--> Abstract: Biodegradaton of Hydrocarbons Associated with Subsurface Reservoirs and Natural Seepage; #90063 (2007)

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Biodegradaton of Hydrocarbons Associated with Subsurface Reservoirs and Natural Seepage

 

Valentine, David L.1, George D. Wardlaw2, Franklin S. Kinnaman2, Susan Mau2, Christopher M. Reddy3, Robert K. Nelson3, J. Samuel Arey4 (1) University of California, Santa Barbara, CA (2) University of California, (3) Woods Hole Oceanographic Institution, (4) Swiss Ferderal Institute of Technology,

 

Microbes are capable of consuming hydrocarbons under favorable environmental conditions which extend from the ocean to the deep subsurface. However, the rates, patterns and variability of biodegradation remain poorly characterized for most environments. The Coal Oil Point (COP) seep field and associated subsurface reservoirs, located offshore Goleta, CA, serve as an ideal natural laboratory to investigate the biodegradation of hydrocarbons. This paper considers the biodegradation of hydrocarbons in sediments, waters and underlying reservoirs of the COP seep field. Subsurface biodegradation is observed to impact oil composition dramatically, as observed using comprehensive two-dimensional gas chromatography. Rapid physical weathering processes become important at the sea surface, where the role of biodegradation remains unknown. Spatial variability in oil composition indicates differential biodegradation levels between nearby reservoirs and seeps. Hydrocarbon gases appear to be biodegraded in the subsurface, though only in select areas. Oxidation of gases in the sediment and water column occurs rapidly, but only impacts the dissolved fraction, and with a strong preference for propane and butane over methane and ethane. The apparent ubiquity of hydrocarbon degradation in the COP seep field underscores the relevance of microbial activity to petroleum systems.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California