Abstract:

The implementation of CO₂ 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 CO₂, CO₂ flooding in heavy oil reservoirs is prone to premature gas channeling. For this reason, the feasibility of low permeability heavy oil reservoirs with CO₂-viscosity reducer to reduce viscosity and improve mobility ratio has been explored, and the mechanism of the combined flooding of CO₂ 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 CO₂ 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 CO₂, and the swept area of CO₂ is larger. The dissolution of CO₂ in the viscosity reducer will reduce the interfacial tension of the CO₂-viscosity reducer system, which can give full play to the synergy between the two displacement effect. The formation of carbonized water after CO₂ 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.

Key words: low permeability reservoir, heavy oil, EOR, water-soluble viscosity reducer, CO₂ compound flooding