Consulta: creatorFacets:"Sultan, Nabil"
Registros recuperados: 64
Data/hora: 15/06/2024 16:57:18

Detection of free gas and gas hydrate based on 3D seismic data and cone penetration testing: An example from the Nigerian Continental Slope
Provedor de dados: 5
Autores: Sultan, Nabil; Voisset, Michel; Marsset, Tania; Vernant, Antoine-mathieu; Cauquil, E; Colliat, J; Curinier, V.
We present a new method to characterize free gas, gas hydrates and carbonate concretions occurrence which are considered as high-risk factors for sub-sea developments in the Niger delta. This method is based on the combination of 3D seismic data to the geotechnical site characterizations using piezocone CPTU tests (Cone Penetration Test with additional measurement of the pore water pressure). A special processing of the 3D seismic data has enabled the determination of the interval compressional velocity. Using the effective-medium theory, velocity anomalies (negative and positive) within the first 15 m were translated in gas hydrate and free gas distribution. The calibration of the P wave velocity anomalies was done thanks to in-situ geotechnical testing...
Tipo: Text
Palavras-chave: Piezocone; Niger delta; Gas hydrate; Free gas; Effective medium theory.
Ano: 2007
URL: http://archimer.ifremer.fr/doc/2007/publication-2610.pdf

Effect of gas hydrates melting on seafloor slope instability
Provedor de dados: 5
Autores: 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

Pockmark formation and evolution in deep water Nigeria: Rapid hydrate growth versus slow hydrate dissolution
Provedor de dados: 5
Autores: Sultan, Nabil; Bohrmann, G.; Ruffine, Livio; Pape, T.; Riboulot, Vincent; Colliat, J. -l.; De Prunele, Alexis; Dennielou, Bernard; Garziglia, Sebastien; Himmler, Tobias; Marsset, Tania; Peters, C. A.; Rabiu, A.; Wei, J.
In previous works, it has been suggested that dissolution of gas hydrate can be responsible for pockmark formation and evolution in deep water Nigeria. It was shown that those pockmarks which are at different stages of maturation are characterized by a common internal architecture associated to gas hydrate dynamics. New results obtained by drilling into gas hydrate-bearing sediments with the MeBo seafloor drill rig in concert with geotechnical in situ measurements and pore water analyses indicate that pockmark formation and evolution in the study area are mainly controlled by rapid hydrate growth opposed to slow hydrate dissolution. On one hand, positive temperature anomalies, free gas trapped in shallow microfractures near the seafloor and coexistence of...
Tipo: Text
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00188/29913/28373.pdf

Morphological control of slope instability in contourites: a geotechnical approach
Provedor de dados: 5
Autores: Miramontes, Elda; Garziglia, Sebastien; Sultan, Nabil; Jouet, Gwenael; Cattaneo, Antonio.
Contourite drifts are sediment bodies formed by the action of bottom currents. They are common features found on continental slopes and are often affected by slope failure. However, processes controlling slope instability in contourite depositional systems are still not well constrained, and it is not clear whether contourites have particular properties that make them more susceptible to slope failure. In this study, we compare sedimentological and geotechnical properties of contouritic and hemipelagic sediments within the Corsica Trough (northern Tyrrhenian Sea) using geophysical data sets and sediment cores in order to get a better understanding of the controlling factors of slope stability. Geomorphological and slope stability analyses reveal that...
Tipo: Text
Palavras-chave: Sediment drift; Submarine landslide; Undrained shear strength; Hemipelagite; Mediterranean Sea.
Ano: 2018
URL: https://archimer.ifremer.fr/doc/00425/53636/56652.pdf

Post-glacial persistence of turbiditic activity within the Rhone deep-sea turbidite system (Gulf of Lions, Western Mediterranean): Linking the outer shelf and the basin sedimentary records
Provedor de dados: 5
Autores: Dennielou, Bernard; Jallet, Laurent; Sultan, Nabil; Jouet, Gwenael; Giresse, Pierre; Voisset, Michel; Berne, Serge.
Emplacement of post-glacial turbidites is commonly controlled by rapid changes in sea level or by seismicity. On the continental rise of the Gulf of Lions (Western Mediterranean), an aseismic area, we identified turbiditic beds deposited during the rising stage and highstand of sea level. Swath bathymetry, sediment cores, in situ Cone Penetrating Tests (CPTU), heavy mineral associations and radiocarbon dating determined the source, composition, distribution and age of the turbiditic beds. Turbidites are composed of homogeneous to positively graded silts to medium sand with quartz (up to 90%), shell debris and shelfal benthic faunas. Their distribution on the sea floor is very patchy and controlled by abundant inherited erosional bedforms. Their source is...
Tipo: Text
Palavras-chave: Holocene; Late Pleistocene; Sea level; Turbidites; Sand; Outer shelf; Canyons.
Ano: 2009
URL: http://archimer.ifremer.fr/doc/2009/publication-6316.pdf

Impact of tides and sea-level on deep-sea Arctic methane emissions
Provedor de dados: 5
Autores: Sultan, Nabil; Plaza-faverola, Andreia; Vadakkepuliyambatta, Sunil; Buenz, Stefan; Knies, Jochen.
Sub-sea Arctic methane and gas hydrate reservoirs are expected to be severely impacted by ocean temperature increase and sea-level rise. Our understanding of the gas emission phenomenon in the Arctic is however partial, especially in deep environments where the access is difficult and hydro-acoustic surveys are sporadic. Here, we report on the first continuous pore-pressure and temperature measurements over 4 days in shallow sediments along the west-Svalbard margin. Our data from sites where gas emissions have not been previously identified in hydro-acoustic profiles show that tides significantly affect the intensity and periodicity of gas emissions. These observations imply that the quantification of present-day gas emissions in the Arctic may be...
Tipo: Text
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00654/76564/77690.pdf

Comment on “Sedimentation Controls on Methane‐Hydrate Dynamics Across Glacial/Interglacial Stages: An Example From International Ocean Discovery Program Site U1517, Hikurangi Margin”
Provedor de dados: 5
Autores: Sultan, Nabil.
In the IODP 372A proposal, working hypotheses used with respect to actively deforming gas hydrate‐bearing landslides were based on an initial calculation considering gas hydrate to occur in fresh water. This initial inaccuracy leads to predict the base of methane hydrate stability zone (MHSZ) to be at around 162 meters below the seafloor (mbsf) at site U1517 while it is expected to be between 85 and 128 mbsf. It is most interesting that important negative chloride anomalies were measured well below the theoretical MHSZ without direct evidence of the presence of gas hydrate. These anomalies are usually a strong indication of gas hydrate occurrence. This initial inaccurate hypothesis provides the opportunity to evaluate the effectiveness of the indirect...
Tipo: Text
Palavras-chave: Hikurangi; Hydrate; IODP; Salinity.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00628/74043/73389.pdf

Triggering mechanisms of slope instability processes and sediment failures on continental margins: a geotechnical approach
Provedor de dados: 5
Autores: Sultan, Nabil; Cochonat, Pierre; Canals, M; Cattaneo, Antonio; Dennielou, Bernard; Haflidason, H; Laberg, J; Long, D; Mienert, J; Trincardi, F; Urgeles, R; Vorren, T; Wilson, C.
The Costa target areas exhibit the variability of slope instabilities needed to improve our understanding of sediment physical and mechanical properties in areas prone to sliding. That is why in this project, we have analysed the different slope failures events from different parts of the Costa target areas, which reflect diverse triggering mechanisms. The aim of the first part of this study was to identify the geotechnical response of the sediment to different external mechanisms (earthquake, rapid sedimentation and gas hydrate melting). We have focused on the relation between external mechanisms and the consequence change in the in-situ stress state and the physical, mechanical, and elastic properties of the sediment. In the second part of the paper, the...
Tipo: Text
Palavras-chave: Slope instability; Sensitivity; Sedimentation; Hydrate; Earthquake.
Ano: 2004
URL: http://archimer.ifremer.fr/doc/2004/publication-700.pdf

Analysis of slope failures in submarine canyon heads: An example from the Gulf of Lions
Provedor de dados: 5
Autores: Sultan, Nabil; Gaudin, Mathieu; Berne, Serge; Canals, Miquel; Urgeles, Roger; Lafuerza, Sara.
To improve understanding of evolution of submarine canyons, a three-dimensional slope-stability model is applied to Bourcart Canyon in the western Gulf of Lions in the Mediterranean Sea. The model builds on previous work by Chen and others, and it uses the upper bound theorem of plasticity to calculate the factor of safety of a kinematically admissible failing mass. Examples of three-dimensional failure surfaces documented in the literature were used to test the model formulation. Model application to Bourcart Canyon employed the results of a detailed stratigraphic analyses based on data acquired by swath bathymetry, sub-bottom profiling, high-resolution seismic reflection surveys, and piston coring. The sediment layers were also characterized using...
Tipo: Text
Palavras-chave: Cascadia accretionary complex; Upper bound theorem; Stability analysis; Continental slope; Limit equilibrium; Western gulf; Offshore; Margin; Initiation; Sediment.
Ano: 2007
URL: http://archimer.ifremer.fr/doc/2007/publication-2410.pdf

Sediment damage caused by gas exsolution: a key mechanism for mud volcano formation
Provedor de dados: 5
Autores: Blouin, Arthur; Sultan, Nabil; Callot, Jean-paul; Imbert, Patrice.
Gassy sediments are common in marine environments and are characterized by a specific mechanical behavior significantly different from that of water-saturated sediments. It is shown that gas causes damage and initiates fractures in sediments. To define the controlling parameters dominating the damage process during gas exsolution and its consequences in terms of hydro-mechanical behavior, we developed a specific consolidation apparatus to test sediments collected from the active Absheron Mud Volcano. Indeed, mud volcano formation is initiated by gas exsolution and subsequent mud generation at depth from stratified sediments. Gas was generated in the samples by circulating carbonated water through the fine-grained sediments, then decreasing the total...
Tipo: Text
Palavras-chave: Consolidation testing; Gas exsolution; Gassy sediments; Sediment damage; Mud volcano.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00588/70043/67974.pdf

Investigation of a possible submarine landslide at the Var delta front (Nice continental slope, southeast France)
Provedor de dados: 5
Autores: Sultan, Nabil; Savoye, Bruno; Jouet, Gwenael; Leynaud, Didier; Cochonat, Pierre; Henry, P.; Stegmann, Sylvia; Kopf, Achim.
The Var prodelta progrades across a straight, narrow shelf (less than 2 km wide) with a very steep continental slope reaching locally more than 30 degrees. Historically, the Var delta front is sadly famous for the 1979 catastrophic submarine landslide that resulted in several casualties and infrastructural damage. Geotechnical and geophysical investigations carried out in late 2007 to the east of the 1979 landslide scar provide evidence for the possible occurrence of a new important sedimentary collapse and submarine landslide. Geophysical data acquired in the area show the presence of several seafloor morphological steps rooted to shallow subsurface seismic reflections. Moreover, in situ piezocone measurements demonstrate the presence of several shear...
Tipo: Text
Palavras-chave: CPTu; Gassy soil; Piezocone; Shear zone; Submarine landslides.
Ano: 2010
URL: http://archimer.ifremer.fr/doc/00004/11481/8096.pdf

A review of undulated sediment features on Mediterranean prodeltas: distinguishing sediment transport structures from sediment deformation
Provedor de dados: 5
Autores: Urgeles, Roger; Cattaneo, Antonio; Puig, Pere; Liquete, Camino; De Mol, Ben; Amblas, David; Sultan, Nabil; Trincardi, Fabio.
Most Mediterranean prodeltas show undulated sediment features on the foresets of their Holocene wedges. These features have been described all along the Mediterranean for the last 30 years and interpreted as either soft sediment deformation and incipient landsliding, and more recently, as sediment transport structures. We perform a review and detailed analysis of these undulated sediment features using ultrahigh-resolution seismic and bathymetric data as well as geotechnical information and hydrodynamic time series and hydrographic transects. In this study we show that the characteristics of the sediment undulations (configuration of the reflections down section and between adjacent undulations and overall morphologic characteristics) are incompatible with...
Tipo: Text
Palavras-chave: Undulated sediments; Prodeltas; Slope failure; Sediment waves; Hyperpycnal flows; Internal waves.
Ano: 2011
URL: http://archimer.ifremer.fr/doc/00043/15388/12841.pdf

Behaviour Of A Piston Corer From Accelerometers And New Insights On Quality Of The Recovery
Provedor de dados: 5
Autores: Bourillet, Jean-francois; Damy, Gilbert; Dussud, Loic; Sultan, Nabil; Woerther, Patrice; Migeon, Sebastien.
Various observations pointed out that cores performed with gravity piston corer show signifi cant distortions mainly located at the top of the core. A series of 15 cores were performed at the same location on a submarine sand wave (Var canyon, France). Six different settings of the corer – three freefall heights and three slacks of the piston cable – were tested, including duplicates. Two accelerometers recorded simultaneously the movements of the core tube and the movements of the triggering arm. Then the z displacements were obtained by a double integration versus time of the measured acceleration. The analyses of results allowed the authors to estimate the amplitude and the duration of the elastic recoil of the aramid cable, andto distinguish four steps...
Tipo: Text
Ano: 2007
URL: http://archimer.ifremer.fr/doc/00071/18198/15766.pdf

Evolution model for the Absheron mud volcano: from in-situ observations to numerical modeling
Provedor de dados: 5
Autores: Blouin, Arthur; Imbert, Patrice; Sultan, Nabil; Callot, Jean-paul.
The morphology of mud volcanoes (MV) has been extensively studied over the last few decades. Although recent research has begun to focus on deep processes and structures, little is known about mud generation mechanisms. This study aims to investigate the feeder system and formation of an active kilometer‐scale MV by relying on a 3‐D seismic survey and an in‐situ dataset on the Absheron anticline (South Caspian Basin). Seismic data show a depleted area in the Anhydritic Surakhany Formation (ASF), whose mineralogical composition fits with surface mud. Well data show that the ASF is a succession of evaporitic beds and low temperature shales near its fracture pressure. Biostratigraphic analysis confirms a Pliocene origin for the mud, suggesting that the ASF...
Tipo: Text
Palavras-chave: Mud volcano; Pore pressure; Methane; Modeling; Seismic.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00481/59304/62057.pdf

Subseafloor stratigraphic profiling and soil classification from piezocone tests: A case study in the Gulf of Lion (NW Mediterranean Sea)
Provedor de dados: 5
Autores: Lafuerza, S.; Frigola, J.; Canals, M.; Jouet, Gwenael; Bassetti, Maria-angela; Sultan, Nabil; Berne, Serge.
We show the results provided by piezocone tests in determining the stratigraphic profile and the soil classification of two drilling sites in the outer shelf and the upper slope of the Gulf of Lion, PRGL2 and PRGL1, respectively. Correlations with grain-size data indicate that sleeve friction can be used for profiling fine-grained sediments (site PRGL1), whereas cone tip resistance is the most adequate for sequences made of alternations of coarse- and fine-grained intervals (site PRGL2). Normalized cone resistance and friction ratio proved to be also appropriate for soil stratigraphy as it depicts trends in the coarse fraction of the tested soil. Silts and clays present in similar proportions at site PRGL1 responded to piezocone testing as pure clays...
Tipo: Text
Palavras-chave: Gulf of Lion; Soil classification; Stratigraphy; Piezocone.
Ano: 2008
URL: http://archimer.ifremer.fr/doc/2008/publication-6121.pdf

Mass-transport deposits on the Algerian margin (Algiers area): morphology, lithology and sedimentary processes
Provedor de dados: 5
Autores: Dan, Gabriela; Sultan, Nabil; Cattaneo, Antonio; Deverchere, J; Yelles, K.
On 21st May 2003, a damaging earthquake of Mw: 6.9 struck the region of Boumerdès 40 km east of Algiers in northern Algeria. The seismic shocks had devastating effects in the offshore area between the cities of Algiers and Dellys, where numerous cable breaks were observed. The submarine area encompassing the 2003 Boumerdès epicenter (central Algerian margin) was recently investigated using geophysical and sampling tools. It has been observed that small-size slides and mass-transport deposits occur across this area. Thus, a detailed analysis was performed on 25 submarine slides identified in water depth from 500 m to 2700 m, by measuring different morphological parameters (i.e. surface, head-scarp height, slope in the source area and in adjacent...
Tipo: Text
Palavras-chave: Triggering mechanism; Morphology; Mass transport deposit; Algeria.
Ano: 2009
URL: http://archimer.ifremer.fr/doc/2009/acte-6453.pdf

Geomechanical constitutive modelling of gas-hydrate-bearing sediments
Provedor de dados: 5
Autores: Sultan, Nabil; Garziglia, Sebastien.
In this work and in order to consider theoretically the effect of gas hydrates on the mechanical properties of their host sediments, hydrate fraction was introduced as a state variable in the framework of a Critical State model. For the proposed model, the process of de-structuration and softening of natural clay was considered as a proxy for the gas-hydrate-bearing-sediments behaviour. The developed constitutive model seemed to reproduce the main key behaviours of gas-hydrate-bearing sands observed by Masui and co-authors: i) the elastic properties (Young Modulus, shear modulus) and the strength of the sediment-hydrate medium increase with the hydrate fraction ii) the mechanical softening of the gas-hydrate bearing sediment is amplified with the hydrate...
Tipo: Text
Ano: 2011
URL: http://archimer.ifremer.fr/doc/00035/14626/11904.pdf

Deep sea in situ excess pore pressure and sediment deformation off NW Sumatra and its relation with the December 26, 2004 Great Sumatra-Andaman Earthquake
Provedor de dados: 5
Autores: Sultan, Nabil; Cattaneo, Antonio; Sibuet, Jean-claude; Schneider, Jean-luc.
The swath bathymetric data acquired during the "Sumatra Aftershocks" cruise from the Sunda trench in the Indian Ocean to the north of the Sumatra Island imaged several scars and deposits. In situ pore pressure measurements using the Ifremer piezometer and coring demonstrate that high excess pore pressure and sediment deformation was generated by a recent event in the scar of the slope failure zone identified by J.T. Henstock and co-authors. This excess pore pressure is localized in the upper sedimentary layers and is not related to an interplate subduction process. Numerical simulations of the hydrological system that take into account the hydro-mechanical properties of the upper sediment layer show that the excess pore pressure and sediment deformations...
Tipo: Text
Palavras-chave: Tsunami; Sumatra; Slope failure; Pore pressure; Earthquake.
Ano: 2009
URL: http://archimer.ifremer.fr/doc/2009/publication-6740.pdf

Quantifying the role of sandy-silty sediments in generating slope failures during earthquakes: example from the Algerian margin
Provedor de dados: 5
Autores: Dan, Gabriela; Sultan, Nabil; Savoye, Bruno; Deverchere, Jacques; Yelles, Karim.
The Algerian margin is a seismically active region, where during the last century, several large magnitude earthquakes took place. This study combines geotechnical and sedimentological data with numerical modelling to quantitatively assess the present-day slope stability of the Algerian margin. Geotechnical laboratory tests, such as cyclic triaxial tests, oedometric tests and vane shear tests were carried out on sediment cores collected on the study area. The liquefaction potential of a sediment column located about 30 km from the BoumerdSs earthquake epicentre of 21st May 2003 was evaluated theoretically for an earthquake of M (w) = 6.8. We show that thin sand and silt beds such as those described on recovered sediment cores are the main cause of sediment...
Tipo: Text
Palavras-chave: Earthquakes; Potential of liquefaction; Slope stability; Algerian margin.
Ano: 2009
URL: http://archimer.ifremer.fr/doc/2009/publication-6448.pdf

Dynamics of gas hydrate: case of the Congo continental slope
Provedor de dados: 5
Autores: 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

Freshwater lake to salt-water sea causing widespread hydrate dissociation in the Black Sea
Provedor de dados: 5
Autores: 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
Ano: 2018
URL: https://archimer.ifremer.fr/doc/00418/52981/53916.pdf

Evaluation of the risk of marine slope instability: A pseudo-3D approach for application to large areas
Provedor de dados: 5
Autores: 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

Altered volcanic deposits as basal failure surfaces of submarine landslides
Provedor de dados: 5
Autores: 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
Ano: 2018
URL: http://archimer.ifremer.fr/doc/00444/55565/57176.pdf

Irregular BSR: Evidence of an Ongoing Reequilibrium of a Gas Hydrate System
Provedor de dados: 5
Autores: 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

Focused hydrocarbon-migration in shallow sediments of a pockmark cluster in the Niger Delta (Off Nigeria)
Provedor de dados: 5
Autores: 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

Sea-level change and free gas occurrence influencing a submarine landslide and pockmark formation and distribution in deepwater Nigeria
Provedor de dados: 5
Autores: 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 &gt;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

The role of sedimentation rate and permeability in the slope stability of the formerly glaciated Norwegian continental margin: the Storegga slide model
Provedor de dados: 5
Autores: 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 &lt; Ms &lt; 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

Hydrate dissolution as a potential mechanism for pockmark formation in the Niger delta
Provedor de dados: 5
Autores: 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

Microevents produced by gas migration and expulsion at the seabed: a study based on sea bottom recordings from the Sea of Marmara
Provedor de dados: 5
Autores: 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

Dynamics of fault-fluid-hydrate system around a shale-cored anticline in deepwater Nigeria
Provedor de dados: 5
Autores: 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
Ano: 2011
URL: http://archimer.ifremer.fr/doc/00060/17106/14624.pdf

In situ equilibrium pore-water pressures derived from partial piezoprobe dissipation tests in marine sediments
Provedor de dados: 5
Autores: 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

Strata formation in the Gulf of Lions during the last glacial cycles : an overview
Provedor de dados: 5
Autores: 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
Ano: 2006
URL: http://archimer.ifremer.fr/doc/2006/acte-4688.pdf

New insights into the transport processes controlling the sulfate-methane-transition-zone near methane vents
Provedor de dados: 5
Autores: 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
Ano: 2016
URL: http://archimer.ifremer.fr/doc/00339/45068/44493.pdf

Submarine slope instabilities in gas hydrate-bearing sediments: peak strength versus strain softening
Provedor de dados: 5
Autores: 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
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00634/74638/74533.pdf

Influence of early diagenesis on geotechnical properties of clay sediments (Romania, Black Sea)
Provedor de dados: 5
Autores: 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

Anomalously deep BSR related to a transient state of the gas hydrate system in the western Black Sea
Provedor de dados: 5
Autores: 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

U-Th isotope constraints on gas hydrate and pockmark dynamics at the Niger delta margin
Provedor de dados: 5
Autores: 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

Excess pore pressure and slope failures resulting from gas-hydrates dissociation and dissolution
Provedor de dados: 5
Autores: 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
Ano: 2007
URL: http://archimer.ifremer.fr/doc/00226/33763/32173.pdf

Yielding and plastic behaviour of Boom clay
Provedor de dados: 5
Autores: 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

3-D slope stability analysis: A probability approach applied to the nice slope (SE France)
Provedor de dados: 5
Autores: 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

Gas hydrate distributions in sediments of pockmarks from the Nigerian Margin - Results and interpretation from shallow drilling
Provedor de dados: 5
Autores: Wei, Jiangong; Pape, Thomas; Sultan, Nabil; Colliat, Jean-louis; Himmler, Tobias; Ruffine, Livio; De Prunele, Alexis; Dennielou, Bernard; Garziglia, Sebastien; Marsset, Tania; Peters, Carl A.; Rabiu, Abdulkarim; Bohrmann, Gerhard.
A joint research expedition between the French IFREMER and the German MARUM was conducted in 2011 using the R/V Pourquoi pas? to study gas hydrate distributions in a pockmark field (1141 – 1199 meters below sea surface) at the continental margin of Nigeria. The sea floor drill rig MeBo of MARUM was used to recover sediments as deep as 56.74 meters below seafloor. The presence of gas hydrates in specific core sections was deduced from temperature anomalies recorded during continuous records of infrared thermal scanning and anomalies in pore water chloride concentrations. In situ sediment temperature measurements showed elevated geothermal gradients of up to 258 °C/km in the center of the so-called pockmark A which is up to 4.6 times higher than that in the...
Tipo: Text
Palavras-chave: Gas hydrate; Pockmark; Chloride profile; Infrared thermal imaging; Fluid flow; Nigerian continental margin; MeBo drill rig.
Ano: 2015
URL: http://archimer.ifremer.fr/doc/00213/32382/30846.pdf

Deep-towed High Resolution multichannel seismic imaging
Provedor de dados: 5
Autores: Marsset, Bruno; Menut, Eric; Ker, Stephan; Thomas, Yannick; Regnault, Jean-pierre; Leon, Pierre; Martinossi, Henri; Artzner, Laurent; Chenot, Damien; Dentrecolas, Stephane; Spychalski, B.; Mellier, G.; Sultan, Nabil.
High Resolution (220–1050 Hz) seismic acquisition performed in deep water using deep-towed systems provides unrivalled lateral resolution when compared to conventional surface seismic. The lateral resolution of these acquisitions is controlled by the width of the first Fresnel zone, taking advantage of their positions close to the sea bottom. No current existing deep towed equipment can benefit from seismic imaging processing techniques to improve this resolution as a consequence of positioning inaccuracies. The technological developments of a digital deep-towed multichannel streamer are presented with a particular attention to positioning: each hydrophone incorporates a pitch, roll and heading sensor in order to monitor the constant deformation of the...
Tipo: Text
Palavras-chave: Deep-towed seismics; Multichannel streamer; Seismic imaging.
Ano: 2014
URL: https://archimer.ifremer.fr/doc/00206/31745/35690.pdf

Initiation of gas-hydrate pockmark in deep-water Nigeria: Geo-mechanical analysis and modelling
Provedor de dados: 5
Autores: Riboulot, Vincent; Sultan, Nabil; Imbert, P.; Ker, Stephan.
A review of recent literature shows that two geomorphologically different types of pockmarks, contribute to gas seepage at the seafloor. Type-1 pockmarks are defined as seafloor craters associated to fluid seepage and are the most classical type referred to as “pockmarks” in the literature. In contrast, Type-2 pockmarks reveal a complex seafloor morphology that may result from the formation/decomposition of gas hydrates in underlying sedimentary layers.  Interpretation of very-high-resolution seismic data, sedimentological analyses and geotechnical measurements acquired from the Eastern Niger Submarine Delta reveal that Type-2 pockmarks are associated to the presence at depth of a conical body of massive gas hydrates. Based on acquired data, theoretical...
Tipo: Text
Palavras-chave: Pockmarks; Gas hydrates; VHR seismic data; Piezocone; Numerical modelling; Niger Delta.
Ano: 2016
URL: http://archimer.ifremer.fr/doc/00301/41215/40643.pdf

26th December 2004 great Sumatra-Andaman earthquake: Co-seismic and post-seismic motions in northern Sumatra
Provedor de dados: 5
Autores: Sibuet, Jean-claude; Rangin, C; Le Pichon, X; Singh, S; Cattaneo, Antonio; Graindorge, D; Klingelhoefer, Frauke; Lin, Jing-yi; Malod, Jacques-andre; Maury, Tanguy; Schneider, J; Sultan, Nabil; Umber, Marie; Yamaguchi, H.
Trench-parallel thrust faults verging both landward and seaward were mapped in the portion of wedge located between northern Sumatra and the Indian-Indonesian boundary. The spatial aftershocks distribution of the 26th December 2004 earthquake shows that the post-seismic motion is partitioned along two thrust faults, the Lower and Median Thrust Faults, the latter being right-laterally offset by a N-S lower plate fracture zone located along the 93.6 degrees N meridian. Between February 2005 and August 2005, the upper plate aftershock activity shifted from southeast of this fracture zone to northwest of it, suggesting that the lower plate left-lateral motion along the fracture zone may have induced a shift of the upper plate post-seismic activity along the...
Tipo: Text
Palavras-chave: Active thrust faults; Co seismic rupture; Aftershocks; 2004 Sumatra Andaman earthquake.
Ano: 2007
URL: http://archimer.ifremer.fr/doc/2007/publication-3508.pdf

Hydromechanical properties of gas hydrate-bearing fine sediments from in-situ testing.
Provedor de dados: 5
Autores: Taleb, Farah; Garziglia, Sebastien; Sultan, Nabil.
The hydro‐mechanical properties of gas hydrate‐bearing sediment are key in assessing offshore geo‐hazards and the resource potential of gas hydrates. For sandy materials, such properties were proved highly dependent on hydrate content (Sh) as well as on their distribution and morphology. Owing to difficulties in testing gas hydrate‐bearing clayey sediments, the impact of hydrates on the behaviour of such materials remains poorly understood. Hence, to provide insight into the characterisation of clayey sediments containing hydrate, this study relies on a unique database of in‐situ acoustic, piezocone and pore‐pressure dissipation measurements collected in a high gas flux system offshore Nigeria. Compressional wave velocity measurements were used as means of...
Tipo: Text
Ano: 2018
URL: https://archimer.ifremer.fr/doc/00466/57746/59974.pdf

Sr/Ca and Mg/Ca ratios in Niger Delta sediments: Implications for authigenic carbonate genesis in cold seep environments
Provedor de dados: 5
Autores: Bayon, Germain; Pierre, C; Etoubleau, Joel; Voisset, Michel; Cauquil, E; Marsset, Tania; Sultan, Nabil; Le Drezen, Eliane; Fouquet, Yves.
We report on a reconnaissance analysis of the geochemical composition of authigenic carbonates and sediment samples collected from various seepage sites on the Niger deep-sea fan. Our aim has been to investigate whether evidence for the presence of authigenic carbonates and gas hydrates within sediments is discernible from solid-phase sediment geochemistry. We show that sedimentary Sr/Ca and Mg/Ca ratios can be used to infer the presence of authigenic aragonite (Sr-rich) and Mg-rich carbonate phases (high-Mg calcite, dolomite) in cold seep settings. Using Sr/Ca and Mg/Ca ratios, the proportion (wt.%) of authigenic carbonates in Niger Fan sediments can be calculated from a mixing model between sediment fractions of terrigenous material, biogenic calcite,...
Tipo: Text
Palavras-chave: Niger Delta; Gas hydrates; Cold seeps; Mg/Ca; Sr/Ca; Authigenic carbonates.
Ano: 2007
URL: http://archimer.ifremer.fr/doc/2007/publication-2696.pdf

Potential role of compressional structures in generating submarine slope failures in the Niger Delta
Provedor de dados: 5
Autores: Sultan, Nabil; Voisset, Michel; Marsset, Bruno; Marsset, Tania; Cauquil, E; Colliat, J.
The study area, offshore Nigeria, is located in one of the compressional zones within the Niger Delta, which is characterized by imbricate thrust structures. Although the low mean slope angle (around 2°), bathymetry data from the study area have shown the existence of several submarine landslides which coincide with known subsurface faulted compressive features.  In this paper, we have focused on a submarine slide occurring in water depths ranging between 1690 and 1750 m. Headwall scars, internal architecture and associated deposits have been characterized using a combination of 3D seismic data, near-bottom echosounder seismic profiles, Kullenberg cores and in-situ geotechnical measurements. The slide shows horseshoe shaped headwall scars and depositional...
Tipo: Text
Palavras-chave: Slope stability; Piezometer; Penetrometer; Niger Delta; Modelling; Compressional structures.
Ano: 2007
URL: http://archimer.ifremer.fr/doc/2007/publication-2408.pdf

Overpressure within upper continental slope sediments from CPTU data, Gulf of Lion, NW Mediterranean Sea
Provedor de dados: 5
Autores: Lafuerza, S.; Sultan, Nabil; Canals, M.; Frigola, J.; Berne, Serge; Jouet, Gwenael; Galavazi, M.; Sierro, F. J.
Data from in situ piezocone tests (CPTU) and laboratory analyses are utilized for the interpretation of the stress history of Quaternary sedimentary sequences in the upper continental slope of the Gulf of Lion, northwestern Mediterranean Sea. A CPTU based preconsolidation pressure profile referenced to the current effective stress indicates that the deposit is underconsolidated from 12 meters below the seafloor (mbsf) down to at least 150 mbsf. Excess pore pressure below 12 mbsf is further supported by results from oedometer and dissipation tests. Subseafloor pockmarks and indications of free gas in seismic reflection profiles reveal four main overpressure sources (SI-SIV) with overpressure ratios &gt; 0.3 at subseafloor depths coinciding with levels where...
Tipo: Text
Palavras-chave: Gulf of Lion; Continental slope; Overpressure; Preconsolidation pressure; Stress history.
Ano: 2009
URL: http://archimer.ifremer.fr/doc/2009/publication-6649.pdf

Mechanical behaviour of gas-charged fine sediments: model formulation and calibration
Provedor de dados: 5
Autores: Sultan, Nabil; Garziglia, Sebastien.
Multi-phase fluid conditions encountered in geotechnical and geo-environmental problems have led to the development of models that account for the influence of gas solubility and compressibility on the behaviour of soils of various grain sizes. Yet, no consideration has been given to damages related to the nucleation and growth of gas bubbles in fine-grained soils. The purpose of this paper is to present a Cam Clay based constitutive model extended to incorporate such detrimental effects on gassy soils. This is achieved by deriving an analytical expression relating the preconsolidation pressure to a damage parameter dependent on the gas content. That expression is coupled to a deviatoric yield surface accounting for inherent and stress-induced anisotropy....
Tipo: Text
Palavras-chave: Compressibility; Constitutive relations; Offshore engineering; Shear strength.
Ano: 2014
URL: https://archimer.ifremer.fr/doc/00245/35621/34133.pdf

Shallow gas hydrate accumulations at a Nigerian deep‐water pockmark ‐ Quantities and dynamics
Provedor de dados: 5
Autores: Pape, Thomas; Ruffine, Livio; Hong, Wei‐li; Sultan, Nabil; Riboulot, Vincent; Peters, Carl A.; Kölling, Martin; Zabel, Matthias; Garziglia, Sebastien; Bohrmann, Gerhard.
The evolution of submarine pockmarks is often related to the ascent of fluid from the subsurface. For pockmarks located within the gas hydrate stability zone, methane oversaturation can result in the formation of gas hydrates in the sediment. A ca. 600 m‐wide sea floor depression in deep‐waters offshore Nigeria, Pockmark A, was investigated for distributions and quantities of shallow gas hydrates, origins of hydrocarbons and time elapsed since the last major fluid ascent event. For the first time, pressure coring of shallow sediments and drilling of more than 50‐m‐long cores with the sea floor drill rig MARUM‐MeBo70 were conducted in this pockmark. Unusually high hydrate saturations of up to 51% of pore volume in the uppermost 2.5 meters of sediment in the...
Tipo: Text
Palavras-chave: Pockmark; Gas hydrate; Methane; MeBo; Pressure coring; Pore water modeling.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00643/75491/76344.pdf

In situ characterisation of gas hydrate-bearing clayey sediments in the Gulf of Guinea
Provedor de dados: 5
Autores: Taleb, Farah; Garziglia, Sebastien; Sultan, Nabil.
Increasing needs for energy resources have moved deep offshore developments and research efforts towards regions where high pressure and low temperature conditions allow gas and water to form Gas Hydrates (GH). However, owing to difficulties in sampling and preserving GH under in-situ stability conditions, GH-bearing sediments remain particularly challenging to characterise using conventional laboratory methods. This paper presents the experience gained in the use acoustic and piezocone soundings in characterising gas-hydrate bearing clayey sediments offshore Nigeria. Acoustic measurements of compressional wave velocity are shown to be an expedient means of both detecting and quantifying GH in sediments. Piezocone data and their location in normalised soil...
Tipo: Text
Ano: 2018
URL: https://archimer.ifremer.fr/doc/00466/57748/60000.pdf

Evolution model for the Absheron Mud Volcano: from stratified sediments to fluid mud generation
Provedor de dados: 5
Autores: Blouin, Arthur; Sultan, Nabil; Pierron, Alexandra; Imbert, Patrice; Callot, Jean‐paul.
Submarine mud volcanoes are one of the most spectacular methane expulsion features at the seafloor and they represent a significant geohazard worldwide. In this work we focus on the physical processes controlling the initiation and early evolution of the Absheron mud volcano (AMV). Our analyses were carried out based on basin modeling calibrated thanks to existing seismic interpretation of the AMV, analysis of sediment samples from seabed, and data from two exploration wells. Acquired laboratory geotechnical data allowed us to derive laws considering the impact of gas exsolution on host sediment behaviors. In this study, we identified key geological and physical conditions that led to mud volcano formation: by coupling diffusion processes with...
Tipo: Text
Palavras-chave: Mud volcano; Numerical modeling; Geohazard; Sediment remobilization; Methane.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00658/77002/78258.pdf

Numerical modeling of bottom trawling-induced sediment transport and accumulation in La Fonera submarine canyon, northwestern Mediterranean Sea
Provedor de dados: 5
Autores: Payo-payo, Marta; Silva Jacinto, Ricardo; Lastras, G.; Rabineau, Marina; Puig, P.; Martin, J.; Canals, M.; Sultan, Nabil.
Bottom trawling leads to recurrent sediment resuspension events over fishing grounds. Recent studies have shown how bottom trawling can drive seascape reshaping at large spatial scales and enhance sediment transport in submarine canyons, which subsequently impacts deep-sea ecosystems. Present knowledge on the transfer and accumulation of sediment flows triggered by bottom trawling is based on localized and infrequent measurements whilst a more complete picture of the process is needed. The present work focuses on the modeling of sediment transport and accumulation resulting from trawling activities in La Fonera submarine canyon, northwestern Mediterranean Sea, thus contributing to an improved assessment of trawling impacts. Based on mooring data within a...
Tipo: Text
Palavras-chave: Bottom trawling; Inverse model; Modeling; Sediment transport; Submarine canyon; Turbidity currents.
Ano: 2017
URL: http://archimer.ifremer.fr/doc/00374/48549/48862.pdf

Identification of Shear Zones and Their Causal Mechanisms Using a Combination of Cone Penetration Tests and Seismic Data in the Eastern Niger Delta
Provedor de dados: 5
Autores: Garziglia, Sebastien; Sultan, Nabil; Cattaneo, Antonio; Ker, Stephan; Marsset, Bruno; Riboulot, Vincent; Voisset, Michel; Adamy, J.; Unterseh,.
In a site investigation of the eastern part of the offshore Niger delta, cone penetration tests (CPTU) showed significant drops in tip resistance, associated with decreases in sleeve friction and induced excess pore pressures at the interface between superficial sediments and the underlying deposits of a mass-transport complex (MTC) called NG1. Such signature characteristics of weakened zones are clearly expressed at three sites where the drop in tip resistance reaches more than 40% over 2-3 m-thick intervals. Correlations between CPTU profiles and both 3D and ultrahigh-resolution 2D seismic data suggest that the weakened zones surround syndepositional the within the frontal part of NG1. Hence, weakening appears associated with the remobilization of thrust...
Tipo: Text
Palavras-chave: Cone penetration tests; Shear zone; 3D seismic data; Ultrahigh-resolution 2D seismic; Mass-transport complex; Slope stability.
Ano: 2010
URL: http://archimer.ifremer.fr/doc/00105/21662/19695.pdf

Comment on "Excess pore pressure resulting from methane hydrate dissociation in marine sediments: A theoretical approach" by Wenyue Xu and Leonid N. Germanovich - art. no. B02103
Provedor de dados: 5
Autores: Sultan, Nabil.
While it is well accepted that gas hydrate dissociation at the base of the Gas Hydrate Stability Zone (GHSZ) can generate high excess pore pressure and leads to sediment deformation, the consequence in terms of pore pressure of the dissolution of the gas hydrate at the top of the Gas Hydrate Occurrence Zone (GHOZ) remains neglected. The purpose of this comment on Xu and Germanovich [2006] article is to demonstrate that gas hydrate dissolution in the GHSZ may generate excess pore pressure and to point out the risk related to hydrate dissolution at the top of the GHOZ.
Tipo: Text
Palavras-chave: Pore pressure; Hydrate; Dissolution; Dissociation.
Ano: 2007
URL: http://archimer.ifremer.fr/doc/2007/publication-2318.pdf

Modeling on gas hydrate formation conditions in the Qinghai-Tibet plateau permafrost
Provedor de dados: 5
Autores: Lu, Zhen Quan; Sultan, Nabil; Jin, Chun Shuang; Rao, Zhu; Luo, Xu Rong; Wu, Bi Hao; Zhu, You Hai.
Based on field investigated gas geochemistry and predecessors' data such as the permafrost ground temperature, thermal gradients within/below the frozen layer, the modeling on gas hydrate formation conditions is conducted in the Qinghai Tibet plateau permafrost. The modeled results show that the permafrost characteristics generally meet gas hydrate formation conditions in the study area. Gas composition, temperature-related permafrost parameters (e. g. permafrost thickness or its ground temperature and thermal gradients within / below the frozen layer) are the most important factors affecting gas hydrate occurrences, whose variance may cause the heterogeneity of gas hydrate occurrences in the study area. The most probable gas hydrate is the kind of hybrid...
Tipo: Text
Palavras-chave: Qinghai Tibet plateau; Modeling; Formation conditions; Gas hydrate; Permafrost.
Ano: 2009
URL: http://archimer.ifremer.fr/doc/2009/publication-6230.pdf

A geomechanical approach for the genesis of sediment undulations on the Adriatic shelf - art. no. Q04R03
Provedor de dados: 5
Autores: Sultan, Nabil; Cattaneo, Antonio; Urgeles, R; Lee, H; Locat, J; Trincardi, F; Berne, Serge; Canals, M; Lafuerza, S.
This study is among the first to examine the genesis of the seafloor and subsurface undulations on the Adriatic continental shelf by integrating stratigraphic information and in situ and laboratory geotechnical measurements. Interpretation of sediment behavior is based on a 32-m-long borehole crossing ( 1) a possible shear plane and ( 2) a silty clay layer at about 20 m below seafloor (mbsf) on which sediment undulations are rooted and could be interpreted as a potential weak layer succession. Our main results in terms of triggering mechanism for the observed undulations show that under an earthquake, liquefaction and/or failure of the silty-clay sediments ( weak layer) leading to deformation of the upper more cohesive sediments is possible only when such...
Tipo: Text
Palavras-chave: Sediment deformation; Shear strength; Earthquake; Adriatic shelf.
Ano: 2008
URL: http://archimer.ifremer.fr/doc/2008/publication-4105.pdf

Empirical expressions for gas hydrate stability law, its volume fraction and mass-density at temperatures 273.15 K to 290.15 K
Provedor de dados: 5
Autores: Lu, Zhengquan; Sultan, Nabil.
A series of empirical expressions for predicting gas hydrate stability, its volume fraction out of pore space and gas hydrate mass-density were established in different systems in consideration of gas composition (CH4, C2H6, H2S) and salinity (NaCl, seawater), and pore size at temperature between 273.15 and 300 K, based on our gas hydrate thermodynamic model (Sultan et al., 2004b, c). Six of the developed expressions for predicting gas hydrate stability were validated against the available published experimental data and they were also compared with other models. At temperature 273.15 to 290.15 K, the ARDPs (Average Relative Deviation of Pressures between the prediction and the experimental data) have shown that these empirical expressions are in agreement...
Tipo: Text
Palavras-chave: Empirical expressions; Mass density; Fraction out of pore space; Stability law; Gas hydrate.
Ano: 2008
URL: http://archimer.ifremer.fr/doc/2008/publication-4958.pdf

Gas hydrate occurrences and seafloor deformation: investigation of strain-softening of gas-hydrate bearing sediments and its consequence in terms of submarine slope instabilities
Provedor de dados: 5
Autores: Sultan, Nabil; Garziglia, Sebastien; Colliat, Jean-louis.
Published laboratory geotechnical data by Masui and co-authors showed that increase in gas hydrates content tend to increase the peak shear strength and stimulate strain softening of the host sediment. Therefore, development of shear strains may lead to an important degradation of the shear strength (strain softening). In the present work, 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 classical limit analysis method a shear strain field compatibility equivalent to the velocity field compatibility. Examples of slope failures related to strain softening behavior documented in the literature were used to test the model formulation. The developed model was then used...
Tipo: Text
Ano: 2011
URL: http://archimer.ifremer.fr/doc/00035/14625/11903.pdf

Mechanical behaviour of unsaturated marine sediments: experimental and theoretical approaches
Provedor de dados: 5
Autores: Vanoudheusden, Emilie; Sultan, Nabil; Cochonat, Pierre.
The COSTA target areas exhibit different slope failure events, which reflect different triggering mechanisms including gas hydrates dissociation. Gas hydrates stability law depends on temperature, pore pressure, gas chemistry, and pore water salinity. Any change in the equilibrium parameters may convert the hydrate to gas plus water, causing significant weakening of the sediment, and generating a rise of pore pressure. A significant consequence of the hydrate melting is the gas production, which alters significantly the behaviour and mechanical properties of the marine sediments and could be very hazardous when the sediment is unloaded in undrained conditions.   The behaviour of the unsaturated marine sediment has to be accurately identified in order to...
Tipo: Text
Palavras-chave: Shear strength; Andrained behaviour; Triaxial tests; Capillary pressure; Unsaturated sediment.
Ano: 2004
URL: http://archimer.ifremer.fr/doc/2004/publication-701.pdf

The 1979 Nice harbour catastrophe revisited: Trigger mechanism inferred from geotechnical measurements and numerical modelling
Provedor de dados: 5
Autores: Dan, Gabriela; Sultan, Nabil; Savoye, Bruno.
In 1979, a catastrophic event occurred on the Nice continental slope (French Riviera) generating the lost of human lives and important material damages. Part of the new harbour constructed at the edge of the International Airport of Nice collapsed into the sea. The main aim of this work was 1) to present a review of facts and details related to the 1979 accident and a review of the geological setting, and 2) to evaluate the slope stability before and after the new harbour construction, by taking into account new available data such as sediment cores and piezocone CPTU data. The CPTU data were of great value to understand the origin of the 1979 event. They show the existence of a sensitive clay bed between 30 mbsf and 45 mbsf Under high deviatoric load a...
Tipo: Text
Palavras-chave: Finite element method; Trigger mechanism; Slope stability; Nice 1979 event.
Ano: 2007
URL: http://archimer.ifremer.fr/doc/2007/publication-3507.pdf

Transient Groundwater Flow Through a Coastal Confined Aquifer and its Impact on Near‐Shore Submarine Slope Instability
Provedor de dados: 5
Autores: Sultan, Nabil; Garziglia, Sebastien; Bompais, Xavier; Woerther, Patrice; Witt, C; Kopf, A; Migeon, Sebastien.
Rare in situ pore pressure and temperature data sets collected over more than one decade in a submarine landslide‐prone area off Nice (Southeast France) have been used to characterize a transient groundwater exchange between a coastal confined aquifer and the near‐shore shallow‐water submarine shelf. The near‐coast study zone is highly exposed to geohazards, and remains sadly famous for the 1979 catastrophic tsunamigenic submarine landslide with several casualties and substantial material damage. Measured pore pressure buildup does not appear to be synchronized with either the discharge of the nearby Var River or with precipitation in the Nice area. Unexpectedly, pore pressure fluctuations synchronizes well with seabed temperature trends indicating that...
Tipo: Text
Palavras-chave: Nice continental slope; Piezometer; Pore pressure; Shear zone; Submarine landslide; Var delta.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00643/75461/76276.pdf

Seafloor instabilities and sediment deformation processes: the need for integrated, multi-disciplinary investigations
Provedor de dados: 5
Autores: Vanneste, Maarten; Sultan, Nabil; Garziglia, Sebastien; Forsberg, Carl Fredrik; L'Heureux, Jean-sebastien.
In this paper, we present the current practice of investigations of seafloor instabilities and deformation processes, based on extensive research conducted over the last years, which sets the scene for future research activities in this field. The mapping of the continental margins and coastal areas with ever increasing resolution systematically reveals evidence of instabilities and deformation processes, both active and palaeo-features. In order to properly assess the hazards and risks related to these features, an integrated and multi-disciplinary approach is essential, but challenging. Such an approach consists of combining field data (geophysics, geology, sedimentology, geochemistry and geotechnical data) with numerical simulations constrained by...
Tipo: Text
Palavras-chave: Marine geotechnics; Slope stability; Sediment failures; Fluid flow; Shear strength; Marine geophysics; Monitoring; Excess pore pressure; Site investigations.
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00173/28378/26692.pdf

The 100-ka and rapid sea level changes recorded by prograding shelf sand bodies in the Gulf of Lions (western Mediterranean Sea)
Provedor de dados: 5
Autores: Bassetti, Maria-angela; Berne, Serge; Jouet, Gwenael; Taviani, M; Dennielou, Bernard; Flores, J; Gaillot, Arnaud; Gelfort, R; Lafuerza, S; Sultan, Nabil.
Thick forced regressive units on the wide continental shelf of the Gulf of Lions (western Mediterranean) recorded the composite effect of sea level changes during the Quaternary. They are mostly composed of coastal siliciclastic and bioclastic wedges showing clinoform geometry. These deposits have been intensively explored through high-resolution seismic investigations, but only recently it was possible to ground truth seismic interpretations, based on a long (100 m) borehole that crossed the succession and recovered a large part of the mainly sandy deposits (similar to 84% recovery). A multiproxy analysis of the sedimentary succession shows that (1) the stratal architecture of the shelf margin is defined by major bounding surfaces that are polygenic...
Tipo: Text
Palavras-chave: Paleoclimate; Mediterranean; Quaternary; Shoreface.
Ano: 2008
URL: http://archimer.ifremer.fr/doc/2008/publication-4929.pdf