Earthquake in Alsace, the future of the compromised geothermal site



It is one shake too many. This Friday, December 4, just before 7 a.m., the inhabitants of the agglomeration of Strasbourg (Bas-Rhin) could feel a seismic shock of magnitude 3.5. Two more were going to be recorded in the morning, no doubt a prelude to a series that could last several days.

In question: the deep geothermal power plant the company Fonroche being installed in Vendenheim, in the north of the agglomeration. The epicenter was located under the well and the company immediately initiated the procedure for stopping all activity on the site, in agreement with the State services.

Although the earthquake has not yet given rise to declarations of damage (slight cracks in the facade have been declared in previous episodes), it worried residents who witnessed crackles and rumblings sometimes suggesting an explosion. . And if the earthquakes are not surprising in the region, the concern here comes from the fact that they are not of natural origin but induced by man.

A series of disappointments

This episode comes after a year of disappointment. In November 2019, the commissioning of the plant was stopped following a first series of abnormal tremors (seismic reactions are normal to a certain point when a geothermal plant starts up, says Fonroche). Tests were started in early October to find the origin of the autumn tremors. They seem to have unleashed further tremors, until Friday’s, of an unprecedented level.

This power plant, originally presented as a green energy project, relies on an existing resource, hot water present five or six kilometers underground. This is pumped, the heat is transformed into energy. The cold water is then reinjected in depth.

A first cogeneration plant

Still in the process of being installed, and not yet at the production stage, it was to be the first in France, not in geothermal energy (there are already two sites in Alsace) but in cogeneration, that is to say in production both electricity and heat. Objective: from 2021 to supply 15,000 to 20,000 households with electricity, 26,000 with heat, and heat 70 hectares of agricultural greenhouses …

For the manufacturer, who has invested 100 million euros in this site, there is no question of talking about the project in the past tense. But the director of the site, Jean-Philippe Soulé, admits himself surprised: “ By creating a path in the rock, geothermal energy necessarily creates microseismicity, but we had not foreseen it at this level. ” According to him, industrialists, scientists and elected officials will give themselves time to understand what he calls abnormal events: “We will no doubt have to adapt our methods, perhaps modify the structures, the location of the well. Then explain, restore the confidence of the population, convince that geothermal energy is indeed a solution for the future, even if project start-ups are not always easy. It would be extremely unfortunate for the sector and the territories for this to end in an impasse “.

“Humility”

Before that, there are many questions waiting to be answered. Does an undetected fault create seismicity? Does the well need to be moved? Was the pressure exerted too great? How come the earthquakes occurred more than three weeks after the tests stopped? “We must recognize our humility in the face of nature, whatever 3D simulations and expertise we have been able to do », Indicates Jean-Philippe Soulé.

→ IN 2019. Teil earthquake: environmental or human cause?

The reaction is more severe on the side of elected officials and the prefecture. Pia Imbs, president of the Strasbourg Eurometropolis, asked “ a final shutdown of the project led by Fonroche in Vendenheim ” at the end of a crisis meeting in the prefecture, during which the prefect announced that it was launching an administrative investigation. Local elected officials such as Catherine Graef-Eckert, president of the group of mayors and independent elected officials and mayor of Lingolsheim did the same.

From December 11, the Eurometropolis will organize a citizen consultation involving all stakeholders and the population, devoted to the energy transition and the special place of geothermal energy.

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