Using carbon, hydrogen and helium isotopes to unravel the origin of hydrocarbons in the Wujiaweizi area of the Songliao Basin, China

Abstract

Although abiogenic hydrocarbons have been found in deep-sourced geofluids, they have not been considered a significant source for global hydrocarbon reservoirs. Here, we report a multi-isotopic (C, H and He) study of gases in the Songliao basin in China, revealing the existence of a giant abiogenic hydrocarbon field in the buried volcanoes and clastics overlying volcanics in this rift basin. The progressive carbon isotopic depletion and hydrogen isotopic enrichment trends for C1-C4 n-alkanes and the strong correlation between the carbon, hydrogen and helium isotopic ratios of gases in the buried volcanoes indicate hydrocarbon production by kinetically-controlled polymerization of methane precursors related to mantlederived fluids. Given the common occurrence of buried volcanic structures in rift basins, there may exist more abiogenic hydrocarbons associated with buried volcanoes in rift basins that are unrelated to source kitchens than previously thought.