For water-wet reservoirs, Craig (1971) gave some general water-oil relative permeability end points. Water will start flowing along with oil once the water saturation is greater than roughly 20–25%. This value is the irreducible water saturation; the volume of water bound and immobilized by adhesive attraction to the surface of the pores. Oil will stop flowing where the water saturation in the rock is about 70–80%. When this happens, there will not be enough oil to provide a continuous volume throughout the rock. Interfacial tension will cause the oil stream to snap off and fragment into immobilized globules and strands of residual oil. | For water-wet reservoirs, Craig (1971) gave some general water-oil relative permeability end points. Water will start flowing along with oil once the water saturation is greater than roughly 20–25%. This value is the irreducible water saturation; the volume of water bound and immobilized by adhesive attraction to the surface of the pores. Oil will stop flowing where the water saturation in the rock is about 70–80%. When this happens, there will not be enough oil to provide a continuous volume throughout the rock. Interfacial tension will cause the oil stream to snap off and fragment into immobilized globules and strands of residual oil. |