Oil Recovery by Synergistic CO2 Flooding Using Viscoelastic Fluids of Low Interfacial Tension Containing Amphiphilic Nanoparticles

Tight-oil reservoirs are abundant but characterized by poor physical properties and strong heterogeneity. CO2 flooding is an important technique for enhanced oil recovery (EOR) and carbon storage, yet CO2 channeling remains a critical issue due to its high mobility, and existing anti-channeling methods have limitations. In this work, a low-interfacial-tension viscoelastic fluid containing amphiphilic nanoparticles (LFNA) was formulated by combining a small-molecule viscosifier (LFLM) with amphiphilic nanoparticles (LQNA). Its performance and synergistic effect with CO2 flooding were systematically evaluated. The LFNA formulation is simple (0.4 wt% LFLM + 0.01 wt% LQNA-3), exhibiting a viscosity of 5.82 mPa·s, an interfacial tension of 0.0296 mN/m, and predominantly elastic behavior (tan δ = 0.791). It shows good tolerance to temperature, salinity, and pH variation, favorable injectivity in tight cores (Kg = 0.45 − 1.07 mD), and selective plugging capability. Core-flooding experiments in both homogeneous and heterogeneous models demonstrate that CO2–LFNA alternating injection after waterflooding outperforms continuous CO2 flooding in EOR. In heterogeneous models, the LFNA slug preferentially plugs high-permeability channels, expands sweep volume, and effectively mobilizes residual oil in low-permeability zones, with incremental recoveries of 12.49% and 15.74% for low- and high-permeability cores, respectively. Overall, the combined incremental recovery of CO2–LFNA alternating flooding (14.26%) exceeds that of water–LFNA alternating flooding (11.49%) and continuous CO2 flooding (9.85%). These results confirm that LFNA provides a synergistic effect of plugging, oil-washing, and sweep improvement. Using LFNA for CO2 channeling control is feasible and effective, and it also benefits CO2 storage and carbon reduction.