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

Abstract

CO2 injection into shale gas reservoirs is deemed as a potential scheme to enhance CH4 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 CO2 adsorption affinity limit its general application. Therefore, the competitive adsorption behavior of CO2 and CH4 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 CO2 adsorption affinity are discussed. Subsequently, the mathematical and geological models of CO2 injection into Longmaxi shale gas reservoir enhancing CH4 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 CO2 relative to CH4 (Sc) decreases with higher CO2 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 CO2. The injection of CO2 into shale gas reservoir shows a promising application prospect in improving CH4 recovery and carbon emission reduction in geological and mathematical models, and the leakage risk is low after CO2 sequestration.