Very high oil recoveries are achieved when an inert gas displaces continuous oil or residual oil downwards in water wet columns of glass beads and in sandstone cores, provided that a semipermeable membrane is used at the production end to prevent gas breakthrough. In this paper, pore level mechanisms that control this displacement process are elucidated, as revealed by experiments in 2-dimensional pore network micromodels and unconsolidated columns of glass beads. Visualizations of the displacement mechanisms are presented and their effect on oil production is discussed. By applying principles of capillarity and by using well defined pore geometries, equations have been developed for predicting both water and oil distributions at the pore level.

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