Thermal conductivity characterization of three geological formations by the implementation of geophysical methods

Abstract

In very low enthalpy geothermal installations it is essential to know the thermal conductivity parameter of the surrounding ground. The present study uses seismic prospecting as a basis for the knowledge of the mentioned thermal property. Using the technique of Multichannel Analysis of Surface Waves (MASW) and seismic refraction, it has been possible to correlate the velocity of the P and S waves with the thermal conductivity of three study areas. Continuous measurements of the thermal conductivity parameter were performed on samples from the areas where the seismic prospecting was made. The maximum and minimum thermal conductivity values were connected to the highest and lowest P and S wave’s velocities. From this relation, an interpolation between the couple of values allows to obtain a linear equation used to predict the intermediate thermal conductivity values. As a result, graphs of thermal conductivity against P and S wave’s velocities were created for each of the study areas. Additionally, 2D images of the spatial distribution of the thermal conductivity of the subsoil of each formation were performed. Thus, seismic prospecting allows, besides knowing the geology of the subsoil, the possibility of estimating the thermal conductivity of a certain ground. This parameter is indispensable for the subsequent process of calculation and dimensioning of a very low temperature borehole heat exchanger.