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Factors Characterizing Stable Seismic Energy Release During Hydraulic Stimulations: Egs Helsinki and Experimental Perspective

Description: 

Near-realtime high-frequency seismic monitoring of fluid injection allowed mitigating induced seismicity during two hydraulic stimulations performed in 2018 and 2020 in a deep geothermal well near Helsinki, Finland. Using near-realtime information on the evolution of seismic and hydraulic energy, pumping was either stopped or varied, following the theoretical predictions from a physics-based model of maximum magnitude, avoiding occurrence of project stopping large earthquakes.

We present factors contributing to the project success: 1) adaptive stimulation strategy, 2) structural inventory of the reservoir and 3) limited stress transfer. Seismic injection efficiency, the ratio of radiated-to-hydraulic energy, allows to identify whether evolution of induced seismic events is stable as predicted by existing models of maximum magnitude or not possible indicating upcoming run-away rupture. Tracking structural inventory of the reservoir with relocated earthquake hypocenters, focal mechanisms and source parameters gives information on potentially hazardous localization processes on major pre-existing structures also indicating potential for significant stress transfer. Finally, seismicity passively responding to injection operations, as in the case of the Helsinki project, is well described by a non-stationary Poisson process modulated by the hydraulic energy input rate. However, observable clustering in space and time, or deviation from random distribution of magnitudes in time and space may suggest emergence of instability in the stimulated reservoir. In the talk we will discuss a pool of physically explainable seismo-mechanical and statistical parameters that could be potentially used in developed ML/AI frameworks to analyze the stability of the seismic release during geothermal stimulations.

Session: De-risking Deep Geothermal Projects: Geophysical Monitoring and Forecast Modeling Advances

Type: Oral

Date: 4/18/2023

Presentation Time: 10:00 AM (local time)

Presenting Author: Grzegorz Kwiatek

Student Presenter: No

Invited Presentation: Yes

Authors