A geometrically based method for predicting stress-induced fracture aperture and flow in discrete fracture networks

Bisdom, Kevin; Bertotti, Giovanni; Nick, Hamidreza M.

doi:10.1306/02111615127

Cited by 43 publications

(51 citation statements)

References 64 publications

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“…The JRC is either defined as the slip angle of a rock sample, measured using the fracture amplitude-length ratio or estimated using roughness profile matching [Barton, 2014]. Throughout this study, we assume irregular rough fractures (JRC = 15), resulting in an initial unstressed aperture of 0.3 mm that is [Barton, 2014;Lei et al, 2014;Bisdom et al, 2016a]. Maximum closure v m (in mm) is the difference between maximum opening and the smallest aperture, and K ni (in MPa/mm) is the initial fracture stiffness [Bandis et al, 1983]:…”

Section: Shear-induced Dilation In Poorly Interlocking Fracturesmentioning

confidence: 99%

“…The block size is the spacing of the fracture set that intersects the fracture of interest [Barton, 1982]. Shear displacement is obtained from numerical models, but an approximation of shear displacement u geom for the parameters used in this study can be obtained from a geometrical function that is dependent on block size, far-field stresses, and the orientation of the fracture with respect to the far-field stresses [Bisdom et al, 2016a]:…”

Section: Barton-bandis Peak Shearingmentioning

confidence: 99%

“…Solving for local stresses requires more robust approaches, such as finite element models [Lei et al, 2014[Lei et al, , 2015Bisdom et al, 2016aBisdom et al, , 2016b. Assuming that the far-field stress equals local stress is a simplification that may overestimate absolute aperture.…”

Section: Model Boundary Conditionsmentioning

confidence: 99%

“…Assuming that the far-field stress equals local stress is a simplification that may overestimate absolute aperture. For the Barton-Bandis model, aperture is up to 5% higher for far-field stress, compared to a local stress distribution modeled using finite element simulations [Bisdom et al, 2016a]. However, our aim is to compare relative aperture and permeability trends, for which we make the assumption that far-field stress is representative of local stress.…”

Section: Model Boundary Conditionsmentioning

confidence: 99%

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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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Section: Shear-induced Dilation In Poorly Interlocking Fracturesmentioning

confidence: 99%

Section: Barton-bandis Peak Shearingmentioning

confidence: 99%

Section: Model Boundary Conditionsmentioning

confidence: 99%

Section: Model Boundary Conditionsmentioning

confidence: 99%

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

2016

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“…Where it is varied with fracture length, this pre‐imposes a scale variance. There are several studies that address the impact of geo‐mechanical aperture on equivalent permeability [ Paluszny and Matthai , ; Nick et al ., ; Bisdom et al ., , , ]. Yet they do not consider the full tensor of equivalent permeability and its potential variation with direction and scale.…”

Section: Introductionmentioning

confidence: 99%

Is the permeability of naturally fractured rocks scale dependent?

Azizmohammadi

Matthäi

2017

Water Resources Research

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The equivalent permeability, keq of stratified fractured porous rocks and its anisotropy is important for hydrocarbon reservoir engineering, groundwater hydrology, and subsurface contaminant transport. However, it is difficult to constrain this tensor property as it is strongly influenced by infrequent large fractures. Boreholes miss them and their directional sampling bias affects the collected geostatistical data. Samples taken at any scale smaller than that of interest truncate distributions and this bias leads to an incorrect characterization and property upscaling. To better understand this sampling problem, we have investigated a collection of outcrop‐data‐based Discrete Fracture and Matrix (DFM) models with mechanically constrained fracture aperture distributions, trying to establish a useful Representative Elementary Volume (REV). Finite‐element analysis and flow‐based upscaling have been used to determine keq eigenvalues and anisotropy. While our results indicate a convergence toward a scale‐invariant keq REV with increasing sample size, keq magnitude can have multi‐modal distributions. REV size relates to the length of dilated fracture segments as opposed to overall fracture length. Tensor orientation and degree of anisotropy also converge with sample size. However, the REV for keq anisotropy is larger than that for keq magnitude. Across scales, tensor orientation varies spatially, reflecting inhomogeneity of the fracture patterns. Inhomogeneity is particularly pronounced where the ambient stress selectively activates late‐ as opposed to early (through‐going) fractures. While we cannot detect any increase of keq with sample size as postulated in some earlier studies, our results highlight a strong keq anisotropy that influences scale dependence.

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References

2020

Applied Concepts in Fractured Reservoirs

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A geometrically based method for predicting stress-induced fracture aperture and flow in discrete fracture networks

Cited by 43 publications

References 64 publications

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

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

Is the permeability of naturally fractured rocks scale dependent?

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