Preparation And Performance Evaluation Of Nano-silica Composite Viscosity Reducer

Energy is an important driving force for social progress.As a kind of energy resource,petroleum occupies a major position in the global energy consumption.Due to the increase of energy consumption caused by social progress,more and more countries turn to the exploitation and utilization of heavy oil,which accounts for more than half of the crude oil,because the exploitation of conventional light crude oil cannot meet our demand.Although the world's heavy oil resources are rich in reserves and widely distributed,they contain a large number of colloids,asphaltenes and waxes,resulting in high viscosity and poor liquidity,which is difficult to be exploited,transported and refined.Therefore,it is an important task to reduce the viscosity of heavy oil and improve its recovery rate.Oil soluble viscosity reducer,as a kind of low cost,good effect,easy operation and no subsequent treatment for the advantages of viscosity reduction process,has attracted extensive attention of domestic and foreign oil industry workers.For viscous oil viscosity reducer,on the one hand,the added viscosity reducer needs to be able to fully contact with the crude oil,on the other hand,the viscosity reducer needs to be able to react with the colloids,asphaltenes and waxes,so as to destroy the complex overlapping structure or network structure.It is a new chemical viscosity-reducing technology to prepare nano-composite materials for petroleum development,which not only retains the function of conventional oil-soluble viscosity-reducing agent,but also adds some new functions of nano-particles.The introduction of nano structure can make the viscosity reducer have more contact area with the heavy oil,and can better act on the structure of colloids,asphaltenes and wax crystals in the heavy oil,and produce the destruction effect through its own nano effect and strong polar groups on the surface.Moreover,under the shear action,the existence of the surface of the micro-nano structure can cause the boundary slip phenomenon of the fluid,resulting in the viscous resistance of the polymer fluid layer in relative motion and the friction resistance in the pipeline transportation to decrease,so as to achieve better viscosity reduction and flow.Using tetraethyl orthosilicate as a silicon source and ammonia as a catalyst,a uniform dispersion of nano-silica was prepared by hydrolysis and condensation reaction,which was modified with 3-(methacryloyloxy)propyltrimethoxysilane.Thereafter,a nanocomposite viscosity reducer(NVR)is prepared by radical polymerization of the modified product with octadecyl methacrylate,styrene and acrylamide,and used in the Karamay crude oil for viscosity reduction effect test.After studying the amount of silica and monomer,the formula with the best viscosity reduction effect was obtained.And then,by changing the reaction temperature,reaction time and addition amount,the viscosity reduction effect was tested,it was found that when the amount of silica was 0.3 g,the reaction temperature was 60?,the reaction time was 6h,and the addition amount was 500 ppm,the viscosity reduction effect was the best,the viscosity reduction rate was 91.46%,and the net viscosity reduction rate could reach 30%or more.By comparing the rheological fitting equation,viscosity-shear rate and viscosity-temperature of crude oil before and after adding nano-composite viscosity reducer,it can be found that the viscosity reduction of crude oil is affected by the viscosity reducer,shear stress and temperature.Through the comparison of non-newtonian fluid index obtained by fitting,it is shown that in the same shear rate,the addition of nano-composite viscosity reducer can destroy the overlapping stack structure or network structure in the crude oil,so that the crude oil can realize the transition from pseudoplastic fluid to Newtonian fluid at a lower temperature.Comparing the viscosity reduction effect of the viscosity reducer before and after adding nano-silica,it was found that the viscosity reducer with nanometer silica was not as effective as the viscosity reducer(VR)without nanometer silica at low shear rate and low temperature.However,with the increase of temperature and shear rate,the viscosity reduction effect of crude oil with the introduction of nanocomposite viscosity reducer increased significantly,showing greater sensitivity to temperature and shear.By comparing the rheological fitting equation of crude oil and viscoelasticity of fluid after adding two viscosity reducers,it can be found that adding nano-composite viscosity reducer can increase the viscosity of crude oil more greatly and make the crude oil change from pseudoplastic fluid to Newtonian fluid more quickly.