obscure. There is a strong link, however, some
aspects of which are described by Urai et al. (1) on page
554 of this issue. Adding to previous work (2, 3), these authors
go some way towards elucidating the marked effects on halite
rheology of the very small quantities of brine inherent in
a polycrystalline salt mass. The investigations have important
implications for the determination of long-term stability
in any rock salt body that is being considered as a repository
of radioactive waste or for material storage. Their findings
are also of importance in the wider field of salt tectonics. |
Rock mechanics;
Permeability of rock salt |
- |
Jewentow, J. S.;
Mileschina, A. G. et al. |
1973 |
Über die Erdöldurchlässigkeit
fossiler Salze. Abgehandelt am Beispiel der Kaspisenke
[On the relative permeability to oil of fossil salts. Using
the Caspi basin as an example] |
Zs. f. angew. Geol. 10 (1973) 2, pp.67-71 |
Journal Article |
German |
Deep exploration wells have penetrated the
salt series in the margins of the basin where it reaches a
maximum thickness of 3000 to 3500 m (Biikshal, Kenkijak, Kindyssai,
and other salt domes). In the centre of the basin it has been
partially penetrated up to 2000 to 2500 m on some domes (Bolgan-Mola,
Dossor, Tschernaja Retschaka, etc.). |
Permeability of rock salt |
- |
Kenter, C. J.;
Doig, S. J. et al. |
1990 |
Diffusion of brine through rock salt roof of
caverns |
SMRI Fall Meeting, Paris, 14.-19.10.90 |
Paper |
|
Operational experience has shown that a fluid
filled cavity in rock salt is tight at normal operating pressures
which are below the ambient lithostatic salt stress. However,
little is known about the tightness at pressures above lithostatic.
It was shown in an experimental set up that fluid will permeate
through the cavity roof under these conditions. The process
is largely governed by a threshold pressure, being the ambient
litho-static stress. Below this threshold flow is negligible;
above the threshold pressure the fluid is opening up intercrystalline
boundaries in the rock salt. Once a flowpath has been opened,
flow appears to be driven by the excess pressure above lithostatic
only and not to be affected by the pressure drop from lithostatic
to hydrostatic. The permeability decreases about proportional
to consolidation pressure and consolidation time of the salt
sample on a log-log scale. |
Cavern abandonment;
Permeability - liquid pressure above confining pressure;
Reservoir Mechanics |
- |
| Kiersten, P. |
1988 |
Laboratory hydraulic fracturing experiments
in rock salt |
Proc. 2nd. Conf. Mechanical Behavior of Salt,
Hannover, 24.-28.09.84, pp. 223-233 |
Paper |
|
The interpretation of in-situ-hydrofrac results
in salt rock is fraught with particular difficulties, if there
is a marked deviation between the measured critical pressure
values and the theoretical results expected. Here the performance
of tests along with rock and rock mass specific parameters
can be attributed special significance. Some laboratory experiments
are presented, which indicate the influence of various test
parameters on the level of the frac pressure measured. Therefore
thick walled cylindrical specimens of rock salt, lithostatically
loaded in a pressure chamber (autoclave) were injected with
internal pressure under different test conditions to initiate
hydraulic fractures. |
Hydrofracturing |
- |
| Kublanov, A. |
1995 |
Experiences in using hydrofracturing at the
holes of Novo-Moscowsk brine field operations |
SMRI Fall Meeting, San Antonio, 22.-25.10.95 |
Paper |
|
Novomoskovsk rock salt deposit is the monobed
ore body of gently sloping occurrence, 40-50 m in thickness,
situated at 900 m depth.
This deposit is being developed from 1960 by "Azot" (Nitrogen)
- a largest in Russia chemical Novomoskovsk Stock Company.
Method for deposit development is the underground salt dissolution
with individual caverns by stepwise method and with hydrocarbon
blanket liquid.
Due to geological peculiarities and some errors in technology
of mining, by early 1990s at the brine field operations occurred
crosscutting of a part of caverns between themselves, which
resulted, in its turn, to caving of over salt rocks, ruptures
and pinchings of casing and operating pipe columns in the
holes. Emergency situation that occurred at the site of crosscut
caverns made impossible further operation of these caverns
and resulted in drastic drop of the brine field facilities
designed capacity. The critical situation urged the Novomoskovsk
Stock Company "Azot" to apply to VNIIG with the order to render
technical assistance in restoring the needed capacity of brine
mining. |
Hydrofracturing |
- |
| Lai, C. S. |
1971 |
Fluid flow through rock salt under various
stress states |
Ann Arbor : Michigan State Univ. |
Thesis |
|
Concern for leakage of reactor fuel waste materials
from underground salt cavities has prompted questions regarding
the permeability of rock salt materials. To provide information
on this question, the flow rate of kerosene through rock salt
specimens was studied for a range of normal and octahedral
shear stresses. Kerosene was used as the fluid because of
a similarity to radioactive waste materials and its nonrusting
properties when In contact with steel. Expressions for the
permeability of the rock salt were developed In terms of the
stress conditions and void ratios of the rock salt material.
A high pressure triaxial cell was designed and constructed
for permeability tests at various stress states. The cell
permitted application of axial loads separate from lateral
pressures. Independent hydraulic systems maintained axial
and lateral pressures to about ± 5 psi of selected
pressures. Fluid flow was permitted axially through the sample
under a head differential of 125 psi.
Rock salt from an underground formation In Louisiana was cut
into cylindrical samples 3 inches high by 3 inches in diameter.
Strain gages attached to the sides of the sample provided
information on tangential and axial strain. Overall axial
deformation, obtained by means of a dial gage mounted outside
the triaxial cell, provided a check on strain gage values.
Kerosene flow through the sample was recorded at given time
Intervals.
The experiment date provided the basis for developing empirical
expressions for the rock salt permeability in terms of the
mean normal stresses and octahedral shear stresses. Strain
measurements permitted incorporating changes in void ratio
into the permeability expressions. The flow of kerosene through
the rock salt appears to obey approximately the same laws
as developed for flow of water through soils. Laboratory permeabilities
for the rock salt varied from 0.0036 to 40.6752 milli-darcy
for various stress states. Very low permeabilities indicate
that leakage of radioactive waste materials from underground
salt cavities will be very small to almost negligible. |
Interdependence rock stress - permeability;
Permeability of rock salt - High deviatoric stress |
- |
| Langer, M. |
1993 |
Use of solution-mined caverns in salt for oil
and gas storage and toxic waste disposal in Germany |
Eng. Geol. 35 (1993) 3-4, pp.183-190 |
Journal Article |
|
The need for storage caverns for oil and gas,
and repositories for toxic chemical waste is increasing world-wide.
Rock salt formations are particularly suitable for the construction
of cavities for such purposes. Owing to its favourable geomechanical
properties, rock salt remains stable over long periods of
time without support, and it can be shown that the geological
barrier of the host rock remains intact for a remarkably long
time.
Safety analysis must be made for each proposed site based
on site-specific data. The methods of doing this are well
known and related technical recommendations exist in Germany.
These recommendations apply to the planning, construction,
opera. tion and post-operational management of salt caverns
used for the underground disposal of hazardous wastes. In
particular, geotechnical site-specific safety verification,
as required by the government's technical regulations on wastes
(TA-Abfall) under the section "Underground Disposal", is required.
This safety verification must cover the entire system comprising
the waste, the cavern and the surrounding rocks. For this purpose
geomechanical models have to be developed. The steps which
must be taken when carrying out geological engineering site
explorations and when determining geotechnical parameters
are discussed. In addition, recommendations are made for the
design and construction of underground repositories.
For liquid-filled caverns, long-term sealing from the biosphere
is of particular interest. In this instance it must be shown
that the natural increase in pressure in the closed cavity
due to long-term convergence does not exceed the fracture
pressure. A special field test (scale 1:1) has been performed
to study this. |
Cavern abandonment |
- |
Langer, M.;
Wallner, M. |
1988 |
Solution-mined salt caverns for the disposal
of hazardous chemical wastes |
Bull. IAEG No. 37 (1988), pp. 61-69 |
Journal Article |
|
The need for storage caverns (oil, gas) and
depositories (radioactive waste, toxic chemical waste) is
rising world-wide. Rock salt (halite) formations are particularly
suitable for the construction of cavities for such purposes.
Rock salt is practically impermeable to gases and liquids.
The solution mining method provides the means for the creation
of large storage capacities at economic costs and, due to
its favourable geomechanical properties. halite remains stable
over long periods of time without support. Moreover, it can
be shown that underground depositories in salt are safer from
an environmental point of view compared with conventional
depositories in shallow ground.
However, safety analysis has to be carried out in each case
based on specific site-investigated data. The geotechnical
behavior of rock salt is well-known, with sufficient details
for dimensioning purposes. For liquid-filled cavities, long-term
scaling from the biosphere is of particular interest. In this
case, the following topics have to be investigated from the
engineering-geological viewpoint : the permanent tightness
of borehole cementation has to be proved and it must be shown
that the natural pressure rise in the closed cavity due to
long-term convergence does not exceed the frac pressure. It
is shown that the risk of hydraulic fracturing can be calculated
with the aid of finite element computations. Hydraulic fracturing
depends on the height and depth of the cavity as well as on
the pressure increase rate. |
Cavern abandonment;
Rock mechanics |
- |
Langer, M.;
Wallner, M. et al. |
1984 |
Gebirgsmechanische Bearbeitung von Stabilitätsfrage
bei Deponiekavernen im Salzgebirge
[Rock mechanical elaboration of stability aspects in rock
salt repository caverns] |
Kali u. Steinsalz (1984) 2, pp.66-76 |
Journal Article |
German |
A number of soundly based modern salt mechanical
methods are available for the rock mechanical elaboration
of stability aspects in rock salt caverns. These are: material
laws and material parameters, failure criteria, and calculation
techniques based on the finite element method. Following a
comprehensive discussion of these tools, the special stability
problems occurring when sealing liquid-filled repository caverns
will be analysed. In particular, the pressure increase in
such caverns will be calculated using models, and these will
be used to derive conclusions on the frac risk. The analysis
shows that the results of conventional hydraulic frac tests
in boreholes cannot be directly extrapolated, but require
prior comprehensive computer analysis. |
Cavern abandonment;
Rock mechanics |
- |
| Le Guen, C. |
1991 |
Mesure de la perméabilité de
roches très peu perméables et étude de
son évolution sous sollicitations thermomécaniques
[The permeability measurement in ultralow permeability rocks
and the study of the evolution under thermomechanical stresses] |
Paris : École Nat. Supérieure
des Mines |
Thesis (Abstract) |
french |
Permeability lower than 10-17 m² can not
be measured using the classical methods. To overcome this
lack, another method, called the "Pulse Decay method", should
be used. It consists in recording the evolution of a pressure
pulse applied on the upstream side of the sample at t=0. A
specific apparatus was built to measure permeabilities of
rocks under thermomechanical stresses using the pulse decay
method. This apparatus can measure permeabilities between
10-15 and 10-22 m².
Two calculation methods have been used: the first one, based
on the Brace equation, is efficient for samples of ultralow
porosity. The second one resolves numerically the diffusivity
equation and is efficient for all types of sample.
Several thermomechanical tests, including intermittent permeability
determinations, have been carried out on samples issuing from
the Bresse basin saliferous lithofacies. The initial permeabilities
are more representative of the state of the sample than of
the in-situ formations. On the other hand, the permeability
evolution during the thermomechanical tests seems to be directly
conneced to the nature and torture of the material and express
quiet well the structural evolution. For example the deformation
tests under constant pressure and temperature show that, for
all the lithofacies, the permeability decreases continuously
in relation with the creep capacity of halite. |
Permeability of rock salt |
- |
Le Guen, C.;
Deveughele, M. et al. |
1993 |
Gas permeability changes in rock salt subjected
to thermo-mechanical stresses |
Quart. J. Eng. Geol. 26 (1993), pp.327-334 |
Journal Article |
|
Permeabilities lower than 10-17 m² cannot
be measured using classical methods. To overcome this problem,
the pulse decay method may be applied. In this method the
evolution of a pressure pulse applied on the upstream side
of the sample at t = 0 is recorded. An apparatus has been
constructed to measure ultra-low permeabilities of rocks under
thermomechanical stresses; intrinsic permeabilities between
10-15 and 10-22 m2 can be measured.
Several thermo-mechanical tests, including permeability determinations
have been carried out on samples from saline lithofacies of
the Bresse basin (France). The initial permeabilities are
more representative of the condition of the test sample than
of the undisturbed state of the formation. Nevertheless, the
permeability changes observed during these tests seem to be
directly connected to the nature and structure of the material
and are indicative of the structural modifications the material
sustains under changes of temperature and stress. During isotropic
deformation tests, the response of permeability to pressure
varies depending on the specific lithological characteristics
of the samples. Deformation tests under deviatoric stress
with constant confining pressure and temperature show that,
for all the lithofacies, the permeability decreases continuously.
This can be attributed to creep deformation of the halite. |
Permeability of rock salt;
Interdependence rock stress - permeability |
- |
Lee, R.;
De Souza, E. |
1996 |
The effect of brine dissolution on the strength
behaviour of evaporites |
Proc. 2nd. North American Rock Mechanics Symp.,
Montréal, 19.-21.06.96, Vol. 1, pp.69-76 |
Paper (Abstract) |
|
In response to interest regarding the effects
of inflow brine on the strength characteristics of pillar
support in soft rock mines, a laboratory research program
which simulated the interaction of brine with potash and salt
rock has been successfully undertaken. Potash and salt cores
were deformed under unconfined, constant load conditions,
both with and without added inflow brine. Factors such as
brine temperature and axial load were varied in order to determine
their relative effects on both deformation rates and dissolution
chemistry. The results indicated a substantial increase in
creep rate in both materials with the addition of inflow brine.
Elevation of brine temperature resulted in further increases
in deformation rates. The dissolution experienced by the salt
material was very small even at elevated temperatures while
that of the potash increased considerably. The implications
to mining are that inflow brine may have a large effect on
the creep rates of evaporate ores through the enhancement
of fracture mechanics processes as well as solution transfer
creep. In potash ore, this weakening is compounded by the
removal of supportive material through the selective dissolution
of sylvite. |
Interdependence rock stress - permeability;
Strength of rock salt in case of brine impregnation |
- |
| Linn, J. K. |
1995 |
Closure and plugging of a cavern disposal well
in domal salt |
in: Suitability of solution-mined caverns for
oil and gas waste disposal, 13.09.95, Railroad Comm. Texas,
p.27 |
Paper (Abstract) |
|
Permanent disposal of wastes in salt caverns
must address the effects of salt closure plugging of the disposal
well. Caverns with liquid components to the waste, or significant
liquid remaining from the leaching / brine removal process,
have the capability to create sufficient pressure that under
some circumstances, the cavern integrity threatened. Our understanding
of the salt creep and thermal processes associated with cavern
waste disposal and current state of the art modeling capabilities
are sufficient reasonably accurate predictions of sealed cavern
pressures. Strategic Petroleum Reserve caverns have been studied,
and pressures following plugging and abandonment analyzed.
Results of FEM analysis are shown that detail the time frame
and, magnitude of the pressurization problem. Waste disposal
would nominally be done in similar geometries, and at similar
depths. The final internal cavern pressures are shown to be
highly dependent on initial temperatures and salinity of the
fluid. For caverns of SPR height and salt dome geometries,
final pressures are not predicted to place the salt in tension
and potentially create salt cracking or fractures. Limited
experimental data available from foreign tests have indicated
problems with maintaining integrity under such conditions.
Until further controlled experiments with real caverns or
wells can be completed, the long-term integrity of sealed
salt caverns with significant liquid components will remain
uncertain. Use of caverns for oil and gas waste disposal must anticipate the potential for long-term pressure buildup and
its long-term effects on the integrity of the salt cavern. |
Cavern abandonment;
Borehole seal |
only abstract |
| Mazariegos, R. A. et al. |
1996 |
Modeling the evolution of salt structures using
nonlinear rocksalt flow laws |
Tectonophys. 256 (1996), pp.101-128 |
Journal Article |
|
We analyzed the evolution of a single wavelength
(l= 13.4 km) salt structure of initial amplitude Ao = 100
m by means of a 2D finite-volume numerical model. The model
incorporated two laboratory-derived rheological laws for rocksalt:
a low-stress, dislocation-creep power law (e a s3.4 ) and
a fluid-assisted diffusion creep law (e a s/Td³), in
which e is strain rate, s is the equivalent stress, T the
absolute temperature and d the grain size. Our model also
accounts for salt thermal conductivity dependence on temperature.
The models comprised 3.6 km of sediments overlying a 1.2-km-thick
salt layer with a density difference between sediments and
salt of 100 kg/m³ and sediments viscosity m2 = 3.0 x
10 to the power of 19 Pa s. We assumed that deformation is
driven solely by buoyancy forces. Results predict that salt
structures evolve faster (2- to 3.5-fold) in fluid-assisted
models than in dislocation creep models. Equivalent stresses
and viscosities predicted by the fluid-assisted law are lower
than those predicted by the power law, by factors of 3, and
1 to 2 orders of magnitude, respectively, depending on the
degree of structural maturity. In contrast, strain rates predicted
by both rheological law., are nearly the same, near 10-14
S-1 for similar degrees of structural maturity. Temperature
distribution in the model domain was controlled by the thermal
conductivity contrast between salt and sediments, the shape
of the salt structure and thermal conditions imposed at model
boundaries. At the early stages of evolution. a positive thermal
anomaly of + 30°C developed at the top of the salt structure.
At more advanced stages (e.g., diapiric stage), the thermal
anomaly decreased, maintaining values between + 5°C and
+ 20°C. |
Creep behavior |
- |
Miehe, R.;
Harborth, B. et. al. |
1993 |
Permeabilitätsbestimmungen im Staßfurt-Steinsalz
in Abhängigkeit von einer Streckenauffahrung [Permeability
determination in Staßfurt rock salt depending on roadway
drifting] |
Kali u. Steinsalz 11 (1993) 5/6, pp.175-184 |
Journal Article |
German |
The first test series to determine permeability
carried out in August 1989 took place prior to drifting the
south barrier roadway in unfractured evaporite. The permeabilities
determined were generally in the range k < 1.0E-21 m2.
The exception was borehole UP5 which had a higher permeability
of 1.3E-19 m2. In this borehole, which was divided into two
measurement intervals, there was communication above the salt
between the measured zones, which was confirmed by marking
with neon, so that both intervals were investigated together
in the following test. The second test series carried out
from April to June 1991, was also carried out prior to drifting
the south barrier roadway. In the interval between these two
test series, boreholes UP3 and UP4 were no longer usable because
of leaking packers. The tests carried out during this test
phase largely confirmed the results of the first test series.
However, the permeability in borehole UP5 had risen. In the
case of borehole UP7 which was still very tight in the first
test series with less than 1.0E-21 m2, the permeability had
increased to around 7.6E-18 m2 to 6.0E-17 m2 during the second
test series.
During the drifting of the south barrier roadway (third test
series), boreholes UP2 and UP6 which terminate a distance
of 2.5 m and 5.6 m respectively above the roof of this roadway
were tested. No effect was noticed during drifting.
Only in the fourth test series carried out after drifting
did borehole UP2 show a slight increase in permeability from
less than 1.0E-21 m2 to 3.0E-21 m2. No permeability increase
was established in borehole UP6 after evaluation with Interpret/2,
which was attributable to the fact that Interpret/2 has a
lower permeability limit of 1.0E-21 m2, which is above the
values for borehole UP6. However, the pressure data pointed
to a slight increase in permeability. Interestingly, borehole
UP8 which had the largest separation from the roof (12.1 m)
had a permeability increase of 2.0E-21 m2 to 6.9E-21 m2. And
boreholes UP5 and UP7 - which previously had higher permeabilities
- also revealed an increase in permeability. A clear increase
in permeability in borehole UP5 which was closest to the roof
(1.6 m separation) pointed to the development of a fracture
zone at the edge of the roadway. The permeability increases
in the 2 furthest boreholes, namely UP7 (8.0 m) and UP8 (12.1
m), may be attributable to far-reaching stress relocations
caused by drifting of the roadway.
In the fifth test series carried out from October to November
1992, borehole UP2 could no longer be tested for technical
reasons. The permeability of borehole UP5 rose after a long
waiting period to a value of 3.3E-15 m2. The permeability
reduced in boreholes UP7 and UP8. Thus, borehole UP7 had a
value of 1.6E-16 m2 and borehole UP8 a value of 1.8E-21 m2.
The permeability reduction points to consolidation in the
vicinity of these boreholes as a result of the plastic behaviour
of rock salt.
Because the resolution of the evaluation method is < 1.0E-21
m2, no significant changes could be recorded in the permeability
of borehole UP6 lying in the middle zone (roof distance 5.6
m), which means that the permeability continued to lie below
< 1.0E-21 m2.
From these results it can be concluded that the drifting of
the south barrier roadway has an effect on the permeability
of the rock and that the rock zone investigated is clearly
still reacting to the cutting of the cavities. Further tests
separated by longer time intervals need to be carried out
in the boreholes still available to monitor the development
of permeability. |
Permeability of rock salt |
- |
Morgan, H. S.;
Wawersik, W. R. |
1989 |
Computed and measured response of a thick-walled
hollow cylinder of salt subjected to both homogeneous and
inhomogeneous loading |
Proc. 30th. U.S. Symp. Rock Mechanics, Morgantown,
19.-22.06.89 |
Paper |
|
Closures and closure rates measured around
excavations in the bedded salt formations at the Waste Isolation
Pilot Plant (WIPP) were at least three times larger than initial
predictions made with a reference creep model for rock salt.
Subsequent investigations uncovered a number of potential
sources of error including questions about the constitutive
behavior of salt in situ (Morgan et al., 1986; Munson &
Fouum, 1986; Munson et al., 1989). In addition, controlled
laboratory experiments on thick-walled hollow cylinders of
salt, subjected to various combinations of axial load, internal
pressure, external pressure, and temperature, were suggested
as one expedient and cost-effective means of narrowing the
existing uncertainties (Lux & Heusermann, 1985, Van Sambeek,
1986; Wawersik & Morgan, 1987). Two recent tests on thick-walled
cylinders of rock salt are discussed in this paper to explore
the merits of this type of experiment and to address four
concerns: (1) differences between behavior of salt core in
the laboratory and behavior of salt masses in situ due to,
e. g., hardening and damage during sample extraction, (2)
generalization of triaxial measurements to three dimensions
requiring choices of strew measures and Bow rules, (3) effects
of inhomogencous stress states with gradients as opposed to
homogeneous stress fields, and (4) effects of pressure and
moisture (Wawersik & Morgan, 1987).
The present evaluations are based on comparisons of measurements
on the hollow cylinders with predictions from three different
constitutive models for rock salt. The three models are (1)
an elastic power-law secondary creep (ESC) model, (2) a revision
of the ESC (RESC) model with greatly reduced elastic moduli
but unchanged creep parameters, and (3) a unified creep plasticity
(UCP) model (Krieg 1980). The ESC model produced the predictions
that differed from the WIPP in situ measurements by the factor-of-three
or more. The modulus reductions in the RESC model are empirical
adjustments that produced matching closures and closure rates
with the WIPP measurements collected over less than five years
(Munson et al.,1987; Morgan & Krieg, 1988). The UCP model
yielded closures that were substantially higher than the ESC
predictions but still less than the in situ measurements.
At the same time, the UCP model produced closure rates in
good agreement with the data (Morgan & Krieg, 1988). |
Creep behavior |
- |
Morgenstern, N. R.;
Sepehr, K. |
1991 |
Time-dependent hydraulic fracturing in potash
mines |
Int. J. Rock Mech. Min. Sci. & Geomech.
Abstr. 28 (1991) 2/3, pp. 187-197 |
Journal Article |
|
This paper investigates by numerical methods
the cause(s) of mine seismicity and mine flooding occurring
at several potash mines in Saskatchewan, Canada. To assist
in the investigation, a finite-element model based on viscoelastic
/ viscoplastic material behaviour has been utilized. From
the analysis of various mining situations it is concluded
that hydraulic fracturing of the brittle Dawson Bay formation
occurs as a result of changes in the stress-strain regime
due to mining and this might be a possible cause of induced
seismicity. Hydraulic fracturing of the Dawson Bay and underlying
evaporites also results in communication of the aquifer with
the top of the mine development openings and rooms and hence
a path for flow of pressurized water into the openings.
Hydraulic fracturing of both the Dawson Bay and underlying
evaporite layer are demonstrated to be dependent upon pore
water pressure in the aquifer, the in situ state of stress
prior to mining and the duration of mining. |
Hydrofracturing |
- |
Munson, D. E.;
DeVries, K. L. et al. |
1993 |
Extension of the M-D model for treating stress
drops in salt |
Proc. 3rd. Conf. Mechanical Behavior of Salt,
Palaiseau, 14.-16.09.93, pp.31-44 |
Paper |
|
The multimechanism deformation model for the
creep deformation of salt is extended to treat the response
of salt to imposed stress drops. Stress drop tests produce
a very distinctive behavior where both reversible elastic
strain and reversible time dependent strain occur. These transient
strains are negative compared to the positive transient strains
produced by the normal creep workhardening and recovery processes.
A simple micromechanical evolutionary process is defined to
account for the accumulation of these reversible strains,
and their subsequent release with decreases in stress. A number
of experimental stress drop tests for various stress drop
magnitudes and temperatures are adequately simulated with
the model. |
Creep behavior |
- |
Munson, D. E.;
DeVries, K. L. et al. |
|
Measured and calculated closures of open and
brine filled shafts and deep vertical boreholes in salt |
DOE Contract No. DE-AC04-76DP00789 |
Report (Abstract) |
|
Results are presented of shaft closure measurements
based on a rather unusual emplacement of very early time closure
points. These data are in good agreement with calculations
based on the prediction to techniques developed for underground
rooms in salt using a complete stratigraphy. However, a simplified
calculational mesh also gives good agreement, which permits
this model to be used for parametric studies of long term
closures of open and brine filled shafts and boreholes. |
In-situ tests |
only Abstract |
Munson, D. E.;
Jensen, A. L. et al. |
1996 |
Brine release based on structural calculations
of damage around an excavation at the Waste Isolation Pilot
Plant (WIPP) |
Proc. 2nd. North American Rock Mechanics Symp.,
Montréal, 19.-21.06.96, Vol. 2, pp.1495-1500 |
Paper |
|
In a large in situ experimental room, circular
in cross section, inflow of brine was measured over a five
year period. After correcting the measured brine accumulation
for initial losses by evaporation into the mine ventilation
air, the measurements gave data for a period of nearly three
years. Predicted brine accumulation based on a mechanical
"snow plow" model of the volume swept by creep-induced damage
as calculated with the Multimechanism Deformation Coupled
Fracture (MDCF) model was found to agree quantitatively with
the experimental results. The calculation suggests the damage
zone at five years effectively extends only some 0.7 m into
the salt around the room. Also, because the mechanical model
of brine release gives an adequate explanation of the measured
data, the hydrological process of brine flow appears to be
rapid compared to the mechanical process of brine release. |
Creep behavior;
Interdependence rock stress - permeability |
- |
| Naujoks, A. |
1989 |
Numerische Analyse geomechanischer Wechselwirkungen
bei der Endablagerung von Sonderabfall in Salzkavernen
[Numerical analysis of geomechancial interactions during final
disposal of hazardous waste in salt caverns] |
Hannover : Univ., Fachber. Bauing.- u. Vermessungswesen;
Forsch.-Erg. 13 |
Thesis (Abstract) |
German |
The final disposal of hazardous wastes in underground
repositories will have an increasing importance in the future.
Salt caverns created by solution mining have to be considered
as a promising alternative to existing repositories excavated
by conventional mining techniques.
As the initial stress in a disposed waste material is lower
than the stress in the surrounding rock mass, closure of the
cavern is the consequence which, however, is influenced by
the back fill material (hazardous waste) in the cavern. The
resulting interactions are investigated by FE-calculations.
It is shown that sealing of a liquid-filled cavern causes
a pressure increase, and that finally the pressure in the
cavern roof exceeds the primary rock stress, the amount of
the excess pressure depending on the cavern geometry. The
resulting divergence is accompanied by tensile strains in
the surrounding rock mass, although no tensile stresses occur.
Under these circumstances, it has to be proved that a disposed
liquid does not spread in the rock mass, and that the long-term
tightness of the sealing construction is maintained.
Considering the final disposal of solid hazardous wastes,
both loose granulated and in situ hardening materials are
analysed. The results of the FE-calculations demonstrate that,
from a geomechanical point of view, those materials are favourable
which quickly achieve a high strength together with a low
deformability. The stress-strain-behaviour of a granulated
hazardous waste has to be investigated in detail, and has
to be described by an adequate material law.
Provided that the (thermo-)mechanical properties of the hazardous
waste (backfill) and the creeping rock mass are well-known,
the presented method of numerical calculation is able to serve
as a base for the proof of stability of future disposal caverns. |
Cavern abandonment;
Rock mechanics |
only Abstract; German original at KBB |
Nelson, R. A.;
O'Rourke, J. E. |
1986 |
Review of hydraulic fracturing tests in salt,
southeastern Utah, compared to other recent salt testing experience |
SMRI Spring Meeting, Baton Rouge, 20.-22.04.86 |
Paper |
|
Hydraulic fracturing stress measurements were
made in five different salt strata of the Permian-Age Paradox
Formation (Nelson, et al., 1982, and Schnapp, et al., 1983).
Test depths ranged from 3130 to 4890 ft.
The measurements were made in the Gibson Dome No. 1 (GD-1)
borehole in southeastern Utah. Sedimentary Permian- and Pennsylvanian-Age
deposits of sandstone, siltstone, limestone, and dolomite
overlie the Paradox Formation to a depth of 2618 ft. The Paradox
Formation consists of distinct beds of salt separated by interbed
sequences of anhydrite, dolomite, and fine clastic rock. The
Paradox Formation was deposited in 29 depositional cycles
with a total thickness of 2890 ft in the GD-1 borehole.
The salt found in each cycle is generally 95 percent pure
and forms beds from 7 to 346 ft thick. Anhydrite bands within
the salt beds comprise 2 to 5 percent of the rock mass in
each depositional cycle. The anhydrite is found in two forms:
(1) laminar anhydrite, which forms bands approximately 0.04
to 0.08 in. thick and spaced 1 to 4 in. apart; and (2) diffuse
1-in.-thick bands of anhydrite sand in a salt matrix. The
anhydrite does not cause planes of weakness within the individual
salt strata.
Care was taken to choose hydraulic fracture test intervals.
that were (1) totally within a single cycle of salt, and (2)
unfractured. To confirm an unfractured interval within the
salt cycle, the core was carefully examined for preexisting
fractures. None was observed within the test zones chosen.
Also, no bedding planes or other planes of weakness were observed
in the test intervals. Thus, all tests were performed in massive
salt without any apparent discontinuities. |
Hydrofracturing |
- |
Niou, S.;
Deal, D. E. |
1989 |
Migration of brine and nitrogen in creeping
salt |
Waste Management '89 Sympl., Tucson, 26.02.-02.03.89,
Vol. 1, pp. 329-335 |
Paper |
|
Although the excavations in bedded salt at
the Waste Isolation Pilot Plant (WIPP) are, for all practical
purposes, dry, small amounts of brine have been observed to
weep from exposed surfaces in the repository horizon and seep
into drill holes in the underground excavations. As part of
the Brine Sampling and Evaluation Program (BSEP) at the WIPP,
this study has been made to formulate the complex problem
of brine and nitrogen flow through deforming salt as completely
as possible. The derived equations are coupled where appropriate
in order to closely describe the natural phenomena. The main
objective of this paper is to suggest a method by which the
formulation might be solved in order to estimate the brine
inflow rate into the excavated rooms at the WIPP repository
level. The suggested solution method requires the modification
and combination of two finite element codes which may necessitate
a large amount of computer memory for data storage. |
Permeability of rock salt |
- |
Nowak, E. J.;
McTigue, D. F. |
1987 |
Interim results of brine transport studies
in the Waste Isolation Pilot Plant (WIPP) |
Albuquerque : Sandia Nat. Lab., SAND 87-0880 |
Report |
|
It is important to have quantitative predictions
of brine movement in a radioactive waste repository for performance
assessment and for seal design evaluations. Experiments to
quantify brine transport to boreholes in multi-heater, full
scale tests simulating high level waste repository environments
have been under way in the bedded salt of the Waste Isolation
Pilot Plant (WIPP) since April 1985. Water vapor released
to the test boreholes has been collected in flowing nitrogen
and weighed periodically. Before heating, water was collected
during several days from four test boreholes at rates in the
range of 5 to 15 g day. This result highlights the need for
an isothermal model for brine movement in the host rock salt.
After heating began, the water collection rates rose to a
peak. decreased, and then remained nearly constant for several
hundred days. Subsequently trends to decreasing rates have
been observed. Cumulative quantities of water were 4.3 kg
at 441 days from each two boreholes in Room A1 (with a 470
W heater in each borehole). and 36 to 38 kg at 600 days from
each of the two boreholes in Room B (with a 1500 W heater
in each borehole). After the early transients. approximately
8 g day borehole were collected in Room A1, and 50 to 80 g
day borehole were collected in Room B. These are much larger
brine inflow rates than were observed during heated brine
migration tests in the domal salt of the Asse mine in the
Federal Republic of Germany. Results from in situ brine transport
tests in domal salt are not necessarily applicable to bedded
salt.
A preliminary analysis of the results was begun with a highly
idealized fluid flow model for porous media. Our water collection
data for unheated boreholes agreed reasonably well with the
brine inflows that were calculated with this model. Agreement
was attained using permeability and porosity values that are
generally consistent with measured WIPP host rock properties.
It was also shown that the WIPP experiments are well within
the transient stage of this model. However, the temperature
dependence of viscosity. when used in this model, is inadequate
to account for the large water collection rates in the heated
boreholes. Further model development and additional experiments
are needed to understand brine movement in the WIPP, with
and without sources of heat. Parametric studies of time, scale,
and salt composition are needed. Measurements of pore pressure
at intervals within a few meters of WIPP excavations were
shown by the model analyses to be important for testing mechanistic
hypotheses concerning brine transport. WIPP hydrologic and
disturbed zone characterization studies can also contribute
to our mechanistic understanding of brine transport to WIPP
excavations. |
Permeability of rock salt;
Reservoir Mechanics |
- |
Nowak, E. J.;
McTique, D. F. et al. |
1988 |
Brine inflow to WIPP disposal rooms: Data,
modeling, and assessment |
Albuquerque : Sandia Nat. Lab., SAND 88-0112 |
Report |
|
A WIPP data base that characterizes brine movement
and accumulation is summarized and analyzed. The data are interpreted
in terms of a model for flow in a saturated porous medium.
The model, summarized in this report, embodies the Darcy-flow
assumption and storage due to linearly elastic compression
of the salt and brine. Comparisons between model calculations
and brine inflow rates measured in the WIPP show order-of-magnitude
agreement for permabilities in the range of 10-21 to 10-20
m² (1 - 10 nanodarcies). These values of permeability
are in accord with independent, in situ determinations of
permeability in the salt. Expected accumulations of brine
in typical WIPP waste disposal rooms were calculated by numerical
methods using a mathematical description for the brine inflow
model. The expected brine accumulation in a disposal room was
calculated to be in the range of 4 m³ to 43 m³ in
100 years. WIPP disposal rooms, filled with waste and backfilled,
are expected to be virtually completely reconsolidated due
to host rock creep in about 100 years, preventing further
accumulation of brine. Calculations show that water-absorbing
tailored backfill materials can readily absorb the maximum
expected brine accumulations in WIPP disposal rooms while
maintaining adequate mechanical strength. |
Permeability of rock salt;
Reservoir Mechanics |
- |
Nur, A.;
Byerlee, J. D. |
1971 |
An exact effective stress law for elastic deformation
of rock with fluids |
J. Geophys. Res. 76 (1971) 26, pp. 6414-6419 |
Journal Article |
|
The exact expressions for the effective stress
(sij) and, in particular, pressure (P) that cause elastic
strain of material with pore fluids are, assuming only that
Hook's law is valid, (sij) = (sij) - aPsij and <P> = Pc
- aPp, where a = 1 - (K/Ka), Pc and Pp are confining and pore
pressures. and K and Ka are the bulk moduli of the rock and
grain, respectively. The equation for <P> was first suggested
by Geertsma (1957) and by Skempton (1960) on empirical grounds.
The expression does not depend directly on porosity, but when
pores vanish the effective pressure <P> equals the confining
pressure Pc, because then K = Ka. Thus the strain of a porous
solid with pore pressure can be completely determined from
the elastic modulus of the solid without pore pressure, if
the effective stress law in the equation for (sij) is used.
The exact expression for the effective stress describes quite
accurately the measured strains in sandstone and granite samples
at confining and pore pressures to 2.5 kb. The results are
not applicable to inelastic processes, such as fracture, or
elastic processes other than strain. |
Creep behavior |
- |
| Paterson, M. S. |
1983 |
The equivalent channel model for permeability
and resistivity in fluid-saturated rock, a re-appraisal |
Mech. of Materials 2 (1983), pp.345-352 |
Journal Article |
|
It is affirmed that a consistent development
of the equivalent channel model for both fluid permeation
and electrical conduction in saturated porous media leads
to the expression CR²/F where R is the hydraulic radius,
F the formation resistivity factor or tortuosity/porosity
ratio and C a numerical factor generally around 0.3 to 0.4.
This expression is approximately supported by observations
reported on granular media and fairly porous rocks. Confirmation
of its applicability to low porosity, microcracked rock is
still lacking but it would appear to be consistent with measurements
on granite in that it indicates that the hydraulic radius
(represented by half the mean crack opening width) decreases
as the confining pressure is increased. In any application
it is important in estimating R and F to take only the connected
porosity into account. |
Permeability of rock salt |
- |
| Peach, C. J. |
1991 |
Influence of deformation on the fluid transport
properties of salt rocks |
Geologica Ultraiectina, Med. Fac. Aardwetenschappen
No.77, Techn. Univ. Utrecht |
Thesis |
|
While the fluid transport properties of rocks
are well understood under hydrostatic conditions, little is
known regarding these properties in rocks undergoing crystal
plastic deformation. However, such data are needed as input
in the field of radioactive waste disposal in salt formations.
Tley are also needed to understand deformation, shear zone
evolution and associated fluid movement, metamorphism and
mineralization in the deep crust and even upper mantle.
The present study is concerned with the development of
a fundamental understanding of the influence of crystal
plastic deformation on dilatancy and permeability evolution
in salt rocks and salt/anhydrite rocks. It is experimentally
based and seeks to explain the influence of deformation
on permeability in the framework of "percolation theory",
currently finding wide application in solid state physics.
The results relate directly to the behaviour of salt rock
in disposal systems and, viewing salt as an analogue material,
provide insight into the effects of plastic deformation
on the fluid transport properties of crystalline rocks in
general.
Chapter 1 introduces the problems to be investigated. Chapter
2 describes the experimental apparatus and methods used
and developed during the study.
The work reported in Chapter 3 was principally directed
at the influence of crystal plastic deformation on dilatancy
and permeability development in natural rocksalt (Asse Speisesalz,
Germany) under repository relevant conditions. The intact
starting material was found to have an extremely low permeability
(< 10-21 m²). In deformed material from gallery
walls, values up to 10-16 m² were measured. In triaxial
deformation experiments performed on intact material at
room temperature, minor amounts of dilatancy (< 0.2 vol%)
accompanying crystal plastic deformation led to extremely
rapid initial increases in permeability, suggesting critical
behaviour of the type described by percolation theory. Microstructural
evidence showed that dilatancy was associated with grain
boundary and transgranular microcracks. Additional short-term
hydrostatic experiments, performed on dry dilated material,
showed deformation-induced permeability to depend on pressure
in a manner best explained by an elastic microcrack closure
model. Long-term hydrostatic experiments on dilated material,
dry and wet, showed permeability to decrease with time.
Permeability decay rates were faster in wet material presumably
due to crack healing processes.
Chapter 4 documents triaxial compression experiments designed
to determine the influence of plastic deformation on dilatancy
and permeability development in fine grained synthetic salt
rock, at room temperature, confining pressures (Pc in the
range 5 - 20 MPa and strain rates (e) of ~ 4 x 10-5 s-1
to total strains of ~ 15%. The samples exhibited broadly
similar mechanical behaviour to the Asse salt, though they
were slightly weaker and showed more dilatancy (up to 3
vol%) in the dilatant field (Pc < 18 MPa) and were slightly
stronger in the non-dilatant field (Pc > 18 MPa). Microstructural
observations confirmed that deformation occurred by dislocation
glide with grain boundary microcracking in the dilatant
field. As in the experiments on Asse material, minor amounts
of dilatancy produced extremely rapid initial increases
in permeability from (< 10-21 m² to ~ 2 x 10-16
m²), again suggesting critical behaviour. The minor
differences observed in mechanical and dilatant behaviour
between the synthetic and natural salts are explained in
terms of the difference in grainsize.
Chapter 5 represents an extension of the work on synthetic
salt (Chapter 4) to systematically determine the influence
of controlled amounts of anhydrite added to the synthetic
material as a rigid second phase. Triaxial compression experiments
were carried out on synthetic salt rock samples containing
0 - 35 vol% anhydrite present in 1 of 3 grainsizes, i.e.
~ 10x, lx, 0.lx the halite matrix grainsize of ~ 350 mm.
All experiments were carried out at room temperature with
e = 4 x 10-5 s-1 and Pc = 20 MPa (i.e. within the non-dilatant
field for pure synthetic salt) reaching total strains of
~ 15%. All samples containing > 10 vol% anhydrite showed
significant dilatation (up to 2.5 vol%). All types of sample
also showed a tendency for flow stress and dilatancy (at
constant strain) to increase with increasing anhydrite content.
Dilatation of low permeability samples containing > 10-20
vol% anhydrite was initially accompanied by extremely rapid
permeability development (from < 10-21 m2, at low anhydrite
content, to ~ 3 x 10-17 m2 in most cases), again consistent
with critical behaviour. Microstructural studies showed
that the salt "matrix" of all samples deformed by dislocation
glide mechanisms with minor grain boundary dilatation. In
contrast the anhydrite always showed extensive microfracture
and/or dilatation. The tendency for flow stresses to increase
with anhydrite content was inferred to be due to concentration
of strain in the halite and rigid particle hardening effects
similar to those seen in some metals.
In Chapter 6 the experimental results are compared with
microphysical models. First, classical Darcian flow models
relating permeability to fully connected porosity are reviewed
and shown to be inapplicable to the experimental data. The
fundamentals of modern percolation theory are then introduced
and used to develop a microcrack linkage model predicting
the critical development (sudden appearance) of permeability
with dilatancy during deformation. When applied to the observed
crack microstructure, this "bond percolation" model successfully
explains the initial rapid growth of permeability seen in
the Asse and pure synthetic salts. From detailed comparison
of the model with the results for these materials, it is
inferred that through going microcrack linkage (the percolation
threshold) occurs at minute dilatations of < 0.05 vol%
and is associated with the linkage of very thin (< 1
mm) grain boundary microcracks. Post-critical permeability
saturation can be explained in terms of a broadening in
crack width distribution, with non-axial cracks remaining
thin and limiting the flow. The bond percolation model is
not appropriate for explaining the permeability development
for the salt/anhydrite rocks, since dilatancy is concentrated
in the anhydrite sites. For this reason the experimental
data are compared with various "site percolation" models,
which essentially describe the initial growth of permeability
in terms of the establishment of physical contact between
the dilated and permeable anhydrite sites. These models
were found to offer a satisfactory explanation of the experimental
results, in particular the influence of anhydrite content
on critical behaviour.
In conclusion the present work has shown that minor dilatancy
during plastic deformation of salt and salt-anhydrite material
can lead to very large increases in permeability. The thesis
is closed, via Chapter 7, with a discussion of the implications
of this for the fluid transport properties of salt rocks
in the waste repository environment and for the fluid transport
properties of regions of the Earth's crust and upper mantle
undergoing plastic deformation. Suggestions for further
work are included here. |
Interdependence rock stress - permeability;
Permeability of rock salt - High deviatoric stress |
- |
Peach, C. J.;
Spiers, C. J. |
1996 |
Influence of crystal plastic deformation on
dilatancy and permeability development in synthetic salt rock |
Tectonophys. 256 (1996), pp.101-128 |
Journal Article |
|
While the fluid transport properties of rocks
are well understood under hydrostatic conditions, little is
known regarding these properties in rocks undergoing plastic
deformation. In this study the influence of macroscopic plastic
deformation on permeability has been investigated experimentally
using synthetic salt rock. Dilatometric triaxial deformation
experiments performed on this material. at room temperature,
confining pressures (Pc) in the range 5-20 MPa and strain
rates of - 4 x 10-5 s-1 to total strains of ~ 15%, exhibited
work hardening behaviour with minor amounts of dilatancy at
Pc < 18 MPa. Microstructural observations confirmed that
deformation occurred by dislocation glide, with grain boundary
microeracking in the dilatant field. At the lowest pressures.
deformation-induced ditatancy of only 0,1-0.2 vol.% produced
extremely rapid initial increases in permeability (from <
10-21 m² to ~ 2 x 10-16 m²), suggesting critical
behaviour of the type described by percolation theory. This
rapid permeability development with dilatancy is well described
by crack linkage models based on percolation theory, provided
a broad range of fluid conductance is incorporated. The study
has shown that minor dilatancy ( < 0.2 vol.%) during plastic
deformation n' salt rock can lead to very large increases
in permeability. This is of direct interest with regard to
the behaviour of salt rock in waste disposal and storage systems,
and may have important implications for the transport of fluids
through. and the interaction of fluids with, crystalline rocks
undergoing crystal plastic deformation in nature. |
Interdependence rock stress - permeability;
Permeability of rock salt - High deviatoric stress |
- |
Peach, C. J.;
Spiers, C. J. et al. |
1987 |
Fluid and ionic transport properties of deformed
rock salt |
Luxembourg : Comm. Europl. Comm. Rep. EUR 10926
EN |
Report |
|
This report represents a final report on work
done on the transport properties of salt during the period
1/1/84 - 30/6/85. The work documented was directed largely
at the measurement of creep-induced permeability in salt rock,
at determining the permeability persistence/decay characteristics
of creep-dilated salt rock under hydrostatic conditions (wet
and dry), and at ion migration/retention experiments on both
deformed and undeformed material. The main conclusions drawn
are summarised below:-
1) Measurements performed using argon gas have shown that
the true (inert liquid) permeability of intact Asse salt rock
(Speisesalz) is <= 10-20 m², even at confining pressures
of only 2.5 - 5.0 MPa. Natural undisturbed material at depths
> 800 m (i.e. confining pressure >= 18 MPa) can be assumed
to have true permeabilities of < 1 x 10-21 m².
2) "Crept" salt rock extracted from gallery walls may exhibit
permeabilities up to 10-17 m², or higher if badly disturbed.
Note, however, that in the case of galleries at the 800m level
in the Asse Mine, the region of substantially increased permeability
seems to be limited to a depth of only 1-2 m from the gallery
wall.
3) Gas permeability measurements made on samples deformed
experimentally under worst case conditions (high deviatoric
stress, low pressure) show increases in permeability from
10-21 m² to ~10-15 m². It is inferred that the maximum
likely value for purely creep-induced permeability in homogeneous
dry salt is probably around 5 x 10-16 m².
4) Argon gas permeability tests performed on experimentally
deformed (work hardened and dilated) Asse salt with a (worst
case) permeability of ~ 10-16 m² have shown that permeability
reduction under hydrostatic conditions (presumably by compaction
creep) occurs only at effective confining pressures (Pe >
1.5 MPa. Measured rates of permeability reduction in the range
Pe = 8.5 - 13.5 MPa are ~ 4 x 10-23 m² s-1. These rates
can not yet be extrapolated reliably to predict long term
behaviour but suggest that the time required to reach a natural,
non-dilated permeability of 10-21 m² from a starting
value of 10-16 m² is of the order of 1 - 1000 years (at
effective pressures Pe = 8.5 - 13.5 MPa). More rapid rates
of permeability reduction can be expected when Pe exceeds
the maximum deviatoric stress reached during deformation.
For lower values of Pe, instantaneous changes in confining
pressure strongly affect the permeability, but in a recoverable,
elastic manner. The magnitude of this effect diminishes with
increasing Pe.
5) Brine permeability tests performed on similar material
(see 4), under hydrostatic conditions, have shown that wet
permeability decay rates depend upon effective confining pressure
(Pe) and brine flow rate (and/or brine pressure gradient).
The flow-rate/pressure-gradient effect was unexpected, but
is apparently very important. It should be noted, however,
that the effect may represent a manifestation of electroviscous
drag phenomena. Further work is required here to understand
and quantify the observed effects adequately. Nonetheless,
at the flow rates and pressure gradients used in our experiments,
the decay of permeability to brine appears to obey a power
law of the form k= At -b, where b= ~0.5 at Pe = 8.5 MPa, and
b= ~l at Pe = 18.5 MPa. The long term validity of this law
is uncertain. Note that at a given permeability and effective
confining pressure, wet dilated Asse salt rock undergoes a
more rapid decay of permeability, during a saturated brine
flow-through experiment, than the equivalent dry material.
This is presumably due to solution transfer effects.
6) Permeability measurements performed on individual samples
using gas (argon) and then brine (under almost identical conditions)
are in excellent agreement, at permeabilities of the order
of 10-17 m2.
7) Migration/retention experiments on intact Asse Speisesalz
placed in contact with brine containing high concentrations
of Cs+ , Sr2+ , or Fe3+ (at NTP) have shown that in the absence
of a hydraulic head, no detectable ionic migration occurs
within laboratory time scales.
8) In similar experiments performed on creep-dilated material,
relatively rapid migration of Sr2+ and Cs+ occurs as a result
of capillarity-driven migration of brine into voids. Further:-
- In the case of Cs+, no detectable retention effects were
observed.
- In contrast, strong retention was observed for Sr2+ . This
retention is primarily due to precipitation of insoluble SrSO4
at polyhalite grains, via ion exchange reactions. Similar
retention effects can be expected for all contaminant ions
having insoluble sulphates.
- There appear to be no significant mutual interaction effects
between Sr and Cs during combined migration.
9) A single migration/retention experiment on deformed (dilated)
Asse Speisesalz, placed in half-space contact with Sr 2+ /Cs+-contaminated
brine at 80 °C, 1 atm, has shown that capillarity-driven
migration effects appear to decrease significantly with increasing
temperature.
10) Note that fluid-assisted recrystallisation occurred in
all migration/retention tests performed on deformed (dilated)
salt using Cs and Sr. We infer that the recrystallisation
process is not sensitive to impurities in solution. Within
SEM/EDS detection limits (100 ppm), no evidence has been found
for ion trapping effects during recrystallisation.
11) A single long term flow-through retention test using Sr
2+ /Cs+ contaminated brine (mean Pe = 4.0 MPa) has shown that
dilated (permeable) Asse salt exhibits a dramatic retention
effect for Sr 2+ at elevated pressures, almost all Sr present
in solution (10% Sr saturation level) being "filtered out"
in the first 3 cm of the salt sample. In contrast, no significant
retention occurs for Cs+ . The Sr retention effect is inferred
to be due to the precipitation of SrSO4 at the polyhalite
grains present in the salt, via ion exchange reactions. It
is concluded that under elevated pressure conditions (i.e.
elevated pore fluid and confining pressures), provided that
brine flow-through rates are relatively slow compared to ion
exchange kinetics, similarly efficient retention effects can
be expected for all contaminant ions having insoluble sulphates.
Note that almost all natural salt rocks contain some polyhalite
or other suitable/similar sulphate phase (e.g. anhydrite).
12) Migration/retention experiments performed on creep-dilated
Asse Speisesalz placed in contact with 99Tc-contaminated brine
(in the form of TcO4 ) at NTP have shown relatively rapid
migration of Tc via capillarity-driven fluid transport. No
significant Tc retention effects were observed.
13) Note that despite early hopes, no suitable non-radioactive
analogues could be found for the long-lived "Mirage Project"
actinides, U, Am, Pu, Np. As a result, no migration/retention
data of direct application to these radionuclides could be
obtained. |
Interdependence rock stress - permeability;
Permeability of rock salt - High deviatoric stress |
- |
Peterson, E. W.;
Lagus, P. L. |
1988 |
Testing of borehole plugs placed in bedded
halite and anhydrite |
SMRI Spring Meeting, Mobile, 25.04.88 |
Paper |
|
This paper will describe experimental techniques
and review the results of two sets of borehole tests aimed
at quantifying the ability of grout plugs to seal boreholes
through either anhydrite or halite formations. One set of
tests was performed on a grout plug placed in a borehole at
depth. A second set of tests was performed on horizontal and
vertical plugs set in shallow boreholes drilled into the ribs
and invert of a mined facility. These tests were performed
in order to evaluate the capability to seal boreholes and
shafts against incursion of aquifer fluid. |
Borehole seal |
- |
Peterson, E.;
Lagus, P. et al. |
1985 |
WIPP horizon in situ permeability measurements:
final report |
Albuquerque : Sandia Nat. Lab., SAND85-7166 |
Report |
|
A total of eighteen (18) gas permeability tests
were conducted by S-CUBED for Sandia National Laboratories
(SNL) as part of SNI Contract No. 58-5831. These tests were
conducted at the Waste Isolation Pilot Plant (WIPP) facility
horizon in southeastern New Mexico. The objectives of the
twelve Phase I tests were to determine:
* The permeability
and porosity of the competent salt,*
* The permeability variation with distance from the mined
surface, and
* The influence of the interspersed clay and anhydrite seams
on the measured permeability values.
Six short duration "order-of-magnitude" permeability tests
were performed as Phase II of this project. These tests
were used to provide confirmation of the Phase I test results.
Two types of test were performed. In one test the downhole
pressure was maintained at an approximate constant value
and the resulting flow measured. In the second, the test
region was pressurized, then shut-in, and the pressure decay
subsequently monitored. The resulting data were then used
to infer permeability and porosity values.
The test system and test technique used for the twelve Phase
I tests were designed to evaluate formations having permeability
to porosity ratios as low as 10-4 darcy. This downhole measurement
system consisted of a dual packer assembly which isolated
a test interval and adjacent guard interval. During a test,
the test interval pressure, temperature, and flow (as well
as the guard interval pressure) were measured. Use of the
guard interval was critical to interpreting data obtained
in these low permeability formations.
Permeability and porosity values were inferred from the
measured data using one-dimensional and two-dimensional
axisymmetric solutions to equations describing gas flow
through an isotropic porous medium. In those cases, where
the analytical/numerical solutions failed to describe the
measured response, additional testing should be performed
to evaluate the formation characteristics.
In this report, the experimental technique is described
in Section 2. The analytical/numerical model used for data
interpretation is presented in Section 3. Section 4 describes
the individual Phase I test results. Conclusions are given
in Section 5. Appendix A contains computer pl ots of the
raw data. Results of the six Phase II tests are given in
Appendix B.
* Salt refers to the rock at the facility horizon excluding
clay and anhydrite. It is over 90 percent halite, but can
be further defined as shown in Section 4. |
Permeability of rock salt;
Pore pressure in permeable salt;
Reservoir Mechanics |
- |
| Piper, T. B. |
1980 |
Hydraulic fracturing applied to solution mining |
SMRI |
Report |
|
A review of the state-of-the-art of the hydrofrac
technique as applied to solution mining - being a method for
obtaining a viable connection between two wells in a salt
bed while enjoying the advantages of minimum cost and time.
Directed to describing the mechanism and applicable technology,
standardizing terminology and identifying unknowns and areas
open to research and further study. |
Hydrofracturing |
- |
| Rice, J. R.; Cleary, M. P. |
1976 |
Some basic stress-diffusion solutions for fluid-saturated
elastic porous media with compressible constituents |
Rev. Geophys. Space Phys. 14 (1976), pp. 227-241 |
Journal Article |
|
This is a study of the formulation, some basic
solutions, and applications of the Biot linearized quasistatic
elasticity theory of fluid-infiltrated porous materials. Whereas
most previously solved problems are based on idealizing the
fluid and solid constituents as separately incompressible,
full account is taken here of constituent compressibility.
Previous studies are reviewed and the Biot constitutive equations
relating strain and fluid mass content to stress and pore
pressure are recast in terms of new material parameters, more
directly open to physical interpretation as the Poisson ratio
and induced pore pressure coefficient in undrained deformation.
Different formulations of the coupled deformation/diffusion
field equations and their analogues in coupled thermoelasticity
are discussed, and a new formulation with stress and pore
pressure as basic variables is presented that leads, for plane
problems, to a convenient complex variable representation
of solutions. The problems solved include those of the suddenly
introduced edge dislocation and concentrated line force and
of the suddenly pressurized cylindrical and spherical cavity.
The dislocation solution is employed to represent that for
quasi-static motions along a shear fault, and a discussion
is given, based on fracture mechanics models for fault propagation,
of phenomena involving coupled behavior between the rupturing
solid and its pore fluid, which could serve to stabilize a
fault against rapid spreading. Also, the solution for a pressurized cylindrical cavity leads to a time-dependent stress field
near the cavity wall, and its relevance to time effects in
the inception of hydraulic fractures from boreholes, or from
drilled holes in laboratory specimens, is discussed. Various
limiting cases are identified, and numerical values of the
controlling porous media elastic parameters are given for
several rocks. |
Interdependence rock stress - permeability |
- |
| Roedder, E. |
1984 |
The fluids in salt |
Am. Min. 69 (1984), pp.413-439 |
Journal Article |
|
The fluids in salt have been used as sources
of information on the geological events leading to the formation
of the enclosing salt beds, and the subsequent changes to
which these beds have been exposed. In recent years, however,
consideration of salt beds or domes as possible sites for
long-term nuclear waste repositories has added new significance
to the study of such fluids.
This paper reviews the current status of the study of the
types of fluid present in salt, their origin and evolution,
and their significance to understanding the geological processes
that have occurred.. These studies are pertinent to the engineering
design of a nuclear waste storage site in salt in that they
tell us what might happen in the future. The fluids in salt
also introduce problems in the engineering design of a safe
nuclear waste installation that must be carefully evaluated
at each suggested site. |
Permeability of rock salt |
- |
Rokahr, R. B.;
Staudtmeister, K. et al. |
1994 |
Development of a new criterion for the determination
of the maximum permissible internal pressure for gas storage
caverns in rock salt |
SMRI Spring Meetin, Houston, 24.-27.04.94 |
Paper |
|
For the design and layout of gas storage caverns
in salt rock it is necessary to develop a new criterion to
determine the permissible maximum internal cavern pressure.
The present concepts for determination of the maximum allowable
internal pressure do not sufficiently consider the response
over time of the salt rock material, the history of internal
cavern pressure and due to the loading conditions the induced
secondary permeability of the rock salt.
Numerous laboratory research studies on the secondary permeability
of rock salt have been published within recent years. The
results of these studies will have to be integrated in the
development of the new assessment criterion. Another main
item to be included will be the time dependent material behaviour
of rock salt in loading and unloading conditions.
The paper points out by the way of example the influence of
some significant parameters for the determination of the maximum
permissible cavern pressure. It will be shown what kind of
improvement is necessary to get a more accurate estimation
for the safety against the loss of tightness of a gas cavern. |
Interdependence rock stress - permeability;
Rock mechanics |
- |
Rokahr, R. B.;
Staudtmeister, K. et al. |
1997 |
Development of a new criterion for the determination
of the maximum permissible internal pressure for gas storage
caverns in rock salt. Final report |
SMRI Research Project Report No. 1-94 |
SMRI Research Report |
|
Beginning with a state of the art review on
criteria for the evaluation of safety at maximum internal
cavern pressure state for gas storage caverns in domal rock
salt designed for seasonal storage, a new criterion has been
developed. It evaluates safety on the basis of a boundary
condition for usability. The limiting state is equated to
that point in time when the infiltration of the storage medium
into the rock mass starts and can not be prevented from continuing.
This is defined by a combined infiltration / safety criterion,
describing the onset of infiltration qualitatively if the
internal cavern pressure exceeds the level of one of the two
components of the local stress state acting perpendicular
to the spreading direction of the infiltration process, with
the spreading direction of the infiltration being normal to
the cavern wall in the vicinity of the cavern. The quantitative
measure is given by the minimum extent of a closed safety
zone surrounding the cavern where the two stress components
of the local stress state in the rock mass, which are acting
perpendicular to the spreading direction of the secondary
induced infiltration, exceed the internal cavern pressure
by a certain level.
Carrying out a sensitivity study including the main influencing
factors on the rock mass state at maximum internal cavern
pressure reveals that the developed criterion works, giving
a qualitative and quantitative measure for the specific state
to evaluate.
From that study it can be stated that the main influences
on safety at maximum internal cavern pressure are associated
with initial conditions such as the primary stress state (densities
of the overlying rocks, depth of the cavern), the geometrical
layout parameters (shape of cavern roof, height of the chimney
between cavern roof and casing shoe) and site location factors
(pillar width).
The operating history conditions assuming a typical seasonal
storage have a medium (time period at preceding minimum internal
cavern pressure) to small (minimum pressure level) and very
small (pressure drop down rate, level of preceding operations)
effect on safety at maximum internal cavern pressure state.
Provided the material parameters for a suitable material law
describing the response of rock salt under loading and unloading
are determined with adequate accuracy, the studied influencing
factors depending on material behavior have very small influence
on the stress state in the rock mass at maximum internal cavern
pressure (comparison of different material laws). But if the
assumed set of material parameters is not representative,
the change in safety conditions will be apparent in the sense
of a declined or even non-existent safety zone (s. variation
of material quality). Creep response of rock salt itself has
a medium influence on safety at maximum internal cavern pressure
state.
From an engineering point of view the time-dependent response
of rock salt under unloading can be neglected, bearing in
mind the initial assumption of an operating history for seasonal
storage of gas. Recovery of creep will be very slow and therefore
the stress state will not change remarkable within the time
periods that have to be considered within this scope.
The recommended new criterion for the determination of the
maximum permissible internal pressure for gas storage caverns
in domal rock salt has been developed on the basis of the
experience and scientific work recovering the past 20 years.
The results of the present research project demonstrate that
the safety at maximum internal cavern pressure can be evaluated
by this criterion taking into account the various different
influencing factors of geometry and location of the cavern,
priman, state of stress, material behavior of rock salt and
the operating history.
The safety margins for the recommendation of the maximum gas
pressure in the cavern naturally can only be fixed specific
to the actual location of that cavern, and considering the
whole set of influencing factors. They strongly depend on
the experience of the consulting engineer. |
Interdependence rock stress - permeability;
Rock mechanics |
- |
Rummel, F.;
Benke, K. et al. |
1996 |
Hydraulic fracturing stress measurements in
the Krummhörn gas storage field, northwestern Germany |
SMRI Spring Meeting, Houston, 14.-17.04.96 |
Paper |
|
The Ruhrgas AG gas storage field Krummhörn
is located near the North Sea harbour town of Emden, NW Germany.
The present storage facility consists of 3 caverns leached
in the Groothusen saltdome (Zechstein 2) at a depth between
1500 and 1800 meters. To investigate the structure of the
saltdome with respect to a future increase of the storage
capacity, 2 deep boreholes were drilled in 1994. In one of
the boreholes, Krummhörn K 6, an extensive hydraulic
fracturing test program was conducted for determination of
the in situ stress within the salt at depth, as the limiting
input parameter for cavern design and storage pressure planning.
Using the MeSy wireline hydrofracturing technique where
the double straddle packer unit is moved within the borehole
on a standard borehole logging cable, a total of 11 hydrofrac
tests were successfully carded out in the 8.5 inch diameter
open hole between app. 1300 and 1800 m depth. Every test
consisted of the initial fracturing cycle and several subsequent
refrac cycles for reliable and precise determination of
the shut-in pressure. Most of the frac cycles demonstrated
distinct breakdown at fracture initiation and reproducible
fracture re-opening pressure values, while determination
of reliable shut-in pressure values required an extensive
analysis of the pressure records. The analysis yields a
welldocumented shut-in pressure profile
Psi, MPa = 29.38 + 0.0194 . (z, m - 1300)
or a shut-in pressure gradient of
dPsi / dz, MPa 1 m = 0.0221
for the depth between 1300 and 1720 m (TVD). The shut-in
pressure profile is in good agreement with the vertical
stress profile derived from various geophysical logs for
the overburden density. |
Hydrofracturing |
- |
| Rutter, E. H. |
1976 |
The kinetics of rock deformation by pressure
solution |
Phil. Trans. Royal Soc. London A 283 (1976),
pp.203-219 |
Journal Article |
|
A simple model for rock deformation by pressure
solution, assuming grain boundary diffusive mass transfer
to be deformation rate controlling, is presented. The model
leads to a constitutive flow law which is of the same form
as that for Coble creep. It is argued that the presence of
a fluid film in stressed grain boundaries leads to enhanced
diffusivity of solute particles in the grain boundary. Some
simple experiments are described, which demonstrate rapid
diffusion in solutions in pores, much slower diffusion in
stressed interfaces and deformation by pressure solution.
By using the theoretical model, and by assuming that the pressure
of the interfacial solution is equal to the applied normal
stress, so that available experimental data on the effect
of pressure on mineral solubility could be used, rates of
deformation by pressure solution have been calculated. These
are compared with rates of deformation by crystal plastic
and high temperature diffusive flow processes, by using deformation
mechanism maps. Predicted transition conditions between various
deformation mechanisms are found to be consistent with those
inferred from the study of textures of naturally deformed
rocks. |
Creep behavior |
- |
Saalbach, B.;
Grüschow, N. et al. |
1990 |
Verfahren zur Endverwahrung von Kavernen im
Carnallititgestein [Procedure for abandonment of caverns in
carnallite rock] |
DD 294 994 A5 |
Patent |
German |
The invention is with respect to a process
for the permanent sealing of caverns in carnallitite constructed
using either hot or cold solution mining and filled with liquid
following completion of the solution mining process. According
to the invention, after termination of solution mining a layer
of sealing solution comprising a highly concentrated MgCL2
solution of at least 0.4 - 0.5 m thickness is injected via
the leaching string directly below the cavern roof, whereby
the solution is either saturated or supersaturated with components
KCl and NaCl and the solution temperature is 5-20 K above
roof temperature such that upon cooling the sealing solution
starts to crystallise forming a primary seal at the cavern
roof and such that in the event of movement of the cover rock
the sealing solution penetrates into possible migration paths
forming a secondary seal. |
Borehole seal |
- |
Saulnier, G. J.;
Domski, P. S. et al. |
1990 |
WIPP Salado hydrology program data report #1 |
Albuquerque : Sandia Nat. Lab., SAND90-7000 |
Report |
|
WIPP Salado Hydrology Program Data Report #l
presents hydrologic data collected during permeability tests
of the Salado Formation performed from August 1988 through
December 1989. Analysis and interpretation of the test data
are presented in a separate report. The report presents the
results of the drilling and testing of six boreholes drilled
from the WIPP underground facility 655 m below ground surface
in the Salado Formation. Permeability tests were conducted
using multipacker test tools with inflatable packers to isolate
borehole intervals to allow formation pore-pressure buildup
and subsequent pulse-withdrawal tests. Test data include pressures
and temperatures in brine-filled, packer-isolated test intervals
and borehole-closure and axial test-tooi-movement measurements.
The test boreholes are 4.0-inch (10.2 cm) in diameter, and
were cored in halite and associated anhydrite interbeds and
clay seams. The boreholes are oriented vertically downward,
angled downward, and horizontal. The boreholes were drilled
and cored using compressed air to remove drill cuttings. Three
boreholes were drilled in Room C2: C2H01, C2H02, and C2H03.
Borehole C2H01 was initially drilled to a depth of 5.68 m
below the floor of Room C2 and later deepened to 8.97 m to
include Marker Bed 139 in the test interval. Borehole C2H02
was drilled to a depth of 10.86 m (7.68 m vertical projection
from the floor of Room C2) at a 45° downward angle from
the junction of the west wall and floor of Room C2. Marker
Bed 139 was included in the test interval in borehole C2H02.
Borehole C2H03 was drilled horizontally into the west wall
of Room C2. Vertically downward boreholes were drilled from
the floor in the North 1420 drift (borehole N4P50); the South
1300 drift (borehole SOP01); and in Room 7, Waste Panel 1
in the waste-storage area (borehole S 1 P7 1).
Permeability tests were performed after installing multipacker
test tools in test boreholes, inflating the packers, and allowing
pressures to build up in the isolated intervals. Pulse-withdrawal
tests were performed after buildup pressures approached the
apparent formation pore pressure. Pulse injections were sometimes
performed to increase the fluid pressures in isolated intervals.
Compliance tests were conducted in lengths of steel and stainless-steel
casing to evaluate the mechanical performance of the muftipacker
test tools. The stainless-steel compliance-test chamber was
installed with externally mounted thermocouples in a downward-angled
borehole in Experimental Room 4. Compliance tests included
leak tests and simulated pulse-injection and pulse-withdrawal
sequences. |
Permeability of rock salt |
only extracts |
| Serata Geomechanics, Inc. |
1984 |
Ultimate stress in the salt envelope of a sealed
liquid-filled solution cavern. Final report |
Berkeley : Serata Geomech. Inc., SMRI Research
Project Report 84-0004-S |
SMRI Research Report |
|
This report summarizes the project work, "Ultimate
Stress in the Salt Envelope of a Sealed Liquid-Filled Solution
Cavern," conducted by Serata Geomechanics, Inc. (SGI) for
SMRI. SGI's finite element code, REM, was used for the computer
simulation portion of this study. The objective of the study
was to analyze the fundamental mechanism of long-term behavior
of a solution cavern sealed with a cement plug. The boundary
conditions of the cavern development and the cement plugging
procedure, as well as the overall scheme of analysis, are
specified by SMRI in our contractual agreement dated September
30, 1983.
The study was conducted in the following three phases:
Phase 1: Equilibrium Analysis
REM computer simulation analysis for the entire process
of sequential cavern development, including temperature
effects, was conducted with regard to the time-dependent
behavior of the cavern. A computer model of the solution
cavern was developed by closely simulating the cavern formation
process, and then sealing the cavern, resulting in brine
pressure build-up. This simulated pressure build-up was
related to the material properties of the rock salt, and
further compared with the actual pressure build-up data
obtained in various field observations. By verifying the
close interrelation among the model behavior, material properties,
and field observation, the REM model of the solution cavern
was quantitatively established.
Phase 2: Plug Analysis
A REM simulation was conducted to examine plug stability
during and after the pressure build-up stage by utilizing
the stress-strain conditions established in Phase 1. The
structural stability of the cement plug and surrounding
ground were examined in this phase.
Phase 3: REM Validity Check
The validity of the REM program was confirmed and illustrated
using two entirely different methods. One method compared
behavior of the laboratory cavities tested at the SGI laboratory
with the REM model of the same cavities. The other method
compared results of the finite element cavern behavior analysis
published by Ghaboussi (5) with an identical run using REM.
The major factors incorporated into the REM simulation analyses
were temperature effects and material properties. Not considered
in this study were the chemical reactivity of the contained
fluid and the effect of impurities in the salt mass. All
other design parameters, such as stress field, cavern shape,
depth, size, and boundary ground conditions, were assumed
to be unchanged. |
Cavern abandonment;
Borehole seal;
Interdependence rock stress - permeability;
Reservoir Mechanics |
- |
Serata, S.;
Fuenkajorn, K. |
1993 |
Permeability study in relation to stress state
and cavern design. Phase I: Constitutive equation of Finite
Element Program GEO. Phase II: Finite Element Model to predict
permeability increase around salt cavern |
SMRI Res. Proj. Rep. No. 91-001 A-S |
SMRI Research Report |
|
Phase I: Constitutive Equation of Finite Element
Program GEO
Results are presented from the first half of an SMRI research
project titled "Permeability studies in relation to stress
state and cavern design". The project work has established
the theoretical basis for developing a finite element for
calculation of salt permeability around a solution cavern.
This development is an outcome of literature studies on theories,
laboratory experiments and in situ measurements of salt permeability,
as well as formulation of a salt deterioration function and
an inelastic volume expansion function.
A large amount of experimental data, including recent results
provided by Sandia National Laboratories, has revealed permeabilities
of undisturbed in situ salt to be less than 10-22 m².
The data also reveal that around an opening, the permeabilities
can be as high as 10-18 m². The magnitude and extent
of this high permeability zone change with time due to the
plastic creep and time-dependent fracture propagation of the
salt. The change is identified as an outcome of chain reactions
of the five basic relations:
1) stress-strain, 2) strain-deterioration, 3) deterioration-volume
expansion, 4) confinement-porosity, and 5) porosity-permeability.
A permeability function has been formulated by presenting
the five component relations of the chain reactions in order
to construct the finite element program of permeability of
salt. Various aspects of the relations have been calibrated
and tested against laboratory and field measurements as preparation
for program development. Phase II: Finite Element Model to
Predict Permeability Increase around Salt Cavern
A finite element program has been developed to predict the
magnitude and distribution as well as their change with tim
around underground openings and solution caverns. A volumetric
dilation function and flow model have been derived and incorporated
into the finite element code GEO to determine the increase
in porosity and permeability of salt during deformation. The
model parameters are evaluated from the results of stress-rate
controlled triaxial tests conducted by Sarbdia National Laboratories.
Model predictability is assessed by comparing the simulation
with the actual permeability measurements obtained at the
WIPP site. Agreements and discrepancies are discussed. Computer
simulations on a spherical cavity model are performed to demonstrate
the capability of the GEO code and to determine the potential
effects of confining and internal pressures and cavern age
on the magnitude and extent of the permeability increase zone
around the caverns in rock salt. The results suggest that
confining and storage pressures may increase the permeabilities
of the surrounding salt from its in situ value of 10-4 microdarcy
(10-22 m²) to as high as 10 4 microdarcy (10-16 m²).
Increasing the internal storage pressure can effectively reduce
the magnitude and extent of the high permeability zone. |
Permeability of rock salt;
Interdependence rock stress - permeability |
- |
Sitz, P.;
Gruner, M. |
1996 |
Langzeitsichere Verschlüsse für Untertagedeponien
und Endlager unter besonderer Berücksichtigung natürlicher
Materialien
[Long term seals for underground repositories focusing on
natural materials] |
Glückauf 132 (1996) 7, pp.327-332 |
Journal Article |
German |
Practical experience already exists on the
technical realisation of seals for underground cavities which,
despite similar terms of reference and conditions, are not
adequately taken into consideration in the conception of underground
repositories. Only natural materials with confirmed long term
stability should be used for the long term safe sealing of
underground repositories. In evaporite caverns, natural stone
(basalt, rock salt blocks) can be used for static massive
seals, and precompacted dry bentonite, or bitumen, asphalt
or mastic asphalt for sealing elements. The use of crushed
salt alone to seal cavities is only possible under certain
conditions. This paper concludes with details of a long term
safe horizontal roadway seal. Long term safe shaft seals can
be constructed using a similar basic concept. |
Borehole seal |
- |
Spiers, C. J.;
Schutjens, P. M. T. M. et al. |
1990 |
Experimental determination of constitutive
parameters governing creep of rocksalt by pressure solution |
Geol. Soc. Spec. Publ. No. 54, pp. 215-227 |
Paper |
|
Theoretical models for compaction creep of
porous aggregates, and for conventional creep of dense aggregates,
by grain boundary diffusion controlled pressure solution are
examined. In both models, the absolute rate of creep is determined
by the phenomenological coefficient Z* = Z()exp (-DH/RT),
a thermally activated term representing effective diffusivity
along grain boundaries. With the aim of determining Z(), DH
and hence Z* for pressure solution creep in rocksalt, compaction
creep experiments have been performed on wet granular salt.
Compaction experiments were chosen since theory indicates
that pressure solution creep is accelerated in this mode.
The tests were performed on brine-saturated NaCl powder (grainsize
100-275 mm) at temperatures of 20-90°C and applied stresses
of 0.5-2.2 MPa. The mechanical data obtained show excellent
agreement with the theoretical equation for compaction creep.
In addition, all samples exhibited well-developed indentation,
truncation and overgrowth microstructures. We infer that compaction
did indeed occur by diffusion controlled pressure solution,
and best fitting of our data to the theoretical equation yields
Z() = (2.79 ± 1.40) x 10-15 m³s-1, DH = 24.53
kJ mol-1 . Insertion of these values into the theoretical
model for conventional creep by pressure solution leads to
a preliminary constitutive law for pressure solution in dense
salt. Incorporation of this creep law into a deformation map
suggests that flow of rocksalt in nature will tend to occur
in the transition between the dislocation-dominated and pressure
solution fields. |
Creep behavior |
- |
Spiers, C. J.;
Urai, J. L. et al. |
1987 |
The influence of fluid-rock interaction on
the rheology of salt rock |
Luxembourg : Comm. Europl. Comm. Rep. EUR10399 |
Report (Abstract) |
|
This report documents work done on the rheological
and dilatant properties of dry and wet salt during the period
1/11/81 - 31/12/83. The report opens with a review of previous
evidence and theoretical models for water weakening effects
in the long-term creep of salt. The programme was largely
designed to look for such effects experimentally. Sections
3 and 4 describe the experimental apparatus and techniques
used. Section 5 reports detailed characterisation work on
the experimental starting material (Speisesalz, Asse, FRG).
Section 6 deals with experiments on the rheological/dilatant
properties of dry salt at ~ 200C. The results show that even
under worst case conditions, creep-induced dilatancy is almost
completely suppressed at hydrostatic pressures > 15 MPa. Experiments
on the influence of brine are reported in Sections 7 and 8.
These show that small amounts of brine (e.g. 0.05 wt% inherent
or added) can cause a significant decrease in the creep strength
of salt at low strain rates. This is related to a change in
deformation mechanisms from dislocation glide/creep (at normal
laboratory rates) to creep involving fluid-assisted recrystallisation
and diffusional creep (at low rates). The results imply that
generally accepted creep laws for salt cannot necessarily
be extrapolated to predict long-term behaviour under natural
conditions. Final conclusions are summarised in Section 9. |
Creep behavior |
only abstract; out of print |
Stavrogin, A. N.;
Georgievskii, V. S. et al. |
1975 |
Effect of atmospheric moisture on creep in
salt |
Soviet Min. Sci.11 (1975) 1, pp.65-67 |
Journal Article |
|
By studying the influence of atmospheric conditions
on the rheological properties of rocks, we can find out more
about their deformation and can study the process of fracture
in nearly narural conditions.
Renzhiglov [l] investigated the influence of moisture in rocks
(argillaceous and arenaceous) on their rheological properties.
He found that moisture activates their creep. Surfactants
strongly alter the mechanical properties of materials [2].
The surfactant may be simply a damp atmosphere. Penetrating
the specimen, atmospheric moisture weakens the elementary
interatomic bonds, so that creep becomes more rapid. Many
investigations have revealed that it is elementary mechanisms
of interatomic bond rupture which are responsible for processes
occurring during long-term tests.
In this article we give a comparative assessment of the results
of rests on the long-term strength of potassium salts (from
the Verkhnekamskaya potash deposit) and rock salt (from the
Starobin potash deposit), when atmospheric moisture was affecting
their properties. The rest method was that described by us
in [3]. |
Rock mechanics;
Creep behavior |
- |
| Stormont, J. C. |
1991 |
An approach to address DRZ (disturbed rock
zone) development and healing in rock salt |
Albuquerque : Sandia Nat. Lab., Memorandum
to distribution |
Paper |
|
An approach for predicting the development
and subsequent healing of the DRZ in rock salt has been developed
to support seal design activities. Structural models of rock
salt behavior are used to predict (1) dilation (inelastic
volume strain) in response to excavation to estimate the extent
of the DRZ, and (2) stress changes in response to seal emplacement
to estimate DRZ healing. This approach focuses on the mechanical
response of the rock salt; permeability changes are not explicitly
considered. By limiting the approach to the mechanical response,
we focus on the more tractable portion of the problem, yet
provide predictions of damage and healing consistent with
their underlying mechanisms.
This approach was applied to a shaft seal location at the
disposal horizon. The damage zone predicted to develop from
excavation-induced stress redistribution was confined to within
1/2 of a shaft radius. Calculated stress changes indicate
this damage is likely to be completely healed within a few
years after the placement of a relatively stiff seal. This
example may be relevant to rock salt damage and healing adjacent
to a panel seal as well.
Confidence in and further applications of this approach require
healing data under deviatoric stresses, and further development
of a damage model for rock salt which includes time-dependency. |
Borehole seal |
- |
| Stormont, J. C. |
1990 |
Gas permeability changes in rock salt during
deformation |
Univ. of Arizona, Dept. Min. Geol. Eng. |
Thesis |
|
Discontinuous behaviour is being observed and
measured in the vicinity of excavations constructed in a bedded
salt formation 650 m below ground surface for the Waste Isolation
Pilot Plant (WIPP) Facility. The 2 m thick salt layer in the
immediate roof acts as a beam, shearing along a thin overlying
anhydrite clay seam. Vertical separations between the immediate
roof layer and the overlying strata are often observed at
the anhydrite clay seam above the centre of excavations of
larger span (11 m). The floor of the excavations is comprised
of a 1 m thick salt layer underlain by a 1 m thick predominately
anhydrite layer (referred to as MB 139). Fractures in MB 139
develop beneath most excavations, with increased fracture
frequency with drift span and age. In the excavations of larger
span (11 m), MB 139 eventually debonds along the underlying
clay layer. The salt layer overlying MB 139 develops both
shear and tension failure. In a few locations below excavations
of large span, continuous fracture systems are developing
from rib to rib through MB 139 and the overlying salt. In
the ribs, there is limited fracturing within the first metre
of most larger excavations. Vertical fractures develop in
pillars at most intersections. The discontinuous behaviour
is qualitatively consistent with analyses of the formation
behaving as a layered medium (elastic beam analysis) and limited
tensile and compressive failure of the rock salt. The significance
of the discontinuous behaviour is that it can dominate the
effective fluid transport properties of the formation near
the excavation, and therefore requires consideration in the
design of repository seals. Discontinuous behaviour must be
monitored and is an important factor in the maintenance programme
designed to assure a safe underground environment. |
Permeability of rock salt;
Interdependence rock stress - permeability |
thesis separately;
(1 copy for SMRI) |
| Stormont, J. C. |
1990 |
Summary of 1988 WIPP facility horizon gas flow
measurements |
Albuquerque : Sandia Nat. Lab., SAND89-2497 |
Report |
|
Numerous gas flow measurements have been made
at the Waste Isolation Pilot Plant (WIPP) Facility horizon
during 1988. All tests have been pressure decay or constant
pressure tests from single boreholes drilled from the underground
excavations. The test fluid has been nitrogen. The data have
been interpreted as permeabilities and porosities by means
of a transient numerical solution method. A closed-form steady-state
approximation provides a reasonable order-of-magnitude permeability
estimate. The effective resolution of the measurement system
is less than 10-20 m².
Results indicate that beyond 1 to 5 m from an excavation,
the gas flow is very small and the corresponding permeability
is below the system resolution. Within the first meter of
an excavation, the interpreted permeabilities can be 5 orders
of magnitude greater than the undisturbed or far-field permeability.
The interpreted permeabilities in the region between the undisturbed
region and the first meter from an excavation are in the range
of 10-16 to 10-20 m². Measurable gas flow occurs to a
greater depth into the roof above WIPP excavations of different
sizes and ages than into the ribs and floor. The gas flows
into the formation surrounding the smallest excavation tested
are consistently lower than those at similar locations surrounding
larger excavations of comparable age. Gas flow measured in
the interbed layers near the WIPP excavations is highly variable.
Generally, immediately above and below excavations, relatively
large gas flow is measured in the interbed layers. These results
are consistent with previous measurements and indicate a limited
disturbed zone surrounding WIPP excavations. |
Permeability of rock salt |
- |
| Stormont, J. C. |
1996 |
The influence of rock salt disturbance on sealing |
in: Aubertin et.al.: Rock Mechanics, 1996,
pp. 1471-1477 |
Paper |
|
The performance of seal systems in rock salt
formations can be dominated by the increased permeability
of the damaged rock adjacent to an excavation. Under favorable
stress conditions this damaged region is expected to "heal"
and return to a condition comparable to intact rock salt.
A simple method is presented for first predicting excavation-induced
damage of rock salt, and then the potential for its subsequent
healing. This method avoids the necessity for developing complicated
coupled models for damage and healing processes, and is appropriate
for locations where conditions favorable for healing are expected
to develop quickly such as adjacent to a relatively stiff
seal. Predictions are consistent with field and laboratory
measurements, and suggest that healing will occur within a
few years after emplacement of a cementitious seal. |
Borehole seal |
- |
Stormont, J. C.;
Daemen, J. J. K. |
1992 |
Laboratory study of gas permeability changes
in rock salt during deformation |
Int. J. Rock Mech. Min. Sci. & Geomech.
Abstr. 29 (1992) 4, pp. 325-342 |
Journal Article |
|
Gas permeability and porosity measurements
have been made during hydrostatic and triaxial quasi-static,
stress-rate controlled compression tests. The permeability
and porosity of the as-received samples decrease significantly
as a result of hydrostatic loading. These changes are largely
irreversible, and are believed to "heal" or return the rock
to a condition comparable to its undisturbed state. The permeability
can increase more than 5 orders of magnitude over the initial
(healed) state as the samples are deformed during deviatoric
loading. The gas permeability and porosity changes are consistent
with a flow model based on the equivalent channel concept.
A model of microcrack initiation and growth based on the frictional
sliding crack suggests the flow paths initially develop along
grain boundaries and then along axial intragranular tensile
cracks. Post-test visual observations support the model predictions. |
Permeability of rock salt |
- |
Stormont, J. C.;
Howard, C. L. et al. |
1991 |
In situ measurements of rock salt permeability
changes due to nearby excavation |
Albuquerque : Sandia Nat. Lab., SAND90-3134 |
Report |
|
The Small-Scale Mine-By was an in situ experiment
to measure changes in brine and gas permeability of rock salt
as a result of nearby excavation. A series of small volume
pressurized brine- and gas-filled test intervals were established
8 m beneath the floor of Room Ll in the WIPP underground.
The test intervals were isolated in the bottom of the 4.8-cm
diameter monitoring boreholes with inflatable rubber packers,
and are initially pressurized to about 2 MPa. Both brine-
and gas-filled test intervals were located 1.25, 1.5, 2, 3,
and 4 r from the center of a planned large-diameter hole,
where r is the radius of the large-diameter hole. Prior to
the drilling of the large-diameter borehole, the responses
of both the brine- and gas-filled test intervals were consistent
with the formation modeled as a very low permeability, low
porosity porous medium with a significant pore (brine) pressure
and no measurable gas permeability. The drilling of the mine-by
borehole created a zone of dilated, partially saturated rock
out to about 1.5 r. The formation pressure increases from
near zero at 1.5 r to the preexcavation value at 4 r. Injection
tests reveal a gradient of brine permeabilities from 5x10-18
m² at 1.25 r to about the pre-excavation value (10-21
m² ) by 3 r. Gas-injection tests reveal measurable gas
permeability is limited to within 1.5 r. |
Permeability of rock salt - High deviatoric
stress |
- |
Stormont, J. C.;
Howard, C. L. et al. |
1991 |
Changes in rock salt permeability due to nearby
excavation |
in: Roegiers: Rock Mechanics as a multidisciplinary
Science, pp. 899-907 |
Paper |
|
Changes in brine and gas permeability of rock
salt as a result of nearby excavation (mine-by) have been
measured from the underground workings of the WIPP facility.
Prior to the mine-by, the formation responds as a porous medium
with a very low brine permeability, a significant pore (brine)
pressure and no measurable gas permeability. The mine-by
excavation creates a dilated, partially saturated zone in
the immediate vicinity of the excavation with an increased
permeability to brine and a measurable permeability to gas.
The changes in hydrologic properties are discussed in the
context of pore structure changes |
Permeability of rock salt - High deviatoric
stress |
- |
Stormont, J. C.;
Peterson, E. W. et al. |
1987 |
Summary of and observations about WIPP facility
horizon flow measurements through 1986 |
Albuquerque : Sandia Nat. Lab, SAND87-0176 |
Report |
|
Numerous gas flow measurements have been made
at the Waste Isolation Pilot Plant (WIPP) Facility horizon
from 1984 through 1986. Almost all tests have been constant-pressure
or pressure-decay tests from single boreholes drilled in the
underground excavations. Results indicate that beyond about
2 m from an excavation, both halite and interbeds (anhydrite
and clay layers) allowed very low gas flows, and calculated
permeabilities are below 1 microdarcy. In regions within 2
m of an excavation, very high flow rates were measured in
the interbeds immediately above and below an excavation when
the test hole was drilled from near the center of the excavation.
Further, measured flow rates increase with the width of the
excavation. The halite also permits substantially greater
gas flow within about 1 m of the excavations. Limited tracer
measurements reveal that flow paths in both the halite and
interbeds in the near field region are significantly larger
than those in the presumed undisturbed condition. The gas
flow measurements are consistent with the development of a
(perhaps partially-saturated) dilatant zone (increased porosity)
around the excavations. Considerable uncertainty is associated
with permeabilities calculated from these flow measurements,
due to unknowns of rock saturation. entry pressure effects,
flow homogeneity, etc.
Observations based on these gas flow measurements will aid
in understanding the behavior and response of rocks surrounding
the WIPP Facility excavations. The implications of these measurements
for seal design are useful, particularly in assessing the
degree of seal bypass to expect in adjacent rock. Results
suggest that seals be emplaced as soon as possible after excavation
and in as narrow drifts as possible to minimize potential
bypass. These data are also useful in separate studies of
brine influx and gas generation/dissipation. Future measurements
will focus on the development and extent of the disturbed
zone, and on obtaining data which will make conversion of
flow data to intrinsic permeabilities more defensible. |
Permeability of rock salt - High deviatoric
stress |
- |
| Struck, D. |
1993 |
Gebirgsmechanische Untersuchungen zur Bestimmung
des Maximaldrucks von Salzkavernen
[Rock mechanical tests to determine the maximum pressure of
salt caverns] |
Hannover : Univ., Forschungsergebnisse a.d.
Tunnel- u. Kavernenbau H.15 |
Report |
German |
Parameters which have a significant influence
on the determination of maximum cavern internal pressure were
derived from the available investigations for determining
the maximum pressure in salt caverns (fig. 7-1). Although
the formation pressure is the critical parameter, the loading
history and the creep behaviour - with their influence on
the determination of maximum pressure - cannot be ignored.
Moreover, a combination of single factors also affects the
maximum pressure. Thus, the loading history in combination
with the creep behaviour and the location of the cavern in
a field can be used to determine a stress field for assessing
the maximum pressure which could not be determined from a
single parameter. The new "concept for determining maximum
pressure in salt caverns by establishing boundary conditions"
proposes the use of safety zones and a minimum pressure stress
for the tangential stress to determine the maximum pressure.
The maximum pressure can be determined on the basis of numerical
calculations in combination with the determination of permeability
in the surrounding rock.
The maximum pressure determined in this way can be used to
guarantee the sustained stability and tightness of a storage
cavern during its operating period. The proposed criteria
for this are:
(1) The maximum internal pressure must be smaller than the
formation pressure! The reference depth is the casing shoe
of the last cemented casing string,
(2) There must be a zone which is unaffected by the stress
relocation associated with the alternating stress in the roof
zone! This zone is designated the "primary sealing zone".
(3) There must be a zone in the area of the secondary stress
field created by the alternating internal pressure that prevents
the propagation of leakiness under maximum pressure conditions.
This zone, which is designated "safety zone II" must be seen
in connection with the primary sealing zone because they interact
and are time-dependent.
(4) A minimum pressure stress for the tangential stress is
proposed to avoid fracturing of the cavern wall. This assumes
a loading history involving a sudden internal pressure increase
from minimum internal pressure to maximum internal pressure.
One cannot exclude the possibility that the storage medium
infiltrates the rock in the proximal cavern wall zone. This
zone may be restricted to the immediate area of the storage
cavern wall if the maximum pressure is determined in compliance
with the recommended criteria.
Moreover, it is a basic fact that the pressure release rate
not only influences the minimum internal pressure through
the lower stressing of the cavity wall and smaller volume
convergence, but that advantages are also apparent for lower
loading rates at maximum pressure in the context of the assessment
of the zone designated as zone sI.
Information on the permeability of salt under long term alternating
pressure stress is currently not available. This should be
the target of further research. Some work in this field has
shown that the extrapolation of laboratory tests to in situ
conditions is only possible to a limited extent. The parameter
Dsj incorporated in the limiting conditions should be assigned
a conservative value when determining maximum pressure in
the absence of more detailed information on the in situ behaviour. |
Interdependence rock stress - permeability;
Rock mechanics |
only abstract; German original at KBB |
Sutherland, H. J.;
Cave, S. P. |
1980 |
Argon gas permeability of New Mexico rock salt
under hydrostatic compression |
Int. J. Rock Mech. Min. Sci. & Geomech.
Abstr. 17 (1980), pp. 281-288 |
Journal Article |
|
Laboratory measurements of the argon gas permeability
for rock salt specimens from the Waste Isolation Pilot Plant
(WIPP) site in Southeast New Mexico (SENM) are obtained by
using a transient, pressure step technique. Permeabilities
of seven specimens are investigated as a function of hydrostatic
compression and time. These data, when evaluated with the
results of other authors, lead to the conclusion that if this
formation is in a state of hydrostatic compression in its
undisturbed state, then its in situ permeability is less than
5 x 10-20 m². And, if any connected porosity is introduced
into formation, as with mining, the formation can 'heal' itself
if it returns to a hydrostatic pressure state. |
Permeability of rock salt |
- |
Sutherland, H. J.;
Cave, S. P. |
1979 |
Gas permeability of SENM rock salt |
Albuquerque : Sandia Nat. Lab., SAND78-2287J |
Report |
|
Laboratory measurements of the argon gas permeability
for rock salt specimens from the Waste Isolation Pilot Plant
(WIPP) site in Southeast New Mexico (SEIIM) are obtained by
using a transient, pressure-step technique. Hydrostatic and
differential pressure states are investigated as a function
of confining pressure and time. These data, when combined
with the results of other experimenters, lead to the conclusions
that the in-situ permeability of the undisturbed formation
is less than 0.05 µd; the introduction of non-lithostatic
stress states into the formation, as with mining, may produce
connected porosity that will increase the permeability of
the formation; and, hydrostatic pressure states applied for
finite time periods tend to "heal" the formation to its original
undisturbed state. |
Permeability of rock salt |
- |
| Thoms, R. L. |
1980 |
Permeability of rock salt for compressed air
energy storage |
SMRI Fall Meeting, Minneapolis, 12.-15.10.80 |
Paper |
|
In situ tests of rock salt for possible gas
flow between boreholes were performed by Louisiana State University
(LSU) personnel in the Jefferson Island (J1) mine of south
Louisiana. The work reported here is part of a more extensive
and general study currently being carried out at LSU for tests
of rock salt relative to compressed air energy storage (CAES)
in salt reservoirs.
A significant finding from this study was that detectable
amounts of Freon-12 (F-12) gas apparently did not penetrate
even 12 in. (305 mm) of salt between parallel boreholes over
a period of approximately 4 hours. During the test F-12 pressure
was maintained at 90-95 psi (620-655 kPa) in a central hole,
while parallel holes on either side were periodically checked
with an electronic F-12 detector ("sniffer") with sensitivity
of 3 ppm (manufacturer's literature).
Test holes were kindly drilled dry by Jefferson Island mining
personnel so as to achieve approximately the desired configuration
indicated in Fig. 1. (1)*. The lower 10 ft. (3m) of the holes
were left open. This configuration was selected so that the
salt tested would be essentially undisturbed and continuously
confined. Further, finite element modeling (2) for similar
sites indicated that relatively large values of confining
stresses would be present around the test holes, "Dry" drilling
of the holes insured that the salt to be tested would not
be "glazed over" by contact with brine (3).
It is well known that pillars in many salt mines tend to fissure
and spall (forming "scales") with time. In addition, pillar
faces are subjected to blasting during mining which tends
to fracture salt, a strain rate dependent material. That is,
salt typically behaves as a brittle material when unconfined
and loaded rapidly, e.g., by stress waves caused by blasting
(4). Thus, permeability tests performed with horizontal holes
drilled to relatively shallow depths near the free faces of
rock salt pillars should not be considered, representative
of in situ salt masses
Two groups of previous workers investigating permeability
of rock salt for possible hydrocarbon storage have reported
widely varying results from in situ tests in the Weeks Island
mine of south Louisiana.
Aufricht and Howard (3) employed a qualitative test (modified
and used in the current study as reported here) in which they
injected F-12 into holes drilled 12 ft. (3.6 m) into salt,
with 3 ft. (.9 m) of open hole at the bottom. They reported,
"after a few minutes, small but detectable quantities of Freon
were found escaping along the salt face at horizontal distances
of as much as 14 ft. from the point of injection". They also
found permeability of salt (from laboratory tests) to be highly
sensitive to apparent glazing effects from brine, i.e., permeability
of salt was sharply decreased when subjected to wetting by
brine.
Mahtab, et. al. (5), reported from in situ tests that Weeks
Island salt was essentially impermeable. And a predominant
number of their test holes were deliberately located in "anomalous
zones" (6) in the mine. However, their test holes were apparently
drilled with brine, thus directly affecting the salt to be
tested (according to the findings of Aufricht and Howard).
In conclusion for this "extended abstract", in situ gas permeability
studies of rock salt for CAES to date indicate that "induced"
permeability obviously exists near free (relatively unconfined)
faces of salt pillars; however, by contrast, rock salt with
a load history of continuous confinement and relatively, little
disturbance appears considerably more impermeable (perhaps
immeasurably small). Work currently is continuing through
the CAES program at LSU to perform quantitative in situ permeability
tests and associated interpretations which are particularly
suited for rock salt and its relevant utilization. Possible
effects on rock salt Permeability due to cyclic loadings will
be given special attention.
*Related reference number. |
Permeability of rock salt;
In-situ tests |
- |
Thoms, R. L.;
Gehle, R. M. |
1990 |
Hydrofrac gradients in two US salt domes (SMRI) |
SMRI Fall Meeting, Paris, 14.-17.10.90 |
Paper |
|
Hydraulic fracturing tests performed in the
Rayburn's and Mclntosh domes indicate that these salt stocks
are capable of withstanding larger pressure values than now
allowed by regulatory agencies. Thus, current solutioning
and storage operations in Gulf Coast domes appear conservative
in character. |
Hydrofracturing |
- |
| Thoms, R. L.; Gehle, R. M. |
1986 |
Hydrofracture gradients in salt domes |
SMRI Fall Meeting, Amsterdam, 22.09.86 |
Paper |
|
This report summarizes results from recent
field tests that were performed for the SMRI project: "Hydrofracture
Gradients in (U.S.) Salt Domes". This project was initiated
in May, 1984, and a relatively detailed report was presented
on the background of this project during the SMRI Spring Meeting
as part of the special technical session on hydraulic fracturing
of rock salt. Thus this presentation will emphasize field
tests performed since that report. A detailed final report
to the SMRI will provide a complete description of this project,
and will include our analyses of field test data and its significance
relative to storage in solution mined caverns in salt domes. |
Hydrofracturing |
- |
| Thoms, R. L.; Gehle, R. M. |
1984 |
Progress report. Hydrofrac gradients in salt
domes |
SMRI Fall Meeting, 1984 |
Paper |
|
- |
- |
no abstract |
| Thoms, R. L.; Gehle, R. M. |
1986 |
Hydraulic fracturing tests in a Gulf Coast
salt dome |
SMRI Spring Meeting, Baton Rouge, 21.-22.04.86 |
Paper |
|
This is a report on field tests performed for
the SMRI project, "Hydrofracture Gradients In Salt Domes".
This project was initiated in May, 1984, with an initial time
period of one year. The time period subsequently was extended
for a second year.
Some preliminary hydraulic fracturing field test results for
the Rayburns Dome were presented at the Fall SMRI meeting
in October, 1985. Additional test data obtained in late December,
1985, are presented here, along with an interpretation of
their significance.
This project has not been completed because of a significant
set back experienced on a "final" field test series in March,
1986. The downhole valves/ controls chamber was flooded, and
a number of test equipment components subsequently were damaged
to an extent that will require their replacement. Thus, another
3 to 4 months are needed to complete this study.
Our current plans are to rebuild the valves/controls downhole
assembly to essentially the same configuration as the predecessor
unit, since the predecessor functioned downhole in a very
satisfactory way prior to flooding. Moreover, a series of
"checks" will be incorproated into the test procedure and
equipment to avoid any possible future flooding mishaps. We
anticipate completing the field test program without additional
significant delays once the rebuilt valves/ controls unit
and incorporated procedure/equipment "checks" are ready. |
Hydrofracturing |
- |
| Thorel, L. |
1994 |
Plasticité et endommagement des roches
ductiles - Application au sel gemme -
[Plasticity and damage of ductile rocks - application of rock
salt] |
Paris : Ècole Nat. Ponts Chaussées |
Thesis |
French |
Elastoplastic short term behaviour and damage
mechanisms of rocksalt are studied experimentally and theoretically.
Review of previous works on rocksalt deformation mechanisms
shows the role of different physical factors on ductile or
brittle behaviour of rocksalt. Mechanical properties of salt
are compared with those of other geomaterials. Experimental
methods for identification of geomaterial damage are reviewed.
Compression and extension axisymmetric triaxial tests are
performed. Volume change measurements are carried out during
the tests. Under deviatoric loading, volumetric strain denotes
the material damage state, especially damage initiation. Variation
of elastic parameters is analysed. It is small, and it is
not taken into account in the constitutive law.
A simple analysis of internal stresses using a self-consistent
model allows to explain that damage appears earlier under
extension loading than under compression. Kinematic and isotropic
hardenings are then discussed.
An elastic-plastic model is proposed. It considers isotropic
hardening and non associated flow rule with plastic distortion
as a hardening parameter. Model parameters are fitted on the
basis of experimental results related to the evolution of
dilatancy angle. A 3D generalisation (using three invariants
of stress tensor) is proposed. The constitutive model takes
into account behaviour difference between extension and compression
loadings. An application to circular cavities is given. |
Rock mechanics |
French thesis separately;
(1 copy for SMRI) |
Thorel, L.;
Ghoreychi, M. |
1993 |
Rock salt damage. Experimental results and
interpretation |
Proc. 3rd. Conf. Mechanical Behavior of Salt,
Palaiseau, 14.-16.09.93, pp.161-175 |
Paper |
|
Axisymmetric triaxial tests have been performed
on rock salt, and global volumetric strains were measured.
Initiation of damage is supposed to be linked to the change
of curvature of volumetric strain from compressibility to
dilatancy due to microcracking. The results are interpreted
in the work space and in the stress space in order to identify
the damage and its evolution, using the classical formalisms
of plasticity or the plasticity associated with damage. |
Rock mechanics |
- |
| Tollert, H. |
1964 |
Beitrag zur Porosität von Salzgesteinen
[Porosity of salt rocks] |
Kali u. Steinsalz 4 (1964) 2, pp.55-60 |
Journal Article |
German |
The influence of depth on porosity was investigated
using rock salt as an example. This first involved eliminating
the effect of the three main contaminants: sylvine, kieserite
and anhydrite. This resulted in the unexpected observation
that each contaminant salt independently generates a periodically
changing porosity in the rock salt with increasing content
of the contaminant salt. This is attributed to the periodically
changing binding strength of the rock salt lattice. No depth
influence on porosity was determined. |
Miscellaneous |
- |
| Tomastik, B. E. |
1993 |
Investigation of active and abandoned class
III salt solution mining projects in Ohio |
SMRI Spring Meeting, Syracuse, 25.-27.04.93 |
Paper |
|
Solution mining for salt in Ohio began in 1889.
Since 1889, at least 234 solution mining wells have been drilled
in Ohio at nine different solution mining facilities. Today,
only two projects and 38 wells remain in operation.
The principal salt beds solution mined in Ohio occur within
the Silurian-aged Salina Group and include the B, D, E, F,,
and F, salt units. Depths to these salt beds range from 1800
to 3150 feet below the surface and individual bed thickness
rarely exceeds 100 feet. A number of different solution mining
methods have been utilized in Ohio since 1889,.but today most
wells are operated as two-well galleries that are either hydraulically
fractured or directionally drilled to achieve interconnection.
In July of 1989, the Ohio Division of oil and Gas (Division)
initiated a study of Class III salt solution mining operations
in Ohio to determine whether current practices and regulations
were adequate to ensure protection of Underground Sources
of Drinking Water (USDWs) . This study involved the investigation
of five solution mining projects; two of which are currently
active, and three which were abandoned.
During this project, the Division investigated 90 oil and
gas wells near the five solution mining facilities to determine
the possible extent of the solution mining caverns and whether
the uncemented surface/production casing annuli of these wells
could pro,yide potential avenues f or fluid migration from
the caverns into USDWs. Special permit conditions for drilling,
completion, and plugging of oil and gas wells have been developed
and implemented as a result of this study. Review areas have
been delineated around all five facilities. If an application
for permit to drill or plug is received for a site located
within a review area, the Division performs a site specific
review and designs special permit conditions for protection
of USDWs.
One of the principal areas of concern investigated during
this study was the abandoned PPG Industries, Inc. solution
mining facility at Barberton, Ohio. Oil and gas drillers have
reported encountering fluids with unusual pressures, volumes,
and properties and/or gases while drilling through the Bass
Islands-Salina Group interval. In addition, the Division found
that plugged solution mining wells were leaking fluids to
the surface. The Division of oil and Gas and the Ohio EPA
sampled 15 oil and gas wells that may have penetrated the
Salina Group and two leaking solution mining wells in an effort
to characterize the cavern fluids. Analyses revealed that
three oil and gas wells and one solution mining well contained
low concentrations of man-made chemicals. The remaining oil
and gas wells and one solution mining well had constituents
commonly found in typical oil-field brines. Although this
initial sampling program revealed the presence of man-made
chemicals, the investigation was not sufficiently exhaustive
to determine all of the constituents present or their source.
On April 5, 1991, U.S. EPA, Region 5 issued an Administrative
Order on Consent (Consent Order) to PPG Industries, Inc. to
expeditiously abate or remove the threats presented by hazardous
waste or hazardous constituents to human health and the environment
at the Barberton plant site. In November of 1991, U.S. EPA
issued a request for additional interim corrective measures
that required the plugging and abandonment of the leaking
solution mining wells. The Ohio EPA and the Division will
continue to assist U.S. EPA with the investigation and remediation
of the Barberton site.
Since the initiation of this project in July of 1989, the
Division of oil and Gas has continued to revise its Class
III Program in order to enhance its ability to protect USDWs.
Through the issuance of special oil and gas drilling permit
conditions and modification of solution mining plugging procedures,
the Division has been able to achieve this goal.
Research and investigation of Ohio's solution mining operations
will continue. Much of the data and information obtained during
this study should prove to be very beneficial to both the
U.S. EPA and other states with regulatory responsibilities
for solution mining activities. |
Cavern abandonment |
- |
| Trimmer, D. |
1982 |
Laboratory measurements of ultralow permeability
of geologic materials |
Rev. Sci. Instrum. 53 (1982) 8, pp.1246-1254 |
Journal Article |
|
A new apparatus is described for determining
permeability (water) in geologic materials as a function of
confining pressure (to 200 MPa), pore pressure (to 25 MPa),
and deviatoric stress (500-800 MPa). The samples are relatively
large (0.15 m diameter x 0.28 m long) and may be intact or
contain a single through-going fracture. Permeabilities of
10-11 - 10-24 m² (10 - 10-12 D) may be measured, simultaneously,
with electrical conductivity and acoustic velocity and amplitude.
Crack closure is also monitored for the fractured samples.
All experimental control and data-acquisition functions are
performed by a microcomputer. A discussion of data-analysis
techniques and typical data are also presented. |
Permeability of rock salt |
- |
Tsenn, M. C.;
Carter, N. L. |
1990 |
Strengthening effect of dislocation networks
in NaCl |
Scripta Metallurgica et Materialia 24 (1990),
pp.1115-1118 |
Journal Article |
|
To model the deformational behavior of any
polycrystalline aggregate, it is necessary to account for,
among other variables, the effect on flow stress of preexisting
microstructures. For example, it is commonly observed that
apparent steady state stress values, following an abrupt reduction
in applied stress or strain rate, reach levels appreciably
higher than those obtained had the test been carried out monotonically
at the reduced conditions. This strengthening caused by the
initial defor,-natiozi, has been attributed to barriers to
dislocation glide during the second stage created by either
subgrain boundaries (1,2) or by stable forest dislocation
networks (3,4). While both types of obstacles may be effective
in impeding free dislocation glide in varying degrees, it
is important to determine the dominant strengthening mechanism.
The strengthening effect of subgrain boundaries is attributed
to those boundaries composed of closely-spaced dislocations
which may serve as barriers to gliding dislocations (5), leading
to a reduced creep rate and larger stress exponent (1). However,
not all subgrain boundaries act as effective barriers to dislocation
glide and the results from many experimental studies question
the importance of subgrains as obstacles. For example, 20%Cr-35%Ni
steel (6), begins to form subgrains during secondary creep
instead of primary creep, as has been generally believed.
Aluminum deformed in torsion has average misorientation angles
increased by a factor of two (from about 0.5° to about
1.2°) over the strain range from the onset of steady state
(e = 20%) to a strain of about 120% (7). Dislocation bands
cutting across many subgrain boundaries in deformed NaCl crystals
(8) also indicates the limited effectiveness of subgrain boundaries
as barriers to dislocation motion. As a final example, the
flow strengths of natural rocksalt specimens deformed at 100°
and 200°C fell to single-stage values at 10-6 s-l following
an abrupt decrement to 10-6 s-1 after 4% strain at 10-4 s-1
(9, 10). Subgrains, with an average diameter of 8 mm, formed
during the initial stage at 200°C but did not form at
100°C. Following the decrement to 10-6 s-1 in the test
at 200°C, steady-state stress was reached by 1 % strain
but 4% strain was required for the subgrain size to equilibrate
with the stress. Thus, in these studies neither the occurrence
nor changes in characteristics of subgrain boundaries altered
steady-state creep rates or stress levels.
Free dislocations in any crystal that has experienced slip
on more than one plane form three-dimensional networks during
deformation at elevated temperature (3). The networks consist
of large numbers of meshes and polygons of varying sizes.
Dislocation lines, or links, constituting edges of polygons
and meshes are pinned at their ends, or nodes, by the elastic
interaction of intersecting dislocations. Under applied stress,
a given link bows in its glide plane into an arc with a radius
of curvature fixed by the shear stress resolved on its slip
line (11). The bowed links may break free from their nodes
and glide freely, as if released from a Frank-Read source
(11, 12), when the applied stress reaches a critical value.
The critical shear stress, t, required to release a link of
length L is given by the well-known relation
t = a Gb/L [1]
where b is the Burgers vectors, G is the shear modulus
and a is a constant which depends on the strength of the
barrier. The link so released may glide freely, without
the need to remain in equilibrium with its own line tension,
until it is recaptured by the network. The dislocation network
is then refined by collisions of gliding and network links
and the stability of the latter is believed to be responsible
for the commonly observed strengthening (13). Therefore,
in this model, stress levels for transient and steady-state
creep are controlled by network refinement by link-network
collisions causing strain hardening and during recovery
by network-coarsening through dislocation climb (14) and
cross-slip (15).
In this study, we attempt to evaluate the influence on the
mechanical response of forest dislocation networks alone.
The procedure adopted (16) was to impose different levels
of cold-work prior to high-temperature deformation. |
Rock mechanics |
- |
| Urai, J. L. |
1983 |
Deformation of wet salt rock. An investigation
into the interaction between mechanical properties and microstructural
processes during deformation of polycrystalline carnallite
and bischofite in the presence of a pore fluid |
Utrecht : Univ. |
Thesis |
|
This work deals with two topics.
First, - as observations on naturally deformed salt rocks
indicate that brine has been present in these during salt
metamorphism, and that this brine has strongly effected rheological
behaviour -, the effect of saturated brine on the rheological
properties of polycrystalline carnallite (KCl.MgCl2.6H2O)
and bischofite (MgCl2O) was investigated. Second, - as salt
minerals are good analogues for other rock forming minerals
-, a fundamental study of microstructural evolution during
dynamic recrystallization was carried out.
Most of the experiments on carnallite were performed using
starting material obtained from the Asse salt mine in W-Gemany.
Microstructural analysis of this material (chapter 2) indicates
a history involving three processes: grain boundary migration,
progressive misorientation of subgrains and mass transfer
through the fluid phase. Detailed investigation of hematite
inclusions found in the carnallite (which give the carnallite
its red colour) reveals that these are decorating dislocation
networks. This provides strong evidence that the hematite
was precipitated after formation of the carnallite.
Experimental deformation of the carnallite has been carried
out at T 60°C, confining pressures between 0.1 and 31
MPa, fluid contents up to 2.5% and strain rates between 10-4
and 10-8 s-l, (chapter 3). At a relatively high strain rate
(5 x l0-5 s-1), rheological behaviour depends in a complicated
way upon confining pressure, brine content and content of
other phases, with a general weakening towards increasing
brine contents. Deformation also results in an up to 1% dilatation,
associated with an about two orders of magnitude increase
in permeability.
Experiments at lower strain rates show power law creep with
a stress exponent between 4 and 5 for wet samples.
Deformation mechanisms are intracrystalline slip, twinning,
cracking and displacement along grain boundaries. Recrystallization
is strongly enhanced by the presence of brine. At low strain
rates, however, overgrowths start to appear at dilatation
sites, indicating that diffusive mass transfer flow is becoming
more important and may become rate controlling at even lower
strain rates. Microstructures in these samples are very similar
to those found in the naturally deformed material.
Experimental deformation of bischofite (chapter 4) was carried
out on artificially prepared samples at temperatures between
40 and 100°C, confining pressures between 0.1 and 28 MPa,
and strain rates between 10-4 and 10-8 s-l.
First, at a strain rate of 10-5 s-l, the effect of grain size,
impurity content and water content on the flow behaviour was
investigated. Addition of 0.1 wt% water was found to decrease
the flow stress by a factor of 5.
Second, the strain rate sensitivity of the flow stress in
selected samples was investigated. Two regimes could be distinguished
one with a stress exponent n=4.5 in the power law creep equation
for values of the differential stress above 2.0 MPa, and one
with n=1.5 for stresses below this value.
Deformation mechanisms were intracrystalline slip, twinning
and grain boundary sliding. Recrystallization occurred by
subgrain rotation and grain boundary migration. Brine was
found to strongly enhance recrystallization. Before and after
deformation, brine was found in fluid inclusion arrays at
grain boundaries.
To get more insight into microstructures during deformation,
0.1 mm thick samples of carnallite and bischofite were deformed
in-situ under the optical microscope (chapter 5). Microstructural
evolution was correlated with observations made on thin sections
of deformed samples.
In the case of bischofite, a number of interesting additional
observations were made in the in-situ experiments.
(a) grain boundary migration rates fell into two different
regimes, one of about 0.1 x 10-6 m/s and one between 1 and
10 x10-6 m/s. Sudden changes of grain boundary migration rate
were observed.
(b) Microstructural evolution during dynamic recrystallization
was characterized by the coalescence of grains, cutting up
of grains, and cyclic changes in a grain's size. By these
processes, "orientation families" developed.
(c) grain boundaries during migration were optically clear.
This, together with the observation of necking-down processes,
led to the conclusion that migrating grain boundaries contain
a fluid film (about 50 nm thick) which develops into an array
of fluid inclusions after the boundary has stopped migrating.
Chapter 6 is an attempt to incorporate the in-situ observations
into existing theories of recrystallization. A classification
of recrystallization into seven regimes is proposed, based
on the relative importance of the three processes "slow" and
"fast" grain boundary migration, and progressive misorientation
of subgrains. The applicability of this classification to
deformed minerals is discussed.
Based on the results of the first four chapters, applicability
of the rheological -data to the deformation of salt rocks
in nature is discussed in chapter 7. It is argued that the
experimentally found flow law for the deformation of wet carnallite
and bischofite is applicable to the deformation behaviour
of these minerals durig diapirism. Based on theoretical models
of diffusive mass transfer flow, it is argued that at strain
rates below those attainable in the laboratory, the weakening
effect of water will increase. |
Interdependence rock stress - permeability;
Creep behavior |
- |
Urai, J. L.;
Spiers, C. J. et al. |
1986 |
Weakening of rock salt by water during long-term
creep |
Nature 324 (1986) Dec. 11, pp.554-557 |
Journal Article |
|
The rheological properties of rock salt are
of fundamental importance in predicting the long-term evolution
of salt-based radioactive waste repositories and strategic
storage caverns, and in modelling the formation of salt diapirs
and associated oil traps. The short-term high rheology of
rock salt is well known from laboratory experiments; however,
extrapolation to appropriately low stream fails to predict
the rapid flow men in certain natural structure. Furthermore,
experiments have failed to reproduce the recrystallized microstructure
of naturally deformed salt. Here we report experiments indicating
that the above discrepancies can be explained by taking into
account the influence of trace amounts of brine. Trace brine
is always present in natural salt but sometimes escapes during
experiments. Our tests on dry dilated salt show more or less
conventional dislocation creep behaviour, but brine bearing
samples show marked weakening at low strain rates. This is
associated with dynamic recrystallization and a change of
deformation mechanism to solution transfer creep. Because
natural salt always contain some brine these results cast
substantial doubt on the validity of presently accepted dislocation
creep laws for predicting the long-term rheological behaviour
of salt in nature. |
Creep behavior |
- |
Urai, J. L.;
Spiers, C. J. et al. |
1987 |
Deformation mechanisms operating in naturally
deformed halite rocks as deduced from microstructural investigations |
Geol. Mijnbouw 66 (1987), pp.165-176 |
Journal Article |
|
In this paper we describe the microstructures
of naturally deformed rocksalt samples from the Asse salt
anticline, FRG, as revealed by a chemical polishing-etching
procedure, and by gamma-irradiation. Evidence is presented
for the operation of dislocation creep processes, accompanied
by extensive strain-induced grain boundary migration. Grain
boundaries can be shown to have contained thin brine films
during recrystallization, suggesting that solution-precipitation
processes could also have been important deformation mechanisms.
Recrystallization and solution transfer processes have not
been reported in most experimental work to date, thus casting
doubt on the validity of extrapolating these data to predict
the long-term creep behaviour of salt during natural flow. |
Creep behavior |
- |
| Van Fossan, N. |
1988 |
Panel discussion questions plugging brine filled
solution mined chamber, and comments related to panel discussion
on plugging of wells |
SMRI Spring Meeting, 1988 |
Paper |
|
1) What is the "upper" limit on the pressure,
in a sealed brine filled chamber, due to natural occurring
forces?
2) What general effect would the numerous near vertical striations
of differing salt compositions, variations of anhydrite in
salt, and anhydrite have on the stress field surrounding the
chamber (i.e., would it tend to be significantly distorted)?
3) Is it likely any of the above striations would be continuous
over an extended vertical interval? Is there likely to be
a significant difference in the mechanical "strength" of the
various striations?
4) If the pressure in a sealed chamber ever reached geostatic
(i.e., the fracture gradient) at the exposed face of a vertical
striation of significantly lesser mechanical strength, is
it likely a long vertical fracture would occur?
5) What do we know about the nature of occurrence and probable
extent of micro-fracture (i.e., area covered, width, orientation,
length, etc.) resulting from over-pressure in a borehole?
Is it likely they would be of the same nature and extent in
the salt face of a large volume solution mined chamber which
had been subjected to a pressure in excess of geostatic?
6) Is it likely micro-fracturing would be concentrated in
limited areas where "weaker" striations exist thus occurring
at a pressure significantly less than geostatic?
7) What is the effect of aging on the strength of the commonly
used oil field type cement (s)?
8) What is known in respect to the shear strength of common
neat cement?
9) What might be the relative values of the shear strength
of the salt in contact face area and that of the cement in
the plug itself?
10) What is generally considered the maximum open hole diameter
within which a plug can be set?
11) In the event it is impractical to emplace an open hole
plug, what criteria should be set for mechanical integrity
in the casing cementation?
12) What data, other than chamber brine pressure, should be
manitered'in a sealed solution mined chamber? (Temperature,
pressure on face of cement plug, shear stress within cement
plug, etc.?) |
Borehole seal;
Cavern abandonment |
- |
| Van Fossan, N. E. |
1981 |
Mechanisms of product leakage from solution
caverns |
SMRI Spring Meeting, 27.04.81 |
Paper |
|
The manner in which solution caverns fail and
the way in which migration of stored products occur in the
event of such failure is generally misunderstood. It is necessary
that the stresses imposed on a solution cavern as a result
of storage operations be thoroughly understood and put in
context with the various mechanisms of cavern failure before
adequate precautions can be made to prevent failure. Eleven
potential failure modes are discussed herein. The manner in
which crude oil could migrate from the cavern in the event
of failure, the degree to which such migration might progress,.
and the eventual accumulation of stored crude oil in natural
occurring traps is also discussed. The migration of crude
oil is used as an example because of the major emphasis now
being placed on the Strategic Petroleum Reserve Program and
the general body of knowledge relating to the characteristics
of oil trapping phenomena on or adjacent to domal salt formations.
The migration of gaseous phase stored products and those having
a low specific gravity or high vapor pressure could be quite
different from crude oil. One scheme for storage cavern wellhead
instrumentation and controls sufficient to restrain operating
conditions within safe limits is covered. |
Miscellaneous |
- |
| Van Sambeek, L. L. |
1990 |
A simple method for modeling the pressure buildup
or flow of an abandoned solution well |
SMRI Spring Meeting, Austin, 24.04.1990 |
Paper |
|
Solution wells in salt are used for either
mineral production or space to store gases, liquid hydrocarbons,
or wastes. During the well's operational lifetime, the pressure
or flow at the wellhead is controlled. Abandonment of a solution
well, however, introduces many questions. What will be the
time-dependent pressure in a plugged solution well? Will the
plug hold? Will the salt hydrofrac? If the well is left open,
what will the flow be from the wellhead?
In this paper, a simple analytical method is described for
computing either the pressure buildup in a plugged well or
the flow from an open well. Pressurization and flow predictions
for a typical storage well are presented and compared to the
results from a sophisticated finite element model. The analytical
model is also used to predict the pressure buildup for two
shut-in wells on the Warren Petroleum property at Mont Belvieu,
Texas. The agreement between the measured wellhead pressures
and the predicted pressures is quite good. |
Rock mechanics;
Cavern abandonment |
- |
| Van Sambeek, L. L. |
1988 |
Mechanical behavior and performance of concrete
seals in rock salt |
Key questions in rock mechanics: Proc. 29th
U.S. Symp., pp.665-672 |
Paper |
|
Small-scale cementitious seal tests in rock
salt are being conducted at WIPP by Sandia National Laboratories.
Measurements of the mechanical behavior from these tests are
compared to numerical modeling results. Factors considered
in the numerical model were the heat of hydration, time-dependent
stillness, creep, and chemical expansivity of the concrete
and the creep of salt. Based on the comparison, salt creep
and concrete chemical expansivity seem to control the early-time
response of the seals, while salt creep dominates the long-term
response. Permeability testing indicates that the penetration
and the salt immediately surrounding the borehole were effectively
sealed. |
Borehole seal |
- |
| Van Sambeek, L. L. |
1993 |
Evaluating cavern tests and surface subsidence
using simple numerical models |
Proc. 7th. Symp. on Salt, Vol. 1, pp.433-439 |
Paper |
|
Cavern tests are routinely conducted to prove
the integrity of solution wells and storage caverns. Because
cavern tests are performed as demonstrations, test data are
not fully analyzed and information that would be useful in
characterizing the well and surrounding salt is ignored. Similarly,
surface subsidence surveys are routinely performed over mining
operations and cavern storage facilities because of regulatory
requirements. The information from these surveys is often
plotted and used to demonstrate that 'normal' subsidence is
occurring without recourse to understanding what the normal
subsidence should be. Two numerical models are described that
aid the interpretation of cavern test data and surface subsidence
measurements. The theoretical basis, construction, and practical
application of each numerical tool is discussed.
The cavern test model is used to interpret shut in and flow-rate
cavern test data based on the cavern geometry, temperature
and density log information, brine or gas properties, and
salt modulus and creep properties. Alternatively, the cavern
model can be used to estimate salt creep properties based
on the cavern test data. The cavern model is demonstrated
for case history test data from storage wells in domal salt
and shaft closure in bedded salt.
The surface subsidence model is used to interpret and predict
surface subsidence and subsurface strains, which result from
underground excavation and creep of salt. The model accounts
for the three-dimensional geometry of underground caverns
or mined rooms, the timewise creation of the openings, and
salt creep. The subsidence methodology is embodied in a personal
computer program developed for the Solution Mining Research
Institute. Case history subsidence data are evaluated to demonstrate
the methodology and use of the numerical tool. |
In-situ tests;
Rock mechanics |
- |
| Van Sambeek, L. L. |
1992 |
Dilatancy of rock salt in laboratory tests |
SMRI Fall Meeting, Houston, 18.-21.10.92 |
Paper |
|
Rock salt in its natural state is typically
considered impermeable (k=10-24 m²). Creation of openings
in salt, which is initially under lithostatic stress conditions,
causes deviatoric stress states and creep begins to occur.
There is no strong evidence to suggest that the permeability
is increased by this creep under most situations. An increase
in test specimen volume has, however, been observed to occur
in some laboratory tests on salt core. Such a volume increase
is called dilatancy and is attributed to microcracking occurring
both during load application through plastic deformation and
during creep tests while loads are held constant. The microcracking
will cause an increase in permeability by increasing the connected
porosity. In this paper the stress conditions applied in laboratory
tests are separated into those that did and those that did
not cause dfiatancy. The types of tests considered are creep,
constant strain-rate, and quasistatic true-triaxial. The laboratory
test data are from published test results.
Until recently, little research was done in terms of relating
stress states, creep rates, and accumulated strain to damage
in rock salt. After reviewing the results of three different
laboratory testing programs, a criterion is proposed that
signifies the potential for dilatancy based on imposed stress
states in laboratory tests. This same dilatancy criterion
can be used to delineate dilatancy around openings in rock
salt (such as shafts, boreholes, and storage caverns) based
on calculated stress states. Dilatancy is in turn relatable
to the risk of increased permeability in the rock salt. An
evaluation of such damage is useful whenever tightness of
the salt formation is a concern to prevent loss of stored
products or the intrusion of brines. The criterion can also
be used to evaluate the potential for healing of damaged regions
if the stress state is modified. |
Interdependence rock stress - permeability |
- |
Van Sambeek, L. L.;
Ratigan, J. L. et al. |
1993 |
Dilatancy of rock salt in laboratory tests |
Int. J. Rock Mech. Min. Sci. & Geomech.
Abstr. 30 (1993) 7, pp. 735-738 |
Journal Article |
|
- |
Interdependence rock stress - permeability |
no abstract |
Varo, L.;
Passaris, E. K. S. |
1977 |
The role of water in the creep properties of
halite |
Proc. Conf. on Rock Engineering, Newcastle
upon Tyne, 04.-07.04.77, pp.85-100 |
Paper |
|
Tests were carried out upon halite to determine
the effect of different humidity levels, and of immersion
of the specimen in saturated brine or water, upon the creep
rate. Tests were also performed to discover how long it took
specimens of halite to reach equilibrium when placed in atmospheric
environments having the same relative humidity as those in
which creep tests were carried out.
It was found that the creep of halite is affected by the relative
humidity of the atmosphere, especially above 75% R.H., when
solution of the sample occurs. Below 75% R.H. no detectable
solution occurs, but creep is still affected by the humidity:
the mechanism for this is uncertain but may be connected with
the Joffé effect.
Creep in saturated brine is affected by recrystallisation
of the sample, as is creep at R.H. levels of over 75%. Creep
in water results in rupture due to solution. |
Creep behavior |
- |
Vons, L. H.;
Andre Jehan, R. et al. |
1985 |
Specific investigations related to salt rock
behaviour |
2nd. Europ. Comm. Conf. on Radioactive waste
management and disposal, Luxembourg, 22.-26.04.85, Summary
Paper VI.2 |
Paper (Abstract) |
|
In this paper results are given of work in
various countries in rather unrelated areas of research. Nevertheless,
since the studies have been undertaken to better understand
salt behaviour, both from mechanical and chemical points of
view, some connection between the studies can be found. In
the French contribution the geological conditions have been
investigated that might promote or prevent the formation of
salt domes from layers, in view of possible use of the latter
type of formation. This was done theoretically by the finite
element method, and a start was made with centrifuge tests.
The density of a number of samples from salt and overburden
from the Bresse basin was measured and it was shown that a
favourable condition exists in this region for waste disposal.
In the German contribution various subjects are touched upon,
one being the effect of water on the mobility in the early
stages of salt dome formation. It was also shown that in the
final stages the water content is very low and that the thermal
release of water occurs at higher temperatures than 250 °C
for polyhalites and, under the prevailing pressure, for carnallite
at temperatures above 140 °C.
Regarding the mechanical properties in the German work evidence
was found for an anisotropy in salt in such a way that fibre
textured material under compression parallel to the fibre
axis shows significantly higher strain that when tested normal
to it.
One Dutch contribution presents results of laboratory and
in-situ measurements at ambient temperatures in the Asse mine,
with an acoustic method to detect the extension of cracks
in stress-relieved locations, such as gallery walls etc.
In the laboratory, tests were done with cubic blocks of rock
salt under 3-D loading. The structural changes in the rock
salt could be followed clearly by means of acoustic travel
time measurements. During the test decompaction and recompaction
of the rock salt was observed as a function of loading. The
formation of macro cracks was clearly observed when the heater
was suddenly switched off. A not relevant loading case however
in a repository!
In the wall of an old room In the ASSE-mine two measuring
holes were drilled. The area between the holes was examined,
open fissures could easily be detected. The measurements in
the area close to the wall of the room points to the occurrence
of micro-cataclasis is parallel to the wall side. Reassuring
was the observation that this effects decreases according
to the increase of the distance from the wall side. This research
is of particular interest for detailed analytical modelling
of i.e. pillars in a HLW-repository.
Another Dutch contribution describes results of studies on
the effect of small amounts of water on the rheology of salt.
The results imply that flow laws obtained for salt at rapid
strain rates and/or low confining pressure (i.e. much of the
preexisting rheological data) cannot be reliably extrapolated
to predict the long term behaviour of wet or even very dry
(0.1 - 0.01 wt% H2O) material under natural (non-dilatant
or elevated pressure) conditions. According to the experimental
data, long term flow of salt under natural, low stress conditions
could be considerably faster than previously expected, particularly
if large amounts of water are present (e.g. 0.25 - 0.5 wt%).
Preliminary results on the effect of water upon ion-mobility
indicate a certain pseudo-absorptive capacity of salt e.g.
for Sr.
A somewhat related type of work is presented in the Danish
contribution where the absorptive capacity of powdered salt
for a range of radionuclides of different valency was measured
both for pure salt and salt with addition of hematite and
anhydrite impurities. Reasonable absorption of Eu and Am was
found for pure halite, whilst impure salt showed a much larger
retention and also other elements such as Co were absorbed.
The effect of anhydrite was less pronounced. |
Rock mechanics |
only abstract |
| Wallner, M. |
1988 |
Frac-pressure risk for cavities in rock salt |
Proc. 2nd. Conf. Mechanical Behavior of Salt,
Hannover, 24.-28.09.84, pp. 645-658 |
Paper |
|
The economic and safe utilization of cavities
in rock salt for the storage of gas and oil or waste disposal
purposes requires stable performance of the cavities. Beside
that, for liquid-filled cavities, long-term sealing from the
biosphere is of particular interest. In that case, the following
problems have to be considered from the rock mechanics point
of view: the permanent tightness of borehole cementation has
to be proved and the natural pressurization of the encapsulated
fluid in the sealed cavity, due to long-term convergence,
must not exceed the frac-pressure. It is shown that with the
aid of finite element computations the risk of hydro-frac
can be calculated. Frac pressure risk depends on the height
and depth of the cavity, as well as on the pressure increase
rate. |
Cavern abandonment |
- |
| Walsh, J. B. |
1981 |
Effect of pore pressure and confining pressure
on fracture permeability |
Int. J. Rock Mech. Min. Sci. & Geomech.
Abstr. 18 (1981), pp.429-435 |
Journal Article |
|
The effective pressure pe for measurements
off fluid permeability < k > is shown to be (pc - spp)
where pc is confining pressure, pp is pore pressure, and s
depends on the topography of the fracture surfaces and rock
type. Measurements of flow through simulated fractures by
Kranz et al. [1] show that s can vary between 0.5 and 1.0.
The analysis here suggests that < k >1/4 should be linearly
related to ln pc. Data from studies by Kranz et al. [1], Brar
& Stesky [2], and Jones [3] follow the theoretical relationship. |
Pore pressure;
Permeability of rock salt |
- |
Wawersik, W. R.;
Stone, C. M. |
1989 |
A characterization of pressure records in inelastic
rock, demonstrated by hydraulic fracturing measurements in
salt |
Int. J. Rock Mech. Min. Sci. & Geomech.
Abstr. 26 (1989) 6, pp.613-627 |
Journal Article |
|
The use of hydraulic fracturing in elastic
rock is described in terms of comprehensive hydraulic fracturing
observations in rock salt in the Salado formation in southeastern
New Mexico. Inelastic rock behaviour involves both rate-independent
and rate-dependent permanent deformations. A combination of
small-volume tests in initially open, horizontal drillholes,
finite-element analyses, and in situ fracture observations
demonstrates that the pressure-time data in inelastic rock
can differ fundamentally from those typically recorded in
competent hard rock. Stable pressure-time signatures with
little or no pressure drop between peak and driving pressure
are obtained in isotropic stress fields. Increasingly unstable
records appear to be characteristic for anisotropic stress
conditions. Qualitatively, the shapes of the pressure-time
records of hydraulic fracturing tests in rock salt appear
to be remarkably sensitive to the ratio of the in situ principal
stresses normal to the fractures. Obtaining quantitative estimates
of in situ stress magnitudes in rock salt and other highly
inelastic rocks, however, hinges on the existence of reliable
rate-dependent constitutive models in conjunction with relatively
complex numerical analyses. Exaggerated contrasts in the greatest
and least in situ compressive stresses are inferred from applications
of elasticity solutions. Time-dependent effects on the characteristics
of hydraulic fracturing in rock salt and associated difficulties
in data interpretations arise if hydraulic fracturing is performed
almost immediately after drilling. |
Hydrofracturing |
- |
Wawersik, W. R.;
Stone, C. M. |
1985 |
Application of hydraulic fracturing to determine
virgin in situ stress state around Waste Isolation Pilot Plant
- in situ measurements |
Albuquerque : Sandia Nat. Lab., SAND85-1776 |
Report |
|
Hydraulic fracturing tests were carried out
in horizontal drillholes in rock salt in the Waste Isolation
Pilot Plant (WIPP) near Carlsbad, NM. It was determined that
the virgin in situ stress field is isotropic or nearly isotropic.
The inferred magnitude of the isotropic in situ stress falls
between bounds of 14.28 MPa and 17.9 MPa for the average breakdown/reopening
pressures and driving pressures. The best estimate from instantaneous
shut-in pressures is 16.61 MPa. Given some uncertainties about
the interpretation of hydraulic fracturing data in salt, all
of the foregoing values are in acceptable agreement with an
average calculated isotropic in situ stress of 14.9 MPa at
an average depth of 657 m below surface. Interpretations of
breakdown and reopening pressures are based on finite element
analyses of the relaxed stress field around a borehole in
salt. This stress field varies little between approximately
50 and 200 days after drilling. The finite element analyses
were also used to interpret the observed stable pressure-time
signatures with little or no pressure drops during primary
breakdown of the salt formation. The conclusion about the
isotropic nature of the virgin in situ stress field is supported
by observations of the induced fracture patterns. The report
includes a comparison of the hydrofrac data in the WIPP with
the published results of hydraulic fracturing tests in salt
at three other locations. |
Hydrofracturing |
- |
Wieczorek, P.;
Rothfuchs, T. |
1986 |
In situ permeability measurements |
in: EUR 10827 EN/I, pp.169-180 |
Paper |
|
Five in situ permeability measurements have
been performed and evaluated based on the assumption of an
unsaturated homogeneous formation using a program for the
computation of one-dimensional pressure fields.
A partly good agreement between measured and calculated pressure
curves was achieved, although in some cases a temperature
reduction would have been required.
The calculated permeabilities were all in the range of 10-9
Darcy. |
Permeability of rock salt |
- |
You, T.;
Maisons, C. et al. |
1994 |
Experimental procedure for the closure of brine
production caverns on the "Saline de Vauvert" site |
SMRI Fall Meeting, Hannover, 25.09.-01.10.94 |
Paper |
|
Elf Atochem - Saline de Vauvert have been solution-mining
a salt formation in Southern France for the last twenty years
and there arises the problem of what to do with the deep caverns
once brine production ceases. The wells are currently open
and instrumented, but this situation can only be temporary.
Elf Atochem - Saline de Vauvert and Géostock in close
collaboration with Elf Aquitaine Production, have put forward
procedures for sealing off the caverns to make them environmentally
safe.
This paper is based on the report submitted to the regulating
authorities further to a site study undertaken over recent
years. It describes an experimental procedure for determining
well-closure safety criteria and appropriate means of monitoring
the reactions of the surrounding ground and fluids. |
Cavern abandonment |
- |
