抄録
Understanding why substantial differences in helium enrichment occur under comparable crustal helium-generation conditions remains a critical challenge for evaluating helium resources in continental petroliferous basins. This study investigates the genetic mechanisms of helium enrichment in Paleozoic natural gas from the Daniudi gas field and compares them with those of the adjacent Dongsheng gas field in the Ordos Basin using integrated analyses of natural gas geochemistry, helium isotopes, basement radiogenic helium-generation potential, and tectonic–fault evolution. The results reveal that helium in the Daniudi gas field exhibits generally low concentrations, with a tendency toward higher abundances in shallow reservoirs, and is dominantly derived from crustal radiogenic 4He generated within Archean–Mesoproterozoic metamorphic rocks and granitoids of the crystalline basement, whereas Upper Paleozoic sedimentary rocks contribute only limited helium. Despite broadly comparable basement compositions and radiogenic helium-generation capacities between the Daniudi and Dongsheng gas fields, their helium abundances differ markedly, demonstrating that source potential alone cannot explain differential enrichment. Instead, helium accumulation is primarily governed by the efficiency of post-generation transformation processes. In the Daniudi gas field, underdeveloped deep-seated faults, weak secondary fracture networks, and limited late-stage tectonic reactivation restricted deep helium migration and reservoir-scale redistribution, resulting in a diffusion-dominated, low-efficiency charging system. In contrast, the Dongsheng gas field developed a long-lived fault-controlled transport network that enhanced deep helium release, vertical migration, secondary redistribution, and preservation, producing a high-efficiency enrichment system. Based on these findings, a source–migration–accumulation–preservation coupling framework is established, and two contrasting helium accumulation modes are proposed: a diffusion-dominated, low-efficiency depletion model and a fault-controlled, high-efficiency enrichment model. This study demonstrates that migration efficiency and tectonic reorganization, rather than helium-generation capacity alone, represent the key dynamic controls on crust-derived helium enrichment, providing a new conceptual framework for helium resource assessment and exploration targeting in continental cratonic basins.
