Biomarker Characteristics And Tracing Filling Direction Of Ordovician Crude Oil In Shunbei

Geochemical analysis of 17 crude oil samples from Shuntogol Low Uplift in Tarim Basin was carried out,including separation of oil compositions,gas chromatography of saturated hydrocarbons,gas chromatography-mass spectrometry of saturated hydrocarbons/aromatics,diamond chromatography-chromaticity,gas chromatography of all hydrocarbons and carbon isotopes.The physical properties,group composition,aromatics,biomarkers and carbon isotopes of crude oil were analyzed.Rock pyrolysis analysis and gas chromatographic analysis of total hydrocarbons were carried out on 35 samples of source rocks.Effective source rocks were selected for oil source correlation.Several conclusions were drawed as follows.1.According to the chromatographic peaks of steroids,hopanes,n-alkanes and acyclic isoprenes,it is concluded that the crude oil is well preserved without or very slight biodegradation and secondary washing.C₂₇-C₂₈-C₂₉ steranes show that hydrocarbon-generating parent materials come from open marine environment.Most of the samples show valley-type characteristics of C₂₃>C₂₁<C₂₀,which indicates that the organic parent materials of these crude oils mainly come from a high salinity sea environment.The carbon isotope compositions of saturated hydrocarbons and aromatics fractions change slightly,but those of non-hydrocarbons,asphaltenes and whole oil change more greatly.2.The various crossplots,including n-C₁₇/Pr versus n-C₁₈/Ph,C₂₉ steroid isomer parameters 20S/（20S+20R）versusββ/（αα+ββ）,alkyl naphthalene ratio parameters DNR versus MNR,and methylphenanthrene versus methyldibenzothiophene,showed positive correlations,indicating that the samples were in a high maturity stage.Parametric diagrams of triarylmethanophytes and triarylmethanes were used to make a oil-source rock correlation,and the results show that Ordovician crude oils in the Shunbei oilfield were derived from both of the Lower Cambrian source rocks and Middle-Upper Ordovician source rocks.5.In terms of oil and gas migration,4,6-/（1,4+1,6）-DMDBT,C₂₇-rearranged steroids/regular steroids,C₂₁-/C₂₂₊and methylphenanthrene index were selected to trace oil filling pathways.The results show that there are mainly four filling pathways:from SHB1-5H Well to SHB3 Well,from SHB1-7H Well to SHB1-8H Well,from SHB1-6H Well to SHB1-9 Well and from SHB1-3CH Well to the north.It was presumed that the orientation of hydrocarbon source ovens in the study area is mainly located in Mangar sag and Shuntogol low uplift,and the oil migration and filling directions of the Ordovician reservoirs in Shunbei area are mainly from south to north.