Metallurgy for downhole equipment

The pressures, temperatures, and potentially corrosive conditions that may be found in a wellbore create the need for metals and materials that can resist such conditions.

Corrosive conditions

Metallurgical requirements are dictated both by the downhole well environment and the design and performance requirements of the packer. Consideration must be given to both when selecting and specifying materials for corrosive environments. Many types of materials that are applicable for tubing and casing in corrosive environments are not always suitable (or practical) for packer manufacture. The NACE International (formerly National Association of Corrosion Engineers) Standard MR-01-75 establishes guidelines and acceptance criteria for material selection for sour service in H₂S environments.

Common materials used for downhole equipment

Some commonly used materials for manufacture of downhole equipment are as follows:

• Low-alloy steels with minimum yield strengths of 110 ksi are used for standard service in noncorrosive environments. These materials are similar in property to P110 tubing and do not meet NACE MR-01-75 requirements for sour service.
• Low-alloy steels with a maximum hardness of Rockwell 22C, which meet NACE MR-01-75 requirements, are intended for use in both standard service and service in sour H₂S environments. Materials that fall into this range would be similar in properties to J-55 to L-80 grades of tubing.
• Martensitic steels such as 9% chromium, 1% molybdenum, and 13% chromium alloy steels are used in some wet CO₂ environments. Certain grades of these steels meet NACE MR-01-75 requirements and can be used in limited H₂S applications.
• 22% chromium and 25% chromium duplex stainless steel are commonly used in some wet CO₂ and mild H₂S environments.
• Austenitic stainless steels, cold worked 3% Mo high-nickel alloy steels, and precipitation-hardening nickel-based alloys are suitable for some environments containing high levels of H₂S, CO₂, and chlorides at moderately high temperatures.

The successful application of any of these materials depends strongly on the specific downhole well environment. Many factors such as temperature, pH, chlorides, water, H₂S, and CO₂ concentrations can have adverse effects on the material performance and can lead to failures associated with:

• Pitting.
• Corrosion.
• Chloride stress cracking.
• Hydrogen embrittlement.

Materials used in packers

Ideally, the packer should be built out of materials that will last the life of the well. Also, in the case of retrievable packers that may be reconditioned and used elsewhere, the advantage of being able to reuse the packer may be lost if the well environment corrodes or damages the tool beyond repair. In potentially corrosive environments, material failure can lead to a packer leak or difficulty in removing a retrievable packer from the wellbore. In these cases, corrosion-resistant alloy materials must be properly selected that are best suited to the downhole well environment.

Because of the vast number and variations of packer designs and tensile requirements of their components, the consumer cannot know which materials are appropriate for each particular design. Ultimately, the user must rely on the packer manufacturer to help make the determination as to which materials will meet the downhole requirements without sacrificing packer performance and reliability.

Noteworthy papers in OnePetro

Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read

External links

NACE International

General references

Allen, T. and Roberts, A.P. 1993. Production Operations, fourth edition, I and II.

Factors and Conditions Which Cause Seal Assemblies Used in Downhole Enviornments to Get Stuck. Baker Oil Tools—Engineering Tech Data Paper No. CS007.

Patton, L.D. and Abbott, W.A. 1985. Well Completions and Workovers: The Systems Approach, second edition, 57–67. Dallas: Energy Publications.

See also

PEH:Completion_Systems