## 7 Discussion  
Building upon the introduction of the single-electrode current excitation method, this paper provides a detailed explanation of the principles and calculation methods for a new dual-electrode current excitation MWD technique. The correctness and effectiveness of this method is verified through an analysis of key factors using theoretical numerical simulations. The main conclusions are as follows:  
1. When the drilling well axis is parallel to the target well axis, the current on the target well casing presents a symmetrical distribution with the ranging point as the center. The current direction is consistent, and the current amplitude reaches its maximum at the ranging point. Along the direction of the casing axis head of the hole or hole bottom, as the distance from the ranging point increases, the casing current amplitude decreases at a rate characteristic of cosine.
2. The attenuation characteristics of the induced magnetic field intensity stimulated by the casing current in the formation are similar to those of the casing current. Under the configuration parameters such as the excitation current amplitude of 10 A and the distance of 25 m, the induced magnetic field intensity at the installation position of the magnetic measurement sub is higher than 1 nT. This indicates that, in this environment, the theoretical value for the maximum effective ranging distance can reach up to 25 m.
3. The configuration parameters of the ranging tools, such as the upper/lower electrode pole distance and the combination of the upper/lower electrode lengths, will have an impact on the current intensity of the target well casing. As the electrode distance increases, the current amplitude of the casing also increases in a near linear proportion. However, when the electrode distance exceeds a certain range, there is an increase in the maximum current amplitude of the casing, and, near the ranging point, the current amplitude tends to become consistent. Additionally, extending the electrode length will increase the contact area between the electrode and the formation, significantly reducing the formation equivalent resistance and increasing the casing current amplitude. Therefore, it is important to select an optimal combination scheme based on the actual ranging environment to facilitate an efficient MWD operation.
4. When the axes of two wells are at an angle to each other, an increase in this angle within the same plane will result in a decrease in the casing current amplitude and the formation of a reverse current flow on the casing. However, when the axes of two wells are at an angle in parallel planes, it only affects the strength of the casing current and not its direction. It is important to note that when the axes of two wells are vertical, the casing current flows symmetrically in reverse with the ranging point as the center, causing the ranging tool to fail to measure the effective induction magnetic field.
5. The high or low formation resistivity will decrease the current amplitude collected on the casing. Additionally, an excessively low mud resistivity will result in more of the excitation current returning through the mud channel, which is not conducive to injecting excitation current into the formation. Therefore, enhancing the mud resistivity can strengthen the casing current and improve the adaptability of the ranging system to changes in formation resistivity.
6. As the research is still in the simulation stage, many practical influencing factors have not been fully considered, and further field experimental research is needed in the future. For instance, there is no consideration of varying geological formations, such as different rock types, varying formation porosity levels, or the presence of faults and fractures. To establish broader applicability, the research should have included validation across multiple scenarios or conditions, ideally supported by real-world field tests.