Experimental Study Of Nano SiO₂-grafted Polymers:Preparation And Properties Evaluation

At present,the water content of most domestic oilfields is increasing year by year.Polymer flooding is the most commonly used method to improve oil recovery.Use polymers to carry out deep regulation and flooding of oil reservoirs can effectively solve the problem of high water content in oilfields and improve oil displacement efficiency at the same time.In this study,an organic/inorganic composite anionic polymer was prepared by modifying nano-SiO₂ and grafting the polymer for deep control and flooding to enhance oil recovery.The modified nano-SiO₂（MS）and the modified nano-SiO₂-grafted polymer（MSP0-MSP3）were firstly characterized in series,and then the effects of NaCl content（ρ（NaCl））,temperature,formation water type and pH on the swelling properties of MSP were investigated.Then,the effects of MSP content（w（MSP））,ρ（NaCl）,temperature and swelling time on the viscosity characteristics and rheological properties of MSP were investigated.Finally,a preliminary study on the plugging performance of MSP was carried out.The results of the study are as follows:（1）The swelling ratio of MSP1 decreases with the increase of NaCl content,and increases with the increase of temperature.It is more affected by CaCl₂ and MgCl₂ type formation water than Na₂SO₄ and NaHCO₃ type formation water.The swelling ratio under acidic and alkaline conditions is significantly higher than that under acidic and alkaline conditions.（2）The viscosity of MSP gradually increased with the increase of MSP content,decreased gradually with the increase of NaCl content and temperature,and gradually increased with the increase of swelling time until the viscosity remained basically unchanged after 7th day,show a certain viscosity stability.At the same time,within this range,the viscosity of MSP increases with the increase of the content of modified nano-SiO₂,and the order of viscosity is MSP0<MSP1<MSP2<MSP3.（3）The apparent viscosity of MSP0 and MSP1 increased gradually with the increase of MSP content and swelling time,decreased gradually with the increase of temperature and NaCl content,and gradually increased with the extension of swelling time.At lower shear rates(γ<10 s^-1),the apparent viscosities of MSP0 and MSP1 decrease with increasing shear rate,which is characteristic of shear-thinning pseudoplastic fluids;at higher shear rates(γ>50 s^-1),the apparent viscosities of MSP0 and MSP1 remain basically unchanged with the increase of shear rate,which is characteristic of Newtonian fluids.At the same time,the apparent viscosity of MSP1 was higher than that of MSP0 at the same shear rate,which indicated that the introduction of modified nano-SiO₂ significantly increased the apparent viscosity of MSP.（4）The nuclear pore membrane filtration experiment shows that there is a corresponding matching relationship between the pore size of MSP1 and the nuclear pore membrane,not the larger the pore size the worse the sealing effect,the smaller the pore size the better the sealing effect.The sand pack experiment shows that after the injection of MSP1,the pressure at pressure measurement point A and pressure measurement point B increased significantly,and then after the post-water drive,the pressure at points A and B dropped slightly and then remained stable,which indicates that MSP1 can break through the transport in the sand pack and form a blockage again,causing the redirection of fluid flow,and then achieve the purpose of deep plugging.