Inhibition Mechanisms of Asphaltene Aggregation during the CO ₂ Flooding Process

The asphaltene (ASP) aggregation during the CO2 flooding process seriously impacts the oil recovery, which could be effectively inhibited by the additional inhibitors. In this work, the molecular dynamics (MD) simulation is utilized to investigate the mechanism of two inhibitors (nonyl phenol (NP) and tergitol nonyl phenol (TNP)) for the injected CO2 causing the aggregation of two typical ASP (ASP1: long aliphatic chain and fewer aromatic rings; ASP2: short aliphatic chain and more aromatic rings). The number density distribution and the radial distribution function (RDF) are employed to evaluate the ASP aggregation behavior in the absence or presence of inhibitors in the kaolinite pore. The analysis of the molecular potential surfaces (electrostatic potential and van der Waals potential) and the effective free energy further illustrate the microscopic interaction (such as the hydrogen bonds, electrostatic interaction, and vdW interaction) of ASP and inhibitors, which dominates the inhibitor performance in the ASP aggregation. TNP prefers to inhibit ASP1 aggregation through vdW interaction affected by the flexible ethoxy chain of TNP and the long aliphatic chain of ASP1, while the hydrogen bonds between NP and ASP2 dominantly inhibit ASP2 aggregation. This work proposes the novel understanding about the underlying mechanism in inhibiting the ASP aggregation during the CO2 flooding process.