## 5 Results and ANN Model Validation
### Effects of a Relief Well
#### 5.1.3 Comparison without and with a Relief Well  
Based on the simulation studies focusing on the existence of the relief well, it was found that the pressure build-up can be effectively managed by a relief well and that a safe injection process can be achieved, although there are potentially reactivatable faults. With  
Figure 12: Optimized location of the relief well for 10 years of injection.  
Figure 13: (**a**) Estimated pore pressures at fault EF1 and EF2 and (**b**) pressure distribution at the end of injection of 7.84 years in aquifers A and B at top layer with a relief well.  
the same operating BHP of 14.0 MPa, the injection rates, total storage capacity, and pore pressure distribution were taken into account to analyze the efficiency of the relief well.  
The injection rates of both cases are illustrated in Figure 14. The injection rates without and with the relief well are, respectively, shown with solid and dashed curves. As soon as the injection process initiates, the injection rates in both cases increased sharply. When there is a relief well installed and operated, the maximum rate of 80 tons/day was achieved in 0.92 years, while it took 1.1 years without a relief well to reach the maximum rate. In addition, this shows that the rate with a relief well after the peak maintains longer than that of the 'without a relief well' case. This is because the relief well provides more injection capability. Therefore, the average injection rate with the relief well was 75 tons/day, which is 3 tons/day higher than that of the no-relief well case. Thus, the total CO\({}_{2}\) storage capacity with a relief well (215 kton) was 19.44% higher compared to the \"without a relief well\" case. Consequently, operating a relief well can provide more injection capability, which may lead to the larger total mass of injected CO\({}_{2}\).  
Effects of the relief well can be found from the pore pressure distribution after the injection process in Figure 15. Note that the distribution of top of aquifer A is only shown for comparison. Before the injection, the pore pressure, determined by the hydrostatic pressure gradient, is in the range between 6.5 and 8.5 MPa (Figure 15a). When the injection process without a relief well is finished at 6.85 years, the pore pressure of aquifer A was increased, with the maximum concentrated location found at the injection well (Figure 15b). Moreover, a high pore pressure concentration was observed at fault EF1, which was expected to be reactivated and caused the termination of the injection. However, as shown in Figure 15c, it was found that the pore pressure build-up in aquifer A was effectively managed with the relief well as the injection period was extended to 7.84 years. Therefore, it was concluded that installing of a relief well to relieve the pore pressure may be an effective solution to manage pore pressure for a safe injection design and to maximize the cumulative mass of injected CO\({}_{2}\).  
Figure 14: CO\({}_{2}\) injection rates for cases with (solid) and without a relief well (dashed). The maximum rates of 80 tons/day are achieved at 0.92 years when the relief well is operated. The injection rate with a relief well is maintained for a longer period (7.84 years) than without a relief well.