The Studies Of Geochemical Characteristics Of Crude Oils From Qaidam Basin And Oil-rock Correlation

The Qaidam basin is a basin abounding in immature and low mature oils and gases. The studies of generation and exploration and exploitation of immature and low mature oils and gases have not only important theoretic sense, but also obvious applied prospect.In this paper, the following studies have been dealt with, including carbon isotopic compositions, geochemical characteristics, and geological background of Qaidam basin. Sedimentary environments, organic source, maturity and characteristics of biomarkers have been discussed.Carbon isotopic studies show that ?sedimentary environments mainly control carbon isotopic compositions and variations of the western Qaidam oils. While carbon isotopic compositions and variations of the northern Qaidam oils are mainly dominated by organic source.Biomarkers compounds studies show that there are low Pr/Ph ratios, abundant gammacerane and >C30 hopanes and dibenzothiophenes for the western Qaidam oils, reflecting an anoxic and saline-hypersaline environment for their source-rocks. High amounts of C27 steranes, regular steranes, 4-methyl steranes, long chain tricyclic terpanes for the western Qaidam oils indicate that the dominant organic matter source is algal material. The low C29 sterane 20S/(20S+20R) andββ/(β+αα) show a variable maturity for the western Qaidam oils, with immature and low maturity oils being dominant.The northern Qaidam oils have high Pr/Ph ratios, low abundance of gammacerane and >C3o hopanes and abundant dibenzofurans which are indicative of a suboxic and freshwater environment. The high abundance of C29 steranes, low______________________________________________Astract______________________________________________abundance of regular steranes and long chain tricyclic terpanes and absence of 4-methyl steranes suggest that source of the organic matter is largely terrigenous organic matter with higher plants being dominant. The high C29 steranes 20S/(20S+20R) and indicate that the north Qaidam oils are mature oils.Oil-rock correlations show the western Qaidam oils were likely originated from Tertiary source-rocks deposited under anoxic and saline-hypersaline lacustrine environment with algal organic matter being dominant. While the northern Qaidam oils derived from the Jurassic source rocks deposited in freshwater lacustrine environments, dominated by terrigenous organic matter.