## 5 Reservoir Dynamic Monitoring Model
### The Location of the Transmitter  
To further investigate the influence of the source position on the effectiveness of reservoir dynamic monitoring, the electromagnetic source is systematically moved along the  
Figure 16: Relative error of amplitude (\(|E_{x}|\)) between the anisotropic and isotropic models at different recovery factors. (**a**) The recovery factor is 0%; (**b**) the recovery factor is 20% extraction; (**c**) the recovery factor is 40%; (**d**) the recovery factor is 60%; (**e**) the recovery factor is 80%; (**f**) the recovery factor is 100%.  
Figure 17: Relative error of phase (\(\Phi_{x}\)) between the anisotropic and isotropic models at different recovery factors. (**a**) The recovery factor is 0%; (**b**) the recovery factor is 20% extraction; (**c**) the recovery factor is 40%; (**d**) the recovery factor is 60%; (**e**) the recovery factor is 80%; (**f**) the recovery factor is 100%.  
underground \(z\)-axis within the depth ranges of 500-800 m and 1200-1500 m. It is assumed that the source emits an electromagnetic signal at intervals of 100 m, with a transmission frequency set at 1 Hz. Based on this setup, the borehole-to-surface electromagnetic responses of the reservoir under varying extraction levels are computed, with the results presented in Figure 18. Additionally, the maximum amplitude values of the electromagnetic responses at different source depths are sampled, and their variations with extraction levels are statistically analyzed, as shown in Figure 19.  
As shown in Figures 18a-d and 19a-d, the maximum amplitude of the electromagnetic response exhibits a positive correlation as the source moves closer to the reservoir. However, when the source is positioned at depths of 500 m, 600 m, or 700 m, the electromagnetic signals received at the surface are minimally influenced by the reservoir, making effective  
Figure 19: Corresponding curves of maximum amplitude \(|F_{x}|\) f electromagnetic component and extraction rate at different transmission depths. (**a**) Transmitter at 500 m depth, (**b**) transmitter at 600 m depth, (**c**) transmitter at 700 m depth, (**d**) transmitter at 800 m depth, (**e**) transmitter at 1200 m depth, (**f**) transmitter at 1300 m depth, (**g**) transmitter at 1400 m depth, (**h**) transmitter at 1500 m depth.  
Figure 18: Response curves of electromagnetic component \(|E_{x}|\) at different transmission depths. (**a**) Transmitter at 500 m depth, (**b**) transmitter at 600 m depth, (**c**) transmitter at 700 m depth, (**d**) transmitter at 800 m depth, (**e**) transmitter at 1200 m depth, (**f**) transmitter at 1300 m depth, (**g**) transmitter at 1400 m depth, (**h**) transmitter at 1500 m depth.  
dynamic monitoring infeasible. When the source is placed at the upper boundary of the reservoir, an analysis of the electromagnetic response under different extraction rates reveals that for extraction rates below 20%, the borehole-to-surface electromagnetic method fails to distinguish variations in reservoir depletion. However, once the extraction rate exceeds 20%, the electromagnetic response begins to show a positive correlation with the extraction rate. Furthermore, when the source is positioned below the reservoir, a linear fitting analysis of the maximum amplitude of different electromagnetic components at varying depths (see Figure 20 and Table 1) indicates that as the transmitter moves closer to the lower boundary of the reservoir, the slope of the fitting curve increases, suggesting a more pronounced sensitivity of the electromagnetic response to reservoir dynamic monitoring.