Molecular Dynamics Simulation Of Emulsification Behavior In Surfactant Flooding

Surfactants are widely used in petrochemical fields such as emulsification,viscosity reduction,solubilization,etc.In recent years,due to its amphoteric characteristics,they have shown great development and application prospects in viscosity reduction of heavy oil,attracting many researchers to study its formula,composition,characteristics and mechanism.Oilfield exploration and experiments have proved that adding surfactants can greatly reduce the viscosity of heavy oil,prevent and curb its deposition in shale formations,but at the molecular level there is still no thorough research and analysis on the mechanism of surfactant emulsification and viscosity reduction,the effects of different heavy oil components and different surfactant addition methods on emulsification and viscosity reduction.The work used molecular dynamics simulation methods to construct molecular models of surfactants and heavy oil components selected the appropriate position parameters and simulation size and studied the relationship and changes of configuration and interaction among different molecules at the molecular level.Expectations It can solve the emulsification mechanism of amphoteric substances represented by surfactants containing different asphaltene of heavy oils,and provide theoretical support for future applications and design of highly reactive emulsifiers.The research content of this paper is divided into the following parts:i)The molecular dynamics method was used to simulate the commonly used surfactant sodium dodecyl sulfonate(SDSn)and the mature heavy oil model developed by previous researchers.The heavy oil droplets and micelles were constructed and randomly placed.In the emulsion,the enviro nment in which an emulsifier was added to an oil well in a real use scenario was simulated.The results showed that the heavy oil containing carboxylate asphaltene is easier to absorb surfactant,to emulsify.The process of the surfactant adsorption in heavy oil can be divided into three stages,approaching,adsorbing,dispersing and migrating.Given the interaction between polar heads and water molecules and the radial distribution function,we propose a hydrogen bond space network structure,which is the main driving force of adsorption and emulsification,especially the main driving force of the uniform migration and distribution of the molecules in the third stage.These gains are expected to provide theory support for production practice,and pay attention to the appropriate addition methods when using,more conducive to the surfactant to maximize the effectiveness.ii)Based on the previous research system,this work continued to study the effects of different amounts of surfactants on emulsified heavy oils,and the subtle differences in emulsification mechanisms of different amounts of surfactants.With the increase of SDSn molecules,it can significantly increase the hydrophilic/hydrophobic area ratio of oil droplets,thus increase the hydrophilic properties of the oil droplets and the emulsification performance;with the increase of SDSn molecules,the composition structure of asphaltene and colloid in the heavy oil molecules changes,and the asphaltene molecules containing carboxylate are more likely to adhere to the surface of oil droplets.With the increase of SDSn molecules,the number of hydrogen bonds formed between the system and water molecules keeps increasing,so that a more stable hydrogen bonding surface structure promotes the emulsification of oil droplets hydration.iii)In the chapter,the effect of nonionic surfactants as emulsifying viscosity reducers on heavy oil was studied.Through analysis,we believe that non-ionic surfactants as emulsifying viscosity reducers are mainly reflected in two aspects:1)The addition of surfactant will be adsorbed on the oil-water interface to increase the hydrophilicity of the oil-water interface,which is conducive to the oil-water mixing and play an emulsifying role;2)Under high concentration of surfactant,some surfactant molecules will enter the oil phase,and the network structure composed of resin and asphaltene in the oil phase will be destroyed,which is conducive to the structural destruction of heavy oil under the action of external forces and plays a role of viscosity reduction of heavy oil.