For the reservoirs after polymer flooding

the heterogeneity is stronger and the remaining oil distribution is more dispersed

conventional chemical flooding in consequence is difficult to further improve oil recovery effectively. Therefore

a heterogeneous combination flooding system consisting of polymer

preformed particle gel（PPG） and highly effective surfactant has been designed according to the features of medium-high permeability sandstone reservoir in Ⅱx layers of Shuanghe Oil Filed after polymer flooding. Thereafter

the selection of flooding agent

evaluation of thermal stability and Optimization of injection mode have been studied. The experimental results showed that the obtained P/PPG/S system has excellent high viscoelasticity

ultra-low interfacial tension

and thermal stability

which can effectively improve reservoir heterogeneity

expand sweep volume and enhance oil displacement efficiency. Core displacement experiments showed that the oil recovery could further enhance by 27.8 % after the combination flooding of P/PPG system and P/PPG/S system under simulated reservoir conditions. Thus it provides a technical method for effectively enhancing oil recovery after polymer flooding in Shuanghe oilfield.