Origin And Source Of Oil And Gas In Key Structures In Wucaiwan-Dajing Area, Junggar Basin

Although the proven reserves of this area are relatively low at the current stage,given that the source rocks of the Carboniferous songkalsu formation are widely distributed in Wucaiwan-Dajing area,Junggar Basin,it still has great potential of exploration and also becomes a key development objective in the east of Junggar in recent years.Since the distribution of oil and gas in Wucaiwan-Dajing area is complicated,the origin and source of oil and gas are controversial.There are two sets of source rocks in this study area:Songkalsu formation of Carboniferous and Pingdiquan formation of Permian.In light of source rocks of Pingdiquan formation,the abundance of its organic matter,whose types mainly are??? 1,is relatively high,reaching the good standard,while the source rocks are in partial mud type and its evolution degree is low,which is reaching the stage of low maturity to maturity.By contrast,the source rocks with large thicknesses of Songkalsu formation are distributed intensively in the whole area.Additionally,with the high level of organic matter abundance,the source rocks in both Wucaiwan and Dajiang area meet the standard of good and medium respectively.The organic matter types of source rock in Songkalsu formation are mainly ?2-? and partially with humus.However,there are also some type ?1 kerogen in Wucaiwan depression,and the maturity of source rock can be considered in the high stage.The natural gas in this study area is distributed major in the Carboniferous strata while less in the Permian strata.The drying coefficient of Carboniferous natural gas is low,mainly wet,and the carbon isotope of natural gas ethane is heavier,which has typical characteristics of coal-type gas.The maturity of natural gas has reached the mature-high mature stage,and the evaluation results of source rocks in the study area are summarized.It is considered that the Carboniferous natural gas is a kerogen pyrolysis gas derived from the source rocks of the Songkalsu formation of the Carboniferous system.The carbon isotope of ethane of Permian natural gas is relatively light,which has typical characteristics of oil-type gas.The maturity is low mature-mature stage,which is the product of source rock of Pingxiaoquan formation of Permian system.There are two different types of crude oil distributed in Carboniferous and Permian strata of this study area.The carbon isotopes of Carboniferous crude oil are heavy and widely distributed in the range of>-25 ‰ and the parent material types are mainly ?2?? and partially in humus type.The evolution degree of crude oil is high,reaching mature to high mature stage,which comes from the source rocks of the Songkalsu formation of Carboniferous system.Different from that,the carbon isotopes of Permian crude oil are lighter,mainly distributing within the range of<-30%‰,and the parent material types a re mainly ???1 type.With the main tape of decaying mud,the maturity of the crude oil is low and only reaches the low mature-mature stage.It is the product of the low mature-mature stage of the source rocks of Pingdiquan formation of Permian system.