Abstract: Petroleum Geology of the Woodford Formation, Anadarko Basin, Oklahoma and Texas
The Upper Devonian Woodford Formation is an important source rock in the Anadarko Basin. The formation is cherty black shale with organic carbon ranging up to 20% locally. The Woodford Formation is directly correlative with the Bakken Formation of the Williston Basin, and the Devonian Shales of the Appalachian Basin, in part.
A vitrinite reflectance map of the Woodford illustrates thermal maturity patterns throughout the Anadarko Basin. Comparison of the map with a basin-wide map of electrical resistivity suggests that it is possible to map areas of elevated Woodford hydrocarbon saturation using well logs.
Cross-plotting average Woodford interval transit time from sonic logs versus depth suggests pore-fluid overpressuring in the Woodford below certain depths. Areas where such elevated pressure gradients occur are partially correlative with the mapped areas of elevated Woodford resistivity. This may represent a relationship between overpressuring and hydrocarbon generation.
Calculation of Poisson's ratio was performed using interval velocities of compressional and shear waves in the Woodford Formation. This allowed the estimation of the natural "frack gradient" for the Woodford.
With this information, a trend was mapped in which the Woodford Formation may be in a naturally fractured state by virtue of elevated pore-pressure due to hydrocarbon generation. As such, this trend may represent a new fractured gas and condensate play fairway.
AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994