Changes

* sigma is the interfacial tension,  

* sigma is the interfacial tension,  

* theta is the contact angle between the wetting fluid and the solid surface, and  

* theta is the contact angle between the wetting fluid and the solid surface, and  

* r is the capillary (pore throat) radius (Vavra et al., 1992).

* r is the capillary (pore throat) radius (Vavra et al., 1992{{citation needed}}).

The volume of water remaining at a given height in a reservoir is a function of the balance of capillary forces pulling the water up from the hydrocarbon-water interface and the force of gravity acting together with the density contrast between the reservoir fluids, acting to pull the water down (Arps, 1964). Thus, a given part of the pore space within the hydrocarbon leg can contain both hydrocarbons and water. The fraction (percentage) of water to total fluid volume is termed the water saturation.

The volume of water remaining at a given height in a reservoir is a function of the balance of capillary forces pulling the water up from the hydrocarbon-water interface and the force of gravity acting together with the density contrast between the reservoir fluids, acting to pull the water down (Arps, 1964{{citation needed}}). Thus, a given part of the pore space within the hydrocarbon leg can contain both hydrocarbons and water. The fraction (percentage) of water to total fluid volume is termed the water saturation.

[[file:Mem91BuoyancyForcesFig26.jpg|thumb|{{figure number|1}}Water saturation decreases with height in an oil column. The volume of water is a function of the balance of capillary forces pulling the water up from the oil-water interface and the force of gravity acting together with the density contrast between the reservoir fluids, tending to pull the water down.]]

[[file:Mem91BuoyancyForcesFig26.jpg|thumb|{{figure number|1}}Water saturation decreases with height in an oil column. The volume of water is a function of the balance of capillary forces pulling the water up from the oil-water interface and the force of gravity acting together with the density contrast between the reservoir fluids, tending to pull the water down.]]