Study on the Mechanism of Swept Volume Expansion of a Nanoparticle–Polymer Compound Flooding System in Low-Permeability Reservoirs

With the advancement of oil field development, oil and gas exploration has gradually shifted to low-permeability reservoirs. When polymer flooding is applied in these reservoirs, the primary challenge is that polymer molecules have a larger size and struggle to enter the pore spaces in the reservoir. To address this issue, this study utilizes a nanocomposite polymer flooding system, leveraging the synergistic effects of nanometer-sized particles to reduce the size of polymer aggregates and thus improve displacement efficiency. To verify the improvement in polymer flooding performance for low-permeability reservoirs, this study conducted several experimental evaluations. First, dynamic light scattering was used to examine the effect of a nanofluid (iNanoW) on the size of the polymer aggregates. The results showed that iNanoW reduced the size of the polymer aggregates by approximately 40%. Next, rheological performance testing revealed that, compared to the original polymer solution, the viscosity of the iNanoW-polymer compound solution remained basically unchanged, while the elastic modulus decreased by about 9%. Finally, nuclear magnetic resonance (NMR) technology, combined with a conventional core flooding setup, was used to compare the displacement performance of polymer flooding and iNanoW-polymer compound flooding in low-permeability cores with a gas permeability of 50 mD. The evaluation was conducted based on injection pressure, NMR <i>T</i> ₂ spectra, and core segmentation sequences. The results show that, compared to traditional polymer flooding, iNanoW-polymer compound flooding allows the polymer fluid to enter smaller and more core pores, thereby expanding the fluid's swept volume. In both small and medium-sized pores in the core, the fluid swept volume increased by approximately 30%. This outcome provides valuable insights for the future application of nanomaterial-polymer compound flooding in low-permeability reservoirs.