Analysis and occurrence of C sub 26 -steranes in petroleum and source rocks
- Chevron Research Company, Richmond, CA (USA)
- Univ. of Kentucky, Lexington (USA)
The C{sub 26}-steranes previously reported in oils and source rocks have been identified as 21-, 24-, and 27-norcholestanes (1A, 1B, and 1C). Various 24-norcholesterols or stanols, possible prescursors for the 24-norcholestanes, occur widely at low levels in marine invertebrates and some algae, and 24-norcholestanes occur in marine petroleums of Tertiary through Paleozoic age. There are reports of 27-norcholesterols and stanols in recent sediments, but the precursor organisms have not been identified. The natural occurrence of the 21-norcholestane structure is unprecedented. Unlike 24- and 27-norcholestane, 21-norcholestane is in low concentration or absent in immature rocks and increases substantially relative to the other C{sub 26}-steranes in thermally mature rocks, oils, and condensates. This suggests an origin involving thermal degradation of a higher molecuar weight steroid. The ratio of 21-norcholestane to the total C{sub 26}-steranes is shown to be an effective maturity parameter in a series of Wyoming (Phosphoria source) and California (Monterey source) oils. Molecular mechanics MM2 steric energy calculations indicate a relative stability order of 21 {much gt} 27 > 24-norcholestane for the major stereoisomers. Authentic 21-, 24-, and 27-nor-5{alpha}-cholestanes and 24- and 27-nor-5{beta}-cholestanes were synthesized and subjected to catalytic isomerization over Pd/C to yield the full suite of stereoisomers for each.
- OSTI ID:
- 5599333
- Journal Information:
- Geochimica et Cosmochimica Acta; (USA), Vol. 55:4; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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58 GEOSCIENCES
PETROLEUM DEPOSITS
SOURCE ROCKS
GEOCHEMISTRY
MATURATION
STEROIDS
MOLECULAR STRUCTURE
BIOLOGICAL MARKERS
CALIFORNIA
CARBON ISOTOPES
CHEMICAL ANALYSIS
ISOMERS
PETROLEUM
WYOMING
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DEVELOPED COUNTRIES
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FEDERAL REGION IX
FEDERAL REGION VIII
FOSSIL FUELS
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GEOLOGIC DEPOSITS
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NORTH AMERICA
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020200* - Petroleum- Reserves
Geology
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580000 - Geosciences