Surfactant-influenced oil–water slip and flow in nanochannels studied by molecular dynamics and theoretical modeling

Abstract

This work uses molecular dynamics (MD) methods to investigate oil–water two-phase flow in hydrophilic nanochannels with surfactants adsorbed at the oil–water interface. We reveal two new discontinuous effects of nanoscale fluid flow: (i) the velocity distribution in the water layer is not a univariate function of the pressure gradient, and (ii) the apparent viscosity in the oil–water interface region is a function of surfactant concentration and pressure gradient. Based on the MD results, a layered theoretical model describing the discontinuous effects at the nanoscale is developed. The theoretical model provides quantitative two-dimensional functions for oil–water interface slip and fluid mass flux with pressure gradient and surfactant concentration. Surfactants significantly inhibit oil–water slip and reduce fluid mass flux. This study thus provides important insights into the theoretical and numerical models for shale or tight oil production predictions.