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AAPG Bulletin


AAPG Bulletin, V. 104, No. 3 (March 2020), P. 657-680.

Copyright ©2020. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/06121918136

Source-rock reservoirs geochemistry of Devonian–Mississippian mudrocks in central Oklahoma

Ibrahim Atwah,1 Jim Puckette,2 Mauro Becker,3 and J. Michael Moldowan4

1Berg-Hughes Center for Petroleum and Sedimentary Systems, Department of Geology and Geophysics, Texas A&M University, College Station, Texas; Geochemical and Environmental Research Group, Texas A&M University, College Station, Texas; [email protected]
2Boone Pickens School of Geology, OSU, Stillwater, Oklahoma; [email protected]
3Berg-Hughes Center for Petroleum and Sedimentary Systems, Department of Geology and Geophysics, Texas A&M University, College Station, Texas; [email protected]
4Biomarker Technologies Inc., Rohnert Park, California; [email protected]


The Woodford Shale and the overlying Mississippian limestone constitute one of the prolific unconventional hydrocarbon targets in central and northern Oklahoma. With the advantage of horizontal drilling technology, Devonian and Mississippian mudrocks have become important topics for research to understand the petroleum system fundamentals, including sources of hydrocarbons for these unconventional reservoirs. In this study, organic geochemistry and petrography of Mississippian mudrocks and the Woodford Shale were examined. The key study core is from Lincoln County, Oklahoma, representing the Mississippian mudstone and Woodford Shale. Three additional cores in Payne County and one core from Logan County were studied. Core samples were assessed for hydrocarbon generation potential using Rock-Eval pyrolysis together with biomarker analysis using gas chromatography–mass spectrometry. Organic and thin-section petrography was performed to identify maceral composition and develop a sedimentary facies classification.

Mudrocks within the Mississippian section exhibited adequate organic richness for petroleum generation, thereby augmenting the established generation potential of the Woodford Shale. Several unique Mississippian biomarkers were identified, including diterpenoids and extended tricyclic terpanes. Macerals of the Mississippian rocks exhibit dominance of lamalginite and bituminite, whereas Woodford macerals are high in telalginite. Based on the organic matter composition and sedimentology, six facies were identified within the Mississippian mudrocks. Furthermore, based on organic richness and key biomarker ratios, the Mississippian succession is divided into three units. Organic and sedimentological signatures suggest a shoaling-upward succession from the Woodford Shale to the Mississippian carbonate.

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