Abstract In response to rising concerns about atmospheric carbon dioxide (CO 2 ) levels and likely regulations on emissions, investigations into geologic carbon storage options across the United States are underway. In the Midwest, Cambrian sandstones are major targets for potential geologic carbon storage. In some localities, the overlying Cambrian–Ordovician Knox Group is also being investigated as a possible target for primary and secondary storage of CO 2 . The thick dolomitic succession contains intervals that may function as both reservoirs and seals. Gas storage fields in Knox carbonates in Kentucky and Indiana demonstrate that methane can be safely stored in paleotopographic highs along the Knox unconformity surface. Numerous injection wells have also been completed in the Knox Group for brine disposal. More significantly, at least seven class 1 injection wells have used the Knox as all or part of a storage reservoir for industrial wastes. Many of these wells have injected millions of gallons of liquid waste annually into Knox reservoirs. The relative scale of these injection operations can be used to estimate the types and sizes of potential reservoirs within the Knox succession in the Midwest. Specific data on the Knox interval relative to its carbon storage and confining potential are currently being collected from wells drilled as part of U.S. Department of Energy administered carbon storage projects, as well as state-administered carbon storage programs. In this chapter, initial results of carbon storage tests are summarized from the Battelle 1 Duke Energy well, Kentucky Geological Survey 1 Blan well, Battelle-American Electric Power (AEP) 1 Mountaineer well, and Battelle-Ohio Geological Survey 1 CO 2 well. The AEP Mountaineer Power Plant will host the nation’s first commercially integrated carbon capture and geologic storage project, and the storage reservoirs will be in the Knox Group. Because the Knox Group is widespread at depth across much of the Midwest, it will be an important part of sequestration programs as confining interval and reservoir.

Abstract Opportunities for the future recovery of hydrocarbons in mature oil-producing basins are often reflected in various recurring themes—"new frontiers in old areas," "geological re-exploration," "improved recovery from existing fields." Such themes continue to find application in the Illinois basin, one of the mature oil-producing areas. The basin has almost 1700 named fields that include approximately 7000 separate sandstone and carbonate reservoirs. The easily discovered oil has been found, and much of it has been produced. In the Illinois basin, stripper production accounts for up to 96% of total production (B. G. Huff, personal communication). This figure, which stands in contrast to the U.S. average of 15% for total production from stripper wells (American Petroleum Institute, 1989), indicates the mature stage of development of discovered reserves. Does this mature area have remaining potential? Is it reasonable to forecast increased basin production? To help answer these questions, the authors examine several of the recurring themes as they apply to the Illinois basin, including (1) the nature and amount of oil remaining in already discovered fields or wells and (2) the nature of past exploration and the amount of undiscovered hydrocarbon resources.