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Effect of gas hydrates melting on seafloor slope instability ArchiMer
Sultan, Nabil; Cochonat, Pierre; Foucher, Jean-paul; Mienert, J.
We present a theoretical study of the thermodynamic chemical equilibrium of gas hydrate in soil by taking into account the influence of temperature, pressure, pore water chemistry, and the mean pore size distribution. The model uses a new formulation based on the enthalpy form of the law of conservation of energy. The developed model shows that due to a temperature and pressure increase, hydrates may dissociate at the top of the hydrate occurrence zone to ensure a chemical equilibrium with the surrounding bulk water. This original result confirms what has been already shown through experiments. The second part of the paper presents an application of the model through a back-analysis of the giant Storegga Slide on the Norwegian margin. Two of the most...
Tipo: Text Palavras-chave: Storegga; Slope failure; GLE; Finite difference; Methane hydrate.
Ano: 2004 URL: http://archimer.ifremer.fr/doc/2004/publication-699.pdf
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Dynamics of gas hydrate: case of the Congo continental slope ArchiMer
Sultan, Nabil; Foucher, Jean-paul; Cochonat, Pierre; Tonnerre, T; Bourillet, Jean-francois; Ondreas, Helene; Cauquil, E; Grauls, D.
A numerical model is developed to study the temperature effect on stability and phase transformation of gas-hydrate. The model uses a mathematical formulation based on the enthalpy form of the conservation law of energy. The use of the enthalpy form instead of the temperature form as often done in the literature has made the problem numerically simpler. The model is then applied to describe the effect of sea bottom temperature variations on the stability of gas hydrate occurrences and on the seafloor reflectivity in sediments of the Congo continental slope. Indeed, a migrating seafloor reflectivity front is observed on 3D seimic images from two surveys performed 6 months apart and interpreted as a migrating gas hydrate stability zone. Seawater temperature...
Tipo: Text Palavras-chave: Temperature; Stefan problem; Seafloor reflectivity; Gas hydrate; Heat flow; Finite difference; Continental margins.
Ano: 2004 URL: http://archimer.ifremer.fr/doc/2004/publication-702.pdf
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Evaluation of the risk of marine slope instability: A pseudo-3D approach for application to large areas ArchiMer
Sultan, Nabil; Cochonat, Pierre; Bourillet, Jean-francois; Cayocca, Florence.
This article presents a methodology developed to evaluate the instability of submarine slopes that extend over a large area. Special attention was paid to (1) the complex geometry (bathymetry) and the expanse of the slope, (2) the heterogeneity of the sediment, and (3) the distribution of the pore pressure. The safety factor was considered as a spatially varying quantity. The General Formulation (GLE, Fredlund and Krahn 1977), which fully satisfies equilibrium conditions, was used for evaluating the stability of the marine slope. The submarine slope failure, which occurred on 16 October 1979 during the construction of the new Nice airport, was studied in order to test the developed model. Geotechnical parameters were taken from experimental tests carried...
Tipo: Text Palavras-chave: Shear strength; Slope stability; Safety factor; Marine sediment; Finite element; Finite difference; Failure.
Ano: 2001 URL: http://archimer.ifremer.fr/doc/2001/publication-698.pdf
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