Long range modelization of the natural hydrothermal convection in the Vendenheim geothermal site.

The Vendenheim geothermal project, located at the north of Strasbourg France, in the Upper Rhine Graben, was halted due to the occurrence of two clusters of induced seismic events. One of these clusters is located far from the wells (4-5 km). Therefore, in the framework of the DT-GEO project (Horizon Europe), we developed a 3D thermo-hydro-mechanical (THM) model to have a better idea of the natural convective hydro-thermal conditions of this reservoir and to propose possible mechanisms that triggered these events. The geometry of this model was obtained from the GEORG platform, including the main geological units and faults. The geological properties and initial/boundary conditions were obtained from nearby reservoirs (such as Soultz-sous-Forets), which are also located in the Upper Rhine Graben. The hydro-thermal-mechanical equations were solved using the open-source finite element code MOOSE/GOLEM. We present here the results of our modelling, which focuses on the hydrothermal circulation in the reservoir area, like temperature and heat flux profiles, and the analysis of fault stability. We therefore propose a model that explains the natural conditions at the site and can serve as the initial conditions that existed prior to injection. In addition, as a perspective, our study can be used to understand the mechanisms that caused the induced events.