Surfactant/Polymer Flooding Combined with Gel and Polymer Microsphere Plugging for Enhanced Oil Recovery in a Low-Permeability Reservoir

Low-permeability reservoirs, a critical component of the global energy supply, exhibit low oil recovery with conventional technologies due to complex pore structures and poor fluid flow. Single chemical flooding is constrained by insufficient salt tolerance and weak deep control. This study proposes a combined system of “surfactant/polymer (SP) flooding → gel blocking → microsphere deep profile control” and investigates its performance under simulated reservoir conditions (25,000 mg/L salinity, 65°C). Results demonstrated: The SP system maintained 35 mPa·s viscosity in high-salt environments, reduced oil-water interfacial tension to 5.0 × 10–3 mN/m, and enhanced recovery by 18.5% alone. Polymer microspheres achieved an 8x equilibrium swelling within 7 days, boosting recovery by 10.1% through deep control. Modified starch gel (G∼H grade strength) achieved a 97% plugging rate for the high-permeability channels. In combined flooding (SP flooding → gel blocking → microsphere deep profile control), the final recovery reached 59.34, 22.28% higher than conventional water flooding. The synergistic effects of near-wellbore gel plugging, deep profile control by microspheres, and the binary composite system effectively expanded the swept volume while significantly improving the displacement efficiency. This study provides a new technical pathway for the efficient development of low-permeability reservoirs.