| The central Junggar basin is rich in oil and gas resources,which is one of the main oil and gas distribution areas in the Junggar basin.However,there are many hydrocarbon bearing structures,sets of source rocks and hydrocarbon generating centers,which result in the complex relationship between hydrocarbon and source rocks and bring great challenges to hydrocarbon exploration in the study area.This thesis systematically analyzes the differences of carbon and hydrogen isotopic composition of individual n-alkanes and biomarkers characteristics of crude oils in typical oil and gas reservoirs in the central Junggar basin,and divides the types of crude oils.In combination with the evaluation of source rocks,the oil-source correlation of various types of crude oils was carried out,and defined the hydrocarbon sources of different structural zones in the central Junggar basin,and the following understandings have been obtained:Based on the characteristics of biomarkers and carbon and hydrogen isotopic composition of individual n-alkanes,the crude oils in the study area were subdivided into four categories.Ⅰcrude oil was distributed in the eastern region in central Junggar basin and well Yong 2（J2x）,which was derived from Jurassic mudstone,with heavy carbon isotopic composition,high Pr/Ph ratios,contains almost no gammacerane andβ-carotene,and low tricyclic terpanes contents.The carbon isotopic composition of individual n-alkanes is relatively heavy and has a descending distribution,indicates the import of higher terrestrial plants.This type of crude oil was depositted in fresh water environment,which is characterized by relatively light hydrogen isotopic composition of individual n-alkanes ranging from-180‰to-160‰.Ⅱcrude oil（well Yong 6 and well Yong 9 K1tg）was derived from Permian mudstone（P1f）,with light carbon isotopic composition,extremely low Pr/Ph ratios,extremely high gammacerane andβ-carotene contents,and medium tricyclic terpanes contents.The carbon isotopic composition of individual n-alkanes is relatively light,decreases rapidly and then gradually stabilizes with the increase of carbon number.This type of crude oil was depositted in saline lacustrine environment,which is characterized by relatively heavy hydrogen isotopic composition and showing“V”line distribution.Ⅲcrude oil is characterized by relatively light carbon isotopic composition,medium Pr/Ph ratios,medium gammacerane,β-carotene,and tricyclic terpanes contents,and complex carbon and hydrogen isotopic composition of individual n-alkanes.This type of crude oil can be subdivided into two small groups.Ⅲa（well Yong1 and well Yong 3 J2x）was mixed oil,which was subjected to biodegraded and two stages of hydrocarbon accumulation.In the first stage oils from Permian（P2w）were biodegraded,and in the second stage oils were derived from Jurassic.Ⅲb crude oil was distributed in Zhengshacun,Moxizhuang oilfield and well Yong 3（J1s）,central Junggar basin and well Yong 2（J2x）,which was similar toⅢa crude oil,and derived from Permian and Jurassic mudstone,but there is no obvious biodegradation.Ⅳcrude oil was distributed in the Mosuowan uplift,which was mixed oil derived from Permian（P2w and P1f）mudstone. |
