Molecular dynamics simulation of SDS-driven silica nanoparticle stabilization for wettability alteration in carbonate reservoirs

• MD reveals SDS adsorption & wettability alteration on calcite. • SDS+SNP nanofluid reduces contact angle from 106°±0.8 to 62.5°±0.5. • Synergy enhances SDS mobility, SNP retention, and oil bond disruption. • Realistic SiO₂ charges modeled from experimental zeta potential. • Na⁺ bridging dominates SDS adsorption below CMC at high salinity. The synergistic use of silica nanoparticles (SNP) and surfactants has shown significant potential for stabilizing nanofluids under harsh reservoir conditions and altering the wettability of carbonate reservoirs to enhance oil recovery. Despite the promising results of experimental findings, the underlying molecular-level mechanisms remain insufficiently understood. This study employs molecular dynamics (MD) simulations to investigate the behavior of sodium dodecyl sulfate (SDS) in the presence o SNPs and its effect on wettability alteration. Based on zeta potential measurements the surface charge of SNPs were assigned realistic, referring a key limitation in prior modeling studies. The results reveal that SDS adsorbs onto similarly charged SNPs, increasing their zeta-potential and improving nanofluid stability. Further simulations explored the wettability alteration of calcite by SDS, SNP, and their combination (SNP+SDS). The results showed the key contributors in wettability alteration by SNP+SDS include SDS adsorption, complex formation with oil polar moieties (octanoate), and SNP interaction at oil-water interface. The synergistic use of SDS and SNPs accelerated the wettability alteration to water-wet so that it reduced the contact angle from 106°±0.8 to 62.5°±0.5 and decreased the number of octanoate at interfacial oil/calcite by 60 % within 50 ns. This study provides molecular-level insight into the dual role of SDS and SNPs under simplified conditions, offering a mechanistic basis for future work that bridges experimental findings and atomistic simulations.