Effect of CO2 diffusion on wettability for hydrocarbon-water-CO2 systems in capillaries

The importance of wettability in enhanced oil recovery with high pressure CO2 has been demonstrated by some authors. When CO2 diffuse in hydrocarbons, it promotes swelling and reduction in contact angle and surface tension, these changes improve the tendency to fill the corners of solid surfaces, therefore filaments arise in corners. In this work, hydrocarbon-water-CO2 behavior was studied in cylindrical and square capillaries. Square capillaries were used in order to observe the wetting in corners. Cylindrical capillaries were used to determine if there is swelling in hydrocarbons due to the CO2 mass transfer, first through the water and then through the hydrocarbon. Contact angle and interfacial tension were measured in an attemp to explain the results. It was demonstrated that the CO2 diffusion occurs first through water and then through hydrocarbons. The CO2 diffusion is evident due to the contact angle diminution and the displacement of water-hydrocarbon interfaces. In addition, it was found that the behavior of water-hydrocarbon interphase depends on contact angle and surface tension. Finally, when interfacial tension is lower, the displacement is different and contact angle increasing is higher, as it was concluded by Campbell and Orr [1].