Mitigating Sucker Rod Corrosion

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Mitigating Sucker Rod Corrosion
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• Corrosion is a problem that is becoming
  increasingly more common in oil and gas as
  existing wells age and as producers push into
  deeper and hotter wells with more aggressive
  fluids. In the artificial lift industry,
  corrosion has been around for many years and with
  significant time and costs associated with
  corrosion mitigation and, where that is not
  effective, corrosion related failures. Each year,
  billions of dollars are spent controlling and
  working over corrosion-plagued wells. Therefore,
  producers must be savvy and build a corrosion
  control plan into their life-of-the-well strategy
  to mitigate problems and maintain production.

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Corrosion Overview

• Corrosion is defined as the deterioration of
  a substance (usually metal) or its properties
  because of a reaction to its environment. This
  means that a typical piece of downhole equipment
  like a carbon steel sucker rod is a magnet for
  corrosion in the presence of water and chemical
  compounds like H2S, CO2, and O2.1

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Examples of Corrosion

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Failures

• In North America, unconventional, directional
  wells are particularly susceptible to costly
  corrosion-related failures due to deep depths and
  high temperatures, which accelerate corrosion.
  When using conventional and continuous sucker rod
  downhole, common corrosion failures include
• Corrosion fatigue to failure whereby a crack
  initiates on a corrosion pit stress riser and due
  to the cyclic loading nature of rod-driven
  artificial lift equipment failure results.

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• Localized corrosion attacks at weld joints.
• Corrosion causing a reduction in the rods
  cross-section to the point where the rod can no
  longer carry the load and fails.

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Corrosion Planning and Mitigation

• While it is impossible to completely prevent
  corrosion and failures downhole, it is possible
  to significantly control and extend the life of
  your equipment. The following are common downhole
  corrosion solutions, each with their own set of
  benefits and challenges

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• Chemical Inhibition
• A chemical inhibitor works to build a
  protective layer on the downhole equipment to
  prevent well fluids from attacking the
  susceptible base layer. Chemical inhibition can
  be effective in corrosive wells, but is often not
  an option in many applications for a few
  reasons1. It can be difficult to get the
  inhibitor to the pump intake and into the
  production tubing (i.e. in wells with high fluid
  levels).

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• 2. It is often incompatible with other
  downhole well equipment (i.e. the elastomer in
  progressing cavity pumping wells).3. In North
  Americas deviated wells, the rod string often
  has many points of contact with the tubing, which
  causes wear. This then causes an inability to
  maintain the protective film generated by the
  corrosion inhibitor on the rod surface.

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• 4. Chemical inhibitor is often cost
  prohibitive, not precise to deploy to targeted
  locations, and inconvenient to implement/maintain.
  When embarking on a downhole well-inhibitor
  program a producer must be ready for a
  life-of-the-well commitment that requires a lot
  of ongoing research and testing, given the well
  changes over time. 

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• Special Sucker Rod Materials
• Special sucker rod materials such as K and D
  special have been explored for corrosion
  resistance due to the slight increase in alloying
  materials. However, often the improvement is
  incremental in performance over D Carbon and D
  Alloy as the alloying quantities still remain
  relatively low. For example, a D Alloy 41-series
  has 1 chromium, while a K 46-series has 2
  nickel, 0.3 molybdenum and a small percentage of
  chromium.

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• In comparison to a material such as stainless
  steel that is classified as corrosion resistant,
  the chromium content is 11 with a high nickel
  content of usually 8 or higher. Note, stainless
  steel is not used for sucker rods due to expense,
  difficulty processing, and the inability to
  achieve the required mechanical properties.

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• Coated Sucker Rods
• Coated sucker rod involves placing a
  protective coating on the rod string before
  deploying downhole. Challenges with coated sucker
  rod include wear and tear of the coating when
  servicing and adhesion difficulties. However,
  when applied properly coated sucker rods are a
  reliable, cost-effective solution.Lifting
  Solutions has researched, tested, and designed
  our Coated Endless Rod continuous sucker rod to
  protect against corrosive conditions including
  C02 and H2s.

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• Our high-strength, proprietary polymer
  coating is available in various grades and sizes
  of Endless Rod continuous sucker rod. To ensure
  product integrity and eliminate wear and tear,
  Lifting Solutions has engineered fit-for-purpose
  equipment to service Coated Endless Rod
  continuous rod without affecting the coating. In
  addition, Coated Endless Rod continuous rod is
  environmentally friendly as it has the unique
  ability to be cost-effectively removed once the
  coating wears. This allows reuse of the string by
  re-running the base rod string in a more benign
  well, thereby avoiding cost.