Evaluation of the origin of natural gas from Cenozoic sedimentary basins in East Asia using position-specific isotope analysis of propane

Abstract

Natural gas in the Cenozoic sedimentary basins in East Asia is important to Japan from both resource and geopolitical perspectives. Historically, bulk carbon isotope analysis of hydrocarbon compounds like propane has been used to evaluate the origin of natural gas (source rock types and thermal maturity). However, this method only provides the average isotopic composition of the entire molecule, making it difficult to capture isotopic composition changes at specific molecular positions related to formation and degradation processes, as well as to identify the characteristic isotopic distribution within precursors like kerogen. In this study, we use a newly developed position-specific isotope analysis (PSIA) for propane, which measures the delta 13C composition at individual molecular positions, to elucidate the relationship between source rock types and thermal maturity levels. In this presentation, we examine and discuss the effectiveness of PSIA in evaluating the origin of natural gas using propane PSIA data obtained from pyrolysis experiment gases and natural gases collected from the Cenozoic sedimentary basins in Vietnam.