Interface stability of gas bubbles in saline-aquifer compressed air energy storage: Heterogeneity-induced fingering evolution

Underground saline aquifers are increasingly considered as viable alternatives to salt caverns for compressed air energy storage (CAES) due to the broad geographic distribution and excellent sealing capacity. However, permeability heterogeneity in reservoirs significantly disturbs gas-water two-phase flow, causing interface instability and fingering phenomena that reduce energy storage efficiency. To investigate these processes, a numerical model was developed to integrate air-water two-phase flow with reservoir deformation and introduce the fingering factor (F) to quantitatively evaluate interface stability. The model simulates the formation and evolution of gas bubbles during compressed-air injection under both homogeneous and heterogeneous permeability conditions. Results indicated that gas bubble formation was divided into three stages: initial pressure core formation, rapid volume expansion, and lateral plume migration. In horizontal layers, the fingering factor (F) increased significantly with permeability ratio (K), while layer thickness (δ) and distance from the wellbore (x) showed relatively minor effects. In inclined weak layers with high permeability ratios, small dip angles promoted elongated, sharp finger-like intrusions along the layer, while larger dip angles promoted dominant flow channels and induced water phase trapping. In contrast, inclined weak layers with low permeability ratios supported relatively uniform gas migration across all dip angles, yielding a more stable gas-water interface.