四川盆地涪陵页岩气田氦气资源潜力与成因机理

The helium resource potential and genesis mechanism in Fuling shale gas field,Sichuan Basin

四川盆地涪陵页岩气田的页岩气中普遍含氦,氦气含量介于0.034%~0.062%之间,分布较均匀、稳定,为典型壳源氦,氦含量高值区无明显分布规律,粗略来看,有机碳含量介于3.7%~3.9%之间,氦含量普遍相对较高,基本都大于0.042%,或许在这一区间,氦气与页岩气含量比值在涪陵地区达到了一个相对最佳值。分别采用组分法和成因法对涪陵页岩气田氦气资源量进行估算,结果显示:氦气资源量均在2.5×10^(8) m^(3)左右,氦气丰度大约是页岩气丰度的0.04%,属于特大型贫氦气田。富有机质页岩也是一种良好的氦源岩,涪陵地区富有机质页岩中放射性元素铀、钍的含量普遍较高,且越靠近龙马溪组底部,样品铀含量越高,该套页岩在漫长的地质历史时期产生了大量的氦气;同时研究区良好的保存条件能有效阻止氦气扩散和渗漏,这对氦气的富集与保存起到至关重要的作用。

Shale gas in Fuling shale gas field generally contains helium,with helium content ranging from 0.034%to 0.062%,and the distribution is uniform and stable.Typically it is of crustal origin,and there is no obvious distribution pattern in the area with high helium content.Roughly speaking,the helium content is generally relatively high,mostly greater than 0.042%,with the organic carbon content between 3.7%and 3.9%.Perhaps in this range,the ratio of helium to shale gas content in Fuling area has reached a relatively optimal value.In this paper,the helium resources in Fuling shale gas field are estimated by using the component method and the genetic method respectively.The results show that the helium resources are about 2.5×10^(8) m^(3),and the helium abundance is about four-thousandth of that of shale gas,which belongs to the super-large helium poor gas field.Organic-rich shale is also a good helium source rock.The content of radioactive elements uranium and thorium in organic-rich shale in Fuling area is generally high,and the closer the sample is to the bottom of Longmaxi Formation,the higher the content of uranium is.This shale has produced a large amount of helium in a long geological history.At the same time,good storage conditions in the study area can effectively prevent the diffusion and leakage of helium,which plays an important role in the enrichment and preservation of helium.