HYDROCARBON POTENTIAL OF THE DEVONIAN ANTRIM SHALE, MICHIGAN BASIN: INSIGHTS FROM ROCK-EVAL PYROLYSIS, THERMAL MATURITY AND ORGANOFACIES STUDIES

The Devonian Antrim Shale is an unconventional biogenic gas accumulation with a technical recoverable resource of 19.9 Tcf. However, major knowledge gaps remain regarding our understanding of the source rock potential, organic facies assemblages and paleo-depositional conditions of the Antrim Shale members. This work utilized Rock-Eval pyrolysis, reflected light microscopy and solid bitumen reflectance to characterize the organic matter properties, organo-facies assemblages, and thermal maturity of the various Antrim members at three different localities in the basin. Results showed that the Lachine and Norwood members are richer in organic matter (up to 24wt%) than the Upper Antrim and Paxton members (< 8wt%). Organic matter in the black shales is mainly dominated by marine Type II kerogen, and Type II and Type II/III in the Paxton Member. Telalginite, which is represented mainly by Tasmanites and Leiosphaeridia cysts, is the dominant organic matter in the black shale members where they account for about two-thirds of the organic matter population. Solid bitumen, which accounts for less than one-third of the organic matter population, is second after alginites. Both alginites and solid bitumen populations decline in abundance progressively in the Upper Antrim and Paxton members at the expense of inertinite and vitrinite. The dominant organofacies groups in the studied Antrim members are within the BP type B and type D. Organic matter maturity determined from Rock-Eval T_max and bitumen reflectance varies from immature to marginally mature across the Michigan basin. The results confirmed that sediment deposition and sea level fluctuations controlled organic facies assemblages within the Antrim Shale members.