Geochemical features and source analysis of crude oils from the western slope of Bayanhushu sag,Hailaer Basin

Date analyses of the group-type fractions,saturated hydrocarbon chromatograms and biomarkers of crude oils from the western slope of Bayanhushu sag,Hailaer Basin showed that they are composed of heavy and normal oils and their depositional environment is an anoxic saline-or brackish-lake strongly-reducing environment.The saturated hydrocarbon chromatograms of the oils are distributed fully,indicating non-biodegradation.Carbon isotopes of the bulk crude oil are relatively lighter,with δ13C values around-32‰.The oils contain gammacerane,β-carrotane,relatively lower tricyclic terpanes but higher pentacyclic hopanoids,and steroids composed mainly of ααα-regular steranes with the dominance of C29 steranes.The oil-source correlation showed that the mature oil of Nantun and Tongbomiao Formation in the western slope is derived from mature source rock of Nantun Formation depocenter,while the low-maturity oil of Nantun Formation originates mainly from the low-maturity source rock of the Nantun Formation.