The invention relates to a method for extracting gas in low air permeability
coal layer by pulse fracture anti-reflection, comprising the following steps: firstly using the blast-proof pulse-type
coal layer
high pressure water
injector with adjustable frequency and pressure from the
coal layer, high tunnel or low tunnel; using the pulse
water effect generated by the periodical change of
high pressure pulse water inside the
drill hole of coal body, wherein the maximum
pulse pressure is 35 MPa, the flow is about 300 L / min, and the
pulse frequency is 0-1460 times / min; forcing the macroscopic fracture in the coal layer to be expanded and communicated; promoting the micro-pore fracture to be formed and extended; forming a new regeneration fracture net; providing a
permeable channel of water inthe coal layer so as to achieve the effects of improving the
mechanical property of the coal body, reducing the stress of the coal body in front of the working face and improving the
discharge rate of the gas. Through the method, the pressure releasing range of the coal layer is enlarged, the whole pressure is adequately released, the
radius of influence range of fracture can reach 10-40 m, and the air permeability of the coal body can be improved by 100-1000 times; and the method is simple, easy to operate and good in effect.