The Composition and Volume of Desorbed and Residual Gas Contained in Coal Beds Recovered from a Deep Core Hole in Southwestern Pennsylvania

ULERY, J. P., U.S. Bureau of Mines, Pittsburgh, PA, and D. DAMON, Consolidated Natural Gas, Pittsburgh, PA

The U.S. Bureau of Mines collected 25 samples for gas content determination from a deep core hole drilled near Waynesburg, Greene County, Pennsylvania. The core hole extended to a total depth of 1750 ft, and 15 coal beds of the Dunkard, Monongahela, Conemaugh, Allegheny, and Pottsville groups were sampled. The gas content of the coal beds was determined using the modified direct method (MDM). Using this method, total gas contents ranged from 3.4 to 8.4 cm3/g on a raw coal basis, and desorbed gas contents ranged from 1.0 to 4.7 cm3/g. Desorbed gases were primarily composed of methane with minor amounts of carbon dioxide, ethane and heavier hydrocarbons, and hydrogen. Carbon dioxide was desorbed in significant quantities almost exclusively from coal beds above the Bakerstown coal bed, w ile ethane and hydrogen were released primarily from coal beds below this horizon. Residual gas content, obtained by crushing the sample, ranged from 1.8 to 4.3 cm3/g. Methane, ethane and heavier hydrocarbons, and carbon dioxide were found to be significant constituents of the residual coal bed gas. Hydrogen was not detected in any of the residual gas, however, some nitrogen often was present. In the coal beds below the Bakerstown coal bed, ethane and heavier hydrocarbons made up 17 to 48% of the total residual gas. Carbon dioxide was detected in the residual gas of coal beds above this horizon, but generally in concentrations significantly below that of the desorbed gas. Conversely, in coal beds sampled below the Bakerstown coal bed, carbon dioxide often was observed in high concentrati ns in the residual gas when it was not a significant desorbed gas.

AAPG Search and Discovery Article #91005 © 1991 Eastern Section Meeting, Pittsburgh, Pennsylvania, September 8-10, 1991 (2009)