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- Min, Ki-Bok, et al.
(författare)
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A Block-Scale Stress-Permeability Relationship of a Fractured Rock Determined by Numerical Experiments
- 2004
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Ingår i: Coupled Thermo-Hydro-Mechanical-Chemical Processes in Geo-Systems — Fundamentals, Modelling, Experiments and Applications. - : Elsevier. ; , s. 269-274
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Bokkapitel (refereegranskat)abstract
- We present the stress induced permeability change in a fractured rock with special focuses on 1) fracture closure/opening process, 2) anisotropic stress conditions, and 3) fracture dilation. In order to overcome the limitations from the experimental study on a single fracture or analytical study on orthogonal and/or persistent fracture models, realistic Discrete Fracture Network (DFN) models were used as a geometrical basis. A series of numerical experiments on fluid flow are conducted under different stress boundary conditions for calculation of equivalent permeability. From the analysis on the realistic DFN model, this paper demonstrates the decrease of permeability with the fracture normal closure, increased anisotropy in permeability with anisotropic stress and increase of permeability and significant channelling effect due to fracture dilation. It is shown that block-scale permeability change in fractured rock depends not only on stress magnitude but also on stress orientation and differential stresses.
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| 2. |
- Min, Ki Bok, et al.
(författare)
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Stress-dependent permeability of fractured rock masses : a numerical study
- 2004
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Ingår i: International Journal of Rock Mechanics And Mining Sciences. - : Elsevier BV. - 1365-1609 .- 1873-4545. ; 41:7, s. 1191-1210
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the stress-dependent permeability issue in fractured rock masses considering the effects of nonlinear normal deformation and shear dilation of fractures using a two-dimensional distinct element method program, UDEC, based on a realistic discrete fracture network realization. A series of "numerical" experiments were conducted to calculate changes in the permeability of simulated fractured rock masses under various loading conditions. Numerical experiments were conducted in two ways: (1) increasing the overall stresses with a fixed ratio of horizontal to vertical stresses components; and (2) increasing the differential stresses (i.e., the difference between the horizontal and vertical stresses) while keeping the magnitude of vertical stress constant. These numerical experiments show that the permeability of fractured rocks decreases with increased stress magnitudes when the stress ratio is not large enough to cause shear dilation of fractures, whereas permeability increases with increased stress when the stress ratio is large enough. Permeability changes at low stress levels are more sensitive than at high stress levels due to the nonlinear fracture normal stress-displacement relation. Significant stress-induced channeling is observed as the shear dilation causes the concentration of fluid flow along connected shear fractures. Anisotropy of permeability emerges with the increase of differential stresses, and this anisotropy can become more prominent with the influence of shear dilation and localized flow paths. A set of empirical equations in closed-form, accounting for both normal closure and shear dilation of the fractures, is proposed to model the stress-dependent permeability. These equations prove to be in good agreement with the results obtained from our numerical experiments.
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