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.
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In September 2004, the American Association of Petroleum Geologists (AAPG) convened a Hedberg Research Conference in Vancouver, British Columbia, Canada titled "Natural Gas Hydrates: Energy Resource Potential and Associated Geologic Hazards." As a continuation of the Hedberg Research Conference in Vancouver, the conveners of the conference and the editors of this Memoir have worked with more than 150 authors and coauthors to prepare this Memoir on gas hydrates. This publication follows the goals of the Hedberg conference; however, the contents of this Memoir were expanded to include all aspects of gas hydrates in nature. This Memoir contains 39 individual contributions, ranging from long topical summaries to shorter focused research papers. This Memoir has been published in two parts, with digital versions of all the complete research papers included on the enclosed CD. The hardcopy portion of the Memoir includes abstracts and several key figures for each of the contributions along with a complete copy of a gas hydrate technical review. The digital portion of this Memoir has been organized into a series of topical sections consisting of review articles, marine gas hydrate papers, and gas hydrate laboratory and modeling studies. Because of the rapidly emerging worldwide interest in gas hydrates, this comprehensive treatise on the geology of gas hydrates will be valuable to both the gas hydrate research community and exploration/development geologists working in arctic and deep marine environments.