Modelling gas fracturing in saturated clay samples using triple-node zero-thickness interface elements

Liaudat, Joaquín; Dieudonné, Anne-Catherine

doi:10.1016/j.compgeo.2022.105128

Cited by 5 publications

(5 citation statements)

References 56 publications

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“…In addition, the continuity assumption is no longer applicable to the stratification and expansion of inter-layer destruction. Scholars initially tried to use zero thickness unit to solve the problem of unit division in the thickness direction [126,127], and then tried to equivalent the interface layer to normal and tangential orthogonal springs to simulate the debonding problem of composite materials [128,129], and achieved certain results, but did not reflect the interaction between normal and tangential when the interface damage.…”

Section: Establishment Of the Interface Model And The Damage Criterionmentioning

confidence: 99%

A review of FMLs performance test methods and index evaluation

et al. 2023

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With its excellent fatigue performance and high damage tolerance and other irreplaceable advantages, FMLs have gradually increased the demand in aerospace, rail transit, ship and other fields, and have put forward higher requirements for the speed and accuracy of its performance test and index evaluation. In this paper, the methods of performance test, analysis and index evaluation of FMLs are introduced from three aspects with carbon fiber and composite materials, mechanical properties and numerical simulation technology, details the common test methods, the latest technology and progress, and analyzes their advantages and disadvantages, so as to provide direction and reference for the performance test method and index evaluation of FMLs. Finally, the main development directions of the current performance testing methods and index evaluation of FMLs are briefly discussed.

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Section: Establishment Of the Interface Model And The Damage Criterionmentioning

confidence: 99%

A review of FMLs performance test methods and index evaluation

et al. 2023

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“…The visco-capillary two-phase flow occurs when the difference between the gas-and the liquid-phase pressures exceeds the material gas entry value, which is a material property determined by the pore structure of the clay. Once the gas entry value is exceeded, the gas mobility is controlled mostly by the intrinsic permeability, the retention properties, and the relative permeability function of the clay [8]. If the gas pressure is high enough and exceeds a sum of minimal principal compressive stress and tensile strength, then gas-induced fractures may develop [8] and provide preferential pathways for groundwater flow and, subsequently, radionuclide migration.…”

Section: Introductionmentioning

confidence: 99%

“…Once the gas entry value is exceeded, the gas mobility is controlled mostly by the intrinsic permeability, the retention properties, and the relative permeability function of the clay [8]. If the gas pressure is high enough and exceeds a sum of minimal principal compressive stress and tensile strength, then gas-induced fractures may develop [8] and provide preferential pathways for groundwater flow and, subsequently, radionuclide migration. Thus, depending on corrosion and gas dissolution/transport rates, the engineered barriers and host rock may become unsaturated, and that will impact radionuclide transport properties.…”

Section: Introductionmentioning

confidence: 99%

Modelling of the Corrosion-Induced Gas Impact on Hydraulic and Radionuclide Transport Properties of Geological Repository Barriers

Narkuniene,

Poskas,

Bartkus

2023

Minerals

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The geological disposal of high-level radioactive waste is the final step in the nuclear fuel cycle. It is realized via isolating the high-level radioactive waste in the geological environment with an appropriate system of engineered barriers. Radionuclides-containing materials must be isolated from the biosphere until the radioactivity contained in them has diminished to a safe level. In the case of high-level radioactive waste, it could take hundreds of thousands of years. Within such a long timescale, a number of physical and chemical processes will take part in the geological repository. For the assessment of radionuclide migration from a geological repository, it is necessary to predict the repository’s behavior once placed in the host rock as well as the host-rock response to disturbances due to construction. In this study, the analysis of repository barriers (backfill, concrete, inner excavation disturbed zone (EDZ), outer EDZ, host rock) thermo–hydraulic–mechanical (THM) evolution was performed, and the scope of gas-induced desaturation was analyzed with COMSOL Multiphysics. The analysis was based on modelling of a two-phase flow of miscible fluid (water and H2) considering important phenomena such as gas dissolution and diffusion, advective–diffusive transport in the gaseous phase, and mechanical deformations due to thermal expansion of water and porous media. The importance of proper consideration of temperature-dependent thermodynamic properties of water and THM couplings in the analysis of near-field processes was also discussed. The modelling demonstrated that such activities as 50 years’ ventilation of the waste disposal tunnel in initially saturated porous media, and such processes as gas generation due to corrosion of waste package or heat load from the waste, also led to desaturation of barriers. H2 gas generation led to the desaturation in engineered barriers and in a part of the EDZ close to the gas generation place vanishing soon after finish of gas generation, while the host rock remained saturated during the gas generation phase (50–100,000 years). Radionuclide transport properties in porous media such as effective diffusivity are highly dependent on the water content in the barriers determined by their porosity and saturation.

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“…In the second approach, zero-thickness interface elements are used to explicitly model the opening of an existing fracture (Fig. 1 (b)), following the work by Liaudat et al [5]. A constitutive law that is capable of describing the fracture initiation, propagation, closing and opening is implemented in this approach, considering heat transfer in the discontinuity.…”

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confidence: 99%

Comparison of two approaches for modelling fracture opening due to cold water injection in geothermal reservoir

Luo,

Josselin,

Vardon

et al. 2023

SEG

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Heat and electricity production from deep hot reservoirs through hydrothermal or petrothermal system requires to inject cold fluid in a naturally or artificially fractured medium. Cold water injection in a hot reservoirs causes thermo-hydro-mechanical (THM) coupled processes that may have several influences on operations and long term production [1]. Cold water has a higher viscosity, which means injection can become difficult due to higher flow impedance, while thermal diffusion in the rock matrix causes shrinkage and thus an increasing fracture aperture over time that can lead to flow channeling and a reduction of operation time. A deep understanding of the contribution of coupled THM processes to injection into fractured media is thus important to predict the long-term performance of a geothermal power plant. In this study, coupled THM processes in a single fracture are numerically investigated with two different approaches to model the discontinuity. The first numerical approach proposes modelling an implicit fracture in a fracture zone using solid elements (Fig.1 (a)). The impact of the fracture is introduced by means of a stress dependent fracture aperture, which in turn determines the fracture transmissivity. This function allows recovery of the opening, and thus the model replicates opening and closure of the fracture. Then, an equivalent continuum permeability [m2] is obtained as follows: where [m] is the elastic opening, br and bmax [m] are the residual and maximum apertures, respectively, a is the stress dependency coefficient; [Pa] is effective normal stress, and [m]the fracture spacing. The combination of the continuum elements to model an implicit fracture embedded in a fracture zone and the evolving permeability has been used successfully used to model elastic opening in volcanic rock [2] and granodiorite rock [3, 4]. In the second approach, zero-thickness interface elements are used to explicitly model the opening of an existing fracture (Fig.1 (b)), following the work by Liaudat et al. [5]. A constitutive law that is capable of describing the fracture initiation, propagation, closing and opening is implemented in this approach, considering heat transfer in the discontinuity. In this approach, the cubic law is used to estimate the longitudinal transmissivity [m3] as a function of the normal fracture aperture: where [m] is the normal separation and [m3] is a constant value which makes it possible to assign an initial longitudinal transmissivity even if the fracture is mechanically closed. In both approaches, the simulation of cold water injection requires to consider the heat and hydraulic flows in the fracture alongside mechanical behaviour, since changes in pore water pressure and temperature influence the fracture aperture, thus modifying the fracture transmissivity. In order to compare both approaches, a simple synthetic model is studied. The model with its boundary and initial conditions are shown in Fig.2. Water with a temperature of 20 °C and pressure varying from 4 MPa – 10 MPa is injected at the centering point of the fracture. Figure 3 shows the injection pressure profile. Fracture permeability evolution is compared in Fig.4, which shows the two different methods capture different characteristics of the natural fracture behaviour. In the continuum method, the fracture is modelled as a continuum element, thus any pressure or stress change will result in corresponding changes in the fracture permeability, which is reflected in Fig.4 showing that the permeability changes with the injection pressure changing, In contrast, in the interface element, Fig.4 shows only when the injection pressure reaches 10 MPa, the permeability increases sharply from the initial value to the peak value. This is because penalty method is used to allow the small overlapping of the two faces of the discontinuity, thus keeping negligible permeability variation, before it opens. The result in Fig.4 also illustrates the effect of thermal stress on the fracture opening, considering the total vertical stress is 10 MPa while injection pressure is below or equal to 10 MPa. In conclusion, though the peak permeability predicted from two methods are consistent, both around 1.5 x 10 -12 D, the behaviour before fracture opens in these two approaches are quite different. For the interface method, permeability variations keep negligible before fracture opens, while for the continuum method, permeability changes with corresponding pressure or stress changes without dependence on the opening of the fracture.

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Modelling gas fracturing in saturated clay samples using triple-node zero-thickness interface elements

Cited by 5 publications

References 56 publications

A review of FMLs performance test methods and index evaluation

A review of FMLs performance test methods and index evaluation

Modelling of the Corrosion-Induced Gas Impact on Hydraulic and Radionuclide Transport Properties of Geological Repository Barriers

Comparison of two approaches for modelling fracture opening due to cold water injection in geothermal reservoir

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