Monitoring of Downhole Corrosion: An Overview

Abstract Wet sour crude oil wells usually require minor attention to minimize or prevent corrosion damage of the production tubulars and well casings. These wells contain, in addition to crude oil, water, salt, and variable quantities of hydrogen sulfide (H2S) and carbon dioxide (CO2). In this paper, an overview of downhole corrosion is presented. This includes corrosion mechanisms, corrosion monitoring techniques, corrosion inhibition, and field applications along with examples. The main mechanisms contributing to downhole corrosion are classified into electrochemical, chemical and mechanical. Chemical corrosion attack is one of the major players in the case of maturing wells. Relevant corrosion monitoring techniques are then discussed. These techniques provide either direct or indirect measurements of corrosion rates (CRs). In case of existing wells, a basic downhole corrosion monitoring program should include the following techniques as a minimum: (a) wet chemical analysis, e.g., iron counts, (b) metal loss corrosion coupons, and (c) electronic corrosion probes, e.g., electrical resistance (ER) probes. The three common corrosion control strategies are briefly discussed, namely: materials selection, coatings, and chemical inhibition. Finally, three examples of field applications are presented. In these examples, different corrosion monitoring techniques were employed depending on the type of corrosion mechanism and the selected corrosion control strategy.