Effects of geomechanical changes on the validity of a discrete fracture network representation of a realistic two-dimensional fractured rock

Lei, Qinghua; Latham, John; Xiang, Jiansheng; Tsang, Chin‐Fu; Lang, Philipp; Guo, Liu

doi:10.1016/j.ijrmms.2014.06.001

Cited by 92 publications

(65 citation statements)

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“…27 stress scenarios) bedding interface) inferred from the simulation results (Figs. 5,7 and 8) suggests that 2D models Zhang 1999, 2004;Latham et al 2013;Lei et al 2014) may provide indicative approximations but not fully capture the polyaxial stress-dependent behaviour of 3D fractured layers, which requires 3D modelling.…”

Section: Discussionmentioning

confidence: 99%

“…During the past few decades, the impact of stress on the permeability of fractured sedimentary rocks has been extensively studied based on two-dimensional (2D) fracture network models with the out-of-plane stress (perpendicular to the bedding interface) effect omitted Zhang 1999, 2004;Latham et al 2013;Lei et al 2014Lei et al , 2015b. However, whether the effect of the out-of-plane stress is negligible may need to be examined through three-dimensional (3D) analysis.…”

Section: Introductionmentioning

confidence: 99%

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Polyaxial stress-dependent permeability of a three-dimensional fractured rock layer

et al. 2017

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A study about the influence of polyaxial (true-triaxial) stresses on the permeability of a three-dimensional (3D) fractured rock layer is presented. The 3D fracture system is constructed by extruding a two-dimensional (2D) outcrop pattern of a limestone bed that exhibits a ladder structure consisting of a Bthrough-going^joint set abutted by later-stage short fractures. Geomechanical behaviour of the 3D fractured rock in response to in-situ stresses is modelled by the finite-discrete element method, which can capture the deformation of matrix blocks, variation of stress fields, reactivation of pre-existing rough fractures and propagation of new cracks. A series of numerical simulations is designed to load the fractured rock using various polyaxial in-situ stresses and the stress-dependent flow properties are further calculated. The fractured layer tends to exhibit stronger flow localisation and higher equivalent permeability as the far-field stress ratio is increased and the stress field is rotated such that fractures are preferentially oriented for shearing. The shear dilation of pre-existing fractures has dominant effects on flow localisation in the system, while the propagation of new fractures has minor impacts. The role of the overburden stress suggests that the conventional 2D analysis that neglects the effect of the out-of-plane stress (perpendicular to the bedding interface) may provide indicative approximations but not fully capture the polyaxial stress-dependent fracture network behaviour. The results of this study have important implications for understanding the heterogeneous flow of geological fluids (e.g. groundwater, petroleum) in subsurface and upscaling permeability for largescale assessments.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Polyaxial stress-dependent permeability of a three-dimensional fractured rock layer

et al. 2017

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“…depending on which method is used. The impact of each method on fluid flow in fractures has been studied extensively [e.g., Baghbanan and Jing, 2008;Lei et al, 2014;Moos and Barton, 2008;Tao et al, 2009]. In particular, the impact of power law aperture scaling and similar statistical distributions on permeability has been studied in 2-D and 3-D [de Dreuzy et al, 2001[de Dreuzy et al, , 2002[de Dreuzy et al, , 2012.…”

Section: Introductionmentioning

confidence: 99%

The impact of different aperture distribution models and critical stress criteria on equivalent permeability in fractured rocks

2016

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Predicting equivalent permeability in fractured reservoirs requires an understanding of the fracture network geometry and apertures. There are different methods for defining aperture, based on outcrop observations (power law scaling), fundamental mechanics (sublinear length‐aperture scaling), and experiments (Barton‐Bandis conductive shearing). Each method predicts heterogeneous apertures, even along single fractures (i.e., intrafracture variations), but most fractured reservoir models imply constant apertures for single fractures. We compare the relative differences in aperture and permeability predicted by three aperture methods, where permeability is modeled in explicit fracture networks with coupled fracture‐matrix flow. Aperture varies along single fractures, and geomechanical relations are used to identify which fractures are critically stressed. The aperture models are applied to real‐world large‐scale fracture networks. (Sub)linear length scaling predicts the largest average aperture and equivalent permeability. Barton‐Bandis aperture is smaller, predicting on average a sixfold increase compared to matrix permeability. Application of critical stress criteria results in a decrease in the fraction of open fractures. For the applied stress conditions, Coulomb predicts that 50% of the network is critically stressed, compared to 80% for Barton‐Bandis peak shear. The impact of the fracture network on equivalent permeability depends on the matrix hydraulic properties, as in a low‐permeable matrix, intrafracture connectivity, i.e., the opening along a single fracture, controls equivalent permeability, whereas for a more permeable matrix, absolute apertures have a larger impact. Quantification of fracture flow regimes using only the ratio of fracture versus matrix permeability is insufficient, as these regimes also depend on aperture variations within fractures.

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“…Fracture aperture plays an important part in permeability analysis of geological systems and also provides a perspective to explicitly investigate the delamination of layer interfaces if they are viewed as pre-existing closed cracks with no cohesion. In this simulation, fracture apertures can be extracted in the post-processing (Lei et al, 2014). The normal apertures of models subject to direct tension with pressure P y = 0 MPa and 10 MPa are shown in Figure 19, which correspond to the fracture patterns in …”

Section: Numerical Results Of Direct Tensionmentioning

confidence: 99%

A numerical study of fracture spacing and through-going fracture formation in layered rocks

Guo

Latham

Xiang

2017

International Journal of Solids and Structures

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Naturally fractured reservoirs are an important source of hydrocarbons.Computational models capable of generating fracture geometries according to geomechanical principles offer a means to create a numerical representation of a more realistic rock mass structure. In this work, the combined finite-discrete element method is applied to investigate fracture patterns in layered rocks. First, a three-layer model undergoing layer normal compression is simulated with the aim of examining the controls on fracture spacing in layered rocks. Second, a seven-layer model with low competence contrast is modelled under direct tension parallel to the layering and bending conditions with the focus on investigating through-going fracture formation across layer interfaces. The numerical results give an insight into the understanding of various mechanisms that contribute to fracture pattern development in layered rocks.

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Effects of geomechanical changes on the validity of a discrete fracture network representation of a realistic two-dimensional fractured rock

Abstract: 06.01.15 KB. Ok to add accepted version, subject to 12 months embargo perio

Cited by 92 publications

References 50 publications

Polyaxial stress-dependent permeability of a three-dimensional fractured rock layer

Polyaxial stress-dependent permeability of a three-dimensional fractured rock layer

The impact of different aperture distribution models and critical stress criteria on equivalent permeability in fractured rocks

A numerical study of fracture spacing and through-going fracture formation in layered rocks

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