In order to find out the formation mechanism and distribution of residual oil after water flooding and tap the potential of residual oil

a parallel pore micro model has been established based on N-S equation. Phase field method has been used to track the phase interface in the process of water flooding. The distribution characteristics of residual oil after water flooding under different wall wetting conditions have been studied. The residual oil after water flooding has been exploited by mobility ratio improved by polymer flooding

interfacial tension changed by surfactant or wettability inversion occurred. And the effects of different mobility ratio and interfacial tension on the micro flow of residual oil in parallel pores after water flooding have been studied. The results show that when the rock surface is water-wet

the residual oil mainly stays in the large pore channels in parallel pores after water flooding. The polymer flooding improving the mobility ratio can effectively displace the residual oil in the pore channels

entirely. When the rock surface is oil-wet

the residual oil after water flooding mainly stays in the wall of parallel pores and small channels. It is difficult to displace the residual oil in the small pore by improving the mobility ratio. However

after changing wettability by surfactant

the residual oil is stretched into oil droplets and congregated

and finally the residual oil saturation is reduced. The lower the mobility ratio or interfacial tension

the higher the oil displacement efficiency. This study reveals the distribution and displacement mechanism of residual oil in parallel pores after water flooding

and provides an important theoretical basis for the effective exploitation of reservoirs by water flooding.