By using the core analysis data before polymer injection and after polymer breakthough from two wells in the polymer-injection area of Block 1

the central Gudao

the change patterns of reservoir parameters after a long-term polymer drive are compared and discussed.It is suggested that the long-term polymer drive has resulted in enlarging some small pore throats

improving the communication among pores and reducing pore tortuosity in the reservoirs.For the microscopic parameters of the reservoirs

the maximum

average

and normal pore-throat radiuses increased

the expulsion pressure

the mercury 50% saturation pressure and the variation coefficient decreased

and the mean coefficient rised.For the macroscopic reservoir parameters

the permeability was enhanced

and the porosity variation was within the range of allowable error.