--> Abstract: Oils and Source Rocks of the Southwestern Los Angeles Basin: Multiple Sources and Different Organic Facies, by T. H. McCulloh, W. L. Orr, D. W. Kirkland, A. J. Koch, and H. M. Chung; #90992 (1993).

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McCULLOH, T. H., W. L. ORR, and D. W. KIRKLAND, (Retired) Mobil, Dallas, TX, A. J. KOCH, Mobil E&P, and H. M. CHUNG, Mobil, Dallas, TX

ABSTRACT: Oils and Source Rocks of the Southwestern Los Angeles Basin: Multiple Sources and Different Organic Facies

The Los Angeles basin, one of the world's most intensively explored basins, is the oil-rich end-member in the global basin richness spectrum (hydrocarbon volume per basin volume). Although first-order factors causing this extreme richness were recognized early, basic questions remain about the petroleum system or systems of this small, deep, hot Neogene basin.

Any extensive sampling of Los Angeles basin crudes shows an extreme range of bulk and isotopic compositions. When organized geographically and viewed geologically, the compositional data reveal patterns that carry genetic information. Where generative source rocks are located, what organic facies have yielded particular oils, what migration directions are implied, for particular traps or accumulations, where mixing from diverse sources has occurred, and when expulsion began in different parts of the basin are questions that can be answered in whole or part. Patterns in the relationships between API gravities and weight-percent sulfur of oils are a key.

Crudes with the highest sulfur at less than 26 degrees API all come from reservoirs at the southwestern basin margin. Their

asphaltenes have elemental compositions relating them to high-sulfur kerogens (type II-S) confined to uppermost middle Miocene phosphatic shales (Monterey facies) west of the Newport-Inglewood and south of the Palos Verdes fault zones. Oils from accumulations closer to the basin center are lower in sulfur and bear the imprint of derivations from ordinary type II kerogens. Mixing of oils from diverse kerogen sources and extremes in levels of thermal maturity implies partly local drainage from separate depocenters.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.