Impact Pressure Characteristics of Carbon Dioxide Phase Transition Fracturing Technique

Carbon dioxide phase transition fracturing (CDPTF) is widely regarded as a promising coal seam mining technique because it can effectively improve coal seam permeability and prevent gas outbursts. An impact pressure test system of CDPTF was developed, and the effects of different factors on impact pressure were investigated by combining CO2 release experiments and smoothed particle hydrodynamics numerical simulation. In addition, based on the Peng–Robinson equation and the pipeline pressure drop formula, new mathematical models for the pressure equation in the buffer tank and the velocity of gaseous CO2 at the nozzle were established. The results show that the impact pressure of CDPTF can be divided into rapid boost, fluctuation, and attenuation stages. The impact distance and impact angle have the most significant effects on pressure. The models of the pressure in the buffer tank and the velocity of gaseous CO2 at the nozzle well-simulated the experimentally obtained impact pressure curves. The research results could provide a reference for the loading study of CDPTF.