Study On Characteristic And Formation Mechanism Of Complex Mixed Crude Oil In Western Junggar Basin

This paper focused the study on complex crude oil in Chepaizi Salient of the western margin of the Junggar Basin the western margin of the Junggar Basin.Gas chromatography-mass spectrometry(GC-MS),tandem mass spectrometry(GC-MS/MS)and individual hydrocarbon carbon isotope mass spectrometry(GC-IRMS)and other analysis technology were used to the geochemical characteristics of the mixed oil.Combined with the studies of source rock and petroleum geology background,the formation mechanism of mixed oil were analysisedResults of whole oil isotope,oil pyrolysis and GC analysis showed that the distribution of crude oil in Chepaizi Salient presented a special characteristic of oil dense,which was domained by the differences of oil source,oil mixing and different levels of biodegradation.Using Detail information of GC-MS,GC-MS/MS and GC-IRMS,the crude oil of Chepaizi Salient could be divided into two categories and four subcategories,including A,B11,B12 and B2.The Class A oils are heavy oils which charged by the late filling;While the Class B oils are lighter crude oils with more complex mixed-source phenomenon.Via detailed study and correlation analysis of the gechemical characteristic and distribution of potential souce depression mud rocks,combined with the distribution of residual formation of Chepaizi Salient and migration system,the characteristics of oil source and mixed-source of crude oil in Chepaizi Salient were studied and the process of its formation was infered.With whole oil isotope,individual hydrocarbon carbon isotope and tricyclic terpanes parameters,the Class A oils and the late fillings were infered as oils charged by Permian source rocks of Changji Depression.The oil migrated into the reservoit through the fault and unconformity,and then sufferd terrible biodegration.As a result,the migration pathway was blocked and the late charging phenomenon occurred at the point of filling.Individual hydrocarbon isotope,diasterane parameters,maturity parameters and tricyclic terpanes parameters showed that the Class B12 oils were oils from Carboniferous source rocks of Chepaizi Salient mixed with other crude oil.The distribution of sand formation and fault led to the distribution of Class B12 mixed oils and mixed-source area.Combined the geochemical analysis results of Ka 003 J3q oil and potential oil source depression,the Class B11 oils were from the Jurassic mud rocks of Sikeshu Depression while the Class B2 comed from the Coal source and Carbonaceous mud rocks of Sikeshu Depression.The main factors of intern differences of B11 and the significantly differences between B11 and B2 were the Internal heterogeneity of Jurassic source and the "geochromatographic" effect of oil migration.The mixed oil characteristics of Chepaizi Salient were determined and some powerful evidence were found to present the different theory of the mixed-source issues in the study area.A breakthrough in the understanding of Carboniferous oil sources was made and the distribution characteristics of mixed-source area were analyzed.