A New Play in an Old Trend; Sangamon Arch in the Illinois Basin

James Blumthal¹ and Joan Crockett²
¹Benchmark Properties, Olney, IL
²Illinois State Geological Survey, Champaign, IL [email protected]

Expansion of an exploration play trend along the basinward flank of the ancient Sangamon Arch (Mount Auburn trend) in Christian and Macon Counties, central Illinois, has led to several recent discoveries there. Multiple new discoveries have been made in what has been described as Middle Devonian “reef wash” or the Upper Devonian “Hibbard Sand,” where Middle Devonian strata lap on to the flanks of the Arch. The producing zone at Sharpsburg’s recent extension is in sucrosic dolomite within Middle Devonian carbonate rocks, at or near the unconformable stratigraphic pinchout onto the Sangamon Arch. The dolomite rests on a Devonian coral rip-up-clast limestone zone, and is overlain by crystalline Devonian lime, which in turn is capped by a thin (less than 2’ thick) bed of very tight fine-grained “Hibbard” sandstone. The New Albany Shale then caps the sand. Atypical Initial Production rates in the new Devonian producers have ranged from 160 BOPD to 1,440 BOPD from depths ranging from 1890 to 2090 feet. The classic or typical targets along the Sangamon Arch were Silurian reef carbonates with characteristic IP’s of 30 to 50 BOPD after sand fracture treatment, with eventual accumulated production of 20,000 to 30,000 BO over a 12 to 20 year well life. In contrast, one well in the new extension at Sharpsburg is on trend to produce this volume of oil in 90 days from the Middle Devonian. We will present information on the lithology, porosity and permeability from cores, describe the log character, and discuss exploration and development models in this hot new Illinois Basin discovery.

AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012