Polymer Flooding in Fractured Reservoirs: Insights from Microfluidic and Simulation Studies

Polymer flooding is one of the most commonly used techniques for enhancing oil recovery (EOR). However, current research remains insufficient in fully elucidating the microscopic displacement mechanisms of polymer flooding in fractured heterogeneous reservoirs. The present study established an integrated experimental–numerical framework combining microfluidic experiments with numerical simulations to systematically investigate the polymer flow in complex pore–fracture networks. In the numerical simulations, shear-thinning behavior was incorporated to characterize the non-Newtonian properties of the polymer solution. Rheological data obtained from experiments were fitted to a power-law model and incorporated into the simulation, yielding exceptional agreement between the numerical and experimental results. Comparative analysis of the global velocity streamline fields revealed that polymer flooding effectively mitigated the “bundled” aggregation of streamlines observed during the water flooding, resulting in more uniform velocity distribution. Furthermore, four idealized pore structure models (H-type, corner-type blind-end, and Y-type bifurcation channel) were constructed and analyzed in conjunction with the residual oil distribution from microfluidic experiments. The results indicated that polymer flooding significantly promoted the pressure gradient between the inlet and outlet compared to water flooding, and the simulated pressure fields clearly illustrated the process by which polymer solution mobilized the residual oil through overcoming the capillary resistance. Additionally, to identify the governing factors of polymer flooding in fractured heterogeneous reservoirs, four-factor three-level orthogonal experimental design was employed to conduct sensitivity analysis. The simulation results showed that the degree of influence on oil recovery was as follows: oil viscosity > injection rate > wettability > interfacial tension, which might provide enlightening insights for the design and employment of industrial polymer flooding. In all, this study not only deepens the understanding of the microscopic mechanisms of polymer flooding but also may offer theoretical guidance for optimizing the operational parameters of polymer flooding in fractured heterogeneous reservoirs.