四川盆地高石梯—磨溪大气田稀有气体特征

Characteristics of noble gases in the large Gaoshiti-Moxi gas field in Sichuan Basin

以四川盆地高石梯—磨溪大气田为例，对震旦系灯影组、寒武系龙王庙组天然气稀有气体进行全组分含量和同位素检测，并判别其成因。高石梯—磨溪大气田天然气中稀有气体He含量高于大气中He含量1～2个数量级，其中灯二段天然气中He平均含量为512×10^-6，达到工业利用标准；而Ne、Ar、Kr、Xe含量相对较低，低于大气含量值。稀有气体全组分含量总体由震旦系灯二段、灯四段至寒武系龙王庙组逐渐降低。高石梯—磨溪大气田天然气中稀有气体^3He／^4He值总体为10^-8量级，^40Ar／^36Ar值总体为1024-9559，^132Xe相对过剩而^129Xe相对亏损，表明He、Ar、Xe均为典型壳源成因，且气田深部没有活动性强的深大断裂和通幔断裂，构造活动较为稳定。

Taking the large Gaoshiti-Moxi gas field of Sichuan Basin as an example, the total composition contents and isotopes of noble gases in the natural gases from the Sinian Dengying Formation and Cambrian Longwangmiao Formation are analyzed, and then their geneses are identified. The content value of helium in the natural gases of the large Gaoshiti-Moxi gas field is generally 1-2 orders of magnitude higher than that of air, and the average content in the second member of the Dengying Formation is 512×10^-6, reaching the industrial utilization standard. The content values of Neon, Argon, Krypton and Xenon are relative low, lower than the corresponding content value in air. The total composition contents of noble gases in the natural gas of the large Gaoshiti-Moxi gas field gradually reduce in the sequence of the second member of Dengying Formation, the fourth memeber of Dengying Formation, and Cambrian Longwangmiao Formation. The noble gases ^3He/^4He value in the natural gases of the large Gaoshiti-Moxi gas field is in 10^-8 order of magnitude, the ^40Ar/^36Ar value is usual from 1 024 to 9 559, ^132Xe is relatively surplus and ^129Xe is relatively loss. The comprehensive genetic identification of Helium, Argon, Xenon indicates that the noble gases in the large Gaoshiti-Moxi gas field are typical crustal source genesis, and the study area has stable tectonic background and does not have active deep fractures or mantle connecting fractures.