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samples of shales and mudstones developed in reducing hypersaline and freshwater setting and 20 oil samples of Bamianhe oilfield, Bohai Bay basin were collected for a detailed study of petroleum system. Composition and distribution, especially significance of steroids, are discussed as a part of those. Abundant steroidal biomarkers, including C 27-29regular steranes, C 28-304-methyl steranes, dinosteranes and aromatic steranes, were detected. Results show that the composition and distribution of the steroids in samples studied are functions of thermal maturity, organic source, paleoenvironment and lithology of potential source rocks. Alga-rich E s 4 shales (brackish water) developed in the south slope of depocenter (Niuzhuang sag) were found particularly rich in steroidal biomarkers including C 304-methyl steranes and dinosteranes. E s 3 mudstones (fresh water) were found devoid of dinosteranes. Distribution patterns of regular steranes are completely different from methyl steranes indicating different origins of the specific compounds of the fraction. Diagnostic distribution of steranes in rock extracts of diverse intervals makes the compounds to be essential indictors of source-rock tracing. Methyl steranes prove to be much more useful in oil-source rock correlation than regular steranes. Results also show that alga-rich E s 4 shales located in the south slope are not likely the primary source rock responsible for the oils discovered based on the composition and distribution of steroids.
samples of shales and mudstones developed in reducing hypersaline and freshwater setting and 20 oil samples of Bamianhe oilfield, Bohai Bay basin were collected for a detailed study of petroleum system. Composition and distribution, especially significance of steroids, are discussed as a part of those. Abundant steroidal biomarkers, including C 27-29 regular steranes, C 28-304-methyl steranes, dinosteranes and aromatic steranes, were detected. Results show that the composition and distribution of the steroids in samples studied are functions of thermal maturity, organic source, paleoenvironment and lithology of potential source rocks. Alga-rich E s 4 shales (brackish water) developed in the south slope of depocenter (Niuzhuang sag) were found particularly rich in steroidal biomarkers including C 304-methyl steranes and dinosteranes. E s 3 mudstones ( fresh water) were found devoid of dinosteranes. Distribution patterns of regular steranes are completely different from methyl steranes indicating different origins of the specific compounds of the fraction. Diagnostic distribution of steranes in rock extracts of diverse intervals makes the compounds to be essential indictors of source-rock tracing. Methyl steranes prove to be much more useful in oil-source rock correlation than regular steranes. Results also show that alga-rich E s 4 shales located in the south slope are not likely the primary source rock responsible for the oils discovered based on the composition and distribution of steroids.