Application Of Surface Modified Silica In Improving The Thermal Stability Of Acrylamide-Based Polymer For EOR

In crude oil extraction,after primary and secondary(water flooding)recovery process,typically in excess of 60%of the original oil in place remains within the formation.It is important to take measures to maintain the supplement of crude oil.Recently,hybrid formed by polymer solution and nanoparticles have achieved great achievements for EOR application.Nanoparticles have been used to improve displacing fluid properties(viscosity enhancement,surface tension reduction);alter fluid-rock interaction properties;reduce the viscosity of heavy oil.In this work,nano-silica was modified by saline coupling agents and the flooding agent was obtained by co-polymerization of nano-silica and monomer or by adding nano-silica into polymer solution.The research content mainly includes the following four aspects.(1).Amino-functionalized nanosilica(ANS)was prepared using nanosilica(NS)and 3-aminopropyltriethoxysilane(APTES);amphiphilic nano-silica(OAS)was obtained by using APTES,octyltriethoxylsilane(OTES)and NS;Many factors including the kinds of saline coupling agent,reaction time,p H,dosage are studied to improve the dispersion properties of nano-silica.Finally,nanoparticles with stable dispersion properties and good compatibility with polymers were successfully prepared.(2).Based on the CNOOC project,the polymer used in this section is copolymer of AM and AMPS.The viscosity-enhancing performance,rheological property,anti-aging performance,interface activity analysis and displacement tests of hybrid solution were carried out.Results show that the structures of ANS samples have a significant effect on the salt tolerance of hybrid solution due to the fact that the amine group density on the ANS surface can affect the strength of intermolecular interaction between nanoparticles and polymer molecules.In Na Cl solution,ANS with low amine group density can enhance the viscosity of hybrid solution effectively.ANS with high amine density has better viscosity-enhancement property than low amine density ANS in Ca Cl₂ solution.(3).In order to simulate polymer(HPAM)structures at different stages during high-temperature flooding,three synthetic hydrolyzed polyacrylamide(PA)samples,whose hydrolysis degrees were 17.8%,29.2%and 47.5%,respectively,were prepared in this study.The effects of the hydrolysis degree of PA and structure of nano-silica on the rheological properties of nano-silica/polymer hybrid were investigated.Benefiting from its structure,compared with highly hydrolyzed polymer solution(hydrolysis degree 47.5%),the viscosity of nano-silica/polymer solution increased by 26.08%,whereas the viscosity of nano-silica/polymer solution only increased by 0.26%when the hydrolysis degree was low(17.8%).We can conclude that the hybrid solution has excellent flowing capacity at the beginning of polymer flooding and it can maintain the viscosity of polymer solution after experiencing severe degradation.The excellent performance of nano-silica/polymer solution can be attributed to high interfacial activity of nano-silica,strong electrostatic and hydrophobic association interaction between nano-silica and polymer chains.These results indicate that nano-silica/polymer hybrid solution could be an effective oil-displacing agent.(4).ANS particles were introduced into the copolymer of AM/AMPS during polymerization.FT-IR,¹H NMR and XPS were used to analyze the structure of the hybrid polymer.Rheological properties and anti-aging performance of hybrid solution were studied,and the result shows that the long-term thermal stability and salt tolerance of polymer solution can be enhanced by the addition of ANS.The long-term thermal stability test shows that the viscosity retention rate of hybrid solution is 33.5%higher than that of non-nano-silica polymer solution.