Moeck, Inga and Bloch, Thomas and Graf, René and Heuberger, Stefan and Kuhn, Peter and Naef, Henry and Sonderegger, Michael and Uhlig, Stephan and Wolfgramm, Markus (2015) The St. Gallen Project: Development of Fault Controlled Geothermal Systems in Urban Areas. In: Proceedings World Geothermal Congress 2015, 19-25 April 2015, Melbourne, Australia.
Full text not available from this repository.Abstract
In areas of average geothermal gradients and conduction dominated heat transport, coupled heat-power generation is the most efficient way of geothermal energy utilization. Since heat for district heating cannot get efficiently transported over large distances, viable geothermal resources should be located close to the point of end-use as it is the case in urban areas. The city of St. Gallen in northeast Switzerland matches these requirements: St. Gallen is located in the Molasse Basin, i.e. the northern foreland basin of the Alps with viable deep geothermal resources, and has an installed and expandable district heating system. The project in St. Gallen started in 2008 with a feasibility study considering different target horizons and different concepts of utilization including hydrothermal and petrothermal resources applying conventional and EGS technologies. An extensive 3D seismic survey in 2010 was followed by a public poll about the geothermal project in 2010. After overwhelming advocacy throughout the voting citizens of St. Gallen, planning of the first well started in 2011. In 2013, drilling operation started and the first target horizon in 4 km deep Upper Jurassic carbonate rocks was successfully achieved. After an injection test and well cleaning, a gas kick and subsequent work-over operation caused a seismic event of ML 3.5. Among other approaches, stress field analysis applying the concept of limiting stress ratios, the concept of effective stresses, and the slip tendency technique helped to decide further steps. After a short interruption, the project continued with a 4-weeks production test, which evidenced a gas reservoir of hitherto unknown extend. One of the main conclusions drawn from the project is the existence of dormant faults, which have to be considered in fault-controlled regions with historic seismicity. Dormant faults may have experienced fault healing and strain hardening evolving to a strong fault with high friction coefficient as indicated from geomechanical parameters gained from the St. Gallen well. A focus on dormant fault investigation and their geomechanical characterization might therefore play an important role on future geothermal research topics. With this article we demonstrate best practices of geothermal project development in urban areas, and delineate concepts and critical data required to guide efficient decision making.
| Item Type: | Conference or Workshop Item (Paper) |
|---|---|
| Uncontrolled Keywords: | dormant faults, induced and triggered seismicity, foreland basins, fault zone drilling, gas and brine production |
| Subjects: | Methodology > Method and procesing > Technology-seismicity interaction Region > Switzerland > St. Gallen Inducing technology > Geothermal energy production |
| Project: | S4CE > ST GALLEN: geothermal project |