Relationships among capillary pressure, permeability, and oil accumulation. The free water surface is defined as that surface beneath which there is 100% water production. It corresponds to Pc = 0 on a capillary-pressure curve. The entry pressure is the pressure at which a hydrocarbon first enters the reservoir, so that both water and oil are produced. The irreducible water saturation is that saturation (height above free water surface) above which no more water—only oil—is produced. The zone between 100% oil production and 100% water production is the transition zone. Sneider (1987). Reprinted with permission of AAPG, whose permission is required for further use.
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