How to prevent corrosion in casing pipe?

Oil pipeline engineering is an important part of the oil industry, and anti-corrosion is an important part of pipeline engineering. Casing pipe is used to transport various media such as oil, natural gas, and chemical products. Doing a good job of oil casing pipe anti-corrosion is an important guarantee for the safe operation of the pipeline.

With the development of the national economy, the advantages of pipeline oil transportation are becoming increasingly obvious. Oil pipelines mainly use carbon steel seamless pipes, straight seam electric resistance welded pipes (ERW), LSAW welded pipe or spiral welded pipes (SSAW). Pipelines are generally laid on the ground or buried. Regardless of the laying method, when the metal pipeline comes into contact with the surrounding medium, chemical or electrochemical reactions will occur, causing corrosion.

Corrosion is an important factor affecting the reliability and life of the pipeline system. Corrosion will change the appearance, color, and mechanical properties of the metal pipeline, affect the quality of the transported oil, shorten the service life of the pipeline, and in severe cases cause leakage, environmental pollution, and even make the pipeline unusable. As oil production enters the middle and late stages, the corrosion problem becomes increasingly prominent, and corrosion accidents occur frequently, causing significant economic losses and serious social consequences. Therefore, it is crucial to understand the causes, mechanisms, influencing factors, and control methods of oil and gas pipeline corrosion and take effective protective measures. Due to the complexity and variability of corrosion, no single anti-corrosion technology is universal. It is necessary to fully understand the corrosion environment and adopt appropriate material selection and design strategies for protection.

Role of casing pipe:

During the drilling process, the oil casing plays a role in supporting and protecting the well wall. It can prevent the well wall from collapsing and ensure the smooth progress of drilling. After the completion of the oil and gas well, the oil casing serves as a channel for oil and gas to transport oil and gas from the underground formation to the surface oil production equipment or oil pipeline. It can withstand the harsh environment of high pressure, high temperature and corrosion in the well to ensure the safe transportation of oil and gas.

In addition, oil casing can also be used for processes such as layered mining and water injection. By installing casings of different specifications at different levels, different oil and gas layers can be mined separately, improving the oil and gas recovery rate. At the same time, the water injection casing can be used to inject water into the ground to maintain the formation pressure and promote the flow and mining of oil and gas.

Casing pipe anti-corrosion technology:

The corrosion of the casing is affected by many factors, including the partial pressure of the corrosive gas, ambient temperature, water content, salinity, flow rate, pH value, etc. The following are several common casing anti-corrosion technologies:

1. Cement plugging anti-corrosion
Early analysis: Early discovery of casing damage was mainly due to incomplete cement plugging, which led to the intrusion of corrosive gases in the formation. In order to enhance the corrosion resistance of the casing, a method of increasing the amount of cement reinjection was proposed in the 1980s. Although this method reduces the degree of corrosion to a certain extent, it cannot completely prevent corrosion, so its effect in improving corrosion resistance is limited.

2. Use corrosion-resistant alloy pipes
Material solutions: Since 2000, the anti-corrosion strategy of offshore oil casing has shifted to the use of material solutions to enhance corrosion resistance. Through years of laboratory research, alloy materials such as chromium-containing pipes (such as 1Cr, 3Cr, 9Cr, 13Cr) suitable for offshore oil and gas fields have been developed and evaluated under specific temperature, pressure and corrosive gas conditions.

3. Injection of corrosion inhibitors
Chemical protection: During the completion process, if the formation contains corrosive oil and gas, chemical corrosion inhibitors are added to the well fluid to prevent scaling, waxing and corrosion. The use of chemical corrosion inhibitors is a common protection method abroad. According to the specific conditions of the oil and gas field, corrosion inhibitors can be injected intermittently or continuously, and the injection amount can be adjusted according to the corrosive environment. Although the use of corrosion inhibitors will increase costs, it has a positive impact on production.

4. Apply corrosion-resistant coatings
Coating method: For casing, applying corrosion-resistant coatings is an effective protection method. Some oil fields use nitriding technology to treat the casing internally and externally, which has good wear resistance, but will accelerate the corrosion of the casing to a certain extent. In addition, epoxy powder coatings, titanium nano coatings, epoxy phenolic coatings, etc. are used for additional protection.

Additional anti-corrosion measures for casing pipe:

1. Ensure that water quality meets standards
Implement separation of clean and dirty water: When injecting water, distinguish clean and dirty water to avoid introducing sewage into the system, reduce the introduction of corrosion sources, and thus reduce the risk of casing corrosion.

Strengthen the cleaning of the main water pipe: Clean the main water pipe regularly to ensure that the water quality meets the standards, reduce the accumulation of corrosion sources, ensure that the water quality of the station and the bottom of the well meets the standards, and control corrosion from the source.

2. Protect newly commissioned water injection wells
Use bactericides: For newly commissioned water injection wells, annular protection fluid containing bactericides is mainly used to inhibit bacterial growth and reduce corrosion.
Regular addition: Establish a regular bactericide addition system to maintain the effectiveness of the annular protection fluid and ensure long-term corrosion protection.

3. Reduce mechanical wear
Install rubber rings: Install rubber rings on tubing joints to reduce friction and wear during operation and prevent tubing from scratching casing.
Use centralizers: Install centralizers in areas with severe well deviation to maintain the stability of tubing during operation and reduce direct contact with casing, thereby reducing mechanical wear.

4. Deal with sulfate-reducing bacteria (SRB) corrosion
Inject high-temperature water or steam: For severe SRB corrosion under scale, regularly injecting 100°C high-temperature water or steam into the annulus can effectively kill SRB and inhibit its growth.
Avoid premature adoption of cathodic protection and coated casing

Delayed adoption: Avoid promoting the use of cathodic protection and coated casing before casing corrosion is effectively controlled. This is because if corrosion control measures have not been fully implemented, the effects of cathodic protection and coating may not meet expectations, which may lead to additional maintenance costs and complexity.

By taking the above measures, the corrosion of the casing can be effectively controlled and reduced, and the service life and safety of the casing can be improved. In practical applications, the anti-corrosion strategy should be adjusted according to the specific situation to ensure the stability and safety of oil production. In short, the anti-corrosion of casing involves a variety of technologies, each of which targets different corrosion problems. The effective application of these methods can greatly improve the safety and durability of the casing and ensure its reliable operation during oil and gas production.

Read more: Difference between Oil Tubing and Casing Pipe or Seamless Casing vs. ERW Casing