Effect Of Thermal Evolution On Typical Biomarker Parameters Reflecting Source And Environment In Source Rocks

The Biomarker is an important research area in organic geochemistry.Biomarker parameters have been widely used to indicate the source input,parent material type,sedimentary environment,maturity,and geological evolution of source rocks and oil.The composition of some biomarkers and their related geochemical parameters are obviously controlled by maturity.These biomarker parameters are often used to evaluate the thermal evolution stage of source rocks.However,some biomarker parameters which are often used to characterize the source and sedimentary environment of source rocks are often affected by maturity.When using biomarker parameters to evaluate source and sedimentary environment,the effect of thermal evolution should be considered.But there are still many unresolved problems in some relevant aspects.In order to explore the effect of thermal evolution on some biomarker parameters used to characterize the sedimentary environment and source,based on previous studies,this paper carried out thermal simulation experiments on source rocks of different lithology and kerogen types.Combining with the analysis of the natural evolution samples,this paper explore the effect of thermal evolution on the common biomarker parameters and determine their applicable maturity range.The experiment results show that,as the degree of thermal evolution increases,the content of high carbon number compounds in normal paraffin series decreases,and there is a clear main peak migration.The Pr/Ph,Ts/(Ts+Tm),Gamma waxane index,?C^-₂₁/?C⁺₂₂,(n C₂₁+n C₂₂)/(n C₂₈+n C₂₉),content of DBF and MPI are obviously affected by maturity.In most source rock samples,the Pr/Ph shows a gradual decrease trend with the increase of thermal simulation temperature,and the final value is basically stable at about 0.5.With the increase of maturity,the Gamma waxane index generally decreases first and then increases.And the?C^-₂₁/?C⁺₂₂,(n C₂₁+n C₂₂)/(n C₂₈+n C₂₉)showe a gradually increasing trend.After high maturity,???20RC₂₇sterane/C₂₉ sterane increases significantly.The MPI-3 values all show a gradual increasing trend.The relative content of DBF in source rocks in different basins showed a decreasing trend with increasing maturity.Before low maturity(Ro<0.7%),the Pr/Ph,C₂₁tricyclic terpene/C₂₃tricyclic terpene,Gamma waxane index,relative content of thiofluorene and fluorene,can be used as an effective parameter to judge the sedimentary environment of source rocks.Before maturity(Ro<1.2%),???20RC₂₇sterane/C₂₉sterane and Sterane/hopane can be used as an effective parameter to judge the source input of source rocks.