Origins And Accumulation Model Of Hydrocarbon In Deep Strata Of The Central Junggar Basin,Northwestern China

The deep strata are important fields for oil and gas exploration globally.This dissertation conducts a case study in the Junggar Basin of northwestern China,and focuses on two key issues including the origins and accumulation models of hydrocarbon and their controls by a comprehensive study of geology and geochemistry.The aims are to provide reference for the next step exploration of deep oil and gas.Meanwhile,the results can also have general implicaitons because the areas like superimposed basins in this study are widely distributed.Based on oil and gas geochemistry,in particular biomarker compositions of oil and isotopes of natural gas,the oils in the study area are divided into five end members and the gases in the study area are divided into three end members.Combined with the types and distribution of regional source rocks,the origins and genesis of these hydrocarbons are identified.Among them,there are two types of oil are in-situ derived,whose density,carbon isotopes and biomarkers are special and are different from the previously-acknowledged oils.This is a new discovery for the first time.The two newly-identified oils are derived from Pif source rock in the Dabasong area and C/P1j source rocks in the Madong slope area/Shixi area,respectively.In contrast,the remaining three types of oil and three types of natural gas are same with the oils in previous literature.According to the variation of geochemistry and properties of deep oil and natural gas in the study area,the differences between the shallow and the deep layers are analyzed from two aspects spatially and vertically.Five possible hydrocarbon fluid phase types were identified,e.g.,medium oil,light oil,condensate,wet and dry gas.In general,the oils are light and may contain gas,which is favorable for exploraiton.Finally,by analyzing the deep oil and gas accumulation conditions in the study area,comparing the successful case(Shixi oil and gas field)with the unsuccessful(Datan 1-Yantan 1 well area),the main model of oil and gas accumulation in the study area is termed "side-contact type" in idiom.Adequate oil and gas filling and excellent migration conditions are key controls for reservoir formation.Accordingly,the Xiayan 1 nose structure,the Shixi nose structure and the Mobei nose structure are the favorable targets for exploration that might be considered in the next step.