Implications of helium accumulation models in helium-rich basins in China for the enrichment and exploration of helium in coal measures

Abstract

BackgroundHelium is a strategic resource in serious short supply in China, and intensifying its exploration is crucial to national resource security. China enjoys abundant coal measure gas and significant potential for associated helium accumulation. However, relevant research remains in its infancy. MethodsBased on a summary and analysis of helium generation, migration, and accumulation theories in natural gas reservoirs, this study systematically investigated the enrichment patterns of helium in coal measures and proposed exploration targets. Results and Conclusions The insights reveal that the helium resources in China exhibit a distribution pattern of zoning in both north-south and east-west directions. Specifically, helium-rich basins in China are distributed in three regions: the eastern mantle-derived helium-rich region, the central crust-derived helium-rich region, and the western region rich in helium from a crust-mantle mixing source. The spatial differentiation of these helium resources is governed by both the structural types of basins and regional evolutionary background. Helium accumulation follows a dynamic process consisting of helium exsolution from source rocks, cross-strata migration, and accumulation in traps. This process is jointly controlled by the sealing performance of helium sources, the effectiveness of migration pathways (fault systems and the capillary pressure of micropores), hydrodynamic fields, and reservoir-cap rock configuration. Among these factors, traps serve as a dominant factor in helium accumulation, helium vertical migration primarily occurs through fault systems, lithological reservoir-cap rock configuration provides auxiliary helium sealing, and the dissolution-exsolution mechanism facilitates local helium enrichment as a supplement. In coal-bearing basins, helium exhibits a prolonged generation period compared to coal-seam hydrocarbons. However, the spatiotemporal coupling of helium and hydrocarbons can be observed during peak helium accumulation. Coal measures serve as dual helium sources (i.e., self-generation endogenous and self-storage exogenous helium), forming multi-layer stacked helium-bearing systems by combining natural gas reservoirs. Helium in coal measure is characterized by multi-source mixing, widespread association with other gases, three-dimensional enrichment, and low concentration. Therefore, its accumulation mechanisms involve multiple critical scientific issues including the contributive degrees of multiple sources, cross-system diffusion dynamics, the accumulation-controlling effect of structures, and the evaluation of low-abundance resources. Future exploration should focus on microstructural systems in tectonically active zones, multiple types of coal measure reservoirs, deep reservoirs, and basin-margin gas reservoirs. It is recommended to conduct the exploration and production of helium in coal measures following the philosophy of “compensating quality with quantity”. Specifically, the risk exploration of helium in coal measures in representative potential regions such as the Ordos Basin, western Guizhou, and eastern Yunnan should be prioritized; it is necessary to develop a comprehensive technical system that incorporates the selection of the optimization target areas and the commingled production of multiple coal measure reservoirs and involves the entire chain covering exploration, development, and utilization, and it is advisable to integrate helium purification technologies and the “helium-coal-gas” collaborative development model. All these will help achieve the efficient production of helium in coal measures. The result of this study will offer a theoretical reference and technical pathway for the exploration of helium in coal measures, thereby contributing to the national helium resource security.

Keywords

• helium
• coal measure gas
• associated gas
• structure
• coal
• accumulation model