Permian Basin Workshop Showcases Benefits From DOE Oil Reservoir R&D

A Texas Permian Basin oil reservoir that has yielded little of its originally estimated 10.5 billion barrels since early waterflooding efforts in the 1950s may soon see increased production levels.

Reservoir operators will apply new information on the field's natural fractures developed in an ongoing demonstration project cofunded by the U.S. Department of Energy's National Petroleum Technology Office.

Pioneer Natural Resources' work on the Sprayberry Sandstone reservoir in Midland County Texas was just one of seven DOE-funded projects the Permian Basin Section of the Society for Sedimentary Geology showcased at a workshop on drill cores held on February 26 in Midland, Texas.

The workshop highlighted drill core displays and information from projects that are contributing significant scientific and technical advances in oil reservoir management. Five oil companies and the Texas Bureau of Economic Geology (BEG) are managing these projects for DOE in seven of the Permian Basin's main reservoirs.

Drill cores from oil wells are primary sources of data on the nature of the rock and fluids in an oil or gas reservoir. These data - size and amount of pore space in the rock, ability of fluids to flow through that pore space, rock fractures that might accelerate (or impede) fluid flow, minerals in the water that could interfere with production processes - and many more factors determine what type of process can be used to recover the oil.

A core workshop presents this information in maps, cross-sections, well logs, thin sections, photos, and the actual cores, with descriptions of conditions in the reservoir from which the core was taken. By examining this type of information from a regional selection of cores, producers are able to gain valuable understanding of reservoir conditions and how they vary throughout a region. This information then determines how an operator will proceed with exploration, development and production activities.

The Midland core workshop was promoted by one of DOE's project research partners as a rare opportunity for Permian Basin operators to examine and discuss cores from a variety of ongoing projects in the region. Information on cores is commonly regarded as proprietary, but data from the DOE projects, developed under Federal cost sharing, is public information, and can provide an effective medium to promote the synergy that accompanies cooperative research efforts.

These DOE projects, designed to achieve more efficient oil production and reduced operational costs, range from applications of horizontal drilling and carbon dioxide (CO2) injection to reservoir characterization (improved methods of obtaining detailed reservoir data). A critical factor in designing optimal oil recovery processes, reservoir characterization comprises a suite of advanced methods for measuring the properties of rock strata that control the flow of fluids through a reservoir. This data gathering process uses such tools as well logs, seismic and electromagnetic surveys, downhole imaging, and the technique that is the heart of this workshop: deriving data on reservoir conditions though analysis of drill cores.

All of the DOE projects that were featured in the Midland workshop include one or more elements of these research topics. The projects are:

• Pioneer Natural Resources (formerly Parker and Parsley) - Obtaining improved knowledge of the reservoir fracture system to facilitate oil recovery by CO2 injection into the Sprayberry Sandstone reservoir, Midland County, Texas.

• Texas Bureau of Economic Geology - Improving knowledge of slope and basin clastic, or fragmented-reservoir strata, through three dimensional seismic surveys and the study of well logs, drill cores, and exposed surface formations of the Ramsey Sandstone in the Ford Geraldine Unit and West Ford Field, Reeves and Culberson Counties, Texas.

• Phillips Petroleum Company - Using improved knowledge of subsurface conditions gained from reservoir characterization to aid in designing a horizontal drilling program that will facilitate the use of injected CO2 to move oil through the Grayburg-San Andres section, South Cowden Field, Ector County, Texas.

• Strata Production Company - Applying advanced reservoir management techniques such as intermediate stage drilling and pressure maintenance to improve oil recovery from the Brushy Canyon Sandstone, Nash Draw Field, Eddy County, Texas.

• Fina Oil and Chemical Company - Using commonly available production data to perform reservoir characterization, analyze waterflood performance, and assess reservoir conditions that limit production, including water quality, in the North Robertson Clearfork Unit, Gaines County, Texas.

• Laguna Petroleum - Improving waterflood design in the Foster and South Cowden Fields, in Ector County, Texas - a region geologists call the Grayburg-San Andres interval - using three dimensional seismic data along with reservoir geologic and engineering information to identify zones where fluids will flow easily, those that pose barriers to flow, and "thief zones" that divert fluids away from the production well.

• Texas Bureau of Economic Geology - Describing how reservoir rocks vary between wells and how the remaining oil in restricted, level carbonate reservoirs is distributed based on complementary studies of a similar formation in the South Cowden Field, Ector County, Texas, and related surface formations in the Brokeoff Mountains of New Mexico.

Prospects for the long-sought production successes in the Sprayberry Sandstone reservoir project have been significantly improved by the the information revealed in Pioneer's core research which was central to the theme of the Midland workshop. Pioneer's goal was to test the feasibility of creating an injected CO2 gas cap that would provide a water-free zone in which oil could be produced by gravity flow, instead of being moved to a production well by waterflooding.

However, the Sprayberry Sandstone reservoir's well-developed system of natural fractures, which commonly tend to channel injected gas away from the residual oil in the rock pores, have until now minimized production. The Sprayberry, in fact, has been referred to as the largest uneconomic field in the world because of the extremely low recovery efficiencies.

Based on previous DOE-supported research indicating that an injected gas/gravity flow process could succeed if the fractures had sufficient vertical relief and significant density, Pioneer drilled and recovered nearly 400 feet of horizontal core. Analysis of this first horizontal core ever obtained from the 3400+ wells in the Sprayberry provided important information regarding fracture data.

New methods of analysis, such as the calibration of well log data against actual conditions shown by cores, developed by Strata Production Company in the Nash Draw project, can increase understanding and interpretation of the fracture system in the upper Sprayberry, providing Pioneer with improved technology to predict productive zones and recover a significant part of the Sprayberry's remaining nearly 10 billion barrels of oil.

- End of TechLine -

For more information, contact:
Herbert A. Tiedemann, National Petroleum Technology Office, 918/699-2017, e-mail htiedema@npto.doe.gov