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Controls on the formation and stability of gas hydrate-related bottom-simulating reflectors (BSRs): A case study from the west Svalbard continental slope

Controls on the formation and stability of gas hydrate-related bottom-simulating reflectors (BSRs): A case study from the west Svalbard continental slope
Controls on the formation and stability of gas hydrate-related bottom-simulating reflectors (BSRs): A case study from the west Svalbard continental slope
The growth and stability of the free-gas zone (FGZ) beneath gas-hydrate related bottom-simulating seismic reflectors (BSRs) is investigated using analytical and numerical analyses to understand the factors controlling the formation and depletion of free gas. For a model based on the continental slope west of Svalbard (a continental margin of north Atlantic type), we find that the FGZ is inherently unstable under a wide range of conditions because upward flow of under-saturated liquid depletes free gas faster than it is produced by hydrate recycling. In these scenarios, the 150-m-thick FGZ that presently exists there would deplete within 105–106 years. We suggest the FGZ is in a stable state, however, that is formed by a diffusion-dominated mechanism that produces low concentrations of gas in a FGZ of steady state thickness. Gas forms across a thick zone because the upward fluid flux is relatively low and because the gas–water solubility decreases to a minimum several hundred meters below the seabed. This newly understood solubility-curvature effect is complementary to hydrate recycling, but becomes the most important factor controlling the presence and properties of the BSR in environments where the rate of upward fluid flow and the rate of hydrate recycling are both relatively low (i.e., rifted continental margins). If the present-day FGZ is in steady state, we estimate that the upward fluid flux in the west Svalbard site must be less than 0.15 mm a?1.
0148-0227
B05104
Haacke, R. Ross
fbe5ce9e-1327-4226-b0ce-82afb806b2fc
Westbrook, Graham K.
ccd95de7-a1a1-4fc9-be37-f1a487bb65ca
Riley, Michael S.
053a25cb-27a2-4770-9c99-3bf104157479
Haacke, R. Ross
fbe5ce9e-1327-4226-b0ce-82afb806b2fc
Westbrook, Graham K.
ccd95de7-a1a1-4fc9-be37-f1a487bb65ca
Riley, Michael S.
053a25cb-27a2-4770-9c99-3bf104157479

Haacke, R. Ross, Westbrook, Graham K. and Riley, Michael S. (2008) Controls on the formation and stability of gas hydrate-related bottom-simulating reflectors (BSRs): A case study from the west Svalbard continental slope. Journal of Geophysical Research, 113 (B5), B05104. (doi:10.1029/2007JB005200).

Record type: Article

Abstract

The growth and stability of the free-gas zone (FGZ) beneath gas-hydrate related bottom-simulating seismic reflectors (BSRs) is investigated using analytical and numerical analyses to understand the factors controlling the formation and depletion of free gas. For a model based on the continental slope west of Svalbard (a continental margin of north Atlantic type), we find that the FGZ is inherently unstable under a wide range of conditions because upward flow of under-saturated liquid depletes free gas faster than it is produced by hydrate recycling. In these scenarios, the 150-m-thick FGZ that presently exists there would deplete within 105–106 years. We suggest the FGZ is in a stable state, however, that is formed by a diffusion-dominated mechanism that produces low concentrations of gas in a FGZ of steady state thickness. Gas forms across a thick zone because the upward fluid flux is relatively low and because the gas–water solubility decreases to a minimum several hundred meters below the seabed. This newly understood solubility-curvature effect is complementary to hydrate recycling, but becomes the most important factor controlling the presence and properties of the BSR in environments where the rate of upward fluid flow and the rate of hydrate recycling are both relatively low (i.e., rifted continental margins). If the present-day FGZ is in steady state, we estimate that the upward fluid flux in the west Svalbard site must be less than 0.15 mm a?1.

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Published date: 2008
Organisations: Ocean and Earth Science

Identifiers

Local EPrints ID: 340096
URI: http://eprints.soton.ac.uk/id/eprint/340096
ISSN: 0148-0227
PURE UUID: 37797d01-0a36-4a6a-b1ce-e42cf63ae027

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Date deposited: 11 Jun 2012 09:17
Last modified: 16 Dec 2019 20:38

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