Theoretical Model of Distributed Parameters for Eccentric Coaxial Line and Its Application in Oil Wells

ABSTRACT Aiming at the current demand for using wellbore coaxial lines with tubing and casing in oil wells, implementing microwave chemical‐assisted crude oil upgrading underground, and promoting “carbon‐zero” mining projects in oil field development, we carried out theoretical analysis, simulations, and applied research on the distributed parameters of eccentric coaxial lines. Assuming that the rate of change of the electromagnetic field distribution along the circumference of the coaxial line is small when the eccentricity is small, we derived a formula for calculating the electromagnetic field intensity of the eccentric coaxial line. Using the “field‐circuit combination” method of electromagnetics, we further established theoretical models for the distributed parameters—including inductance, capacitance, resistance, and conductance—and proposed a new calculation approach. The validity and accuracy of the proposed models are verified through comparison with HFSS simulations and previously established empirical formulas. The new theoretical analysis and HFSS software simulation results demonstrate that conventional tubing and casing structures in oil wells can be utilized to construct coaxial lines for microwave energy transmission. However, the eccentricity of the inner conductor significantly influences the electromagnetic field distribution, characteristic impedance, power‐handling capacity, and energy loss. To ensure efficient microwave propagation, the eccentricity should ideally remain below 30% and must not exceed 40%. The theoretical model in this paper fills the gap in the distributed parameter theory for eccentric coaxial structures and contributes to the advancement of microwave transmission line theory. The proposed modeling approach also provides a practical foundation for the optimized design and application of wellbore coaxial systems in microwave‐assisted oil recovery.