Seismic Risk Mitigation for the Haute-Sorne EGS pilot project in Switzerland

Abstract

The objective of the Haute-Sorne deep geothermal pilot project is to produce electricity and heat using multi-stage stimulation techniques in approx. 5km deep crystalline rock. Lessons learned from previous geothermal projects have shown, that detailed seismic risk assessment and corresponding mitigation measures are key to a successful project.
The mitigation of seismic risk for the Haute-Sorne project consists of several layers:
(1) analysis of the seismic risk using deterministic and probabilistic approaches, (2) incorporating lessons learned from previous projects, (3) a step-wise realization process with potential project halting points based on updated risk analysis (4) a change in stimulation concept following a multi-stage stimulation procedure instead of one massive stimulation of the underground, and (5) the usage of traffic light systems combining ‘classical’ approaches with risk forecasting abilities, so called adaptive traffic light systems.
However, for a successful permit not only presenting a state-of-the-art risk assessment and mitigation concept was sufficient. As the project is to date a one-of-a-kind project, preceding discussion rounds with the authorities, experts from the Swiss seismological service and the project owner itself were necessary to come up with a permitting scheme. Seismic risk had to be illustrated and fit into a permitting scheme that authorities are familiar with. In this case the operator could show that risk curves were comparable and lower as the risk of fire in the community, leading in the end to a successful construction permit.