Aquifer compressed-air field experiment at Pittsfield, Illinois

Compressed air energy storage (CAES) is an electrical generation load-leveling technique. Air is stored within geologic reservoirs for use during peak demand. Aquifers can store natural gas economically and may be suitable for CAES, but differences in geochemistry, cycling period, temperature and viscosity must be evaluated. Geologic exploration has identified a test site near Pittsfield, Illinois. The reservoir is a gently inclined dome consisting of impervious dolomitic caprock overlying permeable sandstone. The closure is 200 m deep, about 200 m in radius, and 10 m thick. Water discovery pressure is near 1100 kPa. Air will be injected at near ambient temperature and relative humidity of about 5%. Cyclic injections will take place at 50/sup 0/, 100/sup 0/, 150/sup 0/ and 200/sup 0/C, each set lasting three months. Temperature, pressure, liquid water content, relative humidity and withdrawn mineral particles will be monitored and analyzed to enable comparisons of reservoir behavior with numerical and experimental models. Pre- and post-test cores will be compared with respect to chemical composition, mineralogy, microstructure, and physical properties. Data from the field, laboratory, and numerical modeling studies will be integrated to develop comprehensive stability criteria for compressed air energy storage within aquifer type reservoirs.