Potential influence of overpressurized gas on the induced seismicity in the St. Gallen deep geothermal project (Switzerland)
Open access
Datum
2019-11-18Typ
- Working Paper
ETH Bibliographie
yes
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Abstract
In July 2013, the city of St. Gallen conducted a deep geothermal project that aimed to exploit energy for district heating and generating power. A few days after an injection test and two acid stimulations that caused only minor seismicity, a gas kick forced the operators to inject drilling mud to combat the kick. Subsequently, multiple earthquakes were induced on a fault several hundred meters away from the well, including a ML 3.5 event that was felt throughout the nearby population centers. Given the occurrence of a gas kick and a felt seismic sequence with low total injected fluid volumes (~ 1200 m3), the St. Gallen deep geothermal project represents a particularly interesting case study of induced seismicity. Here, we first present a conceptual model based on seismic, borehole and seismological data suggesting a hydraulic connection between the well and the fault. The overpressurized gas, which is assumed to be initially sealed by the fault, may have been released due to the stimulations before entering the well via the hydraulic connection. We test this hypothesis with a numerical model calibrated against the borehole pressure of the injection test. We successfully reproduce the gas kick and the temporal and spatial characteristics of the main seismicity sequence that followed the well control operation. The results indicate that the gas may have destabilized the fault during and after the injection operations and could have enhanced the resulting seismicity. This study may have important implications for future deep hydrothermal projects conducted in similar geological conditions. Mehr anzeigen
Persistenter Link
https://doi.org/10.3929/ethz-b-000391352Publikationsstatus
publishedExterne Links
Zeitschrift / Serie
Solid Earth DiscussionsVerlag
CopernicusOrganisationseinheit
02818 - Schweiz. Erdbebendienst (SED) / Swiss Seismological Service (SED)
Förderung
160555 - To induce or not to induce: an open problem. Study on injection-induced seismicity for GeoEnergy applications, from lab to field scale (SNF)
Zugehörige Publikationen und Daten
Is supplemented by: https://doi.org/10.3929/ethz-b-000369225
Is previous version of: https://doi.org/10.3929/ethz-b-000418035
ETH Bibliographie
yes
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