Geochemical Characteristics of the Meso-Neoproterozoic Source Rocks and Oil-Source Correlations in the Yanshan Area
The enrichmentof Meso-Neoproterozoic oil and gas in Yanshan area has been the hot topic focused on by scholars.Total Organic Carbon(TOC)test,pyrolysis,gas chromatography(GC),gas chromatography-mass spectrometry(GC-MS)and other methods are applied in this paper to discuss organic geochemical characteristics of samples.Especially,the biomarker compounds,organic matter sources and sedimentary environment are discussed in detail.The geochemical and biomarker characteristics of oil seepage/asphalt and source rocks are compared to identify the major source rocks of Meso-Neoproterozoic strata in Yanshan Region.The results show that the source rocks of the Xiamaling and Hongshuizhuang formations,featured with high content of organic carbons,great hydrocarbon generation potential and moderate degree of thermal evolution,are good and supreme source rocks.The source rocks of Tieling Formation are poor-medium source rocks,and the degree of thermal evolution of Gaoyuzhuang Formation is excessively high to determine the type of source rocks.According to the characteristics of biomarkers in the researched area,the source rocks are divided into two categories.Wherein,the source rocks of Hongshuizhuang,Tieling and Xiamaling Formations are classified into Category I.The relative contents of acyclic isoprene pristane(Pr)and phytane(Ph)are very low,with certain abundance of regular C20 tricyclic terpane(C20TT),C19TT and special 13α(n-alkyl)-tricyclic terpanes,rich in tetracyclic terpane(C24TeT),norneohopane(Ts and C29Ts)and rearranged hopanes(C30Dia),and are characterized by the absence of sterane compound.Revealing moderate degree of thermal evolution,anoxic sedimentary environment and a special hydrocarbon generating organism of Category I source rocks.Gaoyuzhuang Formation,provided with Category Ⅱ source rocks,is characterized with high abundance of C23‒C25TT and regular hopane,common C27‒C29 regular steranes,low abundance of C24 tetracyclic terpane,norneohopane and rearranged hopane,and no drimane and 13α(n-alkyl)-featured with tricyclic terpene serial compound is detected,showing the characteristics of crude oil in typical marine carbonate sedimentary environment and indicating various biological sources.The oil and source rock correlation shows that Category I oil seepage/asphalt mainly originates from the source rocks of Hongshuizhuang Formation,while the organic geochemical composition characteristics of CategoryⅡasphalt sandstone are extremely similar to the source rocks of Gaoyuzhuang Formation.
Yanshan areaMeso-Neoproterozoiccharacteristics of source rocksbiomarker compoundoil-source correlationgeochemistrypetroleum geology
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