Research On Stability Of Electrical Treatment Effect Of Waxy Crude Oil And Its Influencing Factors

The cold flowability of waxy crude oil can be significantly improved by applying electrical treatment near its gel point.As with other modification methods,the electrical treatment effect of crude oil can be affected by the treatment conditions and its components.However,the effect of both on the stability of treatment effect has not been reported.This thesis firstly investigated the effect of the electric field strength on the stability of the electrical treatment effect of waxy crude oil.For the same waxy crude oil,it was found that both the electrical treatment effect and its stability enhanced with increasing electric field strength in the tested range.Meanwhile,the impedance properties of the oil samples were tested in situ in this research.It was observed that the impedance of the oil samples increased significantly after electrical treatment.However,the impedance of the oil samples decreased gradually with time after the electric field was withdrawn,and the decreasing trend slowed down with increasing field strength.The results implied that the higher strength electric field can drive more charged colloidal particles,i.e.,resins and asphaltenes,to transport and adhere to the wax crystal surface.After removing the electric field for a certain time,more charged colloidal particles are retained on the surface of wax crystals,allowing the electrical treatment effect to be maintained better.Subsequently,the rheology,wax crystal morphology and impedance properties of4 different waxy crudes subjected to different conditions of shearing were tested simultaneously.These data revealed that shear had two opposite effects on the stability of the treatment effect for the 4 different crudes:shear was detrimental to maintaining the viscosity reduction effect of two crudes,but improved the cold flowability of the other two.In addition,the change rate of charged particle concentration in liquid phase oil is positively related to the change rate of viscosity:（35）η/η₀=0.172（（35）C/C₀）^{1.38 64}.Based on this phenomenon,the following conjecture is proposed:shearing can both strip the charged colloidal particles attached to the surface of wax crystals driven by electric field and increase the chance of collision between the free colloidal particles in the liquid phase and wax crystals.For waxy crude oil with low viscosity and small particle size of resins and asphaltenes,shear prevails over the stripping of colloidal particles.Therefore,shear should be detrimental to the maintenance of the electrical treatment effect for these crudes.Conversely,shearing can further reduce the viscosity of waxy crude oil after electrical treatment.The conjecture is justified in terms of the viscosity of liquid phase oil,the size of charged colloidal particles,i.e.resins and asphaltenes,and the high-speed shear effect.Fortunately,the results were all as expected.This research deepened the understanding on the stability of the electrical treatment effect of waxy crude oil,and provided a reference for the engineering application of electrical treatment technology.