Interrelationship of Bulk and Oil-Water Interfacial Properties of Asphaltenes

Prediction and control of the behavior of asphaltenes have always been one of the most challenging topics in the oil and gas industry. To this aim, comprehensive knowledge of the bulk and surface behavior of asphaltenes and the possible interrelationship are required. Many attempts have been done so far to scrutinize the behavior of asphaltenes at the oil/water interface. In this study, the changes in surface behavior of asphaltenes upon aromaticity variation in the bulk are investigated. For this purpose, dynamic light scattering (DLS) experiments are accompanied with dynamic interfacial tension (IFT), and interfacial rheology measurements to analyze the asphaltene aggregation size, mobility and surface activity upon a change in the bulk aromaticity. A wide range of aromatic conditions was used to cover possible changes in asphaltene behavior before and after the onset point. The results revealed that the interfacial activity and the structure of the interfacial film of the asphaltenes are significantly influenced by the bulk properties. Low aromaticity conditions led to an increase in asphaltene surface activity and changed the dilational rheological parameters considerably although the general trend of the asphaltene adsorption remained similar. Moreover, the results demonstrated the importance of the aging time on the measured parameters, particularly for the samples beyond the onset point. Our findings also showed the importance of dynamic interfacial data over static ones. Finally, by applying the concept of diffusion coefficient it was suggested that only a small portion of asphaltenes remain surface-active practically, although their surface activity is directly correlated with the system aromaticity.