Experimental validation of the theory of extending two-phase saturation-pressure relations to three-fluid phase systems for monotonic drainage paths

An experimental apparatus was developed to directly measure functional relationships between fluid saturations S and pressures P of three-phase (air-oil-water) or two-phase fluid systems in unconsolidated porous media. Porous ceramic rings were chemically treated to enable simultaneous measurement or regulation of water and oil fluid pressures. Direct measurements of water and total liquid saturations in three fluid phase systems as functions of oil-water and air-oil capillary heads, respectively, were compared to S-P measurements in two-phase air-oil and oil-water systems for monotonic drainage saturation paths to test commonly employed assumptions of extending these two-phase S-P measurements to air-oil-water fluid systems. Excellent agreement was observed between total liquid saturations in an air-oil-water system and oil saturations in a two-phase air-oil system as functions of air-oil capillary head. Excellent agreement was also found between water saturations in air-oil-water and oil-water fluid systems versus oil-water capillary head. The accordance between two- and three-phase results indicates that two-phase air-oil S-P relations can be used to predict total liquid content in air-oil-water systems and that two-phase oil-water S-P relations can be used to predict water saturation in three-phase systems for rigid water wet porous media subject to monotonic drainage saturation paths. The S-P scaling format proposed by Parker et al. (1987a) to generate a single multiphase retention function capable of describing S-P relations of either two- or three-phase fluid systems was further evaluated using the measured two- and three-phase S-P relations. Comparison of scaled two- and three-phase S-P drainage data indicated that a single scaled multiphase retention function may be employed to describe S-P relations in either two- or three-fluid phase systems.