Abstract
Impressed current cathodic protection (ICCP) systems can be used very effectively to achieve appropriate mitigation of well casing corrosion, but it may be difficult and expensive to define the most convenient anode distribution in order to adequately protect the desired casings and not interfere with nearby structures. Once the system is installed, the cost of redesign may be high if experimental measurements indicate that the required protection is not achieved or that destructive interference is taking place. It is therefore both desirable and cost-effective to establish performance of the ICCP system before it is installed. Such assessment can be achieved through the use of mathematical modelling performed using numerical techniques. Of the available methodologies it is the boundary element method that is applied in this work.
To perform such simulation a model of the well casings is constructed (reflecting the directionally drilled profile) and the multiple anode ground-beds, including the return-path resistances along the cables and well casings. In order to effectively capture the electrical behaviour of the currents, the resistivity of the ground through which current passes must be identified. Running alternative scenarios of the models to readily quantify the effects of alternative assumptions, provides valuable understanding to the CP system designer of probable behaviour, and contributes to design robustness.
At a practical level, the designer can simply carry out tests of alternative anode layouts (depths, location etc.) as an input to selection of an optimised, final, configuration. The objective of this paper is to show how such techniques have been applied to an actual ICCP system protecting well casings in the Amazon rainforest.
Introduction
Process Description
We were asked to develop the cathodic protection design and installation of a pilot system to protect a pad of four directionally-drilled production wells in the Amazon rainforest. This requirement turned into a study that aimed at mitigating the corrosion on the external surface of the well casings in contact with the soil.
