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Formation, Impact, and Prevention of Iron Sulfide in Drilling and Gathering Processes

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Formation, Impact, and Prevention of Iron Sulfide in Drilling and Gathering Processes

2024-08-09 08:51:14

What is the Iron sulfide? The Formation of Iron sulfide

Iron sulfide forms during drilling and gathering processes primarily through the following mechanisms:

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  1. Reaction with Hydrogen Sulfide (H₂S): Underground, hydrogen sulfide gas reacts with iron to form iron sulfide (FeS). H₂S is a common natural gas component, especially in high-temperature, high-pressure formations.
  2. Chemical Precipitation: Iron ions in drilling fluids and muds react with sulfides in the formation, resulting in iron sulfide formation.
  3. Corrosion: Steel equipment exposed to hydrogen sulfide undergoes electrochemical corrosion, leading to the production of iron sulfide.

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Impact

The formation of iron sulfide can lead to several issues:

 

  1. Pipeline Blockage: Iron sulfide deposits on the inner walls of pipelines, causing blockages and reducing fluid transportation efficiency.
  2. Equipment Corrosion: Iron sulfide is corrosive and accelerates the corrosion of metal equipment, shortening their lifespan.
  3. Reduced Drilling Efficiency: Deposits of iron sulfide on drill bits and drill rods increase friction, lowering drilling efficiency.
  4. Safety Hazards: Iron sulfide is pyrophoric and may spontaneously combust when exposed to air, posing a fire risk. 

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How to prevent the Iron Sulfide in Drilling and Gathering Processes?

General Prevention Measures

To prevent and control the formation of iron sulfide, the following measures can be taken:

 

  1. Use of Corrosion Inhibitors: Adding corrosion inhibitors to drilling fluids and gathering media to reduce iron sulfide formation.
  2. Control of Hydrogen Sulfide Concentration: Reducing the concentration of H₂S through chemical or mechanical methods.
  3. Regular Cleaning: Periodically cleaning pipelines and equipment to remove iron sulfide deposits.
  4. Material Selection: Using corrosion-resistant materials like stainless steel and alloy steel to minimize corrosion.
  5. Monitoring and Detection: Enhancing monitoring and detection of H₂S and iron sulfide to identify and address potential issues promptly.

 

Recommended Preventive Measures

To avoid sulfide corrosion failure in existing installations, the following measures can be implemented:

 

  1. Formulating and Implementing Inspections:

   - Confirm whether the operating environment of the equipment can lead to hydrogen sulfide corrosion.

   - Develop an inspection plan based on the consequences of failure, expected corrosion rates, or previous inspection results, considering factors such as temperature changes and service life.

   - Focus on areas prone to higher corrosion rates, such as high-temperature pipelines and injection points, and implement spot thickness measurements as part of the inspection plan.

 

  1. Material Identification:

   - Conduct 100% material inspection of all equipment and pipelines to ensure compliance with material requirements, particularly in critical areas.

   - Portable spectrometers are often used for material identification, assessing the presence of alloy elements like Cr, Ni, and Mo.

   - If substandard materials are identified, a risk assessment should be conducted to determine the need for replacement.

 

  1. Enhanced Detection of Low-Silicon Carbon Steel:

   - Low-silicon (<0.10%) carbon steel is prone to accelerated corrosion under sulfide conditions. Enterprises should map the distribution of low-silicon steel in their installations and enhance detection efforts.

 

  1. Process Adjustment and Optimization:

   - Analyze and identify areas prone to sulfide corrosion and optimize operational parameters, such as temperature and sulfur content, to prevent over-temperature operations and ensure smooth fluid flow.

 

  1. Online Monitoring:

   - Online corrosion monitoring systems, utilizing resistance and electrochemical monitoring technologies, are widely used to monitor corrosion behavior in real-time.

 

  1. Corrosion Inhibitor Injection:

   - Consider the use of inhibitors to suppress sulfide corrosion, although the effectiveness of available inhibitors for high-temperature sulfide corrosion needs further research.

 

  1. Material Replacement or Upgrading:

   - If corrosion rates are too high, consider material replacement or upgrading to more corrosion-resistant materials, such as Cr5Mo steel or stainless steel with over 13% chromium content, particularly in high-temperature areas.

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Conclusion

Sulfide corrosion is a complex process influenced by many factors. When processing high-sulfur crude oil, it is essential to implement a comprehensive integrity solution based on the oil’s properties and operating conditions. The timely detection, monitoring, and prevention of sulfide corrosion can significantly reduce the formation of iron sulfide during drilling and gathering, ensuring production safety and efficiency.