Study on the mechanism of CO2 injection to improve tight sandstone gas recovery

Abstract

Supercritical CO2 can improve gas recovery and achieve carbon sequestration in tight gas reservoir. It is a hot topic but not applied extensively. The main restricts include the unclear mechanism of gas-to-gas displacement and the reduction of the natural gas asset value due to CO2 breakthrough. In this paper, a novel experimental method is used, through constant-volume and constant-pressure experiments, to analyze the mixing process of CO2 and natural gas in different parts of vessel. 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 and input into the numerical model. The 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 verifies the technical feasibility of CO2 flooding in tight gas reservoirs.

Keywords

• CO2 flooding
• Gas reservoir
• Enhanced gas recovery
• Numerical simulation