he Effect of Water-Soluble Compounds of Crude Oil on Wettability of Oil-Wet Calcite Surface in Low Salinity Water Injection

The impact of brine salinity and ion composition on wettability alteration of carbonate reservoir has been studied extensively in recent years. In these researches, the effect of salt water without considering the water-soluble amphiphilic compounds of crude oil has been investigated. In this study, the effect of water-soluble amphiphilic compound of crude oil beside ionic composition of MgCl2 and CaCl2 salt, on wettability alteration of oil-wet calcite surface were investigated. In this turn, distilled water and salt water of MgCl2 and CaCl2 with ionic strength of 0.5 molar were contacted to the crude oil for two weeks to be saturated with crude oil amphiphilic compounds. The effect of these compounds on water properties are examined with pH and total organic carbon (TOC) tests. In the next step, the effect of these compounds on wettability alteration of oil-wet calcite surface were investigated with exposing the oil-wet surfaces to the saturated and pure (without contact with crude oil) water samples and measuring the contact angle of oil droplet. The obtained results show that a low amount of acidic and basic compounds of crude oil (with higher portion of acidic compounds) were dissolved in contacted waters. The wettability of both surfaces which exposed to the pure and saturated waters changed toward water-wet. However, the changes in the presence of pure waters are much more than saturated waters. The results reveal that as well as water-soluble amphiphilic compounds the presence of similar rock composition ions in water can prevent the wettability alteration. In this turn, the wettability alteration of surfaces exposed to the CaCl2 salt waters (in both group of waters) were low and in saturated water was lower.