Predicting fault damage zones by modeling dynamic rupture propagation and comparison with field observations

Abstract

We use a two-dimensional plane strain dynamic rupture model with strongly rate-weakening friction and off-fault Drucker-Prager plasticity to model damage zones associated with buried second-order thrust faults observed in the SSC reservoir. The modeling of ruptures propagating as self-sustaining pulses is performed in the framework of continuum plasticity where the plasticity formulation includes both deviatoric and volumetric plastic strains. The material deforming inelastically due to stress perturbations generated by the propagating rupture is assumed to be the damage zone associated with the fault. Dilatant plastic strains are converted into a fracture population by assuming that the dilatant plastic strain is manifested in the form of fractures. The cumulative effect of multiple slip events is considered by superposition of the plastic strain field obtained from individual slip events. The relative number of various magnitude slip events is chosen so as to honor the Gutenberg-Richter law. Results show that the decay of fracture density (F) with distance (r) from the fault can be described by a power law F = F 0 r À n . The fault constant F 0 represents the fracture density at unit distance from the fault. The decay rate (n) in fracture density is approximately 0.85 close to the fault and increases to~1.4 at larger distances (>10 m). Modeled damage zones are approximately 60-100 m wide. These attributes are similar to those observed in the SSC reservoir using wellbore image logs and those reported in outcrop studies. Considering fault roughness affects local damage zone characteristics, these characteristics are similar to those modeled around planar faults at a scale (~10 m) that affects bulk fluid-flow properties.

From slow to fast faulting: recent challenges in earthquake fault mechanics

“…With the set of parameters used in Andrews's study, off-fault dissipation initially exceeded on-fault dissipation when rupture length surpassed about 300 m, thereafter increasing linearly as a function of rupture length. More sophisticated models were subsequently proposed [36][37][38][39][40][41][42] confirming the findings of [35]. Other studies instead include explicit fault splays branching from the main fault surface [43,44] as a form of broadening the damage zone.…”

Evidence for tectonic, lithologic, and thermal controls on fracture system geometries in an andesitic high‐temperature geothermal field

“…Fluids tend to flow along these joints and contacts between layers (Figure a). In contrast, the spacing of fractures close to faults are commonly clustered according to power law distributions which are scale independent (Figure b) [see Bonnet et al , , for review; McCaffrey et al , ; Johri et al , ]. Power law distributions of fracture mechanical aperture, length, and density are commonly used to generate reservoir‐scale fracture models [ Bonnet et al , ; Davy et al , ], albeit resulting from observations rarely made in volcanic formations.…”

The effect of gradational velocities and anisotropy on fault-zone trapped waves

“…The low velocity waveguide is commonly attributed to the fracture damage zone of the fault caused by past events (Dor et al 2006;Ben-Zion & Ampuero 2009;Faulkner et al 2011;Xu et al 2012). The across-fault profile of the fault might therefore be expected to have a velocity model that behaves in an exponential or power law fashion Li & Vidale 1996;Mitchell & Faulkner 2009;Savage & Brodsky 2011;Johri et al 2014).…”