The invention provides a drilling
methane self-circulation blasting fracturing enhanced extraction method which is suitable for efficient extraction of
coal mine underground gas. The method comprises the steps that firstly, a gas extraction
drill hole, a blasting fracturing
drill hole and a guide hole are constructed in a
coal seam; then a gas extraction
pipe and a gas injection
pipe are placed into the gas extraction
drill hole and the blasting fracturing
drill hole correspondingly and sealed; extracted gas is premixed into
mixed gas with the concentration being 9% to 10% through an extraction pump, a filtering device and a
gas mixing chamber, and the
mixed gas is injected into the blasting fracturing
drill hole through the gas injection
pipe after passing through a gas
storage tank and a
booster pump; an ignition device is started to induce
methane blasting fracturing, high-temperature and high-pressure shock
waves generated by blasting are guided to crack the
coal seam to generate a directional fracture network, meanwhile,
methane desorption is promoted through the high temperature, and the methane concentration of the gas extraction hole and the methane concentration of the blasting fracturing hole are both greatly increased; and finally, gas extraction is synchronously conducted on the gas extraction hole and the blasting fracturing hole. According to the method, the coal seam is utilized for in-situ methane
desorption blasting to construct the three-dimensional fracture network, and the methane extraction efficiency can be remarkably improved.