Abstract
The effect of model size on fluid flow through fractal rough fractures under shearing is investigated using a numerical simulation method. The shear behavior of rough fractures with self-affine properties was described using the analytical model, and the aperture fields with sizes varying from 25 to 200[Formula: see text]mm were extracted under shear displacements up to 20[Formula: see text]mm. Fluid flow through fractures in the directions both parallel and perpendicular to the shear directions was simulated by solving the Reynolds equation using a finite element code. The results show that fluid flow tends to converge into a few main flow channels as shear displacement increases, while the shapes of flow channels change significantly as the fracture size increases. As the model size increases, the permeability in the directions both parallel and perpendicular to the shear direction changes significantly first and then tends to move to a stable state. The size effects on the permeability in the direction parallel to the shear direction are more obvious than that in the direction perpendicular to the shear direction, due to the formation of contact ridges and connected channels perpendicular to the shear direction. The variances of the ratio between permeability in both directions become smaller as the model size increases and then this ratio tends to maintain constant after a certain size, with the value mainly ranging from 1.0 to 3.0.
Highlights
The hydro-mechanical characteristics of single fractures at multiple scales strongly influence the fluid flow through fractured rock masses, the exploitation of unconventional oil and gas reservoirs and the development of nuclear waste repositories.[1,2,3,4] modeling of flow behavior considering the influences of geometrical and hydraulic properties of fracture continues to be an active area of scientific investigation.[5,6,7] The prerequisites of modeling consist, to a large extent, in determining the complex internal topography of a fracture and its evolution under the mechanical stresses
Aperture fields with the size varying from 25 to 200 mm were extracted under different shear displacements to investigate the size effects on the permeability and shear induced flow anisotropy of rock fractures
The results show that aperture fields and flow paths in rough rock fractures are influenced by the topography of fracture surface and shear condition
Summary
The hydro-mechanical characteristics of single fractures at multiple scales strongly influence the fluid flow through fractured rock masses, the exploitation of unconventional oil and gas reservoirs and the development of nuclear waste repositories.[1,2,3,4] modeling of flow behavior considering the influences of geometrical and hydraulic properties of fracture continues to be an active area of scientific investigation.[5,6,7] The prerequisites of modeling consist, to a large extent, in determining the complex internal topography of a fracture and its evolution under the mechanical stresses. Single fracture has been approximately modeled by using two smooth parallel plates that are separated by a constant distance, with the fluid flowing through it that follows the cubic law.[12,13] in the nature, the surfaces of most rock fractures are rough, which results in nonuniformly distributed aperture fields in fractures. Different laboratory sizes that are extracted from the in situ fractures.[28] The distribution of apertures varies with sample size, which results in different flow channels through the fractures. This study aims to investigate the influences of fracture size on the permeability and the shear induced flow anisotropy of the natural rough-walled rock fractures. Size on the flow channels, permeability and the flow anisotropy of the fracture were analyzed
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