Abstract:  The helium gas (He) is one of the important strategic scarce resources, and the understanding of depletion mechanisms and resource potential is extremely weak. The Xinchang gas field from the Sichuan basin is taken as an example in this study to analyze the abundance and origin of helium, and the depletion mechanisms and main controlling factors are revealed with the resource potential being further discussed. The study indicates that natural gas from different strata of the Xinchang gas field displays the He content ranging from 0.007 7% to 0.040 0%with a low He content. The R/Ra ratio ranges from 0.010 to 0.050, suggesting a typically crustal source with little contribution by mantle-derived He. The He content displays positive and negative correlations with the N2 content in natural gas and the content of total dissolved solids (TDS) in reservoir water, respectively. The depletion of helium is mainly attributed to the source of helium being the strata themselves rather than the basement rocks due to the underdevelopment of deep faults, the high gas generation intensity of source rocks and charging intensity of natural gas, as well as the small uplift amplitude and weak dissolution effect since the Cretaceous. The Xinchang gas field is a medium helium gas field with a proven helium reserve of 25.45×106 m3. The exploration of high-helium and helium-rich gas resources in the Sichuan basin is suggested to pay attention to the areas with the development of basement faults, medium gas generation intensity of source rocks, and high uplift amplitude after gas accumulation.

Key words: Sichuan basin, Xinchang gas field, helium, source rocks, natural gas, depletion mechanisms, resource potential