Trenton Oil Fields and Potential Production in Illinois

Grube, John P., Beverly Seyler, Bryan G. Huff, and Joan E. Crockett
Illinois State Geological Survey, Champaign, IL

Lower Paleozoic rocks of the Illinois Basin represent an important, yet incompletely understood hydrocarbon exploration and development target. Of the 4 billion barrels of oil produced from the Illinois Basin only 7.5 percent has been from lower Paleozoic rocks; reservoirs below 3000 feet are rarely targeted. Ordovician rocks have great potential for additional discoveries but remain unexplored in most of Illinois.

Prolific Ordovician age Trenton/Black River reservoirs have been established in the Michigan and Appalachian basins in dolomites associated with fractures and structural lows. Ordovician oil production in the Illinois Basin is from smaller fields with limited production on anticlinal closures that were mostly discovered by drilling deeper into structures with established shallower production. There are no Trenton fields in the Illinois Basin that are established in dolomitic, structurally low areas such as those in the Michigan and Appalachian Basins. Geologic characteristics similar to those found in the Michigan/Appalachian Basin Trenton/Black River model exist in the Illinois Basin including a hydrothermal footprint along faults and fractures. Furthermore, the anticlinal play may be inadequately explored where the Trenton closure is offset to that of the shallower horizons due to a tilted axial plane.

Trenton production associated with the anticlinal play in Illinois falls into three regions: 1) The LaSalle Anticlinal Belt, 2) Western shelf production, 3) And a cluster of fields associated with the DuQuoin Monocline. Some common characteristics of these fields include fractured, low porosity, fossiliferous grainstone reservoirs that are not highly dolomitized and produce paraffinic oil. Horizontal drilling may prove to be a viable means to drain these reservoirs more efficiently.

AAPG Search and Discovery Article #90031©2004 AAPG Eastern Section Meeting, Columbus, Ohio, October 3-5, 2004