T13E-05
Coupled THMC modelling of single fractures in novaculite and granite for DECOVALEX-2015

Monday, 14 December 2015: 14:40
306 (Moscone South)
Alexander Edward Bond1, Neil Chittenden2, Randall W Fedors3, Philipp S. Lang4, Christopher McDermott5, Ivars E. Neretnieks6, Pengzhi Pan7, Jan Šembara8, Ivan Brusky8, Norihiro Watanabe9, Renchao Lu9 and Hideaki Yasuhara10, (1)Quintessa Ltd, Henley ON Thames, United Kingdom, (2)Quintessa Ltd, Henley On Thames, United Kingdom, (3)U.S. NRC, Middletown, MD, United States, (4)Imperial College London, London, United Kingdom, (5)University of Edinburgh, School of Geosciences, Edinburgh, United Kingdom, (6)KTH Royal Institute of Technology, Department of Chemical Engineering, Stockholm, Sweden, (7)Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, State Key Laboratory of Geomechanics and Geotechnical Engineering, Wuhan, China, (8)Technical University of Liberec, Liberec, Czech Republic, (9)Helmholtz Centre for Environmental Research UFZ Leipzig, Leipzig, Germany, (10)Ehime University, Matsuyama, Japan
Abstract:
The host rock immediately surrounding a nuclear waste repository has the potential to undergo a complex set of physical and chemical processes starting from construction of the facility until many years after completion. Understanding the relevant processes of fracture evolution may be key to supporting the attendant safety arguments for such a facility. In the present phase of the international research project DECOVALEX, the experimental work of Yasuhara et al [1,2] has been examined, wherein artificial fractures in novaculite and granite are subject to a mechanical confining pressure, variable fluid flows and different applied temperatures. Differential pressures across the samples were measured to determine permeability and hence hydraulic aperture evolution, while at the same time the chemical composition of the outflows were continually sampled. For the novaculite experiments, the fracture surfaces’ topography were characterised using a high-resolution laser profilometer (see Figure 1), and post-experimental characterisation of the aperture was performed using a Wood’s metal fracture cast.

This paper presents a synthesis of the ongoing work of six separate research teams. A range of approaches are presented including 2D and 3D high resolution coupled THMC models. Homogenised ‘single compartment’ models of the fracture have also been adopted, attempting to upscale the processes so that they could be used in larger network or effective continuum models. Particular attention is given to the competing roles of aqueous geochemistry, pressure solution, stress corrosion and pure mechanics in order to reproduce the experimental observations. The results of the work show that while good, physically plausible representations of the experiment can be obtained, there is considerable uncertainty in the relative importance of the various processes and that the parameterisation of these processes can be closely linked to the physical interpretation of the fracture surface topography.

References

[1] doi:10.1016/j.epsl.2006.01.046

[2] doi:10.1016/j.apgeochem.2011.07.005

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