Geothermal potential in Valais (GEOTHERMOVAL II)
Geothermal potential of high-permeability conduits at the base of the glacial Rhone valley in Valais
The aim of the Géothermoval II project, which follows on from the GEOTHERMOVAL project, is to estimate the geothermal potential of the Rhône valley in order to determine whether this resource can be exploited to meet the growing energy needs arising from the densification of lowland regions.
In order to identify areas of interest for geothermal drilling, it is first necessary to identify the position and depth of the base of the Quaternary fill (thickness and types of deposits) in the glacial Rhône valley, based on seismic studies. In addition to exploiting the results of earlier studies (seismic reflection campaign in the Rhône Valley between Sion and St-Maurice: Prospects for geothermal exploitation of subglacial torrential deposits.(Besson et al. 1993 ), Projet PNR20 “Exploration du soubassement géologique de la Suisse”(Pfiffner et al. 1997)), two further seismic-reflection campaigns co-financed by CREALP and the Canton of Valais were carried out in 2013-2014 in the Martigny and Vétroz areas to confirm and refine the previous results(CREALP 2015, Sonney et al. 2020). More recently in May 2021, a new seismic profile was carried out in the Vétroz area to develop a 3D geological model of the Quaternary fill(work in progress).
These studies have estimated the boundary between Quaternary sediments and bedrock at depths of around 850 m and 1,000 m respectively for the Vétroz and Martigny test areas. The base of the valley fill would be composed of continuous, potentially water-bearing subglacial torrential deposits, varying in thickness from around 50 to 150 m. As the Rhône valley between Martigny and Sierre follows the major Rhône-Simplon fault system, and the various geological formations straighten at the northern edge of this fault system, conditions are favorable for the occurrence of hydrothermal inflows by ascent(Sonney 2010, Sonney et al. 2020). Several areas in the Rhône valley show either thermal manifestations on the surface (Saillon and Saxon) or thermal anomalies in the water table (Fully, Martigny, Sion and Sierre). The geothermal potential of the Rhône valley is therefore high for future medium-depth projects (35°C < T° < 60°C).
Géothermoval II is perfectly in line with the energy objectives of the canton of Valais, which is aiming for a long-term (2060) supply of 100% renewable, indigenous energy, and of the Swiss Confederation (2050 energy strategy), which wishes to encourage the development of geothermal energy. The advantages of geothermal energy are numerous: cascading use of thermal waters, energy that can be modulated according to needs, independence from climate and seasons, availability at all times, low visual impact of infrastructures and very low emissions harmful to the environment.