可控源微波辐射作用下煤体微结构演化及其增透机理研究

The gas drainage in low-permeability coal seam is a significant technical difficult problem that must be solved in the field of mine gas disaster prevention and controlling. And that enhancing permeability of coal is an effective way to solve this problem. The preliminary results obtained by the applicant had shown that the differential thermal effect of controlled microwave on kinds of minerals in coal resulted in the increase of porosity and permeability of coal under the condition of no-load. Hereby, this project proposes a novel idea of using a controlled microwave irradiation to enhance permeability of coal. By means of experimental research, numerical simulation and theoretical analysis, this project will study the influence of controlled microwave irradiation to quantity, scale and connectivity of the microstructures (pore and cranny structures) and the permeability in coal under different stress conditions. Thereby, the relationship between microwave irradiation parameters (power and irradiation time) and microstructure parameters, heating rate and the gas permeability of coal under different stress conditions will be acquired. Subsequently, the microstructure evolution model coupled heat transferring and deformation in coal under controlled microwave irradiation is established. Thus, the evolution law of microstructures and gas permeability of coal under controlled microwave irradiation are found out. This will reveal the permeability enhancing mechanism of coal under controlled microwave irradiation. Finally, the range of microwave irradiation parameters, that is conducive to permeability enhancing of coal, is determined. This research will provide a theoretical basis for the establishment of a new method for permeability enhancing of low-permeability coal seam.

低渗透煤层瓦斯抽采是矿井瓦斯灾害防治领域亟待解决的重大技术难题，而增大煤体渗透性是解决这一难题的有效途径。申请者前期研究发现，在无载荷条件下，可控源微波对煤体内部各矿物所产生的差异性热效应能使煤体的孔隙率及渗透性增加。据此，本项目提出“可控源微波辐射增大煤体渗透性”的新思路，采用实验研究、数值模拟与理论分析相结合的方法，研究不同载荷条件下可控源微波辐射对煤体微结构(孔裂隙结构)的数量、尺度与连通性以及煤体渗透性的影响特性，探索不同载荷条件下微波辐射参量(功率和辐射时间)分别与煤体的微结构特征参数、升温速率和瓦斯渗透率之间的相互关系，建立可控源微波辐射作用下煤体微结构演化的热-力耦合模型，探寻可控源微波辐射作用下煤体的微结构与瓦斯渗透性的演化规律，揭示可控源微波辐射作用下煤体的增透机理，从而确定有利于煤体增透的微波辐射参量范围，为建立低渗透煤层增透的可控源微波辐射新方法提供理论基础。

微波激励技术以其特有的加热特性、能源转换效率高和环保性，被认为是一种极具发展前景的煤层增透新方法。为探索煤体微波致裂增透的可行性与实效性，本项目自主研制了受载煤岩体微波致裂实验装置，开展了不同微波参量条件下受载煤体的微波致裂实验与渗透率测试，研究了微波辐射对受载煤体微结构的数量、尺度与连通性以及煤体渗透性的影响特性，获取了微波参量与煤体的微结构特征参数、升温速率和渗透率之间的相互关系，探寻了可控源微波辐射作用下煤体的微结构演化特征与宏观裂隙发育特征，建立了可控源微波辐射作用下煤体破裂演化的电-热-力耦合模型，揭示了可控源微波辐射作用下煤体的增透机理，初步确定了有利于煤体增透的微波辐射参量范围。研究结果表明：(1) 在微波辐射下，煤体的温度快速升高且含水饱和度较低时，温度场分布更不均匀；当微波功率增加到一定程度时，进一步延长微波辐射时间具有更好的升温效果。(2) 在有载荷和无载荷条件下，微波辐射后煤体微孔的数量与体积均减少、中孔和大孔及微裂隙的数量与体积均增加，各类尺寸孔隙之间的连通性得到改善。(3) 微波辐射下煤体微结构损伤与微波功率、微波辐射时间、微波能量加载顺序以及煤体含水饱和度等因素相关，且存在微波功率阈值现象，在微波功率阈值下延长微波辐射时间对微结构的演化更为有益。(4) 微波辐射前后煤体渗透性均存在Klinkenberg效应，且微波辐射后煤体的增渗效果具有明显的层理效应。(5) 在相同微波辐射参量下，有载荷约束煤体的增渗效果大于无载荷煤体。(6) 本研究建立的电-热-力耦合模型与实验结果具有较高的一致性。(7) 微波辐射对煤体中各类物质的差异性热效应引起煤体基质非均匀膨胀，产生的热应力造成煤中弱胶结物质和弱结构面出现大量微裂缝，引起煤体宏观裂缝发育与破裂，是煤体微波致裂增透的主要原因；同时，微波辐射对煤体的整体性热效应使煤体内矿物发生迁移，对煤体原生微结构造成损伤，并产生新孔隙和结构弱面，对煤体微结构损伤具有重要影响；两者共同表现为微波对煤体的致裂效应，从而增大煤体渗透性。