Asphaltene Aggregation in Oil and Gas Mixtures: Insights from Molecular Simulation

The dynamics of asphaltene molecules is highly impacted by both the nature of the solvent and the physical conditions of the system. We performed molecular simulation to investigate the dynamic behavior of asphaltene during gas flooding. We also consulted the experimental observations for validation purposes when available. Two structures representing the archipelago and continental types are used, whose aggregation and interactions are studied in methane (C1), propane (C3), carbon dioxide (CO2), heptane (C7), and toluene as pure solvents, binary mixtures of toluene and either C1, C3, or CO2, and a representative oil composition. The continental structure is used afterward to evaluate the impact of temperature, pressure, and resin content on the aggregation dynamics in CO2 mixtures. Interestingly, the solvating power of CO2 is dependent on the asphaltene structure where inhibitor-like behavior is observed for the continental structure and precipitator-like behavior is observed for the archipelago structure. The solvent quality is highly correlated with the solvent s ability to replace the interactions among asphaltene molecules with interactions between asphaltene and solvent. The aggregate size is reduced by temperature and enhanced by pressure in CO2. However, limited effect is reported for resins on asphaltene dynamics in CO2. The aggregation of asphaltene is impacted by the physical state of CO2 as its solvating power to asphaltene is significantly enhanced in its supercritical state. Nonetheless, this impact is limited when CO2 is introduced to a representative oil mixture.