Controlling parameters of CH4 and CO2 adsorption on shale—a review

Adsorption is the principal gas storage mechanism in shale, and detailed knowledge of the adsorption behaviour is crucial for successful shale gas production. CO2 and CH4 exhibit distinct and different adsorption behaviour on shale. The various geochemical and geophysical parameters of shale like organic and inorganic content; moisture content; kerogen type; thermal maturity; pore size and shape, connectivity; temperature and pressure; adsorbate molecular size, structure, and mixed gas compositions influence the adsorption behaviour significantly. A higher quantity of organic and inorganic contents enhances the adsorption capacity by providing more active sites. Moisture affects the adsorption process by blocking the pores and affecting the transport of gas molecules. Capillary condensation can enhance the gas adsorption capacity by several times. Compared to CH4, higher and preferential adsorption is observed for CO2 due to its smaller molecular size and linear structure. The current article presents a concise review of the distinct adsorption behaviour of CO2 and CH4 gases on the porous shale matrix. The various geological and physical parameters influencing the adsorption characteristics are also comprehensively discussed.