Process Modeling of CO2 Injection into Natural Gas Reservoirs for Carbon Sequestration and Enhanced Gas Recovery

Injection of CO2 into depleted natural gas reservoirs offers the potential to sequester carbon while simultaneously enhancing CH4 recovery. Enhanced CH4 recovery can partially offset the costs of CO2 injection. With the goal of analyzing the feasibility of carbon sequestration with enhanced gas recovery (CSEGR), we are investigating the physical processes associated with injecting CO2 into natural gas reservoirs. The properties of natural gas reservoirs and CO2 and CH4 appear to favor CSEGR. To simulate the processes of CSEGR, a module for the TOUGH2 reservoir simulator that includes water, brine, CO2, tracer, and CH4 in nonisothermal conditions has been developed. Simulations based on the Rio Vista Gas Field in the Central Valley of California are used to test the feasibility of CSEGR using CO2 separated from flue gas generated by the 680 MW Antioch gas-fired power plant. Model results show that CO2 injection allows additional CH4 to be produced during and after CO2 injection.