C[sub 7] chemistry of biodegraded Monterey oils from the southwestern margin of the Los Angeles Basin, California

Conference · Mon Jan 01 00:00:00 EST 1996 · AAPG Bulletin

OSTI ID:6580867

Kornacki, A S ^[1]; Mango, F D ^[2]

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1. Shell Offshore, Inc., New Orleans, LA (United States)
2. Rice Univ., Houston, TX (United States)

Biodegraded Monterey oils in the Los Angeles Basin can be differentiated from unaltered Monterey oils by utilizing new C[sub 7] parameters supplemented with standard geochemical data, such as gas-liquid chromatograms and biological markers. Unaltered oils occur below c. 4000 ft in the Wilmington, Sunset Beach, and Seal Beach fields. These medium-gravity crudes (>25[degrees]API) exhibit high C[sub 7] primary test sum values (0.90-1.00), and contain relatively low concentrations of sulfur (0.3-1.0 wt%). Most of these oils were generated at low temperatures (1 10-115[degrees]C). Heavier crudes in relatively shallow pay zones at the Wilmington and Huntington Beach fields are transformed oils that have undergone various degrees of biodegradation and water washing. The residual biodegraded oils, which contain 1.2-1.9 wt% sulfur, have lower C[sub 7] primary test sum values that range from 0.51 to 0.88, and exhibit disturbed (elevated) C[sub 7] oil-generation temperatures. As expected, the transformed crudes contain low concentrations of the aromatic gasoline-range compounds benzene and toluene (which are relatively soluble in water), and they also are depleted in the normal alkanes and (in cases of severe biodegradation) the isoprenoid isoalkanes and steranes. Furthermore, the values of several other C[sub 7] parameters -- such as ratios between [open quote]gem[close quote] and [open quote]non-gem[close quote] structural configurations of C[sub 7] compounds (e.g., 2,3-DMP/2,2-DMP; 1,2-DMCP/1,1-DMCP) -- demonstrate the degree to which bacteria preferentially metabolize certain gasoline-range compounds in petroleum. These effects must be considered when C[sub 7] source parameters (such as selectivity ratios) are used to perform oil-oil and oil-source rock correlations.

• OSTI ID: 6580867
• Report Number(s): CONF-960527-; CODEN: AABUD2
• Journal Information: AAPG Bulletin, Vol. 5; Conference: Annual convention of the American Association of Petroleum Geologists, Inc. and the Society for Sedimentary Geology: global exploration and geotechnology, San Diego, CA (United States), 19-22 May 1996; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
CALIFORNIA
OIL FIELDS
SEDIMENTARY BASINS
PETROLEUM
PRODUCTION
SOURCE ROCKS
PETROLEUM DEPOSITS
GEOCHEMISTRY
CHEMISTRY
DEVELOPED COUNTRIES
ENERGY SOURCES
FOSSIL FUELS
FUELS
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
MINERAL RESOURCES
NORTH AMERICA
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USA
023000* - Petroleum- Properties & Composition
020200 - Petroleum- Reserves
Geology
& Exploration