脉冲射流割缝控制压裂技术关键参数研究及应用

为解决常规水压裂缝受地应力影响，导致扩展形态单一、易在裂缝两侧遗留增透空白带等问题，结合脉冲射流破煤岩特点与缝槽-孔隙水压联合诱导裂缝定向扩展作用，研究了煤矿井下脉冲射流割缝控制压裂技术。通过冲击应力波效应分析了脉冲射流充分利用水锤压力高效破碎煤体割缝机理，阐明了脉冲射流割缝控制压裂大幅增加煤层透气性原理，明晰了脉冲射流割缝压力、割缝控制压裂实施压力和压裂钻孔封孔长度等关键参数，探讨了割缝控制压裂技术的工艺流程，并在逢春煤矿开展了割缝控制压裂、常规压裂和钻孔抽采三种现场试验，对比考察了三种方式的煤层瓦斯抽采效果。现场试验结果表明：由于缝槽卸压和孔隙压力场的存在，脉冲射流割缝控制压裂能降低煤层压裂时的实施压力|通过分析压裂后不同距离煤体瓦斯含量和含水率变化规律，得出割缝控制压裂技术比常规压裂的影响范围更远，提高约33%|煤层实施割缝控制压裂后单孔瓦斯抽采纯量为0.034m/min，较常规压裂和传统钻孔抽采技术提高了3.7倍和10.6倍，瓦斯抽采汇总浓度约为73%，提高了1.7倍和2.25倍。

Research on key technical parameters of control fracturing with pulse jet slotting and its application

Crack propagation for conventional hydraulic fracturing is affected by in-situ stress,which leads to single expansion form and the blank zone of permeability enhancement on both sides of crack.The control fracturing technology with pulse jet slotting was studied for underground coal mine by considering the high rock-breaking efficiency of pulse jet and the induce effect of slot and pore water pressure.Through analyzing the impact stress wave effect,the rock-breaking and slotting mechanism of pulse jet is revealed which fully uses the water-hammer pressure.The principle of control fracturing with pulse jet slotting to significantly improve the coal seam permeability was clarified.The key technical parameters,including jet slotting pressure,implementation pressure of control fracturing,and sealing length of the fracturing hole,were theoretically investigated.And the technological process of control fracturing with pulse jet slotting was discussed.Next,the three field tests of control fracturing,conventional fracturing and traditional borehole extraction,were carried out in Fengchun Coal Mine.And the gas extraction effects of three kinds of technologies were compared and analyzed.The results show that the control fracturing with pulse jet slotting can reduce the pressure of coal seam fracturing due to the pressure relief and pore pressure field.Through analyzing the change rules of gas content and water content of coal at different distances after fracturing,it was concluded that the influence range of control fracturing technology was widened about 33%beyond the conventional fracturing.The gas extraction quantity of single borehole was 0.034 m³/min and the gas extraction concentration was about 73%after the control fracturing,the extraction quantity was 3.7 times and 10.6 times higher and the concentration was 1.7 times and 2.25 times higher than those of the conventional hydraulic fracturing and traditional borehole extraction.