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Registros recuperados: 26
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A joint electromagnetic and seismic study of an active pockmark within the hydrate stability field at the Vestnesa Ridge, West Svalbard margin ArchiMer
Goswami, Bedanta K.; Weitemeyer, Karen A.; Minshull, Timothy A.; Sinha, Martin C.; Westbrook, Graham; Chabert, Anne; Henstock, Timothy J.; Ker, Stephan.
We acquired coincident marine controlled-source electromagnetic (CSEM), high-resolution seismic reflection and ocean-bottom seismometer (OBS) data over an active pockmark in the crest of the southern part of the Vestnesa Ridge, to estimate fluid composition within an underlying fluid-migration chimney. Synthetic model studies suggest resistivity obtained from CSEM data can resolve gas or hydrate saturation greater than 5% within the chimney. Acoustic chimneys imaged by seismic reflection data beneath the pockmark and on the ridge flanks, were found to be associated with high-resistivity anomalies (+2-4 m). High-velocity anomalies (+0.3 km/s), within the gas hydrate stability zone (GHSZ) and low-velocity anomalies (-0.2 km/s) underlying the GHSZ, were also...
Tipo: Text Palavras-chave: Gas hydrate; Svalbard; CSEM; Saturation; Pockmark; Vestnesa.
Ano: 2015 URL: http://archimer.ifremer.fr/doc/00283/39458/37928.pdf
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Anomalously deep BSR related to a transient state of the gas hydrate system in the western Black Sea ArchiMer
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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Deep-towed High Resolution multichannel seismic imaging ArchiMer
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
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Deep-towed high resolution seismic imaging II: Determination of P-wave velocity distribution ArchiMer
Marsset, Bruno; Ker, Stephan; Thomas, Yannick; Colin, Florent.
The acquisition of high resolution seismic data in deep waters requires the development of deep towed seismic sources and receivers able to deal with the high hydrostatic pressure environment. The low frequency piezoelectric transducer of the SYSIF (SYstème Sismique Fond) deep towed seismic device comply with the former requirement taking advantage of the coupling of a mechanical resonance (Janus driver) and a fluid resonance (Helmholtz cavity) to produce a large frequency bandwidth acoustic signal (220–1050 Hz). The ability to perform deep towed multichannel seismic imaging with SYSIF was demonstrated in 2014, yet, the ability to determine P-wave velocity distribution wasn't achieved. P-wave velocity analysis relies on the ratio between the...
Tipo: Text Palavras-chave: Deep-towed seismic; Seismic imaging; P-wave velocity distribution.
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00418/52971/53908.pdf
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Développement de méthodes d’imagerie sismique par grand fond et d’analyse multiéchelle par ondelettes pour la caractérisation à haute résolution du sous-sol marin ArchiMer
Ker, Stephan.
High Resolution marine seismic is a common tool to indirectly study the fine scale structures of the sub-seabed and its related geohazards. In water depths, ranging from the continental slope to deep oceanic basin, high resolution seismic imaging cannot be achieved with conventional near-surface system due to a number of shortcomings. Since the 90s, the acquisition strategy has therefore striven for lowering both seismic sources and receivers close to the seafloor. Ifremer has recently developed a deep-towed seismic system (SYSIF), based on piezoelectric transducer technology and dedicated to the study of superficial sediments up to 6000 m water depth. Our objective is to achieve seismic imaging and seismic characterization at small scales consistent with...
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Ano: 2012 URL: http://archimer.ifremer.fr/doc/00160/27153/25352.pdf
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Dynamics of fault-fluid-hydrate system around a shale-cored anticline in deepwater Nigeria ArchiMer
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...
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Ano: 2011 URL: http://archimer.ifremer.fr/doc/00060/17106/14624.pdf
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Evidence from three-dimensional seismic tomography for a substantial accumulation of gas hydrate in a fluid-escape chimney in the Nyegga pockmark field, offshore Norway ArchiMer
Plaza-faverola, Andreia; Westbrook, Graham K.; Ker, Stephan; Exley, Russell J. K.; Gailler, Audrey; Minshull, Tim A.; Broto, Karine.
In recent years, it has become evident that features commonly called gas chimneys provide major routes for methane to pass through the methane-hydrate stability zone in continental margins and escape to the ocean. One of many such chimneys lying beneath pockmarks in the southeastern Voring Plateau off Norway was investigated with a high-resolution seismic experiment employing a 2-D array of sixteen 4-component ocean bottom seismic recorders at approximately 100 m separation and a dense network of shots to define the 3-D variation of the chimney's structure and seismic properties. The tomographic model derived from P wave travel times shows that P wave velocity inside the chimney is up to 300 m/s higher than in the surrounding strata within the...
Tipo: Text Palavras-chave: Travel time tomography; Mid norwegian margin; Storegga slide; Bearing sediments; Voring plateau; Reflection tomography; Continental margins; Marine sediments; Atlantic margin; Velocity models.
Ano: 2010 URL: http://archimer.ifremer.fr/doc/00012/12326/9111.pdf
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Fine-scale gas distribution in marine sediments assessed from deep-towed seismic data ArchiMer
Ker, Stephan; Le Gonidec, Y.; Marsset, Bruno; Westbrook, Graham; Gibert, D.; Minshull, T. A..
In the context of seismic imaging of gas/gas-hydrate systems, the fine-scale structure of subseabed gas-related reflections is assessed by taking advantage of the source signature of the deep-towed high-resolution SYSIF seismic device. We demonstrate the value of an original wavelet-based method and associated multiscale seismic attributes, applied to seismic data recently acquired on the western margin of the Arctic archipelago of Svalbard. From analysis in the wavelet domain, we recognize two types of gas-related reflections associated with submetre-scale distribution of gas. We identify a thin gas-charged layer associated with an apparent normal polarity reflection, and we detect gas patches associated with a reverse-polarity bright spot with...
Tipo: Text Palavras-chave: Wavelet transform; Gas and hydrate systems; Wave propagation; Acoustic properties; Arctic region.
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00175/28602/27019.pdf
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Fractional integration of seismic wavelets in anelastic media to recover multiscale properties of impedance discontinuities ArchiMer
Ker, Stephan; Le Gonidec, Yves.
Multiscale seismic attributes based on the wavelet transform properties have been recently introduced and successfully applied to identify the geometry of a complex seismic reflector in an elastic medium. In the present paper, we extend this quantitative approach to anelastic media where intrinsic attenuation modifies the seismic attributes and thus requires a specific processing to retrieve them properly. The method assumes both an attenuation linearly dependent with the seismic wave frequency and a seismic source wavelet approximated with a Gaussian derivative function. We highlight a quasi-conservation of the Gaussian character of the wavelet during its propagation. We show that this shape can be accurately modeled by a Gaussian derivative function...
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Ano: 2018 URL: http://archimer.ifremer.fr/doc/00409/52034/52700.pdf
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Freshwater lake to salt-water sea causing widespread hydrate dissociation in the Black Sea ArchiMer
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...
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Ano: 2018 URL: https://archimer.ifremer.fr/doc/00418/52981/53916.pdf
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GHASS cruise report ArchiMer
Ker, Stephan; Riboulot, Vincent; Ghass Cruise Team,.
The objectives of the GHASS (Gas Hydrates, fluid Activities and Sediment deformations in the western Black Sea) cruise are twofold but interconnected. The first aim is to study the dynamics of gas hydrates and free gas associated with geological and climate processes. The second aim is to identify the factors at the origin of observed sediment deformations and submarine landslides in two areas in the Romanian sector of the Black Sea. For the cruise we use quantitative approaches based on multidisciplinary studies (geochemistry, geology, geophysics and geotechnics). Gas hydrates and free gas were detected using surface and deep-towed HR seismic (SYSIF) techniques and by performing in situ geotechnical and acoustic measurements using the Ifremer penetrometer...
Tipo: Text
Ano: 2015 URL: http://archimer.ifremer.fr/doc/00300/41141/40329.pdf
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High-resolution seismic imaging in deep sea from a joint deep-towed/OBH reflection experiment: application to a Mass Transport Complex offshore Nigeria ArchiMer
Ker, Stephan; Marsset, Bruno; Garziglia, Sebastien; Le Gonidec, Y.; Gibert, D.; Voisset, Michel; Adamy, J..
P>We assess the feasibility of high-resolution seismic depth imaging in deep water based on a new geophysical approach involving the joint use of a deep-towed seismic device (SYSIF) and ocean bottom hydrophones (OBHs). Source signature measurement enables signature deconvolution to be used to improve the vertical resolution and signal-to-noise ratio. The source signature was also used to precisely determine direct traveltimes that were inverted to relocate source and receiver positions. The very high accuracy of the positioning that was obtained enabled depth imaging and a stack of the OBH data to be performed. The determination of the P-wave velocity distribution was realized by the adaptation of an iterative focusing approach to the specific...
Tipo: Text Palavras-chave: Controlled source seismology; Seismic tomography; Acoustic properties; Submarine landslides; Atlantic Ocean.
Ano: 2010 URL: http://archimer.ifremer.fr/doc/00044/15510/12959.pdf
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Hydrate dissolution as a potential mechanism for pockmark formation in the Niger delta ArchiMer
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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Identification of Shear Zones and Their Causal Mechanisms Using a Combination of Cone Penetration Tests and Seismic Data in the Eastern Niger Delta ArchiMer
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
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Influence of early diagenesis on geotechnical properties of clay sediments (Romania, Black Sea) ArchiMer
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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Initiation of gas-hydrate pockmark in deep-water Nigeria: Geo-mechanical analysis and modelling ArchiMer
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
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La géomorphologie des fonds marins et la présence d’hydrates de gaz contrôlent les émissions de gaz dans la Mer Noire au large de la Roumanie ArchiMer
Riboulot, Vincent; Cattaneo, Antonio; Scalabrin, Carla; Gaillot, Arnaud; Jouet, Gwenael; Ballas, Gregory; Marsset, Tania; Garziglia, Sebastien; Ker, Stephan.
The Romanian sector of the Black Sea deserves attention because the Danube deep-sea fan is one of the largest sediment depositional systems worldwide and is considered the world's most isolated sea, the largest anoxic water body on the planet and a unique energy-rich sea. Due to the high sediment accumulation rate, presence of organic matter and anoxic conditions, the Black sea sediments offshore the Danube delta is rich in gas and thus shows Bottom Simulating Reflectors (BSR). The cartography of the BSR over the last 20 years, exhibits its widespread occurrence, indicative of extensive development of hydrate accumulations and a huge gas hydrate potential. By combining old and new datasets acquired in 2015 during the GHASS expedition, we performed a...
Tipo: Text Palavras-chave: Hydrates de gaz; Gaz libre; Panaches de gaz; BSR; Mer Noire; Géomorphologie; Gas hydrates; Free gas; Gas flares; BSR; Black Sea; Geomorphology.
Ano: 2017 URL: http://archimer.ifremer.fr/doc/00407/51860/53914.pdf
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Multifrequency seismic detectability of seasonal thermoclines assessed from ARGO data ArchiMer
Ker, Stephan; Le Gonidec, Y.; Marie, Louis.
Seismic Oceanography is a developing research topic where new acoustic methods allow high-resolution teledetection of the thermohaline structure of the ocean. First implementations to study the Ocean Surface Boundary Layer have recently been achieved but remain very challenging due to the weakness and shallowness of such seismic reflectors. In this article, we develop a multifrequency seismic analysis of hydrographic datasets collected in a seasonally stratified midlatitude shelf by ARGO network floats to assess the detectability issue of shallow thermoclines. This analysis, for which sensitivity to the data reduction scheme used by ARGO floats for the transmission of the profiles is discussed, allows characterizing both the depth location and the...
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Ano: 2016 URL: http://archimer.ifremer.fr/doc/00347/45801/45446.pdf
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Multiresolution seismic data fusion with a generalized wavelet-based method to derive subseabed acoustic properties ArchiMer
Ker, Stephan; Le Gonidec, Y.; Gibert, D..
In the context of multiscale seismic analysis of complex reflectors, that takes benefit from broad-band frequency range considerations, we perform a wavelet-based method to merge multiresolution seismic sources based on generalized Lévy-alpha stable functions. The frequency bandwidth limitation of individual seismic sources induces distortions in wavelet responses (WRs), and we show that Gaussian fractional derivative functions are optimal wavelets to fully correct for these distortions in the merged frequency range. The efficiency of the method is also based on a new wavelet parametrization, that is the breadth of the wavelet, where the dominant dilation is adapted to the wavelet formalism. As a first demonstration to merge multiresolution seismic...
Tipo: Text Palavras-chave: Wavelet transform; Wave propagation; Acoustic properties.
Ano: 2013 URL: http://archimer.ifremer.fr/doc/00157/26824/24935.pdf
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Multiscale seismic attributes: A wavelet-based method and its application to high-resolution seismic and ground truth data ArchiMer
Ker, Stephan; Le Gonidec, Yves; Gibert, D.; Marsset, Bruno.
We propose a wavelet-based method to characterize acoustic impedance discontinuities from a multiscale analysis of seismic reflected waves. Our approach relies on the analysis of ridge functions which contain most of the information of the wavelet transform in a sparse support. This method falls in the framework of the wavelet response (WR) introduced by Le Gonidec et al. which analyses the impedance multiscale behaviour by propagating dilated wavelets into the medium. We further extend the WR by considering its application to broad-band seismic data. We take into account the bandpass filter effect related to the limited frequency range of the seismic source. We apply the method to a deep-water seismic experiment performed in 2008 during the ERIG3D cruise...
Tipo: Text Palavras-chave: Wavelet transform; Seismic attenuation; Wave propagation; Acoustic properties.
Ano: 2011 URL: http://archimer.ifremer.fr/doc/00049/15994/13449.pdf
Registros recuperados: 26
Primeira ... 12 ... Última
 

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