Practice of gas drainage by hydraulic fracturing of roof pectination boreholes in broken soft coal seam in Hancheng mining area

Broken soft coal seams with poor permeability develop in Hancheng mining area, drilling in the coal seams is difficult, the effect of gas extraction is poor. The hydraulic fracturing technology of pectination boreholes in roof combines the advantages of the two technologies of hydraulic fracturing and directional drilling, it is an effective technical way to solve the problem of gas drainage in broken soft coal seams of low permeability. In Wangfeng coal mine, a long borehole was drilled in the roof siltstone of No. 3 coal seam, and had a branches in coal seams, casing and packer seal were used, hydraulic fracturing engineering test was carried out in the way of integral fracturing. The total length of the borehole was 344 m, the effective fracturing length was 284 m, the accumulative water injection was 874.79 m³, and the maximum pump pressure was 9.4 MPa. After the test, the relevant parameters of borehole gas drainage were continuously monitored for 86 days, the concentration of gas drainage was 27%-51%, 42.11% on average, the pure amount of gas drainage was 8.25-21.41 m³/min, 17.02 m³/min on average, the total amount of gas drainage was about 210×10⁴ m³ by roof long boreholes. Compared with conventional hydraulic punching technology, of gas drainage of 100 meter borehole through this technology increased by 11.48 times, it preliminarily proves the applicability of the technology in the field of enhanced gas drainage in broken soft coal seam.