Webinar cycle in Hydrogeology and Geochemistry
HYDROGEOLOGY GROUP (Associated Unit CSIC-UPC, Barcelona)
Date: Thursday, 2nd March 2023
Starting time: 3:00 pm (Central European Time)
Author: Auregan Boyet, PhD student
Title: Identification of The Processes Triggering Induced Seismicity at the Enhanced Geothermal System of Basel (Switzerland)
Live in: meet.google.com/eyg-mtdm-tyo (free of charge)
- WARNING!: This seminar will not be recorded, therefore it will not be able to be seen as a broadcast delayed or on our You Tube website.
Abstract:
Felt induced seismicity compromises the deployment of geothermal power-plants in urban areas. Enhancement Geothermal Systems (EGS) are located in deep crystalline rocks that require the enhancement of the permeability to improve fluid circulation. Hydraulic stimulation and fluid circulation can induce seismicity. Approaches were developed to limit the nucleation of large magnitude earthquake during fluid injection. But large induced earthquakes, frequently occurring after the shut-in, have led to the shutdown of EGS projects, such as the Deep Heat Mining project in Basel, Switzerland. Induced seismicity is assumed to be triggered by the pore pressure buildup that reduces the effective stresses along faults and fractures, and the occurrence of post-injection large magnitude seismicity is counterintuitive. We investigate the induced seismicity that led to the closure of the Basel EGS project. We set-up a hydro-mechanical finite element numerical model which contains faults designed with the clusters of induced events at Basel and controlled by a Mohr-Coulomb failure criterion. We consider simultaneously pore pressure buildup, poroelastic stressing, shear-slip stress transfer and slip weakening as triggering mechanisms and we identify the process combinations bringing each fault to failure. Fluid-injection increases the pore pressure in the vicinity of the well and reactivate faults during injection. Poroelastic stressing affects the stability of farther faults, inducing reactivation or stabilization. At the shut-in, the poroelastic stress abruptly dissipates and can induce short-term post-injection seismicity along the stabilized faults. The combination of poroelasticity and shear-slip stress transfer is the major triggering mechanism of the post-injection induced seismicity.