HR: 17:35h
AN: NS54A-06    [Abstracts]
TI: Evidence for Focused Accumulations of Methane Hydrate with Possible Resource Implications for the Deep Water Bering Sea Basins
AU: Barth, G A
EM: gbarth@usgs.gov
AF: U. S. Geological Survey, 345 Middlefield Rd. MS 999, Menlo Park, CA 94025, United States
AU: * Scholl, D W
EM: dscholl@usgs.gov
AF: University of Alaska, College of Natural Science and Mathematics, Fairbanks, AK 99775- 7320, United States
AU: Childs, J R
EM: jchilds@usgs.gov
AF: U. S. Geological Survey, 345 Middlefield Rd. MS 999, Menlo Park, CA 94025, United States
AB: Velocity-amplitude anomalies (VAMPs), comprising coincident seismic travel time anomalies and gas bright spots, are features widely identified in seismic reflection images from the deep-water Aleutian and Bowers Basins in the Bering Sea. The structures are interpreted as acoustic images of large deposits of natural methane hydrate directly overlying columns of ascending fluids that deliver methane gas to the hydrate stability zone. Because these chimneys extend downward to depths where thermocatalytic processes are underway, methane involved in Bering Sea VAMP structures is presumed to be petroleum generated. Interval travel time anomalies have been used to objectively detect these features and to quantify implied resource content in several example cases. Relative travel time variation in the sedimentary intervals above and below a gas hydrate bottom simulating reflection (BSR) are a selected diagnostic for VAMP detection, measuring velocity pull-up in the hydrate stability zone and push-down in the underlying gas zone. The largest VAMP anomalies studied, including all of those associated with hydrate indicators, are located above prominent basement highs. This association suggests that long-lived fluid migration patterns in these undeformed deep- water basins were originally established in response to sedimentation and compaction over the oceanic basement topography, perhaps augmented by hydrothermal circulation involving the crust itself. Thousands of VAMP anomalies occur in the Bering Sea. Individual large VAMP structures appear to involve a volume of methane (0.6-0.9 TCF) equivalent to that of a large gas field. If the hydrate interpretation is correct, then a genuinely vast number of targets for concentrated accumulations of methane (either as gas or hydrate) occur in the Bering Sea Basin.
DE: 3004 Gas and hydrate systems
SC: Near-Surface Geophysics [NS]
MN: 2007 Joint Assembly