--> ABSTRACT: Gas Hydrates in a Complex Geologic Province, Northern Gulf of Mexico, by Harry H. Roberts, James M. Coleman, J. L. Hunt, W. W. Shedd, A. V. Milkov, and Roger Sassen; #90906(2001)

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Harry H. Roberts1, James M. Coleman2, J. L. Hunt3, W. W. Shedd3, A. V. Milkov4, Roger Sassen5

(1) Louisiana State University, Baton Rouge, LA
(2) Louisiana State University
(3) Minerals Management Service
(4) Texas A & M University
(5) Texas A & M University, College Station, TX

ABSTRACT: Gas Hydrates in a Complex Geologic Province, Northern Gulf of Mexico

Nearly the entire continental slope of the northern Gulf of Mexico is documented by large, overlapping tracks of high quality 3D-seismic data. Analysis of these data by industry, MMS, and academic geoscientists emphasizes the extreme geologic complexity imposed on this deepwater province by salt and sediments. In this framework faults are confirmed conduits for fluids and gases from deep hydrocarbon-generating areas as well as shallower parts of the sediment column. Within the gas hydrate stability zone this flux produces gas hydrate composed largely of thermogenic gases. Flux rate of fluids and gases conducted to the shallow subsurface and seafloor can preclude or encourage hydrate formation, depending on the heat transfer from deep geothermally heated zones. Therefore, in rapid transport cases, the gas hydrate stability field may be eliminated or highly modified by heat transfer to the seafloor. In contrast, moderate-to-slow flux systems result in massive gas hydrate deposits that fill fractures within fault zones, resulting in mounds of various dimensions at the seafloor. Frequent gas seeps and larger plumes over hydrate zones suggest that fault-supplied gas is consistently bypassing the surface and near-subsurface hydrate deposits and entering the water column, thus providing a constant supply of gas for hydrate formation. Seafloor experiments indicate that exposed hydrate decomposes in sync with water temperature changes ranging in temporal scale from hours to months. 3D-seismic surface amplitude data, wave-form analysis, and manned submersibles reveal associations that have helped identify probable sites of exposed hydrates that span the full depth range of the slope.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado