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

摘要： 为了认识火山岩天然气藏中氦气的资源类型与分布特征,以准噶尔盆地克拉美丽大型火山岩气田为研究对象,基于气田内代表性天然气样品的He含量、稀有气体和常规天然气的地球化学资料,分析了氦的成因类型及来源,以及火山岩储层中氦的资源潜力。研究结果表明:①克拉美丽气田天然气中的He含量为0.021 4%~0.029 5%,平均为0.026 0%,揭示该气田属贫氦气藏;样品中的³He/⁴He比值低,样品与大气的³He/⁴He比值之比为0.024~0.055,揭示天然气中的He组分属于典型的壳源氦,没有明显的幔源氦贡献。②由于克拉美丽气田内火山岩储层的形成时间为石炭纪—二叠纪,远早于其天然气的成藏时间(侏罗纪和白垩纪),火山活动相关的He元素可能在后期演化中大量散失,对现今气藏中的He组分贡献有限。③克拉美丽气田火山岩储层主要由中性—基性岩组成,这些岩石不仅U、Th等放射性元素含量普遍较低,而且相对于盆地的变质基底,形成年代相对较晚,不利于生成和累积可观的放射性衰变He元素。④生氦量估算和⁴⁰Ar/³⁶Ar烃源岩年龄约束表明,克拉美丽气田的石炭系煤系烃源岩及相关壳源岩系可能是气藏中壳源氦的重要潜在来源之一。⑤⁴He与N₂存在较好的正相关关系,说明克拉美丽气田的天然气在成藏过程中伴随有地下水的参与,溶解—脱溶过程可能促进了壳源氦从水相进入气相并协同运聚。⑥由于克拉美丽气藏中缺乏与火山活动相关的幔源氦组分,火山岩体自身的原位产氦潜力有限,加之石炭系煤系烃源岩所形成的氦也有限,气藏因氦源不足而贫氦。因此,火山岩气藏不一定能富氦,需根据源、汇、聚的实际条件进行具体分析。

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