Optimization of Gas-water Slug Ratio in CO2 Flooding of Low Permeability Reservoirs

According to the reservoir conditions of a certain block in Jilin Oilfield,the displacement efficiency in different displacement modes was studied with numerical simulation.The result of numerical simulation shows that compared with continuous CO2 flooding and water flooding,gas-alternating-water flooding could significantly enhance oil recovery.In the alternating displacement process,under certain bottom hole pressure,the optimal gas-water slug ratio is variable,it was related with permeability,the gas injection rate and the bottom hole pressure and other factors.The best slug ratio is more sensitive to the permeability changes,followed by gas injection rate and the bottom hole pressure.As the permeability increases,the best slug ratio gradually decreases,while the recovery also gradually reduces.Within a certain range,the lower the permeability is,the better the gas-alternating-water flooding would be.It is proved theoretically that compared with the high-permeability reservoirs,gas-alternating-water flooding is more suitable for low permeability reservoirs.The result provides a theoretical basis for field implementation of CO2 flooding.