Most Middle East oil and gas field operating companies specify cathodic protection (CP) to onshore wells to mitigate corrosion to the external surface of the steel well casings. The CP current requirements have been established through studies using casing potential/corrosion protection profile logs, E-Log I testing, and mathematical analysis. Modeling has been developed to simulate the circuit characteristics to achieve the predetermined well casings CP current criteria.

This paper presents the applying of electrical circuit theorems to the analysis process to determine design acceptance criteria for design of an impressed current cathodic protection system for a single well casing.

The mathematical formulas obtained from this work, are used to calculate the maximum allowable anode bed resistances, which avoids the “trial-and-error” steps necessary when using simulation software/ modeling. In addition, the process provides useful design parameters of the circuit model, such as the voltage capacity of the DC power supply to achieve the required CP current to the well casing.

The process discussed in this paper incorporates Superposition, Substitution, Reciprocity, Thevenin, and Millman electrical circuit theorems with typical CP modeling programs. Circuit parameters, including resistance-to-remote earth of anode beds, cable resistance, resistance-to-remote earth of casing and flowline, and back EMF of the U/G structures associated with the well, are considered in the process.

This paper does not address circuit theory for designing cathodic protection systems for multiple well casings, which will need to be developed to complement this work.