Applications of light hydrocarbons in petroleum geochemistry:A review

Light hydrocarbons are key components of petroleum and contain a wealth of geochemical information. This review provides a comprehensive summary and comments on the research that has been carried out on light hydrocarbons over the past 50 years. It evaluates the applicability and reliability of the various parameters and diagrams that relate to the light hydrocarbons in petroleum from basins worldwide. The chemical compositions and stable isotope values of light hydrocarbons are valuable for identifying the sources and origins of hydrocarbons, their depositional environments, and the maturity of their corresponding source rocks. In addition to thermochemical sulfate reduction, light hydrocarbon parameters are widely used to identify secondary alteration processes, including evaporative fractionation, water washing, biodegradation, and oil cracking. Light hydrocarbon parameters are more effective for tracing natural gas migration than they are for tracing oil migration. Using current light hydrocarbon parameters to accurately identify contributions of petroleum with mixed origins or overlapping secondary effects remains challenging. These challenges may be addressed by using advanced analytical techniques, such as position-specific isotope and clumped isotope analyses combined with other cutting-edge technologies. Advances in separation techniques, high-resolution mass spectrometry, and isotope analysis have significantly enhanced the accuracy of analyzing the chemical and isotopic compositions of light hydrocarbons, providing a deeper understanding of their formation and transformation at microscales.