A review of microscopic seepage mechanism for shale gas extracted by supercritical CO2 flooding.

Graphical abstract Highlights • Shale gas microscopic seepage mechanism under supercritical CO 2 condition is reviewed. • Adsorption potential theory provides a method for predicting shale gas production. • Desorption model needs to be considered simultaneously due to the hysteresis. • The diffusion between CO 2 and CH 4 should be considered in supercritical CO 2 mining. • Multi-component and multi-field coupling is a challenge for further research. Abstract Shale gas exploitation with supercritical CO 2 is a promising technology that not only improve gas recovery but also achieve geological storage of CO 2. This paper presents the research status of shale gas seepage mechanism under supercritical CO 2 conditions from several aspects including the adsorption and desorption of gas, the competitive adsorption of CO 2 and CH 4 , the multi-scale spatial gas mass transfer process and the shale gas seepage mechanism under multi-field coupling. Adsorption potential theory provides a method for predicting the real shale reservoir adsorption capacity under supercritical conditions. The desorption model needs to be considered simultaneously due to the existence of hysteresis. The adsorption selectivity of CO 2 /CH 4 is always greater than 1, and there is an optimal selectivity coefficient to optimize the in-situ process conditions. For the competitive adsorption mechanism, the reason why CO 2 adsorption capacity of shale is stronger than that of CH 4 is explained in terms of kinetic diameter, critical temperature, molecular polarity and diffusion rate. The interaction between CO 2 and CH 4 will make the shale gas seepage mechanism more complex, so further research is needed on the mass transfer process involving multi-component gas. The changes in reservoir physical properties after supercritical CO 2 fracturing, the mathematical model of multi-field fully coupled gas microscopic seepage and the universal stress-sensitive model are the focus of future research. [ABSTRACT FROM AUTHOR]