Artificial Lift Wells

Many oil wells are produced using some form of artificial lift. The most common form of artificial lift well uses a sucker rod pumping system, while other types involve electric submersible pumps and gas lift systems.

Sucker Rod Wells

Corrosion can occur in any of the major components of sucker rod pumping systems, including the pump, the tubing (click tubing for more information corrosion and prevention in tubing and casing) and the sucker rod itself. Corrosion accounts for at least half of all sucker rod failures, and these failures may result in extensive and costly fishing operations that may even result in the plugging of marginal wells.

Galvanic corrosion  can become a problem when new sucker rod is added to a string of older sucker rod. The newer sucker rod will actually corrode much faster than the old sucker rod.

The presence of CO₂ in the downhole environment can cause or contribute to stress and fatigue related corrosion, resulting in pitting of the sucker rod. The pitting caused by this corrosion can be extensive, and may be found in long lines. The amount of pitting a rod can sustain without failure is related to the stresses on the rod, which in turn is related to the tensile strength of the rod (see below). The following image is an example of CO₂ corrosion on a coupling. This image and the following image are found at the Norris web site listed on the links page.

The presence of hydrogen sulfide H₂S or microbes (see microbiologically influenced corrosion) can also lead to the corrosion of sucker rods. These types of corrosion produces deep pitting along the rod (the two types of corrosion have a similar effect as a byproduct of microbe damage is hydrogen sulfide).

Oxygen enhanced corrosion also occurs in sucker rod systems, usually at the couplings. This type of corrosion is characterized by shallow pitted areas that often join together. A large amount of dissolved oxygen and the presence of other corrosive gasses in the produced water can lead to extensive corrosion.

Another consideration with sucker rod corrosion is the tensile strength of the sucker rod. Normally, the softer the rod, the more corrosion resistant it is. Therefore it is usually a good idea to use the softest rod appropriate for the application. However, high tensile strength sucker rod can be treated to help prevent corrosion. For more information, refer to the Norris online corrosion pages and the API standards found in the references and links pages.

Corrosion of these types can also be a problem in the pumps used in sucker rod artificial lift wells. The use of corrosion resistant materials in the construction of the barrels of the pump is one way the companies can prevent their pumps from corroding. For instance, H-F pumps that will be exposed to corrosive environments use a 5% chrome steel alloy which is corrosion resistant.

Other Artificial Lift Systems

Corrosion is often a problem in other types of artificial lift wells, either in the casing, tubing and annulus (refer to the section on casing and tubing), or in the components themselves. Corrosion inhibitors and coatings may be used in the components of the system to help mitigate corrosion damage. For instance, the power cable used to power an electronic submersible pump is often run through the annulus, where it is exposed to a possibly corrosive environment. Therefore, it is usually sheathed with a corrosive resistant alloy to give it extra protection.