Experimental study of pore-scale clogging–deformation–migration cycles of polymer microspheres and their macroscopic flow-diversion effect

As a pivotal technology in tertiary oil recovery, polymer microsphere flooding demonstrates significant advantages in enhancing oil recovery from high-water-cut reservoirs. In order to reveal the transport behavior and profile control mechanism of polymer microspheres in heterogeneous reservoirs, a dual-scale experimental system combining pore-scale microfluidic visualization and core-scale flooding tests was established. Taking 2 μm polymer microspheres provided by Qiuling Oilfield as the research object, the particle swelling performance, plugging behavior, and profile control effect under different permeability contrasts were systematically investigated. Experimental results show that microsphere swelling is driven by both hydration and aggregation, and the swelling degree increases significantly with hydration time. A typical plugging–deformation–migration–re-plugging pattern is observed under flow field conditions. Based on these observations, a novel mechanism theory of “localized bypassing and global diversion” is proposed to describe the microsphere-induced flow redistribution in heterogeneous porous media. When the permeability contrast is ≤10.13, microspheres can effectively reduce flow in high-permeability zones while increasing it in low-permeability zones, resulting in an enhanced oil recovery of 11.86%–23.04%. However, when the contrast increases to 16.92, the flow redistribution effect becomes negligible and the recovery improvement is limited to 5.45%. This study provides a practical evaluation criterion for determining the application boundary of polymer microspheres and offers theoretical and experimental guidance for profile control optimization in heterogeneous reservoirs.