Effect of mixed surfactant on the wettability and oil recovery of kaolin-oil-asphaltene system

In this study, a series of mixed surfactant solutions were used as mimic flooding solutions, n-paraffin and/or asphaltene was used as mimic oil, and kaolin powder containing oil/asphaltene on its surface was used as an adsorbed oil reservoir. The relationship between the oil:kaolin and asphaltene: kaolin ratio with wettability on the kaolin surface and the corresponding percentage of oil recovery was studied. In this respect, four sets of oil:kaolin ratios, 6.25%, 12.5%, 25%, and 37.5%, were prepared, and for each set, a series of surfactant concentrations was used at a certain asphaltene: kaolin ratio of 0.05%. Moreover, an advanced study was carried at different asphaltene: kaolin ratios of from 0.05 to 12.8% using a 2% surfactant concentration and an oil:kaolin ratio of 37.5%. The wettability of the kaolin powder was studied based on the Washburn equation, which was expressed as contact angles. It was found that the maximum oil recovery was recorded at the minimum contact angle at a concentration value higher than that of the critical micelle concentration (CMC) of the mixed surfactant. The maximum oil recovery for the asphaltene/oil/kaolin phase systems was less than half the oil recovery for the corresponding oil/kaolin phase systems. This may be due to the fact that a molecular film of asphaltene covers the interface in the former case more than in the latter one. Consequently the contact angle of asphaltene/oil/kaolin surface was increased; thus, the penetration rise of oil through the porous media should decrease.