Geochemical Characteristics Of Crude Oil And Oil-source Correlation In Saihantala Sag,Erlian Basin

Saihantala Sag is located in the west of Tengeer depression of Erlian Basin,which is the oil distribution area of Erlian Basin.In this dissertation,the geochemical characteristics of the crude oil in Saihantala Sag are studied by using organic geochemical method,and the types of crude oil are classified.Combining with the analysis of source rock,the oil-source correlation is carried out,and source analysis of low mature oils from the second member of Tengeer formation are studied.According to the organic matter abundance,type and maturity of the source rock,the source rock of Saihantala Sag is evaluated.The study indicates that the source rock of the first member of Tengeer formation is the main source rock in Saihantala Sag,the source rock of the Aershan formation is the subsidiary source rock,and the source rock of the second member of Tengeer formation has limited contribution to the generation of oil due to its low maturity.The Aershan formation is from a brackish weak reducing environment,the first member of Tengeer formation is from a brackish reducing environment,and the second member of Tengeer formation is from a saline strong reducing environment.Based on the physical properties,group composition,saturated hydrocarbon biomarker characteristics of crude oil,combined with the source of organic matter and sedimentary environment,the crude oil in Saihantala Sag are divided into three types.The first type of crude oil is from the second member of Tengeer formation.The Pr/Ph is low and the maturity parameter is low,indicating low mature crude oil.And the content of tricyclic terpane is low and has the advantage of C₂₃TT which reflects that the sedimentary environment of crude oil is a brackish-saline reducing environment.The second type of crude oil is from the first member of Tengeer formation.The Pr/Ph is medium and the maturity parameter is high,indicating mature crude oil.And the content of tricyclic terpane is low which reflects that the sedimentary environment of crude oil is a brackish reducing environment.The third type of crude oil is from the Aershan formation.The Pr/Ph is high and the maturity parameter is higher than other types,indicating mature crude oil.And the content of tricyclic terpane is high and has the advantage of C₂₁TT.The gammacerane is high which reflects that the sedimentary environment of crude oil is a brackish reducing environment.The results of oil source correlation indicates that the first type of crude oil mainly comes from the early generation of the first member of Tengeer formation source rock.The second type of crude oil mainly comes from the contribution of the first member of Tengeer formation source rock,and the third type of crude oil mainly comes from the self-generation and self-storage of the Aershan formation source rock.There are two sources of the low mature oil from the second member of Tengeer formation.One is from the underlying source rock from the first member of Tengeer formation and early generation of hydrocarbon in the salt water environment.The other is from the self-generation and self-storage of the low mature source rock from the second member of Tengeer formation in the depression.