Micro-scale characterization of nanoparticles adsorption onto oil-water interface and detachment capacity of oil film

Nanofluids are widely used in the development of low-permeability reservoirs due to their excellent interface performance, which can also cause formation damage if used incorrectly. In this work, molecular dynamics simulation is employed to investigate the effect of nanoparticle modification on oil-detaching capacity. The Interaction energy ratio is proposed to evaluate the interactions between the nanoparticle and oil as well as the nanoparticle and water. The number of oil molecules separated from the oil film, arranged from 0 to 30, is utilized to assess the oil-detaching capacity of the individual nanoparticle. The results demonstrate that improving surface modification leads to a sharp decrease from 0 to -300 kcal/mol in the interaction energy between nanoparticle and oil. Although the interaction energy between nanoparticle and water slightly increases from -4400 to -3800 kcal/mol with greater modification, it remains significantly lower than that between the nanoparticle and oil due to the inherent hydrophilicity of SiO2. Further, the contact angle exhibits a linear relationship with the interaction energy ratio when it exceeds 0.18, meaning the modified nanoparticle can effectively adsorb onto the interface. Moreover, the number of separated oil molecules demonstrates a linear relationship with the contact angle when it is above 35(degrees), indicating the adsorbed nanoparticle can effectively detach the oil film. At last, the results show that there is an optimal length for detaching oil films, thus scientific design of the modified nanoparticles is necessary to achieve optimum enhanced oil recovery performance.