Numerical simulation of CO2 sequestration in shale gas reservoirs at reservoir scale coupled with enhanced gas recovery

Shale gas resources are very important unconventional fossil fuel resources. Due to the competitive adsorption relationship between CO2 and CH4, carbon capture and sequestration in shale gas reservoirs provide an opportunity to use CO2 for enhanced gas recovery while providing access to CH4. To evaluate the CO2 sequestration and enhanced gas recovery (CO2-EGR), we developed a model that takes into account all the major contributing mechanisms of shale gas dynamics, including viscous flow, gas slippage, Knudsen diffusion, competitive adsorption of different components, and real gas effects. The modeled CO2-EGR system consisted of two CO2 injection wells and a production well. The feasibility of CO2 sequestration and enhanced gas recovery was studied by numerical simulations, and the responses of a shale gas reservoir to the reservoir pressure, temperature, and inherent permeability were analyzed. The results showed that the formation temperature, mean pore size, and injection rate were the most important factors affecting the CO2-EGR. Of the injected CO2, 45%–60% could be sequestered in the shale reservoir, of which about 63% was sequestered in an adsorbed state, while providing 10%–15% incremental gas recovery.