The origins of natural hydrogen in natural gas systems of sedimentary basins and the capacity of these systems to store hydrogen remain inadequately understood, posing crucial questions for the large-scale exploration of natural hydrogen. This study reports on the natural gas composition, stable carbon and hydrogen isotopic values, and helium isotopic values of gas samples collected from the Qingshen gas deposit within volcanic rocks of the Songliao Basin. Natural hydrogen primarily originates from water radiolysis, water-rock interactions (WRI), and mantle. The Qingshen gas deposit contains 95.23 × 10 ⁹ cubic meters of abiotic CH ₄ , of which 15.24 × 10 ⁹ cubic meters was generated through hydrogen conversion via Fischer-Tropsch synthesis, with the maximum original hydrogen reserves calculated to be approximately 61.9 × 10 ⁹ cubic meters. We estimated that the study area has generated a maximum total of 572 × 10 ⁹ cubic meters of radiolytic hydrogen, 248 × 10 ⁹ cubic meters of WRI hydrogen, and 127 × 10 ⁹ cubic meters of mantle-derived hydrogen.

Matrix diffusivity is vital for developing tight sandstone and shale gas reservoirs. This study proposes a method to test the diffusivities of a core under confining pressure conditions using the gas diffusion technique. The diffusivities of methane and helium were examined in fine-grained rocks (sandy shale, silty sandstone, tight sandstone, and shale) under specific stress conditions. The results revealed that the gas diffusivities varied among the samples. The tight sandstones exhibited diffusivity higher than that of silty sandstone, sandy mudstone, and shale. Helium diffusivities in shales and sandy mudstones were 1 order of magnitude smaller, while methane diffusivities were 2 orders of magnitude smaller than those in tight sandstones. A positive correlation was observed between the stress sensitivity factor and the clay mineral content, indicating the influence of the clay minerals' mechanical properties. Additionally, the shale gas diffusivities exhibited significant anisotropy due to slit-like gas channels parallel to laminae in shale. It was found that the impact of adsorption on diffusivity was positively correlated to the amount of adsorption. While the adsorption effect was negligible in tight sandstones, organic-rich shales and sandy mudstones experienced an order-of-magnitude reduction in methane diffusivities compared to helium. This study presents a method to evaluate the diffusion coefficient of a core matrix under a confining pressure. It provides insights into gas diffusion behavior in different fine-grained rocks, considering the effects of stress, clay mineral content, and adsorption. These findings contribute to understanding tight sandstone gas and shale gas reservoirs, aiding in the optimization of gas production strategies.