Developer addresses seismicity concerns related to Alsace geothermal project

Developer addresses seismicity concerns related to Alsace geothermal project Drilling rig on site of Vendenheim project, Alsace/ France (source: Fonroche)
Alexander Richter 6 Jan 2021

Geothermal developer Fonroche has addressed initial findings by authorities related to seismic activity near its geothermal power and heat project at Vendenheim in Alsace, France.

Development company Fonroche Géothermie this week responded to conclusions of an administrative investigation conducted by the Bas-Rhin prefecture after a magnitude 3.3 earthquake in Strasbourg on December 4, 2020. The company claims not to have deviated from the work authorization framework set for the project.

The company denies any deviation in the management of its boreholes in Vendenheim (Bas-Rhin). Its director general, Jean-Philippe Soulé, intends to demonstrate supporting documents, in a statement to the press this week. These will be sent in the coming days to the Regional Directorate for the Environment, Planning and Housing (Dreal) of the Grand Est and to the Bas-Rhin Prefecture, in response to the conclusions of an administrative inquiry launched. The reported seismic event had led the prefecture to demand the definitive stop of this geothermal project.

Scientific purposes

The results of the investigation were unveiled on December 30, 2020, revealing “significant deviations” from the operator compared to the prefectural authorization for the works. Both in terms of drilling depth – up to 5,000 meters, against 4,200 meters authorized with a tolerance of 500 meters -, as well as the pressure of re-injections of geothermal water into the subsoil. Exceedances of up to 150 bars of the permitted ceiling of 100 bars are highlighted by the investigation. However, no link has been formally established, for the time being, between these discrepancies in connection with the performance of “tracing” tests on site and the series of earthquakes recorded on the territory in recent months.

Questioned, the Director of Fonroche Géothermie wanted to respond point by point to this survey. Starting with the operational context: he underlines that “all operations initiated since December 2019”, the date of a first magnitude 3.1 earthquake, were for scientific purposes. This is to try to determine the cause of this event. It is in this context that the decision to extend one of the boreholes 450 meters beyond the initial program was taken in order to study intersecting faults, assures the manager.

Regarding reinjection pressures, the latter notes a “vagueness” in the initial drafting of the decree concerning them. “The authorized pressure is that exerted on the reservoir. Depending on the case, with a pressure of 100 bars at the wellhead, we would have nothing at the bottom because of the pressure drops. He argues that a calculation method taking into account these pressure losses, compared to the pressure measured at the head, was validated by a letter from the Prefect on September 29, 2020. He also insists on regular information from the Dreal of on-site operations, by delivering daily reports.

Asked about the explanation he gives for the failure to take this information into account by the administrative investigation, Jean-Philippe Soulé suggests that it results from the short time allotted to the experts. It lasted less than a month.

Launched on December 4, 2020, the procedure for stopping operations on the site was completed on January 2. The plant, which should have been the first electricity / heat cogeneration site from geothermal energy in France, was never able to start its industrial phase. It represents an investment of EUR 100 million for Fonroche. The operator filed with the administrative court a “question” relating to the order terminating its activity on site.

Three other projects for geothermal power stations in Lower Rhine were temporarily suspended by the prefecture in December as a precaution, two of which were also carried by Fonroche. Regardless of the schedule for the re-authorization of these prefecture projects – unknown to date – the industrialist does not envisage being able to relaunch operations before the second half of 2021, the time to pass the course of observations and analysis of events. from Vendenheim.

Source: Bénédicte Weiss, Les Echos