Severe reservoir heterogeneity in offshore oilfields often leads to dominant flow channels, high water cut, and low sweep efficiency during long-term water flooding. In this study, an in situ self-assembled composite foam system combining soft polymer particles with a low-interfacial-tension foaming agent was developed for profile control and enhanced oil recovery (EOR) in offshore heterogeneous reservoirs. The self-assembly characteristics and physicochemical properties of different particle systems were evaluated to optimize the composite foam structure. Static and dynamic experiments were conducted to assess foam stability, plugging performance, injectivity behavior, and oil displacement efficiency. Results show that the optimized composite foam undergoes in situ self-assembly under reservoir conditions, forming a stable particle–foam structure that enhances selective plugging and mobility control. Core flooding experiments demonstrate that the system increases oil recovery by up to 27.2% across a wide permeability range. Field application further confirms its effectiveness in regulating interlayer water absorption, stabilizing injection pressure, and reducing water cut. These results indicate that the proposed in situ self-assembled composite foam is a promising technique for integrated profile control and enhanced oil recovery in offshore heterogeneous reservoirs.

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.