The Geochemical Significance Of Phenyl Polycyclic Aromatics And Naphthofurans In The Geosphere

Phenyl polycyclic aromatics and naphthofurans are important compounds in petroleum and sedimentary organic matter.However,less work has been done on their identification,occurrence,distribution,origin,and geochemical application.In this paper,phenyl polycyclic aromatics and naphthofurans were unambiguously identified in the coals from the Junggar and Ordos basins,the source rocks and crude oils from the Fushan sag.The distribution characteristics of phenyl polycyclic aromatics and naphthofurans in the samples were also analyzed.Based on the thermodynamic stability of these compounds calculated by quantum chemical calculation,their related maturity indicators were proposed,and have been successfully applied to the maturity evaluation of the source rocks and oils from the Fushan sag.All four phenyldibenzothiophene isomers were unequivocally identified in coals and oils by the co-injection of authentic standards.The retention indices of the phenyldibenzothiophenes were calculated.The thermodynamic properties and optimized geometries of phenyldibenzothiophenes were determined by quantum chemical calculation.At the same time,the distribution of phenyldibenzothiophenes in the coals with different maturity were investigated.Two phenyldibenzothiophene maturity indicators,i.e.,Ph DR1 and Ph DR2,were proposed.Two preliminary calibrations of these parameters against vitrinite reflectance were made.In addition,organic matter source and sedimentary environment have been proven to have no significant effect on the Ph DR1 and Ph DR2 values.Therefore,these two parameters are useful maturity indicators in quantitatively assessing the thermal maturity of oils and source rocks with high maturity levels.Phenylphenanthrenes,binaphthyls,terphenyls,phenylnaphthalenes,and benzonaphthofuran were unambiguously identified in coals,source rocks and oils by comparison of the relative retention time and retention indices with those reported in previous studies.The thermodynamic stability and optimized geometries of these compounds were accurately calculated by quantum chemical calculation.Combined with the distribution characteristics of these compounds in the samples with different maturity levels,the rationality of the relevant maturity parameters documented by researchers was verified,and some new parameters were proposed.Their quantitative relationship with vitrinite reflectance were preliminarily established,and they can be applied as effective maturity indicators to quantitatively assess the thermal maturity of oils and source rocks.All six dinaphthofuran isomers were unequivocally identified in the geosphere,i.e.,coals,oils and sedimentary organic matter,by the co-injection of authentic standards.The retention indices of the dinaphthofurans were calculated.Quantum chemical calculation was carried out to determine the thermodynamic properties and geometric optimizations of dinaphthofuran isomers.Based on theoretical calculations and geochemical data,a dinaphthofuran maturity indicator,defined as DNFR,was proposed.A preliminary calibration of DNFR against the vitrinite reflectance was established.It suggests that DNFR can be applied as effective maturity indicator to quantitatively assess the thermal maturity of geological samples with high maturity levels.In this paper,the maturity parameters of phenyl polycyclic aromatics and naphthofurans were used to evaluate the maturity of source rocks and oils from the Fushan sag.The result shows that the source rocks and crude oils are in low mature to mature evolution stage.It is found that the relevant parameters of binaphthyls and terphenyls are suitable for the maturity evaluation of source rocks and oils.The parameters of phenylphenanthrene,phenylnaphthalene and benzonaphthofuran are not ideal indicators for quantitative evaluation of the maturity of geological samples.