Geochemical properties of helium and its origin in the Indus Basin, Pakistan

The Indus Basin, one of Pakistan's most significant hydrocarbon provinces, is an underexplored region for helium resources. This study investigates the geochemical characteristics of helium in natural gas samples from the Middle and Lower Indus Basins, focusing on its concentration, isotopic composition, and relationships with other noble gases and hydrocarbons. The anomalous decrease in the helium concentration with increasing depth is attributed to the complex geochemical and geological factors influencing helium distribution, through helium migration along faults and fractures, dissolution into formation water, structural trapping in shallower reservoirs, and dilution by other gases. The results reveal a notable variation in helium concentrations, particularly in the Middle Indus Basin, where CO₂-N₂-rich gas samples exhibit higher helium levels. In contrast, helium concentrations in the Lower Indus Basin remain relatively uniform, regardless of depth. The isotopic analysis indicates a crustal origin for helium in the basin, with contributions from sedimentary sources and radiogenic decay within basement rocks. Isotopic ratios of ³He/⁴He range between 1.3 × 10⁻⁸ and 7.8 × 10⁻⁸, while ⁴He/²⁰Ne ratios further distinguish basement and sedimentary contributions. The absence of correlation between helium and hydrocarbons (CH₄, CO₂) underscores their distinct origins and migration pathways before converging into a shared reservoir. A moderate positive association with nitrogen (N₂) and lack of correlation with argon isotopes (⁴⁰Ar/³⁶Ar) highlight the complexity of noble gas accumulation dynamics.