Forward induced seismic hazard assessment: application to a synthetic seismicity catalogue from hydraulic stimulation modelling

Abstract

The 3.2-induced seismic event in 2006 due to fluid injection at the Basel geothermal site in Switzerland was the starting point for an ongoing discussion in Europe on the potential risk of hydraulic stimulation in general. In particular, further development of mitigation strategies of induced seismic events of economic concern became a hot topic in geosciences and geoengineering.Here, we present a workflow to assess the hazard of induced seismicity in terms of occurrence rate of induced seismic events. The workflow is called Forward Induced Seismic Hazard Assessment (FISHA) as it combines the results of for-ward hydromechanical-numerical models with methods of time-dependent probabilistic seismic hazard assessment. To exemplify FISHA, we use simulations of four different fluid injection types with various injection parameters, i.e. injection rate, duration and style of injection. The hydromechanical-numerical model applied in this study represents a geothermal reservoir with pre-existing fractures where a routine of viscous fluid flow in porous media is implemented from which flow and pressure driven failures of rock matrix and preexisting fractures are simulated, and corresponding seismic moment magnitudes are computed. The resulting synthetic catalogues of induced seismicity, including event location, occurrence time and magnitude, are used to calibrate the magnitude completeness and the parameters a and b of the frequency-magnitude relation. These are used to estimate the time-dependent occurrence rate of induced seismic events for each fluid injection scenario. In contrast to other mitigation strategies that rely on real-time data or already obtained catalogues, we can perform various synthetic experiments with the same initial conditions. Thus, the advantage of FISHA is that it can quantify hazard from numerical experiments and recommend a priori a stimulation type that lowers the occurrence rate of induced seismic events. The FISHA workflow is rather general and not limited to the hydromechanical-numerical model used in this study and can therefore be applied to other fluid injection models.

Analysis of induced seismicity in geothermal reservoirs – An overview

“…Dynamic fracture distributions allow computation of seismic moment tensors and radiated seismic energy for comparison with hydraulic energy injected into the EGS system . Seismic catalogues for various stimulation scenarios in dynamic fracture growth models can be used for hazard assessment of specific sites and stimulation treatments (Hakimhashemi et al, 2013(Hakimhashemi et al, , 2014.…”

“…In order to guide reservoir operations, we recommend computing indices to quantify seismic reservoir behaviour as a function of time, in particular in the stimulation and production phase of a reservoir. Hakimhashemi et al (2013) used a hybrid approach for computing induced seismicity. They started from a geomechanical model (approach 1) and applied probabilistic techniques to compute seismic hazard (approach 2).…”

“…The hybrid approach by Hakimhashemi et al (2013) combining deterministic, coupled hydromechanical reservoir models with forward induced seismic hazard assessment (FISHA) seems promising.…”

Particle Based Discrete Element Modeling of Hydraulic Stimulation of Geothermal Reservoirs, Induced Seismicity and Fault Zone Deformation

“…Cumulative frequencies of the red and the green histograms are plotted on right ordinate. This is typical way of plotting frequencymagnitude distribution in order to compute the GutenbergRichter b-values which are very often used in seismology and probabilistic seismic hazard assessment (PSHA) to estimate hazard potential (Hakimhashemi et al 2013 Fig. 8), then the occurrence rate of the relatively larger magnitude events also increases.…”

“…So far, several studies have been carried out in order to understand the coupling between the spatio-temporal stress changes and the seismicity in the geothermal reservoirs and their vicinities (Hakimhashemi et al 2013). The corresponding geomechanical models contain different processes such as pore pressure diffusion (Kohl andMégel 2007, McClure andHorne 2011), the pore pressure stress coupling process (Altmann et al 2010, Hillis 2000), thermal diffusion and combination of these processes (Baisch et al 2010, Bruel 2007, Rutqvist et al 2007, Schoenball et al 2010).…”