Enhancing Design and Monitoring of Cathodic Protection Systems for Deep Well Casings With Computational Modeling

Impressed current cathodic protection (CP) is one of the most effective means of corrosion control for well casings. In addition, computational modeling in this field has reached quite a mature stage, capable of offering cost-effective solutions during both the preliminary design stage and the subsequent monitoring stages in the productive lifespan.  During the design stage, computational modeling can be used to anticipate problems of interference and to identify configurations with optimal design according to the local environmental conditions.  Regarding performance monitoring, in principle CP systems for well casings are similar to pipelines. However, the fact that well casings are deployed in vertical direction makes the monitoring more difficult when compared to pipelines since it is not generally possible from a practical point of view to have access to the soil-to-structure potential at every point. Hence, two different approaches are commonly used: E-Log I tests and voltage gradient measurements along the structure. Then, proper interpretation from specialized personnel allows the level of performance of the complete corrosion control system to be determined. This approach requires experience and, on its own does not always allow provision of more detailed information of potential and normal current density profiles along the structure. The aim of this paper is to demonstrate a number of applications in which computational modeling can benefit the design stage of CP systems for well casings as well as to allow better exploitation of field measurements. The basic mathematical background for 3D modeling with boundary elements is outlined. The conceptual model includes several geological zones which influence the CP system. Then, a number of case studies are solved comparing different CP designs. Finally, a method for reconstructing potentials along the structure coming from a number of field measurements is illustrated and analyzed.