Abstract: After water flooding and polymer flooding,problems can arise,such as a rapid increase of water-oil ratio and water consumption,and poor adaptability of current technologies in the development stage of ultra-high water cut fields.To better analyze the problems,a large-scale heterogeneous physical model was used to explore the EOR methods for the high ultra-high water cut reservoirs after water flooding and polymer flooding.The distribution characteristics of oil saturation in different flooding stages,such as polymer flooding-well pattern adjustment and self-aggregating microsphere-surfactant flooding,were studied and the changes of injection pressure and recovery factor during the test were analyzed.Studies suggested that a combination of streamline direction alteration by well pattern adjustment and sweep coefficient expansion with polymer flooding can be used to increase the recovery ratio of ultra-high water cut reservoirs by 26.0% after water flooding.The new modified self-aggregating microspheres can be transported to the deep reservoir to block the dominant seepage channels and to divert the subsequent oil displacing agent into the remaining oil potential area,hence enhancing oil displacement efficiency of ultra-high water cut reservoirs after polymer flooding.The residual drag coefficient of microsphere-surfactant system is 1.5-1.6 times of that of the polymer,and the recovery ratio after polymer flooding can be further increased by 5% or more.The results showed that the method of well pattern adjustment combined with polymer flooding is suitable for ultra-high water cut reservoirs after water flooding,and the combination of microsphere-surfactant and deep adjustment/plugging oil displacement can be used in polymer flooded reservoirs with high sweep coefficient and high recovery degree.