深部低透气性首采层煤与瓦斯气固耦合模型

MATHEMATICAL MODEL OF COUPLED GAS FLOW AND COAL DEFORMATION PROCESS IN LOW-PERMEABILITY AND FIRST MINED COAL SEAM

立足于消除煤层渗透及扩散特性对于煤与瓦斯气固耦合模型的干扰,在分析首采煤层所处应力状态特点的基础上,建立更符合煤体的孔隙裂隙二重介质特性的修正的P-M渗透率模型,提出考虑解吸–扩散效应及Klinkenberg效应的煤与瓦斯气固耦合模型,详细阐述多物理场之间的耦合作用关系。应用该模型模拟分析深部首采层顺层钻孔预抽消突过程中煤层瓦斯压力及渗透率的演化规律。模拟结果表明,Klinkenberg效应对低渗透煤层瓦斯运移的促进作用显著,并随着瓦斯压力减小促进效果增大;煤体绝对渗透率的动态变化是骨架压缩效应及基质收缩效应的竞争结果,瓦斯压力开始减小时,骨架压缩效应首先起主导作用,渗透率减小,瓦斯压力持续降低时,基质收缩效应逐渐取代其成为主导作用,渗透率增大。

In order to eliminate the disturbances of coal permeability and diffusion coefficient on the correctness of coupled gas flow and coal deformation model. Firstly,the geostress condition of the first mined key seam is analyzed. Secondly,a modified P-M permeability model is proposed to match the pore structure characteristics of coal seam;Finally the governing equations for the coupled gas flow and solid deformation in dry coal seams are proposed,and the Klinkenberg effect has been taken into account,at the same time the relationships of the multiphysics fields have been discussed in detail. The coupled model has been used in simulating gas migration and permeability evolution in the first mined coal seam around drainage boreholes. Numerical results indicate that the Klinkenberg effect can have a critical influence on gas pressure during the entire methane degasification period,and the influence increases with time. The evolution of permeability is controlled by two opposite effects,compressive volumetric strain and matrix shrinkage,and the resulting permeability change is controlled by the mechanism that dominates.