Aiming at the general poor gas drainage effect of coal seams with low permeability in China, the paper put forward the technical measures of hydraulic fracturing for permeability improvement through large-diameter long boreholes, the mechanism of permeability improvement by hydraulic fracturing in long boreholes was dis-cussed, and gas drainage test using hydraulic fracturing in coal seams in underground coal mines was carried out. On the basis of successful drilling of long boreholes along coal seams, a rapid sealing tool assembly suitable for underground hydraulic fracturing operation was developed. The change law of parameters during fracturing was analyzed, the method for evaluation of the influence range of hydraulic fracturing, the effect of hydraulic fracturing and gas drainage was put forward, investigated and assessed. The research indicated that the technology had over-came the problems existing generally in traditional underground hydraulic fracturing, such as poor hole-sealing quality and small influence range of fracturing. After fracturing, the permeability coefficient of seam increased by 2.67 times, the maximum influence range of fracturing reached 58 m, during 130 d totally 31.39×104m3 pure gas was drained with the maximum daily extraction of 2668 m3 and the mean gas volume fraction of 70.05%, the drained pure gas quantity of 100 m of borehole was up to 0.55 m3/min.%针对我国低透气性煤层普遍存在瓦斯抽采效果差的现状,提出了利用大直径长钻孔水力压裂对煤层进行增透的技术措施,探讨了长钻孔水力压裂增透机理,并进行了煤矿井下煤层水力压裂瓦斯抽采试验.在成功施工顺层长钻孔的基础上,研发了一套适合井下水力压裂施工的快速封孔工具组合,分析了压裂过程中参数变化规律,提出了水力压裂影响范围、压裂效果和瓦斯抽采效果评价方法,并进行了考察和评价.研究表明:该技术克服了传统井下水力压裂存在的封孔质量差、压裂影响范围小等问题,压裂后煤层透气性系数提高了2.67倍,压裂最大影响半径达到了58 m,压裂后连续抽采130 d累计抽采纯瓦斯量为31.39万m3,日最高抽采量2668 m3,瓦斯体积分数平均70.05%,百米钻孔瓦斯抽采纯量达到0.55 m3/min.
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