Three-Dimensional Reservoir Architecture and Improved Oil Recovery in a Deltaic Depositional System

H. E. Leetaru
Illinois State Geological Survey, Champaign, IL

Centralia Field, located in Clinton County, Illinois is a good example for the potential of recovering additional oil from mature fields. Most of the production is from the Mississippian Yankeetown (Benoist) Formation. The field has a unique database of 37 wells with whole core, 60 wells with core analyses, and over 90 wells with digitized wireline logs.

The three-dimensional sandstone architecture of the Benoist reservoir in Centralia Field shows significant lateral and vertical reservoir compartmentalization as a result of being deposited in a coastal plain deltaic system. The sandstone architecture is dominated by narrow (less than 1500 ft wide) upward coarsening northeast-trending sandstone bodies that are interpreted to be distributary mouth bars. Sandstones with abundant impermeable shale and limestone beds dominate areas between the sandstone bodies. The impermeable intervals are rarely continuous over more than 800 acres.

The northeast trending sandstone bars produce an anisotropic pattern during waterflooding of the Benoist reservoir. The most likely candidates for bypassed oil are located in the interbar areas. These isolated interbar reservoir compartments would have been only partially drained by the currently producing wells.

AAPG Search and Discovery Article #90900©2001 AAPG Eastern Section Meeting, Kalamazoo, Michigan