<![CDATA[Conventional enhanced oil recovery (EOR) methods often lose effectiveness under high-temperature, high-salinity (HTHS) conditions because of inadequate fluid stability, limited wettability alteration, and insufficient interfacial tension (IFT) reduction. This study developed and evaluated cellulose nanoparticles (CNPs) derived from Acacia auriculiformis as a sustainable nanofluid for EOR. CNPs were extracted using a deep eutectic solvent (DES) process and surface-modified to improve thermal stability and interfacial functionality. Structural, morphological, compositional, and thermal characteristics were evaluated, while the resulting cellulose nanofluid (CNF) was assessed through rheology, IFT, contact-angle, and sand-pack flooding experiments. The process yielded 78.3% CNP, with an average particle size of 19.65 ± 0.2 nm and crystallinity index (CrI) of 76.6%, confirming successful formation of crystalline nanocellulose. At 0.2 wt%, CNF reduced oil-water IFT to approximately 7.8 mN/m at elevated temperature and decreased the sandstone contact angle to 16.5°, indicating strong water-wet alteration. Sand-pack flooding achieved 13.7% incremental oil recovery and 72.3% total recovery, compared with 9.8% incremental recovery and 63.1% total recovery for xanthan. The superior performance is attributed to the combined effects of IFT reduction, wettability alteration, mobility control, and thermal stability. Overall, Acacia-derived CNF demonstrates greater EOR potential than xanthan and represents a promising, environmentally sustainable nanofluid for challenging reservoir conditions. Copyright © 2026 by Authors, Published by Universitas Diponegoro and BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).]]>
