The impact of stress orientation and fracture roughness on the scale dependency of permeability in naturally fractured rocks

Azizmohammadi, Siroos; Sedaghat, Mohammadhossein

doi:10.1016/j.advwatres.2020.103579

Cited by 13 publications

(9 citation statements)

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“…Another limitation of this research is that the current fracture model is analyzed in two dimensions, which corresponds to layered models and is a simplification for naturally fractured porous rocks based on outcrop data [50,55,69]. In the two-dimensional models, the fractures are assumed to extend vertically, whereas when fractures are not vertical and their dip angles scatter randomly, the fracture connectivity and equivalent permeability may vary from two-dimensional to three-dimensional models [39,72].…”

Section: Discussionmentioning

confidence: 99%

“…It should be noted that the flow boundary conditions affect the resulting equivalent permeability. They can be mainly classified into three categories: no-flow, linear, and periodic boundary conditions (e.g., [27,49,54,55]). Regarding the multiple upscaling method, the linear boundary condition is applied as it mimics the realistic flow condition underground to some extent and the resulting equivalent permeability matches well with the analytical solutions [44].…”

Section: Equivalent Permeability Upscalingmentioning

confidence: 99%

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Equivalent Permeability Distribution for Fractured Porous Rocks: The Influence of Fracture Network Properties

Chen

2020

Geofluids

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Equivalent fracture models are widely used for simulations of groundwater exploitation, geothermal reservoir production, and solute transport in groundwater systems. Equivalent permeability has a great impact on such processes. In this study, equivalent permeability distributions are investigated based on a state-of-the-art numerical upscaling method (i.e., the multiple boundary method) for fractured porous rocks. An ensemble of discrete fracture models is created based on power law length distributions. The equivalent permeability is upscaled from discrete fracture models based on the multiple boundary method. The results show that the statistical distributions of equivalent permeability tensor components are highly related to fracture geometry and differ from each other. For the histograms of the equivalent permeability, the shapes of k x x and k y y change from a power law-like distribution to a lognormal-like distribution when the fracture length and the number of fractures increase. For the off-diagonal component k x y , it is a normal-like distribution and its range expands when the fracture length and the number of fractures increase. The mean of diagonal equivalent permeability tensor components increases linearly with the fracture density. The analysis helps in generating stochastic equivalent permeability models in fractured porous rocks and reduces uncertainties when applying equivalent fracture models.

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Section: Discussionmentioning

confidence: 99%

Section: Equivalent Permeability Upscalingmentioning

confidence: 99%

Equivalent Permeability Distribution for Fractured Porous Rocks: The Influence of Fracture Network Properties

Chen

2020

Geofluids

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“…They can be measured by a wide variety of methods, including direct measurements in core or outcrop and deduction from flow data. The aperture for fractured porous rocks can be described by constant (e.g., [24]), statistical models [42], correlation with fracture [27], and mechanical models [38]. The power law relationship between fracture aperture and length (including linear and sublinear) applied in this study is widely observed at the field scale [43] and is derived by linear elastic fracture mechanics [44], which can be expressed by [45]…”

Section: Methodsmentioning

confidence: 99%

“…While many previous studies propose relationships between fracture length and aperture and illustrated their effects on fluid flow through fractured rocks (e.g., [33,35,38,39]), yet they mainly address the equivalent permeability for a grid block at different scales. The influence of correlated length and aperture on equivalent permeability distributions of grid blocks for large-scale fractured porous media has yet to be clarified.…”

Section: Introductionmentioning

confidence: 99%

Equivalent Permeability Distribution for Fractured Porous Rocks: Correlating Fracture Aperture and Length

Chen

2020

Geofluids

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Estimating equivalent permeability at grid block scale of numerical models is a critical issue for large-scale fractured porous rocks. However, it is difficult to constrain the permeability distributions for equivalent fracture models as these are strongly influenced by complex fracture properties. This study quantitatively investigated equivalent permeability distributions for fractured porous rocks, considering the impact of the correlated fracture aperture and length model. Two-dimensional discrete fracture models are generated with varied correlation exponent ranges from 0.5 to 1, which indicates different geomechanical properties of fractured porous rock. The equivalent fracture models are built by the multiple boundary upscaling method. Results indicate that the spatial distribution of equivalent permeability varied with the correlation exponent. When the minimum fracture length and the number of fractures increase, the process that the diagonal equivalent permeability tensor components change from a power law like to a lognormal like and to a normal-like distribution slows down as the correlation exponent increases. The average dimensionless equivalent permeability for the equivalent fracture models is well described by an exponential relationship with the correlation exponent. A power law model is built between the equivalent permeability of equivalent fracture models and fracture density of discrete fracture models for the correlated aperture-length models. The results demonstrate that both the fracture density and length-aperture model influence the equivalent permeability of equivalent fracture models interactively.

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“…Criteria to anticipate the risk of serious artifacts were devised as well as ways to limit them. In addition, Azizmohammadi and Sedaghat (2020) proposed a sampling method to determine the representative elementary volume (REV) size in fractured rock environments. These authors determined the values of the components of the permeability tensor and analyzed its anisotropy using multiscale random sampling and upscaling, considering the fluid stress orientation and the fracture roughness.…”

Section: Current Methods For Computing Effective Parameters In Porous Mediamentioning

confidence: 99%

Editorial: Recent developments in upscaling and characterization of flow and transport in porous media

Lasseux

Valdés‐Parada

Wood

2021

Advances in Water Resources

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Le et al. (2020) studied the flow and transport problem of CO 2 -enhanced coalbed methane recovery also by means of the homogenization technique. They considered a multiscale model that incorporated two levels of porosity that correspond to nanopores and the cleat network. This work includes a set of numerical simulations showing that the cleat permeability decreases significantly near the injection well because of the high injection pressure. In addition, Sharmin et al. (2020) considered two-phase (or unsaturated) incompressible flow in a thin, but long, single pore (a thin strip) with a stratified distribution of the two phases and derived an effective model starting from the Navier-Stokes equations. The upscaled model was obtained using the asymptotic homogenization method. It encompasses different regimes associated to the values of the capillary number and viscosity ratio. It also accounts for surface tension variations (Marangoni effects) which may result from the transport of a solute in one of the two phases. The upscaled model was compared to direct numerical simulations of the 2D pore-scale model. Finally, Airiau and Bottaro (2020) used the adjoint homogenization method to shed new light on the derivation of upscaled models for steady and creeping flow of a shear-thinning fluid in homogeneous porous media. These authors derived a Darcy-like model, where the components of the effective permeability tensor were obtained from the solution of an associated boundary-value problem in a periodic unit cell. Due to the dependence of the viscosity on the pore-scale flow, a coupled solution approach was used that translated into a strong anisotropy of the permeability tensor, even in isotropic geometries.Not all the works corresponding to this research topic used the homogenization method to carry out their analysis. For example, Cotta et al. (2020) studied flow and transport in fractured porous media using the generalized integral transform technique to derive analytical and numerical-analytical solutions. A salient feature of this work is the treatment of multiporosity cases, by means of a single integral transformation process. This approach is illustrated with two examples in fractured media and unsaturated soils. In addition, Angot et al. ( 2020) used an asymptotic analysis to study single-phase inertial flow in the fluidporous boundary. They show that the total inertial work exerted by the fluid over the solid is always positive. Non-equilibrium modeling for transport in homogeneous and heterogeneous porous mediaThis research subject comprises stochastic modeling and upscaling of transport processes. Engdahl and Bolster (2020) proposed to use a

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The impact of stress orientation and fracture roughness on the scale dependency of permeability in naturally fractured rocks

Cited by 13 publications

References 55 publications

Equivalent Permeability Distribution for Fractured Porous Rocks: The Influence of Fracture Network Properties

Equivalent Permeability Distribution for Fractured Porous Rocks: The Influence of Fracture Network Properties

Equivalent Permeability Distribution for Fractured Porous Rocks: Correlating Fracture Aperture and Length

Editorial: Recent developments in upscaling and characterization of flow and transport in porous media

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