“三高”条件下瓦斯抽采钻孔渗流-损伤演化规律及失稳机制

Borehole pre-drainage coalbed gas technology is widely used for underground gas disaster prevention and development of coalbed methane (CBM). Deep coal-seam is in high ground temperature, high ground stress, high osmotic pressure (water and gas) environment, the gas drainage is a complex fluid-solid-heat coupling process. Damage and fracture of coal under the coupling of fluid flow (water and gas) seepage and heat coupling induce gas drainage hole instability and collapse, resulting in more difficult gas drainage and low gas drainage efficiency. This project intends to carry out gassy coal-rock seepage-creep-injury mechanical experiment under the coupling of heat and mechanical. Analysis of the coupling relationship between the damage and the permeability characteristics of gassy coal-rock under the coupled fluid-solid-heat-multi field. Establishing the model of permeability-damage evolution of gassy coal-rock and revealing the rules of damage evolution. The creep mechanical properties and damage evolution of coal under the heat-fluid-multi-field coupling are studied. Establishing the nonlinear creep damage model of gassy coal-rock. On this basis, construct the stability mechanics model of surrounding rock of gas drainage borehole, reveal the surrounding rock of gas drainage borehole seepage creep damage evolution and plastic zone distribution, investigate surrounding rock of gas drainage borehole damage conditions, reveal mechanism of gas drainage borehole seepage-creep-injury coupling disaster-induced instability in deep coal-seam and provide theoretical support for the CBM development.

钻孔预抽煤层瓦斯是井下瓦斯灾害防治及煤层气开发应用最广泛的技术措施。深部煤层处于高地温、高地应力、高渗透压（水或瓦斯）“三高”环境，瓦斯抽采是一个复杂的热流固多场耦合的长期过程，流体渗流与热力耦合作用下煤岩损伤破坏极易诱发瓦斯抽采钻孔失稳坍塌，导致瓦斯抽采愈加困难，瓦斯抽采效率低。本项目拟开展热力耦合下含瓦斯煤岩渗流-蠕变-损伤力学实验，分析热-流-固多场耦合下含瓦斯煤岩损伤特性与渗透特性的耦合关系，建立含瓦斯煤岩渗透-损伤演化模型并揭示损伤演化规律；研究热-流-固多场耦合下煤岩蠕变力学特性及损伤演化规律，建立含瓦斯煤岩蠕变非线性损伤模型；在此基础上，构建瓦斯抽采钻孔围岩稳定性力学模型，揭示瓦斯抽采钻孔围岩渗流-蠕变损伤演化规律及塑性区分布形态，探讨瓦斯抽采钻孔围岩损伤破坏条件，揭示深部煤层渗流-蠕变-损伤耦合条件下瓦斯抽采钻孔围岩灾变失稳机制，为煤矿井下高效抽采煤层瓦斯提供理论。

针对深部煤层处于高地温、高地应力、高渗透压（水或瓦斯）环境，瓦斯抽采是一个复杂的热流固多场耦合的长期过程，流体（水和瓦斯）渗流与热力耦合作用下煤岩损伤破坏极易诱发瓦斯抽采钻孔失稳坍塌，导致瓦斯抽采愈加困难，瓦斯抽采效率低的问题。本项目通过建立煤矿井下穿层钻孔孔壁应力状态计算模型，并建立了基于K线图的钻孔瓦斯异常涌出模型，分析穿层钻孔瓦斯涌出规律；利用瓦斯高压吸附解吸试验仪和含瓦斯煤热流固耦合三轴伺服渗流系统研究了不同温度、应力、渗透压力条件下的煤体三轴强度、渗透特性，并基于煤体三轴强度、渗透特性建立了热力耦合下含瓦斯煤岩渗流-损伤演化模型；采用COMSOL Multiphysics软件建立了卸压增透煤层瓦斯多尺度热流固耦合模型，分析了孔隙-裂缝-多分支钻孔煤层瓦斯流动机理，揭示了热力耦合下含瓦斯煤岩渗流-损伤演化规律；采用等效连续介质理论建立了卸压煤体变形破坏数学方程，利用该方程探讨了不同地应力、分支孔布置等关键参数对煤层裂隙场裂缝密度与数量的影响规律；并通过开展钻孔相似模型试验分析了钻头钻速对煤岩破裂特征的影响规律，采用电镜扫描研究了瓦斯抽采钻孔周边含瓦斯煤岩微观断裂特征。