| Polyacrylamide flocculant is widely used in petroleum exploitation,wastewater treatment and other industries,especially in drilling fluid,fracturing fluid,polymer flooding and other aspects.Nano-SiO2 with different particle sizes was prepared by sol-gel method,the surface of SiO2 was modified by vinyl triethoxysilane,P（SiO2/AM/AMPS）was prepared by aqueous solution polymerization with SiO2 as the core,and P（SiO2/AM/DMDAAC）and P（SiO2/AM/DMDAAC/DMC）three flocculants with inorganic cross-linked structure were prepared by reversed-phase emulsion polymerization.Infrared（FTIR）,loss on thermogravimetry（TG）,nuclear magnetic resonance hydrogen spectroscopy（H-NMR）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,tensiometer and other instruments were used to analyze and characterize the products,and the effects of monomer mass fraction,initiation dose,oil-water mass ratio,emulsifier HLB value,reaction temperature and other factors on the polymerization reaction were analyzed.The synthetic flocculant was optimized and formulated into drilling fluid,and the rheology,filtration,lubricity,harmful solid phase control,salt resistance,temperature resistance,shear resistance,aging resistance and other properties of drilling fluid were evaluated by using rotational viscometer,laser particle size meter,extreme pressure lubrication instrument,mud cake viscosity tester and mud cake adhesion coefficient tester.FTIR,SEM,TEM,TG,H-NMR and other characterization results determined that the product was the target product.The optimum synthesis conditions of P（SiO2/AM/AMPS）were determined as follows:the mass fraction of monomer was30%,the reaction temperature was 50°C,the reaction time was 6 h,and the PH was8.5-9.At this time,the product had the best performance.The optimum synthesis conditions of P（SiO2/AM/DMDAAC）were as follows:the mass ratio of n-hexane,Tween-80,n-pentanol and Span-80 was 15:9:6:1.5,the mass concentration of monomer was 35%,the mass ratio of oil to water was 1:1,the HLB value of emulsifier was about 13,the reaction temperature was 60°C,the reaction time was 4 h,and the mass ratio of SiO2 to monomer was 0.9%.The optimum synthesis conditions of P（SiO2/AM/DMDAAC/DMC）were determined:monomer mass fraction was 25%,monomer mass ratio was 4.5:1.5:1.5,reaction temperature was 55°C,reaction time was 4 h.The introduction of SiO2 improved the adsorption capacity of P（SiO2/AM/DMDAAC/DMC）,and the critical association concentration（CAC）of P（SiO2/AM/DMDAAC/DMC）was determined to be 1 g/L.The performance evaluation results of the product are as follows:P（SiO2/AM/DMDAAC）and P（SiO2/AM/DMDAAC/DMC）have better performance than P（SiO2/AM/AMPS）.The flocculation time of both cations is about 500 s,and the flocculation rate is above 90%.When the salt concentration is 30%,the viscosity retention rate is above 70%;Conduct hot rolling at 180℃,and test the viscosity retention rate of the flocculant at room temperature to be about 70%;After 60 hours of aging,the viscosity retention rate is about 60%.The performance of P（SiO2/AM/DMDAAC）and P（SiO2/AM/DMDAAC/DMC）is better than that of P（SiO2/AM/AMPS）.The results of drilling fluid performance are as follows:the adhesion coefficient is 0.078 and 0.069,the viscosity coefficient is0.3346 and 0.3221,the extreme pressure lubrication coefficient is 0.085 and 0.084,and the filter vector is about 6 m L.When the salinity reaches 30%,the viscosity of drilling fluid remains above 30 m Pa·s.After continuous shearing at 8000 r/min for 150 min,the viscosity of drilling fluid is about 35 m Pa·s.After 96 h aging,the viscosity of the drilling fluid remained above 33 m Pa·s.Studies have shown that nano-silica flocculant shows good salt resistance and aging resistance,and the prepared drilling fluid has good test performance. |
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