## 4 Simulation of the Actual Well Casing  
Well X (a sidetrack horizontal well) is a pre-exploration well, with the shale oil and gas interval as the main target formation. A 3D stratigraphic model is constructed based on the lithology division, seismic horizon division, and logging interpretation results of Well X, and the resistivity of grid cells is assigned according to electric logging data, which is stored as a 3D geoelectric model (Figure 12a). The construction unit has designed a total of 30 sections of perforation operations for Well X, with the designed half-fracture length of approximately 210 m. In this paper, sections 27 and 28 are selected for fracturing simulation (Figure 12b). The depths of the target layers are \(-\)1946.49\(\ldots\)\(-\)1947.24 m (section 27) and \(-\)1945.95\(\ldots\)\(-\)1946.1 m (section 28). The model also incorporated topographic effects. The length, width, and height of the simulated fractures are determined according to the fracturing design, the depth and coordinate positions of the target perforation sections are located, and then coordinate rotation is performed to convert them into a coordinate system with the wellbore extension direction as the X-axis, which is loaded into the grid of the target perforation sections (sections 27 and 28). The fractured bodies are symmetrically distributed with the wellbore as the center. The metal casing of the entire well section of Well X is divided along the wellbore trajectory data to generate multi-segment line sources, simulating the actual transmitter source scenario. The case study conducted systematic optimization of 1.25 Hz and 2.5 Hz excitation frequencies. Figure 13 shows the simulation results of the 27 th section fracturing, and the observation data at a frequency of 2.5 Hz was selected for analysis. Figure 13a-c show _Ex_ component surface electromagnetic response results for hydraulic fracturing in the 27 th section under 1.25 Hz excitation. Figure 13d-f show _Ex_ component surface electromagnetic response results for hydraulic fracturing in the 27 th section under 2.5 Hz excitation. By  
Figure 12: Construction of 3D fracturing model for Well X: (**a**) a 3D geoelectric model; (**b**) the 27 th or 28 th section fracturing model. comparing Figure 13d before fracturing with Figure 13e after fracturing, it can be seen that the amplitude of the _Ex_ component changes slightly near the projection point of the 27 th section, while the amplitude difference of the _Ex_ component before and after fracturing in Figure 13f has a good response to the anomalous body area. Figure 14 shows the simulation results for the 28 th section fracturing, and the observation data at the frequency of 2.5 Hz was selected for analysis. Figure 14a-c show _Ex_ component surface electromagnetic response results for hydraulic fracturing in the 28 th section under 1.25 Hz excitation. Figure 14d-f show _Ex_ component surface electromagnetic response results for hydraulic fracturing in the 28 th section under 2.5 Hz excitation. By comparing Figure 14d before fracturing with Figure 14e after fracturing, it can be seen that the simulation results of single-section monitoring change little near the projection point of the 28 th section. The amplitude difference of the _Ex_ component before and after fracturing in Figure 14f (indicated by the black dotted area) has a good response to the anomalous body area, but the surface response value is small, and the observation of the 28 th section fracturing is greatly affected by the terrain. This case indicates that in practical applications, it is necessary to comprehensively consider the influence of topographic and other interference factors on the monitoring results. In addition, the case study also shows that the electromagnetic responses at different frequencies vary, and the rational optimization of frequency parameters is crucial for improving the accuracy of fracturing monitoring.