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Geologic-Based Assessment of Continuous Resources in the Permian Basin, Texas and New Mexico, USA


The U.S. Geological Survey (USGS) is assessing the undiscovered, technically recoverable oil and gas resources of the Permian Basin, with a specific focus on continuous (unconventional) resources. The most recent USGS assessment of the basin, which concentrated mainly on conventional resources, was completed in 2007. The Permian Basin has had a major upswing in production in recent years, largely due to the increased exploration and development of unconventional plays. Horizontal drilling and multi-stage hydraulic fracturing is increasingly being used to exploit oil and gas accumulations in multiple stratigraphic horizons; a major challenge for the upcoming USGS assessment will be to differentiate comingled production. Following decades of vertical drilling and completions, more than 2,000 horizontal wells have targeted the Wolfcamp Shale in the past 10 years in the Midland and Delaware sub-basins of the Permian Basin. The Wolfcamp Shale occurs at a depth of 7,000 to 8,500 feet, and contains a mixed lithology system that is composed of sand, shale, and carbonate ranging in thickness from 800 to 2,000 feet. Total organic carbon ranges from 2 to 10% weight percent and porosity ranges from 4 to 12%, with low permeability. Initial estimated ultimate recovery calculations display a wide range for Wolfcamp horizontal wells. In addition, the informal Cline shale (sometimes referred to as the lower Wolfcamp) has also recently gained exploration momentum in the Midland Basin. The Cline shale occurs at a depth greater than 9,000 feet deep and covers approximately 10,000 square miles. It is an organic rich shale with interbedded sand and silt and ranges in thickness from 200 to 550 feet. Total organic carbon ranges from 1 to 8 weight percent and porosity ranges from 6 to 12%. Activity in the Cline shale is centered in Glasscock, Andrews, Sterling, Reagan, and Mitchell Counties, Texas, and more than 100 wells have targeted the Cline shale.