Study on the Property and Origin of Crude Oil of Yanchang Formation in Jiyuan Oilfield,Ordos Basin

Based on the comparison of multiple physicochemical properties including the property of crude oil and oilfield water,group composition of crude oil and hydrocarbon source rock,gas phase chromatography of saturated hydrocarbon and the characteristics of terpane,sterane and other biomarkers,the results showed that the properties of crude oil were especially complex for Chang-4+5,Chang-6 and Chang-8 of Yanchang Formation in Jiyuan Oilfield,Ordos Basin;there were obvious differences in the maturity,source rock depositional redox environment and type.The appraisal of hydrocarbon source rock indicated that the quality and type of organic matter of dark mudstone for Chang-4+5,Chang-6,Chang-7,Chang-8 and Chang-9 of Yanchang Formation were different,but all had the ability of hydrocarbon generation and expulsion.The comparison of oil sources further proved that there were multiple accumulation effects of oil supply with mixed sources in the accumulation process;the crude oil of Chang-8 came from hydrocarbon source rock of Chang-7-Chang-8;the crude oil of Chang-6 came from hydrocarbon source rock of Chang-7-Chang-6;the crude oil of Chang-4+5 came from multiple hydrocarbon source rocks of Chang-7,Chang-6 and Chang-4+5.