ABSTRACT: Reservoir Characterization and Recovery Efficiency of the Aux Vases Formation at Stewardson Field, Shelby County, Illinois

RICE, RICHARD J., ROBERT D. COLE, and STEPHEN T. WHITAKER, Illinois State Geological Survey, Champaign, IL

Since its discovery in 1939, Stewardson field has produced approximately 950,000 bbl of oil from sandstone reservoirs within the Aux Vases Formation. The formation is composed of sandstones, shales, and limestones which vary in thickness. The producing facies are interpreted as shoreface sheet sandstones ranging in thickness from 9 to 24 ft. These sandstones are relatively homogeneous laterally, although vertically there appear to be up to five distinct intervals, of which only the upper two pay in the field. The sandstone facies are composed of fine-grained quartzose sand cemented with silica and various amounts of calcite. Clay content ranges from 0.4 to 5.2%. Porosity and permeability of the producing interval are relatively low for Aux Vases reservoirs, averaging 13% and 36.5 md, espectively.

Stewardson field is located on a subtle structural high with about 20 ft of closure on the underlying Ste. Genevieve Formation. Isopach maps indicate that there was a very small paleotopographic high at this locality during deposition of the Aux Vases, which caused slightly less fine material to be incorporated within the sandstones deposited there.

Recovery efficiency from the Aux Vases reservoir averages 18% across the entire field, but averages 42% in the portion of the field that was on the paleotopographic high. This disparity is caused by the slightly higher content of fines and cements in the peripheral parts of the field.

AAPG Search and Discovery Article #91013©1992 AAPG Eastern Section Meeting, Champaign, Illinois, September 20-22, 1992 (2009)