Electrokinetic transport in saturated and unsaturated porous media: A pore-scale view.

Electrokinetic transports in porous media play a crucial role in diverse applications such as geophysical exploration, nuclear waste disposal, water desalination, soil and groundwater remediation, low-salinity waterflooding, and ionic battery operation. This review systematically examines electrokinetic mechanisms in single-phase and multiphase flows in porous media, with a special focus on multiscale and multiphysico-chemical coupling effects. After briefly introducing fundamental theories on microscale electrokinetic transports, we highlight the impact of nanoscale confinement and geometric regulation at first on single-phase electrokinetic flows and ion transport. Next, we discuss the influences of non-uniform ionic concentration and temperature fields on electrokinetic transports, encompassing the impact of surface chemical reactions via charge regulation and reactive transports, and thermodiffusion effects. Furthermore, we provide a concise overview of the current understanding of electrokinetics in multiphase flows, including interfacial charging, wettability alteration, and electrokinetic multiphase dynamics. Finally, we try to outline future research directions, addressing statistics-based theories, multiscale simulations, and advanced experimental designs for electrokinetic transports in porous media.