Reserch On The Oil-source Correlation,charging Episodes And Timing Of The Triassic Crude Oil In Wuerhe-fengnan Area Of Junggar Basin

Junggar Basin is a typical oil-bearing basin,and Wuerhe-Fengnan area?WFA?is a key exploration area in recent years.The origin of oils and their charging history are controversial in WFA in the Junggar Basin.Based on the theories of petroleum geology and petroleum geochemistry,the accumulation process for the Triassic reservoirs is reconstructed through the measurments of the source rocks,crude oils and fluid inclusions.This study includes:1)evaluating the hydrocarbon generating potential of source rocks;2)identifying the sources of Triassic crude oils in WFA area;3)recognizing the migration direction,charging episodes and timing of crude oils in the target intervals;and 4)establishing the accumulation model of the Triassic reservoirs.Several conclusions are drawn.According to these analyses,the Permian Fengcheng Formation?P₁f?and the Permian Lower Wuerhe Formation?P₂w?source rocks contain kerogen type?with good hydrocarbon generation potential.They are chief source rocks of the oils in the northwest margin of Jungar basin.Four types of crude oils were identified by biomarker compounds such as Pr/Ph,Pr/n C₁₇,Ph/n C₁₈and tricyclodecane distribution characteristics,and carbon isotope characteristics.The crude oils in different structural zones come from source rocks of different strata.The oil in the fault zone derive from the Lower Permian P₁f argillaceous dolomite source rocks in situ in WFA and/or from Mahu depression.The oil in the slope area originated from the Middle Permian Lower P₂w mudstone source rocks in the Mahu depression.Oil reservoirs in various regions have different hydrocarbon migration directions.The hydrocarbons in the fault zone mainly migrated from southwest to northeast,while the hydrocarbons in the slope area mainly migrated from southeast to northwest.The migration direction of transition zone is consistent with that of fault zone.The fluorescence spectra and homogenization temperature measurements of the inclusions indicate that three episodes oil charging took place in the fault zone,corresponding to the Early-Middle Triassic,Early Jurassic,and Early Cretaceous,respectively,and the last two episodes are dominant.The reservoirs in the slope zone were charged with two episodes of crude oil,corresponding to the Early Jurassic and Early Cretaceous,and the later episode is dominant.Finally,a comprehensive three-stage oil migration and accumulation model of Triassic reservoirs in WFA was established.The first-stage oil accumulation occurred during the Middle Triassic,which was concentrated only in the fault zone.The second-stage and third-stage oil accumulation occurred during the Early Jurassic and Early Cretaceous,respectively,with the P₁f-sourced oils concentrated in the fault zone and the P₂w-sourced oils concentrated in the slope area.In summary,oil reservoirs in various regions were derived from different source rocks,with different charging time and accumulation model.