Mathematical Models and Calculation Methods for Distribution Parameters of Eccentric Coaxial Lines

To address the practical engineering needs of applying casing and tubing to construct underground wellbore coaxial lines for microwave oil recovery in oilfield development, this study establishes a mathematical model for the distributed electrical parameters of eccentric coaxial lines with minor inner conductor eccentricity using a field-circuit coupling method. The effects of inner conductor eccentricity on the distributed parameters and characteristic impedance are quantitatively analyzed. Validation against classical coaxial line theory and prior research demonstrate the model's high accuracy. The results show that microwave signal transmission reliability declines significantly when eccentricity exceeds three percent, adversely affecting pipeline health monitoring and defect detection. Based on these findings, an optimization proposal for the design of underground wellbore coaxial lines is presented, tailored to the conditions of heavy oil reservoirs in the Keshita Group of Liudong District.