Molecular insights on the interfacial and transport properties of supercritical CO2/brine/crude oil ternary system

In this study, we conducted a series of molecular dynamics simulations to investigate the effect of supercritical carbon dioxide (sc-CO2) on the interfacial and transport properties of brine/crude oil at the reservoir conditions. We also studied the interfacial behavior of asphaltenes in presence of CO2. Crude oil was resembled by several hydrocarbons which are hexane, heptane, octane, nonane, cyclohexane, cycloheptane, benzene and toluene. The results showed that CO2, aromatics and asphaltenes accumulate at the interface at low CO2 mole fraction, however, as CO2 mole fraction increases, the relative density, the ratio of the density at the interface to the bulk density, decreases for both CO2 and aromatics. The decrease in CO2 relative density is due to the amount of CO2 dissolved in the oil bulk, which increases as CO2 mole fraction increase. It also found that CO2 displaces the oil molecules away from the interface, thus the relative density of aromatics decreases. Interestingly, it was found that as CO2 mole fraction increase, it enhances the face-to-face stacking between asphaltene molecules as noticed from the radial distribution function calculations. CO2 also force some asphaltene molecules to leave the interface and being dissolved and aggregated in the oil bulk. It also found that as CO2 mole fraction increased in the system, it dilutes the interface, penetrates to the water phase, forms hydrogen bonds with water and due to these effects, it reduces the interfacial tension of brine/crude oil system. The diffusivity of supercritical CO2/brine/crude oil system was also increased as a function of CO2 mole fraction. This study provides insights of the underlying interfacial properties from molecular level for a more realistic system of brine/crude oil. (C) 2018 Elsevier B.V. All rights reserved.