Study On The Thickening Properties Of Anionic Polyacrylamide Prepared By Aqueous Two-phase Copolymerization

Polyacrylamide?PAM?based fracturing fluids have been used to improve the recovery of ultra-low permeability oil fields in recent years.Powdered Polyacrylamide and water-in-oil polyacrylamide are widely used at present.However,Powdered Polyacrylamide needs a relatively long dissolution time.In the course of the synthesis of water-in-oil Polyacrylamide a large amount of oil phase was added,causing damage to the environment.Furthermore,the thickener needs to be dissolved in seawater directly for offshore production.And the current products with no good salt resistance cannot be applied.Therefore,it was very urgent to develop a stable water-soluble Polyacrylamide thickener with high efficiency and less toxicity.In this paper,a kind of polyacrylamide dispersions with good salt resistance and thickening properties were prepared by aqueous two-phase polymerization.The polyacrylamide dispersions had the advantages of low apparent viscosity,no gel,high efficiency,and no toxicity.Thus,it belonged to environment-friendly green chemical engineering,and had great potential for development.At the same time,the formed polymer is well applied in oil field exploitation because of its excellent water solubility and good salt resistance and thickening properties.Acrylamide?AM?and 2-acrylamido-2-methylpropanesulfonic acid?AMPS?wereusedaspolymerizationmonomersandpoly2-acrylamido-2-methylpropanesulfonic acid?PAMPS?was used as steric stabilizer in this paper.Ammonium sulphate?AS?aqueous was used as the dispersed medium and water-soluble oxidation-reduction initiating system ammonium persulfate and sodium bisulfite were used as initiator.A stable anionic polyacrylamide?PAM-AMPS?aqueous dispersion was prepared by aqueous two-phase polymerization.The effects of reaction conditions such as monomer ratio,ammonium sulfhateconcentration,initiatorconcentrationandp Honthe polymerization system were studied by single factor experiment and the optimum synthesis conditions was obtained.The results showed that when the ratio of AM to AMPS was 4:1,the amount of initiator was 0.50%?based on the total mass of the system?,the total content of monomer in system was 25%and the amount of AMPS was 5%,the amount of AS was 15%,the p H value was6⁷,the reaction temperature was 30?,and under the conditions of reaction 7 h could be obtained PAM-AMPS aqueous dispersion with better stability,and their average particle size were 186.2 nm.The structure of the copolymer PAM-AMPS was characterized by FTIR,¹H-NMR,XRD and SEM,which was in accordance with the structure of the target.Through the test of particle size and TEM,it was known thatPAM-AMPS two-phase dispersion was uniformly dispersed in ammonium sulfate solution in spherical or ellipsoidal droplets.The copolymerPAM-AMPShasgoodthermalstabilitybyusing thermogravimetric analyzer.The PAM-AMPS aqueous two-phase dispersion destabilisation coefficient?TSI?was less than or equal to0.40,so its stability was excellent.The dynamic rheological tested show that the PAM-AMPS aqueous two-phase dispersion was a pseudoplastic fluid with a flow index?n?of 0.59.When the shear rate was 170s^-1,the temperature was 90?,and the concentration of PAM-AMPS was 0.50%,the apparent viscosity of the system remained at 3.15 Pa·s,which showed that it had excellent temperature resistance.Meanwhile,the relationship was studied separately between the viscoelastic modulus of the PAM-AMPS aqueous dispersion and strain,temperature,and time.It was found that the viscoelasticity of the system was increased because of the stable network structure formed between intramolecular and intermolecular.And the PAM-AMPS aqueous dispersion showed higher elasticity.At 25?,the PAM-AMPS aqueous dispersion with different mass fractions were gradually added to sodium chloride solution with different concentrations for testing and analysis.It was found that when the mass fraction of PAM-AMPS aqueous two-phase dispersion was increased from 0.20%to 1%,the viscosity of the mixed system containing 2×10⁴ mg/L sodium chloride was increased from 8.22 Pa·s to 60.74 Pa·s.While the concentration of sodium chloride was increased from 1×10⁴ mg/L to 5×10⁴ mg/L,the viscosity of the mixed system containing 0.2%PAM-AMPS aqueous two-phase dispersion was decreased from 10.80 Pa·s to 5.94 Pa·s.Therefore,the PAM-AMPS aqueous two-phase dispersion showed excellent thickening and salt-resistant properties.