破碎煤岩体变形与瓦斯渗流特性及其应力-破碎-渗流耦合机理

Surface extraction of coalbed methane from abandoned mines in China is still in its infancy. One of the most important reasons that restrict methane production of surface drilling is that the deformation and methane seepage characteristics of crushed coal and rock in caving zone are difficult to grasp. Based on this, the stress path of crushed coal and rock in caving zone are obtained by gob excavation numerical and physical similarity simulation experiments. The non-uniform deformation characteristics and stress-fragmentation coupling mechanism of crushed coal and rock under different lithology, particle size and stress path conditions were investigated by using the self-developed compaction-acoustic emission experimental device and numerical simulation. The seepage characteristics of crushed coal and rock under different lithology, particle size, stress path and gas pressure are revealed based on the independently developed compaction-seepage experimental system for CT scanning. The fragmentation-seepage coupling mechanism under the evolution of porous structure is revealed based on numerical simulation results by importing the digital core of crushed coal and rock into the software. The influence mechanism of drilling location, drilling numbers and extraction parameters on methane extraction effect is explored by numerical simulation model of methane extraction in caving zone. Optimum method of surface drilling and extraction parameters is put forward by considering the numerical results and methane extraction effect in field. The above research will lay a significant theoretical foundation for accurately grasping the seepage characteristics of the caving zone, which have a practical guiding significance for methane extraction in abandoned gob.

我国废弃矿井煤层气地面抽采尚处于起步阶段，制约钻井产气量的重要原因之一是垮落带破碎煤岩体变形及瓦斯渗流特性难以掌握。据此，本项目借助采空区开挖数值、相似模拟实验获取破碎煤岩体应力路径；运用自主研发的破碎煤岩体压实-声发射实验装置结合数值模拟实验，探究不同岩性、粒径、应力路径条件下破碎煤岩体非均匀变形特性及应力-破碎耦合机理；基于自主研发可用于CT扫描的压实-渗流实验系统，揭示不同岩性、粒径、应力路径和瓦斯压力下破碎煤岩体渗流特性，结合数字化岩芯数值模拟实验，揭示破碎煤岩体多孔结构演化过程中破碎-渗流耦合机理；建立符合废弃采空区垮落带瓦斯抽采特性的数值模型，揭示钻井位置、数目、终孔位置及抽采压力、频率对瓦斯抽采效果的影响机制，结合现场抽采效果确定钻井井位及抽采参数优化方法。研究结果将对准确掌握垮落带瓦斯渗流规律提供重要理论基础，对于废弃采空区煤层气地面高效抽采具有较强的现实指导意义。

本项目针对垮落带破碎煤岩体力学渗流行为的黑箱问题。首先探究了垮落带破碎煤岩体应力分布规律；成功研发了第二代破碎煤岩体压实-声发射-可视化观测实验装置，结合数值模拟实验揭示了不同颗粒粒径、应力下破碎煤岩体非均匀变形特性及再破碎机理；成功研发了第二代破碎煤岩体压实-渗流-CT可视化实验系统，揭示了不同粒径、应力及气体压力下破碎煤岩体渗流特性，结合数字化岩芯结果，揭示了应力对破碎煤岩体多孔结构演化的影响规律，探究了应力-再破碎-渗流耦合机理；基于小尺度垮落带破碎煤岩体细观渗流数值模拟实验，探究了不同气体压力（抽采压力）及不同应力状态下垮落带承压破碎煤岩体颗粒体间细观流动特性，揭示垮落带小尺度渗流规律，提出了地面钻井优选方法，并为大尺度老空区瓦斯渗流模拟奠定基础。研究结果对废弃采空区煤层气地面高效抽采具有较强的现实指导意义。