SUBSURFACE CROSS SECTIONS FOR CARBON STORAGE IN THE ILLINOIS BASIN

It is important to understand the potential for safe geologic storage of CO₂ in the subsurface and to be able to convey that information to the public and potential stakeholders. As part of the research efforts of the Midwest Regional Carbon Initiative (MRCI), a north-south cross section of the Illinois Basin has been constructed as a chart to help users visualize the geology of rock units relative to geologic carbon storage. MRCI is a U.S. Department of Energy-sponsored project to accelerate the deployment of carbon capture, utilization, and storage in the Midwest and Northeast United States.

The cross section is based on 31 deep wells, including the Archer Daniels Midland No. 1 CCS injection well, which has injected nearly a million tons of CO₂ into the Cambrian Mount Simon Sandstone. The section highlights the great changes in thickness of Paleozoic strata from less than 1,000 ft on the Wisconsin Arch north of the basin, to more than 20,000 ft above basement in deepest part of the basin in western Kentucky, as well as faulting and structures that influence the dip and depth of key units. All stratigraphic units from the surface to basement are included. Units are color-coded at depths greater than 2,600 ft to highlight the interval where natural pressures beneath the surface should be great enough to allow maximum storage capacity of CO₂. Color coding units below 2,600 ft helps viewers visualize the critical intervals for potential carbon storage, lateral changes in basin geology, and the areas and depths at which different units occur in the subsurface. Units are color-coded based on their potential as (1) storage intervals (regional saline reservoirs), (2) confining intervals with local potential reservoirs, (3) confining intervals, (4) organic-rich shales (important confining zones), and (5) fresh- to brackish-water intervals.

The cross-section is presented as a chart with brief explanatory text concerning geologic structures, key reservoirs and confining intervals, and references to reports on the geology and carbon storage potential of units shown. The chart also includes inset maps of regional structure and oil and gas fields. Secondary recovery of oil and gas with CO₂ may be possible along parts of the section.