Sustainable Enhanced Oil Recovery Fluid Based on Synergic Effects of Cationic, Anionic, and Nonionic Surfactants in Low Salinity: SLS; QA; and SDBS

In the context of the energy transition, petroleum will remain a critical resource for several decades. Enhanced oil recovery (EOR) offers a method for optimizing its production while advancing the United Nations Sustainable Development Goal 12 (SDG 12) and the 2030 Agenda, which emphasize reducing the environmental impact and addressing community concerns. Pre-salt limestone reservoirs, situated far offshore, require customized enhanced oil recovery (EOR) strategies. Although low salinity water has recently gained attention for these reservoirs, further investigation is required to integrate environmentally low-impact surfactants and to minimize their concentrations while maintaining high recovery factors (RFs). Low salinity water formulations containing small concentrations of surfactants were injected into limestone core samples with oil from presalt reservoirs under reservoir conditions. In total, 21 linear formulations and 16 multivariate formulations experimentally designed using Doehlert matrix as the chemometric tool were prepared by combining the nonionic surfactant sodium dodecylbenzenesulfonate (SDBS), the anionic surfactant sodium lauryl sulfate (SLS), and the cationic surfactant tetraethylammonium chloride (QA) at concentration levels above, below, and on their respective critical micelle concentrations (CMCs). The produced water was analyzed using X-ray fluorescence, with spectra evaluated via principal component analysis (PCA) and partial least squares (PLS). Theoretical simulations were also performed with molecular dynamics applied to the two top-performing results. The traditional linear study, varying individual surfactant concentrations, yielded an RF increase of up to 12.8%. However, the covariation approach further improved the results, achieving an RF of 16%, primarily due to the synergistic effects of the cationic and anionic surfactants, which mobilized both bulk oil and surface oil. The balance among micellar SLS, micellar SDBS, and nonmicellar QA proved essential. Theoretical simulations supported these experimental findings, indicating no direct interaction between the surfactants, increased interfacial tension, SLS migration to the surface, and QA retention in the bulk phase.