DEPOSITIONAL ENVIRONMENTS AND STRATIGRAPHY OF THE HARTSHORNE FORMATION, WESTERN ARKOMA BASIN, OKLAHOMA

The Hartshorne Coal is the most actively explored gas-producing reservoir in the western Arkoma Basin, southeastern Oklahoma. The Hartshorne Coal is a member of the Pennsylvanian Hartshorne Formation, which is part of the Krebs Group of the Desmoinesian Series. Integrated wire-line log, core and mapping data were analyzed for parts of Haskell, Latimer, McIntosh and Pittsburg Counties, Oklahoma to determine the depositional environments and stratigraphic relationships between the lithofacies that comprise the formation.

As a result of Hartshorne coalbed methane drilling, numerous modern wire-line logs and some cores are now available within the study area. Gamma-ray and neutron-density curves were used to identify the Hartshorne Coal, and to establish the Hartshorne stratigraphic framework and electrofacies. Isopach maps were constructed for the coal and sandstone bodies. Log signatures were correlated to cores, and depositional electrofacies were established using sedimentary structures, distribution patterns and curve forms.

Preliminary results indicate that the Hartshorne sediments were deposited in a low-energy fluvial-deltaic to marginal marine setting. Depositional environments identified include delta front/marginal marine, deltaic distributary channels, interdistributary bays/overbank deposits and peat marsh. Thicker, east to west trending, elongate sandstone bodies may represent entrenched distributary channels or incised valleys. In the coming months, the present data will be augmented with additional thin section analysis, core data, 3-D seismic and high-resolution micro-imaging wire-line logs. The ultimate goal of this project is to improve the techniques for finding and efficiently developing the Hartshorne coalbed methane gas reserves.