HR: 12:05h
AN: H12A-08    [Abstracts]
TI: Numerical Simulation of Geomechanic Fracture Networks With Isotropic Damage and Transition to Fracture Discrete Representation
AU: * Paluszny, A
EM: apaluszn@imperial.ac.uk
AF: Imperial College, Department of Earth Science and Engineering, London, SW72AZ, United Kingdom
AU: Matthai, S
EM: stephan.matthai@imperial.ac.uk
AF: Imperial College, Department of Earth Science and Engineering, London, SW72AZ, United Kingdom
AB: Fracture networks have a great influence on flow patterns in subsurface hydrological systems. However, these are very difficult to characterize as they are hidden under several layers of subsurface strata. Stochastic methods used to generate fracture datasets rely on sparse data and frequently generate fracture sets that not always obey mechanical laws of fracture initiation and propagation. Alternative geomechanically generated fracture datasets can be developed to generate such fracture networks based on first principle fracture mechanics. However, traditional approaches assume the matrix to be homogeneous, isotropic, and linear elastic. In this work we do not assume the matrix to be linear elastic and implement a finite element based tracking of damage by a sub-grid representation of integrity loss and strain localization. We present an integrated finite-element model which is able to transit from a continuum representation to a discrete representation of damage leading to the formation of new material domains, and the dynamic adaptation of model geometry. The fracture propagation model is based on the growth of a finite set of randomly oriented initial flaws with varying size, capturing the inelastic process zone around fracture tips with a non-linear isotropic damage model. Fracture initiation is determined via a combined Rankine-Mohr-Coulomb failure criterion, and propagation is estimated using a stress intensity-based quasi-static velocity approximation of crack propagation at the fracture tip. Fracture propagation angle is based on the maximum circumferential stress method. Straight and curved fracture geometry is generated on-the-fly by keeping track of fracture-matrix interfaces on the deformed mesh. Fracture apertures are an emergent property of the model. Mesh is adaptively refined around the tips and damaged regions to better capture stress and damage localization patterns. Fracture arrest, closure, coalescence, and intersection are handled geometrically by disallowing displacement over fracture boundaries, and merging polygonal representations of fractures. The finite element method is used to compute stresses, damage of the matrix and propagation of the discrete fractures through the matrix. We use isoparametric quadratic triangles to represent the matrix: the inside of the fractures is not meshed. Material properties are defined at the integration points. Continuous remeshing in the locality of fracture propagation facilitates fracture geometry generation, avoiding costly global remeshing used in classic approaches. This model, implemented in 2D, has been integrated into the mechanical module of the Complex Systems Platform (CSMP++).
DE: 1822 Geomechanics
DE: 5104 Fracture and flow
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8010 Fractures and faults
DE: 8020 Mechanics, theory, and modeling
SC: Hydrology [H]
MN: 2007 Fall Meeting