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| Registros recuperados: 64 | |
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| Riboulot, Vincent; Ker, Stephan; Sultan, Nabil; Thomas, Yannick; Marsset, Bruno; Scalabrin, Carla; Ruffine, Livio; Boulart, Cedric; Ion, Gabriel. |
| Gas hydrates, a solid established by water and gas molecules, are widespread along the continental margins of the world. Their dynamics have mainly been regarded through the lens of temperature-pressure conditions. A fluctuation in one of these parameters may cause destabilization of gas hydrate-bearing sediments below the seafloor with implications in ocean acidification and eventually in global warming. Here we show throughout an example of the Black Sea, the world’s most isolated sea, evidence that extensive gas hydrate dissociation may occur in the future due to recent salinity changes of the sea water. Recent and forthcoming salt diffusion within the sediment will destabilize gas hydrates by reducing the extension and thickness of their thermodynamic... |
| Tipo: Text |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00418/52981/53916.pdf |
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| 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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| Miramontes, Elda; Sultan, Nabil; Garziglia, Sebastien; Jouet, Gwenael; Pelleter, Ewan; Cattaneo, Antonio. |
| One of the main concerns regarding the development of submarine landslides is the role played by weak layers in the failure process and, in particular, their impact in terms of volume, shape, and evolution of mass movements. In the present study we identified a weak layer in the eastern margin of the Corsica Trough (northern Tyrrhenian Sea) that formed the basal failure surface of the Pianosa Slump at 42–50 ka. This layer is characterized by high water content, high plasticity, high compressibility, and post-peak strain softening behavior (i.e., strength loss with increasing strain). These specific mechanical and sedimentological properties seem to be related to the presence of analcime zeolites with a concentration of 2–4% in the muddy sediment. Zeolites... |
| Tipo: Text |
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| Ano: 2018 |
URL: http://archimer.ifremer.fr/doc/00444/55565/57176.pdf |
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| Colin, Florent; Ker, Stephan; Riboulot, Vincent; Sultan, Nabil. |
| Gas hydrate (GH) systems constitute methane sinks sensitive to environmental changes such as pressure, temperature, and salinity. It remains a matter of debate as to whether the large GH system of the Black Sea has reached a steady state since the last glacial maximum (LGM). We report on an irregular free gas distribution in specific sediment layers marking an irregular bottom‐simulating reflector (BSR). This anomalous free gas distribution revealed by very high resolution seismic images, acquired by a deep‐towed multichannel seismic system, might be evidence of an on‐going migration of the base of the GH stability zone (GHSZ). We show that the reequilibrium is not occurring homogeneously as overpressure from hydrate dissociation slows their decomposition... |
| Tipo: Text |
Palavras-chave: Hydrates; Seismic; Very high resolution; Dissociation; Black Sea. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00652/76430/77526.pdf |
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| De Prunele, Alexis; Ruffine, Livio; Riboulot, Vincent; Peters, Carl A.; Croguennec, Claire; Guyader, Vivien; Pape, Thomas; Bollinger, Claire; Bayon, Germain; Caprais, Jean-claude; Germain, Yoan; Donval, Jean-pierre; Marsset, Tania; Bohrmann, Gerhard; Geli, Louis; Rabiu, Abdulkarim; Lescanne, Marc; Cauquil, Eric; Sultan, Nabil. |
| The Niger Delta is one of the largest hydrocarbon basin offshore Africa and it is well known for the presence of active pockmarks on the seabed. During the Guineco-MeBo cruise in 2011, long cores were taken from a pockmark cluster in order to investigate the state of its current activity. Gas hydrates, oil and pore-water were sampled for geochemical studies. The resulting dataset combined with seismic data reveal that shallow hydrocarbon migration in the upper sedimentary section was focused exclusively within the pockmarks. There is a clear tendency for gas migration within the hydrate-bearing pockmarks, and oil migration within the carbonate-rich one. This trend is interpreted as a consequence of hydrate dissolution followed by carbonate precipitation... |
| Tipo: Text |
Palavras-chave: Anaerobic oxidation of methane; Cluster of pockmarks; Fluid flow; Gas hydrates; Pore-water profiles; Transient state. |
| Ano: 2017 |
URL: http://archimer.ifremer.fr/doc/00365/47647/47676.pdf |
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| Riboulot, Vincent; Cattaneo, Antonio; Sultan, Nabil; Garziglia, Sebastien; Ker, Stephan; Imbert, Patrice; Voisset, Michel. |
| A series of pockmarks observed at the seabed matches well the perimeter of a large submarine landslide, called NG1, located on the outer shelf and continental slope of the Eastern Gulf of Guinea. NG1 extends over 200 km2, is covered by a 120-m thick sedimentary layer which tapers downslope, and has an internal structure clearly identified in 3D seismic data consisting of three adjacent units on the upper continental slope. The pockmarks above NG1 have a diameter of several tens of meters and reveal distinct origins: (1) linked to >500 m deep fluid reservoirs, (2) rooted in NG1 internal discontinuities between NG1 units, and (3) well above NG1, superficially rooted in a regional conformity (D40), which marks the lowest sea level of the Marine Isotope... |
| Tipo: Text |
Palavras-chave: Pockmarks; Fluid seepage; Submarine landslide; Sea-level changes; Piezocone; Niger Delta. |
| Ano: 2013 |
URL: http://archimer.ifremer.fr/doc/00159/27031/31906.pdf |
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| Leynaud, Didier; Sultan, Nabil; Mienert, Jurgen. |
| Despite the gently dipping slopes (ca 1 degrees), large-scale submarine slope failures have occurred on the mid-Norwegian continental margin (Storegga, Sklinnadjupet, Traenadjupet), suggesting the presence of special conditions predisposing to failure in this formerly glaciated margin. With a volume estimated between 2,400 and 3,200 km(3) and an affected area of approximately 95,000 km(2), the Storegga slide represents one of the largest and best-studied submarine slides of Holocene age known worldwide. Finite element modeling of slope failure indicates that a large (6.5 < Ms < 7.0) seismic triggering mechanism would not be sufficient to cause failure at more than 110 m below the seabed as observed for the slip planes at Storegga (northern sidewall).... |
| Tipo: Text |
Palavras-chave: Submarine slide; Slope stability; Sediment overpressure; Rapid sedimentation. |
| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/2007/publication-3521.pdf |
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| Sultan, Nabil; Marsset, Bruno; Ker, Stephan; Marsset, Tania; Voisset, Michel; Vernant, Antoine-mathieu; Bayon, Germain; Cauquil, Eric; Adamy, J.; Colliat, J. L.; Drapeau, D.. |
| Based on acquired geophysical, geological and geotechnical data and modeling, we suggest hydrate dissolution to cause sediment collapse and pockmark formation in the Niger delta. Very high-resolution bathymetry data acquired from the Niger delta reveal the morphology of pockmarks with different shapes and sizes going from a small ring depression surrounding an irregular floor to more typical pockmarks with uniform depression. Geophysical data, in situ piezocone measurements, piezometer measurements and sediment cores demonstrate the presence of a common internal architecture of the studied pockmarks: inner sediments rich in gas hydrates surrounded by overpressured sediments. The temperature, pressure and salinity conditions of the studied area have allowed... |
| Tipo: Text |
Palavras-chave: Methane gas hydrate; Sea floor; Marine sediments; Pore pressure; Porous media; Continental margin; Clathrate hydrate; Fluid flow; Stability; Slope. |
| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00012/12300/9092.pdf |
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| Tary, Jean-baptiste; Geli, Louis; Guennou, Claude; Henry, Pierre; Sultan, Nabil; Cagatay, N.; Vidal, V.. |
| Different types of 4-component ocean bottom seismometers (OBS) were deployed for variable durations ranging from 1 week to about 4 months in 2007, over soft sediments covering the seafloor of the Tekirdag Basin (western part of the Sea of Marmara, Turkey). Non-seismic microevents were recorded by the geophones, but generally not by the hydrophones, except when the hydrophone is located less than a few tens of centimetres above the seafloor. The microevents are characterized by short durations of less than 0.8 s, by frequencies ranging between 4 and 30 Hz, and by highly variable amplitudes. In addition, no correlation between OBSs was observed, except for two OBSs, located 10 m apart. Interestingly, a swarm of similar to 400 very similar microevents (based... |
| Tipo: Text |
Palavras-chave: Time series analysis; Gas and hydrate systems; Body waves; Interface waves; Seismic attenuation; Wave propagation. |
| Ano: 2012 |
URL: http://archimer.ifremer.fr/doc/00089/20012/17825.pdf |
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| Sultan, Nabil; Riboulot, Vincent; Ker, Stephan; Marsset, Bruno; Geli, Louis; Tary, Jean-baptiste; Klingelhoefer, Frauke; Voisset, Michel; Lanfumey, Valentine; Colliat, Jean-louis; Adamy, Jerome; Grimaud, S.. |
| Gas hydrates were recovered by coring at the eastern border of a shale-cored anticline in the eastern Niger Delta. To characterize the link between faults and fluid release and to identify the role of fluid flow in the gas hydrate dynamics, three piezometers were deployed for periods ranging from 387 to 435 days. Two of them were deployed along a major fault linked to a shallow hydrocarbon reservoir while the third monitored the fluid pressure in a pockmark aligned above the same major fault. In addition, 10 ocean-bottom seismometers (OBS) were deployed for around 60 days. The piezometers simultaneously registered a prolonged fluid flow event lasting 90 days. During this time, OBS measurements record several episodic fluid release events. By combining and... |
| Tipo: Text |
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| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00060/17106/14624.pdf |
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| Sultan, Nabil; Lafuerza, Sara. |
| L’excès de pression interstitielle a un effet significatif sur la stabilité des pentes sous-marines et sur la déformation des sédiments, alors sa mesure in-situ à l’équilibre est cruciale pour réaliser des évaluations exactes de la stabilité des pentes et pour dériver adéquatement les paramètres géotechniques de conception. La pression interstitielle in-situ à l’équilibre est généralement obtenue à partir de la diminution de la pression interstitielle lors d’essais en piézocône. Cependant, les plateaux et pentes sous-marins sont souvent caractérisés par l’existence de sédiments à faible perméabilité (à granulométrie fine) qui engendrent des tests de dissipation de longue durée, ce qui représente une problématique pour les coûts d’opération en mer. Ainsi,... |
| Tipo: Text |
Palavras-chave: Cavity expansion; Dissipation tests; Marine sediment; Piezoprobe; Pore-water pressure. |
| Ano: 2013 |
URL: http://archimer.ifremer.fr/doc/00198/30926/29346.pdf |
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| Berne, Serge; Bassetti, Maria-angela; Baztan, J; Dennielou, Bernard; Gaudin, M; Rabineau, Marina; Jouet, Gwenael; Sultan, Nabil. |
| Promess 1 was the first scientific drilling operation in the Gulf of Lions. Together with Eurostrataform, these 2 European projects provided a huge amount of new data that allows us to analyse, from « sink to source », the main processes that control strata architecture on a deltaic margin. In the deep-sea, The Rhone deep sea fan functioning is strongly controlled by sea-level changes: it functions as a classical channel/levee system as long as a direct connection exists between the Rhone river and the canyon head. Following MWP1A, only episodic mass wasting, triggered by dense water cascading, feeds the system. At this time, erosion of lowstand shelf shorefaces is the major source of sand to the deep-sea. [NOT CONTROLLED OCR] |
| Tipo: Text |
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| Ano: 2006 |
URL: http://archimer.ifremer.fr/doc/2006/acte-4688.pdf |
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| Sultan, Nabil; Garziglia, Sebastien; Ruffine, Livio. |
| Over the past years, several studies have raised concerns about the possible interactions between methane hydrate decomposition and external change. To carry out such an investigation, it is essential to characterize the baseline dynamics of gas hydrate systems related to natural geological and sedimentary processes. This is usually treated through the analysis of sulfate-reduction coupled to anaerobic oxidation of methane (AOM). Here, we model sulfate reduction coupled with AOM as a two-dimensional (2D) problem including, advective and diffusive transport. This is applied to a case study from a deep-water site off Nigeria’s coast where lateral methane advection through turbidite layers was suspected. We show by analyzing the acquired data in combination... |
| Tipo: Text |
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| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00339/45068/44493.pdf |
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| Sultan, Nabil. |
| Existing laboratory geo-mechanical data show that gas hydrates content can significantly increase the peak shear strength of hydrate bearing sediments while developing its strain softening. On the other hand, some recent publications have reported the occurrence of slope instabilities within the gas hydrate stability zones suggesting a mechanical cause for the failure rather than a thermodynamic one. The purpose of this work aims to examine, through a computational numerical approach, the potential link between gas hydrate content, strain softening behavior and slope stability in gas hydrate-bearing sediments. The strain softening of gas hydrate-bearing sediments was implemented in a 3D slope stability model (SAMU-3D). This was done by adding to the... |
| Tipo: Text |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00634/74638/74533.pdf |
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| Ballas, Gregory; Garziglia, Sebastien; Sultan, Nabil; Pelleter, Ewan; Toucanne, Samuel; Marsset, Tania; Riboulot, Vincent; Ker, Stephan. |
| The geotechnical properties of clay sediments were investigated using laboratory and in-situ measurements as part of the geohazard assessment in the Romanian sector of the Black Sea affected by landslides and seafloor deformation features. The sediments were characterized as predominantly high plastic silty clay of high compressibility, low undrained shear strength, low cohesion and moderate sensitivity. A shallow increase in shear strength exceeding the general trend could have been reconciled with evidence for the precipitation of iron sulfides and calcium carbonates related to early diagenetic reactions of sulfate reduction (e.g. cryptic sulfur cycle) and anaerobic oxidation of methane. Comparison of the compression behaviour of natural and... |
| Tipo: Text |
Palavras-chave: Lacustrine clay sediment; Structured material; Sulfur cement; Carbonate cement; Early diagenesis; Weak layer. |
| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00439/55064/56545.pdf |
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| Ker, Stephan; Thomas, Yannick; Riboulot, Vincent; Sultan, Nabil; Bernard, Céline; Scalabrin, Carla; Ion, G; Marsset, Bruno. |
| A comprehensive characterization of the gas hydrate system offshore the western Black Sea was performed through an integrated analysis of geophysical data. We detected the Bottom Simulating Reflector (BSR), which marks, in this area, the base of gas hydrate stability. The observed BSR depth does not fit the theoretical steady-state base of gas hydrate stability zone (BGHSZ). We show that the disparity between the BSR and predicted BGHSZ is the result of a transient state of the hydrate system due to the ongoing re-equilibrium since the Last Glacial Maximum. When gas hydrates are brought outside the stability zone due to changes in temperature and sea level, their dissociation generates an increase in interstitial pore pressure. This process is favorable to... |
| Tipo: Text |
Palavras-chave: Gas hydrate; BSR; Excess pore pressure; Black Sea. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00474/58531/61081.pdf |
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| Bayon, Germain; Henderson, Gideon M.; Etoubleau, Joel; Caprais, Jean-claude; Ruffine, Livio; Marsset, Tania; Dennielou, Bernard; Cauquil, Eric; Voisset, Michel; Sultan, Nabil. |
| The application of uranium-thorium dating methods to authigenic carbonates provides unique constraints on the temporal evolution of methane seeps at ocean margins. In this study, we report U-Th isotope measurements for carbonate breccias collected from within a hydrate-bearing pockmark located at the Niger Delta margin. These concretions were extracted from a carbonate-rich layer in the upper two meters of a sediment core (N2-KS-44; ~ 1200 m water depth), well above the present-day sulphate-methane transition zone (about 3 m depth) and the presence of gas hydrates in the sediment. The stratigraphy of core N2-KS-44 was established by tuning its downcore Al/Ti profile to a well-dated nearby reference core, and carbonate 230Th/U ages were calculated using... |
| Tipo: Text |
Palavras-chave: Gas hydrates; Pockmarks; U-series; Authigenic carbonates; Niger delta. |
| Ano: 2015 |
URL: http://archimer.ifremer.fr/doc/00286/39708/41518.pdf |
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| Sultan, Nabil. |
| Parameters affecting gas hydrate formation include temperature, pore pressure, gas chemistry, and pore-water salinity. Any change in the equilibrium of these parameters may result in dissociation (gas-hydrate turns into free gas/water mixture) and/or dissolution (gas-hydrate becomes mixture of water and dissolved gas) of the gas hydrate. While, gas-hydrate dissociation at the base of the Gas Hydrate Occurrence Zone (GHOZ) is often considered as a major cause of sediment deformation and submarine slope failures the consequence in terms of pore pressure and sediment deformation of the dissolution of the gas hydrate at the top of the GHOZ remains neglected. In this study, we quantify and compare the excess pore pressure resulting from gas hydrate dissociation... |
| Tipo: Text |
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| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/00226/33763/32173.pdf |
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| Sultan, Nabil; Cui, Y. -j.; Delage, P.. |
| An underground research laboratory (URL) has been excavated in a deposit of Boom clay at a depth of 223 m by the SCK-CEN Belgian organisation near the city of Mol. This URL is devoted to research into nuclear waste disposal. This paper presents the results of an investigation carried out in the triaxial apparatus on specimens that were trimmed from blocks extracted during excavation sequences in the URL. In order to characterise the mechanical behaviour of the natural Boom clay and to examine the effect of initial and induced anisotropy on its constitutive behaviour, two series of triaxial tests were carried out. Special attention was devoted to the yield behaviour and the effects of stress history. Experimental results showed a clear relation between the... |
| Tipo: Text |
Palavras-chave: Anisotropy; Clays; Constitutive relations; Elasticity; Laboratory tests; Plasticity; Shear strength. |
| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00013/12414/9530.pdf |
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| Leynaud, Didier; Sultan, Nabil. |
| Recent geophysical and geotechnical data acquired on the Nice shelf to the east of the 1979 landslide source area, Suggest slow deformations processes which could lead to future catastrophic slope failure. According to these preliminary interpretations, it is of major interest to perform a slope stability evaluation to define the hazard and quantify the danger related to a probable instability on this slope. A probabilistic approach is proposed here using a modified version of the SAMU_3D model, a 3-D slope stability software recently developed by Sultan and others to account for complex geometry. The 3-D analysis is based on the upper bound theorem of plasticity developed by Chen and others. One of the main features of the original model is to allow... |
| Tipo: Text |
Palavras-chave: Probabilistic analysis; Slope stability; Monte Carlo simulation; Shear zone. |
| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00002/11290/7828.pdf |
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| Registros recuperados: 64 | |
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