柴达木盆地阿尔金斜坡氦气富集规律及成藏机制OA

In recent years,helium-rich natural gas resources have been discovered in several gas fields in the Altyn Slope of the Qaidam Basin.However,the helium enrichment patterns,sources and accumulation mechanisms have not been understood completely,which hinders the exploration of helium resources in this area.In this study,natural gas samples collected from Dongping 1,Dongping 3,Jianbei,and Kunteyi gas fields in the Altyn Slope were tested for compositions,carbon isotopes,and noble gas isotopes.Then,the geochemical characteristics,spatial distribution patterns and controlling factors of helium were analyzed systematically,and its accumulation mechanisms were revealed.The following results are obtained.First,the helium content of natural gas in the Altyn Slope exhibits a pattern of"high in marginal uplifts and low in adjacent sags",and it is influenced by multiple factors such as structural position,reservoir horizon,basement lithology,gas reservoir depth,and natural gas charging process.Second,the helium in different gas fields shows multi-source contributions:Dongping 3 and Dongping 1 gas fields feature mixed crustal shallow and deep sources,Jianbei gas field is dominated by deep-source helium,while Dongping 17,Niudong,and Kunteyi gas fields display weak helium supply from in-situ reservoirs or adjacent sources.Third,formation pore-fracture water serves as a key carrier for helium migration and enrichment,and the accumulation of helium in formation water is closely related to the content of radioactive elements U and Th in basement rocks,rock formation age,and formation water activity.Fourth,there are three helium accumulation models in the Altyn Slope:multi-source supply and continuous enrichment,distal supply and multi-stage accumulation,and weak-source supply and proximal accumulation.In conclusion,the helium enrichment in the Altyn Slope of the Qaidam Basin is under the joint control of multiple factors,such as structural position,basement lithology,natural gas charging and formation water activity,and the understanding of helium sources,distribution patterns and accumulation models provides an important theoretical support for the resource potential assessment and targeted exploration and development of helium in this area.