Source Rock Screening Studies of Ordovician Maquoketa Shale in Western Illinois

A. Autrey, J. E. Crockett, D. R. Dickerson, D. F. Oltz, B. J. Seyler, R. Warren

Rock-Eval (pyrolysis) studies of Ordovician Maquoketa Shale samples (cuttings and cores) from the shallow subsurface (500-800 ft deep) in western Illinois indicate that facies within the Maquoketa have potential as hydrocarbon source rocks. Dark, presumably organic-rich zones within the Maquoketa Shale were selected and analyzed for total organic carbon (TOC), Rock-Eval (pyrolysis), and bulk and clay mineralogy using x-ray diffraction. Preliminary results from six samples from Schuyler, McDonough, and Fulton Counties show TOC values ranging from 4.70% to as high as 12.90%. Rock-Eval parameters, measured by heating organic matter in an inert atmosphere, indicate source rock maturity and petroleum-generative potential. Screening studies, using the Rock-Eval process, describ "very good" source rock potential in facies of the Maquoketa Shale. Further studies at the Illinois State Geological Survey will expand on these preliminary results. This study complements a proposed exploration model in western Illinois and further suggests the possibility of source rocks on the flanks of the Illinois basin. Long-distance migration from more deeply buried effective source rocks in southern Illinois has been the traditional mechanism proposed for petroleum in basin-flank reservoirs. Localized source rocks can be an alternative to long-distance migration, and can expand the possibilities of basin-flank reservoirs, encouraging further exploration in these areas.

AAPG Search and Discovery Article #91041©1987 AAPG Eastern Section Meeting, Columbus, Ohio, October 7-10, 1987.