A dissipative particle dynamics simulation of water/oil flow characteristics in nano-sized shale slits

Aiming to study the effect of fluid-solid interaction on nano-scale flow, based on the dissipative particle dynamics method, a single-phase flow model and contact angle model of oil and water in quartz slits were established. In the flow model, the slit width is 5–20nm, and the driving force ranges 1–20 kcal/(mol A). The LJ96x potential function is used to characterize the fluid-solid interaction. The contact angle model contains three phases of oil/water/quartz and no external force is applied. Due to the attractive force of the solid wall, the density of fluid on the edge of the slit increases, then the flow resistance increases, and the velocity decreases. Along the cross section of the slit, the fluid velocity profile is parabolic, but velocity gradient near the wall is higher. When the driving force is small, the flow is significantly affected by thermal motion, and the velocity profile oscillates very violently. There are two peaks of number density profile of fluid beads on the edge of the slit. The curve is approximately horizontally distributed in the center of the slit. The radial distribution function curve shows that the fluid shows a high degree of aggregation near the wall. In a slit with a width of 20nm, the radial distribution function of oil and water decreases as the distance between the fluid and the wall becomes longer, showing obvious gradual characteristics.