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

Abstract

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. Key words: Gaoshiti-Moxi large gas field, Sinian, Cambrian, noble gases, total composition content, isotope composition, genetic identification, Sichuan Basin