Abstract
We present a discussion of the state-of-the-art on the use of discrete fracture networks (DFNs) for modelling geometrical characteristics, geomechanical evolution and hydromechanical (HM) behaviour of natural fracture networks in rock. The DFN models considered include those based on geological mapping, stochastic generation and geomechanical simulation. Different types of continuum, discontinuum and hybrid geomechanical models that integrate DFN information are summarised. Numerical studies aiming at investigating geomechanical effects on fluid flow in DFNs are reviewed. The paper finally provides recommendations for advancing the modelling of coupled HM processes in fractured rocks through more physically-based DFN generation and geomechanical simulation.
Highlights
Fractures such as joints, faults, veins and bedding planes are ubiquitous in crustal rocks
In the linear elastic fracture mechanics (LEFM) model, fracture patterns can be simulated by four main steps in an iterative fashion [150,151]: (1) generation of initial flaws to mimic the process that natural fractures initiate from microcracks, (2) calculation of the perturbed stress field in the rock caused by the presence and evolution of fractures under an imposed boundary condition, (3) derivation of the stress intensity factor (KI) at the tip of each fracture, and (4) propagation of fractures which satisfy a growth criterion, e.g. a subcritical law KO 6 KI 6 KIC, where KO is the stress corrosion limit and KIC is the material toughness [152]
The numerical methods for geomechanical modelling of fractured rocks can be categorised as continuum and discontinuum approaches with the classification based on their treatment of displacement compatibility [12]
Summary
Faults, veins and bedding planes are ubiquitous in crustal rocks. Many computational schemes based on extended continuum, discontinuum, or hybrid continuum-discontinuum methods have been developed to solve a numerical system with fracture geometries explicitly represented Another important question is about the hydrological behaviour of fractured rocks under geomechanical conditions. The objective of this paper is to review the current state-of-theart of fracture network models and to provide some discussions and recommendations for HM modelling of fractured rocks In this context, the issues arising in the aforementioned three key subject areas (i.e. geometry, geomechanics and hydromechanics) will be examined progressively. The paper will present a summary of various approaches used in developing fracture network models that represent natural fracture geometries often with different degrees of simplification, and different numerical frameworks that integrate discrete fracture representations for modelling geomechanical and HM behaviour of fractured rocks. More in-depth discussions about stress effects on fluid flow in fractured rocks can be found in Zhang and Sanderson [26], and Rutqvist and Stephansson [2]
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