Climatic Forcings on the Deposition of Soft-Hard Bed Couplets in Black Shales: Insights from the Woodford Shale, Anadarko Basin, Oklahoma

Abstract

Numerous studies have been conducted to better understand the highly productive late Devonian-early Mississippian Woodford Shale of the Anadarko basin, OK. Notwithstanding, fundamental questions remain unresolved about the origin of the formation’s soft-hard bed couplets. These couplets exhibit distinct lithological, geomechanical, and geochemical characteristics that facilitate the formation excellent potential for hydrocarbon production. Based on its high clay and total organic content (TOC), the soft-shale beds are proposed to have been deposited in a restricted/oxygen depleted environment whereas the hard-cherty beds were deposited in an environment with abundant oxygen. In general, the Woodford is assumed to be of marine origin deposited over an extensive regional unconformity karsted during the Devonian. However, its origin and depositional history have long been an enigma to geoscientists and petroleum explorationists. This research will test the hypothesis that the development of the soft-hard bed couplets that constitute the Woodford is influenced by climate/external forcings. Thin section, Spectral Analyses, X-Ray Fluorescence (XRF), Scanning Electron Microscope (SEM) and isotope geochemical analyses of outcrop and core samples of the Woodford will be employed to assess proxies for climatic controls that can indicate alternating wet-dry, and high-low oxygenation environments. Understanding the generation, transport and deposition of these organic-rich fine-grained rocks not only holds important significance for global geoscience as it addresses sedimentary system response to external forcings but also poses great economic significance for the oil and gas industry as it will provide fundamental information on the depositional environment of the Woodford.

AAPG Datapages/Search and Discovery Article #90351 © 2019 AAPG Foundation 2019 Grants-in-Aid Projects