Oil-Source Correlation And Oil-Gas Migration Of The Fengcheng Formation In Southern Mahu Sag

As the main source rock,the Permian Fengcheng Formation in Mahu Sag of Junggar Basin provided a large amount of oil and gas for the Carboniferous-Mesozoic reservoirs.The existing exploration practice shows that the sag has great potential for oil and gas exploration and development.At present,there are a lot of research achievements on petroleum geology in Mabei area,but few in Manan Area,especially there still are many problems in the research on types,sources and distribution of crude oils and hydrocarbon migration of the Fengcheng Formation.This limits the next exploration and development of oil and gas in the Manan area in a large extent.According to the Fengcheng Formation source rocks and the crude oil samples test results,including the pyrolysis of organic carbon,extract fractionation,saturated fraction GC-MS analysis,this paper evaluated organic geochemical characteristics of the crude oil and source rock in the study area.Based on the distribution patterns of C₂₀,C₂₁ and C₂₃ tricyclic terpanes,the crude oils of the Fengcheng Formation are divided into four types of A,B,C and D.Their configuration of C₂₀,C₂₁ and C₂₃ tricyclic terpanes changes from ascending pattern,mountain peak pattern,valley pattern to descending pattern,with a gradual increasing maturity.The distribution of different type of crude oils displays that A,B,C and D crude oils occurence in order from high slope area to the inner sag.The oil-source correlation results show that the four types of crude oils came all from the source rocks of the Fengcheng Formation,and the type A crude oils were mainly from the source rocks locating in slope area.Type B crude oil mainly came from the source rocks in the lower slope position.Type D crude oil mainly came from the source rocks in the deep sag,while type C was mainly the mixture of type A and type D.The physical properties and geochemical migration parameters of crude oil indicate that the oil mainly migrates from east to west and from the inner position of the sag to the high position of the edge of the sag,in which the permeable strata is the main migration channel,and the faults are slightly adjusted vertically.In the high position of the structure,buoyancy is the main driving force of oil and gas migration,while in the low position of the structure,residual pressure is the main driving force of oil and gas migration.