Mississippian Barnett Shale, Fort Worth Basin, Texas: A Model for Global Exploration of Continuous (Unconventional) Shale Gas Reservoirs

Pollastro, Richard M., U.S. Geological Survey, Denver, CO

Commercial production of natural gas from unconventional shale reservoirs takes place primarily in the contiguous U.S. where about 0.6 trillion cubic feet (TCFG) of shale gas is produced annually from about 40,000 wells in 6 petroleum basins. The largest shale-gas producing formation is the Mississippian Barnett Shale of the Fort Worth Basin, Texas, which accounted for more than 0.35 TCFG in 2004. Presently, known recoverable reserves for the Barnett are about 4 TCFG. The U.S. projects that at least 1 TCFG will be produced from shale-gas reservoirs by 2015, accounting for about 5 percent of U.S. production in the lower 48 states.

The U.S. Geological Survey (USGS) recently completed a total petroleum system study and resource assessment of the Barnett Shale, the source rock for more than 2 billion bar­rels of oil and 7 TCFG produced from conventional reservoirs in the Fort Worth Basin area. Using framework geology and historical production data, the USGS assessment was per­formed after: (1) mapping critical geologic and geochemical characteristics to define areas with future potential, and (2) defining drainage area distributions (cell size) and estimated ultimate recovery and future success ratios. The Barnett Shale assessment resulted in a mean total undiscovered recoverable volume of 26.2 TCFG.

Technological success and giant resource potential of the Barnett Shale has provided an analog for exploration throughout North America. Successful application of the Barnett model is demonstrated most recently by production from the Mississippian Fayetteville Shale of the Arkoma Basin, and early exploration success of other shale-gas reservoirs of the U.S. and Western Canada.