Coal and Coalbed Methane Resources of Texas

A. Scott¹ and D. F. Balin^2
1Altuda Geological Consulting, Austin, TX
²Balin and Associates, Austin, TX

Interest in coalbed methane in Texas is growing, however there has been no estimate of coalbed methane resources to date. Coals in Texas are Pennsylvanian to Eocene in age and range in rank from lignite to high-volatile B bituminous at the surface, probably approaching high-volatile A bituminous at depth. Known net coal thickness in the Tertiary Jackson, Claiborne, and Wilcox Groups ranges from 3 to 28+ feet. The thickest Jackson and Wilcox Group coals are located in east-central Texas, whereas the thickest Claiborne Group net coal (20+ ft) is in south Texas. Cretaceous Olmos coal beds in south Texas are generally less than 10 ft thick but are higher in 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.

Based on published coal isopleth and structure maps and utilizing low-rank gas content trends from other coal basins, Texas coal and coalbed methane resources to depths of 6,000 feet are estimated to be 78.7 billion tons and 7.2 Tcf, respectively. The data, however, suggest a wide range of possible coalbed methane resources (between 2.9 and 13.5 Tcf) due to uncertainties regarding true gas content values. The Wilcox Group contains approximately 5.4 Tcf, representing 76% of the total coalbed methane resource. Estimates for other stratigraphic units are as follows: Jackson Group (636 Bcf), Claiborne Group (487 Bcf), Olmos Formation (540 Bcf), and the Pennsylvanian of north-central Texas (129 Bcf).

AAPG Search and Discovery Article #90905©2001 AAPG Southwest Section Meeting, Dallas, Texas