Study on salt tolerance mechanism of hydrophobic polymer microspheres for high salinity reservoir

Hydrophobic polymer microsphere (PM-C16) was synthesized by adding cetyl dimethylallyl ammonium chloride (C16) to study the mechanism of salt resistance. The structure of PM-C16 was analyzed by Fourier transform infrared spectrometric analyzer (FTIR), scanning electron microscope (SEM) and atomic force microscopy (AFM). The kinetic characteristics of PM-C16 water absorption was studied by analyzing and fitting the swelling law of PM-C16 under different NaCl concentrations. The viscoelasticity, shear resistance and swelling properties of PM-C16 were studied. The injection capacity and oil displacement effect of microspheres was studied by core displacement experiment. The results showed that compared with PM, PM-C16 with average particle size of 64.14 nm had better viscoelasticity at a salinity of 85053.48 mg/L. And PM-C16 particle size retention rate was higher than PM particle size retention rate under the same shear condition. With the increase of salinity, the swelling of PM-C16 could first decrease and then increase. The kinetic equation of PM-C16 water absorption was proposed. The excellent salt tolerance of PM-C16 was demonstrated by AFM from the microscopic point of view. The salt tolerance mechanism of PM-C16 was that the hydrophobic chains in the PM-C16 could bond with each other to form new spatial network structures in high-salt reservoirs. The molecular chain shrinkage of the microspheres was prevented. The PM-C16 had a double spatial network structure. The hydrophobic chains between PM-C16 was combined with each other. Therefore, PM-C16 also had good viscoelastic and shear resistance. In core permeability greater than or equal to 6 × 10−3 μm2, PM-C16 could be injected smoothly. Moreover, the recovery rate of PM-C16 was 7.22% higher than that of PM. The PM-C16 with hydrophobic chain structure could play a good salt resistance role in high salinity reservoirs.