Introduction
Problematic Gases in Drilling
Oxygen, carbon dioxide, and hydrogen sulfide gases pose significant challenges due to their reactions with steels. Among these gases, oxygen has the lowest solubility, whereas carbon dioxide and hydrogen sulfide have solubility levels approximately one hundred times higher than oxygen.
Detection of Problematic Gases
Measuring Oxygen, Carbon Dioxide, and Hydrogen Sulfide
Oxygen: Difficult to measure with standard oxygen meters.
Carbon Dioxide and Hydrogen Sulfide: Quickly detected through their impact on the drilling fluid’s surface, particularly in alkaline conditions. These gases can also acidify the drilling fluid.
Corrosive Effects
Oxygen: Causes iron oxide formation on rings.
Carbon Dioxide: Leads to the formation of iron carbonate.
Hydrogen Sulfide: Results in the formation of iron sulfate.
Factors Affecting Corrosion in the Drilling Industry
pH Levels: Corrosion rates generally increase as pH decreases.
Temperature: Higher temperatures typically accelerate corrosion.
Fluid Velocity: Increased velocity can lead to higher corrosion rates.
Heterogeneity: Variations in elemental concentrations within pipes can enhance corrosion.
High Stress: Areas under greater stress corrode more rapidly, particularly in drill pipes above the Drill Collars.
Oxygen Corrosion
Corrosive Nature of Modern Muds
Contemporary muds are more corrosive than in the past. Oxygen absorbers are essential to manage the levels of dissolved oxygen in the mud. If the dissolved oxygen exceeds one PPM, corrosion is likely to occur. Corrosion rates also increase with lower pH and higher electrical conductivity in the mud.
Sources of Oxygen in Mud Systems
Oxygen can enter the mud system in various ways, leading to oxygen saturation by the time the mud reaches the pump. Corrosion often occurs in drilling pipes and mud pumps where the metal surface is covered with mud or protective rubber. Inadequately cleaned drill pipes can accumulate mud, promoting corrosion.
Factors Affecting Oxygen Corrosion
Oxygen Solubility: Cold water has higher oxygen solubility. At 0°C, oxygen solubility is 14.6 ppm, compared to 7.8 ppm at 25°C. Temperature changes within the well do not significantly reduce dissolved oxygen levels.
pH Levels: Oxygen corrosion occurs in alkaline pH environments. Generally, corrosion rates decrease at higher pH levels. Salt-saturated solutions naturally lower oxygen solubility, reducing the need for oxygen absorbers and inhibitors.
Recognizing and Monitoring Oxygen Corrosion
Detection Methods
Accuracy: Essential for detecting oxygen corrosion.
Environmental Conditions: Assess if conditions are suitable for oxygen corrosion.
Measurement Tools: Use corrosion rate measurements and oxygen-sensitive devices.
Treatment of Oxygen Corrosion
Using Oxygen Absorbers
Oxygen absorbers reduce corrosion by adding them to the drilling fluid via the suction area of the mud pump. If these absorbers are used, sulfide (SO3) levels in the drilling fluid should be maintained between 50-150 mg/l. The reaction for oxygen uptake by sulfide is:
12O2+SO3→SO4\frac{1}{2} O_2 + SO_3 \rightarrow SO_421O2+SO3→SO4
Monitoring Sulfide Levels
Special kits are available to measure excess sulfide in the drilling mud.
Steps for Oxygen Corrosion Treatment
Inject oxygen absorbers directly through the mud pump suction or via specialized continuous injection equipment.
Adjust the amount of oxygen absorber based on the oxygen content in the mud and its circulation speed.
Measure sulfide levels in the flow line to ensure they remain within the recommended range of 50-150 ppm.
Chromite Inhibitors
Usage of Chromite Inhibitors
If oxygen absorbers are ineffective, liquid chromite inhibitors can be used. Available in 55-gallon barrels, these inhibitors should be injected similarly to oxygen absorbers. To prevent corrosion, maintain at least 500 ppm chromite in the fluid. Special kits are used to measure chromite levels. Avoid using chromite inhibitors with sulfide oxygen absorbers.
TEAMChem: Your Trusted Supplier for Corrosion Control Solutions
When it comes to controlling corrosion in drilling operations, TEAMChem stands out as the leading supplier of high-quality corrosion control solutions. We provide a range of oxygen absorbers, chromite inhibitors, and specialized kits designed to manage corrosion effectively in various drilling environments. Our products are formulated to ensure optimal performance, prolonging the life of your equipment and reducing maintenance costs. With a focus on reliability, safety, and efficiency, TEAMChem is your trusted partner for managing corrosive gases in drilling operations.