In France, the main exploited low enthalpy geothermal reservoir is embedded within the Jurassic fractured limestone formation of Dogger located in the central part of Paris Basin, where 34 doublets are currently heating 600 000 people since 30 years. The development of renewable energy combined with the energy demand implies to search other geothermal reservoirs either below the Paris area or either in other promising areas in the country.
In this framework, a co-funded Ademe-BRGM project, namely CLASTIQ (CLAyed SandSTones In Question), was launched in order to study the deep geothermal potential of the Rhine Graben for heat production, or even electricity if temperature conditions are high enough. This resource is located in argillaceaous and clastic formation of the lower Triassic unit, namely the Buntsandstein.
The goal of this study is to make a first assessment of this reservoir at regional scale in order to delineate the most favourable areas for exploration and exploitation of the geothermal resource.
In this framework, we have done maps based on modelled geological layers. These maps were built from former data based on a geothermal compilation (Munck et al. 1979). Main characteristics of the Buntsandstein aquifer, such as depth, thickness, and temperature, have been mapped by interpolation method. Based on these maps, the quantity of heat in place has been computed for the whole Upper Rhine Graben from Basel to Karlsruhe.
It appears that the northern part of the Rhine graben constitutes a more favourable area than the southern part. The top of the Buntsandstein reservoir is located at around 2000-3000m depth with a temperature of about 150°C and the sandstone thickness is around 500-600m. The exploitable geothermal potential is between 15 and 30GJ/m2.
This study confirms that the Buntsandstein formation of the Upper Rhine Graben has a good geothermal potential for heat or electricity production based on binary geothermal power plants. Some promising areas have been identified and the need of new geophysical acquisition such as 2D or 3D seismic profiles should be very helpful for providing relevant information about the reservoir structure.
Munck F., Walgenwitz F., Maget P., Sauer K, Tietze R. (1979) – Synthèse géothermique du Fossé rhénan Supérieur. Commission of the European Communities. BRGM Service Géologique Régional d’Alsace – Geologisches Landesamt Baden-Württemberg.