Interrelationship of bulk and oil-water interfacial properties of asphaltenes

Abstract

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, many attempts have been done so far to scrutinize the behavior of the asphaltenes in the bulk and at the oil/water interfaces. However, still more comprehensive knowledge about the relationships between the bulk and interfacial properties of the asphaltenes is required. In this study, the changes in the surface behavior of the asphaltenes upon aromaticity variation in the bulk are investigated. For this purpose, dynamic light scattering (DLS) experiments are accompanied by dynamic interfacial tension (IFT), and interfacial rheology measurements to analyze the asphaltene aggregates 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 adsorbed layers 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. For instance, the results illustrate the instantaneous elasticity of about 40 mN/m (around 0.08 Hz) for 500 mg/L asphaltene in heptol (50–50) while for the toluene sample, this value is reduced to about 30 mN/m and occurs at higher frequencies (about 0.12 Hz). 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 can be assumed that only a small portion of the asphaltenes are practically surface-active, and their surface activity is directly correlated with the aromaticity of the solution.