Experimental Study on the Effect of CO2 Displacement Mode on Enhanced Oil Recovery

There are three conventional CO2 flooding methods, namely continuous CO2 flooding, water flooding to CO2 flooding and water /CO2 alternating flooding. Different flooding methods will obtain different displacement effects. Therefore, in order to study the influence of CO2 displacement mode on the effect of enhanced oil recovery, this paper carried out three flooding experiments: continuous CO2 flooding, water flooding to CO2 flooding and water /CO2 alternating flooding. In addition, three groups of different water-bearing CO2 flooding experiments were conducted to explore the influence of different degrees of water shield barrier on CO2 oil flooding effect. The experimental results show that the final recovery rates of the three displacement modes of conventional CO2 flooding are 74.24%, 75.53% and 78.11%, respectively, and the oil recovery rate of the alternate injection mode of water /CO2 is the highest. In the process of CO2 flooding from water flooding to water saturation of 30%, 50% and 80%, the CO2 flooding recovery increased by 26.9%, 27.8% and 26.2%, respectively, and the best effect was achieved under the condition of water saturation of 50%. Through the analysis of the alternate water /CO2 injection mode, it is found that a certain degree of water shield barrier is beneficial to CO2 flooding, but too high or too low water shield barrier will have adverse effects on the enhanced oil recovery of CO2 flooding.