煤微观结构三维表征及其孔-渗时空演化模式数值分析

THREE-DIMENSIONAL REPRESENTATION OF COAL?S MICROSTRUCTURE AND NUMERICAL ANALYSIS OF ITS PORE-PERMEABILITY SPATIAL-TEMPORAL EVOLUTION MODE

探讨煤岩微观孔隙结构统计意义上的等效构建方法,并于孔隙尺度下模拟流体运移行为的时空演化过程。首先,结合煤岩孔隙结构的各向异性及非线性特征,采用修正的四参数随机生长(QSGS)算法构建煤岩多孔介质模型。随后,采用格子Boltzmann方法(LBM)模拟孔隙中气体单相流的运移过程,并基于数值试验结果,分析煤岩介质中影响渗透率的主要因素及流体运移达到平衡态前的演化模式。分析结果表明:(1)多孔介质的渗透性能受控于少量、连通性好的大孔所形成的通道,而小孔及微孔中气体的行为基本属于浓度扩散过程;(2)孔隙属性空间变异条件相同情况下,孔隙度同渗透率之间满足乘幂关系,但幂率系数随孔隙属性变异因子的降低而增加;(3)渗透率随时间呈减少趋势,自运移开始达到动态平衡的耗时量同孔隙度之间是一种负相关的幂率关系。

Equivalent construction method in statistics of coal＇s pore structure was discussed; and the spatialtemporal evolution process of fluid flow was simulated at pore scale. First of all, the porous media model of coal medium was constructed using modified quartet structure generation set（QSGS） algorithm which integrates the nonlinear and anisotropic characteristics of coal＇s pore structure. And then, single-phase gas flow through pores was simulated using lattice Boltzmann method. Based on the numerical simulation results, the main influential factors and the evolution pattern of coal＇s permeability before fluid flow achieve equilibrium state were analyzed. The analysis results show that： （1） Permeability in porous media is dominated by the channels connected by pores with large size, but the migration in the paths connected by small pore and micropore was concentration diffusion behavior; （2） In the same spatial distribution variability pattern, there is a power law relation between porosity and permeability, but the power rate coefficient increases with the decrease of spatial variability; （3） Permeability is reduced gradually over time in porous media and the time needed before the flow reaches its stable state meets negative correlation power rate relation with porosity.