Molecular dynamics simulation of oil displacement using surfactant in a nano-silica pore

Molecular Dynamics (MD) simulations of oil droplet displacement have been performed using pressure driven surfactant flooding at typical reservoir condition (T=330 K and P=20 MPa). The behavior of the micellization of surfactant molecules has been validated. A micelle with a radius of 22.85 Å is formed by 60 anionic sodium dodecyl benzenesulfonate (SDBS) surfactant molecules in aqueous solution. Surfactant additions result in significant reduction of interfacial tension (IFT) for oil/water system and such reduction is dependent on surfactant surface concentration. The microscopic mechanism of IFT reduction is described. Interfacial thickness increases from 3.5 Å to 22.5 Å at T=300 K andP=1 atm after surfactant molecules are adsorbed at oil/water interface, indicating high miscibility of two phases and thus results in interfacial tension reduction; the calculated interface formation energy of a single surfactant molecule is -145.7 Kcal/mol, which means the additions of surfactant would lead to the decrease of system energy and thus a more steady system. For surfactant flooding simulation, oil droplet static contact angle increases with surfactant additions. The larger the static contact angle of oil droplet, the stronger the drop deformation and the higher the displacement speed. Limited deformation is observed as oil droplet detaches from the solid substrate. Compared with water flooding, surfactant additions can significantly increase oil displacement speed by up to 80%.