Program > Browse abstracts by speaker > Lagardere Carla

The high-temperature geothermal potential of Crustal Fault Zones (CFZ) is of great interest for heat and electricity production. This study provides new petrophysical and geophysical data that can be used to better target the permeable lithologies of these zones. Permeability, porosity, and electrical conductivity measurements at room temperature and 1MPa were carried out on 32 borehole samples from the four different lithology groupings representative of the Pontgibaud CFZ in the French Massif Central: fresh (country rock), fractured (damaged zone), mineralized and argillaceous (core zone). A nitrogen permeameter, a helium pycnometer, and an impedance spectrometer were used, respectively. Electrical conductivity was measured successively on both dry and wet (H2O-NaCl – rich) samples to compare the response signal. A H₂O+0.2%NaCl solution was selected based on preliminary tests with varying salinities. Fractured samples have the highest permeability values and, together with the argillaceous samples, they also have the highest porosities and wet conductivities. A clear relationship between porosity, permeability, and electrical conductivity is revealed for the wet samples, indicating not only a global trend but also a group-dependent trend. An additional investigation was performed on porosity topology and connectivity using Archie's mixing laws and 3D X-ray microtomography analysis. Preliminary X-ray diffraction data for clay gouge will also be presented. The main results of this work are of great interest for geothermal applications, as they provide new clues to understand the electrical signals associated with high permeability and porosity in a CFZ.