Field testing and fracturing mechanism of coal seam fracturing driven by high-pressure gas combustion

A combustion-driven high-pressure air fracturing apparatus was researched and developed to address the challenges of pressurising high-pressure gas. The apparatus underwent pressure testing and simulated sample experiments, subsequently implementing underground fracturing operations in coal mines while concurrently conducting microseismic monitoring. The main results were: (1) As the depressurisation pressure increased, the rate of decline in wellbore pressure was reduced. When the depressurisation pressure reached 40 MPa, the rate of decline stabilised at approximately 6%. (2) The combustion system boosted pressure from an initial 40.38 to 155.38 MPa, subsequently dropping to zero megapascals upon instantaneous release. (3) Field testing indicated an effective radius of 5–10 m for the initial pre-cracking effect and 7–12 m for subsequent operations, both enhancing gas desorption and increasing methane concentration within the reflux channels. (4) A high-pressure air–water coupled coal-rock fracturing model was established, analysing the fluid–solid–thermal coupling mechanism throughout the fracturing process.