Geological controls on focused fluid flow through the gas hydrate stability zone on the southern Hikurangi Margin of New Zealand, evidenced from multi-channel seismic data.

Crutchley, Gareth , Gorman, A.R., Pecher, I.A., Toulmin, S. and Henrys, S.A. (2011) Geological controls on focused fluid flow through the gas hydrate stability zone on the southern Hikurangi Margin of New Zealand, evidenced from multi-channel seismic data. Marine and Petroleum Geology, 28 (10). pp. 1915-1931. DOI 10.1016/j.marpetgeo.2010.12.005.

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Abstract

Highly concentrated gas hydrate deposits are likely to be associated with geological features that
promote increased fluid flux through the gas hydrate stability zone (GHSZ). We conduct conventional
seismic processing techniques and full-waveform inversion methods on a multi-channel seismic line that
was acquired over a 125 km transect of the southern Hikurangi Margin off the eastern coast of New
Zealand’s North Island. Initial processing, employed with an emphasis on preservation of true amplitude
information, was used to identify three sites where structures and stratal fabrics likely encourage focused
fluid flow into and through the GHSZ. At two of the sites, Western Porangahau Trough and Eastern
Porangahau Ridge, sub-vertical blanking zones occur in regions of intensely deformed sedimentary
layering. It is interpreted that increased fluid flow occurs in these regions and that fluids may dissipate
upwards and away from the deformed zone along layers that trend towards the seafloor. At Eastern
Porangahau Ridge we also observe a coherent bottom simulating reflection (BSR) that increases markedly
in intensity with proximity to the centre of the anticlinal ridge. 1D full-waveform inversions conducted at
eight points along the BSR reveal much more pronounced low-velocity zones near the centre of the ridge,
indicating a local increase in the flux of gas-charged fluids into the anticline. At another anticline,
Western Porangahau Ridge, a dipping high-amplitude feature extends from the BSR upwards towards the
seafloor within the regional GHSZ. 1D full-waveform inversions at this site reveal that the dipping feature
is characterised by a high-velocity zone overlying a low-velocity zone, which we interpret as gas hydrates
overlying free gas. These results support a previous interpretation that this high-amplitude feature
represents a local “up-warping” of the base of hydrate stability in response to advective heat flow from
upward migrating fluids. These three sites provide examples of geological frameworks that encourage
prolific localised fluid flow into the hydrate system where it is likely that gas-charged fluids are converting
to highly concentrated hydrate deposits.

Document Type: Article
Keywords: Gas hydrates; Fluid flow; Gas hydrate; Waveform inversion; Blanking zone; Anticline; Hikurangi Margin
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Refereed: Yes
Open Access Journal?: No
Publisher: Elsevier
Date Deposited: 07 Feb 2011 10:42
Last Modified: 26 Jul 2017 07:37
URI: https://oceanrep.geomar.de/id/eprint/10960

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