Waterflood residual oil saturation, in mixed wettability reservoirs, is often a strong function of pore volumes (PV) injected. The Endicott Field, Alaska displays typical mixed wettability behavior with coreflood remaining oil saturation varying from 40% at 1 PV to 12% at infinite PVs. Although only about 1 PV will be injected in the reservoir, surface film drainage may act to reduce oil saturation making determination of the correct effective residual oil saturation difficult.

Accurate determination of waterflood residual oil saturation is essential for assessment of waterflood performance and evaluation of enhanced recovery processes. To minimize uncertainty in predicting effective residual oil saturation in mixed wettability reservoirs it is necessary to consider the competing effects of relative permeability, gravity forces, and imbibition capillary pressure. A mechanistic simulation approach is presented for scaling up laboratory results, that considers all active forces.

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