@inproceedings{epos2268,
       booktitle = {Proceedings World Geothermal Congress 2015},
           month = {April},
           title = {The St. Gallen Project: Development of Fault Controlled Geothermal Systems in Urban
Areas},
          author = {Inga Moeck and Thomas Bloch and Ren{\'e} Graf and Stefan Heuberger and Peter Kuhn and Henry Naef and Michael Sonderegger and Stephan Uhlig and Markus Wolfgramm},
            year = {2015},
        keywords = {dormant faults, induced and triggered seismicity, foreland basins, fault zone drilling, gas and brine production},
             url = {https://episodesplatform.eu/eprints/2268/},
        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.}
}