Characteristics and accumulation processes of helium gas fields in the deep part of Xujiaweizi area of the Songliao Basin

Objective and Methods The Xujiaweizi area of the Songliao Basin has numerous gas fields containing helium. However, the helium generation mechanisms and accumulation models remain insufficiently understood. With 3D seismic data and logging data from 24 wells, this study quantitatively evaluates the helium generation in the deep formations of Xujiaweizi area by using an improved helium resource assessment method based on natural gamma curves. Additionally, this study also analyzed the helium trapping models of this region in conjunction with hydrocarbon trapping characteristics. Results and Conclusions The results indicate that the average potential generation of helium of the deep formations in this area is 0.96×10^-4 cm³/g, with the K₁yc at 1.22×10^-4 cm³/g, the K₁sh at 1.08×10^-4 cm³/g, and the J at 0.90×10^-4 cm³/g. The total helium generation from deep formations in the region is 7.4 km³, which means the production is modest and source rocks are not good at generating helium. The crust-derived helium generated by the radioactive decay of uranium and thorium in deep mudstones of the study area migrated on a large scale starting at 95 Ma. Carried by hydrocarbon gases, it rapidly charged the overlying volcanic and clastic rock reservoirs of the K₁yc Formation through fracture systems to form inside-or-near source helium accumulations. Meanwhile, mantle-derived helium, carried by mantle-sourced inorganic gases such as carbon dioxide, ascended through deep-seated faults, volcanic conduits, and unconformity surfaces. These two distinct helium sources finally accumulated in traps, maintaining a dynamic equilibrium where the charging rate exceeded the escape rate, thereby forming composite helium reservoirs.