New Geochemical-Chemometric Evidence for Multiple Miocene and Eocene Oil Families in the San Joaquin Basin, California

Chemometric analyses of geochemical data for 165 crude oils allowed identification of genetically distinct oil families and their inferred source rocks and provided insights into migration pathways, reservoir compartments, and filling histories in the San Joaquin Basin. In the first part of the study, 17 source-related biomarker and stable carbon isotope ratios were evaluated using principal components analysis (PCA) to identify genetic families. In the second part of this study, ascendant hierarchical clustering (AHC) based on the Ward aggregation method was applied to the terpane (m/z 191) fingerprints for the oil samples in order to compare with the PCA results. The results for the two chemometric methods are remarkably similar, despite differing data input and assumptions. Recognized source rocks for the oil families include the (1) Eocene Kreyenhagen and Tumey formations, (2) Miocene Monterey Formation (Buttonwillow depocenter), and (3) Miocene Monterey Formation (Tejon depocenter).

AHC identifies 22 oil families in the basin as corroborated by independent data, such as stable isotope ratios, sample location, reservoir unit, and thermal maturity maps from a three-dimensional basin and petroleum system model. Eight oil families originated from Eocene source rock in the basal Kreyenhagen Formation (five families) and the overlying Tumey Formation (three families) in the Buttonwillow depocenter. Fourteen Miocene families are from upper and lower Monterey Formation source rocks and migrated from the Buttonwillow and Tejon depocenters north and south of the Bakersfield Arch, respectively. Both the Eocene and Miocene families show little cross-stratigraphic migration due to seals within the source rocks. The results help to explain the different filling histories of the oil families in Elk Hills and other fields and improve understanding of migration paths and potential zones of bypassed oil in the San Joaquin Basin. They also show the value of chemometrics applied to large petroleum databases where all samples are analyzed using the same procedures and instrumentation.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California