Effect of Alkaline Preflush in an Alkaline-Surfactant-Polymer Flood

An ultralow interfacial tension alkali-surfactant-polymer formulation was developed for a sandstone reservoir. Phase behavior was studied with the reservoir oil at different water–oil ratios and varying salt/alkali concentrations. The rheology of the resulting microemulsion phases was measured with and without polymers. The surfactant formulation was tested with a field core and an out-crop core, with and without an alkaline preflush. Waterflood recovered about 48% of the oil in place and reduced the oil saturation to 35% for the field core. The tertiary ASP injection in the field core without alkaline preflush yielded 80% cumulative oil recovery; the recovery increased to 85% in the same core (and the same surfactant formulation) if the alkaline preflush was used. The oil recovery in the out-crop core with the alkaline preflush was 94%. Alkaline preflush increases the core salinity to the optimum salinity of the surfactant formulation before the surfactant slug.