| Polyaromatic hydrocarbons and their alkylated homologues carry much information regarding the depositional environment and the maturity of crude oils and sedimentary rocks.However,there is a rather limited understanding of the phenyl derivatives of these compounds on the application of geochemistry.Moreover,the geochemical applications of oxygen-heterocyclic aromatic compounds are far less than that of their sulfur counterparts.By co-injection of internal standards,in this study,a series of phenyl-polyaromatic hydrocarbons in rock extracts and oils derived from marine and terrestrial sediment environments are identified.Then,the distribution characteristics of phenyl-polyaromatic hydrocarbons and methyldibenzofurans in samples are analyzed.This study certified some geochemical indicators documented by researchers,and proposed some new parameters.Here,phenyldibenzofurans(PhDBFs)are detected firstly by co-injection of internal standards in lacustrine shales.Two maturity parameters,i.e.4-/2-PhDBF and4-/(2+3)-PhDBF(designated as the PhFR-1 and PhFR-2,respectively),are also proposed.With increasing maturity,these two ratios show an overall increasing tendency.It seems striking that the vitrinite reflectance has a better exponential relationship with PhFR-1(with a R~2 of 0.89)and PhFR-2(with a R~2 of 0.88)than with methylphenanthrene index-1(with a R~2 of 0.75)and methyldibenzothiophene ratio(with a R~2of 0.70).Therefore,PhFR-1 and PhFR-2 can be used as effective maturity indicators.These two ratios are more suitable for mature source rocks and crude oils(Ro?0.6%).For samples from terrestrial sedimentary environment in the m/z 182 mass chromatograms of aromatic fractions,three peaks formed by 4-methyldibenzofuran(4-MDBF),2-+3-MDBF,and 1-MDBF show a reversed“V-shaped”distribution pattern.However,there is not such a reversed“V-shaped”distribution pattern in samples from marine depositional environment.By comparing the distribution patterns of MDBF isomers in rocks and oils from various depositional environment,a cross-plot of(1+4)-/(2+3)-MDBF ratio versus pristane/phytane ratio(Pr/Ph)was proposed.In this cross-plot,samples derived from various depositional environments can be basically distinguished.Compared with the cross-plot reported by literature(such as the cross-plot of dibenzothiophene/phenanthrene ratio versus Pr/Ph ratio,or the cross-plot of alkyldibenzothiophene/alkyldibenzofuran ratio versus Pr/Ph ratio),the cross-plot of(1+4)-/(2+3)-MDBF ratio versus Pr/Ph ratio can distinguish marine shales and lacustrine shales.In this study,benzo[b]naphtho[2,1-d]thiophene/(benzo[b]naphtho[2,1-d]thiophene+benzo[b]naphtho[1,2-d]thiophene)ratio is firstly used to investigate oil migration orientations and filling pathways in typical lacustrine clastic reservoirs(the Eocene lacustrine clastic reservoirs in the Fushan Depression of the Beibuwan Basin).Morever,the 4-/1-methyldibenzothiophene ratio(4-/1-MDBT)and the total content of DBTs are also applied to identify oil filling pathways in the Fushan Depression.The results show that the overall migration direction is from northeast to southwest in this area,and the traps situated upstream of the preferred oil filling pathways in the Bailian Sub-sag are likely to be the most favorable prospecting regions.It can be predicted that the crude oils in this study area should be sourced from the source kitchen at the Bailian Sag.In addition,by compared with molecular surface area,this paper indicates that4-MDBT with a greater molecular surface area has more intense adsorption capacity than 1-MDBT in carrier beds.Molecular surface area is also one of the factors affecting the geochromatography effect. |
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