Mechanistic understanding of asphaltenes surface behavior at oil/water interface: An experimental study

Asphaltene precipitation during natural depletion and enhanced oil recovery (EOR) methods is one of the problematic challenges, which can affect the production in oil reservoirs. Asphaltenes as the most surface-active agents in the crude oil can interfacially interact with water molecules. As asphaltenes absorb to oil/water interface, water potentially can be involved and affect asphaltenes surface activity. This paper set out to investigate the surface activity of asphaltenes at the oil/water interface. Extensive sets of IFT tests were conducted with synthetic oil extracted from three different real reservoir crude oil samples in the presence of the distilled water. Results showed that IFT changes are not the dominant function of asphaltenes bulk concentration. However, it was revealed that asphaltenes surface concentration, which is dependent on the thermodynamic stability of asphaltenes within the bulk, controls IFT changes. Further, it was shown that IFT changes versus pressure are non-linear, indicating a non-linear function of asphaltenes surface behavior against pressure. Diluting a crude oil sample with normal heptane (n-C7) at various dilution ratios, indicated that dilution with a precipitantcauses asphaltenes to be less surface active. The results of this study indicated that aging reduces asphaltenes surface activity only when the crude oil is diluted which revealed that asphaltene precipitation is a time-dependent phenomenon. Finally, it identified that sudden pressure shocks have no significant effect on asphaltenes behavior in crude oil. The results of this study shed new light on the mechanism of the asphaltenes surface behavior at oil/water interface which could be of crucial importance in flow assurance engineering as well as water flooding process. (C) 2019 Elsevier B.V. All rights reserved.