Abstract
The effect of shear displacement on the directivity of permeability in fractures is studied in this paper. The studied fracture surface has 3D self-affine fractal characteristics that are created using the modified successive random addition (SRA) method. Fluid flow through the fracture is simulated using the COMSOL Multiphysics code based on the finite element method (FEM) by changing the angle between the shear direction and macroscopic flow direction. The evolutions of the aperture distribution and flow paths with changes in shear displacement are investigated, and the change in the equivalent permeability is evaluated. The results show that the mean aperture and its deviation for rough fractures increase as the shear displacement increases, and this change is accompanied by an increase in void spaces and decreasing contact areas between the upper and lower fracture surfaces. The flow paths become more tortuous, and the channeling flow effect occurs during the shear process. The equivalent permeability of the fractures varies as the inclination between the shear direction and macroscopic flow direction changes. The permeability with the largest magnitude exists in the direction perpendicular to the shear direction, and the permeability with the smallest magnitude exists in the direction parallel to the shear direction. The equivalent permeability of the fractures at other inclinations varies between the smallest and greatest values. Notably, larger inclinations correspond to higher permeability magnitudes. The ratio of the directional permeability to the permeability in the direction parallel to the shear direction varies between 1.03 and 2.71. This ratio tends to decrease as the shear displacement and JRC increase, which indicates that the directivity of the permeability is more obvious for fractures with smaller JRCs and smaller shear displacement.
Highlights
Understanding the hydraulic response of fractured rock masses with respect to shear stress is of great importance in various fields of rock engineering, such as the construction and maintenance of dam foundations and radioactive waste repositories, unconventional oil and gas exploration, and hydrocarbon recovery [1,2,3,4]
The frequency corresponding to b = 0 decreases as u increases, which indicates that the contact area between the two fracture surfaces decreases and more void spaces are generated by shearing
All aperture fields are extracted from the models parallel to the shear direction, with θ = 0°
Summary
Understanding the hydraulic response of fractured rock masses with respect to shear stress is of great importance in various fields of rock engineering, such as the construction and maintenance of dam foundations and radioactive waste repositories, unconventional oil and gas exploration, and hydrocarbon recovery [1,2,3,4]. Geofluids rough fractures with parallel plates to examine the tortuosity induced by the geometry of void spaces They found that in a rough fracture, fluid flows through connected channels that bypass the closed zones. Li et al [21] conducted a series of laboratory tests to examine the shear effect on the evolution of the permeability of natural rough rock fractures. In nature, the fracture orientation and position are arbitrarily distributed with respect to the in situ stresses, and the flow direction, which is controlled by the hydrogeological conditions, is not always exactly parallel or perpendicular to the shear direction [26, 27]. To characterize the hydraulic properties of natural rough fractures, a self-affine fractal model is proposed to generate fracture surfaces that have different joint roughness coefficients (JRCs) using the modified successive random addition (SRA) method. The hydraulic anisotropy that results from the different inclinations between the shear direction and the macroscopic flow direction is systematically investigated
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