富氦天然气藏形成主控因素与成藏类型OA

Helium is a noble gas resource,and differs significantly from hydrocarbon gases in generation,migration,and accumulation.The formation of helium-bearing natural gas reservoirs requires a helium supply in addition to the natural gas source and thus belongs to a reservoir system characterized by different sources but the same reservoir.To clarify the core factors controlling helium abundance in helium-rich natural gas reservoirs and provide theoretical guidance for the exploration and development of high-helium and helium-rich gas reservoirs,this paper starts from the basic geological conditions for helium accumulation and systematically discusses the controlling effects of carrier gas reservoir pressure,reservoir scale,and helium supply capacity on helium abundance.The results show that:(1)helium generated from helium source rocks is released from minerals,migrates into pore water,accumulates in dissolved form,and is transported over long distances by large-scale fluid migration;(2)helium enrichment in natural gas reservoirs is a dynamic equilibrium process.When the rate of helium exsolution into the reservoir approaches the efficiency of caprock leakage,helium abundance reaches a stable state.Henry's law governs the exsolution and dissolution of helium and plays a key role in helium accumulation;(3)helium partial pressure changes synchronously with reservoir pressure.When helium partial pressure decreases,helium exsolves more efficiently from the aqueous phase into the reservoir,while caprock sealing capacity is enhanced,favoring helium enrichment;(4)owing to the dilution effect of natural gas,large gas reservoirs generally contain lower helium contents,whereas small and medium-sized reservoirs are more likely to form high-grade helium-rich reservoirs;and(5)areas with relatively unfavorable conditions for natural gas accumulation are instead more favorable for the development of helium-rich reservoirs.Therefore,the exploration direction for helium-rich reservoirs differs from that for high-quality natural gas reservoirs,and intrabasinal uplifts and basin margins are the main target areas for helium-rich gas exploration.In conclusion,these results deepen the understanding of the differences between helium enrichment and hydrocarbon gas accumulation,clarify the exploration strategy for helium-rich gas reservoirs,and support the enhancement of helium resource security in China.