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A New Look at the Organic Geochemical Variability in the Woodford Shale of the Ardmore Basin: Paleoweathering and Organic Matter Source


The Woodford Shale (Devonian-Mississippian) of the southern United States has become one of the most important unconventional hydrocarbon reservoirs in the country. Chiefly responsible for its efficacy as a resource are its remarkably high TOC, brittle structural nature, and an abundance of Type II marine kerogen. Recently the Woodford has been placed within a sequence stratigraphic framework in order to understand the subtle heterogeneities throughout the formation, and organic geochemical analyses may be able to increase the resolution of this ambition. Our study, which has the goal of using biomarkers to assess weathering and paleoenvironment, has determined that a number of aromatic hydrocarbons occur in the bitumen recovered from the Woodford Shale in southern Oklahoma, notably pyrosynthetic compounds including benzo[e]pyrene and benzo[ghi]perylene. Additionally, the hopanoid and steroid hydrocarbons display significant levels of biodegradation. The nature of these altered compounds, along with several other aromatics, may be indicative of modern weathering, paleoweathering, and an influx of weathered terrigenous organic matter into the depositional system. In terms of hydrocarbon producibility, delineating the boundaries of such a zone within the Woodford Shale may provide some benefit to those parties actively looking to utilize it as a resource play.