Management of Galvanic Corrosion in Oil Fields

Middle East Oil fields mainly produce oil from aggressive sour corrosion reservoirs with high H2S and CO2 levels. Therefore, extensive efforts were made by one operator to understand the corrosion failure of these oil wells, by establishing a downhole corrosion management programme. This programme’s initial strategy was based on a sophisticated corrosion risk matrix that ranks the production wells according to different parameters, such as reservoir souring, severity of the corrosion damage, well production, failure frequency, and well operational and inspection data. A corrosion mitigation programme was then designed, and implemented, for these wells, based on a thorough analysis of the corrosion for the well, and which has successfully controlled the corrosion issues. Due to the aggressiveness of the corrosion environment in the field reservoirs, different corrosion mechanisms, such as H2S sour corrosion, CO2 sweet corrosion, under deposit corrosion, microbially induced corrosion, and galvanic corrosion, occurred in the wells.

The electrical submersible pump (ESP) is widely used, and is currently the fastest growing form of artificial-lift pumping technology. About 15 to 20 percent of almost one million wells worldwide (including in the N Sea) produce oil with the help of ESPs [1]. It is the main artificial lift production method in the Middle East Fields.
Although ESPs have different components such as a multistaged centrifugal pump, three-phase induction motor, seal-chamber section, power cable and surface controls, the most critical aspect of the ESP is the power cable. This cable transmits the required surface power to the ESP motors. Typically, it is banded or clamped to the production tubing from below the wellhead to the ESP unit because it is not designed to support its own weight. It is a specially constructed three-phase power cable designed specifically for downhole well environments.

Mitigation of the galvanic corrosion

There are several ways to minimise or prevent galvanic corrosion, including, design changes, electrical isolation or insulation, exclusion of the environment, anode-to-cathode area ratio control, corrosion inhibitors, cathodic protection, and counter-current devices. Each of these corrosion control methods seeks to reduce, or eliminate, one of the requirements for galvanic corrosion to occur.

The proposed failure mitigation strategy was based on avoiding the usage of a galvanized steel armoured shield for the ESP cable, due to its weak corrosion resistance in high chloride and high H2S environments, in addition to its electronegativity in the galvanic corrosion cell formed as a result of its coupling with the production tubing. Therefore, upgrading the ESP cable to a Monel armoured shield was considered the optimum method of protecting the ESP cable in the corrosive environment. Monel has a high corrosion resistance to chloride and H2S, and it is less electronegative to the production tubing. Although the production tubing will act as an anode in this galvanic corrosion cell, the corrosion action will be negligible due to the relatively large anodic area of the production tubing, and the relatively small cathodic area of the Monel armoured shield.

Hassan, S. (2023). Management of Galvanic Corrosion in Oil Field Wells. A journal of the Institute of Corrosion Management. Issue 172 March/April 2023. Retrieved from https://www.icorr.org