煤矿井下水力压裂中经常出现裂缝扩展无序、闭合快等现象,导致裂缝导流能力较差,无法实现瓦斯的高效抽采。针对此问题,提出采用水射流射孔强化裂缝导流能力的方法,即采用高压水射流在煤孔段垂直于钻孔轴向射孔。采用FLAC3D分析了射孔周边煤体应力分布,结果表明,射孔尖端处存在耳状塑性区。根据最大主应力的准则判断,塑性区的存在可促使裂缝在射孔尖端处起裂。采用RFPA2D-Flow分析了不同水平应力组合下的裂缝扩展特性,结果表明,裂缝在射孔尖端处起裂后,在塑性区内沿水平方向延伸,然后平行于最大水平主应力方向延伸。视压裂裂缝面为粗糙面,基于Y模型分析了裂缝面微凸体分布规律。采用Hertz接触理论研究了两缝面单个微凸体接触受力状态,得出压裂裂缝面微凸体受力与裂缝闭合量呈正指数关系。基于N-S方程分析了真实压裂裂缝内瓦斯渗流速度分布,得出了煤岩体裂缝中瓦斯流量与裂缝面高度成立方关系。对比分析得出,射孔煤体周边应力明显小于不射孔煤体周边应力。通过以上分析得出,射孔导向裂缝在煤层中有序扩展,降低了煤岩体有效应力,减小了压裂裂缝的闭合量,实现了瓦斯长时高效抽放。 In coal-mine hydraulic fracturing, cracks often appear to be disordered and closed quickly, which leads to poor ability of guiding the fractures and can not achieve efficient gas drainage. In response to this problem, a method of using water jet perforation to enhance fracture conductivity is proposed, that is, a high-pressure water jet is used to perforating the coal perforation perpendicular to the axial direction of the hole. The FLAC3D was used to analyze the stress distribution around the perforations. The results show that there are ear plastic zones at the tip of perforation. Judging from the criterion of maximum principal stress, the existence of plastic zone can promote the initiation of cracks in the tip of perforation. The fracture propagation characteristics under different horizontal stress combinations were analyzed by RFPA2D-Flow. The results show that the fracture propagates along the horizontal direction within the plastic zone and then extends parallel to the direction of the maximum horizontal principal stress. Depending on the Y-model, the distribution of asperity on the fracture surface is analyzed. The Hertz contact theory was used to study the contact force of single asperity with two slits. It was found that the stress of the asperity of fracturing face was positively exponential relationship with the crack closing amount. Based on the N-S equation, the gas velocity distribution in the real fracturing fissure is analyzed, and the cubic relationship between the gas flow and the height of fracture surface in coal and rock fracture is obtained. The comparative analysis shows that the perimeter stress of perforation coal is obviously smaller than the perimeter stress of non-perforation coal. Through the above analysis, it is concluded that the perforation-oriented fractures are expanded in the coal seam in an orderly manner, reducing the effective stress of the coal and rock mass, reducing the closing amount of fractures and achieving long-term and high-efficiency gas drainage.