Recognition of Oolite-Filled Channels, Ste. Genevieve Formation, Illinois Basin

BANDY, WILLIAM F., JR., Vincennes University, Vincennes, IN

Porous oolitic grainstones in the Ste. Genevieve Formation (Mississippian) of the Illinois basin have typically been viewed as bar-shaped reservoirs. However, a reservoir discovered in the Allendale Pool, southern Lawrence County, is an oolitic grainstone with a channel geometry. A similar, oolite-filled channel has been recognized in southern Lawrence field, approximately 4 mi north of the Allendale channel. This reservoir, previously thought to be a bar, was discovered over 80 years ago and is much larger than the Allendale channel. Both reservoirs have proven prolific, with high initial and cumulative productions and relatively little water. In contrast to oolitic bars, which are convex upward in geometry, oolite-filled channels are flat-topped and convex downward, with relatively reater average thicknesses and porosities. Laterally, bars thin gradually, whereas channels may thin very abruptly. Similar, undiscovered channels probably occur elsewhere in the Illinois basin.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)