Xingbei block in North Jiangsu Oilfield is a complex fault block with heavy oil and bottom water reservoir. High viscosity and poor flowability of crude oil lead to low oil recovery. As it is difficult to realize the economical and effective development of this heavy oil reservoir by conventional technique

a method of combined stimulation of CO

2

and viscosity reducer is proposed for EOR in heavy oil reservoir with bottom water. Viscosity reducer plays an important role in this method. A new polymer surface active agent for viscosity reduction is synthesized by introducing the benzene ring structure into viscosity reducer. The performance evaluation of this new visco

sity reducers is carried out from the aspects of concentration

temperature

salinity and pH value. It shows that the viscosity reducer has good temperature resistance and salt tolerance. When the viscosity reducing agent concentration is 0.5 %

the viscosity reducing rate of heavy oil reaches more than 90 %. It also has a stable viscosity reducing ability mixing with CO

2

. Good effects of increasing oil production and reducing water cut have been achieved in the in-site implementation. There will be a promising prospect in the economic and effective development of North Jiangsu Oilfield and other similar domestic heavy oilfields with complicated fault block.