UDEGBUNAM, EMMANUAL O., S. K. SIM, and D. F. OLTZ, Illinois State Geological Survey, Champaign, IL

ABSTRACT: Critical Parameters Affecting Productivity from Three Small Illinois Fields

The Energy and Zeigler fields and the Thompsonville unit in the Dale Consolidated field are three separately-owned mature fields with a cumulative oil production of more than 2.8 million barrels. The reservoirs, located several miles apart, consist of lenticular sandstones of the Missippian Aux Vases Formation interpreted as shallow marine sandstone bars affected by varying degrees of diagenesis.

Computer-aided 3-D geologic models were constructed using input from stratigraphy, petrophysical data and the regional geology. Flow units within the geologic model and their corresponding reservoir attributes needed for reservoir simulation were interactively selected for development of the simulation grids and layers. Various effects of formation damage, uncertainties in rock and fluid data, early pressure maintenance programs, large-scale heterogeneities, well placement, injection fluids, rates and patterns, and induced fractures on reservoir performance were studied.

Results from this comparative study demonstrate the effects of large-scale heterogeneities, early pressure maintenance, rock/fluid and fluid/fluid interactions, hydraulic fracturing and well placement on reservoir productivity. At Zeigler, waterflood performance was affected by large-scale interwell and vertical heterogeneities while reservoir productivity at the Thomsponville units is being affected by east-trending induced fractures. Formation damage, caused by reactions between injection waters and clayminerals in the reservoir rocks, seems to be most pronounced at Energy field. Field production practices have a strong influence on oil recovery and affect potential for incremental oil recovery from these fields.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.