Study On Micro-Mechanism Of Oil-Water Interfacial Behavior Considering The Components Of Produced Liquid

Crude oil is generally produced with water,so it is inevitable to create emulsions during oil production.However,the stability of emulsions presents a significant challenge in surface process particularly,both in terms of crude oil dehydration and produced water treatment.For produced liquid of polymer flooding,alkali/surfactant/polymer(ASP)flooding,and other chemical flooding process,not only the polar components in crude oil contribute to oil-water emulsification and its stability like the conventional water flooding liquid,but also polymer,surfactant,alkali and other components determine that these produced liquid have complex emulsification characteristics,high emulsification stability and difficult separation.Facing the demand and situation of improving the quality and efficiency of produced liquid treatment,multi-scale research on the mechanism of oil-water emulsification and the formation of a systematic understanding of the oil-water interface behavior of emulsion system are of great significance to promote the development and application of high-efficiency treatment technologies for different properties of produced liquid in oil fields.Therefore,in order to explore the influence of asphaltene and resin,especially the polymer and surfactant,on the formation and stability of oil-water emulsion,molecular dynamics simulation combined with characterization methods of visualization,emulsion system density distribution,molecular radial distribution function,interface formation energy and molecular diffusion coefficient were used to research the role of the molar ratio of asphaltene and resin,polymerization and hydrolysis degree of polymer,surfactant type and concentration,and p H value in the micro-mechanism of oil-water interfacial behavior.The results indicated that the higher the molar ratio of asphaltene,the more obvious the stacking structure is.The thickness of interfacial film and the interface formation energy increases from 2.748nm and-163.34 k J/mol to 3.365 nm and-249.37 k J/mol respectively,when the molar ratio of asphaltene enhances from 20%to 80%.The asphaltene molecules play a more significant role in promoting the formation of interfacial film and maintaining its structure stability than the resin molecules.The stability of oil-water interfacial film continues to increase with the increase of polymer polymerization degree.However,the effect of increasing degree of hydrolysis on the stability of oil-water interfacial film is concentrated in the range of hydrolysis degree of 15%to 35%.The increase of p H value of aqueous phase will enhance the number of-COO^-groups in the system,promote the conversion of HCO₃^-into CO₃^2-in aqueous phase,and decrease the Ca²⁺concentration,thereby enhancing the electrostatic repulsion force of-COO^-in polymer molecules,increasing the molecular radius of gyration,and enhancing the stability of oil-water interfacial film.Whether for anionic or cationic surfactants,their presence in oil-water system will aggravate the degree of emulsification,and there is a positive correlation between the oil-water interface film thickness and structural strength.Different from the oil-water emulsion system with polymer,when the p H value of aqueous phase increases,there is no significant change of the interfacial formation energy in the oil-water emulsion system with surfactant.For both the oil-water emulsion system with polymer and the oil-water emulsion system with surfactant,the effect of inorganic cations on the film formation and stability of oil-water interface is not only related to their valence and hydration properties,the increase of their concentration also significantly inhibits the formation of stability oil-water interface structure.The study is of great significance for enriching the theory of oil-water emulsification and demulsification,and it is of value to form regular understanding from micro scale for the optimization design of gathering and transportation system and development of novel oil-water separation technologies in the chemical flooding field.