Effect of polar organic components on wettability as studied by adsorption and contact angles

Adsorption of polar organic components onto the rock surface is one of the mechanisms that is believed to cause wetting alteration of a reservoir rock. Polar compounds in crude oil that are believed to be responsible for surface interactions and wetting properties include carboxylic and phenolic acids, organic bases and metal complexes. Known compounds, representative of these naturally occurring polar organic compounds in crude oil, have been chosen for adsorption and contact angle studies. Contact angles and adsorption isotherms in solid–oil–brine model systems have been examined as a function of component concentration in either water or oil and of salinity and pH of the water phase. The systems investigated consist of isooctane oil phase and water solutions of NaCl and CaCl2 as the water phase. Silicate glass and α-alumina were used as solid phases. The polar compounds were 1-naphtoic acid, 5-indanol, quinoline, vanadyl–octaethyl–porphyrin (VO OEP) and dihydrogen–octaethyl–porphyrin (H2 OEP). The compounds chosen represent functionalities that are found in polar crude oil fractions, such as asphaltenes, but still can be considered well-defined model substances. The components were adsorbed from the oil phase as well as from the water phase, both for contact angle and adsorption isotherm experiments. The results demonstrate the difference in adsorption behaviour between compounds with different functional groups of varying polarity and acidity. The importance of solid–solute interactions compared to solvent–solute interactions is demonstrated.