Crosslinked polyacrylamide microspheres are widely used as in-depth flooding agents in petroleum development due to their unique properties of thickening, salt-resistance, high-temperature resistance, low cost, etc. To solve the problem of their injections in heterogeneous reservoirs, polyacrylamide nanospheres were synthesized. However, mechanisms of polymer nanospheres in enhanced oil recovery were not investigated comprehensively. In this study, we synthesized polymer nanospheres with different size distributions and studied their mechanisms in enhancing the oil recovery. First, the effects of polyacrylamide nanospheres in enhanced oil recovery of heterogeneous sand-packed tubes was explored by sand-packed tube oil displacement experiments. Second, the rheological properties of polyacrylamide nanosphere dispersion were explored using a rheometer. Third, through the visual microchannel experiment, the mechanism of polymer nanosphere emulsion on the removal of the residual oil film was explored. Finally, through the crude oil removal experiment, it was found that polymer nanospheres with a particle size of about 54 nm can cooperate with surfactants to accelerate the removal of oil droplets.
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