It is well known that the majority of carbonate reservoirs are neutral to oil-wet. This leads to much lower oil recovery during waterflooding since there is no spontaneous imbibition of water in heterogeneous reservoir displacement. It has been verified by a number of researchers that Adjustment of ion concentration in brine solutions, or adding surfactant solutions can enhance the oil recovery by altering the wettability. In the published literature, contact angle studies usually refer to measurement on calcite crystals and there are no results for the contact angle of carbonate porous media representative of reservoir rocks. Moreover, there are few studies on the effect of non-ionic surfactants, compared to those for ionic surfactants. Understanding the effect of various ions and their concentration in the injection brine on the wettability of the Limestone outcrop core samples is the first step for tailoring of the optimum injection brine. This will be followed by a study of the effect of surfactant on the wettability of calcite crystal samples. The evaluation of the results may provide guidelines for the design of injection brines for efficient enhanced oil recovery from carbonate reservoirs. In this work, a procedure is established for the measurement of the contact angle on limestone outcrop core samples. Results showed that, at atmospheric conditions, low salinity CaCl 2 solution induced the most significant improvement on the wettability of the outcrop sample. Moreover, among all the non-ionic surfactants studied, only the presence of the two first members of the 15S analogous series might lead to a slight decrease of the contact angle.

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.