Role of relative permeability hysteresis in modified salinity water flooding

Abstract

Many laboratory and field scale trials have shown that modified salinity water flooding increases the mobility of oil and improves oil recovery. However, field scale simulation of the process guided by core flooding data leads to inaccurate prediction of oil recovery if the effect of the saturation history of the reservoir on relative permeability is ignored. Here, we address this problem by proposing three models illustrating the interplay among wettability alteration, hysteresis effect, and fluid flow transport in porous media. The models provide the variation of imbibition and secondary drainage saturation curves versus salinity caused by wettability alteration. Our simulations show that including hysteresis together with the wettability alteration process can better quantify the re-trapping of the oil that is mobilized due to wettability alteration of the reservoir. We further show that in the capillary transition zone, where water saturation varies from top to bottom of the reservoir, oil recovery continues for a long time, although the water cut starts early, in comparison with a reservoir with an initial uniform water saturation. Despite many experiments conducted for advanced waterflooding, our observations show that measuring the secondary drainage and imbibition saturation curves is essential and serves as a valuable input for the field scale simulation of modified salinity waterflooding of water flooded reservoirs with highly non-uniform saturation history.