Variations in the sterane carbon number distributions of marine source rock derived crude oils through geological time

Journal Article · Fri Jan 01 04:00:00 EST 1988 · Org. Geochem.; (United States)

DOI:https://doi.org/10.1016/0146-6380(88)90115-5· OSTI ID:5326427

Grantham, P J; Wakefield, L L

The analysis of the sterane data of a large set of crude oils (414) derived from marine carbonate (27) and siliciclastic source rocks (14) where influences of terrestrial or lacustrine derived organic matter can reasonably be excluded, shows that there are increases in the relative content of C/sub 28/ steranes and decreases in the relative content of C/sub 29/ steranes through geological time. There are no consistent variations in the relative content of C/sub 27/ steranes through time. With one major exception (a Proterozoic oil from Oman), Paleozoic and older crude oils are thus generally characterized by strong predominances of C/sub 29/ steranes and low relative concentrations of C/sub 28/ steranes. Significantly higher proportions of C/sub 28/ steranes and lower proportions of C/sub 29/ steranes occur in oils derived from Jurassic and Upper Cretaceous source rocks. These changes through time do not appear to reflect the chemical evolution of the sterols of one particular variety of marine organism: the increase in C/sub 28/ steranes may be related to the increased diversification of phytoplantonic assemblages in the Jurassic and Cretaceous. Possible sources of the C/sub 28/ sterols necessary for the observed changes in crude oil steranes includes diatoms, coccolithophores and dinoflagellates. Although the technique does not give an accurate means of determining the age of the source rock of a crude oil it is possible to distinguish younger crudes derived from the Upper Cretaceous and Tertiary from Palaeozoic and older crudes.

• Research Organization: Koninklijke/Shell Exploratie en Produktie Laboratorium, Rijswijk (Netherlands)
• OSTI ID: 5326427
• Journal Information: Org. Geochem.; (United States), Journal Name: Org. Geochem.; (United States) Vol. 12:1; ISSN ORGED
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
023000* -- Petroleum-- Properties & Composition
AGE ESTIMATION
CARBONATE ROCKS
DISTRIBUTION
ENERGY SOURCES
FOSSIL FUELS
FUELS
GEOLOGIC HISTORY
HYDROXY COMPOUNDS
MOLECULAR WEIGHT
ORGANIC COMPOUNDS
PETROLEUM
ROCKS
SEDIMENTARY ROCKS
SOURCE ROCKS
STEROIDS
STEROLS
STRUCTURAL CHEMICAL ANALYSIS
TIME DEPENDENCE