Oxygen scavenger
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This document discusses the impact of dissolved oxygen on corrosion in oilfields, emphasizing its severity compared to CO2 and H2S. It outlines methods for monitoring and controlling dissolved oxygen levels, including the use of oxygen scavengers and mechanical treatments. Case studies illustrate the effects of dissolved oxygen on corrosion rates and recommend strategies for mitigation and monitoring.
Oxygen scavenger
- 1. OXYGEN SCAVENGER IN OILFIELD BONY BUDIMAN 2021
- 2. OBJECTIVES • Know how dissolved oxygen will cause corrosion • Sharing hot to monitor dissolved oxygen • Sharing mitigation of dissolved oxygen especially by oxygen scavenger • Field cases study
- 3. • INTRODUCTION • MONITORING • CONTROL • TREATMENT METHOD • FIELD APPLICATION • SUMMARY OUTLINES
- 4. DISSOLVED OXYGEN : GENERAL INFORMATION • Oxygen not common found in the reservoir, the concentration usually below 20 ppb (0.02 ppm).This concentration is very low compare to dissolved oxygen in the seawater (sea graph beside) • Oxygen may ingress to the production water through leaking in the topside or when mixed with other liquid that already contain oxygen.
- 5. DISSOLVED OXYGEN EFFECT TO CORROSION RATE (1) • Dissolved oxygen (DO) in water can cause destructive oxygen corrosion to metal pipes and process equipment • Corrosion caused by DO is more severe than corrosion by CO2 and H2S at similar concentration
- 6. DISSOLVED OXYGEN EFFECT TO CORROSION RATE (2) • Corrosion rate will increase when temperature increase and with additional others corrosive dissolved gas such as CO2 and H2S. • If the allowable corrosion rate is less than 5 mpy, the DO shall be maintained below 45 ppb • The common specification for DO is less than 20 ppb.
- 7. • INTRODUCTION • MONITORING • CONTROL • TREATMENT METHOD • FIELD APPLICATION • SUMMARY OUTLINES
- 8. MONITORING DO could be measured using oxymeter or using rapid onsite test kit such as Chemetric Rapid test principle : reaction between DO with reagent will create change of color. Darker color indicate higher DO. The formed color compare to standard comparator. Important during conduct rapid test: • Shall be onsite, cannot take sample to the lab • Shall avoid contact with open air
- 10. DO ANALYSIS Video Analysis Dissolved Oxygen
- 11. • INTRODUCTION • MONITORING • CONTROL • TREATMENT METHOD • FIELD APPLICATION • SUMMARY OUTLINES
- 12. CONTROL 1. Avoid leaking at any facilities 2. Use blanketing nitrogen 3. Use mechanical method such as stripper or deaerator. 4. Work principle of deaerator is by evaporate dissolved oxygen at temperature below 100 oC and at vacuum condition. Deaerator could decrease DO below 50 ppb. 5. Using chemical treatment : oxygen scavenger
- 13. OXYGEN SCAVENGER (OS) • OS is chemical that react stoichiometric with DO.The reaction is usually irreversible. For example of reaction : 2Na2SO3 + O2 2Na2SO4 • More DO require more OS • OS may not efficient to decrease DO above 1000 ppb (1 ppm). • OS could decrease DO to < 10 ppb
- 14. TYPES OF OS Actual/Field dosage will depend on temperature and DO level At low level of DO, the dosage of OS per part O2 will be higher Field dosage could be 10 – 50x of theoretical dosage.
- 15. • INTRODUCTION • MONITORING • CONTROL • TREATMENT METHOD • FIELD APPLICATION • SUMMARY OUTLINES
- 16. TREATMENT METHOD • OS injected continually to once through production system or batching at closed system. • At close system with batching method, residual of OS shall be monitor regularly. • OS is and oxidator that may react with other chemicals and lead to decrease the efficiency for both OS and others chemicals. It is important to keep the dosage and injection point to avoid incompatibility issue.
- 17. • INTRODUCTION • MONITORING • CONTROL • TREATMENT METHOD • FIELD APPLICATION • SUMMARY OUTLINES
- 18. OXYGEN INGRESS Injection Point CI Washtank Watertank Shipping Tank Corrosion coupon • Corrosion rate at Alpha GS still high even injection corrosion inhibitor increased • Corrosion rate is > 20 mpy meanwhile the specification < 5 mpy
- 19. WATER QUALITY ANALYSIS Sampling Point Wash Tank Alpha GS Level 13’10” Suction Water Pump Alpha GS Suction Water Pump Alpha GS Date Analyze 7 Sept 7 Sept 15 Sept CO2 ( ppm ) 40 60 40 SO3 ( ppm ) 6.5 6 4.5 H2S ( ppm ) n.d n.d n.d SRB ( coll / cc ) 100 100 n.a Temperature ( oF ) 130 134 n.a O2 ( ppb ) 20 50 >100
- 20. WHY DO INCREASE AT WATER TANK ? At watertank, water flow through goose neck called water leg. Waterleg not fully close Hypothesis : oxygen from open air ingress to the water through this gap Open
- 21. RECOMENDATION • Close the gap • Inject Oxygen Scavenger at inlet watertank RESULT AFTER OS INJECTION • DO decrease to 20-30 ppb • Corrosion rate decrease < 10 mpy
- 22. PLUGGING OS • MEG (monoethylene glycol) injected continuously to avoid hydrate at gas field. • Return MEG recovery at topside and the recovered MEG injected back to the wellhead. • Sulphite type Oxygen Scavenger injected continuously to maintain oxygen level at MEG below 20 ppb). MEG Tank Subsea Wellhead
- 23. PLUGGING FOUND • Every 2-4 weeks the injection point was plugged • The deposit is sulphite salt and MEG. • The OS may not compatible with the temperature, pressure or MEG itself. • Propose to change the type of OS from sulphite to carbohydrazide type • No plugging issue after chemical replacement.
- 24. OXYGEN STRIPPER - DEAERATOR • Produced water used as injection water • Oxygen scavenger injected at dosage 50 ppm upstream of stripper • DO outlet stripper < 20 ppb • But why DO outlet water tank > 100 ppb ? Produced Water Water Tank O2 Stripper To Injection Well OS
- 25. OXYGEN STRIPPER - DEAERATOR • Some gaps found in the roof of water tank • Relocate the flow direction of stripper and OS • OS dosage decrease to 5 ppm • DO downstream of OS injection point < 10 ppb Produced Water Water Tank To Injection Well O2 Stripper OS
- 26. • INTRODUCTION • MONITORING • CONTROL • TREATMENT METHOD • FIELD APPLICATION • SUMMARY OUTLINES
- 27. SUMMARY • Dissolved oxygen is one of corrosive agent and more aggressive than CO2 and H2S • Dissolved oxygen usually increase when water contact with the open air. • Dissolved oxygen may decrease using mechanical or chemical method • Oxygen scavenger is chemical that react stoichiometric with the dissolved oxygen • The effectiveness of OS depend on temperature, concentration, others process and field condition.