Research On Crude Oil Emulsion Demulsification And Water Droplet Dynamic Characteristics Under Electric Field

The dehydration of crude oil is an essential process in the petroleum industries.At present,chemical demulsification and electric demulsification are used mostly in onshore oil fields.However,the research on the demulsification properties of demulsifier under external electric field is little to see,and the theoretical system of water droplet deformation and coalescence mechanism has not been deveploped at home and abroad.Aiming at the existing problems,the research works are carried out as follow:In order to research the demulsification properties of demulsifier under external electric field,the distribution of demulsifier on oil-water interface and the diffusion of demulsifier in emulsion undr electric field were simulated by Material Studio.The results show that emulsifier can be replaced by the demulsifier on oil-water interface to form a low intensity of interfacial film,and the interfacial tension of system can be reduced,which can realize the demulsification for crude oil emulsion.The external electric field can enhence the the demulsifier diffusion coefficient,and it is advantageous for the demulsifier to diffuse to the oil-water interface with increasing the electric field strength within a certain scope,and then the effect of demulsification can be improved.To study the dynamic characteristics of water droplet under electric field,the droplet deformation and coalescence behavior were simulated by Comsol based on the method of flow field coupled in electric field,and the main factors that affect the droplet dynamic characteristics were analyzed.The results show that the higher electric field strength can cause the larger degree of droplet deformation and the faster rate of coalescence,but when the electric field strength is too high,the droplet will be ruptured,and the rupture form depends onthe interfacial tension of emulsion.It is also found that larger droplet diameter or smaller interfacial tension could cause larger degree of droplet deformation and coalescence.In addition to the deformation,water droplets can move to the higer electric field area under non-uniform electric field,caused by dielectrophoresis force.To testfy the above simulation results,the experimental study on the dehydration of crude oil emulsion in AC electric field was carried out with the small and medium dehydration test system in laboratory.Meanwhile,the phenomenon of droplets deformation,rupture and coalescence in the emulsion were observed by the high-speed camera.The experimental results show that dehydration rate increases with increasing the electric field strength within a certain scope,however it will decrease when the electric field strength is higher than the critical electric field strength.It is also found that the reduction of the interfacial tension and increase of the drop diameter can lead to the enhancement of dehydration rate.For the emulsion with lower moisture content,the dehydration rate of cylindrical electrode is higher than that of plate electrode due to the dielectrophoresis force.It's also found that the combination of demulsifier and electric field dehydration performs better than the electric field dehydration or the demulsifier dehydration,and the interfacial tension of emulsion can be decreased by increasing the content of demulsifier in a certain scope,which can lead to the increase of dehydration rate.The above experimental results have the good consistent with the simulation results.