Print this pageAbstract: Carbon Isotopic Compositions Identify Four Petroleum Types in Northern California
Leslie B. Magoon, Paul G Lillis, Augusta Warden, Richard C. Stanley, John Castano
On the basis of carbon isotopic compositions of saturated and aromatic hydrocarbons in 16 oil and 6 condensate samples from fields and seeps in northern California, four petroleum types have been identified. The isotopically heaviest type is represented by oils from the Petrolia, Petaluma, and Pinole Point fields with saturated hydrocarbon (SH) ^dgr13C values of -22.9±0.6^pmil and aromatic hydrocarbon (AH) ^dgr13C values of -22.1±0.5^pmil. Oil seeps in the Clear Lake area and oil samples from the Arbuckle and Bunker gas fields have SH ^dgr13C values of -26.4±0.9^pmil and AR ^dgr13C values of -25.1±1.1^pmil and represent a second petroleum type. Condensate samples from Dutch Slough, Knightsen, Lindsey Slough, nd Rio Vista gas fields are considered a third type and have a whole condensate ^dgr13C value of -26.2±0.5^pmil. Oil samples from the Brentwood and Livermore oil fields have a SH ^dgr13C value of -28.7±0.5^pmil and AH ^dgr13C value of -27.4±m0.3^pmil, and represent the fourth type.
Volumetrically, the amount of oil and condensate recovered from these fields is small when compared to the fields in southern California. However, the petroleum potential of northern California may be underestimated because the petroleum geology is poorly understood and source rocks are poorly documented. The geographic distribution of these four petroleum types in northern California, predominately a dry-gas province, suggests that the petroleum geology is complex. For example, the Petrolia field is 180 miles northwest of the Petaluma and Pinole Point fields, and the Brentwood and Livermore oil samples are isotopically similar but come from contrasting geologic settings. Although ^dgr13C values are similar, the relationship of the condensate in the Rio Vista area to the oi samples in the Clear Lake area is unclear. Their isotopic similarity but physical dissimilarity could be due to migration or to source facies variations.
AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California