Simulation of the effect of salinity-clay variation on the electrical potential of the quaternary aquifer using multiphysics modeling

Salinity and clay content are effective factors in influencing the hydro-geoelectric properties of porous rocks, such as electrical conductivity. The COMSOL Multiphysics model was used in this study to simulate this parameter, to realize the effect of the variation of salinity and clay on the electrical potential of the Quaternary aquifer in the fresh groundwater zone, brackish groundwater zone and saline groundwater zone across the middle Nile Delta of Egypt, by applying the Direct Current resistivity method. The electrical model included four different geological layers in lithology and resistivities. Nine VESes were performed to calculate the electrical potential and the apparent resistivity of these layers, focusing on the Quaternary aquifer. The coefficient of decreasing and rate of decreasing in the electrical potential were calculated and it was found that it reflects a weak, medium, and high to very high significant effect of salinity and clay content in the fresh groundwater zone, brackish groundwater zone and saline groundwater zone, respectively. The results indicated the expected errors in resistivity measurements, estimation of hydro-geoelectric parameters and sediments description in the three water zones and the accuracy of their separation. This simulation helped to understanding the effect of salinity-clay variation on the electrical potential of porous sediments. It can, therefore, be considered as an essential step to solve the hydro-geoelectric and environmental problems of aquifers affected by this variation, focusing on clarifying how this variation has reduced the accuracy of the hydro-geoelectric parameters and lithologic description.