Gas, oil, and brine: An undersea mud volcano

Ian R. Macdonald, Ph.D., David B. Buthman, William W. Sager, Michael B. Peccini, Norman L. Guinasso, Jr.

Wednesday, March 29, 1999
3:00 p.m.—Pacific Forum

This figure shows a sub-scene of RADARSAT synthetic aperture radar from the northern Gulf of Mexico collected on 6 Aug '97. The red outline indicates the approximate boundaries of Auger Basin, a commercial oil field. Black streaks in the image are created by floating oil. Their prominence on this date corresponds to peak temperatures recorded in a mud volcano in Auger Field.

Natural oil slicks were detected in satellite synthetic aperture radar (SAR) images from the northern Gulf of Mexico. Repeated, order-of-magnitude changes in the size of slicks indicate that oil venting waxed and waned over periods of approximately 40 days. The oil came from a complex of fluid expulsion features at seafloor depths of about 600 m. One feature was 50-m wide crater, located on a large fluid expulsion mound and filled with mud suspended in hypersaline brine (133 PSU). Temperature in this fluid exhibited rapid fluctuations between 27 July 1997 and 11 July 1998 (min 6.1°C, max 48.3°C, mean 26.1°C, stdev 9.07) and expelled sheets of mud that overflowed the crater. The largest oil slicks detected by SAR coincided with the most rapid increase in fluid temperature. These fluctuations result from dynamic, multi-phasic events in conduits to hydrocarbon reservoirs that extend at least 2 km below the seafloor.

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Last updated: December 19, 2000