Geochemical Characteristics Of Trace Elements In Marine Oils From Tarim Basin And The Implications For Oil Source Correlation

The main source rocks of marine oil in Tarim Basin are the Cambrian Lower Ordovician or middle upper Ordovician.The inorangic geochemical indicators of crude oil are less affected by thermal evolution and secondary alteration,which can be applied to oil-source correlation.Based on the trace element composition characteristics of marine crude oil and two source rock samples,source rocks comparison,oil-oil comparison,and oil-source comparison were performed to find effective oil-source correlation indicators such as Cu/V,Mo/Co,and Ni/Mo.Using cluster analysis to classify crude oil samples into three categories,pointing out their source rock horizon.The comparison indicators of the oil sources of the Type I crude oil are always between the Type ? and Type ?,with mixed source characteristics.They are mainly produced in the northern,central part of the Tarim Basin,only Qu-3 Wells is in the southwestern part.The type ?oil including an end-member oil of the Middle-Upper Ordovician source from Yingmai 2 well has a Cu/V ratio of 0.0005?0.07,when the Mo/Co ratio is mainly distributed in 0.20?5.42 and the Ni/Mo ratio is greater than 62.55,which are comparable to the middle-Upper Ordovician source rocks,mainly found in the northern and the central part.The type III crude oil is mainly produced in southwestern and central part of the basin,and Lunnan-631 well in Lunnan Oilfield,including the end-member oil of the Cambrian source rock from Zhongshen-1C wells.The Cu/V ratio is between 0.13 and 5.47,Mo/Co ratio is mainly distributed in 5.42?21.95,Ni/Mo ratio is not more than 11.97,the lowest is 0.86,comparable with the Cambrian Lower Ordovician source rocks.The distribution of Pb isotope ratios in the three types of crude oil is highly coincident,only samples from Tazhong-103 and Ma-4 belonging to the type ? has light Pb isotope ratios,which are comparable to the Pb isotope composition of Cambrian-Lower Ordovician source rocks in early Hydrocarbon Expulsion stage.Sr isotopes are no significant difference between various types of crude oil,thus it can be confused to correlate oil and source with Sr isotope.