四川盆地乐山—龙女寺古隆起气田氦气差异富集特征及地球化学证据OA

Weiyuan gas field,Anyue gas field,and Ziyang gas province are located in the Leshan-Longnvsi paleouplift of the Sichuan Basin.The helium concentration of economic value is detected in Weiyuan gas field,while the helium content is extremely low in Anyue gas field and Ziyang gas province.The mechanisms for this difference have not been figured out,which restricts the deeply understanding on the helium source and enrichment patterns in the paleouplift.Based on the analysis of natural gas geochemistry and noble gas isotopes,combined with the He and N2 coupling relationship,this paper systematically discusses the causes of the differential helium enrichment in Weiyuan and Anyue gas fields,as well as the geological conditions for helium enrichment in Weiyuan gas field.The following results are obtained.First,the helium in both gas fields is mostly crust sourced.The gas content(0.18%-0.26%)in Weiyuan gas field reaches the industrial standard,while that in Anyue gas field is lower.The mantle derived 3He content in Weiyuan gas field is higher than that in Anyue gas field.Second,the Sinian He and N2 are well correlated in Weiyuan and Anyue gas fields,and the 20Ne,4He,40Ar and 36Ar contents and the 20Ne/4He and 40Ar/36Ar ratios in Weiyuan gas field are significantly higher than those in Anyue gas field,which confirms that the helium in these two gas fields are closely related to underground water.Third,the limited helium supply capacity of the Qiongzhusi Formation source rocks in the Ziyang area makes it difficult to form a helium-rich gas reservoir only based on its radioactive decay.Fourth,the large amplitude of structural uplift in Weiyuan gas field during the Himalayan period promoted the ascent and exsolution of the basement helium-rich underground water,and caprock,formation pressure and faulting induced pressure relief channels achieve a balance between helium supply and dissipation.In conclusion,the helium enrichment in Weiyuan gas field is the collaborative product of basement helium supply,underground water migration and exsolution,Himalayan structural uplift and preservation condition,while the geological conditions in Anyue gas field can hardly meet the requirement of He enrichment in the gas reservoirs.