Method and system for lowering the water dew point of a hydrocarbon fluid stream subsea

Patent metadata

Field	Value
Publication number	US-9950293-B2
Application number	US-201114130393-A
Country	US
Kind code	B2
Filing date	Jul 1, 2011
Priority date	Jul 1, 2011
Publication date	Apr 24, 2018
Grant date	Apr 24, 2018

Abstract

The present invention concerns a method for lowering the water dew point subsea in a produced multiphase hydrocarbon fluid stream containing water, the method comprising the steps of: separating ( 10 ) the hydrocarbon fluid stream ( 1 ) into a liquid phase ( 3 ) and a first gas phase ( 2 ); cooling ( 20 ) the first gas phase in a controlled manner to knock out water or condensing water and optionally other condensates while keeping the fluid above a hydrate formation temperature thereof; separating off condensed liquids ( 6 ) and a second gas phase; wherein the second gas phase ( 8 ) has a water dew point which is lower than that of the initial multiphase hydrocarbon fluid stream. The invention also concerns a system for lowering the water dew point subsea.

First claim

The invention claimed is:

1. A method for water dew point depression subsea in a produced multiphase hydrocarbon fluid stream containing water, the method comprising the steps of:
subsea separating the hydrocarbon fluid stream into a first liquid phase and a first gas phase;
subsea cooling the first gas phase in a controlled manner to knock out water or condense water and optionally other condensates into a second liquid phase while keeping the fluid above a hydrate formation temperature thereof;
subsea separating off the second liquid phase and a second gas phase; wherein the second gas phase has a water dew point which is lower than that of the first gas phase and/or the initial multiphase hydrocarbon fluid stream;
adding hydrate inhibitor to the second gas phase;
cooling the second gas phase in a controlled manner to knock out water or condense water and optionally other condensates into a third liquid phase; and
separating off the third liquid phase and a third gas phase, wherein the third gas phase has a lower water dew point than the second gas phase.

2. A method according to claim 1 , wherein the first gas phase is cooled down to a temperature above 20° C.

3. A method according to claim 1 , wherein the cooled first gas phase is free of hydrate inhibitor and/or absorbent.

4. A method according to claim 1 , wherein the second gas phase is cooled down to a temperature below 25° C.

5. A method according to claim 1 , wherein a hydrate inhibitor is added to the third gas phase before further transport over a distance subsea.

6. A method according to claim 1 , wherein the third gas phase is compressed before optional addition of hydrate inhibitor and transport over a distance subsea.

7. A method according to claim 1 , wherein the cooled second gas phase is choked after the step of cooling the second gas phase and before the step of separating off the third liquid phase and third gas phase.

8. A method according to claim 7 , wherein the second gas phase is cooled down to a temperature of about sea temperature, or below sea temperature.

9. A method according to claim 1 , wherein liquid water additionally is separated from the produced multiphase hydrocarbon fluid stream in the step of subsea separating the hydrocarbon fluid stream into the first liquid phase and the first gas phase.

10. A method according to claim 9 , wherein said separated liquid water is re-injected in sub terrain formations.

11. A method according to claim 1 , wherein knocked out water or condensed water and other condensates from the separation in the step of subsea separating off the second liquid phase and second gas phase and optionally the step of separating off the third liquid phase and third gas phase are mixed with the first liquid phase from the separation in the step of subsea separating the hydrocarbon fluid stream into the first liquid phase and first gas phase.

12. A method according to claim 1 , wherein the second liquid phase from the step of subsea separating off the second liquid phase and second gas phase and optionally the third liquid phase from the step of separating off the third liquid phase and third gas phase are recycled to the separation in the step of subsea separating the hydrocarbon fluid stream into the first liquid phase and first gas phase.

13. A method according to claim 1 , wherein the first liquid phase, optionally mixed with the second liquid phase and optionally the third liquid phase is transported to further processing plants, alternatively with the help of boosting.

14. A method according to claim 1 , wherein the hydrate inhibitor is chosen from one or more of:
thermodynamic inhibitors, ethanol, methanol, glycols, monoethylene glycol (MEG), dicthylcnc glycol (DEG), methylene glycol (TEG), amines, monoethanolamine (MEA) or methyldiethanolamine (MDEA); or
kinetic inhibitors, anti-agglomerants, low dosage hydrate inhibitors (LDHI), polymers, copolymers or surfactants.

15. A method according to claim 1 , wherein the second gas phase is cooled down to a temperature to about the surrounding sea water temperature.

16. A method for water dew point depression subsea in a produced multiphase hydrocarbon fluid stream containing water, the method comprising the steps of:
subsea separating the hydrocarbon fluid stream into a first liquid phase and a first gas phase;
subsea cooling the first gas phase in a controlled manner to knock out water or condense water and optionally other condensates into a second liquid phase while keeping the fluid above a hydrate formation temperature thereof; and
subsea separating off the second liquid phase and a second gas phase; wherein the second gas phase has a water dew point which is lower than that of the first gas phase and/or the initial multiphase hydrocarbon fluid stream,
wherein a hydrate inhibitor is added to the second gas phase so as to remain present in the second gas phase during further transport over a distance subsea.

17. A method according to claim 16 , wherein the first gas phase is cooled down to a temperature above 20° C.

18. A method according to claim 16 , wherein the cooled first gas phase is free of hydrate inhibitor and/or absorbent.

19. A method according to claim 16 , wherein the second gas phase is compressed before addition of hydrate inhibitor and transported over a distance subsea.

20. A method according to claim 16 , wherein liquid water additionally is separated from the produced multiphase hydrocarbon fluid stream in the step of subsea separating the hydrocarbon fluid stream into the first liquid phase and first gas phase.

21. A method according to claim 20 , wherein said separated liquid water is re-injected in sub terrain formations.

22. A method according to claim 16 , wherein knocked out water or condensed water and other condensates from the separation in the step of subsea separating off the second liquid phase and second gas phase are mixed with the first liquid phase from the separation in the step of subsea separating the hydrocarbon fluid stream into the first liquid phase and first gas phase.

23. A method according to claim 16 , wherein the second liquid phase from the step of subsea separating off the second liquid phase and second gas phase is recycled to the separation in the step of subsea separating the hydrocarbon fluid stream into the first liquid phase and first gas phase.

24. A method according to claim 16 , wherein the first liquid phase, optionally mixed with the second liquid phase is transported to further processing plants, alternatively with the help of boosting.

Assignees

• Kaasa Baard
• Rusten Bernt Henning
• Marak Knut Arild
• Fredheim Arne Olav
• Statoil Petroleum As

Inventors

• Kaasa Baard
• Rusten Bernt Henning
• Marak Knut Arild
• Fredheim Arne Olav

Classifications

• B01D2256/245

  Methane · CPC title

• C10L3/106

  of water · CPC title

• C10L3/107

  Limiting or prohibiting hydrate formation · CPC title

• B01D53/265 Primary

  by refrigeration (condensation) · CPC title

• F25J3/06

  by partial condensation (F25J3/08 takes precedence; by rectification F25J3/02 {; purification of hydrocarbons in general C07C7/00}) · CPC title