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The Leading Edge; January 2001; v. 20; no. 1; p. 87-91; DOI: 10.1190/1.1438888
© 2001 Society of Exploration Geophysicists
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Deep-sea gas hydrates on the northern Cascadia margin

M. Riedel, G. D. Spence and N. R. Chapman

University of Victoria

R. D. Hyndman

University of Victoria and Pacific Geosciences Center, Geological Survey of Canada

Corresponding author: M. Riedel, mriedel@geosun1.seos.uvic.ca

The first 20% of the full text of this article appears below.

This article describes recent work on marine hydrates off western Canada. Natural occurrences of gas hydrates have been reported in the geoscience literature since the early 1970s. Gas hydrates are solid ice-like structures in which gas molecules (largely methane) are trapped within cages of water molecules. Some 50 regions of hydrate occurrence have been reported in marine, permafrost, and lake environments worldwide. Interest in gas hydrates is due to the fact that the total amount of hydrocarbons locked up in them probably exceeds other known fossil hydrocarbon resources.

Gas hydrates contain large concentrations of methane. The stability of natural gas hydrates is mainly affected by temperature and pressure, but secondary influences include pore fluid salinity, the nature of gas enclosed, and the grain size of the host material. Thus, stability occurs at ocean depths greater than 500 m at temperate latitudes but in shallow water and on land in the Arctic.

On seismic sections, hydrates can be detected primarily by the occurrence of a bottom-simulating reflector (BSR) which is thought to represent the base of the hydrate stability field, marking the transition between hydrate-bearing sediments above and the occurrence of free gas below the interface. Gas hydrates were first observed at the northern Cascadia margin off Vancouver Island in seismic data acquired in 1985. They have been investigated intensively over the last decade by 2-D single and multichannel surveys, ocean-bottom (OBS) recordings, electrical resistivity and seafloor compliance studies, and ODP Leg 146 drilling and downhole logging. A high-resolution 3-D multichannel seismic survey was completed in August 1999 around ODP Site 889. An area of active gas/fluid venting mapped during this survey was further investigated in July-August 2000 by sediment piston-coring and seafloor observation and sampling with an unmanned submersible (ROPOS).

The area of investigation is on the accretionary sedimentary prism . . . [Full Text of this Article]




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A. R. Gorman, W. S. Holbrook, M. J. Hornbach, K. L. Hackwith, D. Lizarralde, and I. Pecher
Migration of methane gas through the hydrate stability zone in a low-flux hydrate province
Geology, April 1, 2002; 30(4): 327 - 330.
[Abstract] [Full Text] [PDF]


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