Effect of water-extractable carboxylic acids in crude oil on wettability in carbonates

The acidic components of the crude oil have a profound effect on the initial wetting conditions and possible wettability alteration by seawater in carbonates. In this work, three types of crude oils with different concentrations of water-extractable acidic components were prepared from a base oil: (1) a reference oil, RES-40 [acid number (AN) = 1.90 mg of KOH/g and base number (BN) = 0.51 mg of KOH/g], (2) a treated oil depleted in water-extractable acidic components, termed treated oil (TO) (AN = 1.50 mg of KOH/g and BN = 0.53 mg of KOH/g), and (3) a crude oil containing only water-extractable acidic components, termed EWS-oil (AN = 1.90 mg of KOH/g and BN < 0.01 mg of KOH/g). Outcrop chalk cores were used as the porous medium, and the difference in oil displacement efficiency and wettability was compared. The spontaneous imbibition (SI) process was performed in two steps: first imbibing with formation water without any wettability modification and then with seawater, which acted as a wettability modifie...

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