Anticipating Facies-Related Coal Mining Problems in Hartshorne Formation, Arkoma Basin: GEOLOGIC NOTES

Abstract

The close relationship observed between sedimentary facies and potential coal mining problems within the Hartshorne Formation of the Arkoma basin provides the basis for anticipating where mining problems may jeopardize safe and economical coal production in undeveloped parts of the basin. Deltaic facies within the Hartshorne include distributary-channel sandstones and interdistributary-bay shales, siltstones, and sandstones. A thick, linear, distributary-channel sandstone is closely related to several potential mining problems: (1) both underlying and overlying coalbeds are locally thin and discontinuous along the trend of the sandstone; (2) coal quality decreases significantly adjacent to the sandstone (decrease in free swelling index and increase in sulfur); (3) the sandstone is a natural gas reservoir which may emit gas into adjacent coal mines; and (4) geologic factors favoring unstable roof conditions and coalbed rolls are locally associated with the sandstone. In contrast, interdistributary-bay deposits, because of relative homogeneity and lateral persistence, do not present potential facies-related mining problems. Basin-wide availability of geophysical logs from gas wells makes facies mapping and delineation of potential problem areas a straightforward procedure which must be integrated into formulation of exploration strategy, evaluation of reserves, and mine planning if Hartshorne coal resources are to be safely and economically exploited.