Synthesis And Solution Rheological Properties Of Polymer Coated Nanomagnetic Thickener

Thickeners have significant influences on the properties and construction effects of working filuids in oil and gas field such as fracturing fluids,drilling fluids,chemical water shut-off profile control agents and oil displacement agents in enhanceed oil recovery,etc.At present,the most widely used thickeners are organic polymers.However,organic polymers have been increasingly unable to meet the requirements of oil and gas production due to the properties of organic polymers themselves and increasingly complicated conditions of oil and gas reservoirs.Therefore,organic polymers must be modified to improve their properties.In the existing modification methods of organic polymers,introducing inorganic nanoparticles into organic polymers to synthesize polymer coated nanomaterials is an ideal method,but this method will further increase the production costs of thickeners.From the perspective of reducing production costs,the nano-Fe3O4 is introduced into organic polymers.The polymer coated nanomagnetic thickener with better properties and magnetic response is synthesized through copolymerization of the nano-Fe3O4 precursor,acrylamide(AM)and 2-acrylamido-2-methyl-1-propane sulfonic acid(AMPS).If the polymer coated nanomagnetic thickener can be recycled by magnetic separation technologies,it will reduce production costs.In this paper,one-step method was used to synthesize and modify the nano-Fe3O4 simultaneously.In other words,the oleic acid(OA)was regarded as a modifier added into the process of synthesizing nano-Fe3O4,and then obtained the nano-Fe3O4 precursor that can participate in the copolymerization reaction and has a good dispersibility.The preparations were made for the synthesis of polymer coated nanomagnetic thickener.The molecular structure of the polymer coated nanomagnetic thickener was designed,and the microemulsion polymerization method was selected to make the nano-Fe3O4 precursor copolymerize with AM and AMPS.Combining orthogonal test and single factor analysis method,the synthesis conditions of the polymer coated nanomagnetic thickener were obtained.The total concentration of monomer is 10.0wt%,the sodium dodecyl sulfate(SDS)dosage is3.0wt% of the total monomers mass,the molar ratio of AM with AMPS is 9,the initiator dosage(ammonium persulfate(APS)and sodium bisulfite(SHS))is 2.0wt% of the totalmonomers mass,the molar ratio of APS with SHS is 3.5,p H is 9,time is 5h,temperature is55�C and the nano-Fe3O4 precursor dosage is 10.0wt% of total mass of AM and AMPS.Infrared analysis,thermogravimetric analysis,morphology and particle size analysis,magnetic property analysis and stability analysis were used to confirme the target product was synthesized,which in accorgance with structure designed,shape is spherical with diameter of153 nm,saturation magnetization is 20.0 emu/g,and has a good stability.Finally,the rheological properties of the polymer coated nanomagnetic thickener solution were systematically measured by rheological methods.The results showed that when the concentration was greater than 1000 mg/L,the polymer coated nanomagnetic thickener showing stronger thickening properties.Polymer coated nanomagnetic thickener solution had good salt resistance and shear resistance,and its apparent viscosity at 7.34s-1 was still more than 25 m Pa�s at 140�C.When the angular frequency was greater than 1rad/s,the polymer coated nanomagnetic thickener solution mainly exhibited viscosity characteristics.The rheological curve of the polymer coated nanomagnetic thickener solution can be well fitted by the power-law model,it is a pseudoplastic fluid.Meanwhile,the polymer coated nanomagnetic thickener solution had good thixotropic properties and creep-recovery properties.