HUCKA, V. J., and DAVID M. BODILY, University of Utah, Salt Lake City, UT

ABSTRACT: Retention of Methane in Utah Coals

The methane contents of the Sunnyside, Rock Canyon, and Sub 3 seams, Utah, were determined by in- situ and laboratory measurements. Methane retention is interpreted in terms of the physical and chemical properties of the coal and the geochemical and geological history of the coal seams under investigation.

The amount of methane stored in coal depends on the rank and the depth of the coal, with higher rank and deeper coals having higher gas content. Most of the methane gas is adsorbed onto the walls of microvoids in the coal. The capacity of coal to hold gas decreases with increasing temperature in the range of coal-bed temperatures, but increases with pressure. Tectonic pressure may cause folding and faulting of coal beds, thus contributing to the release of gas from the coal matrix. Consequently, some gas may migrate into cavities of surrounding rocks and through cracks and fissures to the surface. Therefore, one would expect that the methane gas would be trapped in the crest of anticlines at depths as shallow as 300 ft and synclines would be free of gas at great depths.

The distribution of gas in the coal beds under investigation will be discussed in relation to stratigraphy, tectonics (domes and other folded structures), lithology, and overburden.

AAPG Search and Discovery Article #90993©1993 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah, September 12-15, 1993.