Subsurface potential for the energy transition

Outstanding result / Good practices for controlling induced seismicity in deep geothermal energy projects

BRGM, in collaboration with Ineris, published a good practice guidebook designed primarily as an operational tool for operators, in 2023. Together with a training course, it aims to improve the prevention of seismicity induced by these operations.

View of the Vendenheim deep geothermal site in Alsace. © Fonroche Géoth_2

On 12 November 2019, a widely felt earthquake hit the Strasbourg region. Not far from there, in Vendenheim, two boreholes were being drilled with a view to installing a geothermal doublet extending down to 5 kilometres underground. A committee of experts concluded that the operations had induced an earthquake. Although exploration of the site was halted, the event highlighted the need to better assess and address this risk. Hence the decision to draw up a guidebook aimed at reinforcing preventive measures for deep geothermal operations.

At the request of the General Directorate for Risk Prevention (DGPR) within the Ministry of Ecological Transition and Territorial Cohesion, and the General Directorate for Energy and Climate (DGEC) within the Ministry of Energy Transition, BRGM and Ineris are tackling the task, in the wake of the 2021 reform of the Mining Code and the Climate and Resilience Act. There are many, complementary challenges: "The need is to secure the investments of deep geothermal energy operators, support the public policies of local authorities in terms of energy transition and reassure the population that operations are carried out in a responsible and controlled manner," explains Pascal Dominique, a seismologist. "In a context of climate change, this renewable, non-intermittent energy source can contribute to the transition to a lower-carbon energy mix."

Applicable to all deep geothermal energy projects

Published in June 2023 and available on institutional (ministries, BRGM, Ineris, etc.) and specialist websites (geothermies.fr), the “Guide to good practice for controlling seismicity induced by deep geothermal operations” is aimed at all stakeholders in the sector: operators, public authorities, local residents, elected representatives and associations. It is also applicable to all deep geothermal projects, covering the different types of geothermal reservoirs and operating methods encountered in mainland France and the French overseas departments and regions.

Designed as an instruction manual, it is based on extensive feedback, and on the current state of scientific knowledge in the field of seismicity induced by the injection of fluid deeply into the subsurface and a method developed by BRGM and Ineris. "We have chosen," explains Julie Maury, a seismologist, "to propose 'decision trees': at each key stage of a project, from before the first drilling to the end of the activity, and during the stimulation periods, the guidebook helps operators to assess the level of induced seismic risk. It also provides recommendations on the data to be acquired to anticipate the hydromechanical behaviour of the reservoir as far as possible, as well as on the monitoring network and the management of operations according to the level of seismic risk." Furthermore, it lays the foundations for defining protocols for deploying operations based on the technologies used and the micro-seismicity detected.

The Guide to good practice for the control of seismicity induced by deep geothermal operations is intended to be enriched in the future by the experience and knowledge of the various players in the sector. © BRGM

At the interface between research and industry

The publication of this guide was accompanied by training days in October 2023. In addition, BRGM and Ineris will be offering a training course based on the lessons learned and the recommendations made, at the end of 2024 and every year thereafter. The aim is the same: to encourage operators to take more care to prevent the risks associated with seismicity induced by deep geothermal operations. “For any project of this type, it is essential to have thorough knowledge of the subsurface geology and to understand the natural phenomena, particularly seismic phenomena, likely to be triggered by the work, in order to minimise their probability and intensity,” concludes Pascal Dominique.

Located at the interface between research and industry, the guidebook will be updated regularly. "Depending on the applications to which it is put, advances in knowledge and new feedback, the content may be enriched, clarified or modified," says Julie Maury. “The guidebook," continues Pascal Dominique, "is the first reference framework – there were none until now – for this risk. It fills a real gap and enables the dissemination and sharing of best practice to encourage the continued development of deep geothermal energy in France, by strengthening project management."

Map of potential deep geothermal resources and active deep geothermal facilities under development for heat production. © BRGM

Julie

Maury

Seismologist

Pascal

Dominique

Seismologist

This guidebook fills a real gap and enables the dissemination and sharing of best practice to encourage the continued development of deep geothermal energy in France, by strengthening project management.