C3.2.11. Chemical Injection_2020

1. Offshore Production Technology
Chemical Injection
Marine & Offshore Technology

2. Learning Outcomes
1. Understand the problems that require chemical injection in
subsea, topside processing and water injection systems.
2. Explain the functions of various chemicals provided in various
parts/location of the subsea, and topside processing systems.
3. Explain the functions of various chemicals provided in various
parts/location of the water injection system.

3. 1. Understand the problems that require
chemical injection in subsea, topside
processing and water injection systems.

4. Introduction to Chemical Injection
Threats to production
•Simultaneous flow of oil, water and gas mixture
•Slugging in flowlines
•Emulsions in flowines
•Foaming in flowlines
•Blockage due to wax, asphaltene and hydrates
•Formation of scale due to effects of temperature
•Corrosion due to production fluids
Solution? Chemical treatment

5. 2. Explain the functions of various
chemicals provided in various parts/location
of the subsea, and topside processing
systems.

6. Chemical Injection System
for Production Fluids
• Demulsifier
– used to break stable emulsions and disperse
droplets to aggregate intact or coalesce and
form large droplets, that increase separation
force between oil and water
• What cause emulsions?
– Water droplets disperse into the oil phase
• Problems with emulsions?
− Increase viscosity resulting in increase
pressure drop
− Decrease the performance of separators

7. Chemical Injection System
for Production Fluids
• Anti-foam
– injected into the well fluid to prevent
the formation of foam in the separators
• What cause foaming?
– Small amount of surface-active is added
into the oil that is being agitated in the
presence of gas
• Problems with foams?
− Cause partial blockage in flowline
− Carry over crude into other phases
(water and gas)

8. Chemical Injection System
for Production Fluids
• Corrosion Inhibitors
– injected into oil and hydrocarbon gas stream to prevent /
limit corrosion of carbon steel
• What cause corrosion?
– Carbon dioxide, hydrogen sulphite
– Changes in temperature, pressure, flow rates, flow regimes
• Solutions?
– Use corrosion-resistant alloys (in subsea pipelines)
– Chemicals which react with metal surfaces to form
protective layer
– Chemical which reduce the rate of ion diffusion to metal
surfaces and increase electrical resistance

9. Chemical Injection System
for Production Fluids
• Asphaltene/Wax Inhibitors
– injected mainly subsea to prevent or
limit asphaltene and/or wax
formation in subsea flow lines and
pipelines
Causes?
– Due to cold surfaces in pipeline walls
– Increase in oil viscosity, decrease in
pour point
Other solutions?
– Pig scraping (mechanical method)

10. Chemical Injection System
for Production Fluids
• Scale Inhibitor
– injected to inhibit crystal nucleation,
thus limiting and preventing scale
formation
Causes?
– Presence of in organic salts in
formation water e.g. calcium
carbonate, barium sulphate,
strontium sulphate
Other solutions?
– Pig scraping (mechanical method)

11. Chemical Injection System
for Production Fluids
• Methanol
– injected subsea in the wells and the flow
lines (for start-up and shutdown) as well
as on the topsides in the high pressure
hydrocarbon gas coolers (for start-up) to
prevent hydrate formation
• What cause gas hydrate formation?
– Hydrocarbon molecule entrapped in a
caged structure composed of water
molecules
• Problems with gas hydrates?
− Cause partial or complete blockage in
flowline

12. Chemical Injection System
for Production Fluids

13. Chemical Injection System
for Production Fluids

14. Chemical Injection System
for Production Fluids

15. 3. Explain the functions of various
chemicals provided in various parts/location
of the water injection system.

16. Chemical Injection System
for Injection (Sea) Water
• Hypochlorite or Chlorine
– to limit bio-fouling in the
seawater system and to
improve the performance of the
fine filters
• Poly-electrolyte and Coagulant
– injected into the seawater
upstream of the fine filters to
improve filtration

17. Chemical Injection System
for Injection (Sea)Water
• Oxygen Scavenger
– injected into the deaerator to achieve the required
specification
Oxygen Scavenger Unit

18. Chemical Injection System
for Injection (Sea)Water
• Biocide
– injected into the deaerated
seawater on a shock dosing
basis to prevent SRBs
(Sulphate Reducing Bacteria)
and associated corrosion.
• Scale inhibitor
– injected with the injection
water into the reservoir to
prevent scale formation in
the reservoir.

19. Chemical Injection System
for Produced Water
• Anti-foam
– may be injected upstream of the Deaerator to prevent
foaming in the Deaerator.

20. Key Questions
1. Explain the functions of various chemicals provided in various
parts/location of the subsea, and topside processing systems.
2. Explain the functions of various chemicals provided in various
parts/location of the water injection system.
Summary table in Notes Chapter 3.2.11 (Pg 3-26 to 3-27)