开采应力扰动下深部裂隙煤岩细观结构及渗透性质演化机理研究

Underground coal mining in China becomes deeper and deeper each year, which usually faces severer dynamic disasters such as coal-bed methane outburst. On the other hand, a large amount of methane in coal seam provides new opportunities in green mining, i.e., the simultaneous extraction of coal and methane. The key to solving these engineering problems is quantitatively characterizing the fracture evolution pattern and related coal permeability change. However, existing theories only provide disciplinary conclusions. In order to have a deeper understanding of the coal permeability changes along the mining activities, one has to focus on the fracture evolution pattern at mesoscale. The rapid development of X-ray CT scanning technology provides a new way to characterize the fractures in coal. However, the sample in the scan is in a pressure-free state which causes the discrepancy with the real case. Aiming at solving this problem, this project employs the in-situ X-ray CT scanning system to obtain the fracture evolution and related permeability change pattern under excavation induced stress state. Moreover, the lattice Boltzmann method (LBM) is used to calculated the gas flow behavior in the obtained fracture networks. The purpose of this project is to gain a deeper understanding of the coal permeability evolution mechanism and provided a theoretical basis for the safe and green underground mining in China.

我国煤炭井工开采逐年加深，深部开采面临更严峻的瓦斯突出灾害，但同时高瓦斯含量也为煤与瓦斯绿色共采提供了新的机会。然而，开采扰动下煤岩内部裂隙结构演化难以定量表征，裂隙结构演化过程中煤岩内部气体渗流基础理论尚未建立，导致开采过程中煤岩物理力学性质演化机理认识不清，制约了我国深部煤炭资源安全、绿色开采的有效实施。针对上述问题，本项目拟开展与深部开采扰动对应的三轴加载与渗流条件下裂隙煤岩高精度原位CT扫描，原位再现开采扰动下煤岩内部裂隙结构演化及其内部示踪气体分布规律，建立开采扰动下裂隙煤岩结构演化数字模型。发展适用于裂隙煤岩结构演化过程中气体渗流行为计算的高效格子玻尔兹曼方法（LBM），定量描述开采过程中不同应力阶段裂隙煤岩内部气体渗流行为。结合实验及数值计算，揭示开采扰动下裂隙结构演化规律及其对煤岩渗透性质演变的细观控制机理，为实现深部煤炭资源安全、绿色开采提供研究基础。

煤岩宏观物理力学行为本质上由其内部微细观结构及其演化所决定，开采扰动下煤岩内裂隙结构演化以及由此导致的煤岩渗透性质演变对深部煤炭开采至关重要。经典岩石力学及渗流理论基于连续介质力学，在代表性体积单元（RVE）上描述煤岩的力学及渗流特性，当考虑裂隙结构演化导致煤岩物理力学性质演变时需依赖大量试验测试数据，但由于煤岩自身性质的离散型，导致误差较大。针对此问题，本研究利用在线CT扫描获得了煤岩内部裂隙及其演化行为，针对煤岩内微裂隙难以准确提取的问题，发展了煤岩裂隙智能识别技术，准确提取了煤岩不同尺度裂隙结构，建立了受载破坏煤岩三维裂隙结构演化数字模型；发展了适用于裂隙结构演化过程中渗流行为计算的并行多松弛格子玻尔兹曼方法（MRT-LBM），揭示了加载破坏新生裂隙是煤岩渗透率显著升高的主要原因；开展了非均质孔隙结构内多相渗流及转向机理的可视化研究，获得了多渗透率组合复杂孔隙结构模型多相运移的主控因素；开展了地层条件下孔尺度多相渗流行为，分析了储层环境条件及储层三维复杂孔隙几何特征对于多相运移的影响。项目实施过程项目负责人以第一作者发表学术论文5篇（其中中科院TOP期刊SCI论文2篇，国内核心论文3篇，均为本基金第一标注），获授权美国发明专利2件，澳大利亚专利1件，获奖1项。本项目的研究成果对于认识开采扰动下裂隙结构演化及渗流行为演变具有重要意义，为实现深部煤炭开采安全预警和煤与瓦斯共采提供理论基础。