Speaker: Clémence Pavageau
Date: Thursday 8th of October 2026, 1:15pm
Abstract:
Low-enthalpy geothermal energy, characterized by temperatures below 90°C and exploitation at shallow depths (i.e. normally less than 500m), represents a sustainable energy alternative for residential and industrial heating and cooling, while offering a reduced environmental impact. However, the sustainable exploitation of these resources requires a thorough understanding of reservoir behavior and accurate monitoring of the thermal evolution of aquifers. Electrical geophysics provides valuable insights into subsurface thermal processes; therefore, understanding the coupled evolution of heat and electrical charge across multiple scales is of significant interest.
This study, first, presents an experimental approach to establish the relationship between the electrical resistivity of water-saturated rocks and temperature variations with simple yet realistic assumptions and then presents a numerical counterpart. The experimental study was conducted in the laboratory using a cylindrical water-saturated sandstone sample containing a central axial conduit through which water was circulated in a closed loop. The experimental protocol consisted of injecting either hot or cold water through the conduit to induce heating and/or cooling scenarios within the sample. Temperature was monitored using thermocouples positioned at the inlet and outlet of the water circuit, as well as at two radial locations within the rock sample. Electrical resistivity measurements were acquired using a Syscal Junior resistivity meter with a Wenner–Schlumberger electrode array. Measurements were recorded over roughly 30-minute periods, enabling the analysis of the coupled evolution of fluid temperature and the electrical conductivity of the saturated porous medium during both heating and cooling experiments. Through this, bulk resistivity evolution of the quadrupole was measured directly and verified later with the model.
The experimental scenarios were simulated using direct numerical simulation of coupled flow and heat transfer in porous media with electrical current density distribution. The petrophysical model of Waxman and Smits (1968), applied to saturated porous media, in which temperature primarily affects the electrical conductivity of the pore water is used to link temperature effects to electrical conductivity of the DC current injected. We assume and show that the temperature dependence primarily resulted from temperature-induced changes in ionic mobility and fluid viscosity, resulting in the evolution of water electrical conductivity measured directly in the experimental phase. Within the temperature range characteristic of low-enthalpy geothermal systems, this relationship can be considered approximately linear. The surface conductivity effects have secondary importance and can be expressed through the temperature dependence of equivalent conductance of exchange cations (i.e. parameter B).
The experimental and numerical results validate the assumption on the evolution of the electrical conductivity of the saturated Vosges sandstone as a function of temperature. Laboratory validation and calibration of this model provide the basis for its integration into a numerical framework capable of reproducing the experimental observations. At a larger scale, this approach could be extended to Electrical Resistivity Tomography (ERT) surveys, providing a non-invasive tool for in situ thermal monitoring of geothermal reservoirs.