Effects of gas components, reservoir property and pore structure of shale gas reservoir on the competitive adsorption behavior of CO2 and CH4

CO 2 injection into shale gas reservoirs is deemed as a potential scheme to enhance CH 4 recovery and achieve the ambition of carbon neutral. The insufficient research of binary gas competitive adsorption behavior at in-situ conditions of shale gas reservoirs, and the coupling control of gas components, shale properties, and pore structure on CO 2 adsorption affinity limit its general application. Therefore, the competitive adsorption behavior of CO 2 and CH 4 at in-situ conditions is simulated using high-pressure multi-component adsorption experiments, and the effects of binary gas components, shale properties and pore structure on CO 2 adsorption affinity are discussed. Subsequently, the mathematical and geological models of CO 2 injection into Longmaxi shale gas reservoir enhancing CH 4 recovery and achieving carbon sequestration are established based on experimental parameters and reservoir geological parameters, and the feasibility and expectation benefits are discussed. The results exhibit that selectivity coefficient of CO 2 relative to CH 4 (Sc) decreases with higher CO 2 mole fraction, whereas it increases with higher total organic carbon content (TOC) and clay content. Both pore volume (PV) and specific surface area (SSA) have clear positive correlations with Sc. Overall, TOC is a crucial controlling factor of pore structure and adsorption capacity of shale, further, affects the adsorption affinity of CO 2 . The injection of CO 2 into shale gas reservoir shows a promising application prospect in improving CH 4 recovery and carbon emission reduction in geological and mathematical models, and the leakage risk is low after CO 2 sequestration. • Adsorption affinity is controlled by feed gas composition and shale property. • Sc are coupling affected by TOC, clay content, and pore structure parameters. • Ultra-micropores dominate pore volume and specific surface area of micropores. • EGR-CCS has a promising application prospect.