Castor Project: Chronicle of a Death Foretold
Cushion gas injection at the Underground Gas Storage (UGS) project of Castor, Spain, induced hundreds of induced seismic events, including a sequence of felt earthquakes in September-October 2013. The sequence included the three largest earthquakes (M4.08, M4.01 and M3.97) ever induced by any of the more than 640 UGS facilities all around the world. This high-magnitude seismicity ended up with the project cancellation and a subsequent investment compensation to the operating company that may cost up to 4.73 billion euros to Spanish citizens. Yet, the causes of the induced seismicity had not been clarified. We have worked in an interdisciplinary research team combining hydrogeology, geomechanics and seismology to proposed a plausible combination of triggering mechanisms that explains the induced seismicity at Castor (Vilarrasa et al., 2021). Seismicity was initially induced by gas injection, which reactivated through pore pressure buildup and buoyancy the critically stressed Amposta fault. The Amposta fault is a critically stressed fault that has become ductile due to the large slip, 1 km, accumulated in the recent geological history. Thus, reactivation of Amposta fault induced aseismic slip that progressively accumulated due to the buoyancy of the injected gas, which continue to act even after the stop of injection. The accumulated slip perturbed the stress around the rupture area of the fault and caused the reactivation of a critically stressed unmapped fault placed in the crystalline basement. The reactivation of this deep fault induced the sequence of felt earthquakes, which was triggered by shear slip stress transfer and slip-induced pore pressure changes that controlled the timing of the earthquakes. A detailed characterization prior to gas injection, including fault stability analysis, would have identified the high risk of inducing seismicity at Castor.
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| Format: | material didáctico biblioteca |
| Language: | English |
| Published: |
2021-06-15
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| Subjects: | Gas injection, Castor Project, |
| Online Access: | http://hdl.handle.net/10261/246856 |
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| Summary: | Cushion gas injection at the Underground Gas Storage (UGS) project of Castor, Spain, induced hundreds of induced seismic events, including a sequence of felt earthquakes in September-October 2013. The sequence included the three largest earthquakes (M4.08, M4.01 and M3.97) ever induced by any of the more than 640 UGS facilities all around the world. This high-magnitude seismicity ended up with the project cancellation and a subsequent investment compensation to the operating company that may cost up to 4.73 billion euros to Spanish citizens. Yet, the causes of the induced seismicity had not been clarified. We have worked in an interdisciplinary research team combining hydrogeology, geomechanics and seismology to proposed a plausible combination of triggering mechanisms that explains the induced seismicity at Castor (Vilarrasa et al., 2021). Seismicity was initially induced by gas injection, which reactivated through pore pressure buildup and buoyancy the critically stressed Amposta fault. The Amposta fault is a critically stressed fault that has become ductile due to the large slip, 1 km, accumulated in the recent geological history. Thus, reactivation of Amposta fault induced aseismic slip that progressively accumulated due to the buoyancy of the injected gas, which continue to act even after the stop of injection. The accumulated slip perturbed the stress around the rupture area of the fault and caused the reactivation of a critically stressed unmapped fault placed in the crystalline basement. The reactivation of this deep fault induced the sequence of felt earthquakes, which was triggered by shear slip stress transfer and slip-induced pore pressure changes that controlled the timing of the earthquakes. A detailed characterization prior to gas injection, including fault stability analysis, would have identified the high risk of inducing seismicity at Castor. |
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