Gas network development in a precompacted bentonite experiment: Evidence of generation and evolution

Harrington, J.F.; Graham, C.C.; Cuss, R.J.; Norris, Simon

doi:10.1016/j.clay.2017.07.005

Cited by 44 publications

(35 citation statements)

References 15 publications

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“…To simulate the scenario of a radioactive waste canister hosted in a hard rock repository, testing is conducted in a constant volume apparatus that mimics the properties of an unyielding host rock wall. Gas migration within this test has been shown to occur through an induced network of localised pathways [17], which is consistent with direct observations using nanoparticle traces (Harrington et al, 2012). This paper describes three experimental scenarios examining (i) flow rate control on the mobility of gas, (ii) influence of boundary condition on the stability of gas pathways, and (iii) stimulation of the microfracture network.…”

Section: Introductionsupporting

confidence: 83%

“…The initial test stages [1] through [11] are described in detail by Harrington et al [17] which focussed on the processes governing resaturation, gas entry, and the establishment of steady-state gas flow. In contrast, this paper primarily focusses on post gas breakthrough data from the same test, Mx80-A, designed to examine the impact of variable gas pressure gradient to the mass transfer rate of gas and changes in drainage configuration on the distribution of gas flow, pressure, and stress within the bentonite (Table 2).…”

Section: Geofluidsmentioning

confidence: 99%

“…In contrast, this paper primarily focusses on post gas breakthrough data from the same test, Mx80-A, designed to examine the impact of variable gas pressure gradient to the mass transfer rate of gas and changes in drainage configuration on the distribution of gas flow, pressure, and stress within the bentonite (Table 2). For clarity, all new stages reported in this paper are labelled alphabetically to distinguish them from those presented by Harrington et al [17]. 4 Geofluids…”

Section: Geofluidsmentioning

confidence: 99%

“…Under these circumstances, dilatancy can occur [16]. Here, gas transport is not directly governed by permeability tensors or phase saturations but by a complex hydromechanical coupling between the gas pressure and stress state [17]. In addition, studies examining the degree of instability in immiscible flow systems highlight that even in idealised, smooth, and parallel plate fractures, flow is both localised and unstable [18].…”

Section: Introductionmentioning

confidence: 99%

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Gas Network Development in Compact Bentonite: Key Controls on the Stability of Flow Pathways

et al. 2019

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Compacted bentonite is proposed as an engineered barrier material within facilities for the geological disposal of radioactive waste. Barrier performance and its interaction with a free gas phase must be considered as part of sound repository design. This study involved the long-term experimental examination of gas flow in precompacted bentonite, with particular consideration of gas network stability. Results demonstrate that the stress field experienced by the clay is strongly coupled with gas flow. For the first time, three controls on this behaviour are considered: (i) injection flow rate, (ii) constant vs. variable gas pressure, and (iii) stimulation of the microfracture network. A detailed stress analysis is used to examine changes in the gas flow network. The results indicate a degree of metastability despite these changes, except in the case of stimulation of the microfracture network by removal of the primary drainage route. In this case, a rapid redevelopment of the gas flow network was observed. As such, availability of drainage pathways will represent a key control on the generation of peak gas pressures and distribution of gas within the engineered barrier. The cessation of gas flow is shown to result in crack closure and self-sealing. Observations from this study highlight that characterisation of the gas network distribution is of fundamental importance in predicting gas dissipation rates and understanding the long-term fate of gas in radioactive waste repositories.

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Section: Introductionsupporting

confidence: 83%

Section: Geofluidsmentioning

confidence: 99%

Section: Geofluidsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Gas Network Development in Compact Bentonite: Key Controls on the Stability of Flow Pathways

et al. 2019

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“…A wealth of laboratory and field-scale experimental studies have investigated gas transport processes through natural (host rock) and engineered barriers. These studies have provided considerable evidence suggesting that gas flow at gas pressures above a reference level is accompanied by the creation of pressure-induced preferential pathways and dilation of the clay, yet have not been able to determine the exact mechanisms which control gas entry, flow and pathway sealing Horseman et al 1999Horseman et al , 2003Graham et al 2012;Harrington et al 2012Harrington et al , 2017Cuss et al 2014;Sellin 2014;Bennett et al 2015).…”

mentioning

confidence: 99%

Development of a mathematical model for gas migration (two-phase flow) in natural and engineered barriers for radioactive waste disposal

Dagher

Nguyen

Sedano

2018

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In a deep geological repository (DGR) for the long-term containment of radioactive waste, gases could be generated through a number of processes. If gas production exceeds the containment capacity of the engineered barriers or host rock, these gases could migrate through these barriers and potentially expose people and the environment to radioactivity. Expansive soils, such as bentonite-based materials, are currently the preferred choice of seal materials. Understanding the long-term performance of these seals as barriers against gas migration is an important component in the design and long-term safety assessment of a DGR. This study proposes a hydro-mechanical linear poro-elastic visco-capillary mathematical model for advective-diffusive controlled two-phase flow through a low-permeability expansive soil. It is based on the theoretical framework of poromechanics, incorporates Darcy's Law for both the porewater and poregas, and a modified Bishop's effective stress principle. Using the finite element method (FEM), the model was used to numerically simulate 1D flow through a low-permeability expansive soil. The results were verified against experimental results found in the current literature. Parametric studies were performed to determine the influence on the flow behaviour. Based on the results, the mathematical model looks promising and will be improved to model flow through preferential pathways.

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Experimental Basis

Zhang,

Wang,

Kaufhold

et al. 2024

Thermo-Hydro-Mechanical-Chemical (THMC) Processes in Bentonite Barrier Systems

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Gas network development in a precompacted bentonite experiment: Evidence of generation and evolution

Cited by 44 publications

References 15 publications

Gas Network Development in Compact Bentonite: Key Controls on the Stability of Flow Pathways

Gas Network Development in Compact Bentonite: Key Controls on the Stability of Flow Pathways

Development of a mathematical model for gas migration (two-phase flow) in natural and engineered barriers for radioactive waste disposal

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