dos Observance out-of Fault Permeability Improvement During the Fluid Injections Tests

Contained in this investigation, i manage injections-induced “aseismic” slip and you may, specifically, the way the enhancement from blame permeability impacts the development away from slip. So you can unravel potential controls with the aseismic slip, i first review the newest development out of fault permeability with the aseismic deformations noticed throughout an out in situ try out away from fluid injections towards a heavily instrumented fault in the a beneficial carbonate development (Guglielmi, Cappa, mais aussi al., 2015 ). Second, we make paired hydromechanical simulations off liquid shot in a single planar blame lower than stress and you can liquid stress conditions the same as those based in the in the situ try out. I concentrate on the effectation of the change within the fault permeability for several 1st worry requirements and you may rubbing laws in order to clarify just how this could change the growth of aseismic sneak.

where ?f is the viscosity of fluid (Pa.s) and w is the fault width (m). In a parametric analysis, we find values of hydraulic aperture that minimize the misfit between model predictions and observed pressure and flow rate histories at the injection point. The permeability is then defined from the best fit value of hydraulic aperture. Thus, this experiment christian cupid odwiedzajД…cych offers ideal conditions to evaluate how fault permeability evolves with accumulated displacements, both during aseismic deformation and seismic activity, and to constrain further hydromechanical modeling analyses of fault slip (see section 4).

step three Hydromechanical Modeling of Blame Sneak by the Liquid Shot

Findings exhibited an elaborate interplay between water stress, blame deformation, and you may fault permeability transform. Guglielmi, Cappa, ainsi que al. ( 2015 ) revealed that the increase when you look at the water stress induces blame beginning and you may aseismic slip at the treatment. The newest seismicity will then be brought about indirectly at a distance out-of injections by the stress import on the propagating aseismic slip. Duboeuf ainsi que al. ( 2017 ) confirmed which apparatus for the a number of 11 treatment experiments during the the same site. In these tests, seismic occurrences had been found between 1 and you can 12 yards in the injection products where in fact the counted fault slip try aseismic. Next, Guglielmi, Cappa, ainsi que al. ( 2015 ) discover an excellent fourteen-fold increase of one’s blame permeability from 0.07 to a single.0 ? ten ?ten yards dos during the period of aseismic sneak, symbolizing regarding 70% of total cumulative permeability increase (20-fold) in shot months (Contour 1). On the other hand, while in the a subsequent age of seismic craft far away of injections, the fault permeability simply expands from a single.0 ? 10 ?ten to a single.35 ? 10 ?10 m 2 . And that, this type of outlined observations regarding blame permeability enhancement through the fault activation emphasize your development off blame hydraulic variables is very important understand the growth regarding sneak throughout the water shot. Obviously, the rise inside the fluid tension causes blame beginning and you may slip that result in permeability changes. After that, the many modes from fault permeability alter seem to influence new sneak behavior.

step three.1 Design Configurations

The procedure has been previously used to test the fresh hydromechanical choices away from fractured stones and you may blame areas throughout fluid pressurization (Cappa mais aussi al., 2006 ; Guglielmi mais aussi al., 2008 ), exhibiting your evolution off blame hydraulic diffusivity are a completely combined state based be concerned and you may liquid tension (Guglielmi, Elsworth, et al., 2015 ).

We select a simplified yet representative 2-D model (200 m ? 50 m) that considers fluid injection into a horizontal flat fault in a homogeneous elastic and impervious medium (Figure 2a). The remote normal (?n) and shear stress (?) resolved on the fault plane are constant. During injection, the fluid pressure in the fault is increased step by step in 0.5-MPa increments every 150 s. Injection occurs in a point source (Figure 2a) in order to reproduce a loading path consistent with the in situ data presented in Figure 1. The total time of injection is 1,050 s. We focus on the period of largest increase of fault permeability observed in the in situ experiment (Figure 1b). For numerical accuracy, the mesh size is refined along the fault (0.15 m) and gradually increases to 0.5 m in the direction normal to the fault toward model boundaries.

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