Differences of Nitrogen Isotopes in Crude Oils from Different Depositional Environments

As an important element of oil and organic matter, the contents and isotopes of nitrogen are different due to different sources from different environments and different late diagenetic processes after burial. The contents and isotopes of nitrogen in urea and caffeine show that these nitrogen parameters of samples are highly variable and indicate different depositional environments. The carbon and especially the nitrogen isotopes of crude oils formed in marine environments are lighter than those in continental environments, For samples from the same environment, high?temperature cracking causes nitrogen isotope fractionation. 14 N is enriched in crude oils and nitrogen isotopes are lighter in high?maturity oils.