卸载煤体损伤与瓦斯非稳态解吸对渗透性的耦合作用机制

The permeability of Coal seam is a key parameter of pressure-relief methane drainage and also the coupling link between stress field and gas flow field. Nevertheless, the acting mechanism of effect factors on permeability evolution is not clear for depressurized coal seam. The project set up the experiments to study the unloading damage and methane unsteady desorption change the permeability in pressure-relief gas drainage in depressurized mining process. First of all, two seepage experiments of coal specimens are set up, one without any coal-adsorbed gas to measure the permeability changing with the stress, another with methane to measure the permeability changing with methane desorption under the same unloading path, to study the permeability evolution mechanism and contribution separately, of unloading damage without adsorption/desorption interference and methane unsteady desorption under effective stress keeps constant. Finally, the dynamic characterization caused by unloading damage and unsteady desorption is integrated, according to the mechanical path and stress state. The coupling action and the internal mechanism of unloading damage and methane unsteady desorption on permeability of coal seam will be revealed highlighted. The project researches the coupling mechanism between the permeability of coal and unloading damage and methane unsteady desorption coupling action in unloading process from many angels. And couple model for coal permeability will be established for the interaction of unloading damage and methane unsteady desorption, which set up a bridge between mining stress and gas flow and provide the theoretical foundation for the pressure-relief gas drainage.

煤岩渗透性是决定卸压瓦斯抽采效果的关键参数，也是应力场与瓦斯流动场耦合作用的纽带。针对采动卸载过程中煤层渗透性演化特征及其影响因素的作用机制尚不清楚的现状，项目采用理论研究与实验室实验相结合的方法从卸压瓦斯抽采角度研究卸载过程中煤体损伤、瓦斯非稳态解吸对渗透性的耦合作用机制。首先，开展相同卸载力学路径下不含吸附气体煤的渗透试验和瓦斯解吸渗流试验，分别独立研究无吸附/解吸干扰作用下卸载损伤、有效应力恒定条件下瓦斯非稳态解吸对渗透率演化的作用机理与贡献；然后，按力学路径和应力状态整合卸载损伤、非稳态解吸对渗透性作用机制的力学表征，重点研究卸载过程中煤体损伤与非稳态解吸对渗透率演化的耦合作用及内在机理。本项目实现了从细观多层面对卸载过程中煤体损伤和瓦斯非稳态解吸对渗透性的耦合作用研究，建立卸载损伤-非稳态解吸-渗透率耦合模型，搭建采动应力与瓦斯流动相互作用的桥梁，为采动卸压瓦斯抽采提供理论基础。

项目针对采动卸载过程中煤层渗透的复杂变化特征，从渗透率的增减角度将采动卸荷的过程渗透率的影响因素解析分解为无新生裂隙和有新生裂隙两个状态，然后通过相同力学路径下静水压力（等气体压力、等围压和等有效应力）、全应力-应变及等差应力卸围压等条件下的非吸附He和甲烷渗透试验分步屏蔽其他因素来研究某一因素对渗透率演化的贡献，实现了从卸压瓦斯抽采角度研究卸载过程中煤体损伤、瓦斯非稳态解吸对渗透性的耦合作用机制。项目首先测定了试样的基本物性参数以及吸附和解吸特性，提出了可很好的预测瓦斯抽采效果的初始结构渗透率概念。为了实现原煤的平行渗透试验，利用超声探测技术获得的煤样动弹性力学参数确定了平行试样，然后开展了含瓦斯和不含瓦斯煤的单轴和三轴力学特性试验，获得了游离瓦斯与吸附瓦斯对煤体弱化作用的定量结果，阐述了游离瓦斯与吸附瓦斯对煤体强度弱化的机制。而后通过在等气体压力条件屏蔽了孔隙压力和吸附膨胀变形对渗透率的影响，得到了反映煤中裂隙对应力敏感的响应特性的裂隙压缩系数及其变化规律。通过固定有效应力条件屏蔽了外界应力和孔隙压力的作用研究了基质吸附变形对渗透率的影响，发现煤基质中吸附瓦斯后压缩了裂隙的宽度而引起渗透率的减小。通过等围压条件屏蔽了外界应力，研究了有效应力与基质吸附变形对影响渗透率的竞争机制，获得了有效应力与基质吸附变形主导煤的裂隙开度的条件。通过全应力-应变和恒定差应力卸围压状态下煤体渗透试验来研究煤体出现新生裂隙过程中渗透率演化特性，前者发现原煤的渗透率与损伤扩容存在滞后现象，原煤的破坏以明显的垂直贯通裂隙或者剪切裂隙为主；而后者发现型煤的渗透率在卸荷初期增长缓慢，而后随着损伤破坏程度的加剧而迅速增长。最后项目在传统孔隙率-渗透率模型基础上建立了包含损伤扩容效应和基质解吸收缩效应的煤体卸荷损伤渗透率模型，搭建了煤体卸荷与增透的桥梁，为深部煤储层改造和瓦斯抽采提供了理论基础。