The prefecture of Bas-Rhin presented on Wednesday the conclusions of an administrative investigation carried out after earthquakes caused by the activity of a geothermal power plant. The operator disputes these conclusions.
Le Monde avec AFP
The investigations were carried out after numerous earthquakes linked to the activity of a geothermal energy. The prefecture of Bas-Rhin presented, Wednesday, December 30, the conclusions of this administrative investigation, reporting “significant deviations” committed by the operator, who disputes these conclusions.
Carried out on request of the prefecture after the earthquakes which shook the Strasbourg metropolitan area on December 4, one of which was magnitude 3.5, the survey “shows that there were significant deviations from the authorization” granted at the Fonroche Géothermie company, announced the prefect Josiane Chevalier at a press conference.
“This analysis revealed two non-conformities”, detailed Hervé Vanlaer, director of the management Regional Environment, Development and Housing (Dreal) of Grand-Est. “The first is drilling deeper than planned”, carried out up to 5,000 meters, against an authorization at “4,200 meters, with a tolerance of 600 meters”. “We have fully entered the crystalline massif, granite”, he said, “and we know that granite can have more important seismic reactions”. The second “deviation” noted concerns the pressure at which the water taken from deep was then reinjected into the subsoil.
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“It was planned not to exceed 100 bar pressure at the wellhead, but in November 2019 and August 2020, higher pressures were observed, of 150 and 140 bar respectively”, explained Mr. Vanlaer . In November 2019, a magnitude 3.1 earthquake had already been recorded 5 km from the geothermal site, the origin of which, natural or linked to human activity, is not defined with certainty. The prefecture and Dreal stressed that the cause and effect link between these “deviations” and the earthquakes was not established. An “expert committee” will be set up “at the beginning of the year” 2021 to look into this issue.
The project definitively stopped
“The company does not respect not what is provided for in a prefectural decree, it is a fault “, concluded the prefect, adding that prosecutions were” a hypothesis not to be excluded “. Contacted by Agence France-Presse (AFP), Jean-Philippe Soulé, the director of Fonroche Géothermie, strongly contested these conclusions.
Initially, “we drilled to a depth of 4,700 meters “, he assured. The extension of the drilling, up to 5,000 meters, was then carried out, from the end of January 2020. “This extension is not to allow us to produce, it is an extension for research purposes. scientific data, carried out as part of an expertise commissioned by the prefecture itself “, to determine the causes of the earthquake of November 2019, according to Mr. Soulé. It also ensures that the 100 bar limit applies to the pressure measured at the lower end of the injection well and not at the wellhead, allowing overpressures on the surface.
This geothermal power plant project, located in Vendenheim, in the Strasbourg metropolitan area, was definitively shut down after the earthquakes of December 4. It represented an investment of nearly 100 million euros. On site, in order to limit the seismic risks, shutdown operations are progressively continuing. “We have come about halfway,” said Vanlaer, recalling that a magnitude 2.5 tremor was recorded on Christmas Day.
For the time being, the three other geothermal power plant development projects in the department, led by Fonroche Géothermie and Electricité de Strasbourg, are suspended. “I doubt very much that in 2021 we can restart something, it will take time, warned the prefect. The social acceptability of geothermal energy has become very low.”
