Design, preparation and properties of new polyacrylamide based composite nano-microspheres with like “ball in ball” structure

Recently, polymer gel nano-microspheres as a new kind of depth profile control agent have achieved preliminary effects in enhancing oil recovery (EOR), especially, for some low-permeability reservoirs that are difficult to enter by conventional polymer flooding. To synergistically improve the water-oil mobility ratio on the basis of blocking pore throat and adjusting water flooding profile by microgel, a new polyacrylamide composite nano-microspheres with like "ball in ball" structure are designed and prepared via inverse microemulsion polymerization in the case of pre-introducing hyperbranched polyacrylamide (HBPAM) in the water phase. Like-spheroid (HBPAM) with high rheological properties are gradually released from microspheres to achieve the synergistic effects of plugging pore throat of reservoir and viscosity improvement of the dispersion. This article uses FTIR, SEM, TEM, TGA and laser particle size analyzer to characterize the structure, morphology, thermo-stability and particle size distribution of composite microspheres. The swelling dynamics, temperature, and salt resistance of the composite microspheres are then analyzed. More importantly, the rheological properties, dispersion stability, thickening ability, emulsifying property, and oil displacement mechanism of microspheres are systematically studied. The plugging rate and oil displacement efficiency are analyzed by simulated core experiments to evaluate the application effect of microspheres. The composite microspheres designed in this paper are expected to solve the challenge that conventional polyacrylamide used in EOR is difficult to be injected in low permeability reservoirs and synergistically enhance the profile control and EOR effect of nanospheres.