| With the increasing shortage of oil resources,high temperature and high mineralization oil wells have become the main target of oilfield exploitation,and the high temperature and high mineralization environment has led to a substantial decline in the thickening capacity of general thickeners.Therefore,it is imperative to develop polymer thickeners with good temperature resistance and salt resistance.In this paper,based on the summary and analysis of the composition of polyacrylamide thickener,the selection of raw materials and polymerization method,the formulation of polyacrylamide thickener was systematically studied through single-factor experiments,mainly including the optimization of polymerization method,each monomer dosage,initiator dosage,reaction temperature,reaction time and total monomer concentration.By systematically studying the influence of various influencing factor on the thickening performance of polymer thickener,the optimal formulation for polymer synthesis was determined:the mass ratio of acrylamide,2-acrylamido-2-methylpropanesulfonic acid and octadecyl acrylate was 67:30:3,the dosage of compound initiator was 0.1%of the total mass of monomer,the total concentration of monomer was35%,the optimal reaction temperature was 60℃,and the optimal reaction time was 5 h.The polymer was characterized using infrared spectroscopy,thermogravimetry,and particle size analyzer.The infrared spectra showed that absorption peaks of sulfonic acid group（-SO3H）and ester group（-COOR）could be observed for the polymer.The thermogravimetric results indicated that the polymer could be used at temperatures up to380°C.The particle size test results showed that the polymer emulsion had a uniform particle size distribution and good stability.Then,from the perspective of analyzing the performance of the polymer solution,the critical association concentration of the polymer was investigated,the micromorphology of the polymer solution was observed and the effects of high temperature,mineralization and shear stress on the thickening performance of the polymer were studied.The results showed that the critical association concentration of the polymer was 1.1%.The microscopic morphology of the polymer solution was observed by scanning electron microscopy,and a dense mesh structure was formed in the aqueous solution.The viscosity of 2%polymer solution could still reach 90 m Pa·s at 180°C and 170 s-1,showing good temperature resistance.The viscosity of 2%polymer solution could reach 100 m Pa·s at a mineralization level of 5,000 mg/L,showing good salt resistance.The storage modulus G′and loss modulus G″both decreased first and then remained unchanged with the increase of shear stress,showing good shear resistance.Finally,from the perspective of polymer application,the configuration of fracturing fluid was carried out for the preferred polymer,and the effects on the fracturing fluid were systematically studied when gum-breakers and cross-linkers were used,and the properties of shear recovery,sand suspension,cross-link activation energy and gum-breaking residue of the fracturing fluid were studied in depth.The results showed that the fracturing fluid had good shear recovery performance.When ammonium persulfate was used as the breaking agent and the dosage was 0.04%,the gum-breaking performance was the best,and the content of residue after gum breaking was less than 390 mg/L,which belonged to a clean fracturing fluid.When poly（ethylene imine）was used as the cross-linking agent and the dosage was 0.5%,the activation energy of cross-linking was 18.1 KJ/mol,which was far lower than the activation energy of cross-linking between general polyacrylamide and poly（ethylene imine）（41.57 KJ/mol）.It had good cross-linking performance.The sand suspension test showed that the settling rate of 2%concentration of fracturing fluid could reach 2.36×10-3 cm/min at 30℃and 6.25×10-3 cm/min at 80℃,indicating that the fracturing fluid had good sand suspension ability. |
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