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AAPG Bulletin

Abstract

AAPG Bulletin, V. 100, No. 1 (January 2016), P. 115-135.

Copyright ©2016. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/08031515068

Chemometric recognition of genetically distinct oil families in the Los Angeles basin, California

K. E. Peters,1 T. L. Wright,2 L. S. Ramos,3 J. E. Zumberge,4 and L. B. Magoon5

1Schlumberger, 18 Manzanita Place, Mill Valley, California 94941; Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Stanford, California 94305; [email protected]
2Chevron Corporation (retired), 136 Jordan Avenue, San Anselmo, California 94960; [email protected]
3Infometrix, Inc., 11807 North Creek Parkway South, Suite B-111, Bothell, Washington 98011; [email protected]
4GeoMark Research, Ltd., 9748 Whithorn Drive, Houston, Texas 77095; [email protected]
5Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Stanford, California 94305; [email protected]

ABSTRACT

The prolific Los Angeles basin in California may be the most petroliferous province on Earth per volume of sedimentary fill. However, because most exploration in the basin occurred prior to the advent of modern geochemical methods, genetic relationships among the various petroleum accumulations and their source rocks have remained speculative. A training set of 24 source-related biomarker and stable carbon isotope ratios for 111 non- or mildly biodegraded oil samples from the basin was used to construct a chemometric (multivariate statistics) decision tree. The decision tree allows genetic classification of additional oil or source-rock extract samples that might be collected. The decision tree identifies 6 tribes and a total of 12 genetically distinct oil families. The families have different bulk properties, such as API gravity and sulfur content, which were previously explained as resulting from secondary processes, including thermal maturity or biodegradation. However, the chemometric assignments are based on genetic properties that reflect distinct organofacies. The oil families occur in different locations and reservoir intervals in the basin, consistent with their origins from different organofacies of active source rock. The source-rock depositional environment for each oil family can be inferred using biomarker and isotope ratios. The samples show stable carbon isotope ratios for saturate and aromatic hydrocarbons that indicate different organofacies of Miocene marine source rocks. Tribes 1 and 2 straddle the central trough, mainly occur east of the Newport-Inglewood fault zone (NIFZ), and show evidence of proximal, clay-rich source rock deposited under suboxic conditions with elevated angiosperm input. Tribes 3–6 occur west of the NIFZ and show evidence of more distal, clay-poor source rock deposited under anoxic conditions.

Geochemistry and stratigraphy of the oil tribes (1–6 below) suggest the following source-rock organofacies:

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