Seismic and Thermal Characterization of a Bottom-simulating Reflection in the Northern Gulf of Mexico
Deborah R. Hutchinson, Patrick E. Hart, Carolyn D. Ruppel, Fred Snyder, Brandon Dugan, 2009. "Seismic and Thermal Characterization of a Bottom-simulating Reflection in the Northern Gulf of Mexico", Natural Gas Hydrates—Energy Resource Potential and Associated Geologic Hazards, T. Collett, A. Johnson, C. Knapp, R. Boswell
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High-resolution multichannel seismic reflection data, exploration industry three-dimensional (3-D) seismic data, and heat-flow measurements collected on the southeast side of a mini basin (Casey basin) in the northern Gulf of Mexico continental slope have been used to characterize a bottom-simulating reflector (BSR). The BSR, which covers a small area of about 15 km2 (6 mi2), is identified by crosscutting relationships with seismic stratigraphy. Two mounds are identified. The larger Alpha mound is structurally formed at the junction of three arms of the structural high east of the mini basin. The smaller Beta mound may be a seep site. Conventional heat-flow measurements yield higher gradients (39–49 mK/m) to the northeast of the structural high and lower values (30–38 mK/m) to the south and west along the edge of the mini basin, which is separated from the structural high by the eastern Casey fault zone. When the near-sea-floor thermal gradients are extrapolated to the depth of the BSR, the resulting temperatures are generally too low if the BSR marks the base of the hydrate stability zone in a methane-only gas-hydrate system. Plausible changes in pore-water salinity or gas composition cannot account for this disparity, and thermal perturbations caused by fluid down welling, mass wasting, or depth-dependent thermal conductivity variations might best explain the low predicted BSR temperatures. The recognition of a BSR in the study area provides geophysical evidence that a hydrate stability zone with trapped free gas at its base exists in the northern Gulf and that minibasins can be locations for finding subsurface hydrate-associated free gas and probable gas hydrate.