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

Abstract

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.