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Riedel, M., E. C. Willoughby, N. Edwards, R. D. Hyndman, G. D. Spence, R. Chapman, M.-A. Chen, I. Novosel, and K. Schwalenberg, 2009, Gas hydrate offshore Vancouver Island, northern Cascadia margin, in T. Collett, A. Johnson, C. Knapp, and R. Boswell, eds., Natural gas hydrates—Energy resource potential and associated geologic hazards: AAPG Memoir 89, p. 433–450.

DOI:10.1306/13201115M893353

Copyright copy2009 by The American Association of Petroleum Geologists.

Gas Hydrate Offshore Vancouver Island, Northern Cascadia Margin

M. Riedel,1 Eleanor C. Willoughby,2 Nigel Edwards,3 Roy D. Hyndman,4 George D. Spence,5 Ross Chapman,6 Marc-Andre Chen,7 Ivana Novosel,8 Katrin Schwalenberg9

1Department of Earth and Planetary Science, McGill University, Montreal, Quebec, Canada
2Department of Physics, University of Toronto, Toronto, Ontario, Canada
3Department of Physics, University of Toronto, Toronto, Ontario, Canada
4Natural Resources Canada, Geological Survey of Canada, Pacific Geoscience Center, Sidney, British Columbia, Canada; Present address: School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada
5School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada
6School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada
7School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada; Present address: Imperial Oil Limited, Calgary, Alberta, Canada
8School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada; Present address: Shell International Exploration and Production Inc., Houston, Texas, U.S.A.
9Bundesanstalt fur Geowissenschaften und Rohstoffe (BGR), Hannover, Germany

ACKNOWLEDGMENTS

We thank the Ocean Drilling Program and the Integrated Ocean Drilling Program, the Geological Survey of Canada, the Canadian Natural Sciences and Engineering Research Council (NSERC), the U.S. National Science Foundation (NSF), and the U.S. Department of Energy, National Gas Hydrate Research Program for making this research possible. We acknowledge the contribution of the shipboard party of ODP Leg 146 and IODP Expedition 311, as well as the numerous participants in the geophysical studies conducted on the margin over the past 25 yr. The authors would further like to acknowledge the contributions of the Coast Guard crews onboard the research vessel John P. Tully and other ships involved in surveys. M. Riedel and G.D. Spence wish to acknowledge Seismic Micro Technology for the academic use of their Kingdom Suite seismic analysis software. Funding for these studies was from many sources but mainly through the Geological Survey of Canada Gas Hydrate Program and NSERC. The authors also would like to thank the reviewers (especially Joel Johnson) for useful comments on the manuscript.

ABSTRACT

This chapter reviews the extensive geophysical studies and Ocean Drilling Program (ODP) results that provide constraints on the occurrence, distribution, and concentration of deep-sea gas hydrate beneath the northern Cascadia margin offshore Vancouver Island. Most of this information comes from a wide range of seismic surveys and includes the mapping of the bottom-simulating reflector (BSR), as well as estimating gas-hydrate and free-gas concentrations. Recent additional constraints on the distribution and concentration of gas hydrate come from sea-floor-towed, controlled-source electromagnetic surveying and sea-floor compliance studies. These surveys and studies have been primarily deployed around a cold vent field, where seismic data show several broad blank zones, interpreted as fault-related conduits for focused fluid-gas migration, and where gas hydrate has been recovered in piston cores at the sea floor.

Results from the ODP Leg 146 and the recently completed Integrated Ocean Drilling Program (IODP) Expedition 311 further constrain concentration estimates for gas hydrate and free gas in the sediments along the margin and also give insight into the complex formation mechanisms and controlling factors for gas hydrate occurrence in an accretionary complex.

This summary was first presented in September 2004 at the AAPG Hedberg Research Conference on gas hydrates. Subsequently, 1 yr later, the drilling of IODP Expedition 311 resulted in a significant amount of new information and insight into the occurrence and formation processes of gas hydrate at the northern Cascadia margin. This chapter provides only a short summary of the results from that IODP Expedition. Reviews of the results from that drill coring and the downhole measurements are in progress.

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