ABSTRACT: Characterization of Mississippian Aux Vases Sandstone Reservoirs, Southwestern Dale Consolidated Field, Franklin, Hamilton, and Saline Counties, Illinois

BEATY, D. SCOTT, and JOSEPH P. FAGAN, Illinois State Geological Survey, Champaign, IL

Several petroleum reservoirs at the southwestern end of Dale Consolidated field, Franklin, Hamilton, and Saline Counties, Illinois, consist of structural]y modified stratigraphic traps formed in the Mississippian Aux Vases Sandstone. The Aux Vases was deposited in a mixed carbonate-siliciclastic environment, and the reservoirs are shallow-marine bars formed in shoals against older carbonate paleotopographic highs. The bars are "shingled," i.e., separated by shale beds as thin as 2 ft. Bar sandstones grade laterally to less permeable shaly sandstone. While the sandstones contain fossil fragments and carbonate clasts consistent with deposition in high-energy conditions, production characteristics of the reservoirs are controlled by the degree of diagenetic modification of the sandstones Differential calcite cementation creates significant reservoir heterogeneity. Flow unit fence diagrams reveal that calcite cementation affects recovery efficiency by creating both vertical and lateral permeability variations in the rocks.

Waterflooding has been effective in the field, but has not been attempted in every area. Application of this technique should substantially improve recovery in the remaining unflooded areas. Infill drilling should improve recovery in those portions of the field already waterflooded, because permeability variations lead to low sweep efficiency and additional wells probably are needed to contact bypassed mobile oil.

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