Geothermal project St. Gallen

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The St. Gallen geothermal project was the largest geothermal project in Switzerland . It was considered an internationally significant pilot project for the use of geothermal energy in non-volcanic subsoil.

methodology

The city ​​of St. Gallen's geothermal project is based on the "hydrothermal system" method. This method is used when hot water is present in deep rock layers, so-called aquifers . The water is taken from the aquifer via a first deep borehole and brought to the surface for use. After use, the cooled water is returned to the aquifer via a second borehole at another point. This creates a water cycle through which thermal energy can be continuously extracted from the subsurface . If the hot water flows in sufficient quantities, it can be used directly to generate heat. If the water temperature is higher than approximately 100 degrees Celcius, it can also be used to drive a steam turbine to generate electricity . In the underground of St. Gallen, water temperatures of 140 degrees Celsius were expected in advance of the drilling.

Political decisions

On August 24, 2010, the St. Gallen City Parliament approved a credit line of CHF 159 million by a large majority. The loan is intended to finance drilling to a depth of 4500 m, the construction of a geothermal heating plant and the expansion of the district heating network. On November 28, 2010, the St. Gallen sovereign approved the credit line with 82.9% yes-votes.

realization

drilling

Drilling began in early March 2013 and was expected to take approximately 100 days. First about 1000 m was drilled vertically and then in two stages another 3000 m laterally into the target area, where at about 4000 m depth below Abtwil 140 degrees hot water was assumed.

Interruption after earthquake

On July 20, 2013, several earthquakes at a depth of 4000 m with a magnitude of 3.6 were recorded in the vicinity of St. Gallen . During the scheduled cleaning of the bottom of the borehole at a depth of 4450 m with dilute hydrochloric acid , natural gas was suddenly released. The available blowout preventer did not have to be used. Heavy mud was initiated to stabilize the borehole , which can probably be blamed for triggering the quake. The drilling was interrupted in order to stabilize the borehole and to examine possibilities for the continuation of the geothermal project. On the night of July 21st, a controlled flaring of the gas that had accumulated in the borehole and technical stabilization of the borehole began, which was achieved in the following days. The St. Gallen city ​​council decided on August 27, 2013 to resume and complete the ongoing drilling phase.

Production test

In November 2013, the production tests were successfully completed, the well sealed and the derrick dismantled. Water at 140–145 degrees Celsius was found in significant quantities, and methane in unexpectedly large quantities and purity. The extent to which the water and gas reserves can be used economically was clarified through an in-depth analysis of the data collected. An initial evaluation of the data was presented in February 2014. At 145 degrees, the expected water temperature was slightly exceeded, but the measured delivery rate of 6 liters per second was too low to implement the originally planned project. This would have required 50 liters per second. On the other hand, the actually undesirable gas deposits turned out to be unexpectedly large. The gas production was up to 5000 standard cubic meters per hour, which roughly corresponds to the average consumption in the city of St. Gallen on a spring or autumn day. However, the amount of gas present in the subsurface cannot be reliably estimated at the moment. As a result, three alternative scenarios for the geothermal project were examined in depth: reduced use by means of a second borehole (double), modified water and gas use by means of the existing borehole (singlet) and the insertion of a deep geothermal probe in the existing borehole.

Possible natural gas production

The city council announced in May 2014 that it would no longer pursue the two scenarios of the second borehole and the deep geothermal probe. A second well (duplicate) would be uneconomical because of the low production rate and would also entail a permanently increased risk of earthquakes. The original plans for a large geothermal power plant could therefore definitely not be implemented. The installation of a deep geothermal probe is uneconomical in view of the low thermal output to be expected (0.4–0.7 MW). A feasibility study by the city of St. Gallen came to the conclusion that gas production was technically and legally possible. The high methane content of the natural gas found allows it to be fed into the gas network with relatively little effort. After further clarification, however, the city council decided not to realize the natural gas production in 2016 for economic reasons. According to estimates, the investments of around 6.5 million francs would have clearly exceeded the possible income of around 3.5 million francs.

Web links

Individual evidence

  1. ↑ Neue Zürcher Zeitung : St. Gallen digs into the depths , accessed on December 1, 2013
  2. ↑ Neue Zürcher Zeitung: St. Gallen is drilling for heat , accessed on December 1, 2013
  3. ↑ St. Galler Tagblatt : From now on it's only going downhill , accessed on December 1, 2013
  4. ↑ Swiss Seismological Service, current report on July 20, 2013 ( memento of the original from October 25, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / edit.seismo.ethz.ch
  5. ↑ Geothermal project St. Gallen: reports on the drilling process , accessed on July 21, 2013
  6. ↑ Neue Zürcher Zeitung: Geothermal drilling temporarily stopped , accessed on July 20, 2013
  7. ^ Neue Zürcher Zeitung am Sonntag: Geothermal energy is threatened , accessed on July 21, 2013
  8. ↑ St. Gallen geothermal project: media release of July 21, 2013 (PDF; 45 kB), accessed on July 21, 2013
  9. ↑ News.ch: Stable situation in St. Gallen , accessed on July 26, 2013
  10. ↑ St. Gallen continues the project. A second chance for geothermal energy
  11. ↑ Jörg Krummenacher: Gas and water from the borehole. Neue Zürcher Zeitung , November 7, 2013, accessed on December 1, 2013 .
  12. ↑ Jörg Krummenacher: Too little water in the St. Gallen underground. Neue Zürcher Zeitung , February 14, 2014, accessed on April 3, 2014 .
  13. ↑ Singlet remains an option. City Council St. Gallen, May 14, 2014, accessed on May 14, 2014 .
  14. ↑ St. Gallen geothermal project: gas extraction possible. Neue Zürcher Zeitung, September 18, 2014, accessed on September 18, 2014 .
  15. ↑ Daniel Wirth: City refrains from gas production. In: St. Galler Tagblatt. April 14, 2016. Retrieved February 26, 2017 .

Coordinates: 47 ° 24 '54.6 "  N , 9 ° 19' 44.2"  E ; CH1903:  742 645  /  253313