Wettability effects in three-phase gravity drainage

We first analyze stable configurations of gas, oil and water in single pores with different wettabilities. The existence and stability of oil-layers in fractionally-wet systems is investigated for a triangular pore geometry. We find that for spreading systems there are always paths for oil to drain to low saturations, and that the final oil saturation increases as the fraction of oil-wet surface is increased. Water changes from being the most wetting phase to the most nonwetting phase as the fraction of oil-wet surfaces increases from 0 to 100%. We then describe experiments on sand columns with different fractions of water- and oil-wet sands. Percolation concepts are employed to relate the pore-level configurations of fluids to the measured residual water and oil saturations.