HR: 0830h
AN: OS51B-0857    [PDF]
TI: Constraints on Subsurface gas and gas Hydrate Distribution in a Gulf of Mexico Mound
AU: * Wood, W T
EM: warren.wood@nrlssc.navy.mil
AF: U. S. Naval Research Laboratory, Code 7432, Stennis Space Center, MS 39529 United States
AU: Hutchinson, D
AF: U. S. Geological Survey, 384 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Hart, P
AF: U. S. Geological Survey, 384 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Snyder, F
AF: Western Geco, 3600 Briar Park Dr., Houston, TX 77079 United States
AU: Voss, C
AF: U. S. Geological Survey, 384 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Dutta, N
AF: Western Geco, 3600 Briar Park Dr., Houston, TX 77079 United States
AU: Muller, L
AF: Western Geco, 3600 Briar Park Dr., Houston, TX 77079 United States
AU: Lee, M
AF: U. S. Geological Survey, 384 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Gardner, J
AF: U. S. Naval Research Laboratory, Code 7432, Stennis Space Center, MS 39529 United States
AU: Dugan, B
AF: U. S. Geological Survey, 384 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Ruppel, C
AF: Georgia Tech, 311 Ferst Drive, Suite 1250 ES&T Building, Atlanta, GA 30332-0340 United States
AU: Coffin, R
AF: U. S. Naval Research Laboratory, Code 7432, Stennis Space Center, MS 39529 United States
AU: Evans, R
AF: Woods Hole Oceanographic Institute, Clark South 172, Woods Hole, MA 02543 United States
AU: Jones, E
AF: Chevron Texaco, 2811 Hayes Road, Houston, TX 77082-6696 United States
AB: The Gulf of Mexico is well known for seafloor methane hydrate accumulations associated with hydrocarbon seeps, but the distribution of free gas, gas in solution and gas hydrate below the mounds is poorly known. Numerical simulation of fluid flow and analyses of industry 3-D seismic data (reprocessed for higher resolution in the shallow sediments), and high resolution seismic data recently acquired by the USGS provide some constraints on the distribution of these phases via their significantly different effect on seismic returns. Below an 8 m high, 300 m diameter mound at 1300 m water depth in Atwater Valley lease block 14, lies a convex upward, bell-shaped, subsurface reflection. The reflection can be modeled quite closely as a reflection from the base of hydrate stability (top of gas here) perturbed from about 300 to 45 m below the seafloor by localized, upward fluid and heat flux. The flow modeling therefore predicts free gas much higher below the mound than away from the mound. This is confirmed in the USGS data by a push down of 24 percent on a reflection passing below the perturbation, suggesting a velocity below the mound of less than 1400 m/s, indicative of at least some free gas. A strong upward perturbation to the base of the hydrate stability zone significantly constrains the volume available for methane hydrate formation below the seafloor, potentially impacting volume estimates of methane hydrate below seafloor mounds.
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1635 Oceans (4203)
DE: 3015 Heat flow (benthic) and hydrothermal processes
DE: 3022 Marine sediments--processes and transport
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting