--> Abstract: Chemometrics Identifies Families of Crude Oils, Seep Oils, and Stranded Tarballs in Coastal California; #90063 (2007)

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Chemometrics Identifies Families of Crude Oils, Seep Oils, and Stranded Tarballs in Coastal California

 

Peters, Kenneth E.1, Frances D. Hostettler2, Thomas D. Lorenson1, Robert J. Rosenbauer1 (1) U.S. Geological Survey, Menlo Park, CA (2) U. S. Geological Survey, Menlo Park, CA

 

Biomarkers (molecular fossils) and carbon isotope ratios were measured for >600 samples of produced oils, seep oils, and tarballs from coastal California. Chemometrics (multivariate statistics) of the data included principal components analysis (PCA) to establish genetic families. A unique, multi-tiered decision tree consisting of multiple K-Nearest Neighbor (KNN) models was constructed to classify new samples. The decision tree assigns confidence limits to each classification using soft independent modeling of class analogy (SIMCA). The data were also used to infer the age, lithology, organic matter input, and depositional environment of the source rock for each sample. Results identify three tribes of oil samples that originated from organofacies of Miocene source rock, including the Monterey Formation. Tribe 1 contains four families having C22/C21 and C24/C23 tricyclic terpane ratios typical of marine shale source rock. This tribe has high Ts/Tm, low C35S/C34S, and abundant oleanane, indicating clay-rich, oxic-suboxic source rock with higher-plant input. Examples include produced oil from Platform A (Dos Cuadras Field), nearby seep oils, and tarballs from Goleta and Gaviota in southern California. Tribe 3 contains five families that lack oleanane and have geochemical characteristics of anoxic marine carbonate source rock. Examples include tarballs from Point Reyes and Drakes Bay in northern California. Tribe 2 contains four families with intermediate compositions indicating marine marl source rock. Examples include produced oils from the Harvest, Hondo, and Heritage wells, nearby seep oils, and tarballs from Santa Rosa and San Miguel Islands. Some tarballs correlate with samples of produced oils or seep oils, thus establishing a link between source and collection site.

 

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