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Rock-Eval Data Relating to Oil-Source Potential of Shales of New Albany Group (Devonian-Mississippian) in Illinois Basin

Mei-in M. Chou, Donald R. Dickerson, Michael L. Sargent

Only limited data on petroleum source rock potential of New Albany Group (Devonian-Mississippian) shales have been reported, with the exception of vitrinite reflectance and some petrographic analyses. The New Albany Group contains the thickest and most widespread continuous black shale beds in the Illinois basin. The New Albany extends from northwestern Illinois to southwestern Indiana and western Kentucky and is thought to have played a major role in petroleum generation throughout the basin. In this study, Rock-Eval pyrolysis was used to measure the petroleum-generative potential and production index of the shale.

Seven geochemical logs, based on 143 core samples from across the basin, and a production index map, based on a total of 252 samples (cuttings and cores) in Illinois, were generated. Systematic variations of petroleum-generative potential of the shale were observed. The variations are related to the differences in shale lithofacies, depth, and geographic location. The upper portion of the New Albany--the Hannibal and Saverton Shales--has the lowest oil-generative potential. The Grassy Creek, Sweetland Creek, and other stratigraphically lower shales of the New Albany Group generally have good oil-generative potential. However, samples from the Hicks dome area of extreme southern Illinois are overmature and have no oil-generative potential. Source rocks that have both good oil-generativ potential (> 6 kg hydrocarbons per ton of rock) and a higher production index (> 0.09) are generally located at depths of 2,500-5,300 ft.

AAPG Search and Discovery Article #91031©1988 AAPG Eastern Section, Charleston, West Virginia, 13-16 September 1988.