Abstract: Subsurface Definition of the Allegheny Group Coalbed Methane Prospect Interval in Southwestern Pennsylvania and New Gas Content Results

Antonette K. Markowski

A preliminary reconnaissance of coalbed methane gas content data from exploratory coal cores and pre-existing data implies that the greater the depth and rank, the greater the total and cumulative gas content. The coal seams studied, ranging in age from the Pennsylvanian-Permian Dunkard Group to the Middle Pennsylvanian Allegheny Group, are from the Main Bituminous Field and two of the anthracite fields.

Consequently, the Pennsylvania Geological Survey and the West Virginia Geological and Economic Survey conducted a mapping investigation to evaluate the regional geology of the coal-bearing intervals and its influence on coalbed methane potential. Phase I of this study involved the entire Pennsylvanian coal-bearing interval; Phase II focused on a stratigraphic delineation and evaluation of Allegheny coalbeds and associated sandstones. A variety of cross sections and isopach maps show several prospective coalbeds and facies relationships with channel-fill sandstones. This suggests that some of these sandstones may be traps for coalbed methane.

Often overlooked in reservoir characterization is the quality of a coal seam. Coal rank, grade, and type influence the reserves and production of coalbed methane; the higher the rank, the greater adsorptive capacity of the coal. The integration of coal quality with other critical tools of exploration may increase the success rate of finding "sweet spots." Additional Pennsylvania Geological Survey drilling occurred in Beaver, Lawrence, Somerset, and Washington counties. Gas contents were graphically displayed against depth, thickness, and time for a variety of samples from 21 coal seams; average gas composition and Btu values were determined for selected samples.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas