The influence of gas injection and production rates on pore-scale gas-water movement in low-permeability heterogeneous gas storage based on microfluidic technique

Low permeability heterogeneous gas storage is one of the important types of gas storage currently, and clarifying its microscopic gas water movement laws is crucial for improving the operational efficiency of gas storage. This study investigated the impact mechanism of gas injection and production rates on the gas-water movement behaviors at the pore-scale in low-permeability heterogeneous gas storages. To achieve this, a series of microfluidics experiments was conducted using large-scale chips under different injection and production rate conditions. The dynamic evolution of gas-water distributions, migration pathways, and gas-bearing pore spaces was recorded and quantitatively analyzed. The results indicate that slow injection combined with fast production significantly improved the utilization efficiency of gas-bearing pore spaces. Slow injection promoted more uniform gas displacement and reduced fingering, while the fast production suppressed water occupation in pore throats and mitigated water-locking effects. Conversely, fast injection and slow production led to rapid early gas invasion but increased the formation of water-locked capillary valves, resulted in a higher proportion of bound pore-throats and reduced effective gas storage spaces during subsequent rounds. Microscopic observations showed that repeated injection–production processes progressively increase water-locked throats, limiting further gas migration. Parameter analysis based on capillary number demonstrated that the slow injection/fast production strategies favored the expansion of dynamic gas-bearing boundaries and lowered bound-throat ratios. Furthermore, pore-scale transport mechanisms are discussed using single pore-throat models, highlighted the roles of wettability, corner flow, and capillary resistance in controlling gas advance and retreat behaviors. The findings providing valuable insights into optimizing injection-production strategies for low-permeability heterogeneous gas storages, and offering theoretical support for improving gas storage efficiency and reducing water-locking effects.