THE PENNSYLVANIA ANTHRACITE DISTRICT – A FRONTIER AREA FOR THE DEVELOPMENT OF COALBED METHANE?

The anthracite region of eastern Pennsylvania consists of four major coal fields that are within the folded and faulted Appalachians, in the Valley and Ridge and Appalachian Plateaus physiographic provinces. These are, from south to north, the Southern Anthracite field, the Western Middle Anthracite field, the Eastern Middle Anthracite field, and the Northern Anthracite field. Rank of the coal ranges from semi-anthracite to anthracite. In general, the anthracite fields consist of Pennsylvanian strata that are complexly folded, faulted, and preserved in structural synclines within older Paleozoic strata.

Published gas-in-place (GIP) data for Pennsylvania anthracite range from 6.4 SCF/ton (0.2 cc/g) for the Orchard coal bed to a high of 691.2 SCF/ton (21.6 cc/g) from a sample of the Peach Mountain coal bed that was collected in the Southern Anthracite field at a depth of 685 feet. This is the largest GIP value that the U.S. Bureau of Mines (USBM) (Diamond et al, 1986) reported for coalbed methane (CBM) nationwide. Of the 11 CBM analyses reported for the Southern Field by USBM, seven exceed 396 SCF/ton (12.4 cc/g) (average of 11 samples: 325.8 SCF/ton [10.2 cc/g]). In addition, adsorption isotherms for the Mammoth, Seven-Foot, and Buck Mountain coal beds in the Southern Field indicate that these beds have a very high capacity to hold methane under pressure (Lyons et al, 2003), with values that range from about 320 to 850 SCF/ton (10 to 27 cc/g).

In spite of the complex geologic structures, there are several areas in the Southern Anthracite field where subhorizontal to moderately inclined coal beds may be accessed by the drill. For example, a detailed map and sections by Wood (1972) in Schuylkill County, Pennsylvania, has defined several areas of subhorizontal to gently inclined strata that contain 10 or more coal beds at depths of 500 to 2000 feet (150 to 600m), and with a cumulative coal thickness of 50 feet (15m), or more.

These data suggest that the Pennsylvania anthracite district is, at least, worthy of testing for CBM, using current desorption methodology and with coal samples collected from several coal beds in a single core hole.