  In the present study, we report our findings on various asphaltenes-water
interactions at a high reservoir condition (550 K and 200 bar) and the role of
water in asphaltene association during the waterflooding process. Molecular
dynamics (MD) simulations are performed on oil/water and oil/brine systems. The
oil phase is composed of asphaltenes (10 wt%) and o.xylene in which asphaltenes
are entirely soluble. Seven different model-asphaltenes with diverse molecular
weights, architectures, and heteroatom contents are employed. Interestingly, MD
results indicate that asphaltenes become less soluble in oil when water is
partially misciblized in the oil phase. All model-asphaltenes containing
nitrogen and/or oxygen atoms in their structures are prone to association. The
driving force behind asphaltene aggregation is shown to be an asphaltene-water
hydrogen bond. The utilization of the brine (3.5 wt% NaCl) instead of pure
water induces a slight decrease in asphaltene propensity for aggregation due to
salt-in effect. MD results suggest that face-to-face contact is the prominent
stacking of asphaltene molecules in their aggregates.

Chemical Physics