应力-瓦斯吸附解吸-损伤-各向异性耦合作用下卸压煤层渗流特性研究

Gas seepage characteristics in stress-relief coal seam is mainly affected by the coal permeability. Effects of stress and gas adsorption/desorption are generally taken into account in permeability models, while lacking considering effects of two significant factors of coal damage and anisotropy. This results in the unclear seepage characteristics analysis in stress-relief coal seam. From perspectives of the sharp increase in permeability of damaged coal, the anisotropic effective stress and matrix deformation, the relationships between damage variable, damage influence coefficient and permeability jump is studied. Meanwhile, the joint control mechanism of coal damage and anisotropy on permeability is revealed. The stress-gas adsorption/desorption-coal damage-anisotropy coupled permeability model is established. The dynamic evolution law of multi-factor coupled seepage characteristics in unloaded coal seam is investigated. The mutual affecting mechanism between gas adsorption/desorption and drainage seepage is explored. The dynamic response mechanism of gas pressure to gas-extraction process is obtained. The effects of coal microstructure characteristics and gas adsorption\desorption parameters on seepage characteristics and drainage efficiency are analyzed. Finally, gas drainage test is conducted to verify numerical simulation results. Results of this project benefit for increasing the accuracy of seepage characteristics prediction, providing guidance for real-time optimization of drainage parameters and accurate and efficient drainage in the stress-relief coal seam.

渗透率是影响卸压煤层瓦斯抽采渗流特性的主要参数，渗透率模型普遍考虑应力和瓦斯吸附解吸的影响，而缺少兼顾煤体损伤和各向异性两个重要因素，导致卸压煤层抽采渗流特性尚不完全清楚。从损伤煤体渗透率跃变、有效应力和基质变形各向异性的角度，研究损伤变量和损伤影响系数与渗透率跃变之间的函数模型，揭示煤体损伤和各向异性对渗透率的联控作用机制，建立煤体应力、瓦斯吸附解吸、煤体损伤和各向异性多种因素耦合的渗透率模型。研究卸压煤层抽采多因素耦合渗流特性动态演化规律，探究瓦斯吸附解吸与抽采渗流的互馈机理，获得瓦斯压力对抽采进程的动态响应机制。探明煤体微观结构特征和瓦斯吸附解吸参数对渗流特性和抽采效率的影响，开展瓦斯抽采试验检验数值模拟结果。研究成果可以协助提高渗流特性预测的准确性，为实时优化卸压煤层抽采参数、实现精准高效抽采提供一定的参考。

我国高瓦斯低透气性煤层居多，瓦斯事故风险大，瓦斯抽采是防治瓦斯事故的重要方法，具有显著的安全、经济、环境及社会效益，基于保护层开采的卸压煤层瓦斯抽采是提高抽采效率最经济、最有效的方法之一，而渗透率是影响卸压煤层瓦斯抽采流动的关键参数。项目针对以往渗透率模型缺乏考虑煤体损伤和各向异性的影响，导致卸压煤层渗透率变化被低估的现状，研究了损伤变量和损伤影响系数与渗透率跃变之间的指数式关系模型，采用渗透率变化受裂隙主控的假设，一个方向的渗透率变化主要受到与其垂直的另外两个方向裂隙发育情况的影响，建立了煤体应力、瓦斯吸附解吸、煤体损伤、各向异性多因素耦合的渗透率模型。通过开展有限元数值模拟解算和实验室实验，获得了卸压煤层应力、渗透率变化及多因素耦合渗流特性动态演化规律，探明了不同煤体特征参数、首采层与卸压层之间的夹层参数对卸压层渗透率分布和瓦斯渗流特性的影响规律。在首采层工作面推进过程中，重新分布的应力场整体沿采空区中部对称分布，工作面顶板上方及底板下方的应力得到不同程度的卸除，煤岩体卸压区域近似为椭圆形，在采煤工作面两端出现应力集中现象。随着采煤工作面的不断推进，采空区周围煤岩体卸压范围逐渐增大，且卸压程度以及两端的应力集中程度也不断增加，卸压层充分卸压长度与采煤工作面推进距离成非线性正相关。首采层底板处基于损伤的渗透率值增加680倍左右，瓦斯不断地向上涌出至开采工作面，卸压层瓦斯压力不断减小。研究结果有助于提高卸压煤层渗流特性分析的准确性，为卸压煤层瓦斯抽采设计、抽采过程参数优化提供理论指导，进一步提升瓦斯抽采效果，对国家能源安全保障和温室气体减排具有一定的促进意义。