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Numerical modeling of fracturing in permeable rocks via a micromechanical continuum model
Author(s) -
Eghbalian Mahdad,
Wan Richard,
Pouragha Mehdi,
Fung Larry S.
Publication year - 2019
Publication title -
international journal for numerical and analytical methods in geomechanics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.419
H-Index - 91
eISSN - 1096-9853
pISSN - 0363-9061
DOI - 10.1002/nag.2940
Subject(s) - poromechanics , mechanics , constitutive equation , materials science , anisotropy , representative elementary volume , geotechnical engineering , coalescence (physics) , material properties , microscale chemistry , porous medium , geology , finite element method , porosity , physics , structural engineering , engineering , composite material , mathematics , mathematics education , quantum mechanics , astrobiology
Summary The paper presents a micromechanical approach to describe the failure of low‐permeability brittle rocks as a multiscale fracturing process based on a poroelastic microcrack‐damage model. Failure is formulated deep down at the fine pore scale as a material degradation phenomenon driven by microcrack growth that also impacts upon hydromechanical properties. A set of damage tensors describes the effect of dual‐scale porosities (nanopores and microcracks) on both the hydraulic and poroelastic rock properties. Essentially, the multiscale model reconstructs the coupling effect of hydromechanical forces at the continuum level from the ground up through the upscaling of multiphase interactions at the fundamental structural level of the material. As a result, many macroscopic characteristics emerge naturally such as friction angle, fracture properties, and most importantly, Biot's coefficient taking on a tensorial form that is generally anisotropic. The model is validated within the framework of finite elements to illustrate various baseline constitutive features such as the effect of microcrack growth on the nonlinear stress‐strain response and the induced anisotropy in the context of lab experimental tests and boundary value problems. Heterogeneities of the rock samples were incorporated by choosing material properties to be stochastic following Weibull and lognormal distributions. Numerical results appropriately replicated typical experimental observations where fracture localization and propagation are shown to be a multiscale phenomenon emerging from microcrack growth and coalescence at the microscale, with concomitant enhancement in fluid conductivity.