Abstract: Based on the flow rate formula of power-law fluid in the tube，the relationship between shear rate and flow rate
was established. The improved effective viscosity model of Carreau fluid in the tube was derived by submitting the corrected
relationship into the Carreau model. In the new model，the effective viscosity is the function of flow rate. The original nonlinear
equations are simplified as linear equations. Applying the new effective viscosity model，the microscopic simulation model for
polymer flooding is provided together with polymer seepage mechanism. Through the microscopic simulation，laws of remaining
oil after polymer flooding are statistically analyzed. Microscopic simulation shows that the retained oil of network shape
decreases significantly while the volume ratio of single grain/island shape，fleck shape and oil-water mixed shape increases.

Key words: network model, polymer flooding, seepage mechanism, remaining oil, retention