Hydraulic 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.

中文翻译：

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低渗透煤层重复水力压裂顶板应力变化规律及增透效果

开展水力压裂试验，研究煤矿反复水力压裂作用下初始破裂压力和顶板应力的变化，考察对煤层的实际增贯效果。结果表明，随着压裂的重复，需要较低的起始压力。顶板应力随注水压力而变化。首先，注水孔周围区域的应力逐渐增大，然后应力向周围转移。随着压裂的重新实施，增加应力的区域扩大，水力压裂的影响范围也变大。煤矿压裂时，在相同的总压裂时间下，重复压裂的总注水量比单次压裂高35%，受影响面积增加了31%。重复水力压裂浓度比单次水力压裂提高约36%，瓦斯抽采纯流量提高约1.3倍。研究结果可以指导煤矿井下水力压裂的高效实施，从而实现更大的煤层水力压裂影响范围和更好的瓦斯抽采效果。