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High-resolution 3D seismic investigations of hydrate-bearing fluid escape chimneys in the Nyegga region of the Voring Plateau, Norway

High-resolution 3D seismic investigations of hydrate-bearing fluid escape chimneys in the Nyegga region of the Voring Plateau, Norway
High-resolution 3D seismic investigations of hydrate-bearing fluid escape chimneys in the Nyegga region of the Voring Plateau, Norway
Hundreds of pockmarks and mounds, which seismic reflection sections show to be underlain by chimney-like structures, exist in southeast part of the Vøring plateau, Norwegian continental margin. These chimneys may be representative of a class of feature of global importance for the escape of methane from beneath continental margins and for the provision of a habitat for the communities of chemosynthetic biota. Thinning of the time intervals between reflectors in the flanks of chimneys, observed on several high-resolution seismic sections, could be caused by the presence of higher velocity material such as hydrate or authigenic carbonate, which is abundant at the seabed in pockmarks in this area. Evidence for the presence of hydrate was obtained from cores at five locations visited by the Professor Logachev during TTR Cruise 16, Leg 3 in 2006. Two of these pockmarks, each about 300-m wide with active seeps within them, were the sites of high-resolution seismic experiments employing arrays of 4-component OBS (Ocean-Bottom Seismic recorders) with approximately 100-m separation to investigate the 3D variation in their structure and properties. Shot lines at 50-m spacing, run with mini-GI guns fired at 8-m intervals, provided dense seismic coverage of the sub-seabed structure. These were supplemented by MAK deep-tow 5-kHz profiles to provide very high-resolution detail of features within the top 1-40 m sub-seabed. Travel-time tomography has been used to detail the variation in Vp and Vs within and around the chimneys. Locally high-amplitude reflectors of negative polarity in the flanks of chimneys and scattering and attenuation within the interiors of the chimneys may be caused by the presence of free gas within the hydrate stability field. A large zone of free gas beneath the hydrate stability field, apparently feeding several pockmarks, is indicated by attenuation and velocity pull-down of reflectors.
hydrate, chimney, high-resolution 3D seismic
5597-[12p]
International Conference on Gas Hydrates
Westbrook, G.K.
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Exley, R.
5cd1ff59-0c9b-4d1b-8866-7f49bf8a455e
Minshull, T.A.
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Nouze, H.
6dbfe767-23ae-4136-80a0-dae99f47d8f5
Gailler, A.
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Jose, T.
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Ker, S.
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Plaza, A.
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Westbrook, G.K.
ccd95de7-a1a1-4fc9-be37-f1a487bb65ca
Exley, R.
5cd1ff59-0c9b-4d1b-8866-7f49bf8a455e
Minshull, T.A.
bf413fb5-849e-4389-acd7-0cb0d644e6b8
Nouze, H.
6dbfe767-23ae-4136-80a0-dae99f47d8f5
Gailler, A.
ccb3f498-66af-4ed7-936d-f2989767d9fd
Jose, T.
acdc3a92-b087-488d-9604-c901f246e726
Ker, S.
f7a7a4dd-77ac-4c80-a5d2-356b9ecdfc61
Plaza, A.
e2c06d61-a386-46e0-8496-4828c72c7173

Westbrook, G.K., Exley, R., Minshull, T.A., Nouze, H., Gailler, A., Jose, T., Ker, S. and Plaza, A. (2008) High-resolution 3D seismic investigations of hydrate-bearing fluid escape chimneys in the Nyegga region of the Voring Plateau, Norway. In Proceedings of the 6th International Conference on Natural Gas Hydrates. International Conference on Gas Hydrates. 5597-[12p] .

Record type: Conference or Workshop Item (Paper)

Abstract

Hundreds of pockmarks and mounds, which seismic reflection sections show to be underlain by chimney-like structures, exist in southeast part of the Vøring plateau, Norwegian continental margin. These chimneys may be representative of a class of feature of global importance for the escape of methane from beneath continental margins and for the provision of a habitat for the communities of chemosynthetic biota. Thinning of the time intervals between reflectors in the flanks of chimneys, observed on several high-resolution seismic sections, could be caused by the presence of higher velocity material such as hydrate or authigenic carbonate, which is abundant at the seabed in pockmarks in this area. Evidence for the presence of hydrate was obtained from cores at five locations visited by the Professor Logachev during TTR Cruise 16, Leg 3 in 2006. Two of these pockmarks, each about 300-m wide with active seeps within them, were the sites of high-resolution seismic experiments employing arrays of 4-component OBS (Ocean-Bottom Seismic recorders) with approximately 100-m separation to investigate the 3D variation in their structure and properties. Shot lines at 50-m spacing, run with mini-GI guns fired at 8-m intervals, provided dense seismic coverage of the sub-seabed structure. These were supplemented by MAK deep-tow 5-kHz profiles to provide very high-resolution detail of features within the top 1-40 m sub-seabed. Travel-time tomography has been used to detail the variation in Vp and Vs within and around the chimneys. Locally high-amplitude reflectors of negative polarity in the flanks of chimneys and scattering and attenuation within the interiors of the chimneys may be caused by the presence of free gas within the hydrate stability field. A large zone of free gas beneath the hydrate stability field, apparently feeding several pockmarks, is indicated by attenuation and velocity pull-down of reflectors.

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westbrook_et_al_2008a.pdf - Accepted Manuscript
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More information

Published date: 2008
Venue - Dates: 6th International Conference On Gas Hydrates, 2008-07-06 - 2008-07-10
Keywords: hydrate, chimney, high-resolution 3D seismic

Identifiers

Local EPrints ID: 55302
URI: http://eprints.soton.ac.uk/id/eprint/55302
PURE UUID: 35e3b7e0-7771-4c54-9a9f-e8a0c0d8432f
ORCID for T.A. Minshull: ORCID iD orcid.org/0000-0002-8202-1379

Catalogue record

Date deposited: 28 Jul 2008
Last modified: 14 Mar 2019 01:48

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