Assessment of remaining recoverable oil in selected major oil fields of the Permian Basin, Texas and New Mexico

Reserve Growth Assessment Fact Sheet

he U.S. Geological Survey (USGS) recently completed an estimate of technically recoverable, conventional oil in selected oil fields in the Permian Basin in west Texas and southeastern New Mexico. The mean total volume of potential additional oil resources that might be added using improved oil-recovery technologies was estimated to be about 2.7 billion barrels of oil.

Introduction

A team of U.S. Geological Survey (USGS) scientists recently completed an assessment of the potential for additions to oil reserves that could result from applying improved oil-recovery technologies in 18 large oil fields in the Permian Basin in west Texas and southeastern New Mexico. During the Paleozoic Era (542 to 251 million years ago), the region was an extensive complex of carbonate shelves and platforms (areas where shallow-marine limestones were deposited), separated by intervening basins, that lay along the southern margin of North America. These include the Northwest Shelf, Central Basin Platform, and Eastern Shelf and the Delaware and Midland Basins.

The oil fields analyzed in this study include some of the larger fields in the conterminous United States and were discovered between 1923 and 1950. Individual estimates of recoverable oil volumes in the 18 fields range from about 430 million barrels of oil (MMBO) to 3 billion barrels of oil (BBO) as of 2006. Estimates of volumes of original oil in place (OOIP) in individual fields range from about 700 MMBO to more than 5 BBO. Between 1979 and 2004, estimates of the volume of recoverable oil in these 18 fields increased by 4.7 BBO (from data in Nehring, 2007).

The principal oil reservoirs in the Permian Basin are carbonate shelf and platform strata with variable porosity and generally low permeability. Primary recovery efficiencies were low, typically 10 to 20 percent of the OOIP. Beginning in about 1950, waterfloods (water injected into reservoirs to force oil out) were increasingly used to improve oil recovery. Starting in about 1970, carbon dioxide (CO2) injection began to be used in some larger fields to increase oil recovery. Recovery efficiency has reached 50 to 60 percent in a few fields with extensive CO2 injection, particularly in reservoirs within the Permian (299 to 251 million years ago) San Andres Limestone on the Northwest

Artesia-Maljamar

Map showing oil fields (green) in the Permian Basin of west Texas and southeastern New Mexico. Oil fields individually assessed are shown in darker green and labeled. Most of the assessed oil fields are composites, consisting of aggregated fields and reservoirs, indicated on the map by hyphenated field names or by the term “Area.” Compiled from maps of individual oil plays in Dutton and others (2004); gray hachured lines are paleogeographic shelf and basin boundaries. SACROC, Scurry Area Canyon Reef Operators Committee.

Shelf and Central Basin Platform and in reef limestones of the Pennsylvanian (318 to 299 million years ago) Canyon Group in the Midland Basin. Because the supply of CO2 for injection is limited and injection adds substantial expense to operators’ costs, operators of many of the fields studied have only used waterfloods to increase recovery, and the fields therefore still have relatively low recovery efficiencies. In addition, many less-exploited reservoirs have less ideal reservoir properties than those in which advanced recovery technologies have been used. The USGS assessment estimates the range

Vacuum

Eunice Area Shelf Wasson Area

South

of additional volumes of oil reserves that could be added within the 18 fields analyzed by using CO2 injection or other advanced oil-recovery technologies. The analysis was made without regard to cost or to availability of CO2.

Recently, CO2 injection has begun in several fields within a zone of low oil saturation below the main reservoir interval, called the “residual oil zone.” These efforts have met with some success, but because detailed data with which to evaluate them are not yet available, the USGS analysis did not consider potential reserve additions from the residual oil

Fullerton Area

Central Basin Platform Goldsmith-Andector Midland Basin

Howard-Glasscock

Ozona Arch Salt Creek

Eastern Shelf

zone. It is possible that such additions could be substantial.

Methodology

Of the 18 oil fields (or composites of related fields) in the Permian Basin evaluated by the USGS, most exhibited significant additions to reserves from 1982 to 2006. Production and reserves information, as of 2006, came from a proprietary commercial database. To assess the potential for future additions to reserves, an evaluation was made of each field (Klett and others, 2011). The geology of each field was analyzed, and its

Scurry (SACROC)

development history reviewed. Estimates of OOIP in each field were made using information available from various published and proprietary sources. Potential growth was evaluated by estimating the range of recovery efficiency that might be realized with further application and refinement of existing technologies, regardless of economic factors or availability of CO2.

Results

The USGS analysis indicates that there is significant remaining potential for additions to oil reserves in the 18 Permian Basin oil fields evaluated. The largest reservoirs—the San Andres, Grayburg, and Canyon—have contributed the most to growth to oil reserves in recent decades and have already achieved high recovery efficiencies with the extensive use of waterflood and CO2 recovery programs. Reserves within them are not likely to grow as much in most of the fields as within less intensively developed, deeper reservoirs, but the magnitude of additions may be less than in the past because reservoir character in the deeper reservoirs is poorer. The mean USGS estimate is that an additional 2.68 BBO could be added to reserves in the 18 fields evaluated. There is little chance that reserve additions could be more than 4.5 BBO or less than 1.05 BBO. These volumes may not be currently economic to recover and will require a significantly greater supply of CO2 for injection than is presently available.

Oil reserves will also continue to be added in fields within the Permian Basin that were not included in this analysis. Most such fields are smaller than the fields studied, and their additions to reserves will also be smaller, although they may be significant. Statistical methods, like those used in previous USGS reserve growth estimates, are being used to approximate a volume of additional reserves that might be expected to come from these smaller fields.

References Cited

Dutton, S.P., Kim, E.M., Broadhead, R.F., Breton, C.L., Raatz, W.D., Ruppel, S.C., and Kerans, C., 2004, Play analysis and digital portfolio of major oil reservoirs in the Permian Basin— Application and transfer of advanced geological and engineering technologies for incremental production opportunities, final report: Austin, Texas, Bureau of Economic Geology, and Socorro, New Mexico, New Mexico Institute of Mining and Technology, accessed March 8, 2012, at http://www.beg.utexas.edu/resprog/permianbasin/playanalysis.htm.

Klett, T.R., Attanasi, E.D., Charpentier, R.R., Cook, T.A., Freeman, P.S.,

Waterflooding begins

Millions of B arrels Main San Andres reservoir discovered

Gautier, D.L., Le, P.A., Ryder, R.T., Schenk, C.J., Tennyson, M.E., and Verma, M.K., 2011, New U.S. Geological Survey method for the assessment of reserve growth: U.S. Geo-

Assessment results for volume of additional oil potentially recoverable from selected oil fields in the Permian Basin, west Texas and southeastern New Mexico (technically recover- able resources). [Mean estimates add to a total mean, but fractile values for individual fields are not additive; fractiles

Carbon dioxide injection begins in main San Andres reservoir

logical Survey Scientific Investigations Report 2011–5163, 8 p., available at http://pubs.usgs.gov/sir/2011/5163/.Nehring, R. 2007, The oil recovery growth of the Permian Basin, USA: Colorado Springs, Colo., Nehring Associates, accessed March 7, 2012, at http://www.nehringdatabase.com/images/pdfs/Permian%20Growth%20 Poster.pdf.

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