For the experts, there is no doubt that Georhin (formerly Fonroche Géothermie) and its prospecting and injection operations are responsible for the occurrence of strong seismic episodes in the Vendenheim region (Bas-Rhin). ) in December 2020. The company is also no stranger to the seismicity recorded, since November 2019, in the area of La Robertsau, a district north of Strasbourg, about ten kilometers away.
In its report published on Wednesday May 4, the committee of experts – made up of researchers from various universities, the National Institute for the Industrial Environment and Risks and the Bureau of Geological and Mining Research – set up by the prefecture in February 2021, estimates that the “continuous pressure” in one of the two wells, as well as “the cumulative volumes injected (in particular from August 2020)” did lead to the instability of the faults near the site.
On October 27 and 28, 2020, seismic events were recorded in La Robertsau, with a local magnitude of 2.1 and 2.8, then, on December 4, a 3.6 earthquake in Vendenheim. This seismic activity should therefore be related to the operations then carried out by Fonroche Géothermie. For Jean Schmittbuhl, co-author of the report and geophysicist, director of research at the National Center for Scientific Research at the Earth and Environment Institute in Strasbourg, “These seismic events, among the strongest ever recorded due to human activity in France, are clearly linked to the Fonroche geothermal project”. In the document, the experts point out that the occurrence of a “persistent seismicity” between November 5 and November 13, 2020, in the same area, with several elements with a magnitude greater than 2, “should have alerted to the occurrence of an instability phenomenon” et “should have called into question the continuation of the injections”.
“Bad Faith”
On reading the report, the company recognizes problems related to the“accumulation of water around the injection well, following a poor communication of water in the rock with the producing well”, this accumulation having destabilized the fault zone. Geothermal technology relies on injecting water into a well, says “injector”connected to a second, the “producer”, which allows the warm waters found at a depth of some 5,000 meters to be brought up. Heat exploited on the surface for the production of energy, then this cooled water is returned to the injection well.
You have 43.13% of this article left to read. The following is for subscribers only.