An Overview of Coalbed Natural-Gas Production  in the Arkoma Basin of Arkansas

William Lee Prior. Arkansas Geological Commission, Little Rock, AR  [email protected]

The Pennsylvanian coal fields of west-central Arkansas encompass approximately 1,700 square miles in the Arkoma basin. The coal-bearing formations are listed in ascending stratigraphic order as the Atoka, Hartshorne, McAlester, and Savanna with the thickest and most extensive coalbed being the Lower Hartshorne that occurs near the base of the McAlester Formation in Arkansas. The Arkansas coals vary in rank from low-volatile bituminous in the western part of the basin to semi-anthracite in the easternmost one-third of the coal fields. Since 2001, some 30 horizontal wells and 15 vertical wells have been drilled in southern Sebastian County and northern Scott County, and cumulative production is reported at 8.4 Bcfg as of November 2006. Existing coalbed natural-gas wells are producing from the Lower Hartshorne coal and range in depth from 565 to 1,980 feet with approximately 479,099 feet of horizontal pinnate lateral development. The distribution and depth to all Arkansas coal seams are not only controlled by the initial sedimentary depositional environments, but also by later east-west folding and faulting. There are some 24 other coal seams with many such as the Charleston and Paris that occur over limited areas or of too shallow a depth; whereas, coals in the upper Atoka Formation are reported to be up to 24 inches thick and occur at depths < 3,000 feet.