The Cause of Gas Saturation in the Coals of the Cherokee Formation (Desmoinesian Age) in the Cherokee and Forest City Basins, Mid-Continent, USA
The cause of significant gas saturation in Pennsylvanian age coals and carbonaceous shale of the Cherokee Group, Cherokee and Forest City basins has been generally not well understood. Some coals are gas productive whereas others within the same strata are not. The Cherokee and Forest City basins are shallow intracratonic depressions that are sub-basins of the Pennsylvanian age Western Interior Basin. The coals in both basins were partially or completely subject to thermal maturation caused by migration of low temperature hydrothermal fluids expelled from the Anadarko, Ardmore and Arkoma basins in Oklahoma to the south that migrated north through the Cherokee and Forest City basins in late Carboniferous times. These fluids thermally altered the carbonaceous shale and coals within select areas of both basins causing significant gas generation. In both basins select seams are more highly gas saturated due to higher sulfur content in productive versus non-productive coals. The Riverton, Rowe, Weir-Pittsburg and Mulky coals and the Excello shale are gas productive in the Cherokee Basin. Only the Riverton coals in the Forest City Basin are productive. The area of primary production from unconventional reservoirs in the Cherokee Basin is also situated over the Silurian-Devonian age Chautauqua Arch. The coal bed methane production in the Forest City Basin is related to a localized intrusion(s) in the Leavenworth and Jefferson county area. Identifying the relationship between sedimentary thins, structural elements, timing of fluid migration, migration paths and sulfur contents of unconventional reservoirs provide an exploration model that can be useful in identifying potentially coal bed methane productive areas.
AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015