Pressure relief gas drainage by directional drilling hydraulic fracturing in hard roof

Aiming at the difficult problems of gas prevention and control in hard roof fully mechanized caving face of extra thick coal seam in Jiaoping mining area, the roof directional long borehole staged hydraulic fracturing technology was proposed, and the 2305 fully mechanized caving face of Shaanxi Cuijiagou Energy Co., Ltd. was taken as the object for engineering application research. Three directional long boreholes were drilled on site, with the maximum single hole length of 602 m. Three directional long boreholes were hydraulically fractured by backward staged fracturing technology. The cumulative injection volume was 983.1 m³, the total fracturing time was 5 231 min, and the maximum peak pressure of single section was 37.5 MPa. The results show that, after hydraulic fracturing of the roof directional long borehole, the first weighting step of working face is shortened by 29.37%, the average concentration and purity of directional long borehole gas drainage are increased by 1.92 times and 1.57 times respectively, the concentration and purity of pre-drainage gas in this coal seam area are increased by 1.79 times and 2.01 times respectively, and the absolute gas emission is reduced by 19.9% in the initial mining and initial discharge stage. Roof directional long borehole staged hydraulic fracturing technology reduces the integrity of hard roof, increases the development degree of top coal and surrounding rock fractures, broadens the gas migration channel, and improves the effect of pressure relief gas drainage through accurate pre-splitting of high pressure water, and provides technical support for gas control in Jiaoping mining area under similar geological conditions.