Study on the rheological properties and salt resistance mechanism of an amphiphilic polymer with twin-tailed group

Partially hydrolyzed polyacrylamide (HPAM) is the most widely used polymer for oil recovery. Its thickening ability has been severely compromised in high salinity reservoirs. To improve polymer viscosity in high salinity reservoirs, a twin-tailed amphiphilic polymer P(AM/AMPS/DtC18) was developed by radical copolymerization method using AM, AMPS and DtC18 monomers, abbreviated as PAAD18. The contrast polymer P(AM-AMPS) was prepared by the same method and reaction conditions. The structure of PAAD18 was characterized by Fourier Transform Infrared Spectroscopy (FTIR) and H Nuclear Magnetic Resonance Spectra (1H NMR). The relationship between its rheological properties and microstructure was studied using rheological analysis and Scanning Electron Microscope (SEM). The mechanism of salt resistance was revealed. The results show that under the condition of XJ reservoir with 98558 mg/L and 40℃, the viscosity of PAAD18 with concentration of 2200 mg/L is 25 mPa·s. PAAD18 has better temperature and salt resistance than HPAM and P(AM-AMPS). P(AM-AMPS) has better temperature resistance and salt resistance than HPAM. The salinity ranges from 0 to 5 × 104 mg/L, the viscosity of PAAD18 is reduced due to the action of electrostatic shielding. At a salinity of 5 × 104 mg/L, the electrostatic shielding effect and the hydrophobic association effect reach a balanced point, and the solution viscosity is the lowest. The salinity increases from 5 × 104 mg/L to 15 × 104 mg/L, then the hydrophobic association is enhanced due to the increased polarity of the solution. It was found that the polymer network structure of PAAD18 was more complex, the viscosity of the solution increased instead. The salt thickening properties were demonstrated in the rheology measurement. This work provides a new material for polymer flooding technology in high salinity reservoirs, with good application potential and guiding significance.