Subsurface gas-shale samples of the Upper Cretaceous Eagle Ford Shale, San Marcos Arch, central Texas: core sampling for measured vitrinite-reflectance (Ro) determination

This report outlines the activities conducted by the Bureau of Economic Geology (BEG) during Fiscal Year (FY) 2009 for the National Coal Resources Data System State Cooperative Program (NCRDS project). Continuing the sampling strategy initiated in the previous fiscal year for measured vitrinite-reflectance (Ro) determination, this report focuses on collecting oil- and gas-shale samples from the Upper Cretaceous (Cenomanian—Turonian) Eagle Ford Shale in Texas. While in FY2008, Eagle Ford samples were obtained from the Rio Grande Embayment and associated Maverick Basin in the southern part of the Eagle Ford play area, this year's samples primarily come from the San Marcos Arch to the north in south-central Texas (Fig. 1). In recent years, explorationists and producers in the gas-shale industry have expanded their activities beyond the Maverick Basin, with the San Marcos Arch area showing increasing interest and exploration.

Gas-shale samples have been collected from whole cores of the Eagle Ford Shale from seven wells located in Frio, DeWitt, Gonzales, Guadalupe, Caldwell, and Brazos Counties (Fig. 1). These samples have been sent to Dr. James Hower of the University of Kentucky for measured vitrinite-reflectance (Ro) analysis. The precise geographic location of each sampled shale is identified using GIS applications.