Parent Command
> OBSERVATION
Subcommand
-
Description
This command selects points in time at which step changes are to be made to individual
elements or element groups. At this specific point in time, the user can either change
the element’s volume, porosity, permeability, or any of its primary variables.
Such times are termed "restart times" because in standard TOUGH2 one would have to stop
the simulation, and restart it after having changed the initial conditions of certain elements.
This option is useful for modeling well tests, where the condition in the borehole is changed
at certain points in time. For the simultaneous calibration of well tests consisting of many
test events, it is imperative to model the entire sequence in a single simulation run, i.e.
individual events must be connected. Recall, that complicated, time-varying boundary
conditions can also be programmed into subroutine USERBC.
The specification of a restart time is identical to specifying calibration points (see command
Variables ipv and value in Command RESTART |
abs(ipv) | value |
---|---|---|
0 | Element volume | |
1 <= ipv <= NEQ | Primary variable No. ipv | |
NEQ + 1 | Porosity | |
NEQ + 2 | (+)Permeability or (-) permeability modifier | |
NEQ + 1 + i | Variable USERX(i) |
The general format is as follows:
>> RESTART TIME: 1 (time_unit)
restart_time
elem ipv value
elem ipv value
.... ... .....
A comprehensive example is given below.
This option can also be used to periodically generate a SAVE file. This may be desirable for
very long TOUGH2 simulations. In case of a computer failure, the run can be restarted at the
time of the last restart time.
If keyword NEW is present, a new SAVE file with unique file name is created for each restart time.
Example
> OBSERVATION
This example demonstrates the use of restart times to connect four individual test events into
a single simulation. The test sequence starts with a shut-in recovery period, i.e., in the
TOUGH2 input file the actual interval volume is assigned to the element representing the
borehole. At time tCP, a constant pressure pumping test is initiated, i.e. the element volume
is increased to a very large number, and the prescribed interval pressure is specified as
initial conditions. A shut-in pressure recovery period starts at time tREC,
modeled by reassigning the actual interval volume. Finally, a pulse test is simulated,
assuming that all the gas that potentially accumulates in the borehole interval has been
released at time tPULSE, prior to applying a short pressure pulse. The pressure response in
the injection well is schematically shown in the figure below, followed by the appropriate
iTOUGH2 block with restart times and boundary condition specifications.
>> RESTART TIME: 1 [HOURS]
2.56 (tCP)
BOR_1 0 1.0E+50 (large volume for const. pressure b.c.)
BOR_1 1 1.3E+05 (set constant interval pressure)
>> RESTART TIME: 1 [HOURS]
3.51 (tREC)
BOR_1 0 0.73 (actual volume for shut-in recovery)
>> RESTART TIME: 1 [HOURS]
5.44 (tPULSE)
BOR_1 2 0.00 (prescribe single-phase liquid cond.)
BOR_1 1 4.85E+05 (pressure pulse)
See Also