Stress analysis in fault damage zones taking the transverse anisotropy into account

in: 2017 Ring Meeting, pages 1--16, ASGA

Abstract

The stress in zones impacted by faults undergoes a certain number of changes and can greatly differ from the regional stress. Faults are usually described as plane surfaces between two blocks of rocks but the fault-strain envelope model represents them as volumes, which is closer to reality. It defines the fault as an envelope divided into two parts: the fault core which is the innermost part of the fault and the damage zone around it. The density of microfractures is greater inside the fault envelope and increases with the proximity to the fault core. It greatly affects the elastoplastic properties of the rocks like the Young's modulus which increases with the distance to the fault core or the Poisson's ratio which decreases. These changes of properties impact directly the stress in the whole zone. The goal of this study is to offer new ways to model the stress inside the fault damage zone by taking into account this phenomenon. To simplify the problem, we only considered the case of rocks with perfect elastic behavior. We first considered a cellular isotropic case where the elastic coefficients vary inside the fault envelope depending on the direct distance to the fault core but it doesn't totally respect the real behavior. Studies have indeed shown that the fault envelope isn't an isotropic material but is closer to a transversely isotropic material, the main direction of anisotropy being perpendicular to the fault. The cellular isotropic case is fully implemented and its results show stress accumulation on the extremities of the fault. The transversely isotropic case is partially implemented, but it still needs further studies to determine realistic values of the elastic parameters along with analytical solutions to validate the results.

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BibTeX Reference

@INPROCEEDINGS{Frantz2017,
    author = { Frantz, Yves and Mazuyer, Antoine and Cupillard, Paul and Conin, Marianne },
     title = { Stress analysis in fault damage zones taking the transverse anisotropy into account },
 booktitle = { 2017 Ring Meeting },
    number = { 1987 },
      year = { 2017 },
     pages = { 1--16 },
 publisher = { ASGA },
  abstract = { The stress in zones impacted by faults undergoes a certain number of changes and can greatly differ from the regional stress. Faults are usually described as plane surfaces between two blocks of rocks but the fault-strain envelope model represents them as volumes, which is closer to reality. It defines the fault as an envelope divided into two parts: the fault core which is the innermost part of the fault and the damage zone around it. The density of microfractures is greater inside the fault envelope and increases with the proximity to the fault core. It greatly affects the elastoplastic properties of the rocks like the Young's modulus which increases with the distance to the fault core or the Poisson's ratio which decreases. These changes of properties impact directly the stress in the whole zone. The goal of this study is to offer new ways to model the stress inside the fault damage zone by taking into account this phenomenon. To simplify the problem, we only considered the case of rocks with perfect elastic behavior. We first considered a cellular isotropic case where the elastic coefficients vary inside the fault envelope depending on the direct distance to the fault core but it doesn't totally respect the real behavior. Studies have indeed shown that the fault envelope isn't an isotropic material but is closer to a transversely isotropic material, the main direction of anisotropy being perpendicular to the fault. The cellular isotropic case is fully implemented and its results show stress accumulation on the extremities of the fault. The transversely isotropic case is partially implemented, but it still needs further studies to determine realistic values of the elastic parameters along with analytical solutions to validate the results. }
}