Oil-Source Correlation And Migration Trace In The Lower Member Of The Palaeogene Xingouzui Formation In Jiangling Depression

The hydrocarbon source rocks in the lower member of Xingouzui formation is one of the most important hydrocarbon source rocks in Jiangling Depression.Taking hydrocarbon source rocks and crude oils from different areas of Jiangling Depression as research objects,combined with a series of geochemical analysis techniques such as maceral?vitrinite reflectance?kerogen carbon isotope?GC-MS?single hydrocarbon carbon isotope analysis?and analysis of nitrogen compounds in crude oil,the comprehensive geochemical study of the source rocks in the lower member of Xingouzui Formation was carried out in this paper.On the basis of the classification of crude oil in Jiangling Depression,this paper makes oil-source comparison in combination with the geological background of the study area,explores the source of crude oil in each region,and finds out the contribution of source rocks in each region.Through the analysis and statistics of the hydrocarbon source rocks of Xingouzui Formation,it is found that there is an obvious correlation between the formation color of the development environment of the hydrocarbon source rocks and the TOC.It is found that the source rocks of X-?in the lower member of Xingouzui Formation are mainly miscellaneous rocks with low organic matter abundance,while the color of X-?and X-?is dark,which reflects the relatively reductive sedimentary environment and relatively developed organic matter.In terms of the abundance of organic matter in the source rocks,the effective source rocks of X-?in the lower member of Xingouzui Formation are generally underdeveloped,and effective source rocks are only developed in the western part of Jingzhou,Huayuan area and Balingshan area.In general,effective source rocks are developed in the X-?in the whole region,and the high value area of TOC is mainly concentrated in the area from west Jingzhou to Wancheng sag,In addition,Zifusi sag to the southern slope also has a certain distribution of high abundance of hydrocarbon source rocks.The Nige formation also widely develops effective source rocks,and the high value area is from the west side of Zifusi syncline belt to the area of Wancheng syncline.High value of TOC of the X-III is distributed in Wancheng syncline belt and Zifusi syncline belt.In terms of organic matter in the source rocks,the types of organic matter in source rocks varies from region to region.The organic matter type is?-?₁ in the two layers of Wancheng area.The X-?and the Nige formation of Jingzhou anticline zone are mainly humic organic matter,the type of organic matter of the X-?is relatively good,which is mixed type sapropel-type organic matter.The two layers of northern Jingzhou anticline zone are dominated by?organic matter.In terms of the maturity,the source rock samples have all reached the mature stage,and the source rocks of X-?which is from Jingzhou anticline zone and the X-??X-?which are from northern Jingzhou anticline zone are lower than other regions.Based on the analysis of biomarker,single hydrocarbon isotope and nitrogenous compounds in the lower member of Xingouzui Formation of Jiangling Depression,the oil sources in each area were determined.It is found that all the crude oils in the study area show the characteristics of mature oil and formed in a relatively deep and relatively highly reducible environment.According to the differences between the parameters of biomarkers,the crude oil in the study area is divided into two categories:The first kind of crude oil is from Wancheng area and the southern region,in this kind of crude oil,homohopane compounds content is very low and high maturity and less contribution of terrestrial organic matter;Another type of crude oil is from the Jingzhou anticline zone,its maturity is lower than the first kind of crude oil,it has some terrestrial organic matter contribution and there is a certain abundance of homohopane series compounds,and the oil maturity in the northwest of Jingzhou anticline zone is significantly greater than that in the central and southeastern part.The results of oil-source comparison show that the two types of crude oil may have the contribution of source rocks in different regions and different layers:the two layers of northern Jingzhou anticline zone are the main source rocks of two kinds of crude oil,but the contribution of different layers is different.In addition,the two layers of Wancheng area have some contributions to?kind of crude oil and?₂ kind of crude which is distributed in the central and southeastern part of Jingzhou anticlinal belt.From the perspective of oil and gas migration,the crude oil of Xinguouzui formation in the northwest of Jingzhou anticline belt and the north of Wancheng area should come from the southeast of Wancheng area,while the south part of Jiangling Depression moved to the southeast of Jingzhou anticline as the oil source area.In addition,the analysis indicates that the crude oil from ling66-p8 well should be contributed by double sources from Wancheng and the south area.There may also be local near-source contributions in the Li3-10 and Li3-12well.