On the influence of asphaltic molecules on the precipitation of acid-induced sludge: Molecular dynamics perspective

• Published in: Fuel (Guildford) 2025-01, Vol.379, p.133002, Article 133002
• Main Authors: Esmaeilbeig, Mohammad Amin, Khorram, Mohammad, Koleini, Mohammad Mehdi, Ayatollahi, Shahab
• Format: Article
• Language: English
• Subjects: Asphaltene to resin ratio; Asphaltic sludge; Crude oil; Micelle formation; Molecular dynamics simulation
• ISSN: 0016-2361
• DOI: 10.1016/j.fuel.2024.133002

During the matrix acidizing treatment, asphaltic molecules precipitate solidly as a consequence of contact between acidic and oil phases at the oil–acid interface. Molecular dynamics simulation, a powerful tool, has not been utilized to investigate this phenomenon comprehensively. In the present study, this powerful technique was used to shed the light on the movement of polar molecules such as asphaltene and resin in the oil phase as well as hydronium ions in the aqueous acid phase toward the oil–acid interface during acid treatment. Additionally, the influence of significant variables such as crude oil type and asphaltene-to-resin ratio were studied. To achieve the aforementioned objectives, the oil and acidic phases were equilibrated separately under specific thermodynamic conditions and then the two phases were put into intimated contact. The precipitation of polar molecules during close contact of acid phase with paraffinic oil was opposite to aromatic oil for both high and low asphaltene-to-resin ratios. On the other hand, oil mixtures with equal number of asphaltene and resin molecules behaved differently. Our research indicates that the type of oil, either paraffinic or aromatic, has a significant effect on the formation of asphaltic sludge. Surprisingly, the influence of the asphaltene-to-resin ratio is so strong that it can offset the effect of the oil type. This is a result of the formation of micellar structures in the crude oil phase over a limited range of asphaltene-to-resin ratios. Additionally, more hydronium ions are attracted toward the interface in oil mixtures containing micelles. •Acidifying paraffinic-based oil mixes releases a significant amount of sludge.•The asphaltene-to-resin ratio significantly affects the amount of sludge formation.•The formation of micellar structures attracts ions in the acidic phase and moves them toward the interface.