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

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 _CO ) 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.