基岩型富氦气藏形成条件——以柴达木盆地东坪气田和美国中部潘汉德—胡果顿气田为例

Formation conditions of helium-rich gas in bedrock reservoirs:Taking Dongping Gas Field in Qaidam Basin and Panhandle-Hugoton Gas Field in central United States as examples

氦气是一种广泛应用于军工、航天、医疗等高新技术产业的稀缺战略资源,但其在世界分布极其不均,中国是贫氦国家面临着严峻的氦气供给安全问题。在系统总结前人研究成果基础上,结合本次实验分析对比了世界上最成熟的氦气生产气田(美国潘汉德—胡果顿气田)与中国氦气生产潜力较大的东坪气田,探讨两者的成藏要素及富氦机理。结果发现:两者均是以天然气作为载体气的基岩型富氦气藏,储层物性好,均发育以膏岩为主的低渗致密的良好盖层。两者的差异性在于,前者花岗岩形成年代更为古老,尤其是碳酸盐岩地层中富含的花岗岩碎屑,其年龄集中在元古宙,平均比东坪气田花岗岩的形成年代早400 Ma;前者氦气运移模式偏向于单一的饱和地下水脱溶释放,而后者存在“过路”古老花岗岩储层的天然气“萃取”释放。两者对比之下,提出形成年代久远的高U、Th氦源岩、充足的载体气、良好的基岩风化壳储层与致密的盖层,和充足的地下水(边底水)作为媒介参与氦气运移,是形成基岩型富氦气藏的必要条件。

Helium is a scarce strategic resource widely used in military,aerospace,medical and other high-tech industries;however,the world's helium resources are extremely unevenly distributed,and helium-poor countries such as China are facing serious helium supply security problems.Through a combination of research literature and experiments,we analyzed the world's most mature helium producing gas field(Panhandle-Hugoton Gas Field in the United States)and the Dongping Gas Field,which has a high potential for helium production in China,and explored the reservoir formation elements and helium enrichment mechanisms of both.The results show that both are helium-rich reservoirs with natural gas as the carrier gas and good reservoir properties,both are capped by low-permeability evaporites,and both have undergone multiple phases of tectonic alteration.Both reservoirs have experienced multiple phases of tectonic alteration.The differences between the two types of reservoirs lie in the fact that the former is older in granite formation,especially the granitic material rich in carbonate formations,which is concentrated in the Proterozoic.The former granites are older in age,especially the granitic material in the carbonate strata,which is concentrated in the Proterozoic,and is on average 400 Ma earlier than the granites in Dongping Gas Field.In the former,the helium transport pattern is biased toward a single saturated groundwater desolvation release,while in the latter,there is an“extraction”release of natural gas from the ancient granite reservoirs that“passed through”.By contrast,it is proposed that the formation of ancient high U and Th helium source rocks,sufficient carrier gas,good reservoir and cap properties,and sufficient groundwater(marginal water)are involved in the helium release.The helium-rich bedrock reservoirs are required for the formation of helium-rich rocks with high U and Th source rocks,sufficient carrier gas,good reservoir and cap properties and sufficient groundwater(bottom water)as a mediator for helium transport.