Fabrication Of Surface Modified Nano-Silica And Its Based Oil Displacement Agent For Enhancing Oil Recovery

China is the world’s first oil-consuming country,oil energy consumption accounts for 19.3% of China’s energy consumption,China’s oil resources supply imbalance is serious,2022 foreign dependence has reached 72.2%.At present,most of the oil reservoirs in China have gone through primary and secondary oil recovery and stepped into the stage of tertiary oil recovery,and the existing technology can only increase the crude oil recovery rate to about 30%.Due to the special nano-effect,the research and application of nanomaterials and technologies in the field of oilfield production enhancement and other fields are receiving increasing attention.Zero-dimensional nanoparticles（e.g.,SiO₂,Al₂O₃）have been applied to enhance crude oil recovery,improve foam stability,and modify the rheological behavior of crude oil.However,as nano-SiO₂ contains a large number of hydroxyl groups on its surface,it is very easy to agglomerate and sink under the environment of high temperature and high mineralization of oil reservoir,so improving the dispersion stability of nano-SiO₂ in the working fluid of oil reservoir is the urgent technical key to realize the field application in oil field.In this paper,functionalized SiO₂ nanoparticles with different structures were prepared by liquid-phase in situ surface modification using hydrophilic/hydrophobic long-chain compounds as modifiers and introduced into a traditional ternary composite system（polymer,alkali,surfactant）to prepare a water-based quaternary composite flooding with high stability and to study the oil flooding performance and mechanism of action.The main research components and conclusions are as follows:（1）Preparation and performance study of highly stable quaternary composite flooding based on superhydrophobic nano-SiO₂By using liquid-phase in situ surface modification technology,the modified nano-SiO₂ was hydrophobically modified with hydroxy silicone oil as the modifier,and the modified nano-SiO₂ was dispersed in aqueous solution and blended with polymer to obtain a highly stable quaternary composite flooding based on superhydrophobic nano-SiO₂.The effects of nano-SiO₂structure,chemical crushing agent dosage,temperature and mineralization on the stability of the quaternary composite flooding and the oil displacement performance of the composite flooding were investigated respectively.The results showed that（1）The modified nano-SiO₂ has super-hydrophobicity（water contact angle of 172.4°）and can maintain its super-hydrophobicity in acidic and alkaline solutions with p H 0-14 at 60℃,80℃ and 100℃,and has strong hydrophobic stability at high temperatures（200-450℃）.（2）Under the synergistic effect of surfactant and chemical crushing agent,hydrophobically modified nano-SiO₂ was stably dispersed in water with particle size less than 10 nm,and the specific surface area was as high as 394.28 m²g^-1.（3）The quaternary composite oil flooding prepared by nano-SiO₂ dispersing solution and polyacrylamide has good dispersing stability with nanoparticle size less than 10 nm and zeta potential of 30-60 m V.The quaternary composite flooding（simulating the mineralization of Shengli reservoir）can be stably dispersed at room temperature for 360 days（until now）and at 60℃for 25 days.（4）The quaternary composite flooding combines the properties of nanomaterial flooding and ternary composite flooding,with the synergistic effects of reducing water-oil interfacial tension（IFT）,changing wettability,and wedge extrusion,it further increases the recovery rate by 25.8%from the primary water drive recovery rate of 28.7%,and the injection fluid has a lower working pressure（15%lower than that of the ternary composite flooding）.（2）Preparation and performance study of quaternary composite flooding based on amphiphilic modified nano-SiO₂ Wettability regulation is one of the important means to improve the recovery of crude oil.Based on the significantly improved stability of hydrophobically modified nano-SiO₂ quaternary composite flooding,this paper further prepares amphiphilic modified nano-SiO₂ quaternary composite flooding by introducing hydrophilic modifier and compounding with hydrophobic modifier to regulate the hydrophilic/oleophilic properties of nano-SiO₂ in order to further improve the oil displacement performance.By adjusting the order and ratio of hydrophilic/hydrophobic modifiers,two series of amphiphilic modified SiO₂ nanoparticles were prepared（the order of modifier addition was hydrophilic followed by hydrophobic and hydrophobic followed by hydrophobic）,which were dispersed in water to obtain SiO₂ nanoparticles dispersion and blended with polyacrylamide to obtain a quaternary composite flooding with target concentration.The dispersion stability and displacement performance of nano-SiO₂ quaternary composite flooding with different modifier ratios were investigated,and their potential oil repelling mechanisms were analyzed.The results show that（1）Hydrophobically modified nano-SiO₂ is stably dispersed in water with particle size less than 10 nm under the synergistic effect of surfactant and chemical crushing agent.（2）The amphiphilic modified SiO₂ quaternary composite flooding maintains good dispersion stability with nanoparticle size less than 10 nm and zeta potential of 40-60 m V.The quaternary composite flooding（simulating the mineralization of Shengli reservoir）can be stably dispersed at room temperature for 236 days and at 60℃for 21 days.（3）The displacement performance of the amphiphilic modified nano-SiO₂ composite flooding was significantly improved,and the secondary recovery of the composite oil drive agent was 39.3%based on the primary water drive recovery of 29.9%when the nano-SiO₂ modified with hydrophilic modifier was added first and the ratio of hydrophilic to hydrophobic modifier was 1:2.In this paper,we prepare a highly stable composite flooding suitable for reservoir environment by modulating the structure of nano-SiO₂.The composite flooding significantly reduces the oil-water interfacial tension and improves the micro/macro wave efficiency,thus significantly improving the recovery of crude oil.Meanwhile,the quaternary composite flooding has lower viscosity,reduces the working pressure of core replacement,reduces construction cost,equipment requirements and power consumption,it is expected to be a new type of additive for the development of low-grade reservoirs with low permeability and high water content.