Controls on the variation of crude oil quality, Santa Maria basin, California
- Geological Survey, Denver, CO (United States)
Previous studies have documented that early generation of oil from the Miocene Monterey Formation produces low-gravity (6-20{degree} API), high-sulfur (4-8 wt.%) crude, although some fields in the Santa Maria basin, California, contain higher gravity (20-39{degree} API), lower sulfur (0.5-4 wt.%) oil. Geohistory analysis and geochemical data suggest that the variation in gravity appears to be controlled primarily by the timing of oil generation and migration and the age of the traps. Biodegradation and other secondary processes that alter the oil gravity occasionally are significant. Early generation began in the late Miocene, with low-gravity oil migrating into existing traps. These older traps were mostly stratigraphic (Santa Maria Valley field), although normal faults and minor folds may also have been effective traps. Anticlines of Pliocene and Quaternary age (Orcutt field) trapped higher gravity oil that was generated and migrated at a later and more mature stage. This younger oil is higher quality because (1) at higher levels of thermal maturity the source kerogen contains reduced amounts of sulfur due to earlier pulses of generation and expulsion; and (2) some of the Monterey Formation kerogen in the basin is lower in sulfur initially and requires higher levels of thermal maturity to generate oil.
- OSTI ID:
- 5184052
- Report Number(s):
- CONF-9103128--
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (United States), Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States) Vol. 75:2; ISSN AABUD; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
023000* -- Petroleum-- Properties & Composition
API GRAVITY
BIODEGRADATION
CALIFORNIA
CENOZOIC ERA
CHEMICAL COMPOSITION
CHEMICAL REACTIONS
CHEMISTRY
DECOMPOSITION
DENSITY
DEVELOPED COUNTRIES
ENERGY SOURCES
ENVIRONMENTAL TRANSPORT
FOSSIL FUELS
FUELS
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
MASS TRANSFER
MATURATION
MINERAL RESOURCES
MIOCENE EPOCH
NORTH AMERICA
PETROLEUM
PETROLEUM DEPOSITS
PHYSICAL PROPERTIES
RESOURCES
SEDIMENTARY BASINS
SULFUR CONTENT
TERTIARY PERIOD
USA