Geochemical Characteristics of Crude Oil and Oil Source Correlation in Yanchang Formation(Upper Triassic) in Wubao Area, Ordos Basin

Key words: 
• oil geochemistry /
• oilsource correlation /
• Yanchang Formation /
• Wubao area /
• Ordos Basin /

Abstract: The oil sources in the Yanchang Formation of the Ordos Basin has always been controversial, especially in the reservoir Chang8 to Chang10.According to the crude oil of Chang6 to Chang10 of Yanchang Formation in Wubao area, the article discusses the physical properties, the group composition, the biomarkers, and the oiloil and oilsource correlation in terms of their geneses and the origin of petroleum in respective reservoirs so as to provide the geological basis for the area's petroleum exploration and prediction. The result shows that the group composition of Chang6 to Chang10 is characterized by the highest content of the saturated hydrocarbon, which follows the aromatics, and non hydrocarbons are the lowest. Chang6 to Chang10 are all mature crude oil, revealing the hybrid origin of the lower hydrobionts and the higher plants, however, the crude oil in Chang6 is distinctively different from that in Chang7 to Chang10 in terms of its group composition. The crude oil in Chang6 is the early migration result of hydrocarbons in the source rock of Chang7 to Chang10, whose maturity is the lowest, while the crude oil in Chang7 to Chang10 is migration result of hydrocarbon generating peaks, whose maturity is superior. And the oil and source correlation demonstrates that Zhangjiatan shale, at the bottom of the Chang7, contribute to the oil pools in Chang6 and Chang7, in addition, the effective source rocks on the top and middle of Chang7 and Chang6 make difference. The oil pools in Chang8, mixed geneses crude oil, are mainly the down migration result of the lower source rocks in Chang7, secondly Chang8 and Lijiapan source rocks on the top of Chang9 do. The oil pools in Chang9 are formed by the downward flow of Lijiapan shale, but the petroleum in Chang10 is accumulated may by the downward migration of the effective source rocks of Chang92. The thermal maturity should be the most responsible for the differences between crude oil group compositions which are far away from the dominant source rocks.