关键词: 准噶尔盆地, 克拉美丽气田, 氦气, 稀有气体同位素, 火山岩气藏, 壳源氦, 氦气富集

Abstract: To clarify the resource types and distribution patterns of helium in volcanic gas reservoirs, this study investigates the Kelameili large-scale volcanic gas field in Junggar Basin. Based on helium concentrations, noble gas and conventional natural gas geochemical data of representative gas samples collected from the gas field, the genetic mechanisms and sources of helium were determined, and the helium resource potential of volcanic reservoirs was evaluated. The results show as follows. (1) The helium content in the Kelameili gas field ranges from 0.021 4 % to 0.029 5 %, with an average of 0.026 0 %, indicating a helium-poor gas reservoir. The ³He/⁴He ratio in the sample is low, and the ratio to that in the atmosphere ranges from 0.024 to 0.055, indicating a typical crustal origin with no significant contribution from mantle-derived helium. (2) The volcanic reservoirs formed during the Carboniferous-Permian period, which significantly predates the main natural gas accumulation stages in the Jurassic and Cretaceous. Therefore, volcanism-related helium elements may have been extensively lost during subsequent geological evolution, contributing only marginally to the present-day helium in the gas reservoir. (3) The volcanic reservoirs are mainly composed of intermediate-to-mafic rocks, which generally contain low concentrations of radioactive elements such as U and Th. Moreover, these rocks formed later than the metamorphic basement of the basin, making them unfavorable for the long-term generation and accumulation of substantial amounts of radiogenic helium. (4) Helium generation assessments and source rock age constraints inferred from ⁴⁰Ar/³⁶Ar ratios indicate that Carboniferous coal-measure source rocks and associated crustal lithologies may represent important potential sources of crust-derived helium in the gas reservoir. (5) The strong positive correlation between ⁴He and N₂ suggests the involvement of groundwater during natural gas accumulation. The dissolution and exsolution process may have facilitated the transfer of crustal helium from the aqueous phase into the gas phase, thereby promoting its coupled migration and accumulation with natural gas. (6) The helium deficiency of the gas reservoir is primarily attributed to insufficient helium sources, including the absence of significant mantle-derived helium associated with volcanic activity, the limited in-situ helium generation potential of the volcanic rocks, and the negligible helium contribution from Carboniferous coal-measure source rocks. Therefore, volcanic gas reservoirs are not necessarily enriched in helium, and their helium resource potential should be evaluated based on the specific conditions governing helium generation, migration, and accumulation.

Key words: Junggar Basin, Kelameili gas field, helium, noble gas isotopes, volcanic gas reservoir, crust-derived helium, helium enrichment