EGU2020-12863
https://doi.org/10.5194/egusphere-egu2020-12863
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

The role of fault offset in induced seismicity potential

Victor Vilarrasa1,2, Francesco Parisio3, Roman Makhnenko4, Haiqing Wu2,5, and Iman Rahimzadeh Kivi6
Victor Vilarrasa et al.
  • 1Consejo Superior de Investigaciones Científicas, IDAEA-CSIC, Barcelona, Spain (victor.vilarrasa@idaea.csic.es)
  • 2Associated Unit: Hydrogeology Group (UPC-CSIC), Barcelona, Spain
  • 3Chair of Soil Mechanics and Foundation Engineering, Technische Universitaet Bergakademie Freiberg, Germany
  • 4Department of Civil & Environmental Engineering, University of Illinois at Urbana-Champaign, USA
  • 5Department of Civil and Environmental Engineering (DECA), Universitat Politècnica de Catalunya (UPC), Barcelona, Spain
  • 6Department of Petroleum, Gas and Petrochemical Engineering, Shahid Chamran University of Ahvaz (SCU), Ahvaz, Iran

Geological media is envisioned as a strategic resource to store large volumes of CO2 and mitigate climate change. Geo-energy applications, such as geologic carbon storage, geothermal energy, and subsurface energy storage, involve injection and extraction of fluids that cause pressure diffusion. Pore pressure changes may induce seismicity, especially in faults that intersect the injection formation or are hydraulically connected with it. We numerically study with finite element analysis of coupled hydro-mechanical conditions how fault stability is affected by fluid injection into a porous aquifer that is overlaid and underlain by low permeability clay-rich formations. We model a layered sedimentary basin with alternating soft and low permeability with stiff and high permeability formations and include the crystalline basement at the bottom. Additionally, a low permeability steep fault, whose offset ranges from zero to the reservoir thickness, crosses the system. We consider a normal faulting stress regime typical of extensional environments. Simulation results show that the reservoir pressurization as a result of fluid injection causes significant stress changes around the fault that affect its stability. The stress changes depend on the stiffness of the rock juxtaposed to the pressurized reservoir. If there is no offset, the rock is stiff on both sides of the fault, inducing a homogeneous horizontal total stress increase along the thickness of the reservoir. As a result, the deviatoric stress becomes smaller and the induced seismicity potential is low. As the fault offset increases, some part of the base rock gets juxtaposed to the pressurized reservoir. The soft base rock deforms more than the reservoir rock in response to the reservoir expansion, inducing a lower horizontal total stress. Thus, fault stability reduces when the pressurized reservoir rock is juxtaposed with the softer base rock. This finding shows that the induced seismicity potential may increase with the fault offset.

How to cite: Vilarrasa, V., Parisio, F., Makhnenko, R., Wu, H., and Rahimzadeh Kivi, I.: The role of fault offset in induced seismicity potential, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12863, https://doi.org/10.5194/egusphere-egu2020-12863, 2020

Comments on the presentation

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Presentation version 1 – uploaded on 30 Apr 2020
  • CC1: Comment on EGU2020-12863, Nikita Bondarenko, 07 May 2020

    Hello!

    Thank you very much for interesting presentation. I have a few questions and appreciate if you answer it. I wonder about the reason why shear-normal stress ratio is higher for offset of half reservoir rather than for full reservoir offset. It seems to me that pressurization should be higher for full offset and it should provide the highest value for shear-normal stress ratio. What is the reason for higher value for shear-normal stress ratio in case of half reservoir offset? Does it means that half offset fault have higher potential for induced seismicity than full offset?

    Thank you!

    • AC1: Reply to CC1, Victor Vilarrasa, 12 May 2020

      Dear Nikita,

       

      Thank you very much for your interest. The maximum shear stress to effective normal stress ratio is similar in both the half offset and the full offset. Additionally, the portion of the fault with a ratio higher than the typical fault strength, i.e., shear stress to effective normal stress ratio equal to 0.6, is larger for the full offset case than the half offset. As a result, since earthquake magnitude scales with the rupture area, the induced seismicity is expected to have a higher magnitude in the full offset than the half offset.

      You should also take into account that fault stability is not only affected by pore pressure changes, but also by poromechanical stress changes, which depend on the stiffness of the rock placed on the other side of the pressurized fault. You can find more details in Vilarrasa et al. (2016), Journal of Rock Mechanics and Geotechnical Engineering.

      I hope I've clarified your doubt, if not, just write another comment.

      Best wishes,

      Víctor