Geologic overview and quantitative assessment of undiscovered oil and gas resources in the Woodford and Barnett Shales, Permian Basin

The availability of geologic and production data for the Woodford Shale and Barnett Shale of the Permian Basin province of Texas and New Mexico has significantly increased since 2007, when the U.S. Geological Survey (USGS) last published an assessment of undiscovered, technically recoverable oil and gas resources. These new data were integrated with insights from the literature and internal USGS research to develop the conceptual geologic models that underpin the 2025 USGS assessment. Using specific geologic criteria, including true vertical depth, thickness, lithology, depositional environment, total organic carbon (TOC) content, and thermal maturity of source rock, assessment units (AUs) were defined. For the 2025 assessment, the USGS identified nine AUs: one conventional assessment unit (AU) and four continuous AUs for the Woodford Shale, and four continuous AUs for the Barnett Shale. The geological framework developed for this assessment is described in detail in this paper, as well as the method employed to estimate resource potential. The total mean estimates for undiscovered, technically recoverable resources for the nine continuous and conventional AUs in the Woodford and Barnett Shales of the Permian Basin province are 1.6 billion barrels of oil (BBO), 28.3 trillion cubic feet of natural gas (TCFG), and 813 million barrels of associated natural gas liquids (MMBNGL).