Source and primary factors controlling differential enrichment for helium in the Dongping gas field, Qaidam Basin

Background In recent years, promising helium-rich natural gas shows have been discovered in the Dongping gas field. However, the helium resources in the gas field exhibit lateral heterogeneity and vertical differential accumulation in multiple sequences, which restrict the further exploration of these resources.

Methods By analyzing the lateral and vertical distribution characteristics of helium in the Dongping gas field, this study explored its origin and sources, analyzed the differences in geological backgrounds between helium-rich and helium-deficient gas reservoirs, and systematically summarized the differential enrichment pattern across different blocks within the Dongping gas field.

Results and Conclusions In the Dongping gas field, helium-rich gas reservoirs are predominantly distributed in the shallowly buried Dongping-3 well block, where there is a significant positive correlation between helium and nitrogen concentrations. In contrast, the Dongping-1 and Dongping-17 well blocks exhibit gas reservoirs with a low helium concentration. Helium in the Dongping gas field is typically of the crustal origin, derived primarily from ancient basement rocks including granites and granitic gneiss. The differential helium enrichment is jointly controlled by multiple factors, including source rock availability, groundwater dynamics, natural gas charging intensity, and tectonic framework. The Dongping-3 well block is characterized by U- and Th-rich ancient granites, active groundwater circulation, relatively weak natural gas charging, and traps located in structurally high parts, and the basement exhibits the highest helium generation intensity of 1.02×10⁻¹² cm³/(a·g). In this well block, small traps located in the structurally high parts were formed by the large-amplitude tectonic uplift during the Himalayan period. These traps are conducive to the upward migration of ancient formation water containing He and N₂ at depth while also determining the small intensity of natural gas charging. Conversely, the Dongping-1 well block, despite its higher helium reserves, features weak groundwater hydrodynamics, intense natural gas charging, and traps in structurally low parts, which restrict helium migration and enrichment. The Dongping-17 well block shows the lowest helium concentration due to helium source rocks comprising schists, slates, and limestones with low U and Th concentrations and deeply buried traps. Based on research on differential helium enrichment in gas reservoirs with different basal lithologies and tectonic morphologies in the Dongping gas field, it is predicted that the structurally high parts in the piedmont paleo-uplift and paleo-slope area of the Altun Mountain are potentially play fairways for helium enrichment. This prediction is expected to provide guidance for the subsequent helium exploration and development work in the Qaidam Basin.