Characteristics and Petroleum Geochemical Significance of Trace Transition Elements in Crude Oils and Organic Materials Extracted from Jianghan Oil Field

With the method of neutron activation analysis(NAA), the concentrations of trace transition elements: Sc, V, Cr, Mn, Fe, Co, Ni, and Zn in crude oils and organic materials extracted from source rocks from the Jianghan oil field have been determined. The concentrations of these elements in the separated fractions: asphaltene, non-hydrocarbon and aromatic hydrocarbon have been also studied. The comparison of the concentrations of trace transition elements in different fractions and the correlations among all the elements have been studied and discussed in detail. To research the relationship among the sources of crude oils and source rocks, the biomarkers have been determined from several samples of crude oils and source rocks, and the results show that these samples are of the same source. Meanwhile, the concentrations of trace transition elements in the same samples have also been determined. The logarithmic distributions normalized to the ratios of concentrations and the concentrations normalized to the related values of elemental concentrations in the North American Shale Composites have been studied. The results show that the patterns of the logarithmic distributions among the crude oils or source rocks, which are of same source, are very similar, and so are among the correlated fractions of these samples. Therefore, it is proposed that these patterns are useful in the correlation among crude oils and source rocks, and it may be better to use these patterns in the correlation than to directly use the concentrations or rations of some trace elements.