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Assessment of Undiscovered Continuous Oil Resources in the Wolfcamp Shale of the Midland Basin, West Texas


The U.S. Geological Survey (USGS) completed a geologic-based assessment of the undiscovered, technically recoverable continuous oil resources of the Pennsylvanian-Permian Wolfcamp shale in the Midland Basin of west Texas. The Midland Basin is the eastern subbasin of the Permian Basin, which covers west Texas and southeastern New Mexico. Traditionally, the Wolfcamp shale has been targeted by vertical wells that have comingled production with the overlying Spraberry Formation (Wolfberry Play), or a combination of other stratigraphic horizons containing oil. Recent drilling has focused on targeting organic-rich, tight shale intervals of the Wolfcamp shale throughout the Midland Basin, with drilling extending onto the Eastern shelf. Over 3,500 horizontal wells have been drilled and are producing from the Wolfcamp in the Midland Basin. The Wolfcamp shale is divided by industry into four producing “benches”, A, B, C, and D. The Wolfcamp D (also known as the Cline shale) was deposited during the Pennsylvanian and extends onto the Eastern shelf of the Permian Basin. The overlying units were deposited during the Early Permian, as the shelf edges prograded west through time. The Wolfcamp shale is deepest adjacent to the Central Basin platform, and the thickness exceeds 2,000 feet in the southern part of the Midland Basin. It consists of siliciclastic units interbedded with carbonates. The siliciclastic units have interbedded intervals of organic-rich shale, which are mature for oil generation throughout the Midland Basin. The Wolfcamp shale was divided into six continuous assessment units (AU) based on geologic data, thermal maturity data, extent of the formation, shale thickness, and production data. The assessment also included data on drainage areas based on horizontal drilling, and calculated estimated ultimate recovery from horizontal wells in the Midland Basin with over 18 months of production. The six continuous AUs for the Wolfcamp in the Midland Basin are: (1) Midland Basin Wolfcamp A Continuous Oil AU; (2) Midland Basin Wolfcamp B Upper Continuous Oil AU; (3) Midland Basin Wolfcamp B Lower Continuous Oil AU; (4) Midland Basin Wolfcamp C Continuous Oil AU; (5) Midland Basin Wolfcamp D Continuous Oil AU; and (6) Midland Basin Northern Wolfcamp Continuous Oil AU. Assessment results will be presented in future reports.