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Geothermal Energy in Switzerland

In Switzerland, there have been two pilot geothermal energy projects at two different locations with the aim of producing electricity using geothermal energy. Both projects were terminated, which is why there is currently no electricity being produced in Switzerland from geothermal sources (as at December 2015). There are however several deep geothermal systems in operation, which are used to supply heat, for example for district heating grids.

 

Switzerland’s first geothermal energy project with power generation was launched in Basel. Following an exploratory phase, water was injected into the crystalline basement rocks for two weeks in December 2006. The goal was to increase the permeability of the rocks at a depth of 4,000 to 5,000 meters and create a reservoir in which liquid circulates and is heated.

The process of injecting the water was observed by means of a close monitoring system that also included six borehole seismometers operated by the SED at a depth of 300 to 2,700 meters, which recorded thousands of microearthquakes as planned. The injection rate (quantity of liquid) was gradually increased until the maximum rate was reached on the fifth day.

Shortly afterwards, an earthquake with a magnitude of 2.6 occurred. The injection rate was then drastically reduced, and the process was terminated altogether after a few hours. Approximately five hours later, an earthquake with a local magnitude of 3.4 (average = 3.1) was recorded. With an intensity of V, it was widely noticeable and caused small-scale damage. Three further noticeable earthquakes subsequently occurred up until February 2007 and, in total, over 900 earthquakes with magnitudes of 0.9 or greater were recorded. The project managers suspended their plans, terminating the project permanently in 2009 following an extensive risk analysis.

Reports of damage primarily involved small cracks in building facades, and claims amounted to a total of CHF 6 million, the majority of which was settled.

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The geothermal energy project in St. Gallen in 2013 aimed to make use of naturally circulating water in existing aquifers at a depth of over 4,000 meters for power production. Comparable projects in southern Germany, which involved drilling into the same layers of rock, had been implemented with success.

Existing fault zones in the subsoil offer optimal conditions for hydrothermal systems, as they offer greater permeability. A suitable location for drilling work was identified in Sittertobel with the aid of a seismic 3-D model. The decision was made in favor of a fault zone whose seismic potential was rated as low by the operators and by the St. Gallen public utilities company (Sankt Galler Stadtwerke) based on past seismic activity.

The SED installed a seismic network with seven stations – six on the surface and one in a borehole – in advance of the drilling work for the purpose of seismic monitoring.

The drilling work began at the start of 2013, and the first test and simulation measures were implemented in the summer of the same year. The number and intensity of the microearthquakes induced were as expected and not noticeable to the public. On the evening of July 19, 2013, seismic activity began to increase; the earthquakes became stronger and more frequent. Following an initial event with a magnitude of 1.6, the traffic light system as a central precautionary element issued a yellow alarm, indicating that pumping work should be terminated immediately. Because the counterpressure was too high due to rising gas in the borehole and presented a potential risk for the system as a whole, however, the pumping work was continued. Seismicity continued to increase, reaching a climax on the morning of July 20, 2013, with a noticeable earthquake with a magnitude of 3.5. This corresponded to an intensity of IV. While the earthquake was noticed extensively by the public, very few reports of damage were received in comparison with Basel.

Earthquake activity then declined constantly as expected, but increased again in connection with preparations for the production tests from September 16, 2013. During this period, a total of 232 microearthquakes were recorded. The strongest took place on October 2, 2013, and had a magnitude of 2.0. With the start of the production tests on October 15, 2013, during which gas and water were extracted from the subsoil, earthquake activity decreased considerably. Since that time, the SED has recorded only four very weak events. These microearthquakes may have been aftershocks from the earthquake on October 2, 2013, and are thus not necessarily attributable to the production test.

According to the latest findings, the earthquakes triggered are directly linked to the steps taken to tackle the gas-water leak observed on July 19, 2013. Increased rates of earthquakes occur above all when pumping fluids into the subsoil (injection). Pumping fluids out of the subsoil (production), on the other hand, generally results in a decrease of the earthquake rate, provided there is no substantial solidification of sediments (compaction). What is more, if the fault zone reacts sensitively to changes in pore pressure, this is an indication that the zone is subject to critical tectonic tension, and that earthquakes are likely to occur.

The St. Gallen public utilities company concluded the first phase of its geothermal energy project following the production tests, and the project was terminated permanently in spring 2014 following further investigation. The St. Gallen public utilities company explained the reason for the termination of the project as a “combination of insufficient water availability, increased earthquake risk and unexpected gas flow in the layers of rock accessed”.

A detailed chronology of seismicity in connection with the geothermal energy project in St. Gallen can be found here.

Information on real-time monitoring of induced seismicity in St. Gallen can be found here.

Numerous deep geothermal energy projects are currently being planned in Switzerland, and are at various stages of progression. The following map provides an overview:

Planned Projects 1
Source of overview map www.geothermie.ch (as 2016)

Within the framework of the GEOBEST-CH project supported by SwissEnergy, the SED therefore offers competent and project-based seismological consulting and monitoring services for national, cantonal, and local supervisory authorities. Services are only provided to the industrial sector if these do not impact the independence of the SED in any way. The SED also informs the media and the public of any associated potential induced seismicity.