CO2 sequestration coupled with enhanced gas recovery in shale gas reservoirs

Carbon capture and storage in depleted shale gas reservoirs offers an opportunity to utilize CO2 for enhanced gas recovery while providing access to fossil fuels. To evaluate CO2 sequestration coupled with enhanced gas recovery (CO2-EGR), we have developed a model that takes into account all the major contributing mechanisms in shale gas dynamics including viscous flow, gas slippage, Knudsen diffusion, competitive adsorption of different components, pore size variation and real gas effect. The CO2-EGR process is divided into periods of primary production, CO2 injection, soaking and secondary simultaneous production of CO2 along with other natural gas components. Numerical simulations are conducted to study the feasibility of CO2 sequestration and enhanced gas recovery and analyze the response of the shale gas reservoir to input variables including reservoir pressure, temperature and intrinsic permeability. The results show that the stronger adsorption of CO2 over CH4 molecules to shale surface is the main influencing mechanism on CO2 sequestration. It is shown that 30-55% percent of the injected CO2 can be trapped as adsorbed phase in shale while providing 8-16% incremental gas recovery. Comparing trapping efficiency of CO2-EGR with other methods of accelerating CO2 dissolution in deep saline aquifers, adsorbed phase trapping is promising.