ALBERT

Description: This article describes the primary geologic characteristics and criteria of the Barnett Shale and Barnett-Paleozoic total petroleum system (TPS) of the Fort Worth Basin used to define two geographic areas of the Barnett Shale for petroleum resource assessment. From these two areas, referred to as “assessment units,” the U.S. Geological Survey estimated a mean volume of about 26 tcf of undiscovered, technically recoverable hydrocarbon gas in the Barnett Shale. The Mississippian Barnett Shale is the primary source rock for oil and gas produced from Paleozoic reservoir rocks in the Bend arch–Fort Worth Basin area and is also one of the most significant gas-producing formations in Texas. Subsurface mapping from well logs and commercial databases and petroleum geochemistry demonstrate that the Barnett Shale is organic rich and thermally mature for hydrocarbon generation over most of the Bend arch–Fort Worth Basin area. In the northeastern and structurally deepest part of the Fort Worth Basin adjacent to the Muenster arch, the formation is more than 1000 ft (305 m) thick and interbedded with thick limestone units; westward, it thins rapidly over the Mississippian Chappel shelf to only a few tens of feet. The Barnett-Paleozoic TPS is identified where thermally mature Barnett Shale has generated large volumes of hydrocarbons and is (1) contained within the Barnett Shale unconventional continuous accumulation and (2) expelled and distributed among numerous conventional clastic- and carbonate-rock reservoirs of Paleozoic age. Vitrinite reflectance (Ro) measurements show little correlation with present-day burial depth. Contours of equal Ro values measured from Barnett Shale and typing of produced hydrocarbons indicate significant uplift and erosion. Furthermore, the thermal history of the formation was enhanced by hydrothermal events along the Ouachita thrust front and Mineral Wells–Newark East fault system. Stratigraphy and thermal maturity define two gas-producing assessment units for the Barnett Shale: (1) a greater Newark East fracture-barrier continuous Barnett Shale gas assessment unit, encompassing an area of optimal gas production where dense impermeable limestones enclose thick (≥300 ft; ≥91 m) Barnett Shale that is within the gas-generation window (Ro ≥ 1.1%); and (2) an extended continuous Barnett Shale gas assessment unit covering an area where the Barnett Shale is within the gas-generation window, but is less than 300 ft (91 m) thick, and either one or both of the overlying and underlying limestone barriers are absent. Rich Pollastro received an M.A. degree in geology from the State University of New York at Buffalo in 1977. Rich joined the U.S. Geological Survey in 1978 and serves as a province geologist on the national and world energy assessment projects. His recent accomplishments include petroleum system assessments of the Fort Worth, Permian, and South Florida basins and the Arabian Peninsula. Dan Jarvie is an organic geochemist and president of Humble Geochemical Services. Dan earned his B.S. degree from the University of Notre Dame and was mentored in geochemistry by Don Baker and Wallace Dow. He has studied unconventional oil and gas systems extensively since 1984. Dan's work on the Barnett Shale spans much of the last decade, which has resulted in several AAPG awards. Ronald Hill specializes in petroleum geochemistry and has more than 12 years of oil industry experience. Currently, he is a research geologist for the U.S. Geological Survey. His research interests include shale-gas resources and processes that control petroleum generation. Ron holds geology degrees from the Michigan State University (B.S. degree) and the University of California, Los Angeles (Ph.D.), and a geochemistry degree from the Colorado School of Mines (M.S. degree). Craig Adams worked as an exploration geologist with Amoco Production Company for 13 years before becoming an independent in 1996. As president and co-owner of Adexco Production Company, his primary focus is conventional and unconventional oil and gas in Texas and the mid-continent. Craig has worked the Barnett Shale for 6 years, where his company was one of the first to expand beyond the core area of the Newark East field.