Stability and Efficient Hydrocarbon Recovery via Carboxymethyl Cellulose and Polyethylene Glycol Interactions in the CuO–Surfactant Nanofluid System

Nanofluids have emerged as promising candidates for target-specific applications in petroleum research due to their ability to modify interfacial/wettability properties and improve rheological characteristics. This study investigates the formulation, stability, and performance of copper oxide (CuO)-based nanofluids stabilized using sodium dodecyl benzenesulfonate (SDBS) surfactant and polymeric additives, namely polyethylene glycol (PEG) and carboxymethyl cellulose (CMC). The nanofluids were synthesized through a high-energy homogenization process to ensure long-term stability. Dynamic Light Scattering (DLS) analysis showed that the optimal formulation (0.04 wt% CuO + 0.08 wt% SDBS) demonstrates a nanoparticle size distribution that minimizes aggregation. Zeta potential measurements confirmed the colloidal stability of CuO nanofluids, with the optimized nanofluid maintaining a high negative charge over a long period. Further stabilization with 0.20 wt% CMC and 0.40 wt% PEG produced comparatively strong zeta potential values. Interfacial tension (IFT) measurements indicated a substantial reduction relative to waterflooding. Rheological analysis revealed shear-thinning behavior supporting improved injectivity and oil displacement efficiency. The physicochemical evaluation of surfactant-stabilized nanofluids highlights the contrasting effects of low-molecular-weight PEG and high-molecular-weight CMC. Laboratory oil displacement tests demonstrated enhanced tertiary oil recovery, validated through spectroscopy, contact angle measurements, and core-flooding experiments.