Comprehensive Optimization of CO2 Sequestration and Gas Recovery in China Offshore Depleted Gas Reservoir

A large number of CO2 rich gas reservoirs have been explored and developed in the South China Sea, which poses significant pressure to reduce emissions during natural gas export and terminal processing; at the same time, there are many depleted high hydrocarbon natural gas reservoirs in the vicinity that have entered the near-depleted stage of development with recovery over 75% and pressure below 5 MPa. In view of above issues, it’s necessary to study the feasibility of CO2-flooding for enhanced gas recovery in target depleted gas reservoirs. At the same time, it could explore new paths for the offshore sequestration for coastal land CO2 emission sources. In this study, we perform a systematic analysis through integrating reservoir engineering, phase behavior analysis and reservoir simulation for the mechanisms and impacts of the CO2 injection for EGR and storage based on actual depleted gas field data. The key technologies such as the CO2 injection time and injection model in near-depleted gas reservoirs, the influence of impurity gas on CO2 flooding, and the control technology for dispersion-mixing of CO2 into natural gas were investigated; finally, the design and optimization of the CO2 flooding scheme in IIU gas reservoir were conducted, which could increase the gas recovery by 9.9% with sequestration about 20 million tons of CO2 in target gas reservoir. Above research could provide valuable technical support for the research on EGR technologies and carbon neutralization research in offshore depleted gas reservoirs.