High-Temperature and High-Pressure Two-Dimensional Miscible Water–Gas Injection and WAG Experimental Study

In this study, a high-pressure large-scale 2D physical model was independently developed to conduct indoor 2D simulation experiments of miscible gas–water injection and water-alternating-gas (WAG) under reservoir temperature and pressure conditions. The experimental results show that when the water–gas ratio is 1∶1, the recovery rate in the gas-drive area is 2.8% to 5.4% in absolute terms higher than that in the water-drive area in different permeability zone, indicating that miscible gas drive can effectively increase the recovery rate compared to conventional water drive. When the water–gas ratio changed from 1∶3 to 1∶1 after gas breakthrough, the gas–oil ratio curve is close to that of 1∶1 injection, and the final recovery rate increased by 0.42%, indicating that increasing the gas injection volume before gas breakthrough has a minor effect on the final development outcome. After changing from a water–gas ratio of 1∶3 to WAG 1∶1 injection, the overall recovery rate increased by more than 10%, with the recovery rates in the water-drive and gas-drive areas increasing by approximately 12% and 6.5%, respectively, and the improvement in the relatively low-permeability area is more significant. This suggests that during the gas–water alternation process, the bubbles formed due to the mixture of gas and water increase the seepage resistance through the Jamin effect, inhibiting the flow of injected fluid in the high-permeability zone, while diverting more injected fluid to enter the low-permeability zone, thereby increasing the sweep efficiency of the low-permeability zone and partially mitigating the impact of reservoir heterogeneity. The research results provide experimental support for the selection of development methods and optimization of water-gas injection for deep-water oil fields.