Lignin-based nanoparticles as sustainable agents for enhanced oil recovery in sandstone and carbonate reservoirs

Lignin-based nanoparticles (NPs) derived from alkali lignin (AL) and kraft lignin (KL) were investigated as sustainable nanofluids for enhanced oil recovery (EOR) in sandstone and carbonate reservoirs. Nanoparticles with three distinct size ranges (~ 200, ~ 330, and ~ 500 nm) were synthesized and systematically evaluated to clarify the effects of particle size, lignin type, exposure time, and rock type on interfacial properties and oil recovery performance. The NPs were characterized in terms of size, surface charge, stability, and morphology. Their influence on oil-water interfacial tension, surface tension, and wettability alteration was examined through contact angle measurements on sandstone and carbonate substrates. Core flooding experiments under various injection scenarios were conducted to assess EOR efficiency. The results demonstrate that lignin NPs effectively alter rock wettability toward more water-wet conditions and improve oil displacement, with performance strongly dependent on NP size and lignin source. Among the tested nanoparticles, the intermediate-sized AL-based nanoparticles showed the best overall sandstone EOR performance increasing oil recovery by about 23.64 ± 2.49% in sandstone cores, while intermediate-sized KL-based nanoparticles could increase the oil recovery to 19.61 ± 3.54%. Under the sequential brine-nanoparticle flooding scheme, cumulative oil recovery improvements of about 53.48 ± 5.53% and 34.95 ± 3.46% were obtained in sandstone and carbonate cores, respectively. This study demonstrates lignin NPs as promising, environmentally friendly agents for EOR applications.