FACIES ARCHITECTURE OF THE THICK IVF CYPRESS SANDSTONE AT DALE OIL FIELD, HAMILTON COUNTY, ILLINOIS: A MICROCOSM FOR REGIONAL-SCALE CORRELATION

The thick, incised valley-fill (IVF) deposits of the Cypress Sandstone (Late-Mississippian) in the Illinois Basin (ILB) are potential targets for carbon dioxide enhanced oil recovery (CO₂-EOR) and storage. However, the regional stratal architecture, lateral connectivity, and reservoir quality variations of these reservoirs is not yet defined at a resolution needed to assess the regional CO₂-EOR and CO₂storage potential of the Cypress Sandstone.

Cores and geophysical log suites from Dale Oil Field, Hamilton County, Illinois, were used to create complementary sedimentological and geophysical log facies schemes. Thirteen sedimentological facies were calibrated to seven corresponding geophysical facies to reduce uncertainty in subsurface correlation of like sedimentary facies. The Lower Cypress contains a thick (> 49 ft [15 m]), laterally continuous sandstone that lacks a preferred orientation. Sandstone in this interval exhibits smooth-cylindrical and serrated-cylindrical spontaneous potential (SP) log responses that correspond with cross-stratified, ripple cross-bedded, massive, and planar-bedded facies. Upper Cypress sandstones are thin (< 30 ft [9 m]), laterally discontinuous, and trend north-south. Sandstone in this interval exhibits serrated-shale and hourglass log facies that correspond with bidirectional ripple cross-bedded and planar-bedded facies. A transitional serrated-bell log response composed of heterolithic facies commonly exists between upper and lower intervals. Although the IVF Cypress is laterally heterogeneous, a fining-upward trend is observed across the field.

Comparison of results from Dale Oil Field with existing regional maps and correlations of the IVF Cypress shows that the facies variability and distribution within the field may serve as a microcosm to guide future high-resolution regional correlation in the IVF Cypress. Facies analysis of new and existing cores, various geophysical log suites, and outcrops will be integrated to (1) provide the sequence stratigraphic framework necessary for assessing the CO₂-EOR and storage potential of the thick Cypress Sandstone, (2) advance our knowledge of Late-Mississippian sedimentation in the ILB, and (3) contribute to a better understanding of the sedimentary architecture of IVFs in low accommodation settings.