Experimental and numerical analysis of flow through a natural rough fracture subject to normal loading
Trinchero, Paolo (AMPHOS 21 Consulting S.L)
Zou, Liangchao (KTH Royal Institute of Technology. Department of Sustainable Development, Environmental Science and Engineering)
de La Iglesia, Miquel (Universitat Autònoma de Barcelona. Departament de Didàctica de la Matemàtica i de les Ciències Experimentals)
Iraola, Aitor (AMPHOS 21 Consulting S.L)
Bruines, Patrick (Swedish Nuclear Fuel and Waste Management Company)
Deissmann, Guido (Forschungszentrum Jülich GmbH. Institute of Energy and Climate Research: Nuclear Waste Management (IEK-6) and JARA-CSD)

Data:	2024
Resum:	Fractured crystalline rocks have been chosen or are under consideration by several countries as host rock formations for deep geological repositories for spent nuclear fuel. In such geological formations, flow and solute transport are mostly controlled by a network of connected natural fractures, each of them being characterised by internal heterogeneity, also denoted as roughness. Fractures are, in turn, subject to variable load caused by various factors, such as the presence of thick ice sheets formed during glaciation periods. Understanding how coupled hydro-mechanical (HM) processes affect flow and transport at the scale of a single natural fracture is crucial for a robust parameterisation of large-scale discrete fracture network models, which are not only used for nuclear waste disposal applications but are also of interest to problems related to geothermics, oil and gas production or groundwater remediation. In this work, we analyse and model an HM experiment carried out in a single natural fracture and use the results of both, the experimental and the modelling work, to get insights into fundamental questions such as the applicability of local cubic law or the effect of normal load on channeling. The initial fracture aperture was obtained from laser scanning of the two fracture surfaces and an equivalent initial aperture was then defined by moving the two fracture surfaces together and comparing the results obtained using a Navier-Stokes based computational fluid dynamics (CFD) model with the experimental flowrate obtained for unloaded conditions. The mechanical effect of the different loading stages was simulated using a high-resolution contact model. The different computed fracture apertures were then used to run groundwater flow simulations using a modified Reynolds equation. The results show that, without correction, local cubic law largely overestimates flowrates. Instead, we show that by explicitly acknowledging the difference between the mechanical aperture and the hydraulic aperture and setting the latter equal to 1/5 of the former, cubic law provides a very reasonable approximation of the experimental flowrates over the entire loading cycle. A positive correlation between fluid flow channeling and normal load is also found.
Nota:	Open access funding provided by Royal Institute of Technology
Drets:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan es reconegui l'autoria de l'obra original.
Llengua:	Anglès
Document:	Article ; recerca ; Versió publicada
Matèria:	Hydrogeology ; Geophysics ; Fluid dynamics
Publicat a:	Scientific reports, Vol. 14, num. 5587 (March 2024) , ISSN 2045-2322

DOI: 10.1038/s41598-024-55751-w
PMID: 38454042

14 p, 2.6 MB

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