Stratigraphic Locations and Rank Determination of Subsurface Pennsylvanian Coals in North-Central Texas: Pilot Study for Coalbed Methane Potential Assessment

Edgar H. Guevara¹, Paul C. Hackley², Shinichi Sakurai¹, Peter D. Warwick², Caroline L. Breton¹, Martina S. Hopkins², and Rosalba Mendoza^1
1 The University of Texas at Austin, Austin, TX
² U.S. Geological Survey, Reston, VA

A study conducted by the Bureau of Economic Geology (BEG) in collaboration with the U.S. Geological Survey (USGS) demonstrates the feasibility of using drill cuttings and well logs to determine the depth, stratigraphic location, and rank of Pennsylvanian coals in North-Central Texas to assess coalbed-methane (CBM) potential. Paleozoic bituminous coals have been known since the mid-1800s in this region, and coal was mined through the mid-1900s. However, information on coal rank and CBM potential in this area is scarce. Recently established CBM gas production from Cretaceous bituminous coals in the Maverick Basin, South Texas, focused attention on the potential for CBM gas production from coals of comparable maturity in North-Central Texas and on basic data acquisition to assess this potential.

Drill cuttings and well logs on open file at the BEG were used in the study, which followed an initial geographic information system compilation of selected published data on Texas coals conducted by the BEG for the USGS. More than 100 coal and coaly shale samples, mostly from depths of <2,000 ft, were collected from washed cuttings from 10 wells in Archer and Young Counties.

SP-resistivity logs of the sampled wells, on which sample locations were plotted, were correlated by using published cross sections of Pennsylvanian stratigraphy in this area and unpublished stratigraphic annotations on the logs. These correlations determined the stratigraphic position of the samples collected within the Pennsylvanian Cisco, Canyon, and Strawn Groups. Selected samples were used in coal-rank determinations by means of vitrinite reflectance measurements.