OBS Data Analysis to Quantify Gas Hydrate and Free Gas in the South Shetland Margin (Antarctica)

Song, Sha; Tinivella, Umberta; Giustiniani, Michela; Singhroha, Sunny; Bünz, Stefan; Cassiani, Giorgio

doi:10.3390/en11123290

Cited by 11 publications

(10 citation statements)

References 48 publications

(86 reference statements)

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“…Singhroha et al () and Goswami et al () document a gas hydrate system in this area where different components of the gas hydrate system, that is, methane hydrate and free gas, strongly affect the bulk seismic velocity. The presence of gas hydrates increases the P ‐wave velocity, and the presence of free gas in sediments decreases the P ‐wave velocity (Chand et al, ; Ecker et al, ; Gei & Carcione, ; Lee & Collett, ; Song et al, ). High seismic velocity anomalies observed in the GHSZ above the BSR in some azimuths (Figures ) can be due to the presence of gas hydrates.…”

Section: Discussionmentioning

confidence: 99%

“…Seismic velocity analysis provides a means to study the distribution of gas hydrates (Chand et al, 2004;Kumar et al, 2006;Madrussani et al, 2010). Seismic velocities estimated using oceanbottom seismic (OBS) data have been successfully used in different geological settings to estimate gas hydrate saturations in the GHSZ (Bünz et al, 2005;Kumar et al, 2007;Satyavani et al, 2013;Song et al, 2018;Westbrook et al, 2008). Gas hydrate bearing sediments have a higher bulk modulus and thus exhibit higher seismic velocities (Chand et al, 2004;Ecker et al, 1998;Gei & Carcione, 2003;Lee & Collett, 2001).…”

Section: Introductionmentioning

confidence: 99%

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Detection of Gas Hydrates in Faults Using Azimuthal Seismic Velocity Analysis, Vestnesa Ridge, W‐Svalbard Margin

et al. 2020

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Joint analysis of electrical resistivity and seismic velocity data is primarily used to detect the presence of gas hydrate‐filled faults and fractures. In this study, we present a novel approach to infer the occurrence of structurally controlled gas hydrate accumulations using azimuthal seismic velocity analysis. We perform this analysis using ocean‐bottom seismic data at two sites on Vestnesa Ridge, W‐Svalbard Margin. Previous geophysical studies inferred the presence of gas hydrates at shallow depths (up to ~190–195 m below the seafloor) in marine sediments of Vestnesa Ridge. We analyze azimuthal P‐wave seismic velocities in relation with steeply dipping near‐surface faults to study structural controls on gas hydrate distribution. This unique analysis documents directional changes in seismic velocities along and across faults. P‐wave velocities are elevated and reduced by ~0.06–0.08 km/s in azimuths where the raypath plane lies along the fault plane in the gas hydrate stability zone (GHSZ) and below the base of the GHSZ, respectively. The resulting velocities can be explained with the presence of gas hydrate‐ and free gas‐filled faults above and below the base of the GHSZ, respectively. Moreover, the occurrence of elevated and reduced (>0.05 km/s) seismic velocities in groups of azimuths bounded by faults suggests compartmentalization of gas hydrates and free gas by fault planes. Results from gas hydrate saturation modeling suggest that these observed changes in seismic velocities with azimuth can be due to gas hydrate saturated faults of thickness greater than 20 cm and considerably smaller than 300 cm.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Detection of Gas Hydrates in Faults Using Azimuthal Seismic Velocity Analysis, Vestnesa Ridge, W‐Svalbard Margin

et al. 2020

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“…OBS data have been widely used to study gas hydrates (Hobro et al, ; Katzman et al, ; Posewang & Mienert, ; Song et al, ; Spence et al, ). Different methods have been used to derive velocity models using OBS data (Kumar et al, ; Shinohara et al, ; Zelt & Smith, ; Zillmer et al, ).…”

Section: Methodsmentioning

confidence: 99%

“…The presence of free gas does not alter the shear strength of sediments overly and thus has little effect on the shear velocity ( Vs ) of the sediments (Dash & Spence, ). Thus, saturation of gas hydrates and free gas and their distribution patterns in the host sediments can be estimated by performing velocity analysis of both P and S waves from seismic data (Bünz et al, ; Kumar et al, ; Song et al, ; Westbrook et al, ).…”

Section: Introductionmentioning

confidence: 99%

Constraints on Gas Hydrate Distribution and Morphology in Vestnesa Ridge, Western Svalbard Margin, Using Multicomponent Ocean‐Bottom Seismic Data

2019

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Gas hydrates occur within sediments on the western Svalbard continental margin and the Vestnesa Ridge, a large sediment drift that extends in a west-northwest direction from the margin toward the mid-ocean ridge. We acquired multicomponent ocean-bottom seismic (OBS) data at 10 locations on the crest area of the eastern segment of the Vestnesa Ridge, an area with active gas seepage. P and S wave velocities are estimated using traveltime inversion, and self-consistent approximation/differential effective medium rock physics modeling is used to estimate gas hydrate and free gas saturation at OBS stations. We apply 1-D full waveform inversion at a selected OBS station to study detailed variations of P wave velocity near the bottom simulating reflection (BSR). High interval P wave velocity (Vp ≈ 1.73-1.82 km/s) and S wave velocity (>0.35 km/s) are observed in a layer above the BSR and low interval P wave velocity (Vp ≈ 1.28-1.53 km/s) in a layer below the BSR. We estimate 10-18% gas hydrate and 1.5-4.1% free gas saturation at different OBS stations in a layer above and below the BSR, respectively. We find significant variation in gas hydrate and free gas saturation across faults suggesting a structural control on the distribution of gas hydrate and free gas in the Vestnesa Ridge. Differences in gas hydrate saturation derived from P wave velocities and earlier estimates obtained from electromagnetic surveys indicate the presence of gas hydrates in faults and fractures. Moreover, beneath some OBS sites, the combined study of P and S waves, resistivity and seismic quality factor (Q), suggests the coexistence of free gas and gas hydrates.

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“…The seismic technique, which is used mostly for gas hydrate investigation, allows for detecting a clear indicator of the boundary between hydrate and free gas accumulation, known as bottom simulating reflector (BSR), i.e., [17]. Moreover, the seismic data provide information about the geometry of the main geological structures, allowing for possible explanations of the presence/absence of gas hydrate [18,19]. In the last few years, the integration of geophysical (mainly seismic and electromagnetic data), geochemical, and heat-flow data have allowed for detecting and characterizing gas hydrate and free gas volumes and their distribution in the sediments, i.e., [20][21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Gas Hydrate: Environmental and Climate Impacts

et al. 2019

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This Special Issue reports research spanning from the analysis of indirect data, modelling, laboratory and geological data confirming the intrinsic multidisciplinarity of the gas hydrate studies. The study areas are (1) Arctic, (2) Brazil, (3) Chile and (4) the Mediterranean region. The results furnished an important tessera of the knowledge about the relationship of a gas hydrate system with other complex natural phenomena such as climate change, slope stability and earthquakes, and human activities.

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OBS Data Analysis to Quantify Gas Hydrate and Free Gas in the South Shetland Margin (Antarctica)

Cited by 11 publications

References 48 publications

Detection of Gas Hydrates in Faults Using Azimuthal Seismic Velocity Analysis, Vestnesa Ridge, W‐Svalbard Margin

Detection of Gas Hydrates in Faults Using Azimuthal Seismic Velocity Analysis, Vestnesa Ridge, W‐Svalbard Margin

Constraints on Gas Hydrate Distribution and Morphology in Vestnesa Ridge, Western Svalbard Margin, Using Multicomponent Ocean‐Bottom Seismic Data

Gas Hydrate: Environmental and Climate Impacts

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