Study on the Mechanism of Co2 Injection to Improve Tight Sandstone Gas Recovery

Supercritical CO2 can improve gas recovery and achieve carbon sequestration in tight gas reservoir. It is a cutting-edge topic, not applied in large scale. The main restricts include the unclear mechanism of gas-to-gas displacement and reduction the value of the natural gas asset due to CO2 breakthrough. In this paper, a novel experimental method is used to analyze the mixing process of CO2 and natural gas in different parts of vessel through constant-volume and constant-pressure experiments. Moreover, the mechanism and impact factors of natural gas displaced by supercritical CO2 are demonstrated in laboratory and numerical simulation. Based on the experiments, the diffusion coefficient of CO2 in natural gas (CH4) is measured to input into the numerical model. This results show that supercritical CO2 in the reservoir is ‘partially miscible’ with the natural gas. CO2 displaces CH4 to move upward due to the gravity differentiation, and CH4 is produced in the process of CO2-subsidence. CO2 flooding can enhance gas recovery by 18%, which means the technical feasibility of CO2 flooding in tight gas reservoirs