USGS Assessment of Undiscovered Technically Recoverable Gas Resources in Cretaceous-Tertiary Coal Beds of the Gulf Coast Region

Peter D. Warwick
U.S. Geological Survey, Reston, VA

The U.S. Geological Survey (USGS) recently completed an assessment of the undiscovered continuous gas potential of Cretaceous-Tertiary coal beds of the onshore areas and State waters of the northern Gulf of Mexico coastal region. The assessment was based on geologic elements including hydrocarbon source rocks, availability of suitable reservoir rocks, and hydrocarbon traps in three coalbed gas total petroleum systems (TPS) identified in the region: 1) the Upper Cretaceous Olmos Coalbed Gas TPS, located in south Texas and northeastern Mexico, 2) the Paleocene-Eocene Wilcox Coalbed Gas TPS, and 3) the Cretaceous-Tertiary Coalbed Gas TPS. Four continuous assessment units (AU) were defined within the three TPSs: 1) the Olmos Coalbed Gas AU, the 2) the Rio Escondido Basin Olmos Coalbed Gas AU, 3) the Wilcox Coalbed Gas AU, and 4) the Cretaceous-Tertiary Coalbed Gas AU which includes all other Cretaceous and Tertiary coal beds not included in the other AUs (not assessed).

The USGS assessment of the technically recoverable undiscovered continuous coalbed gas resources resulted in an estimated mean of 4.06 trillion cubic feet of gas in the AUs that were assessed. Most (95%) of the undiscovered continuous gas resources that were estimated (3.86 TCFG) are in the Wilcox Coalbed Gas AU. The unconventional gas resources reside in coalbed reservoirs and in adjacent or interlayered sandstones. The assessment was conducted via the established USGS methodology for continuous petroleum accumulations, and reflects estimates of undiscovered resources based on vertical (non-horizontal) drilling technology.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas