Improvement of Waterflood Oil Recovery by Wettability Alteration in Carbonate Reservoirs

Abstract

Most carbonate rocks tend to be oil wet, which negatively affects the recovery of hydrocarbons in waterflooding. Studies have shown that alteration of wettability through ion adjustment and surfactant addition can alter the wettability of the carbonate rock from oil wet to moderate or water wet. Through alteration of wettability recovery can be increased to higher values than what is expected when the reservoir is flooded with seawater. Adjustment in concentration of Mg2+, Ca2+, and SO42− ions and addition of surfactants have shown to be most effective in altering wettability. There has been limited research related to imbibition of carbonate rock samples representing reservoirs in brines containing solely Mg2+, Ca2+, or SO42− at atmospheric conditions. The effect of Non-Ionic and mixed Non-ionic with cationic surfactants on the alteration of wettability has been addresses in previous research. In this study, Imbibition experiments were done on samples using brines of different ion components and concentrations to study the effect of salinity and ion composition on the recovery. Imbibition of lower salinity brines showed noticeably higher recovery than high salinity brines. The results are presented in dimensionless form of recovery and time for better comparison of wettability alteration and effect between samples. Lower salinity brines of Ca2+ and SO42− ion composition showed highest improvement in recovery. Surfactants were added during the imbibition measurement to view any further enhanced recovery at atmospheric conditions.