Abiogenic hydrocarbons in commercial gases from the Songliao Basin, China

This paper discusses the kinetic fractionation, composition and distribution characteristics of carbon and hydrogen isotopes for various alkane gases formed in different environments, by different mechanisms and from different sources in nature. It is demonstrated that the biodegradation or thermodegradation of complex high-molecule sedimentary organic material can form microbial gas or thermogenic gas. The delta C-13(1) value ranges from-110 parts per thousand to -50 parts per thousand for microbial gases but from -50 parts per thousand to -35 parts per thousand (even heavier) for thermogenic gases. Controlled by the kinetic isotope fractionation, both microbial and thermogenic gases have delta C-13 and delta D values characterized by normal distribution, i.e. delta C-13(1) delta C-13(2)>delta C-13(3)>delta C-13(4) and delta D-CH4