## 5 Reservoir Dynamic Monitoring Model
### Comparison of Anisotropic Model and Isotropic Model  
In order to demonstrate the significant impact of resistivity anisotropy on reservoir dynamic monitoring, this study constructed an isotropic model alongside the anisotropic model for a comparison and analysis of the differences between the two in reservoir dynamic monitoring. By comparing the calculation results of the isotropic and anisotropic models, this study delves into the influence of resistivity anisotropy on the reliability of reservoir dynamic monitoring. To obtain the isotropic resistivity corresponding to the anisotropic resistivity, the corresponding expression for isotropic resistivity, based on Equation (3), is as follows:  
\[\sigma=\sqrt{\frac{{{\sigma_{xx}}^{2}+{\sigma_{yy}}^{2}+{\sigma_{zz}}^{2}}}{3}} \tag{14}\]  
By substituting the resistivity values from the anisotropic model, the resistivity of the first rock layer is 21.61 \(\Omega\cdot\)m with a thickness of 400 m, the resistivity of the second rock layer is set to 90.37 \(\Omega\cdot\)m with a thickness of 1400 m, and the resistivity of the third rock layer is 21.61 \(\Omega\cdot\)m. The resistivity of the unexploited reservoir is set to 887.41 \(\Omega\cdot\)m, while the resistivity of the exploited reservoir is set to 451.85 \(\Omega\cdot\)m. The transmitter is placed at the center of the lower reservoir boundary at coordinates (0, 0, \(-\)1200) m, with an emission frequency of 1 Hz. As shown in Figure 14a-f, when the measurement points extend along the profile from -4000 m to 4000 m, the amplitude gradually decays as the lateral distance \(\mid\)x\(\mid\) increases and reaches its minimum value at the center, exhibiting a typical bimodal distribution. Overall, the amplitude (\(\mid\)\(E_{x}\)\(\mid\)) of the isotropic model is higher than that of the anisotropic model at most measurement points. Additionally, as the reservoir recovery factor increases from 0% to 100%, the amplitude generally shows a progressive increase. A further comparison of the peak values of the curves for both models reveals that as the recovery factor increases, the peak value difference between the isotropic and anisotropic models gradually expands, indicating that the anisotropic effect on the amplitude response becomes more pronounced with an increasing recovery factor. As shown in Figure 15a-f, the phase variation trends for both the isotropic and anisotropic models generally remain consistent, although there are some local differences. Specifically, in areas far from the reservoir, the phase value of the anisotropic model is slightly higher than that of the isotropic model, while in regions closer to the reservoir, the phase difference between the two models is relatively small. Furthermore, as the recovery  
Figure 13: Schematic of the 3D reservoir model (red indicates unexploited reservoir layers, blue indicates exploited reservoir layers). (**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%. factor increases from 0% to 100%, the phase values of both models do not show significant changes, suggesting that the recovery factor has a weak effect on the phase. Combined with Figures 16a-f and 17a-f, it can be observed that there are significant relative errors in the amplitude and phase values calculated from both the anisotropic and isotropic models, with the average relative error in some local regions approaching 100%. Figure 14: Comparison of the amplitude (\(|E_{x}|\)) between the anisotropic model and isotropic model under 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 15: Comparison of the phase (\(\Phi_{x}\)) between the anisotropic and isotropic models at different recovery factors.