Control of Asphaltene Deposition by Chemical Inhibitors in Calcite Pore: Molecular Dynamics Approach

Asphaltene deposition is a major problem during oil production and transportation that imposes extra treatment costs and reduces oil production. Historically, various chemical inhibitors have been developed to resolve the asphaltene deposition issue. However, the inhibitors are usually effective for a specific type of crude oil and asphaltene since asphaltene's nature is different for various oil samples. To develop a proper chemical inhibitor, the interaction between the inhibitor and asphaltene needs to be explored. This work employs a molecular dynamics (MD) simulation strategy to study asphaltene deposition on a calcite surface considering chemical inhibitors. Two asphaltene structures with potential to form hydrogen bond (A2) and without potential to form hydrogen bond (A3) are considered in this study. The selected inhibitors, including n-octylphenol (OP) and 1-butyl-3-methylimidazolium chloride (as an ionic liquid (IL)), can form van der Waals, Coulomb, and hydrogen bonds with asphaltene molecules. The results show that the OP reduces the asphaltene aggregation by attaching to the asphaltene through hydrogen bonds. In the presence of OP, the Lennard-Jones (LJ) and Coulomb energies between asphaltene (A2) and calcite are reduced by 400 and 1000 kJ/mol units, leading to the asphaltene deposition reduction by adsorbing on the calcite surface and providing a hindrance layer. The IL is able to cope with the quadrupole-quadrupole interaction between asphaltene polyaromatic cores and reduce the asphaltene face-to-face aggregation. However, IL cannot provide a hindrance layer near the calcite surface since it does not have a long hydrocarbon tail. Therefore, the combination of inhibitors can benefit the inhibition process as both prevention mechanisms will be active. The 3:1 OP-IL ratio shows the optimum efficiency. At this ratio, inhibitors reduce the aggregation from 20 to less than 10 and the deposition rate from 1 to 0.8 compared to the case without the inhibitors. Also, the deposited aggregates have low compaction with a spherical shape, which is easy to dislodge in a dynamic situation. This research aims to demystify the asphaltene-inhibitor behaviors during asphaltene deposition, which can be a useful practice for designing of future chemical inhibitors for flow assurance issues.

Automated summary

This study utilized molecular dynamics simulation to investigate asphaltene deposition on a calcite surface with chemical inhibitors. The results showed that n-octylphenol reduced asphaltene aggregation through hydrogen bonding, while 1-butyl-3-methylimidazolium chloride could mitigate face-to-face aggregation of asphaltene. The combination of inhibitors demonstrated improved efficiency in reducing deposition and aggregation compared to using a single inhibitor.