Illinois Basin; potential of under-explored lower Paleozoic strata

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. This presentation will include updates on drilling and production activity, information compiled from source rock studies, interpretive cross sections, lithologic studies, an updated series of contoured structure maps, initial production maps, and representative reservoir studies set in a regional framework. Cross sections and subsurface maps examine unconformity-bound sequence packages relevant to Lower Paleozoic reservoir development. Devonian reservoirs, both siliciclastic and carbonate, have been established though lightly explored in the Basin. There are opportunities for additional reef and non-reef discoveries in Silurian strata. Ordovician reservoirs are limited to closed structures in the Trenton carbonate, leaving the prolific hydrothermal play as unrealized potential. 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. A series of contoured structure maps examine structural evolution. 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. Preliminary results suggest that applying new exploration strategies to the Illinois Basin can result in significant new discoveries in Lower Paleozoic units.