Mid-Continent Section

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The relationship between specific reservoir characteristics and the gas productive coals and carbonaceous mudstones in the Cherokee Basin


The Cherokee Basin is a shallow intracratonic basin that has significant gas production from the Desmoinesian and Atokan age Cherokee Formation coals and carbonaceous mudstones at less than 2,000 feet. The Cherokee Group's coals in the Cherokee Basin were deposited on an abandoned deltaic surfaces in a coastal setting. Only specific coals, the Mulky, Weir-Pittsburgh, Rowe and Riverton and the Excello Shale within the Cherokee Formation are generally productive whereas the remaining seams and carbonaceous shale are not productive. The basin was subject to thermal maturation in late Pennsylvanian and Permian time caused by expulsion of low temperature hydrothermal fluids from the Anadarko, Ardmore and Arkoma basins that migrated north through the Cherokee Basin into the Forest City Basin. Proximate analysis of the coals indicates that select seams are gas productive due to higher sulfur contents, which allowed hydrocarbon generation at lower temperatures. The Excello Shale is productive because it has over 50% quartz-carbonate minerals making it more brittle allowing hydraulic fracturing stimulation to be effective. The main productive area is in the central part of the basin and is related to the apex of the Silurian-Devonian age Chautauqua Arch. By mapping sulfur trends in coals and quartz-carbonate percentage content trends in carbonaceous mudstones allows a more definitive method to identify areas that will be gas productive.