Petrogenesis And Accumulation Analysis Of Middle And Western Member Of Southern Margin Of Junggar Basin

Based on the study and analysis of the organic facies and source ranges of source rocks,it is considered that the source rocks of Anjihaihe formation(E_2-3a)in the southern margin of Junggar basin are in the immature low mature stage and can not be used as effective source rocks;The middle and lower Jurassic(J₁₊₂)is in the mature over mature stage,and the oil and gas found in the current exploration in the southern margin should mainly contribute to the Jurassic source rocks.The location and scale of source foci determine the distribution of oil and gas reservoirs.Hydrocarbon generation centers are mainly distributed in Sikeshu sag and homatu anticline,and the main oil and gas reservoirs are also found in these two areas.The maturity of the middle and lower Jurassic coal measure source rocks is"low in the West and high in the East",and the overall hydrocarbon phase behavior is the pattern of"oil in the West and gas in the East".Crude oil can be divided into two categories according to its characteristics:the middle crude oil belongs to the characteristics of high salinity,reducing environment and maturity high maturity;The crude oil in the west section is characterized by low salinity,oxidation environment and low maturity maturity.There is a good correlation between oil sources in the southern margin,and natural gas contributes to the high mature coal measure source rocks in the middle and lower Jurassic;The light oil in the west section contributes to the humic source rock of the middle and lower Jurassic in the middle and lower mature stage;The middle section is dominated by gas production,light oil and condensate mainly contribute to Jurassic humic source rocks,and Cretaceous crude oil may be mixed in the upward migration process.The oil and gas in the middle section of the southern margin are mainly distributed in Ziniquanzi formation(E_1-2z),and the west section is mainly distributed in the bottom strata of Jurassic and Cretaceous.The hydrocarbons are discharged from Jurassic and migrate upward along the fault.The mudstone and gypsum of Cretaceous and Anjihaihe formation（e2-3a）provide sealing effect and form oil and gas reservoirs.