The surface forces between a crude-oil and its components (oil, resin, and asphaltenes) and a glass substrate have been measured in brine of different salinity and pH using an atomic force microscope. The force vs. distance curves are used to measure the critical disjoining pressure for wettability alteration, i.e., departure from water-wet conditions. The measured data are compared with the classical DLVO theory to explore the nature of interaction of these components with mineral substrates.

The results indicate that the resins and asphaltenes obey the DLVO theory, i.e., the stability of the brine film decreases with increasing brine salinity and increases with increasing solution pH. The opposite trend is observed with increasing salinity for the nonpolar (pentane soluble) fraction and for the crude oil itself. The deviation from DLVO predictions indicates that for nonpolar oils, hydrophobic interactions may play an important role in the interaction of oils with minerals and, therefore, in wettability reversal