Understanding the mechanism of fluid droplets attached to micro/nano channels being displaced by another fluid can shed light on the transport law in unconventional oil and gas development. The cross-scale nature of the process and the strong interaction between droplet and displacement fluid determine that a hybrid simulation method must be used. In previous researches

the commonly used interface conditions of adding an external force interfere with the transfer of shear stress from the continuous domain to the molecular domain

resulting in incorrect calculation of the flow resistance. A new method of arranging a virtual wall instead of adding a force was used to solve the problem of incorrect shear stress transfer. Based on this new method

the cases are compared where the droplets are monoatomic molecules and butane

and the cases that the wall is completely rigid and the wall particles are allowed to vibrate

respectively. The results show that the traditional method of adding a force could lead to errors up to 65% in the flow drag

while arranging a virtual wall could keep error within 1%

thus has significant advantage. The introduction of droplet molecular structure and the wall particle vibration both have a great influence on the flow resistance.