Abstract: In order to solve the problem of how to efficiently extract the coal seam with low permeability, the hydraulic measures of stimulation fracturing through strata borehole has been adopted to improve the permeability of coal seam. The gas migration process through borehole in the hydraulic enhanced technology has been analyzed. The effect of hydraulic reinforcement measures on hard and soft coal seam permeability has been studied, and the effect and mechanism of hydraulic reinforcement on the permeability of coal mass has been analyzed, and finally, the field experiment of hydraulic fracturing has been carried out. Research results show that the hydraulic measures of stimulation fracturing through strata borehole technology can improve the permeability of coal seam and contribute to form gas flow channel. There is “virtual reservoir” in roof and floor in hard coal seam and the gas shows seepage mainly, while, in soft coal seam gas shows diffusion migration mainly. The hydraulic measures of stimulation fracturing can increase the permeability of coal seam through formation of cave and cracks in it, release ground stress and reduce gas flow attenuation coefficient, and consequently improve efficiency of the gas drainage. By using hydraulic fracturing measures in coal seam the pure quantity of gas drainage increases from 14.8 m3 to 31.9-42.8 m3; the gas concentration increases from 14.1% to 73.9%-77.5%. This technology has very wide popularization and application prospects.

Key words: stimulation fracture, hydraulic reinforcement, gas permeability