Chemicals

such as Cabazoles

phenols and dibenzothiophenes

in oils and source rocks may serve as ideal tools for hydrocarbon migration researches.Alkylated carbazoles concentration and shield and semi-shield isomersexposed isomers ratios and benzocarbazole [a]/([a]+[c]) ratios are considered perfect indexes for migration.However

the distribution of these chemicals may be affected by input of organic matters

depositional environment

thermal maturity

primary and secondary migration

and biodegradation.For example

different environments may lead to different distribution of carbazoles

and carbazole migration parameters may increase with maturity increasing at low maturity environment but decrease in a highly matured environment

reducing the reliability of these parameters as the indexes of hydrocarbon migration.Alkylated phenols concentration may serve as migration index but it also affected by many other factors such as sedimentary facies

environments

maturity

and biodegradation.The parameters of alkyldibenzothiophenes of cogenetic oil such as 4-/1-MDBT

2

4-/1

4-DMDBT and 4

6-1

4-DMDBT can fit as migration indexes for oils with different maturity

biodegraded oils

and mixed cogenetic oils of two separated charges

thus can serve as excellent tools for migration direction assessment.It is also suggested that many other factors shall be taken into consideration when molecular geochemistry parameters of crude oils and source rocks are used to trace hydrocarbon migration since these parameters are easily affected by changes in maturity

facies and depositional environment in rifted-basins.