Subsurface Pennisylvanian Coal Samples Lower Atoka Group Fort Worth Basin Wise an dAck Counties North Texas Core Sampling for Coal-Rank Determination

Tasks conducted at the Bureau of Economic Geology (BEG) during Fiscal Year (FY) 2006 for the National Coal Resources Data System State Cooperative Program (NCRDS project) involved sampling of deep (5,400-5,500 ft) subsurface bituminous coal beds from the Fort Worth Basin of North Texas. Identification of their precise stratigraphic position, geographic location, and general depositional setting was a primary objective. This study is one part of a program of sampling and characterization of Texas coals as part of BEG's continuing NCRDS project of coal inventory and investigation of U.S. bituminous coals as a coalbed methane resource.

Seven coal samples were collected from the whole cores of two wells in Boonsville field (Wise and Jack Counties), which produces mostly natural gas from the lower Atoka Group (Lower Pennsylvanian). Chronostratigraphic correlations throughout Wise and eastern Jack Counties show that the coal beds correspond to gamma-ray maxima capping retrogradational intervals above thicker progradational sections and are interpreted to represent maximum flooding surfaces within continental deposits of fourth-order transgressive systems tracts. These flooding surfaces can be correlated throughout Wise and eastern Jack Counties. The sampled coal beds in the Oxy Tarrant #A-4 well are inferred to represent peat-swamp deposits that mark the abandonment of a broad braided-river (braidplain) system. The distribution of mapped primary channel and interchannel areas offers an approximation of the total extent of coal beds within this genetic interval.

In contrast, the sampled coals in the EP Operating Tarrant WB #3 well were deposited within a fourth-order transgressive succession deposited above proximal delta-front sandstones.