Study on gas drainage effect of hydraulic fracturing in soft coal seam

Aiming at the difficulty of gas drainage by drilling along the seam in soft coal seam, the permeability of coal seam was increased by hydraulic fracturing test in the field, and the permeability and gas drainage parameters of coal seam before and after fracturing were studied. The results show that: (1) The fracture initiation pressure of 3# coal seam in Guojiahe coal mine is 15 similar to 20MPa. When the water injection is 30 similar to 40m(3), the fracturing radius is 15m, when the water injection is 50 similar to 60m(3), the fracturing radius can reach 20m, when the water injection reaches 70m(3), the fracturing radius can reach 30m; (2) Driven by high pressure water, the gas in the fractured area migrates to the unfractured area, and the gas content in the fractured area decreases; (3) The attenuation coefficient of natural gas flow after fracturing is reduced by 50% compared with that before fracturing, and the permeability coefficient of coal seam after fracturing is increased by 50 times compared with that of original area; (4) The recovery concentration after fracturing is much higher than that before fracturing.