Preliminary Assessment of Hydrocarbon Potential in Southern Illinois

Joan E. Crockett, Donald F. Oltz

Hydrocarbon exploration has been sparse south of the Cottage Grove fault system in southern Illinois. Over 240,000 ac in this area are within the Shawnee National Forest (SNF). Upcoming review of mineral exploration policy on SNF land and a recent amendment to the Mineral Leasing Act (1987) will result in release of portions of the SNF for competitive and potentially noncompetitive bidding for mineral exploration tracts in the near future.

Preliminary assessment of hydrocarbon potential has been carried out in southern Illinois. Numerous oil shows occur in Paleozoic strata south of the Cottage Grove fault system, which, at present, describes the southern boundary of most oil production in Illinois. Only Mitchellsville oil field in southern Saline County lies south of the Cottage Grove fault system.

The Upper Devonian New Albany Shale, thought to be the primary source rock for Illinois basin hydrocarbons, underlies most of the area. Older potential source rocks may be present. Depositional trends of prolific oil-productive Mississippian strata in Illinois continue southward through the area. Few drill holes have tested strata older than Mississippian in the area. Complex faulting in the Rough Creek-Shawneetown fault system may have improved the potential for hydrocarbon emplacement and entrapment in this region. Preliminary assessment of hydrocarbon potential indicates that this wildcat region deserves further tests.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.