## 3 Results and Discussion  
### Base Case Analysis  
The cumulative oil production, CO\({}_{2}\) storage amount, and CO\({}_{2}\) storage efficiency of the base model as a function of time are shown in Figures 5 and 6. The values of cumulative oil production, CO\({}_{2}\) storage amount, and CO\({}_{2}\) storage efficiency are derived as the three labels for machine learning. The CO\({}_{2}\) storage amount is obtained by subtracting the cumulative CO\({}_{2}\) production from the cumulative CO\({}_{2}\) injection. The CO\({}_{2}\) storage efficiency is expressed as the ratio of the CO\({}_{2}\) storage amount to the CO\({}_{2}\) injection. Figure 4: The training process of the random forest algorithm. Figure 5: Cumulative oil production in the production process. Figure 6: CO\({}_{2}\) storage in the production process: (**a**) injection, production and storage amount of CO\({}_{2}\), and (**b**) CO\({}_{2}\) storage efficiency. As shown in Figure 5, at first, the oil production rate goes up quickly because there is enough energy in the reservoir. As the reservoir energy gradually depletes, the oil production curve begins to level off gradually in the fifth year. Then, the reservoir energy is replenished by the nineth year after the CO2-WAG started, and the oil production rate begins to increase rapidly. The oil production rate begins to decrease slowly from the twentieth year to the end of production. At the beginning of the CO2 injection, the CO2 storage amount is almost equal to the CO2 injection amount from the nineth year to the fifteenth year with little CO2 produced (Figure 6a). CO2 production begins in the fifteenth year and has a relatively stable rate. From the sixteenth year, the growth rate of CO2 storage starts to be lower than that of CO2 injection. With the increase in CO2 production, the CO2 storage amount nearly stopped increasing by the thirty-sixth year. Consequently, the CO2 storage efficiency is almost equal to 1 at the beginning and then gradually decreases, as shown in Figure 6b. As shown in Figure 7, the overall effects of oil production on both CO2 flooding and CO2-WAG are higher than those of water flooding. CO2 flooding has higher oil production in the early stages of development before the thirty-sixth year because CO2 is more mobile than water. CO2 flooding produces oil at a higher rate than both water flooding and CO2-WAG at this stage. Due to the heterogeneity of the reservoir, the CO2 injected into the formation tends to form a dominant channel. So, the CO2 flooding method starts to produce more oil in a slow way around the twenty-second year of its late stage of development. The CO2-WAG method effectively combines the advantages of water flooding and CO2 flooding and maintains a high oil production rate, especially after the thirty-sixth year, although the oil production rate is relatively lower than that of CO2 flooding before the thirty-sixth year. The overall oil production of CO2-WAG is better than that of water flooding and CO2 flooding. For further analysis of the difference between the CO2-WAG method and the CO2 flooding method, this work compares the gas-oil ratio of the produced flow. As shown in Figure 8, the gas production rate starts to increase from the twelfth year (4 years after CO2 injection) in the CO2 flooding method and rises sharply from the nineteenth year onwards. This can be explained by the fact that the injected CO2 forms a dominant channel, and thus the injected CO2 returns to the surface directly from the dominant channel as an output gas. Figure 7: Cumulative oil production of CO2-WAG, CO2 flooding and water flooding. In the CO\({}_{2}\)-WAG method, the gas production rate is basically unchanged in the early stage of production and increases at a low rate in the late stage of production. Thus, the gas production volume is much smaller than that of CO\({}_{2}\) flooding. It can be speculated that the injected water in the CO\({}_{2}\)-WAG method effectively hinders the breakthrough of CO\({}_{2}\) and the formation of a CO\({}_{2}\)-dominant channel.