Experimental Investigation of the effect ions concentration, aging temperature and pH on Wettability alteration Process in Carbonate Rocks by Contact Angle Measurement

Naturally fractured carbonate reservoirs have very low oil recovery efficiency owing to their wettability and tightness of matrix. Recovery efficiency can be considerably improved by changing reservoir rock wettability from oil-wetting to water-wetting state. In this work، the effect of different ions، pH، and temperature on wettability of carbonate rocks was investigated by means of contact angle measurements. The results indicate that the Ca2+، Mg2+ and SO42- ions can change the wetting state of carbonate rocks toward water-wetting، both individually and when they are mixed. According to our measured contact angle data، simultaneous increase of the concentration of both Mg2+ and SO42- ions has positive impact on wettability alteration of the carbonate surface more than that of obtained by variation of individual ions. It is also found that addition of NaCl salt changes the wettability to more oil-wetting. We did، moreover، measure the impact of temperature on the wettability change of the carbonate surface. It is observed that higher temperatures result in water-wet surfaces، owing to facilitating fatty acid desorption. However، the impact of pH on wettability alteration is found to be complex، resulting in various wettability states by changing pH from 3 to 10.