The implementation of CO

2

flooding in heavy oil reservoirs with low-permeability is currently the main comprehensive utilization technology for enhanced oil recovery. However

due to the low viscosity and high mobility of CO

2

CO

2

flooding in heavy oil reservoirs is prone to premature gas channeling. For this reason

the feasibility of low permeability heavy oil reservoirs with CO

2

-viscosity reducer to reduce viscosity and improve mobility ratio has been explored

and the mechanism of the combined flooding of CO

2

and water-soluble viscosity reducer for low-permeability heavy oil reservoirs to EOR is obtained. The results show that the KD-45A water-soluble viscosity reducer can only emulsify the surface of crude oil to reduce the viscosity without external stirring. The viscosity reduction effect is poor

but the viscosity reducer slug can improve the mobility ratio caused by viscosity differences

which can effectively control the CO

2

rushing along the airflow channel. The O/W-shaped emulsion transition zone formed by the emulsification of the water-soluble viscosity reducer has a viscosity close to the water phase

which can prevent the fingering of the water-soluble viscosity reducer

so that the viscosity reducer slug has a more obvious control and displacement effect on CO

2

and the swept area of CO

2

is larger. The dissolution of CO

2

in the viscosity reducer will reduce the interfacial tension of the CO

2

-viscosity reducer system

which can give full play to the synergy between the two displacement effect. The formation of carbonized water after CO

2

dissolves in the viscosity reducer can greatly reduce the influence of gravity and viscosity differences on the swept area

forming a relatively stable and continuous displacement interface. The displacement mechanisms of the combined flooding system are synergistic and superimposed

which can significantly improve the recovery rate of heavy oil.