Development of numerical model for simulating resistivity and hydroelectric properties of fractured rock aquifers

Abstract

Studying fractured aquifers have been always a challenging subject due to the complexity of their physical and hydrogeological properties. In this study, it is therefore aimed to investigate the electrical conductivity of the saturated fractures as conductive zones and the role of these zones in changing and reducing the host rock resistivity. To achieve this goal and estimate the hydro-electrical characteristics of these aquifers, a 3D numerical modeling (Comsol Multiphysics Model, CMM) was developed for simulating the resistivity and hydro-electrical properties of these aquifers by applying the Vertical Electrical Sounding technique (VES). The calibration between the analytical solution and numerical model showed an error percentage less than 0.03%. The resulted VES-curves depending on porosity increasing, which in its turn is depending on increasing in fractures density, distribution and their orientation, confirmed that the resistivity of fractured aquifer decreases with increasing the fractures density and porosities. The results were considerably representative exhibiting the nature of the relationship between porosity and resistivity of fractured aquifers. This relationship was found to be linear and inverse with high evidence and correlation results. Corresponding to these findings the resulted empirical equation can be used in predicting the porosity with taking into account the saturated weathered and fractured basement rocks resistivity which ranges between 7-85 Ω.m. The error percentages should also ranging between 0.0015%–0.0668%. Accordingly, this model produces reliable solutions of the resistivity method forward problem for arbitrary electrical resistivity in the subsurface depending on the fractures density and porosity of fractured aquifers. The apparent resistivity curve obtained from this model was compared with the measured field apparent resistivity curve of the fractured aquifer. The results are consequently testifying the effectiveness of Comsol Multiphysics Model in studying, solving, and understanding the different electrical and hydrogeological conditions of these aquifers.