富氦天然气藏成藏特征及主控因素

在充分调研全球探明氦资源分布及开采现状的基础上,对国外典型富氦天然气藏的空间分布特征、氦气成因来源和气藏类型进行解剖,再结合地质背景分析了富氦天然气藏的成藏主控因素。研究结果表明,美国是目前世界上探明氦资源最多的国家;由于受技术手段等条件的制约,目前主要是从富氦、高氦天然气藏中获取氦气资源。通过对国外富氦天然气藏的解剖发现,富氦天然气藏平面上主要分布在古老克拉通地区,垂向上以埋藏较浅的元古界和古生界为主;绝大多数富氦天然气中的氦气主要是由地壳中的铀、钍等放射性元素衰变形成。根据天然气组成特征可将富氦天然气藏划分为富氦烃类气藏、富氦二氧化碳气藏和富氦氮气藏,其中大多数富氦烃类气藏主要位于克拉通内部隆起带之上,气藏规模和氦资源量较大;富氦二氧化碳/氮气藏多位于克拉通边缘活动带,气藏规模和氦资源量较小。在对气藏特征进行总结的基础上,综合实际地质背景提出两种富氦天然气藏成藏模式:古老克拉通内部隆起富氦天然气藏成藏模式和古老克拉通边缘活动带富氦天然气藏成藏模式,其中具备花岗岩基底隆起、深大断裂、晚期构造活动和区域性盖层等地质条件的地区是氦资源勘探的重点有利区。

Accumulation characteristics and main controlling factors of helium-rich gas reservoirs

Based on the full investigation of the distribution and exploitation status of global proved helium resources, this paper explores the spatial distribution characteristics, the origin of helium as well as the types of typical helium-rich gas reservoirs at abroad. Further, the main controlling factors for the accumulation of helium-rich gas reservoirs has been analyzed according to the geological background. The results show that the United States has the largest proved helium resources in the world; as restricted by technical means and other conditions, helium resources are mainly obtained from helium-rich and high-helium gas reservoirs. Through analyzing the helium-rich gas reservoirs abroad, it is found that helium-rich gas reservoirs are mainly horizontally distributed in the ancient craton, dominated by the shallow buried Proterozoic and Paleozoic strata in the vertical direction; the helium in most of helium-rich gas is mainly formed by the decay of uranium, thorium and other radioactive elements in the crust. According to the characteristics of gas composition, helium-rich gas reservoirs can be divided into helium-rich hydrocarbon gas reservoirs, helium-rich carbon dioxide gas reservoirs and helium-rich nitrogen gas reservoirs. Located in the uplift zone inside cratons, most of the helium-rich hydrocarbon gas reservoirs possess large-scale gas reserves and a large amount of helium resources; mainly located in the activity zone on the margin of cratons, helium-rich carbon dioxide/nitrogen reservoirs have small-scale gas reserves and a small amount of helium resources. Based on summarizing gas reservoir characteristics and the actual geological background, two kinds of helium-rich gas reservoir accumulation modes are proposed: the helium-rich gas reservoir accumulation model of the internal uplift of ancient craton and the helium-rich gas reservoir accumulation model of the activity zone on the margin of ancient craton, in which the regions with geological conditions such as granite basement uplift, large deep faults, late tectonic activity and regional cap rocks are the key favorable areas for helium resource exploration.