The distribution, characteristics, and potential viability of geological carbon sequestration options in the Illinois Basin are being assessed through a Regional Sequestration Partnership funded by the U.S. Department of Energy (DOE) and co-funded by state government, industry, and non-governmental organizations. The Illinois Basin is a cratonic basin covering most of the state of Illinois and parts of western Indiana and western Kentucky in the Midwestern United States. Major uneconomic coal resources, oil reservoirs potentially amenable to enhanced oil recovery (EOR), and deep, brine-filled sandstone reservoirs are all present in the basin as potential carbon dioxide sinks. Illinois, in fact, contains the largest bituminous coal resource of any U.S. state. Peak Illinois oil production occurred more than 50 years ago, indicative of a highly mature resource base, yet perhaps 60 percent of assessed original-oil-in-place remains unrecovered. Illinois ranks second in the U.S. in natural gas storage capacity, thus enhancing geological understanding of brine-filled reservoirs and their seals. Assessments of geological carbon dioxide sinks have emphasized the possible economic return from adsorption on deep, uneconomic coals with release of coalbed methane and from EOR with ultimate abandonment of carbon dioxide in the reservoir. Saline reservoir injection yields no economic product but may have greater storage capacity and greater certainty of containment than in coals or oil reservoirs. Over 120 years of mining activity has largely been concentrated around Basin margins leaving large areas over the deep central and southeastern parts of the Basin unlikely to be mined. Major coals in these areas occur at about 365 m (1,200 ft) in depth. Integrated assessment of geological sequestration opportunities using Geographic Information Systems (GIS) suggests potential areas where two or more carbon sinks may be vertically stacked. Depth and temperature will determine the applicability of miscible versus immiscible EOR technologies applicable to Illinois Basin oil reservoirs, and the overlap of oil and coal sinks will define sequestration fairways coincident with hydrocarbon recovery potential. Extensive past drilling will help define these fairways, yet each data point also represents a potential leakage point, particularly with respect to the condition of oil well casing and cement (current and future). Therefore, considerations of economic return and sink integrity in the Illinois Basin may favor delivery of carbon dioxide to locations where hydrocarbons can be recovered with ultimate storage taking place in the Mt. Simon Sandstone or similar saline reservoirs beneath the same location. Hydrocarbon recovery would offset the cost of surface infrastructure (pipelines, compression, metering, etc.), injection would take place where drilling and surface operations are already familiar to the general public, and the condition of hundreds of oil wells in a field following EOR would not become a long-term integrity issue.
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