– Gravity settling Gelling in flowlines, storage tankes etc.
•
Pressure transducer malfunction etc.
•
Key parameters:
Wax appearance temperature (WAT) Wax content
What happens in the pipeline? 7
40 35
Wax after 7 days
6 ) m 5 m ( s s4 e n k c i 3 h t x a w2
30 25
Wax after 2 days 20 15 Wax after 1 day
Temperature
1
10 5
0 0
10
20
30
40
50
60
70
Length (km)
80
90
0 100 110 120
) C ( e r u t a r e p m e T
Wax deposition challenges
Stuck pigs
•
HSE
•
Inspection tools
•
Plugged pipelines
•
Outline Flow Assurance in Statoil
•
What is wax and what problems may it cause?
•
How to cont rol w ax depositi on
•
Case example: How to not control wax deposition
•
Methods for controlling wax deposition Pipeline insulation External insulation coating on single pipes Pipe-in-pipe systems Pigging Chemicals Inhibitors Dispersants Dissolvers Heat Bundles Electric heating Hot oil flushing
F
Wax control strategies
F
F
F
F
F
F F
F F
F F
F F
F F
F F
F F
F F
F F
– Wax control normally by regular pigging
F
F
F
F F
F F
H H
F
F
F
F
1. Single phase oil/condensate pipelines:
F
F
F
H H
H H
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
H
H
H
O
SiO2
2. Medium length multiphase oil and gas condensate pipelines: – Normally insulated (or heated) – Prevents wax deposition and hydrate formation
3. Long-distance multiphase pipelines: a) Low-wax gas condensates (Snøhvit): •
Wax deposition will normally not be an issue
b) Oils and waxy gas condensates: •
No general, proven way to control wax deposition…
•
Wax-repellent surface coatings?
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
H
F
H
H
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
H
H
H
F F F F F F F F F F F F F H H
Si O
O
F F
H
Si O
O
F
F
F
H
Si O
F
F
H
Si O
F F
Si O
O O
O
Outline Flow Assurance in Statoil
•
What is wax and what problems may it cause?
•
How to control wax deposition
•
Case exam ple: How t o not cont rol w ax deposition
•
Heimdal – Brae condensate export pipeline Huldra
Vale Vale Skirne
Heimdal
Statpipe Brae
Short history 2002 2008
2002: Vale on stream
•
2003: Pressure increase
•
2004: Pigging program
•
August: 6” pig stuck 32 m3 wax pumped back
) 200 a r a 190 b ( e r 180 u s s 170 e r P 160 t r o p 150 x E l 140 a d m130 i e H120 0
50
100
150 200 250 Time (days)
300
350
400
Short history 2002 2008 2005: Chemical wax removal program
•
2006: Wax deposition layer increased (!)
•
– New pigging program launched, +50 pigs
2007: New stuck pig incident
•
2008: New chemical wax removal
•
project
– Comprehensive screening of wax dissolvers
Heimdal – Brae wax characteristics
Heimdal – Brae wax consists mainly of high molecular weight paraffins that are hard to dissolve.
•
Supported by indications of high melting temperature (60 C +).
•
Wax removal must be based on a combination of dissolution and ”break-down” of the wax deposit.
•
”Fill & soak” wax removal operation Chemical Gel Sea water Hydrocarbon
Heimdal
Brae
Fill and soak operation – August 2008 •
•
~1000 m3 of wax dissolver injected in the Heimdal Brae pipeline the 19th to 20th August Left to soak for about one week. Production restarted and chemical flushed downstream into FPS
•
Only minor changes to pressure drop and wax content after restart
•
11th September 2008: STUCK PIG agai n
Summary and lessons learned The Heimdal Brae pipeline is currently faced with a severe wax related problem
•
– ~500 m3 wax deposited over 80 km! Several projects/initiatives/methods have been tried so far. No major improvement despite the large efforts.
•
– No easy solution once wax deposition is out of control Problem would not have occurred if regular pigging of the pipeline had been implemented when the Vale field was started.
•
Lessons learned?
•
– Implementation of a proper wax control strategy from day one is essential for all fields producing waxy fluids!
