基于微观PNP多离子运移模型的多孔介质曲率系数分析

Tortuosity analysis of porous media based on micro-scale PNP multi-ions transport model

采用数值分析研究多孔介质的曲率系数.应用微观Poisson-Nernst-Planck多离子运移模型描述离子在微观多孔介质孔隙中的运移,通过空间体积平均获得曲率系数.以NaCl盐溶液在黏土中的扩散试验为例,建立数值分析模型,分析了微观结构、离子种类、背景浓度、颗粒表面电荷密度等对曲率系数的影响.研究表明:不考虑电场作用,曲率系数与孔隙率符合Archie定律的指数关系,曲率系数与离子浓度、离子种类无关;考虑电场作用,曲率系数不仅与微观结构的几何形状有关,而且与相伴离子种类、离子背景浓度、颗粒表面电荷密度等关系密切.阳离子的曲率系数普遍高于不考虑电场作用时的曲率系数,而阴离子的曲率系数则相反.

The tortuosity of porous media was studied by numerical analysis.PNP（Poisson-Nernst-Planck） multi-ions transport model at micro-scale is setup for describing ions transport in charged porous media,and tortuosity can be get by upscaling microscopic PNP multi-ions transport model.Numerical model on NaCl salt solution diffusion in the clay was built,and the relationship between the tortuosity and porosity,type of ions,background concentration of ion and surface charge density of particle was researched.For uncharged porous media,the relationship of the tortuosity to porosity is consistent with the exponential function of Archie＇ Law and the tortuosity is independent from type of ions and background concentration of ion.On the contrary,for the charged porous media,the tortuosity is not only dependent on microstructure of porous media but also dependent on the porosity,type of ions,and background concentration of ion and surface charge density of particle.The tortuosity of cations in charged porous media is generally higher than in uncharged porous media,which is contrary to that of anions.