| Abstract |
After 20 years dedicated to research and development, the European EGS pilot project of Soultz-sous-Forêts (France) has entered a new phase, aiming at the building, testing and commissioning of a geothermal power plant. One of the major concern of the project was, and still is, the induced seismicity. During the development of the project, several hydraulic and chemical stimulation tests generated thousands of seismic events. Some of them were felt at the surface, provoking unwanted nuisance for the neighbouring population. As the power plant is expected to run continuously for years, it is necessary to study the behaviour of the geothermal reservoir under circulation conditions, in order to observe and understand the occurrence of microseismic activity. Three circulation tests were carried out at 5 km depth using the 3 deep geothermal wells. During the first 6-months test, operated in 2005 under artesian conditions, around 600 earthquakes were induced. Among them, 4 were above magnitude 2 and thus likely to be felt. During the two other tests, involving downhole production pumps installed in the wells, the seismic activity was of the same order, but no event reached magnitude as large as in 2005. The location of seismic events shows that the same zones of the reservoir were activated in the three tests. Finally the microseismic activity is linked to the hydraulic parameters of the circulation tests, so as to better understand the conditions of generation of the seismicity and try to avoid any repetitive disturbance for the population. |