SCOTT, ANDREW R., and ROGER TYLER , Bureau of Economic Geology, The University of Texas at Austin

Coalbed methane is an important part of the natural gas supply for the United States and now represents more than 6 percent of total gas production. 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 natural resource in Texas.

Coal beds in Texas are Pennsylvanian to Eocene in age and range in rank from lignite to high-volatile B bituminous. Net coal thickness in the Jackson, Claiborne, and Wilcox Groups ranges from 3 to 28+ ft. The thickest Jackson and Wilcox Group coals are located in east-central Texas, whereas the thickest (20+ ft) Claiborne Group net coal is in south Texas. Cretaceous Olmos coal beds in south Texas are generally less than 10 ft thick. 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 coal mining rather than coalbed methane. Therefore, although there are abundant data on near-surface lignite coal beds and coal quality, there are very limited studies on the geometry and hydrology of deeper coal beds. This absence of data inhibits the evaluation of the coalbed methane potential of Texas. However, a coalbed methane producibility model that integrates key hydrogeologic factors can be used to delineate areas of higher coalbed methane potential. Evaluation of the updip migration of thermogenic gases, in situ generation of secondary biogenic gases, and migration of gases is critical for identifying areas of higher gas content.

AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas