Abstract
Fluid pressure perturbations in subsurface rocks affect the fault stability and can induce both seismicity and aseismic slip. Nonetheless, observations show that the partitioning between aseismic and seismic fault slip during fluid injection may strongly vary among reservoirs. The processes and the main fault properties controlling this partitioning are poorly constrained. Here we examine, through 3D hydromechanical modeling, the influence of fault physical properties on the seismic and aseismic response of a permeable fault governed by a slip-weakening friction law. We perform a series of high-rate, short-duration injection simulations to evaluate the influence of five fault parameters, namely the initial permeability, the dilation angle, the friction drop, the critical slip distance, and the initial proximity of stress to failure. For sake of comparison between tests, all the simulations are stopped for a fixed rupture distance relative to the injection point. We find that while the fault hydraulic behavior is mainly affected by the change in initial permeability and the dilation angle, the mechanical and seismic response of the fault strongly depends on the friction drop and the initial proximity of stress to failure. Additionally, both parameters, and to a lesser extent the initial fault permeability and the critical slip distance, impact the spatiotemporal evolution of seismic events and the partitioning between seismic and aseismic moment. Moreover, this study shows that a modification of such parameters does not lead to a usual seismic moment-injected fluid volume relationship, and provides insights into why the fault hydromechanical properties and background stress should be carefully taken into account to better anticipate the seismic moment from the injected fluid volume.
Highlights
Fluid injection in the upper crust induces earthquakes (Keranen and Weingarten, 2018)
The spatiotemporal distribution of induced seismicity as well as the partitioning between seismic and aseismic moment released during injection are deeply influenced by the initial proximity of stress to failure of the fault and by its friction drop with slip, and, to a lesser extent, by the initial permeability of the fault and the critical slip distance Dc
We find in our models that an increase in the friction drop or the Shear Capacity Utilization (SCU) leads to a faster migration of the rupture and of the seismicity (Figures 5J–L) and to an increase of both the magnitude and the number of seismic events (Figure 7)
Summary
Fluid injection in the upper crust induces earthquakes (Keranen and Weingarten, 2018). Some studies show that the deformation induced by the injection is dominantly aseismic, with an area totally devoid of seismicity around the injection These observations were made at reservoir scale (Cornet et al, 1997; Calò et al, 2011; Cornet, 2012, 2016; Zoback et al, 2012; Schmittbuhl et al, 2014; Wei et al, 2015; Lengliné et al, 2017; Eyre et al, 2019; Hopp et al, 2019), in laboratory (Goodfellow et al, 2015; Wang et al, 2020) and from meterscale in-situ experiments (Guglielmi et al, 2015a; De Barros et al, 2016; Duboeuf et al, 2017). The aseismic deformation estimated in these small-scale experiments represents more than 95% of the total deformation released during injection (Goodfellow et al, 2015; De Barros et al, 2016, 2018, 2019; Duboeuf et al, 2017)
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