Paper waste derived cellulose nanofluids for enhanced oil recovery in high temperature high salinity sandstone reservoirs

Conventional enhanced oil recovery (EOR) methods often exhibit reduced efficiency under high-temperature and high-salinity (HTHS) reservoir conditions, necessitating sustainable and high-performance alternatives. This study investigated cellulose nanoparticles (CNPs), defined as nanoscale cellulose particles derived from paper waste, for HTHS EOR applications. High-purity CNPs were synthesized using a deep eutectic solvent (DES) and subsequently surface-modified with (3-aminopropyl)triethoxysilane (APTES) to improve dispersion stability and interfacial properties. The synthesized CNPs and APTES-functionalized modified cellulose nanoparticles (m-CNPs) were characterized to evaluate their morphology, chemical structure, crystallinity, thermal stability, and elemental composition. The resulting m-CNPs exhibited a uniform rod-like morphology with an average particle size of 19.5 ± 0.2 nm, a yield of 79.3%, and a crystallinity index of 81.84%. The m-CNP nanofluid (m-CNPF) exhibited shear-thinning and pseudoplastic behaviour, while reducing interfacial tension from 23.02 ± 1.1 to 5.9 ± 1.2 mN/m and contact angle from 134.88 ± 0.2° to 14.5 ± 0.12°. HTHS sandpack flooding achieved incremental oil recoveries of 9.1 ± 0.2% (fine sand) – 14.4 ± 0.3% (coarse sand) OOIP and reduced residual oil saturation to 10%. These findings demonstrate the potential of paper-waste-derived, APTES-modified cellulose nanofluids as sustainable EOR agents for challenging HTHS reservoir conditions.