Modelling advective gas flow in compact bentonite: Lessons learnt from different numerical approaches

Tamayo-Mas, E.; Harrington, J.F.; Brüning, T.; Shao, H.; Dagher, E.E.; Lee, J.; Kim, K.; Rutqvist, J.; Kolditz, O.; Lai, S.H.; Chittenden, N.; Wang, Y.; Damians, I.P.; Olivella, S.. 2021 Modelling advective gas flow in compact bentonite: Lessons learnt from different numerical approaches. International Journal of Rock Mechanics and Mining Sciences, 139, 104580. https://doi.org/10.1016/j.ijrmms.2020.104580

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Official URL: http://dx.doi.org/10.1016/j.ijrmms.2020.104580

Abstract/Summary

In a repository for radioactive waste hosted in a clay formation, hydrogen and other gases may be generated due to the corrosion of metallic materials under anoxic conditions, the radioactive decay of waste and the radiolysis of water. If the gas production rate exceeds the gas diffusion rate within the pores of the clay, a discrete gas phase will form and accumulate until its pressure becomes large enough to exceed the entry pressure of the surrounding material, at which point dilatant, advective flow of gas is expected to occur. The purpose of Task An under DECOVALEX-2019 is to better represent the processes governing the advective movement of gas in both low-permeability argillaceous repository host rocks and clay-based engineered barriers within numerical codes. In this paper special attention is given to the mechanisms controlling gas entry, flow and pathway sealing and their impact on the performance of the engineered clay barrier. Previous work suggests gas flow is accompanied by the creation of dilatant pathways whose properties change temporally and spatially within the medium. Thus, four new types of approaches have been developed: (i) standard two-phase flow models (continuous techniques) incorporating a range of different mechanical deformation behaviours, (ii) enhanced two-phase flow models in which fractures are embedded within a plastic material (continuous techniques) or incorporated into the model using a rigid-body-spring network (discrete approaches), (iii) a single-phase model incorporating a creep damage function in which only gas flow is considered, and (iv) a conceptual approach used to examine the chaotic nature of gas flow. The outputs from these different approaches are compared. This is an essential step as the choice of modelling approach strongly impacts the representation and prediction of gas flow in a future repository. In addition, experience gained through this task is of direct relevance to other clay-based engineering issues where immiscible gas flow is a consideration including hydrocarbon migration, carbon capture and storage, shale gas and landfill design. This paper summarises the outcomes of work in Task A conducted between May 2016 and May 2019 and provides a brief overview of the experimental data and a synthesis of the work of the participating modelling teams.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1016/j.ijrmms.2020.104580
ISSN:	13651609
Date made live:	22 Apr 2021 08:54 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/530129

Item Type:

Publication - Article

Digital Object Identifier (DOI):

https://doi.org/10.1016/j.ijrmms.2020.104580

ISSN:

13651609

Date made live:

22 Apr 2021 08:54 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/530129