Influence of surface roughness and asymmetry on flow regimes of water and gas in clay nanopores

The understanding of gas–liquid two-phase flow in rough nanopores is essential for efficient shale gas extraction. In this study, we employed the molecular dynamics simulation to investigate the mechanisms of water–gas two-phase flow in rough shale nanopores using illite clay minerals. To construct rough nanopores, the rough particles are introduced onto smooth wall surfaces, resulting in two types of rough pore structures: symmetric and asymmetric rough nanopores. The simulation results reveal distinct gas cluster shapes during two-phase flow in different rough nanopores: bullet-shaped clusters in smooth channels, bulb-shaped clusters in symmetric rough channels, and wave-like clusters in asymmetric rough channels. Furthermore, the presence of rough particles near the pore walls leads to the formation of three adsorption layers of water molecules. These layers are attributed to the exposed hydroxyl groups on the rough particles. Additionally, the configuration of rough particles influences the formation of low-speed and high-speed flow regions. Comparatively, the velocity of water and methane phases is observed to be higher in asymmetric nanopores than in symmetric nanopores, indicating a greater obstruction effect on fluid flow in symmetric rough channels. The afore-mentioned findings provide valuable insights into the gas–liquid two-phase flow behavior in rough nanopores, which is crucial for optimizing transport and mass transfer processes in nanoscale systems.