Large scale hydro-thermal circulation in the deep geothermal reservoir of Soultz-sous-Forêts (France)

Abstract

Abstract Many numerical models of the deep geothermal reservoir at Soultz-sous-Forets (France) have been developed over the past decades. However, a reservoir model that integrates most of the geophysical large scale measurements is still missing. For this purpose, we developed a simplified thermo-hydro-mechanical model in two-dimensions (10\u202fkm in horizontal scale and 5\u202fkm in depth) based on a finite element method. Our approach neglects the details of the fluid flow along the major faults using a representative elementary volume of 100\u202fm. The specificity of our approach is to invert from large-scale temperature and stress profiles, several key parameters through the reservoir like thermal conductivity, permeability, Young s modulus and Poisson s ratio. Our study provides new insights on the extension of the hydro-thermal convection cells through depth, on the interpretation of the linear temperature gradient at shallow depth and on the up-scaling of rock physics properties from laboratory scale to field scale. It supports a weak influence of the lithological transition between the sediments and the granitic basement on the hydro-thermal circulation contrary to previous studies. We also show the significant effect of the brine viscosity on the hydro-thermal circulation. Lateral variability of temperature profiles with depth in the Upper Rhine Graben is shown to be consistent with the predictions of this simple model.