Abstract: In order to clarify the response characteristics of gas-water alternate flooding with CO₂ after water flooding in ultra-low permeability reservoirs, the research on dynamic characteristics of gas-water alternate flooding with CO₂ was carried out. In the research, through the combination of dynamic and static methods, the dynamic data obtained by physical simulation experiments and the static data of CO₂ solubility in oil-water solution measured in high-temperature and high-pressure phase system were used. The results show that appropriately increasing the gas-oil ratio during the CO₂ flooding process can produce oil and gas to dissolve CO₂, forming a single-phase oil zone under reservoir conditions, and the contribution rate of this stage to the oil displacement effect is 71.98%. It is suggested to appropriately increase the size of the CO₂ slug in the first cycle when designing the reservoir plan, and to select the critical point of gas channeling to inject water, which can effectively increase the utilization rate of CO₂ and improve the oil displacement effect. The research results have a certain guiding significance for the optimization of injection parameters for gas-water alternate flooding.

Key words: CO₂ flooding, ultra-low permeability, gas-water alternation, occurrence state of displacement characteristic, facies zone distribution