Geochemistry on mantle-derived volatiles in natural gases from eastern China oil/gas provinces (I)——A novel helium resource——commercial accumulation of mantle-derived helium in the sedimentary crust

摘要

Commercial accumulation of mantle-derived helium in the sedimentary shell is discussed. Generally speaking, a commercial helium pool is formed by accumulated 4He that comes from uranium and thorium via a-decay; therefore, it has a very low He/4He value in the magnitude of 10 . The helium concentration in some gas wells of eastern China oil/gas provinces is about or over 0.05%-0.1%, consequently forming commercial helium wells (pools), such as the Wangjinta Gas Pool in Songliao Basin, Huangqiao Gas Pool in North Jiangsu Basin and some gas wells in Sanshui Basin. Studies have proved that when the 3He/4He value of a helium gas pool is about 3.7×10 -6 -7.2× 10-6, namely mantle-derived helium in its total helium concentration accounts for 33. 5%-65.4%, it is a crust-mantle dual-source or dominantly mantle-derived helium gas pool, which is a novel helium resource and its formation is mainly related to the distribution of megafractures.