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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions, 2011
Pages 105-122

Structural and Stratigraphic Relationships of Hydrocarbon Seeps in the Northern Gulf of Mexico and Geological Factors Contributing to Migration Variations

Margaret Dalthorp, Thomas H. Naehr

Abstract

The presence of modern and ancient hydrocarbon seeps is well documented in the literature. Scientists estimate 1.5 million barrels of oil naturally seep into worldwide waters each year, with 250 to 690 thousand barrels of this seepage occurring in the Gulf of Mexico. Hydrocarbon seeps are generally associated with continental margins like the Gulf of Mexico where numerous hydrocarbon seeps are documented through seismic, carbonates, geothermal patterns, chemosynthetic communities, geochemistry, gas hydrates, and/or remote sensing. Satellite images reveal the presence of numerous locations of oil slicks in the Gulf of Mexico, with 566 potential slick sites in the northern Gulf of Mexico recently identified on Synthetic Aperture Radar (SAR) data. Some of the slick sites are in areas of known sea floor seepage and some known sea floor seepage areas have no sea surface slick indicated. Most slicks are present in the salt basin area of the northern Gulf of Mexico, however many geological factors other than just salt movement can be involved to create a sea floor seep or sea surface slick. To determine the controls for sea surface slick creation, a study of surface and subsurface geological factors was conducted that considered structural setting, sediments, and hydrocarbon fluid properties. The purpose of the study is to investigate the factors influencing sea surface slick creation in order to provide a more accurate assessment of source and pathway relationships for hydrocarbon migration and transport.

Most (76%) of the sea surface slicks are observed in the salt basin region and most (64%) of these slicks are in areas of shallow salt. Other areas of slick concentrations include the Wanda fault system and the salt-withdrawal minibasins. Slicks are observed in association with all hydrocarbon flux rates and therefore are not good predictors of the sea floor geological and biological expressions of hydrocarbon seeps associated with variations in flux rates. Reservoir pressure and fluid density relationships to depth may indicate fluid migration pathways and timing.


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