Enhanced oil recovery (EOR) by alkaline flooding for conventional oils has been extensively studied.For heavy oils,investigations are very limited due to the unfavorable mobility ratio between the water and oil phases.In this study,the displacement mechanisms of alkaline flooding for heavy oil EOR are investigated by conducting flood tests in a micromodel.Two different displacement mechanisms are observed for enhancing heavy oil recovery.One is in situ water-in-oil (W/O) emulsion formation and partial wettability alteration.The W/O emulsion formed during the injection of alkaline solution plugs high permeability water channels,and pore walls are altered to become partially oil-wetted,leading to an improvement in sweep efficiency and high tertiary oil recovery.The other mechanism is the formation of an oil-in-water (O/W) emulsion.Heavy oil is dispersed into the water phase by injecting an alkaline solution containing a very dilute surfactant.The oil is then entrained in the water phase and flows out of the model with the water phase.