Abstract

Although coal gas exploration and development were initially conducted by major oil companies and larger independents, smaller operators will play a progressively more important role in developing this potential resource in Texas. Coal beds in Texas are Pennsylvanian to Eocene in age and range in rank from lignite to high-volatile B bituminous at the surface, but probably approach high-volatile A bituminous at depth. Known net coal thickness in the Tertiary Jackson, Claiborne, and Wilcox Groups ranges from 3 to 28+ ft (1.0 to 8.5 m). The thickest Jackson and Wilcox Group coals are located in east-central Texas, whereas the thickest (20+ ft; 6.1 m) Claiborne Group net coal is in south Texas. Cretaceous Olmos coal beds in south Texas are generally less than 10 ft (3 m), but are higher rank than most other coals. Pennsylvanian coal beds in north central Texas are bituminous in rank but are generally thinner and less continuous than Tertiary coals.

Previous research efforts have focused on surface-mineable coal rather than coal bed methane associated with deeper coal seams. However, application of a coalbed methane exploration model that integrates key hydrogeologic factors can be used to delineate areas of higher coalbed methane potential. Thick fluvial-deltaic coal beds in the Wilcox of East-Central and East Texas have the greatest coalbed potential and may contain economic quantities of coal gas, whereas the coalbed methane potential of Pennsylvanian coals of North-Central Texas and Eocene Wilcox coals in South and South-Central Texas may be limited because of thin, laterally restricted coals and low coal rank. The coalbed methane potential of the Cretaceous Olmos, Eocene Claiborne and Jackson Groups remains largely unknown because of the absence of adequate gas content and hydrologic data. Accurate assessment of coalbed methane potential requires a regional geologic and hydrologic evaluation of the key factors affecting coalbed methane producibility rather than evaluation of a smaller prospect area.