Mechanism of Enhanced Gas Recovery and Carbon Storage Capacity in Gas Reservoirs With CO2 Injection: An Example of Dongfang Gas Field

Abstract

China's Yinggehai Basin gas field is in the middle and late stages of development and has a large CO2 sequestration potential. Moreover, the gas recovery is low, and it can be further enhanced by injecting CO2. In order to study the recovery ratio of the gas field and realize CO2 storage, numerical simulation studies were carried out on three types of gas reservoirs in Dongfang A gas field, including hypotonic, mesotonic depletion, and mesotonic water intrusion. The results show that: (1) competitive adsorption improves CO2 storage and CH4 recovery in low-permeability gas reservoirs; CO2 injection can effectively supplement the formation energy, and competitive adsorption and pressurization are the main controlling factors for the development of low-permeability gas reservoirs; (2) the recovery mechanism of medium permeability depleted gas reservoirs is to improve pressure and energy. Adsorption has almost no effect on methane recovery and cumulative production, and gas injection rate and gas injection components are the main controlling factors affecting CO2 sequestration; (3) CO2 injection in medium-permeability water intrusion gas reservoirs can inhibit water intrusion. The higher the injection–production ratio, the better the effect of inhibiting water intrusion. CO2 should be injected into the gas layer in the process of gas injection development, and the injection-production ratio and the gas injection components are the main controlling factors to improve CO2 storage. It is concluded that CO2 injection can improve pressure and energy, inhibit water intrusion, enhance gas recovery, and realize carbon sequestration, which makes CCUS-EGR expected to be a potential technology for the stable and increased natural gas production in the Yinggehai Basin and provides a theoretical basis for the further development of the integrated technology of gas injection, recovery, and sequestration.