Reservoir engineering calculations frequently require consideration of coexisting oil, water, and gas phases. Such three-phase flow occurs when a reservoir is produced below the solution gas/oil pressure or when enhanced recovery processes such as water-alternating-gas flooding or simultaneous gas/water flow occurs. For this reason, reservoir simulators generally include three-phase relative permeability prediction methods. Two- and three-phase relative permeabilities were measured on a mixed wettability carbonate sample having a bimodal pore size distribution. The results of the three-phase measurements were compared with values obtained from prediction models based on two-phase data. A model has been proposed that includes a "trapped gas effect" which leads to a reduced waterflood residual oil saturation. The proposed model appears to be superior to the Stone Model II, especially in the low oil saturation range.

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