Study On The Effect Of Nano-SiO₂ Graft Polyacrylate On The Wax Deposition Of Shengli Crude Oil

Most of the crude oil produced in oil fields in China is waxy crude oil,among which the crude oil represented by Daqing,Central Plain,North China,and Shengli Oil Field is high waxy crude oil,which has high pour point,high viscosity,and poor fluidity at low temperature,it is easy to cause flow safety risks such as the crude oil solidification and wax blockage in the process of pipeline transportation.Therefore,it is of great significance to study the pour point reduction,viscosity reduction and wax deposition of waxy crude oil.In this paper,octadecyl methacrylate and maleic anhydride were used as raw materials to prepare octadecyl methacrylate-maleic anhydride binary polymer pour point depressant(MPPD),to modify nano-silica to obtain modified nano-silica(NSiO₂),and then MPPD was grafted onto NSiO₂ to prepare nano-silica composite pour point depressant(NPPD),referred to as nano-pour point depressant.Then,the effects of octadecyl methacrylate-maleic anhydride pour point depressant and nano pour point depressant on waxy crude oil and simulated oil were investigated with a waxy crude oil and formulated simulated oil from Shengli oilfield.The main contents include the effects of MPPD and NPPD on the freezing point,viscosity,and yield stress of waxy crude oil,and the morphological changes of wax crystals precipitated out of waxy crude oil before and after the addition of pour point depressants was observed using a polarizing microscope.The results show that the pour point depressing effect on crude oil is the best when the dosage of NPPD is 400ppm,the pour point depressing range is 14?,the viscosity reduction rate is 41.2%at 30?,yield stress value can be reduced by 5.13Pa.NPPD can greatly reduce the viscosity of crude oil in the low-temperature range and has an obvious effect on improving the low-temperature fluidity of crude oil.The results of polarizing microscope observation show that compared with MPPD,the wax crystal morphology of crude after adding NPPD is more compact,which can release liquid oil wrapped in wax crystals,reduce the viscosity of crude oil and improve the fluidity of crude oil.Under the same conditions,NPPD can reduce the freezing point of the simulated oil by 6?,and the optimal viscosity reduction rate is 25.9%.The wax crystals in the simulated oil are in the shape of bars and rods,which are more closely arranged than the wax crystals in crude oil.Finally,combined with the measured physical properties of crude oil and the equations of shear stress and temperature gradient of oil samples in wax deposition device,the viscosity,shear rate,shear stress,and temperature gradient parameters of waxy crude oil under different working conditions were simulated and calculated by Fluent software.Combined with Huang Qiyu wax deposition model,the wax deposition rate was predicted,and the influence of nano pour point depressant on wax deposition rate was analyzed.The results show that nano pour point depressant can reduce wax deposition rate by 2.5737g/(m²·h)at oil temperature of 39?and wall temperature of 33?.The wax deposition rate of crude oil can be reduced by 0.8006 g/(m²·h)at the rotating speed of 100 r/min.