2025 Volume 59 Issue 2 Pages 59-71
To achieve position-specific isotope analysis (PSIA) of carbon and hydrogen in hydrocarbons in natural gas, various methods have been developed, including NMR spectrometry, high-resolution isotope ratio mass spectrometry, chemical and enzymatic degradation, or on-line pyrolysis coupled with isotope ratio mass spectrometry. PSIA has been applied to propane in natural gas from petroleum basins and on-land hot springs, as well as to propane generated by laboratory pyrolysis experiments to elucidate the origins of natural gas. Site-preference (SP) value, defined as the difference of δ13C values between terminal and central C-atom positions of propane shifts from positive to negative as the maturity of natural gas increases. This change in SP value suggests alterations in the source organic matter of propane associated with thermal maturity or the effects of thermal cracking of propane itself. Position-specific δ13C value of propane can also be effective indicators for detecting and quantitatively assessing biodegradation of natural gas. In case that natural gas has abiotic origin, the SP value of propane has a potential to identify different polymerization mechanisms. Joint efforts from different laboratories will be needed to establish a propane standard or to improve analytical methods to verify the accuracy of PSIA data.
