NATURAL GAS AND COMPRESSED AIR STORAGE FIELDS IN CENTRAL IOWA

One general truism of old rocks is that they should be low porosity. Another truism is that there is little complexity to the structural geology of Iowa. Neither of these truisms work in Central Iowa where anticlinal traps likely related to reactivated Midcontinent Rift Faults host Paleozoic reservoirs with over interparticle 20% porosity and several hundred millidarcies of permeability. Natural gas has been cycled through the Redfield Dome since the 1950s using the Cambrian Mt. Simon Sandstone, the Ordovician St. Peter Sandstone, Galena Limestone, and Elgin Limestone reservoirs at depths of 1500-3000 ft below surface. This facility contains approximately 130 billion cubic feet (Bcf) of natural gas piped in from fields in Texas, Oklahoma, and Kansas, though only approximately 55 Bcf cycles on an annual basis. In the 2000s, a comprehensive survey was undertaken to evaluate using compressed air storage in similar reservoirs in nearby anticlinal traps to store energy from wind turbines. Data from seismic surveys and several exploration wells, suggest a lack of permeability may hinder such a system. Most recently, the Mt. Simon is being extensively investigated in the Illinois Basin as a possible reservoir for carbon dioxide sequestration. Core from each reservoir at Redfield will be shown, while focusing on the Mt Simon, which is volumetrically the most important. Thin section photomicrographs, helium porosity, and mercury intrusion pore throat size distributions characterize the nature of intra-reservoir baffles in the arkosic sandstone that locally reduce porosity from approximately 25% to 6%.