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Factors Controlling Rate and Magnitudes of Induced Seismicity

Description: 

Advancements central to the world’s transition to a greener economy such as geothermal energy are hampered by a lack of understanding and control of the maximum magnitude event. We develop a physical model for induced seismicity rate and identify the dominant factors on induced event magnitudes in the context of a control and optimization framework that may be utilized for sophisticated design of injection schedules.

Induced seismicity observed during Enhanced Geothermal Stimulation (EGS) at Otaniemi, Finland is reproduced by a physical model based on pore pressure diffusion and rate-and-state friction. The physical model produces simulations closest to the observations when assuming rate-and-state friction for shear failure with a diffusivity matching the pressure build-up at the well-head at onset of injections. At the same time, pressure drawdown immediately following shut-in's is best modelled with a lower diffusivity, indicating a significant change in diffusivity through fracture opening and closure. The physical model shows that the time-dependent nucleation process significantly affects the spatial evolution of seismicity. This implies that neglecting rate-and-state effects can bias estimates of fluid diffusivity from the seismicity triggering front. The potential of the model to serve as a forecasting tool is demonstrated by a pseudo-forecast that closely matches the entire seismicity rate history, using only the first injection stage as the training period.

Next, we focus on the magnitude-frequency distribution of seismicity and how they may correlate to the injections. We observe a dominant, negative correlation of the b-value and Mmax to depth, and additional negative correlations to cumulative injected volume. We observe a non-linear relationship between magnitudes and distance from the injection source, similarly to the geothermal stimulation operation in Basel. We aim to identify the dominant factor from injections and possibly the initial conditions of the nucleation sources that is consistent with the non-linear relationship of the magnitudes to distance.

Session: Seismic Monitoring, Modelling and Management Needed for Geothermal Energy and Geologic Carbon Storage - II

Type: Oral

Date: 5/2/2024

Presentation Time: 10:30 AM (local time)

Presenting Author: Taeho

Student Presenter: Yes

Invited Presentation: 

Authors