Asphaltene stability can be perturbed during the oil production and transportation, leading to asphaltene precipitation and deposition. Chemical inhibitors are usually added to the oil phase to postpone asphaltene deposition. The chemical bonding between asphaltene and inhibitor molecules, and the steric hindrance are the key mechanisms of aggregation inhibition. Nevertheless, the interaction mechanisms between asphaltenes and chemical inhibitors still need more research investigations. In this paper, we use an advanced computational chemistry tool, molecular dynamics (MD), to analyze the inhibitory effect of noctylphenol (OP) on three different asphaltene structures at 1 bar and 300 K. To meet the objectives, the asphaltene aggregation and aggregate characterization in both cases of pure and mixed asphaltenes are studied. It is concluded that the archipelago asphaltene (A1) does not aggregate appreciably in the absence of OP; nevertheless, OP reduces the aggregation. The addition of OP is more effective in reducing the aggregation rate for the continental asphaltene, containing hydroxyl and pyridine groups (A2), which is due to the formation of strong hydrogen bonds between the asphaltene and OP, compared to the aromatic stacking between asphaltene and asphaltene. The presence of hydrogen bonds significantly changes the characteristics of aggregates in both scenarios: in the absence and presence of OP. Hence, OP exhibits less efficiency for the continental asphaltene case without hydrogen bond potential (A3). For the mixed asphaltene systems, OP considerably lowers the aggregation rate when A2 and A3 are simultaneously present; the higher relative portion of OP to A2 is the main reason for this behavior. This study reveals that the OP can be an effective inhibitor, depending on the distribution of different types of asphaltenes in the crude oil. The same strategy can be used to screen proper inhibitors or inhibitor mixtures for various types of asphaltenes.
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 noctylphenol (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.
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