Variation law of roof stress and permeability enhancement effect of repeated hydraulic fracturing in low‐permeability coal seam

AbstractHydraulic fracturing experiments were conducted to study the change of initial fracture pressure and roof stress under repeated hydraulic fracturing in coal mines and to investigate the actual penetration enhancement effect on coal seams. The results show that as the fracturing is repeated, a lower initiation pressure is required. The roof stress changes consistently with water injection pressure. First, the stress in the area around the water injection hole gradually increases, and then stress transfers to the surroundings. With the re‐implementation of fracturing, the area of increased stress expands, and the scope of influence of hydraulic fracturing also becomes larger. When fracturing in a coal mine, for the same total fracturing time, the total water injection volume of repeated fracturing is 35% higher than that of single fracturing, and the affected area is increased by 31%. The concentration of repeated hydraulic fracturing is about 36% higher than that of a single hydraulic fracturing, and the pure flow of gas drainage is increased by about 1.3 times. The results of this study can guide the efficient implementation of hydraulic fracturing underground in coal mines, so as to achieve a larger impact range of coal seam hydraulic fracturing and better gas drainage effects.