Oxygen scavenger commonly used as chemical to reduce the dissolved oxygen in water phase and prevent oxygen corrosion.

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.