Project challenges
The Rhine Graben has been the site of a long history of mining for energy purposes. Indeed, it is in this region that pioneering oil explorations were carried out (from 1741 to 1970) with the discovery of the Pechelbronn oil field. Geophysical explorations and numerous drillings also revealed an abnormally high thermal gradient of 100°C/km in the sedimentary cover, which led to the European deep geothermal project of Soultz-sous-Forêts, the first operational site of an enhanced geothermal system (EGS) in the world. It has become one of the best documented natural laboratories for studying geothermal systems in magma-poor continental rift systems.
In the global context of energy transition, the importance of the Rhine Graben is not only to explore and extract geothermal energy (heat and/or electricity) and associated co-products (e.g. lithium), but also to serve as a laboratory to better understand the potential of deep fractured reservoirs and their hydrothermalism, in the production and storage of decarbonated energy while controlling environmental and seismic risks. A major challenge is to know how to optimize the identification of locations for the exploitation of these geo-energy resources in order to build energy plants that are economically viable, environmentally sustainable and socially acceptable.
While recent failures in geothermal exploration in the Rhine Graben may have reduced economic enthusiasm and societal acceptance of this low-carbon energy, they demonstrate that additional research is needed to assess the risks, understand the processes involved in geothermal exploitation, and better locate sites for future geothermal power plants. These failures also show that future geothermal exploration and production must better interact industrial projects and academic research. It also requires a better understanding of the geologic setting, requires direct access to data sets and measurements from ongoing projects to learn while exploring, drilling, and stimulating reservoirs, especially along regional faults where the georesources are expected to be most favorable, but the seismic risk most significant.
Subsurface use has been highly controversial in this region, due to its importance to local energy transition plans and seismic crises. The Rhine Graben is the ideal site, not only from a geological and historical perspective, but also because of these debates and the close interaction between the academic community, industry, and local policymakers as they strive to make geothermal energy sustainable, economically viable, and socially acceptable. The lessons learned from the Rhine Graben can be transferred to other basins, outside of the magmatic contexts, which are widespread in Western Europe.
