Study on Microscopic Flow Law of Ionized Water Flooding

Abstract Ionized water flooding is a low-cost enhanced oil recovery method, but its microscopic behavior in tight sandstone nanopores remains insufficiently understood. Molecular dynamics simulations were conducted to evaluate the effects of temperature (325–415 K), displacement pressure (5–20 kcal/(mol·Å)), mineral surfaces (hydroxylated silica, Illite, kaolinite, and montmorillonite), and crude oil composition (naphthenic acid, propyl mercaptan, toluene, n-octane, and a mixed-component model) on crude oil mass density, velocity, interfacial slip, flooding efficiency, and wettability evolution. Crude oil exhibited parabolic velocity profiles with nonzero wall velocities, indicating interfacial slip within the nanopores. Flooding efficiency increased from approximately 65% at 325 K to 77% at 415 K, while increasing displacement pressure enhanced crude oil velocity and slip length. Ionized water reduced oil-mineral contact and promoted wettability alteration toward a more water-wet state, with more pronounced spreading on kaolinite and montmorillonite. By systematically comparing multiple reservoir and fluid factors within a unified molecular-scale framework, this study links flow behavior, interfacial slip, flooding efficiency, and wettability evolution, providing a theoretical basis for evaluating the applicability of ionized water flooding in tight sandstone reservoirs.