Vitrinite Reflectance of Woodford Shale in Anadarko Basin, Oklahoma: ABSTRACT

The Woodford Shale (Upper Devonian-Lower Mississippian) is a black shale thought to be an important oil-source bed in the Anadarko basin of western Oklahoma. The reflectance in immersion oil (R_O) of first-generation vitrinite particles found in this stratigraphic unit is related to temperature history and thus hydrocarbon-generating potential. Samples of the Woodford Shale were obtained from 18 wells drilled in the Anadarko basin by various operators, and polished sections of the shale were prepared and interpreted by the author while working at the Oklahoma Geological Survey. A minimum of 60 vitrinite reflectance measurements were recorded for each well. The Woodford was sampled at depths of from 5,060 ft (1,542 m) in the northeastern shelf to 20,308 ft (6,190 m) in the deepest part of the basin in Beckham County, southwestern Oklahoma. A systematic increase in mean vitrinite reflectance (mean R_O) with depth was observed. From northeast to southwest across the Anadarko basin mean R_O increased from 0.51 to 2.60%. An isoreflectance map for the Woodford Shale in the Anadarko basin was prepared using data collected during this study. The Woodford Shale should have generated commercial quantities of oil in those areas of the basin where the shale has a mean R_O of from 0.60 to 1.35%. In Kiowa County, Oklahoma, the Woodford Shale was sampled in a fault block bordering the Wichita uplift on the southern boundary of the basin. It has, in this well, an anomalously low mean R_O of 0.48%, possibly due to a shallow depth of burial throughout its history.