陕西渭河盆地富氦天然气异常的影响因素

The factors responsible for the unusual content of helium-rich natural gas in the Weihe Basin, Shaanxi Province

通过对渭河盆地22口钻井中富氦天然气的同位素分析,认为盆地中氦气以壳源氦为主,局部伴有少量幔源氦。针对盆地中氦气异常的现象,结合对盆地特性的分析,认为渭河盆地氦气异常的影响因素包括:1盆地地壳较薄,莫霍界面呈明显的隆起,热流体活动发育,有利于氦气运移;2花岗岩体和通过水系统运移到沉积地层中的放射性元素衰变,为氦气成藏提供了有力的气源保障;3盆地内十分发育的断裂体系,不仅为氦气运移提供了连通通道,还在活动过程中释放氦气,为氦气局部聚集提供了有利空间。

The isotope analyses of the helium-rich natural gas based on 22 wells of the Weihe Basin show that the helium gas belongs to crust-derived helium with a little mantle-derived one. Based on analyzing anomalies of helium and characteristics of the Weihe Basin, the authors summarized three impact factors of helium anomalies in the Weihe Basin： ①high degree of hydrothermal fluid activity, thin basin crust and Moho rise, which are favorable for helium transport; ②the radioactive element decay of the granite and strata provides abundant gas for the helium accumulation;③the fracture system of the Weihe Basin not only provides pathway for the helium migration but also releases helium and serves as space for helium accumulation.