LOOKING FOR CARBON STORAGE IN THE CAMBRO-ORDOVICIAN KNOX CARBONATES OF THE EASTERN MIDCONTINENT U.S.A

In the eastern Midcontinent, the Mount Simon Sandstone and other Cambro-Ordovician sandstones are prime saline reservoir targets for geologic CO₂ storage. The Knox carbonate section will be an important part of the confining interval for many of these sands, as much of the Knox is dominated by well-cemented dolomites with little or no permeability (<.01 md). The Knox, however, locally exhibits discrete zones of porosity and permeability, and drillers often encounter saline water when drilling the Knox. In Kentucky, there have been two industrial waste injection sites in recent years, and both have been in the Knox. The DuPont waste-injection site at Louisville, abandoned a thick Mount Simon section in favor of a permeable, vuggy dolomite facies in the Knox. Injectivity rates as high as 4.8 barrels/minute were recorded. Injection of plant brines lasted for three years. Likewise, waste waters at the IMCO Recycling plant in Butler County have injected into several Knox porosity zones for more than eleven years. Injection rates vary from 200 to 4,700 barrels/day depending on need. Paleotopographic highs along the Knox unconformity surface are known oil reservoirs and have also been used for natural gas storage along the western flank of the Cincinnati Arch. Because the Knox has demonstrated storage history in the eastern Midcontinent, it should be investigated as a potential deep saline reservoir target for future CO₂ storage. The Knox may be particularly important in areas where the Mount Simon and other Cambro-Ordovician sands are too deep, too well cemented, or too thin for large-scale CO₂ storage. Even where other saline reservoirs have demonstrated storage potential, the Knox should be tested for secondary storage potential where feasible. Reservoir testing of permeability zones will be needed to show connectivity in the discontinuous and heterogeneous carbonate facies that characterize the Knox. More data are also needed to characterize potential Knox reservoirs at depth, and to determine best practices for completing Knox and other similar carbonate injection wells for the purpose of carbon storage. Some of these data are being collected through U.S. Department of Energy's Carbon Sequestration Regional Partnership programs, as well as through state ventures such as the Kentucky Consortium for Carbon Storage.