New insights on supercritical CO 2 fracturing coal mass: a staged analysis method

As a water‐less fracturing mining technology, supercritical CO2 fracturing has attracted increasing attention in the mining industry. Based on detailed analysis of CO2 phase behavior in the whole process of supercritical CO2 fracturing, the whole cycle of supercritical CO2 fracturing was divided into the supercritical CO2 fracturing stage and the CO2 phase transition–induced fracturing stage, and according to the characteristics of each fracturing stage, the fracturing mechanism of supercritical CO2 was analyzed in stages, and the roles of the two stages in the life cycle of the entire supercritical CO2 fracturing process were obtained. Through the laboratory test of supercritical CO2 fracturing coal mass, the pressure–time curves during the whole process of supercritical CO2 fluid fracturing were analyzed, and the rationality and correctness of the supercritical CO2 fracturing staged analysis method proposed in this paper were verified. Based on the energy conservation theory and the state function equation of classical thermodynamics, the burst energy of the CO2 phase transition–induced fracturing stage was estimated. By comparing the trinitrotoluene equivalent of phase‐transition energy with the trinitrotoluene amount of explosive explosion, it was proved that the CO2 phase transition–induced fracturing stage was not negligible. The research results of this paper are of considerable significance for the full understanding of the supercritical CO2 fracturing mechanism. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.