Abstract

Coal samples were collected from gassy and nongassy mines of the Book Cliffs and Wasatch Plateau fields of Utah and the Coal Basin field of Colorado. The methane content of selected mines was measured in situ. Chemical and physical properties of the coals were measured in the laboratory. Chemical structure was studied by dipolar dephasing nuclear magnetic resonance spectroscopy. The yield of methane on pyrolysis was used as a measure of the propensity for the coal to produce additional methane by coalification processes. The methane content of the seams was correlated with the properties of the coal and the geology of the coal-bearing formation. Accumulation of methane in the seam is the result of the production of methane by coalification processes and the loss of methane from the seam by transport processes. Over the narrow range of rank studied, coalbed methane does not correlate with conventional rank parameters. For the Book Cliffs field, methane content generally increases with depth and pressure of the seams and with increasing formation of pyrolysis methane. A medium volatile bituminous sample from the Colorado Coal Basin field showed much less methane content than predicted by the correlation for the Book Cliffs field. Differences in methane loss due to differences in pressure history, geological history, and geological conditions could account for the observed differences in methane content in the two fields.