Porosity/Permeability Trends in a basal Pennsylvanian channel sandstone, Caseyville Formation, Crawford County, Illinois
BANDY, WILLIAM F., JR., DAVID E. BRITTON, and JEFFREY L. HOY
Team Energy, L.L.C., Bridgeport, IL
During the drilling of the Valdez #7A in the fall of 2001, a 30-foot core was cut through a basal Pennsylvanian channel in section 1, T5N, R13W, Crawford Co., Illinois. The core, cut at a depth of 1219-1249 feet, recovered 24 feet of basal Pennsylvanian sandstone, underlain by six feet of Mississippian sandstone, limestone and shale. The following aspects of the core are notable:
· The core includes the entire channel reservoir, plus the Mississippian-Pennsylvanian unconformity. A basal pebble conglomerate marks the unconformity.
· The sandstone is coarse grained and relatively clean, with little or no shale laminations, and was oil-saturated throughout the entire interval.
· Porosity averages only 15.4%, but permeabilities are high, especially in the upper 11 feet of the reservoir. Horizontal permeabilities range from 1360 to 2536 millidarcies. Vertical permeabilities are 60 to 100% of horizontal permeability, and actually exceeded horizontal permeability in one foot, reflecting the clean nature of the reservoir.
The Valdez #7A was a twin to Valdez #7, and therefore was not logged with geophysical tools. However, a remarkable correlation exists between the resistivity curves recorded in Valdez #7 and the porosity and permeabilities observed in the core recovered from Valdez #7A.