Abstract

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 experienced a major upswing in production in recent years. Horizontal drilling and multistage hydraulic fracturing are increasingly being applied to exploit oil and gas accumulations in multiple stratigraphic horizons in the Midland and Delaware sub-basins of the Permian Basin.

Using a geology-based assessment methodology for continuous resources, which incorporates assessment unit area, sweet spot area, cell sizes (drainage areas), and estimated ultimate recovery (EUR) of producing wells, the informal Wolfcamp shale will be the first unit assessed for continuous resources by the USGS in the Permian Basin. Following decades of vertical drilling and completions, more than 2,000 horizontal wells have targeted the Wolfcamp Shale in the past 10 years. The Wolfcamp shale occurs at a depth of 7,000 to 10,000 feet, and contains a mixed lithology system that is composed of sand, shale, and carbonate ranging in total 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 associated low permeability. Vitrinite reflectance data suggests the Wolfcamp is mature for oil generation in both the Midland and Delaware sub-basins. Initial EUR calculations display a wide range of values for Wolfcamp horizontal wells.