Helium accumulation in natural gas systems in Chinese sedimentary basins

Helium is an important, scarce, and strategic resource that is critical to national security and advanced technology development. Although helium originates from mantle degassing and the radioactive decay of uranium (U) and thorium (Th) in minerals, commercial helium resources are primarily derived from natural gas reservoirs with He concentrations higher than 1000 ppm. The gas geochemistry characteristics of 920 natural gas samples from nine petroliferous basins in China were used to classify and discuss the enrichment mechanisms of helium. Helium-bearing natural gas reservoirs can be divided into the following three types: basement source-migration-rich accumulation, self-generating and self-preserving, and crust–mantle complex types. The basement source-migration-rich accumulation, which is the most common type of proven helium-rich natural gas reservoir, occurs primarily in inherited anticlines and dome traps located on basement uplifts. Ancient shale systems demonstrate the potential to form helium-rich shale gas that belongs to the self-generating and self-preserving type. Crust–mantle complex helium-rich natural gas reservoirs develop in petroliferous basins in active magmatic–tectonic areas. The origins of helium and hydrocarbon gas are different, but the entrainment of helium during hydrocarbon gas accumulation is a key factor influencing the formation of helium-rich natural gas reservoirs. The nitrogen concentration in helium-rich gas samples is often extremely high, indicating that the nitrogen and the helium are derived from the same source rock or both are extracted from water by migrating gas.