Adhesion Mechanism of Heavy Oil in Low-temperature Transportation Pipeline
In order to reveal the adhesion mechanism of low-temperature transportation of high water-content heavy oil from a microscopic point of view,molecular dynamics simulation was used as the main method to study the adhesion mechanism of heavy oil/water/pipe wall system from the perspectives of interfacial properties,diffusion properties,distribution of components and characteristic structures,and resin-asphaltene synergistic effect.The results show that the interfacial properties of the system significantly affect the adhesion of heavy oil,and there is a positive correlation with the asphaltene content,while the van der Waals gravitational interaction in the system is one of the main roles affecting the adhesion of heavy oil.Asphaltene and resin molecules were found to be mainly distributed near the oil-water interfacial layer and the oil-pipe wall interfacial layer,whereas n-heptane and toluene molecules were distributed in the hydrophobic interior of the oil droplets,which is due to the polarity of resin and asphaltene molecules.Asphaltene molecules containing O-atom functional groups preferentially distributed in the oil-water interface,through hydrogen bonding with water molecules to prevent the movement of water molecules to the pipe wall and with the hydrocarbon mixture molecules to produce competitive adhesion.Containing N-atom and S-atom functional groups in the oil droplets and the pipe wall of the adhesion between the adhesion of the phenomenon of preferential contact adhesion to the adhesion layer to play the role of the"articulation and bridge".C5 atoms and S-atoms in the oil droplets and the pipe wall of adhesion phenomenon of preferential contact adhesion to play"bridges and bridges".The long side chain of C5 inhibits the transportation of resin and asphaltene molecules to the oil-water and oil-pipe wall interfaces,weakening the adhesion strength of heavy oil.In the resin and asphaltene synergistic action,asphaltene content exceeds 8wt％,the solubilization effect of gum molecules is inhibited,and asphaltene polymers are gradually formed in the system,which promotes the occurrence of heavy oil adhesion phenomenon and jeopardizes the safe and smooth operation of the gathering pipeline.It can be seen that the adhesion mechanism of low-temperature transportation of heavy oil with high water content is dominated by van der Waals gravitational interaction at low temperatures,and the heteroatomic functional groups of polar macromolecules such as resin and asphaltene are preferred to contact with the pipe wall as a bridge,and the asphaltene aggregation and resin solubilization effects are synergistic and complex microscopic action mechanism.
high water-content heavy oillow-temperature transportationadhesion mechanismmolecular dynamics simulationintermolecular interactionsresin and asphaltene
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