Two-phase imbibition of water-oil displacement in silica nanochannels

Classical imbibition theory cannot describe imbibition flow dynamics in nanoporous media in tight reservoirs and other industrial applications. In this work, the two-phase imbibition flow of water-oil displacement in silica nanochannels is studied by using molecular dynamics simulations. Interestingly, it is found that the two-phase imbibition length is shown to increase linearly with increasing time, which is inconsistent with the variation of single-phase imbibition length. The imbibition rate increases with the increase of external driving force, and the large channel height can accelerate the two-phase imbibition flow. As the increase of chain length of alkane molecules, the imbibition rate reduces gradually. The more oil-wet the silica surface is, the slower the imbibition rate is. Furthermore, we derive a theoretical model to describe the two-phase imbibition flow of water-oil displacement in nanochannels by considering the static force equilibrium of external driving forces, capillary forces, and viscous forces of the water and oil phases. The theoretical model can well describe the two-phase imbibition flow under various conditions using the pre-calculated oil-water interfacial tension, the viscosity of fluids, and the three-phase contact angle. This study will enrich the theoretical understanding of oil-water two-phase flow at nanoscale.