| Junggar Basin is an important large-scale superimposed petroliferous basin in western China.The shallow oil and gas exploration can be traced back to the Qing Dynasty,it has an important position in the history of China’s oil and gas exploration,the mind of the exploration has undergone a complex and tortuous process,but the foreland basin has been the focus of attention. According to the latest division scheme of tectonic units formulated by Xinjiang Oilfield Company,the Sikeshu sag basin of the study area is one of the forty-four full secondary structure elements belonging to the southern edge of North Tianshan piedmont thrust belt of the first level structural units.The west of the sag is Aibi Lake in Jinghe region,the east of the sag is the southern area of the Hongche fault and it is connectted with the anticline of Houmatu;The southwest of the sag is the Erin black bilgen mountain of Tianshan mountains,the southeast of the sag is Qigu fault-fold belt,the northern of the sag go through Aika fault and it gradually transits to Chepaizi bump.The main part of the sag is a big strike of NWW monoclinic.It is mainly located in the territory of Wusu and Kuitun in Xinjiang.The oil and gas exploration area is approximately6400square kilometers.The depression is developed on Carboniferous and Cambrian crystalline and it turns into extruded depression.It experienced three evolutionary stages of pressure twist,depression,foreland successively. The main construction formed in Himalayan stage.The main sedimentary strata are Jurassic and Quaternary.The depression has experienced exploration about80years since1937and it has been found four oil and gas structure,including Dushanzi,West lake,Kain Dick and Gao Quan.But the multiphasic structural evolution process makes the region become more complicated between conditions of reservoir-forming and correlation of oil-source,which has failed to achieve a breakthrough in recent years. With the oil company paying more attention to the middle-shallow layer of the southern margin gradually and the importance of the petroleum system and the petroleum accumulation dynamics becoming more and more prominent in the present research of oil and gas exploration and development,The research of the rules of petroleum accumulation of the Sikeshu sag is imminent especially in source rocks and oil source correlation.This study collects major seismic data,well logging,well testing and laboratory analysis data of rock systematically and comprehensively and it is based on the principles and methods of structural geology,sedimentology,reservoir geology,petroleum systems and petroleum accumulation dynamics, oil and gas geochemistry and petroleum geology.It uses basin modeling applications, multi-criteria oil-source correlation index and fluid inclusion analysis techniques to research the conditions of source rocks and oil and gas migration and accumulation and divises the favorable area of the mid-upper assemblage in the region by using source-control theory as a guide and uniting basic geological.The results show that the Sikeshu sag mainly developed the Middle-Lower Jurassic source rocks and the Anjihaihe formation of Paleogene source rocks and the Middle-Lower Jurassic source rocks focus on Sangonghe formation.The thickness of the mudstone from Badaowan formation is small and the thermal evolution stage is high.However,the organic matter abundance of Xishanyao formation is lower,which are poor source rocks.Carbon isotopic composition,saturated hydrocarbons and the biomarker characteristics display that the kerogen of Sangonghe formation source rocks is largely type Ⅱ2formed by terrestrial kerogen in the sedimentary environment of weak oxidation-weak reduction.The measured Ro and thermal history modeling show that its source rocks have high degree of thermal evolution in the region and it have reached the hydrocarbon generation threshold now.Ro can be up to about1.3%in the southern piedmont region and its thickness is large and distribution is wide,which is the main source rocks.The kerogen of Anjihaihe formation source rocks is type Ⅱ1formed by typical aquatic organisms kerogen deposited in a weak reduction environment.It is controlled by violent settlement of Paleogene sag and water is deep and stable,which make the organic matter abundance of Anjihaihe formation source rocks be high and TOC can reach more than0.6percent in the region.According to the relationship between sedimentary facies and organic matter abundance,it can be inferred that TOC generally reaches to about1.5%in south-central furrow region. Due to the fast deposition rate,the thickness of Anjihaihe formation source rocks is great.But its interment is shallow,generally in the range from2000meters to3000meters.It is also controlled by Junggar basin.The thermal evolution stages of Anjihaihe formation source rocks are low and only reach to the hydrocarbon generation threshold in the south-central area.The main reservoiring period which reach to the hydrocarbon generation threshold is only exist in the the southern piedmont.The distribution of the effective source rocks is small,which can be the secondary source rocks in the study area.The middle and upper combination of crude oil can be divided into three kinds.A class crude oil originates from middle and lower Jurassic series,and in vertical direction it mainly exists in the Ziniquanzi groups and in the plane in the Xihu anticline and Kayindike Lake anticline.B class crude oil belongs to mixed source,It only exists in the Ziniquanzi group in Kayindike anticline.C class crude oil come out from Anjihaihe group and it vertically mainly originates in Shawan group while modicum in Anjihaihe group.It exists in all area in the plane.however,the output is low.The oil and gas in the study area is mainly dominated by close vertical migration.It is mainly controlled by the poor connectivity of sand body form different provenance.It does not have ability of the long-range migration because of conditions A small amount of oil and gas migrates through Cretaceous-Jurassic regional unconformity from south to north and it accumulates in the middle-upper trap through the fault,but the scale is small such as Sicanl and Ka9well.The study area can be summarized into two main accumulation models.One is near-source with single stage,which is found in Gaoquan,Xihu,Dushanzi,the other is heterology with two stages,which exists in Kayindike region.The main controlling factors of hydrocarbon accumulation have differences between the north and the south.It is mainly controlled by the source rock and fault in Kayindike region.Meanwhile,it is affected by the configuration relationship between the fracture and sand body in Gaoquan,Xihu and Dushanzi.In a word,the condition of the source rock and migration are the keys for hydrocarbon accumulation.Through analyzing the exploration potential of the study area based on the theory of controlled by the source rock,the southern anticline is the most favorable area and north central part of Aika fault,northwest slope take the second place.However,with the further exploration and the deepening understanding of structure,sedimentation and other basic geology,especially the discovery of oil sources faults in slope,it will have the potential to further enhance the conclusions of this study. |
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