ABSTRACT: Integrated Geological and Engineering Description of Aux Vases Reservoirs in the Zeigler Field, Franklin County, Illinois

SEYLER, BEVERLY, STEVE S. K. SIM, and EMMANUEL O. UDEGBUNAM, Illinois State Geological Survey, Champaign, IL

Zeigler field, located in Franklin county, has produced over 2 million bbl of oil since 1963 from Aux Vases sandstones. Because all wells were cored, Zeigler field provides a unique opportunity for a comprehensive and detailed geological and reservoir description. Core characterization included thin section petrography, SEM/EDX and XRD analyses. Porosity and permeability values were determined at one foot intervals. A computer-aided geologic modeling program was used to create three-dimensional visualizations of permeable sand distribution and to estimate interwell values of the petrophysical parameters. In addition, a geostatistical approach was used to delineate and distinguish sand flow units within each sand bar and to estimate permeability variability. The reservoir flow model re ulting from the integration and analyses of geological and engineering data was used to determine the OOIP and as a framework for reservoir simulation of primary depletion and prediction of alternative secondary recovery processes. While a clean sandstone isopach of the Aux Vases at Zeigler indicates a continuous horse-shoe shaped sandstone body, fence diagrams and the three-dimensional computer visualizations of the field reveal several isolated, shingled, and narrowly connected sandstones with convex upward geometries. These sandstone bodies comprise the reservoir and are interpreted as off-shore marine tidal sandbars. Subtleties in SP, gamma ray, and resistivity logs are related to observable variations in rock properties and were used to limit reservoir boundaries, thereby improving eserve estimates.

Permeability variability was very high. Heterogeneity indices, determined from a combination of Dykstra-Parson coefficient and variogram analyses indicate a high degree of permeability anisotropy. The original oil-in-place (OOIP) and recovery efficiencies from material balance calculations and from the operator's records are being compared to those determined from the computer-generated and the krigged reservoir models. Results of these comparisons and estimates of unproduced mobile oil (UMO) and potential for incremental oil recovery will be reported.

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