Oil-gas Source Correlation And Migration Tracing In The Deep Western Central Depression Of Junggar Basin

The western Central Depression of Junggar Basin is a typical oil and gas accumulation area of superimposed basins in central and Western China.The northwest margin of the basin has the richest oil and gas resources,not only conventional crude oil,but also a large number of heavy oil,light oil and natural.The existence of various types of oil and gas reservoirs reveals the complexity of hydrocarbon accumulation and distribution,and there are many disputes about the source of oil and gas.The paper mainly studies oil-gas source correlation.Its purpose is to ensure the hydrocarbon generation capacity of source rocks in the study area,clarify the genetic relationship between oil-gas reservoirs and source rocks,so as to provide reference for regional oil and gas exploration and geological research.Firstly,through the analysis of rock pyrolysis,organic elements and kerogen microscopy data of source rocks,analyze the abundance,type and maturity of organic matter of source rocks in this area,and define the hydrocarbon generating potential.The results show that there are four sets of source rocks developed in the area.The abundance of organic matter reaches medium to good quality,the types are diverse,and the maturity generally reaches the stage of maturity to high maturity.Source rocks are well-founded and have excellent oil-generating and gas-generating abilities.By studying the characteristics of four sets of biomarker compounds in source rocks,good hydrocarbon source correlation indexes were found:Pr/n C₁₇,Ph/n C₁₈,Ga./C₃₀hopance,Ts/Tm and?-carotene content.The source rocks of Lower Wuerhe Formation are characterized by low Pr/n C17 and Ph/n C18,low Ga./C₃₀hopance,high Ts/Tm,very low or none?-carotene content;the source rocks of Fengcheng Formation are high Pr/n C17 and Ph/n C18,high Ga./C₃₀hopance,low Ts/Tm and very high?-carotene content;the source rocks of Jiamuhe Formation are low Pr/n C17 and Ph/n C18,high Ga./C₃₀hopance,low Ts/Tm and medium?-carotene content.The Carboniferous source rocks are low Pr/n C17 and Ph/n C18,low Ga./C₃₀hopance,high Ts/Tm and medium?-carotene content.The hydrocarbon source correlation shows that the Carboniferous-Permian crude oil in the western Central Depression of Junggar Basin mainly comes from Fengcheng Formation source rocks,followed by Jiamuhe Formation source rocks,and natural gas mainly comes from oil-type gas of Fengcheng Formation source rocks,coal-type gas of Jiamuhe Formation secondly.Through the study of crude oil density and biomarker migration parameters,it is concluded that crude oil in Hongche and Zhongguai southern areas in the western Central Depression comes from Shawan Sag,crude oil in northern Zhongguai,Kebai and Wuxia areas comes from Mahu Sag,and the overall direction of oil and gas migration is from southeast to northwest.