|Title (Primary)||Approaches to multi-scale analyses of mechanically and thermally-driven migration of fluid inclusions in salt rocks|
|Author||Shao, H.; Wang, Y.; Kolditz, O. ; Nagel, T.; Brüning, T.|
|Journal||Physics and Chemistry of the Earth|
|Keywords||rock salt; fluid inclusion; coupled HM and THM processes; multi-scale modelling concepts; DECOVALEX|
Fluid inclusions are found within mineral crystals or along grain boundaries in many sedimentary rocks, notably in evaporite formations, and can migrate along a thermal or hydro-mechanical gradient. Shale and salt rocks have been considered potential host rocks for radioactive waste disposal, due to their low permeability. Previously stagnant inclusions may become mobilised by a perturbation of the in situ state by a geotechnical installation or the emplacement of heat-generating waste. The migration of fluid inclusions can thus have important impacts on the long-term performance of a geologic repository for high-level radioactive waste disposal. As a part of the international research project DECOVALEX-2019, two aspects of fluid inclusion migration in rock salt are currently investigated under different boundary conditions: a) altered hydro-mechanical conditions as a consequence of tunnel excavation or borehole drilling and b) coupled thermo-hydro-mechanical-chemical conditions during the heating period of the post-closure phase of a repository.
To obtain a mechanistic understanding of underlying physical processes for fluid inclusion migration, a multi-scale modelling strategy has been developed. Microscale hydraulic and time-dependent mechanical conditions related to the creep behaviour of rock salt are constrained by considering the macroscale stress evolution of an underground excavation. An analysis using a coupled two-phase flow and elasto-plastic model with a consideration of permeability variation indicates that a pathway dilation along the halite grain boundary may increase the permeability by two orders of magnitude. The calculated high flow velocity may explain the fast pressure build-up observed in the field. In addition, a mathematical model for the migration and morphological evolution of a single fluid inclusion under a thermal gradient has been formulated. A first-order analysis of the model leads to a simple mathematical expression that is able to explain the key observations of thermally driven inclusion migration in salt. Finally, numerical methods such as a phase field method for solving a moving boundary problem of fluid inclusion migration have also been explored.
|Persistent UFZ Identifier||https://www.ufz.de/index.php?en=20939&ufzPublicationIdentifier=22037|
|Shao, H., Wang, Y., Kolditz, O., Nagel, T., Brüning, T. (2019):
Approaches to multi-scale analyses of mechanically and thermally-driven migration of fluid inclusions in salt rocks
Phys. Chem. Earth 113 , 1 - 13