中文摘要：

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。

英文摘要：

This paper aims to bring about a novel method for strengthening the fracture conductivity by the water jet perforation by using highpressure water jet to make it perpendicular to the drilling axial in coal seam. In this paper, we have first of all analyzed the stress distribution of the coal seam around the perforation via the FLAC3D, and the results prove that the two plastic earshaped zones would be coming up at the both ends of perforation. Based on the maximum principal stress regulation, the presence of plastic zones may lead to the fracture initiation. And, then, we have analyzed the expansibility features of the said fracture under various stresses via software known as the RFPA2D Flow. The result of the analysis may indicate that after the comingup of the tip of perforation, the fracture tends to be expanding horizontally in the plastic zone and eventually turning parallel in the direction of the max horizontal principal stress. Assuming that the fractures were to be roughsurfaced, and based on model Y, it would be possible for us to carry out the analysis of the regularity of distribution of the asperities on the rough fractured sur face. At the same time, we have also applied the Hertz Contact The ory to disclose the stress state of a single asperity when the asperities were made to contact. What＇ s more, we have also made clear the exponential relationship between the stress state of asperity and the fracture width. And, now, we have to study the flow velocity of the coalgas through N S equation in the fracture and make out the rela tionship between the gas flow and the fracture width in a cubical man ner. And, last of all, a comparative analysis of the stress distribution with or without perforation helps us to confirm that the stress of the coal seam with the perforation proves to be much lower than that with out the perforation. Therefore, summing up the above facts, it can be concluded that the perforation oriented to the fracture propagation to wards the coal seam tends to decrease the effecti