构造煤体原位瓦斯扩散动力学演化机制及在抽采中的应用

Tectonic coal mass is formed by strong extrusion, shear and deformation of intact coal under the action of multiple tectonism. The tectonic coal mass has the characteristics of weak cohesiveness, low strength and low permeability, so the gas drainage is difficult and outburst disaster is serious. Considering the defect that the tectonic coal mass is unable to get complete block specimen as intact coal because it forms bulk solids after stress unloading and the problems of in situ gas diffusion kinetics evolution mechanism, this project uses theoretical analysis, laboratory tests and field application verification methods to reconstruct coal matrix and obtain tectonic coal block specimens under certain stress and temperature environmental conditions with tectonic coal particles. The evolution characteristics of the pore structure of the tectonic coal mass after the reconstruction of the matrix are studied, the parameters of the pore structure of the coal mass are finely quantified, and the complexity model of the pore system of the coal matrix is constructed. The evolution and characterization of matrix shape factors are studied. Based on the fractal diffusion theory of pore complexity, the gas fractal diffusion mechanism of tectonic coal mass is established. The diffusion kinetics mathematical model with parallel slab and columnar matrix are established under in situ condition. The gradual release characteristics of in situ gas of the tectonic coal mass are analyzed, and the gas-solid coupling model for tectonic coal mass containing gas is established. This project will lay a theoretical foundation for efficient gas drainage and utilization of low permeability tectonic coal seams.

构造煤体是原生煤在多期构造运动作用下受到强烈挤压、剪切和变形而形成的，具有弱粘结、低强度和低渗透性等特点，瓦斯抽采困难，突出灾害严重。针对构造煤体在解除应力条件下形成散体颗粒，无法如原生煤那样获取完整块体试样，以及在原位状态下瓦斯扩散动力学演化机制等发面存在的不足，拟采用理论分析、实验室试验与现场应用验证相结合的研究方法，将构造煤颗粒在一定应力和温度等环境条件下进行基质重构，获取构造煤体试样；研究基质重构后构造煤体的孔隙结构演化特征，精细定量化表征构造煤体孔隙结构参数，并构建构造煤体基质孔隙系统的复杂度模型；研究基质形状因子演化及表征方法，基于孔隙复杂度的分形扩散理论，建立构造煤体瓦斯分形扩散机制；构建原位条件下基质形状为平行板形和圆柱形的构造煤体扩散动力学数学模型，分析构造煤体原位瓦斯逐级放散特性，构建含瓦斯构造煤体气固耦合作用模型；为低渗透性构造煤层瓦斯高效抽采和利用奠定理论基础。

构造煤是突出发生的必要条件，也是瓦斯抽采的难点，建立适用于构造煤的等效物理结构模型，定量描述基质扩散和裂隙渗流相结合的原位条件下构造煤瓦斯运移规律，直接影响煤层瓦斯抽采与突出灾害防治工作的开展。本项目通过对煤中微观连通拓扑学网络结构的定量表征，获得了煤体微观结构对瓦斯流动的影响。结合基质形状因子，获得了基质重构过程中构造煤的等效物理结构演化模型以及瓦斯运移规律，并基于应力参数及扩散长度建立高应力煤体扩散模型。最后，构建了深部高应力构造煤的气固多场耦合数学模型，通过数值仿真获得应力作用下煤中扩散和渗流主导因素转化下的瓦斯运移规律，为深部构造煤层瓦斯高效抽采和利用奠定理论基础。主要结论如下：.1)分析构造型煤成型特征以及试验煤柱渗透率应力敏感性，建立了原生煤和构造煤的等效立方体和立方柱物理结构模型，其中具有大孔隙度和小曲折度构造煤颗粒扩散系数较大，但由于在应力作用下基质重构和扩散背压的提高，构造煤体表现为更小的扩散能力。.2)构建了考虑类树状分支和毛细管状简化结构的原生煤和构造煤瓦斯输运数学模型，结合煤中大分子结构演化模式以及微观分形几何学结构复杂度系数，获得了构造作用下孔隙结构及孔隙类型的改造机制，其中构造煤丰富的微孔空间提供了主要的瓦斯吸附场所，且由于微观结构复杂程度较低，有着更快的瓦斯解吸。.3)构建以基质微元体为基础的高应力煤体扩散模型，获得了高应力煤体物理结构改造下的瓦斯扩散特征，同时由于基质的重构作用，致使原位煤体瓦斯转化为表面扩散，其体扩散系数在扩散背压递减时是增加的，并且随着压力梯度的增大而增加。.4)分析了煤层瓦斯运移主控作用角色转换的影响机制，构建了以渗流和扩散主控角色转换规律为基础的深部煤层气固耦合模型，基于此分析了深部煤层瓦斯难以抽采的原因，为瓦斯抽采参数和钻孔布置等方面提供了指导。