Gas-Water Two-Phase Seepage Model of Capillary Bundle Considering Pore Throat Structure and Analysis of Influencing Factors.

The technology for geological storage of carbon dioxide (CO2) involves a complex gas-water two-phase seepage process. It is essential to clarify the two-phase seepage law in porous media to increase the efficiency of the CO2 storage. In this paper, based on the classical capillary bundle seepage model, parameters such as roughness, water film thickness, and pore throat ratio are introduced to modify the model, and the physical model of a rough curved capillary bundle considering pore throat structure is constructed. According to the concept of critical displacement aperture, the distribution states of the gas phase and water phase are set respectively, and the two-phase seepage model of a rough curved capillary bundle with pore throat structure is finally obtained. The model's validity was confirmed by comparison with the classical model and findings from nuclear magnetic resonance experiments. At the same time, the sensitivity characteristics of effective permeability and displacement efficiency to each influencing factor are analyzed. It is found that the effective permeability mainly increases with the increase of saturation and maximum pore size, and decreases with the increase of the diameter ratio of pore belly to pore throat. The efficiency of fluid displacement is primarily enhanced by higher levels of saturation, larger minimum pore sizes, and greater gas injection pressures. Conversely, it is reduced when there is an increase in the thickness of water films and a higher ratio of the diameter of the pore belly to that of the pore throat.