Wettability Alteration with Smart Water on Carbonate Reservoirs - Effect of Phosphate and Sulfate Multivalent Anions

Increasing evidence has shown that the adjusting of ionic composition of water injection in the reservoir can improve oil recovery. The carbonate reservoirs comprise about the 50% of oil reservoirs and most of them are neutral to oil wet. More than 65% of carbonate reservoirs are oil wet and 12% are intermediate wet. Wettability is a very important factor in the oil recovery mechanisms. Because it has drastic effect on the distribution and flowing of the oil and water in the reservoirs. Ionic composition adjusting of water which is referred as smart water is known as one of wettability alteration method in the carbonate reservoirs. Although the mechanisms behind of this technic don’t have recognized as well but wettability alteration is a result of these mechanisms. The effect of individual ions must be investigate for better recognition of mechanisms causing improving oil recovery. For complete investigation of mechanisms of smart water technic it must be studied about the crude oil/formation water/injection water/rock system but this system is very complex and for better understanding it must become simpler. In this study, the aim is the wettability alteration deal with smart water using sessile drop method for contact angle measurement. The effect of phosphate and sulfate multivalent anions in different temperature, pH and concentration of them was studied. Modified brines containing phosphate salt were more effective than with sulfate salt. In acidic pH both anions have not good effect but in upper pH they can alter wettability to more water wetting. The phosphate was more soluble in upper temperatures and both anions have better wettability alteration properties to water wetting.