Helium characteristics and resource potential analysis of Wufeng-Longmaxi Formation in Changning area, southern Sichuan

Helium has characteristics such as a low boiling point, high thermal conductivity, and strong inertness. It plays a key role in fields such as low-temperature superconductivity, protective gas, refrigeration, medical treatment, and electronics, and is referred to as the “golden gas” and “rare earth of gas”. In order to analyze the helium characteristics and resource potential of Wufeng-Longmaxi Formation in southern Sichuan province, helium resources of Wufeng-Longmaxi Formation in Changning area of southern Sichuan Province were studied based on rare gas isotope test and trace element test. The results showed that: (1) the uranium (U) and thorium (Th) contents in the shales of the Wufeng-Longmaxi Formation in the Changning area were relatively high, with the highest mass fractions reaching 6.57×10-5 and 2.96×10-5 respectively, indicating a strong potential for helium generation. The helium isotope ratio (R/Ra ≈ 0.01) and the 4He/20Ne ratio of the samples indicated that they had typical crustal helium characteristics. The concentrations of U, Th, and potassium (K) in the front and back limbs of the anticline structure were similar, but the content of radiogenic argon (40Arrad) in the back limb was significantly higher than that in the front limb. Considering the difference between the theoretical and measured values of 4He/40Ar, it was inferred that deep crustal helium had a mixing effect on the primary helium in the shale, forming a crustal helium mixture of near-source and far-source components. (2) There were two main sources of helium in the shale of Wufeng-Longmaxi Formation in Changning area: one was the helium continuously generated by the shale itself since its deposition, and the other was the helium gas that migrated into the Wufeng-Longmaxi Formation with the subsurface fluid through material exchange. (3) Calculations showed that the cumulative amount of helium produced during the natural evolution of the Wufeng-Longmaxi Formation shale in the Changning area was about 4.76×108 m3. The helium resource of Wufeng-Longmaxi Formation in the Changning area was at least 2.86×108 m3 based on the calculation of reservoir helium concentration. The findings of this study provide important guidance for further research on the potential, enrichment mechanisms, and distribution patterns of shale helium resources in the Sichuan Basin, as well as for achieving large-scale helium production and improving helium supply capacity.