Integrated characterization of the Woodford Shale in the southern Cherokee Platform, Oklahoma

Abstract

The Late Devonian-Early Mississippian, organic-rich Woodford Shale is considered as one of the most important unconventional resources for oil and gas in the United States of America. This formation was targeted for gas exploitation until 2008 mostly in the Anadarko and Arkoma basins (Oklahoma), however, recent studies in the Cherokee P latform of Ok lahoma have demonstrated that there are large volumes of hydrocarbons at depths of 3,500 to 6,500 feet in Cleveland, Pottawatomie, and McClain Counties (Althoff, 2012). This study characterizes the Woodford Shale in an area located in the southern end of the Cherokee Platform in order to identify its hydrocarbon reservoir potential by analyzing well logs, well cuttings and 3D pre-stack seismic data. Sequence stratigraphy techniques were applied in order to identify high-resolution depositional cycles that allow differentiating the vertical heterogeneity of this formation to the south of the Pottawatomie County. X-Ray Diffraction (XRD) analyses along with total organic carbon (TOC) analyses of well cuttings were combined with seismic attributes analysis and seismic inversion techniques to understand some physical characteristics of the rocks and their lateral distribution within each transgressive-regressive cycle. As a consequence, two prospective zones containing 1.46MMbls of oil-in-place in an area of approximately 260 acres has been identified after effectively integrating geological, geochemical and geophysical data. Finally, a five-stage evolutional model is proposed for the study area where incised valley development, karstification and the progressive collapse of carbonatedissolution features on the underlying Hunton unconformity surface enhanced the accommodation space at certain locations and favored the deposition of thick and organic-rich strata of the Woodford Shale. These anomalous intervals with their contained organic content (TOC) can be mapped seismically, and illustrate the lateral, as well as vertical heterogeneity of strata in the study area.