Effect of microstructure on the electrical conductivity of clay-rich systems

It is well established that the electrical conductivity of clayey materials has two components: (a) a volume conductivity, proportional to the salted water content and (b) a surface conductivity, proportional to the cation exchange capacity. For a good understanding of the surface component associated with the electrical double layer, two fundamental aspects have to be taken into account: (a) the physical and chemical processes in the electrical double layer and (b) the effect of the clay distribution in the material. The present paper proposes a numerical approach to study the impact of clay microstructure on the macroscopic electrical conductivity.The application of such an approach is illustrated for three topics. In the first, a sensitivity analysis of the effect of the elementary structural units (platelet and aggregate) shows the significant impacts of the aggregation process and the anisotropy of the elementary structural units (platelet and aggregate). The second corresponds to a low mineralized water–clay gel: when some montmorillonite clay is added in to the gel, the surface conductivity should increase in order to reproduce experimental data. The third is related to a clay rock consisting in aggregates and pores, which are saturated or not: the numerical results show that the effective conductivity of the saturated and the unsaturated clay rock depends linearly on the volumetric water content.