Experimental and numerical investigations on fluid flow and corresponding influencing factors in a single rough-walled fracture surrounded by permeable matrix#br#
(1. Key Laboratory of Rock Mechanics and Geohazards of Zhejiang Province，Shaoxing University，Shaoxing，Zhejiang 312000，China；2. School of Civil Engineering，Shaoxing University，Shaoxing，Zhejiang 312000，China；3. Zhejiang Collaborative Innovation Center for Prevention and Control of Mountain Geologic Hazards，Shaoxing University，Shaoxing，Zhejiang 312000，China；
4. College of Civil Engineering，Tongji University，Shanghai 200092，China；5. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education，Tongji University，Shanghai 200092，China)
Abstract：To accurately assess matrix permeability and its role in the fluid flow through fractured rocks，flow-through experiments are conducted on both intact and split rock cores(including mudstone，sandstone and limestone) subjected to hydro-mechanically coupling conditions. By varying confining pressures(10–18 MPa) and fracture roughness(1.64 to 15.52)，the influence of the confining pressure and the fracture roughness on the fluid flow within fracture and matrix were explored. The experimental results indicate that the permeability of both matrix and fracture shows a decreasing trend with increasing the confining pressure，and the permeability of fracture(Kf) declines faster than that of matrix(Km)，resulting in a decrement in the ratio between them(Kf/Km). Specifically，when the confining pressure increases to 18 MPa，Kf/Km of mudstone reduces to 7–8(depend on fracture roughness)，reflecting fracture permeability is in the same order with matrix permeability，and then matrix permeability should not be neglected. Furthermore，the numerical simulations were performed on fractured rocks with fracture roughness of 2.58–17.4，and under confining pressures of 3–53 MPa. The fluid flow in matrix and fracture were assumed to obey Darcy law and Forchheimer law，respectively. The numerical results match experimental ones well，and it successfully reproduces the evolutions of fracture and matrix permeability with confining pressure and fracture roughness. If we take Kf/Km of 10 as a threshold，below which matrix permeability should be considered，then the critical confining pressure of 18，20，and 46 MPa can be determined for mudstone，sandstone and limestone，respectively. In addition，it is found that the contact area between rough-walled fracture surfaces increases with confining pressure and fracture roughness，leading to shrinkage in the flow channels，which consequently lowers the fracture permeability. Meanwhile，the velocity of flow within the narrowed channels will then accelerate，resulting in vortex inside the flow field，which further reduce the permeability of rough-walled fractures. This study systematically explores the fluid flow evolution within fracture and matrix，and provides a quantitative index Kf/Km to evaluate the role of matrix permeability in fluid flow through fractured rocks.
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2023, Vol. 42 
