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| Titel |
Computational study of flow anisotropy in sheared fractures with self-affine surfaces |
| VerfasserIn |
Michael Selzer, Martin Schoenball, Kumar Ankit, Britta Nestler, Thomas Kohl, Natalie Kühnle, Jean Schmittbuhl |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250078518
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| Zusammenfassung |
| Characterization of the hydraulic conductivities of rock masses is imperative for the
development and engineering of various underground installations like geothermal power
plants, waste repositories or tunnelling. The intrinsic permeability of intact rock is extremely
low; however the rock mass usually contains a dense network of fractures with a relatively
high hydraulic conductivity, which determines the hydraulic properties of the rock mass.
Conventionally, in order to estimate the hydraulic conductivities of fractures, the cubic law
for laminar fluid flow in a parallel plate model with constant aperture is applied. However, the
surface of natural fractures is rough, which strongly affects the hydraulic properties of
fractures and causes deviation from the analytical result. To enhance fluid flow in a fractured
rock mass, well bores in an intact rock mass are pressurized with fluid to reduce effective
normal stresses on pre-existing fractures to enable shearing. The shearing motion
of rock enhances hydraulic anisotropy, since the rocks become more conductive
parallel to the shearing direction and less conduction perpendicular to the shearing
direction.
In the current work, we present a numerical study of hydraulic anisotropy introduced as a
result of shearing of algorithmically generated fractures. A rough surface can be
mathematically described as self-affine structure with a correlation between heights of
asperities and their spatial distribution. Fractures are generated by displacing two identical
fractal rough surfaces incorporating dilation to obtain an aperture distribution. To investigate
the geometrical and hydraulic properties of generated fractures, we use a finite element
method to solve the Reynolds equations in a simplified 2D model. We identify a regime,
where a simplified hydraulic fracture model is permitted. Using the 2D model, we
make a statistical study of the hydraulic anisotropy for a representative set of 1000
algorithmically generated fractures. For the purpose of validation, we solve the 3D
Navier-Stokes flow equations using the finite volume method and compare it with
2D simulation results. Thus, the two independent methods used in conjunction,
facilitates the quantification of the impact of fracture tortuosity and roughness on the
hydraulic behavior. On the basis of flow simulation results, we conclude that the
magnitude and the scatter of hydraulic anisotropy between the fractures increase
with increasing shear displacement. Invariably, all sheared fractures show a larger
flow permeability perpendicular to the shearing direction as compared to parallel
direction. |
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