Petroleum Potential of Under-Explored Lower Paleozoic Strata in the Mature Illinois Basin

Beverly Seyler¹, John P. Grube¹, Joan E. Crockett², Philip M. Johanek², Bryan G. Huff², Rex A. Knepp², Steven R. Gustison², and Randy D. Lipking^2
1 Illinois State Geological Survey, Champaign, IL
² Illinois State Geological Survey

Devonian, Silurian and Ordovician reservoirs account for 7.5% of the 3.2 billion barrels of petroleum produced in Illinois. Established reservoirs and recent discoveries represent a guideline to the potential for Lower Paleozoic production and the opportunity for new exploration targets in the mature Illinois Basin. Devonian reservoirs, both siliciclastic and several types of carbonate, have been established though lightly explored in the Basin. Silurian reservoirs, commonly associated with various reef settings, exhibit compartmental characteristics that extend both development and new play production. Non-reef Silurian production has also been established. Ordovician reservoirs are limited to closed structures in the Trenton carbonate, leaving the prolific hydrothermal play as pure potential. The Lower Paleozoic units have not been extensively explored, in part because of the greater drilling depths and the practice of penetrating deeper horizons mostly in fields where shallower production has been established. This strategy has brought sporadic results because structural closure may shift with depth and numerous traps in Lower Paleozoic units are stratigraphic.

An Illinois Basin Consortium project funded in part by the U.S. DOE is focusing on existing petroleum reservoirs and the potential for new discoveries in Lower Paleozoic units. Major tasks for this project include creating a digital catalogue of existing reservoirs and developing models of the stratigraphic and structural framework of Lower Paleozoic units using available subsurface data. These products will be available in digital format on an ArcIMS website. Preliminary results suggest that applying new exploration strategies to the Illinois Basin can result in significant new discoveries in Lower Paleozoic units.