The Antrim Shale is the Michigan basin equivalent of Devonian-Mississippian black shales of the eastern United States. The Dow Chemical Co., with DOE funding, has investigated the possibility of in-situ gas production from the Antrim by underground combustion. This paper summarizes some results obtained in the shale characterization program that was a part of that study.

Antrim Shale is rather uniform in composition and contains about 30% Si, 8% Al, 4% Fe, 2% Mg, 3% Ca, 2% S, and 5% organic carbon. Mineralogically, Antrim Shale consists of 50 to 60% quartz, 20 to 35% illite, 5 to 10% kaolinite, 0 to 5% chlorite, and up to 5% pyrite. Calcite and dolomite, when present, occur as limestone nodules, lenses, and interbeds up to 5 ft (2 m) thick in the lower half of the Antrim. Bedford Shale, which overlies the Antrim in eastern Michigan, contains more total clays, illite and kaolinite, and less quartz. Ellsworth Shale, which interfingers with the upper part of the Antrim in western Michigan, contains up to 25% dolomite.

Antrim Shale contains up to 12.8% organic material, as measured by low-temperature ashing. Bitumen contents range from 0.2 to 0.8%. Average molecular weights of bitumen components are 360 to 370. Deeper drill holes have higher bitumen contents. Kerogen, which makes up the rest of organic material, is of low functionality, about 1 functional group per 25 carbon atoms. Hydroxyl (1 group/50 C atoms) and alkene double bonds (1 group/50 C atoms) are the most common groups present.

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