## 3 Analysis of Experimental Results
### Water Invasion Simulation Experiment for Multi-Well Development of Fracture Model
As shown in Figure 17, in the early stage of water invasion, in addition to the increase in water saturation in the fracture area and the matrix area within the fracture range, the water saturation of the high-permeability zone was also slightly increased. The formation water quickly invaded simulation well 3 through the fracture, resulting in a significant reduction in the recovery rate of simulation well 3. At the same time, it quickly invaded simulation well 2 through the high-permeability zone, and the water saturation in the high-permeability zone increased rapidly (Figure 18). Due to the rapid water flow out of simulation well 3 and simulation well 2 along the fracture and high-permeability zone, there was a presence of a large amount of water-trapped gas around the fracture-high-permeability zone and at the edges of the gas reservoir at the end of the experiment, indicating that the development of the gas reservoir was not sufficient (Figure 19). Figure 5:2 Relationship between production water–gas ratio and recovery rate of fracture–high-permeability zone model. (**a**) Three times water body; (**b**) seven times water body; (**c**) seven times water body (shut-in after water breakthrough). Figure 5:3 Variation in water saturation in different areas of the fracture–high-permeability zone model at the end of the experiment (3 times water body). Figure 5:4 Variation in water saturation in different areas of the fracture–high-permeability zone model during early water invasion (3 times water body). Figure 5:5 Variation in water saturation in different areas of the fracture–high-permeability zone model at the water breakthrough time of simulation well 3 (3 times water body). Characteristics of Residual Gas Distribution in Multi-Well Development of Sandstone Gas Reservoir with Strong Water Drive  
In general, the water invasion effect increased with the increase in water body multiples, and the water body advanced rapidly along the fractures and high-permeability zone, resulting in premature waterflooding of gas wells, reduced cumulative gas production, a decreased ultimate recovery rate, and an increased actual residual gas volume of the model. The low-position gas wells immediately shut in after the water breakthrough will lead to rapid water invasion to the high-position gas wells, resulting in rapid waterflooding of the high-position gas wells after the water breakthrough, high gas saturation in some areas, and enrichment of the residual gas. As shown in Figures 20a and 21, the residual gas in the fracture model was mainly distributed around the fracture zone and at the edge of the gas reservoir. Under different water body multiples and production systems, the ultimate recovery rate ranged from 38.5% to 58.2%, with an average of 49.8%. The overall waterflood efficiency ranged from 32.5% to 42%, with an average of 37.2%. As shown in Figures 20b and 22, the residual gas in the fracture-high-permeability zone model was mainly distributed around the fracture-high-permeability zone and at the edge of the gas reservoir. Under different water body multiples and production systems, the ultimate recovery rate ranged from 28.3% to 41.8%, with an average of 34.5%. The waterflooding efficiency ranged from 25.3% to 34.5%, with an average of 29.9%. As shown in Figure 23, the residual gas volume depends on the drainage-production ratio and the water body scale. The residual gas can be significantly reduced when the drainage-production ratio (drainage speed-gas recovery speed) reaches a certain value. Figure 5:6 Water saturation distribution of the fracture model at the end of the experiment. (**a**) Three times water body; (**b**) seven times water body; (**c**) seven times water body (shut-in after water breakthrough). Figure 5:7 Recovery rate and waterflood efficiency under different water body multiples and different production systems. (**a**) Fracture model; (**b**) fracture–high-permeability zone model.