Research Of Emulsion Electric Dehydration Characteristics And Mechanism Under A Non-uniform Electric Field

Electric dehydration is the important part during the crude oil production. When the oilfield has entered high water cut stage, for the increasing of oil field production, a large number of chemical reagent are added to the oil well,that make dehydration difficult, dehydrate efficiency decreases, electric field instability in the process of electric dehydration. In order to improve existing electric dehydration technology and increase electric dehydration efficiency of crude oil, research of emulsion electric dehydration characteristics and mechanism under a non-uniform electric field is carried out to increase the coalescence rate of water droplets and stability of electric field.In order to research the electric dehydration characteristics of emulsion under non-uniform electric field, the simulating model of droplet under non-uniform electric field was established through the phase field method based on Cahn-Hilliard formulation. Through the simulation of water droplets dynamic behavior in non-uniform electric field, dynamic characteristics of droplet movement, droplet coalescence and rupture were analyzed. In order to study the emulsion dehydration effect at different non-uniform coefficients of electric field, electric field type and strength, water content of emulsion, quantity of demulsifier, electric dehydration experimental system was designed and set up, and emulsion dehydration experiments under AC and DC electric fields were carried out. In order to study the influences of water droplets on the movement, coalescence and electrodispersion behaviors of water droplets under non-uniform electric field, force models of droplet under non-uniform electric field was established through the polarization characteristics of water droplets. Meanwhile, the influences and action mechanism of polarization charge and demulsifier for the rupture of oil-water interfacial film were analyzed in the process of water droplet coalescence. The rules of droplets motion in the emulsion under different conditions was observed and analyzed by high-speed camera, which proved the theoretical analysis.The results of the simulation and emulsion dehydration experiments show that one of the main reasons of water droplet dielectrophoresis was that the distribution of polarization charges was unsymmetrical on the droplet surface under non-uniform electric field, increasing from the center to both ends of the droplet. The non-uniform coefficients of electric field, electric field intensity and type, particle distribution of water droplets were the important factors influencing the coalescence efficiency of droplets. The higher electric field intensity or larger non-uniform coefficient could lead to faster speed of coalescence. Under excessively high electric field intensity, the droplets will be easily ruptured and the dehydration rate will decrease. AC electric field is suitable for emulsion with high water content, and it can ensure the stabilization of electric field and improve the dehydration speed. DC electric field is suitable for emulsion with low water content, and it can deep dehydrate the emulsion. The increase of droplet diameter could lead to the bigger droplet deformation, faster moving speed of droplet to concentrated electric field area and higher coalescence rate. The increase of water droplets distribution uniformity could make the more water droplet coalescence increase dehydration rate of emulsion.The experiment result of emulsion dehydration experiments and movement behaviors of water droplet can be well explained through the analysis of dynamics simulation model and polarization force model proposed in this paper. Theoretical analysis shows that the dielectrophoresis force of water droplets and dipole coalescence force between the droplets are proportional to elect ric field intensity, water droplet radius and non-uniform coefficient of electric field, and they are inversely proportional to the distance between the center of the electrode and water droplet, and the distance between the water droplets. The electric fi eld intensity of electrodispersion for water droplets is related to surface charge density of water droplet, droplet size and surface tension. When the water droplet is charged, the intensity of electrodispersion will decrease.The polarization of water droplets in the electric field makes the rate of oil-water interfacial film thining and coalescence increase. The addition of demulsifier decrease the voltage amplitude generated the hole on the oil-water interfacial film and increase coalescence rate of water droplets.