Basin analysis and aqueous chemistry of fluids in the Oriskany Sandstone, Appalachian Basin, USA

The Oriskany Sandstone of the Appalachian basin is a widely distributed saline aquifer which has produced large quantities of hydrocarbons. Currently the Oriskany is host to numerous gas storage fields and is a potential target for large-scale geologic storage of CO2. Published and unpublished data of rock characteristics, pressure, temperature, and formation water geochemistry, along with new brine samples were integrated within a geographical information system to better understand the regional-scale hydrogeological regime and its relation to geologic CO2 sequestration potential. The up-dip flow of the Oriskany Sandstone formation waters is generally controlled by outcrops at high elevation to the east and at low elevation to the west, and opposed by increased salinity-induced buoyancy forces down-dip. The flow pattern is substantiated by the salinity distributions, with relatively lower salinity at recharge to the east and west due to mixing with fresh meteoric water and higher salinity at depth. The Oriskany is generally underpressured, which would aid in sequestering CO2 by lowering injection and displacement pressures. The geothermal gradient for the Appalachain basin, approximately 20°C/km, is lower than what is expected for cratonic rocks. This could lower the potential for and relative speed of CO2 migration. Large variations in brine geochemistry, temperature, and pressure will have a major influence on potential for long-term entrapment of CO2 in the Oriskany Sandstone.