Background Helium, with advantages such as stable chemical properties and high thermal conductivity, has been extensively applied in high-tech sectors like national defense, military, aviation, and aerospace, playing an irreplaceable role. Presently, helium in China is primarily imported from other countries, manifesting a high degree of dependence on foreign trade, suggesting a prominent issue concerning helium resource security. Previous studies on helium principally focus on conventional natural gas, rendering helium in coal measures relatively under-studied.
Objective and Methods To determine the distribution and potential of helium resources in coal measures, this study analyzed the coal-measure gas sampled from the eastern margin of the Ordos Basin, systematically investigating the distribution patterns of helium and its controlling factors. In combination with the helium test results of coalbed methane (CBM) in the Qinshui Basin, this study compared the helium accumulation mechanisms of coal measures in the Ordos and Qinshui basins and delved into the helium resource potential in the coal measures.
Results and Conclusions The results indicate that deep CBM exhibits higher helium content than moderately shallow CBM in the Hancheng and Daning-Jixian blocks along the eastern margin of the Ordos Basin. Specifically, the helium in deep and moderately shallow coal seams in the Hancheng block exhibits average volumetric fractions of 0.0428% and 0.0130%, respectively; the corresponding values of the Daning-Jixian block are 0.0307% and 0.0121%, respectively. The tight gas in coal measures and the deep CBM manifest similar helium content. The helium in the tight gas of the Hancheng and Daning-Jixian blocks displays average volumetric fractions of 0.0467% and 0.0355%, respectively, suggesting helium-deficient CBM. Contrastingly, the coal-measure gas in the Sanjiaobei block displays relatively high helium content (average volumetric fraction: 0.0930%), with nearly half of the gas wells reaching the criterion for helium-rich coal-measure gas. The coal measures along the eastern margin of the Ordos Basin bear minimal content of in-situ authigenic helium, which originates primarily from deep basement rocks, bauxites, and the Zijinshan pluton. The distribution of helium source rocks determines the distribution of helium in the coal measures. The fault system along the eastern margin of the Ordos Basin provides favorable migration pathways for helium in the deep helium sources and the Zijinshan pluton. The development intensity and location of the fault system play a crucial role in helium migration and accumulation. Meanwhile, effective cap rocks and the closed water environments are essential for helium preservation. Besides, the Qinshui Basin shows a relatively low content of in-situ authigenic helium, and the significant tectonic uplift in the late stage of helium accumulation is the primary cause of the loss of nearly 90% helium in coal seams. Despite relatively low helium content, tight gas in the coal measures and the deep CBM demonstrate considerable helium resources, thus warranting more endeavors to helium resource exploration in coal measures. Moreover, it is necessary to put more effort into tackling technological challenges in helium recovery from helium-deficient to helium-bearing coal-measure gas. The purpose is to effectively utilize the low-content helium in coal-measure gas in order to ensure China’s helium resource security.
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