Review of Competitive Adsorption of CO2/CH4 in Shale: Implications for CO2 Sequestration and Enhancing Shale Gas Recovery

The injection of CO2 into shale gas reservoirs can not only enhance shale gas recovery (ESGR), but also realize CO2 geological storage (CGS). In this study, the competitive adsorption behaviors of CO2 and CH4 in shale were systematically reviewed, and the implication for shale gas recovery efficiency and CO2 storage potential were discussed. The adsorption advantage of shale for CO2 compared to CH4 provides a guarantee of the feasibility of supercritical CO2 (ScCO2) enhanced shale gas exploitation technology. The selective adsorption coefficient of CO2 and CH4 by shale (S CO2/CH4 ) is an important parameter in evaluating the competitive adsorption behavior of CO2/CH4 in shale gas reservoirs, which is closely related to the mineral composition, reservoir temperature, pressure conditions, water content, and mixed gas composition ratio. In addition, the injection type, injection mode, and injection rate of gases also exhibit different effects on CO2/CH4 competitive adsorption. Furthermore, the interaction between ScCO2 and the water-rock system will change the mineral composition and microstructure of shale, which will lead to changes in the adsorption behavior of shale on CO2 and CH4, so its influence on the competitive adsorption of CO2/CH4 cannot be ignored. Future research should integrate different research methods and combine with practical engineering to reveal the competitive adsorption mechanism of CO2/CH4 in shale reservoirs from both micro and macro aspects. This study can provide support for the integration technology of ScCO2 enhanced shale gas exploitation and its geological storage.