Investigation of Wettability Alteration due to Smart Water Injection into Carbonate Reservoirs by Zeta Potential and Contact Angle’s Tests

Nowadays, a wide-range of EOR methods are used to enhance oil recovery from carbonate reservoirs. They arethe most scattered reservoirs all over the world.Smart water injection is one of the popular and newest methods in EOR. It controls the wettability of rocks. In this study, wettability alteration and the rate of wettability modification are investigated by zeta potential and contact angle experiments. Smart water is a kind of water with controllable salinity and ion concentration. In this regard, five different samples of smart water were synthesized by different concentrations of SO42-, Ca2+, Mg2+ ions, based on Persian Gulf seawater TDS. Then, the results were compared to those obtained from formation water and seawater, as the blank samples. The ability of the smart waters in controlling rock wettability was examined by pursuing of zeta potentials in the presence of different water samples at ambient condition. According to the results, the zeta potential of carbonate sands in the presence of water samples SW#4SO4, SW#2SO4, SW, and formation water was -9.61,-7.13,-1.25 and15.8, respectively. The data suggested that the samples SW#4SO4 and SW#2SO4 are the two most effective smart water samples in wettability alteration. After that, the most capable smart water samples with the most negative zeta potential was selected to be used for the contact angle experiment. The results showed that, in the presence of SW#4SO4, SW#2SO4, SW and formation water, the final contact angle decreased from their initial values (144.23˚, 149.68˚, 136.63˚, and 139.89˚) to 87.10˚, 105.17˚, 135.66˚, and 143.13˚, respectively, which is in a good agreement with the results of zeta potential. These data showed that the amount of sulfate ions in the smart water can control the wettability of rock from oil to water-wet state.