Methane Hydrate and Free Gas on the Blake Ridge from Vertical Seismic Profiling

Seismic velocities measured in three drill holes through a gas hydrate deposit on the Blake Ridge, offshore South Carolina, indicate that substantial free gas exists to at least 250 meters beneath the bottom-simulating reflection (BSR). Both methane hydrate and free gas exist even where a clear BSR...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 1996-09, Vol.273 (5283), p.1840-1843
Main Authors: Holbrook, W. Steven, Hoskins, Hartley, Wood, Warren T., Stephen, Ralph A., Lizarralde, Daniel
Format: Article
Language:English
Subjects:
Applied geophysics
Blanking
Conceptual Tempo
Drilling
Earth sciences
Earth, ocean, space
Exact sciences and technology
Fluids
Gas hydrates
Geology
Hydrates
Internal geophysics
Least Squares Statistics
Lithology
Low speed
Marine
Marine geology
Methane
Natural gas
Porosity
Reflectance
Sediments
Seismic prospecting
Seismic surveying
Seismology
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Summary:Seismic velocities measured in three drill holes through a gas hydrate deposit on the Blake Ridge, offshore South Carolina, indicate that substantial free gas exists to at least 250 meters beneath the bottom-simulating reflection (BSR). Both methane hydrate and free gas exist even where a clear BSR is absent. The low reflectance, or blanking, above the BSR is caused by lithologic homogeneity of the sediments rather than by hydrate cementation. The average methane hydrate saturation above the BSR is relatively low (5 to 7 percent of porosity), which suggests that earlier global estimates of methane in hydrates may be too high by as much as a factor of 3.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.273.5283.1840