Experimental research on supercritical CO2 true triaxial pneumatic fracturing

Abstract The application of supercritical CO 2 pneumatic fracturing technology to the development of shale gas and coalbed methane was explored. Experimental tests were conducted using the first true triaxial SC-CO 2 pneumatic fracturing experimental system, and the effects of initial air pressure and energy-accumulation agent dosage on pressure changes and the initiation and propagation of fracturing were studied. Through the analysis of the pressure curve, it is found that, at a certain volume, the efficiency of reaction pressurisation can be improved by appropriately increasing the amount of accumulator and increasing the initial air pressure; compared with hydraulic fracturing and SC-CO 2 fracturing, the process of pneumatic fracturing is more similar to that of blasting in rock. The reverse tensile stress wave generated in the process of pneumatic fracturing is the cause of the annular cracks; the cracks on the surface of the sample after the cracking exhibit fractal characteristics, with a good linear fit between the fractal dimension Fd and the damage variable w, as defined by the cracked area. Since the fractal dimension can better describe the complexity of the crack, using the fractal dimension as the damage variable can better describe the degree of damage. The research provides a reference for the engineering problem of the new waterless fracturing technique of SC-CO 2 pneumatic fracturing in shale gas production.