Study On Synthesis And Properties Of Water-soluble Oil Displacement Polymer With Dynamic Covalent Bond

In the tertiary recovery,the injected polymers with high viscosity can reduce the water-oil mobility ratio,increase the sweep volume and carrying force,and thus displace more crude oil.However,high salinity and strong shear make the viscosity loss of oil displacement polymers extremely large,up to 80%.To achieve the required effect,the oil displacement agent must have good viscosity,salt resistance,and shear tolerance.Currently,a large of methods to further improve the properties of polymers have been proposed according to the corresponding theories,especially hydrophobic associating polymers and crosslinked polymers with chemical bonds,whereas there are few ways of improving the salt and shear resistance of polymers.Therefore,it is of great practical significance to develop excellent oil displacement polymers with good viscosity,salt tolerance,and shear resistance to have wide applications.Based on this,this thesis designed a series of water-soluble oil flooding polymers with dynamic covalent bond,and the viscosity,salt resistance,shear tolerance,interface activity were mainly discussed.The dynamic balance of the dynamic covalent bond is beneficial to recover the molecular weight and viscosity of polymer after shearing,improving the shear resistance of polymers.(1)Poly(acrylamide/diacetone acrylamide)was synthesized by free radical copolymerization in aqueous solution using industrially available monomers,and the cross-linked macromolecule system based on dynamic acyl hydrazone bond was formed by adipic dihydrazide.The structure of the copolymer was characterized by 1H NMR spectra,FT-IR spectra,elemental analysis,static light scattering and dynamic light scattering.The effects of copolymer concentration,crosslinking agent content and salt ion concentration on copolymer viscosity,rheological properties and micro structure were investigated by rotary viscometer,rheometer,scanning electron microscope and transmission electron microscope.The shear resistance of the copolymer solution was analyzed by multi-stage shear and mechanical shear simulation of pump shear and subsurface porous media shear.Finally,the application performance of the copolymer was studied by core displacement experiment.The crosslinking of the hydrazone bond enhanced the network structure of the copolymer,and the viscosity of 3 g/L polymer in 6576 mg/L mineralized water solution could reach 1400 mPa·s.The molecular weight of the broken chain could be recovered by reforming the dynamic hydrazone bond,achieving a viscosity recovery rate of 68%and enhancing oil recovery by 13.1%-16%.(2)A hydrophobic monomer,hexadecyl dimethylallyl ammonium chloride,was prepared by quaternization reaction,and the terpolymer was obtained by free radical copolymerization of acrylamide,diacetone acrylamide with hexadecyl dimethylallyl ammonium chloride.Finally,a dual network copolymer coordinated by physical hydrophobicity and chemical cross-linking was constructed by the cross-linking of hydrazine.The structure was characterized by 1H NMR spectra,FT-IR spectra,elemental analysis and static light scattering.The aggregation behavior of the copolymer solution was studied by dynamic light scattering,and the salt resistance and shear resistance of the copolymer solution were investigated by rotary viscometer,rheometer,scanning and transmission electron microscope.The surface activity and interfacial activity of copolymer solution were analyzed by surface and interfacial tension test.The results showed that the polymer had excellent salt resistance with Na+3.0×10^4 mg/L and Ca2+300 mg/L and interfacial activity.The viscosity of copolymer solution(3 g/L)in mineralized water reached 1400 mPa·s,and the interfacial tension of 1 g/L polymer solution was 3 mN/m,which can effectively prevent oil-water aggregation.Laboratory core flooding experiments further demonstrated that the secondary water flooding produced a continuous oil,resulting in an enhanced oil recovery by 10.2%.(3)The anionic water-soluble copolymers containing hydrazone bond were obtained by the reaction of adipic dihydrazide with ternary anionic polymers synthesized by free radical copolymerization of aqueous solution using acrylamide,diacetone acrylamide and sodium styrene sulfonate,and complexed with cetyltrimethyl ammonium obtaining the composite system based on dynamic covalent bond crosslinking and electrostatic interaction.1H NMR spectra,IR spectra,elemental analysis,static and dynamic light scattering,and the surface and interfacial tension test were used to study the properties of the solution.The viscosity and viscoelasticity of the solution under different compound ratios and different salt concentrations were investigated by viscosity and rheology tests.The viscosity of the compound solution increased by more than 100 times than that of the original solution at the same salt ion concentration,and the contribution rate of electrostatic action reached 80%as the temperature exceeded 55℃.The surfactant gives the composite system high surface activity and interfacial activity,and the effective combination of the advantages of polymer flooding and surfactant flooding,which can not only drive oil with its high viscosity,but also prevent oil and water from aggregation.