Abstract
Due to the existence of pores in the fracture surface, the permeability of pore-fracture media is more complicated, and its permeability law and mechanism are worthy of an in-depth study. The rough fracture surface of this paper is obtained by 3D laser scanning technology, taken a small part of the middle area to carry out the finite element simulation of single fracture seepage, and studied the distribution of flow velocity fields and the nonlinear characteristics by changing the inlet flow rate, fracture thickness, and size of fracture surface. Given that for the same fracture opening, the flow velocity decreases from the middle position to both sides. When the roughness increases locally, the flow velocity suddenly increases. The nonlinear coefficient decreases as the fracture thickness increases. A dual-media model which consists of porous matrix and a single rough surface was established to study the seepage characteristics through two media. Given that it takes less time to reach a steady state when the permeability coefficient of the matrix is greater than that of the fracture. After reaching the steady state, the flow direction of the fluid in the matrix is consistent with the fluid direction in the fracture, and both are perpendicular to the isosurface of pore water pressure.
Highlights
The results indicate that the flow behaviors, flow capacity, and permeability evolution through single fractures are influenced by many factors such as fracture opening, roughness coefficient, and inlet water pressure [6, 18,19,20]
The smaller the fracture aperture thickness, Geofluids the more obvious the nonlinear characteristics of fluid flowing through the fracture for an identical flow velocity
(2) The fluid flowing behavior is closely related to the pore water pressure, and the overall flow direction is vertical to the pressure isosurfaces
Summary
A good understanding of fluid flowing characteristics through pore-fracture dual media is of great significance for safety prediction and performance assessment of many underground projects such as exploitation of geothermal resources, disposal of nuclear waste, and stability analysis of tunnel water inrush [1,2,3,4,5,6,7,8,9,10,11,12]. The results demonstrate that the deformation of fracture with increasing normal stress and shear causes nonuniform changes in void space geometry and further influences fracture permeability These studies generally illustrated the impacts of surface roughness and weak inertial effects on the flow behaviors through 3D rough rock fractures. Xiong et al [25] studied the nonlinear fluid flow behaviors in rough-walled rock fractures by simulating two 3D fracture models, with and without shear, which showed that the effective transmissivity is a function of local apertures with serious uncertainties even when Re (Reynolds numbers) is small. Even though the hydraulic properties of pore-fracture dual media have been studied by scholars [35, 36], the nonlinear flow behaviors, evolution of permeability, and contribution of fracture and matrix have rarely been reported. The pore water pressure in the two models, Darcy’s velocity in matrix and fractures, and contributions of matrix and fractures to the overall discharge capacity of the pore-fracture models were individually discussed
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