The Experts below are selected from a list of 189 Experts worldwide ranked by ideXlab platform
Graham K Westbrook - One of the best experts on this subject based on the ideXlab platform.
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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
Journal of Geophysical Research, 2015Co-Authors: Bedanta Goswami, Karen Weitemeyer, T A Minshull, Martin C Sinha, Graham K Westbrook, Anne Chabert, Timothy J HenstockAbstract: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 observed. Joint analysis of the resistivity and velocity anomaly indicates pore Saturation of up to 52% hydrate with 28% Free Gas, or up to 73% hydrate with 4% Free Gas, within the chimney beneath the pockmark assuming a nonuniform and uniform fluid distribution, respectively. Similarly, we estimate up to 30% hydrate with 4% Free Gas or 30% hydrate with 2% Free Gas within the pore space of the GHSZ outside the central chimney assuming a nonuniform and uniform fluid distribution, respectively. High levels of Free-Gas Saturation in the top part of the chimney are consistent with episodic Gas venting from the pockmark.
Christian Berndt - One of the best experts on this subject based on the ideXlab platform.
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RV SONNE Fahrtbericht / Cruise Report SO227 TAIFLUX : Fluid and Gas migration in the transition from a passive to an active continental margin off SW Taiwan, 02.04. - 02.05.2013, Kaohsiung - Kaohsiung (Taiwan)
2013Co-Authors: Christian BerndtAbstract:The underlying scientific motivation of SO227 was to constrain the geological processes that control the distribution and Saturation of hydrate in marine sediments. The most important objective of the cruise was to observe the effect of additional fluid advection along blind thrusts into the Gas hydrate stability zone. With its clear distinction into a passive margin and an active margin the area SW of Taiwan is particularly well suited for this kind of research because it is very well studied and it is known where the tectonic structures of the compression and subduction zone disturb the otherwise fairly homogeneous surface sediments of the margin. After a reconnaissance survey using multi beam echo sounder and side scan sonar we selected two sites that are typical for the active and passive margin, respectively. At these two sites we carried out comprehensive geophysical experiments including high-resolution 3D seismic imaging with the P-Cable system, ocean bottom seismometer (OBS) deployments, controlled source electromagnetic (CSEM) measurements, heat flow measurements, and ground-truthing using HyBis and TV grab. While the P-Cable data allow us to determine the internal structure of the study areas down to a depth of approximately 500 m below sea floor, the OBS and CSEM data will constrain the hydrate and Free Gas Saturation along twodimensional transect through the 3D seismic cubes. The heat flow data will provide information on the thermal conditions of the sediments. The first site covers the Formosa Ridge on the passive margin of the South China Sea. The ridge is the result of canyon erosion in the north, west, and east. The high-resolution threedimensional seismic data show a continuous bottom simulating reflector (BSR) marking the base of the hydrate stability zone. Particularly, underneath the canyon in the north the BSR is much shallower than underneath the centre of the ridge. This may indicates that the canyon incision has changed the hydrate stability field and that hydrate formation at depth has not been able to adjust to the new pressure and temperature conditions. The second site includes a roll over anticline called Four-Way-Closure Ridge which is the surface expression of an underlying blind thrust. In this area numerous high amplitude reflectors occur above the BSR. This unusual observation may suggest very high Gas hydrate Saturations and coeval presence of Free Gas and Gas hydrate in the sediments. Evaluation of the OBS and CSEM data will allow to test this hypothesis. The 3D seismic data clearly show fluid migration pathways through the Gas hydrate stability to the sea floor. Sea floor video footage and sampling confirmed the presence of on-going methane seepage at the Formosa Ridge above the fluid migration pathway imaged in the 3D seismic data. They also establish that there is at least one seep on the Four-Way-Closure Ridge at which methane is released into the ocean above another seismically imaged fluid migration pathway. This is the first active seep site with chemosynthetic ecosystems discovered on the active margin SW off Taiwan.
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Failure mechanisms of Ana Slide from geotechnical evidence, Eivissa Channel, Western Mediterranean Sea
Marine Geology, 2012Co-Authors: Sara Lafuerza, Nabil Sultan, Miquel Canals, Galderic Lastras, Antonio Cattaneo, Jaime Frigola, S. Costa, Christian BerndtAbstract:This work deals with the failure mechanisms of Ana Slide in the Eivissa Channel, in between the Iberian Peninsula and the Balearic Islands, under the effects of Gas charging and seismic loading. In situ geotechnical tests and sediment cores obtained at the eastern Balearic slope of the Eivissa Channel suggest that the basal failure surface (BFS) developed as a result of subtle contrasting hydro-mechanical properties at the boundary between a fine-grained unit (U6) overlying a methane-charged relatively coarser unit (U7). Past methane seepage is inferred from seismic reflection profiles and high magnetic susceptibility values in sediments from the slide headwall area. Past methane charging is also supported by further seismic reflection data and isotopic analyses of benthic foraminifera published separately. The possibility of failure for different critical failure surfaces has been investigated by using the SAMU-3D slope stability model software taking into account the role of Free methane in the development of the landslide. Failure would occur after SAMU-3D if the undrained shear strength of units U6 and U7 is strongly degraded (i.e. 95%). Wheeler's theory suggests that a 9% Free Gas Saturation would be required to reduce the undrained shear strength by 95%. However, the theory of the undrained equilibrium behaviour of Gassy sediments for this methane concentration shows that the excess fluid pressure generated by Gas exsolution, estimated at 12% of the effective stress, is not high enough to bring the slope to fail. This led us to consider seismic loading as an additional potential failure mechanism despite the lack of historical data (including instrumental records) on seismicity in the Balearic Islands, therefore assuming that the historical period is not necessarily representative of seismic activity further back in time (i.e. when Ana Slide occurred similar to 61.5 ka ago). Considering current slope conditions, the most critical failure surface obtained by SAMU-3D relates to peak ground accelerations (PGA) of 0.24g. which relates to magnitude moment Mw = 5 at epicentral distances of 1 km, and 7 >= Mw >= 5 at epicentral distances
Timothy J Henstock - One of the best experts on this subject based on the ideXlab platform.
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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
Journal of Geophysical Research, 2015Co-Authors: Bedanta Goswami, Karen Weitemeyer, T A Minshull, Martin C Sinha, Graham K Westbrook, Anne Chabert, Timothy J HenstockAbstract: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 observed. Joint analysis of the resistivity and velocity anomaly indicates pore Saturation of up to 52% hydrate with 28% Free Gas, or up to 73% hydrate with 4% Free Gas, within the chimney beneath the pockmark assuming a nonuniform and uniform fluid distribution, respectively. Similarly, we estimate up to 30% hydrate with 4% Free Gas or 30% hydrate with 2% Free Gas within the pore space of the GHSZ outside the central chimney assuming a nonuniform and uniform fluid distribution, respectively. High levels of Free-Gas Saturation in the top part of the chimney are consistent with episodic Gas venting from the pockmark.
Anne Chabert - One of the best experts on this subject based on the ideXlab platform.
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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
Journal of Geophysical Research, 2015Co-Authors: Bedanta Goswami, Karen Weitemeyer, T A Minshull, Martin C Sinha, Graham K Westbrook, Anne Chabert, Timothy J HenstockAbstract: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 observed. Joint analysis of the resistivity and velocity anomaly indicates pore Saturation of up to 52% hydrate with 28% Free Gas, or up to 73% hydrate with 4% Free Gas, within the chimney beneath the pockmark assuming a nonuniform and uniform fluid distribution, respectively. Similarly, we estimate up to 30% hydrate with 4% Free Gas or 30% hydrate with 2% Free Gas within the pore space of the GHSZ outside the central chimney assuming a nonuniform and uniform fluid distribution, respectively. High levels of Free-Gas Saturation in the top part of the chimney are consistent with episodic Gas venting from the pockmark.
Zeyu Nan - One of the best experts on this subject based on the ideXlab platform.
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Logging evaluation of Free-Gas Saturation and volume content in Wufeng-Longmaxi organic-rich shales in the Upper Yangtze Platform, China
Marine and Petroleum Geology, 2019Co-Authors: Li Jun, Wu Qingzhao, Jin Wujun, Lu Jing, Zeyu NanAbstract:Abstract The Wufeng-Longmaxi shale is the most important target for the exploration and production of shale Gas in China. There are two important parameters of great importance to shale Gas evaluation: Free Gas Saturation and content. However, current models that have been proposed based on the use of sandstone are not applicable to this shale Gas reservoir due to differences in conductivity mechanisms between these two types of reservoirs. In this study, after the pore volume of Gas shale had been classified into three phases, those being the adsorbed phase pore, Free phase pore, and bound water pore, we proposed a method to calculate the Free Gas Saturation and content from well logging data based on the pore volume model. Our method utilizes the following procedures: 1) determining the total porosity on the basis of the matrix value of dry clay; 2) establishing a quantitative correlation of the bound water content to the clay content and then determining the bound water porosity; 3) calculating the absorbed Gas content by Langmuir formula; 4) calculating the adsorbed phase porosity according to the principle of mass conservation after determining the underground density of the adsorbed phase (in the range of 0.4–1.2 g/cm3); and 5) determining the Free Gas Saturation and Free Gas content. Field examples show that the predicted shale porosity, Free Gas, and adsorbed Gas contents calculated by using our proposed model accurately coordinate with the core derived results, which verified that the proposed method was valuable to evaluating the Wufeng-Longmaxi shale Gas reservoir.
