深部复杂煤层树状压裂网络化造缝均匀增透机理

Increasing the permeability of coal seam is the fundamental guarantee for the safe exploitation of coal and the efficient development of coalbed methane in deep coal seam. Due to the traditional hydraulic fracturing prone to a single crack and damage the roof and floor of the coal seam, resulting in the existence of “blank area” and support difficulties of roof and floor in the follow-up coal mining and other issues, the applicant proposed a new method of tree-type hydraulic fracturing network uniform. It is necessary for this method to solve the key scientific problems of “mechanism of mesh expansion and gas seepage of tree-type hydraulic fracturing in deep complicated coal seams ". Based on the study of the multiple fields coupling macro, micro-characterization and stress-fracture field evolution of deep coal-rock mass, this project builds a multiple field and multiphase coupled coal-rock seepage - stress and damage coupling model. And compared with broken evolution law under water jet in the homogeneous and heterogeneous, deep and shallow of coal and rock mass, the purpose aims at revealing the mechanism of damage and instability of coal and rock. Through the similarly physical simulation experiment in the laboratory, the fracture mechanics and damage mechanics are used to reveal the crack initiation and expansion law of the fractured crack in the deep complex coal seam. Analyze the gas migration and enrichment mechanism of coal seam under multi-field and multiphase coupling, and predict the gas enrichment area, which provides strong basic theoretical support for the technology and process of tree-type hydraulic fracturing.

大幅增强煤层透气性是我国深部复杂煤层煤炭安全开采和煤层气高效开发的根本保证。由于传统水力压裂易出现单一裂缝及损伤煤层顶底板，导致增透存在盲区及后续煤炭开采时顶底板支护困难等问题，申请人提出树状压裂网络化造缝均匀增透的新方法。针对该方法亟需解决“深部煤岩树状压裂导控裂纹网状扩展及均匀增透机理”的关键科学问题，本项目拟在研究深部煤岩体多场耦合宏、细观表征及应力-裂隙场演化规律的基础上，建立深部多场耦合煤岩多相渗流-应力-损伤耦合模型；对比分析深部与浅部、均质与非均质煤岩体水射流破碎演化规律，揭示水射流冲击深部煤岩体损伤与失稳破碎机理；通过实验室物理相似模拟实验，运用断裂力学、损伤力学等揭示深部复杂煤层树状压裂裂纹网状起裂及扩展规律；分析多场、多相耦合作用下煤层瓦斯运移及富集机理，预测出瓦斯富集区，为树状压裂高效增透技术及工艺提供有力的基础理论支撑。

大范围均匀增透煤层是我国煤层气高效开发和煤炭安全生产的重大需求，因此项目提出了树状压裂增透煤层方法。针对树状压裂导控裂纹网状扩展及均匀增透机理这一关键科学问题，开展了注气驱水以及加注条件下煤的孔隙结构演化规律研究，揭示了深部煤岩体在多场耦合条件下孔隙结构发生破裂、闭合、重组的孔隙演化规律。进行了水射流破碎深部及非均质煤岩体实验，发现射流破深部煤岩以压剪破坏为主且整体损伤值下降近65%；分析了自旋转射流流场特性并建立了射流冲击应力波方程，揭示煤岩体动态损伤与失稳破碎机理。开展了树状钻孔卸压煤体数值模拟研究，探讨了诱导形成均匀卸压缝网的重要影响因素；建立了煤层树状压裂水力裂缝起裂、扩展导向的预测模型，揭示了导控裂缝网状扩展均匀增透机理，理论模型与实验结果最大偏差不大于6%。建立了深部煤岩热流固多场耦合模型，阐明了低透煤层内树状钻孔高效抽采煤层瓦斯原理：裂缝密集单元与稀疏单元内煤体瓦斯先后被抽采，逐渐形成与裂隙场差不多大小和形状的高效抽采区域。在重庆能投、河南平煤集团等煤矿区进行了现场应用，与密集钻孔相比，抽采影响半径提高了4.7倍，抽采纯量提高8.12倍。发表SCI论文12篇，出版著作1部；培养博士2人（其中1人获重庆市优秀博士论文），硕士5人（其中1人获校级优秀硕士论文）。申请发明专利4项（授权2项），获重庆市科技进步一等奖1项，同时项目申请人获聘教育部“青年长江学者”以及“重庆市青年拔尖人才”称号，参加国内外学术会议7次。