Effect of polar organic components on wettability as studied by adsorptionand 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 surf ace interactions and wetting properties include carboxylic and phenolic aci ds, organic bases and metal complexes. Known compounds, representative of t hese naturally occurring polar organic compounds in crude oil, have been ch osen for adsorption and contact angle studies. Contact angles and adsorptio n isotherms in solid-oil-brine model systems have been examined as a functi on of component concentration in tither water or oil and of salinity and pH of the water phase. The systems investigated consist of isooctane oil phas e and water solutions of NaCl and CaCl2 as the water phase. Silicate glass and or-alumina were used as solid phases. The polar compounds were 1-naphto ic acid, 5-indanol, quinoline, vanadyl-octaethyl-porphyrin (VO OEP) and dih ydrogen-octaethyl-porphyrin (H-2 OEP). The compounds chosen represent funct ionalities 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 fu nctional groups of varying polarity and acidity. The importance of solid-so lute interactions compared to solvent-solute interactions is demonstrated. (C) 1999 Elsevier Science B.V. All rights reserved.