Advances in geological research of coal-measure natural helium and hydrogen as strategic gas resources

The evaluation and exploration of strategic natural helium and hydrogen resources are of significant national importance. Studies on the occurrence, distribution, genetic mechanisms, and enrichment patterns of helium and hydrogen in coal measures are therefore of particular relevance. This paper systematically reviews domestic and international research progress, and integrates analyses of geological conditions, high-abundance anomaly distributions, and controlling factors in representative basins. Comparative studies were carried out on typical cases such as the Xujiaweizi Fault Depression in the Songliao Basin, the Zhanhua Sag in the Bohai Bay Basin, and the Sanjiaobei area on the eastern margin of the Ordos Basin. The results can be summarized as follows: ① Coal-measure helium and hydrogen resources are characterized by multiple-source supply and widespread distribution. Coal-measure helium is dominated by crustal radiogenic helium with “internal-external” multi-source supply, whereas coal-measure hydrogen is jointly generated by organic matter thermal decomposition, water-rock interaction, deep degassing and microbial processes. In coal-bearing basins such as the Songliao, Ordos, Sichuan and Junggar basins, uranium-rich source rocks, favorable reservoirs and effective seals commonly occur in combination, providing geological conditions favorable for the formation and enrichment of helium and hydrogen anomalies. ② The enrichment processes are controlled by the coupling of source-reservoir-seal assemblages and fault transport systems. Coal seams and mudstones serve both as reservoirs and local sources, while thick mudstone and evaporite layers act as key seals. Deep faults function as conduits for crustal or mantle gases during active tectonic periods and form closed systems during quiescent stages. ③ The enrichment patterns are governed by the synergy of “generation-migration-accumulation-preservation” with different basins exhibiting varied combinations of source intensity, fault transmissibility, caprock integrity, and reservoir quality, reflecting both basin aggregation and tectonic belt constraints. ④ The occurrence states of gases are diverse: helium is mainly present in the free state, hosted in pores and fractures and partly dissolved in formation water, while hydrogen occurs in free, adsorbed, and dissolved states. Gas accumulations are commonly developed in synclinal cores, faulted depressions, and areas with well-developed caprocks. Tectonic stability and caprock continuity are the key factors determining preservation and industrial potential.