Objective In view of the problems that in the injection process conventional polymers for oil displacement are not shear resistant, and the viscosity loss is large, which affect the oil displacement effect, the method of emulsion polymerization and interfacial polymerization is adopted to introduce a shell outside the polyacrylamide to synthesize a polyurethane encapsulated polyacrylamide microencapsulated polymer.

Method This paper studied the microstructure and particle size before and after shell breaking, as well as the slow release and viscosity increasing performance, shear resistance, injection ability, profile adjustment ability, and oil displacement effect.

Result The result showed that the size of microcapsule before shell breaking was between 170―800 nm, and after releasing the polymer, the molecular size was between 50―350 nm; after heating at 65 ℃ for 2 h, the shell began to break and release, after 20 h, the viscosity release rate was above 80%; the Wuyin mixer vigorously sheared for 3 min before shell breaking, the viscosity retention rate was still above 92%; the polymer could be effectively injected into rock cores with a permeability of 50×10⁻³―500×10⁻³ μm² before shell rupture, but its ability to adjust profiles was weak. After shell breaking, the polymer could increase injection pressure in rock cores with a permeability greater than 100×10⁻³ μm² and had good profile adjustment ability; injecting microencapsulated polymer after water flooding could enhance oil recovery by 15.5 percentage points. After injecting microencapsulated polymer into the mine, the wellhead pressure increased significantly.

Conclusion It proves that microencapsulated polymers can break the shell and increase viscosity in the formation, and it is a new type of oil displacement polymer with good application prospects.