Molecular Insights into CO₂-Rich Industrial Waste Gas Enhanced Shale Gas Recovery and Sequestration in Real Shale Gas Reservoirs

Abstract

In response to the current carbon-neutral policy, the appropriate utilization and sequestration of CO 2 -rich industrial waste gases have become a key concern in greenhouse gas management. In this work, the application of CO 2 -rich industrial waste gas for shale gas displacement and the feasibility of shale gas reservoirs as a site for CO 2rich industrial waste gas sequestration was investigated from the molecular-scale. In order to restore the extensive pore structure and complex composition of shale reservoirs, three shale slit models were developed based on the Longmaxi shale formation in Sichuan, China, with the compositions of quartz-kerogen (QK), illite-kerogen (IK), and calcite-kerogen (CK). The CH 4 displacement effect by each gas component injection in the shale slits under real reservoir conditions were studied. The results show that the gas adsorption capacities in all shale slits are ranked as SO 2 > CO 2 > NO > N 2 ≈ CH 4 > CO in the pressure range of 0.5−30 MPa. Triatomic gas molecules, including SO 2 and CO 2 , have larger molecular diameters and more intense competitive adsorption between molecules, leading to a decrease in the CH 4 displacement effect with reservoir depth. CO 2 -rich industrial waste gas in depleted shale gas reservoirs at varied water contents was investigated. It was found that an increase in water content from 0% to 4 wt % led to a decrease in CO 2 sequestration capacity and relative stability ratio of 0.52 mmol/g and 0.068, respectively, at a depth of 2 km in IK slit. The QK slit is ideal for large quantities of nontoxic exhaust gas sequestration, whereas the CK slit is suitable as a site for sequestering CO 2 -rich industrial waste gas with a relatively high level of hazardous gas. This study provides deep insights into the mechanisms of competitive adsorption and sequestration in shale slits, which is instructive for CO 2 -rich industrial waste gas enhanced recovery of shale gas and sequestration.