Analysis On Geochemical Characteristics Of Hydrocarbon Accumulation In Huizhou Depression Which Is Rich In Hydrocarbons

Huizhou Sag,the important offshore petroleum area in Souththern China Sea,is the rich hydrocarbon generating sag in Zhu I Depression of Pearl River Mouth Basin,which have been proven by the exploration,developing two sets of main hydrocarbon source rocks(Wenchang group and Enping group).Lots of work in this study area have been done,however,there have been inadequate understanding about the issues that the contribution of main hydrocarbon source rocks to oil-gas reservoirs,and the characteristics of the hydrocarbon generation and accumulation in all depressions have to be summarized and realized gain and gain,as well as the oil and gas migration concrete paths.Combining with geophysical and geochemical data,we studied the geochemical characteristics of hydrocarbon source rocks,oil-gas migration and accumulation rule,by virtue of the characteristic technology such as the measuring stable carbon isotopic.Through the collection of a large number of hydrocarbon source rock pyrolysis in the study area,combined with studying the hydrocarbon source rocks in other areas,the hydrocarbon source kinetics are divided,based on the exact evaluation standard of hydrocarbon source rocks(Wenchang Formation and Enping Formation)and the sequence units of source rock.Through the development of the lake basin,high productivity and the preservation environment of organic matter,we have confirmed that the Huizhou sag is a rich hydrocarbon depression.The ancient lake in Huizhou sag has gone through three development stages,where the Eocene is the peak period of the lake basin development with the development of phytoplankton groups which reflects that the hot and humid climate was tropical-subtropical.In combination with the potential of hydrocarbon generation of hydrocarbon source rocks,biomarkers of crude oil and hydrocarbon source rocks,the composition of carbon isotope,it is found that the phenomenon of algae blooming happened in the west of hydrocarbon-rich sag and Panyu area(PY4 sag)during Wenchang period,which controls the features and distribution of rich-hydrocarbon sag to some extent.In the area with algae blooms during Wenchang period,the carbon isotope of the source rocks is heavy,and the better the type of organic matter is,the higher the potential of hydrocarbon generation is.However,in the area without algae blooms,such as Enping group,the lighter carbon isotope ?13C of the hydrocarbon source rocks is,and the better the type of organic matter is.This research helps the exploration of rich-hydrocarbon sag not to be drilled.In addition,through studying the floating algae in the rich hydrocarbons and organic phase,it is found that,between the lake environment where hydrocarbon source rocks formed and the formation of the high quality hydrocarbon source rocks,there have been close contact.The rich algae and abundant amorphous layer in lake facies formation are alternative signs of rich oil source rocks,and the corresponding of oil-rich source rocks have high HI and high TOC.The pollen phase and organic geochemical indicators can be well combined.In the study,the tracer of crude oil migration is mastered by the geochemical characteristics of sandstone extract samples,based on the analysis of saturated hydrocarbon chromatography-mass spectrometry of 108 sandstone extract samples,and it is a more profound understanding that the contribution of Enping group was realized.On the basis of this study,combined with previous studies,the regular pattern of hydrocarbon accumulation in Huiliu structural ridge Panyu area(PY4 sag)is concluded.