LITHOLOGIC CHARACTERISTICS AND GAS PRODUCTION POTENTIAL OF WOODFORD SHALE IN THE SOUTHERN MIDCONTINENT

Woodford Shale is a prolific hydrocarbon source rock throughout the southern Midcontinent of the United States, and in south-central and southeastern Oklahoma it produces both oil and natural gas. The dominant Woodford lithology is black shale, but chert, siltstone, sandstone, dolostone, and light-colored shale are common locally. In general, proximal lithofacies and basin depocenters contain more silt and sand and distal lithofacies more chert. The highest concentrations of organic carbon are found in intermediate settings remote from clastic source areas and bypassed by turbid bottom flows.

The primary sites of hydrocarbon generation coincide mostly with the principal depocenters of the Delaware and Anadarko Basins; however, mature source beds are found in adjacent provinces. Mass balance calculations indicate that on the order of 830 x 10¹² ft³ of natural gas and 250 x 10⁹ bbl of oil reside in Woodford Shale in Oklahoma, northwestern Arkansas, West Texas, and southeastern New Mexico. Producing this resource is feasible where the subcrop contains competent lithofacies that are highly fractured (e.g., chert, sandstone, siltstone, dolostone, cherty black shale, and silty black shale). Because Woodford Shale is currently in the oil- or gas-generation window in much of the southern Midcontinent, fracture porosity would be pressurized by hydrocarbons generated in the enclosing source rocks. Areas having the greatest gas potential and most favorable lithologies include (1) the northern flank of the Anadarko Basin and the Nemaha Uplift (chert, sandstone, dolostone, cherty black shale, silty black shale), (2) Marietta-Ardmore Basin (chert, cherty black shale), (3) Arkoma Basin and frontal zone of the Ouachita Tectonic Belt in Oklahoma (chert, cherty black shale), and (4) drillable flanks of the Delaware and Val Verde Basins in West Texas and New Mexico (siltstone, dolostone, silty black shale).