Viscoelastic displacement mechanism of fluorescent polymer microspheres based on macroscopic and microscopic displacement experiments

Polymer microspheres represent a novel oil displacement agent that has demonstrated significant efficacy in oilfields. Recent research indicates that the viscoelastic properties of polymer microspheres are crucial for oil displacement. To further elucidate the viscoelastic displacement mechanism, a series of fluorescent polymer microspheres, P(AM-BM-AA-[Br−Flu]), with varying elasticity were synthesized via inverse suspension polymerization, incorporating fluorescent monomers derived from fluorescein (Br−Flu). The micromorphology and viscoelastic properties were systematically characterized using an infrared spectrometer, scanning electron microscope, inverted fluorescence microscope, laser particle size analyzer, and rheometer. Through microscopic and macroscopic oil displacement experiments, along with microsphere concentration tests, the viscoelastic displacement mechanism of polymer microspheres was investigated. The results indicate that P(AM-BM-AA-[Br−Flu]) exhibiting green fluorescence was successfully synthesized. By adjusting the crosslinker concentration, polymer microspheres with different elasticities were produced. During the displacement process, the elasticity of the microspheres governs their migration mode within the pore throats. Microspheres with higher elasticity exhibit greater sweep efficiency. The pushing and carrying effect of microspheres on residual oil droplets, the positive pressure breakthrough effect resulting from microsphere trapping, and the displacement of blind-end residual oil collectively enhance the oil displacement efficiency of microspheres. From a force analysis perspective, the elasticity of microspheres plays a pivotal role in improving both sweep efficiency and oil displacement efficiency. These findings provide experimental support for understanding the oil displacement mechanisms of polymer microspheres and for developing new polymer microsphere-based oil displacement agents.