Structural design and mechanical optimization of a downhole bidirectional flow electromagnetic measurement sub

Complex oil and gas reservoir exploitation is subject to accident risks, such as overflow and leakage. The downhole bidirectional flow electromagnetic measurement short section (hereinafter referred to as the measurement sub) enables real-time monitoring of flow parameter changes near the drill bit, thereby reducing drilling risks. This study integrates mechanical modeling with electrode structure optimization. First, based on material mechanics theory, the operating principle and structure are analyzed to establish a stress model for the measurement sub. Second, mechanical simulation software is used to analyze the stress distribution of the main structure and the stress characteristics of critical sections, while optimizing the structural dimensions of the signal electrodes. Results indicate that the main body exhibits satisfactory mechanical performance under two operating conditions, with safety factors of 1.78 and 1.3, respectively. Under the ultimate condition, the maximum stresses in most critical sections peaked at around 200 MPa, with average stresses on the inner and outer surfaces of 58.326 MPa and 56.621 MPa, respectively. Simulation comparisons of different electrode structures revealed that long conical electrodes exhibited the most pronounced trend of stress reduction as their neck diameter increased. When the neck diameter was optimized to 10 mm, the maximum stress decreased to 119.86 MPa, achieving a safety factor of 7.22. This fully satisfies the strength and reliability requirements for complex downhole conditions. Through modeling, simulation, and optimization, this study provides systematic mechanical guidance and feasible optimization pathways for the structural design of downhole bidirectional flow electromagnetic measurement subs, demonstrating clear theoretical significance and engineering application value.