煤层瓦斯既是矿井灾害的主要来源，又是优质的清洁能源。钻孔瓦斯抽采是矿井瓦斯治理和煤层气资源开发的主要方式，目前煤层瓦斯抽采钻孔处于“重生不养”阶段，开展钻孔修复技术的研究迫在眉睫。本文基于水射流破岩和射流技术的基本理论，综合理论分析、实验室试验、数值模拟和现场实践等手段深入研究了钻孔水射流修复技术。

在Hoke-Brown强度准则和断裂力学理论的基础上分析了钻孔失稳力学机理，研究了钻孔坍塌堵塞效应对瓦斯抽采的影响，提出了瓦斯抽采钻孔水射流高效修复方法；然后应用水射流破煤理论建立了水射流破煤过程的数学模型，分析了钻孔修复过程中的自驱动力，阐明了钻孔水射流修复增透的作用机理；基于相似原理搭建了钻孔水射流修复物理相似模拟试验平台，研究了修复过程中钻孔孔周和孔底煤体应变时空演化规律；建立了单股水射流冲击煤体的数值模拟模型，研究了水射流荷载作用下煤体的损伤破裂规律；最后应用自主研发的井下移动式瓦斯抽采钻孔水射流修复增透装备开展了瓦斯抽采钻孔水射流修复增透作业实践。结果表明：（1）当射流动压大于煤体破坏强度时，水射流对煤体产生破坏作用，而当射流动压小于煤体破坏强度时，破煤过程终止；水射流的破煤作用一方面扩大钻孔塑性区范围，增加了钻孔的有效瓦斯抽采区域，另一方面使孔周煤体增透率得到了提升，从而增加了煤体的渗透率。（2）水射流不仅对钻孔有着解堵作用，更对孔周煤体有着扩孔增透和射流冲击煤体增透的双重增透机制。（3）在钻孔修复过程中，水射流的扩孔现象是多个射流冲击破碎坑持续性积累的结果；越靠近射流的煤体单元，其损伤越明显；随着煤体与射流的距离增加，煤体损伤程度减小。水射流对钻孔的修复现象是射流长时间冲击煤体累积作用导致的，在现场破煤扩孔作业实践环节中，水射流需要多次冲击钻孔才能实现扩孔目的。（4）通过分析水射流扩孔修复措施钻孔前后的瓦斯抽采数据得出，水射流扩孔修复措施可将瓦斯抽采浓度提升4.4倍，瓦斯抽采纯量提升10倍。该措施显著提高了低透气性煤层瓦斯抽采钻孔在抽采过程中的瓦斯浓度和瓦斯抽采流量。瓦斯抽采钻孔水射流修复增透技术既提升了瓦斯抽采效果又减少了瓦斯抽采达标时间，可有效缓解矿井采掘接替紧张的局面。

Coal seam gas is not only the main source of mine disasters, but also a high-quality clean energy. Borehole gas extraction is the main way of mine gas control and coalbed methane resource development. At present, coal seam gas extraction boreholes are in the stage of " rebirth without maintenance, " and it is urgent to carry out research on borehole repair technology. This paper is based on the basic theory of water jet rock breaking and jet technology. Comprehensive theoretical analysis, laboratory test, numerical simulation and field practice, the drilling water jet repair technology is studied in depth.

On the basis of Hoke-Brown strength criterion and fracture mechanics theory, the mechanical mechanism of borehole instability is analyzed, the influence of borehole collapse and blockage effect on gas extraction is studied, and the efficient repair method of water jet in gas extraction borehole is proposed. Then, the mathematical model of water jet coal breaking process is established by using the theory of water jet coal breaking. The self driving force in the process of borehole repair is analyzed, and the mechanism of borehole water jet repair and permeability enhancement is expounded. Based on the similarity principle, a physical similarity simulation test platform for borehole water jet repair was built. The temporal and spatial evolution law of coal strain around the borehole and at the bottom of the borehole during the repair process was studied. The numerical simulation model of single water jet impacting coal body is established, and the damage and fracture law of coal body under water jet load is studied. Finally, the application of independent research and development of underground mobile gas drainage borehole water jet repair antireflection equipment to carry out the gas drainage borehole water jet repair antireflection operation practice. The results show that : ( 1 ) When the jet flow pressure is greater than the failure strength of the coal body, the water jet has a destructive effect on the coal body, and when the jet flow pressure is less than the failure strength of the coal body, the coal breaking process is terminated. On the one hand, the coal breaking effect of water jet expands the plastic zone of borehole and increases the effective gas extraction area of borehole. On the other hand, the permeability increasing rate of coal body around borehole is improved, thus increasing the permeability of coal body. ( 2 ) The water jet not only has a plugging effect on the borehole, but also has a double antireflection mechanism of reaming and jet impact on the coal body around the hole. ( 3 ) In the process of drilling repair, the reaming phenomenon of water jet is the result of continuous accumulation of multiple jet impact crushing pits. The closer the coal unit to the jet, the more obvious the damage is. With the increase of the distance between the coal and the jet, the damage degree of the coal decreases. The repair phenomenon of water jet to borehole is caused by the cumulative effect of jet impacting coal body for a long time. In the practice of coal breaking and reaming operation on site, water jet needs to impact borehole many times to achieve the purpose of reaming. ( 4 ) By analyzing the gas extraction data before and after the drilling of the water jet reaming repair measures, it is concluded that the water jet reaming repair measures can increase the gas extraction concentration by 4.4 times and the gas extraction purity by 10 times. This measure significantly improves the gas concentration and gas extraction flow during the extraction process of gas extraction boreholes in low permeability coal seams. The water jet repair and permeability improvement technology of gas extraction borehole not only improves the gas extraction effect but also reduces the time of gas extraction reaching the standard, which can effectively alleviate the tension of mine mining replacement.

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