How can you prevent corrosion in wellbore casings?

1 Causes of corrosion

Corrosion, the chemical or electrochemical reaction of a metal with its environment, can cause the deterioration of its properties and structure. Corrosion in wellbore casings can be caused by several factors, such as the composition and temperature of formation fluids, which may contain corrosive agents, mechanical stress and fatigue due to pressure changes, vibrations, and bending, bacteria producing corrosive byproducts, and the interaction of different metals in the casing or completion equipment creating galvanic corrosion. All these factors can lead to corrosion in wellbore casings.

2 Types of corrosion

Corrosion in wellbore casings can take on different forms, depending on the mechanism and location of the reaction. Some of the most common types include uniform corrosion, pitting corrosion, crevice corrosion, stress corrosion cracking, and microbiologically influenced corrosion. Uniform corrosion is caused by an even attack of the metal surface by a corrosive environment, resulting in a uniform loss of thickness and weight. Pitting corrosion is caused by a local attack of the metal surface, resulting in small holes or pits that can penetrate deep into the metal. Crevice corrosion occurs when a narrow gap or crevice shields the metal surface from the corrosive environment, creating a localized acidification. Stress corrosion cracking is caused by exposure to a tensile stress and a corrosive environment, resulting in cracks that can propagate and coalesce. Microbiologically influenced corrosion is caused by bacteria colonizing the metal surface and producing corrosive substances or altering the local chemistry and pH.

3 Prevention methods

Preventing corrosion in wellbore casings requires a comprehensive approach that includes selecting the right casing material, designing the casing and completion, monitoring corrosion rate and condition, and applying corrosion inhibitors or coatings. Material selection should involve choosing a casing material with adequate resistance to the expected corrosive environment, such as carbon steel, low-alloy steel, stainless steel, or corrosion-resistant alloys. Casing design should optimize size, weight, grade, and connection type to minimize mechanical stress and crevice formation. Completion design should select equipment and components compatible with the casing material and corrosive environment. Corrosion monitoring should measure and evaluate corrosion rate and condition using various techniques such as coupons, probes, logs, inspections, and tests. Corrosion inhibition involves injecting or circulating chemical inhibitors that form a protective film on the metal surface or scavenge corrosive agents. Lastly, corrosion coating involves applying physical or chemical coatings that isolate metal surface from corrosive environment like paints, epoxy, or plastic.

4 Prevention benefits

Preventing corrosion in wellbore casings can have significant benefits for the oil and gas industry, such as improving the well integrity and reliability to reduce the risk of leaks, failures, and blowouts, extending the well life and productivity to increase the recovery and revenue of hydrocarbons, and reducing the maintenance and repair costs to lower operational expenses and downtime. These improvements enhance safety and environmental performance, optimize the use of resources and assets, improve profitability, and increase efficiency.

5 Prevention challenges

The oil and gas industry can face some challenges when it comes to preventing corrosion in wellbore casings, such as the complexity and variability of the corrosive environment. This can necessitate constant monitoring and adjustment of the prevention methods and materials, while also having to consider the performance and cost of such materials. Moreover, the availability and accessibility of these materials can depend on the supply chain, logistics, and regulations of the industry and region.

6 Here’s what else to consider

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