Wax Control
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Transcript of Wax Control
Classification: Internal 2011-03-08
Wax control
Narve Aske, Leading advisor, Multiphase Fluid Control
Classification: Internal 2011-03-08
Outline
•Flow Assurance in Statoil
•What is wax and what problems may it cause?
•How to control wax deposition
•Case example: How to not control wax deposition
Classification: Internal 2011-03-08 Classification: Internal
Wellbore hydraulics Transient pipeline thermohydraulics
Chemical Injection Package
Fluid propertiesRheology
Multiphase equipment:• Multiphase meter
ProcessSeparatorSlug catcher
Scale control Asphaltene controlWax control
Hydrate controlEmulsion control
Corrosion control
• Multiphase pump
Main deliverables/competence:Thermohydralic multiphase analysis
System design
Hydrate- and wax control philosophies
Slug control
Operational support
Multiphase metering
Flow Assurance
“Flow assurance” = safe, uninterrupted and simultaneous transport of gas, oil and water from reservoirs to processing facilities.
Classification: Internal 2011-03-08
Fluid control – the problems
Asphaltenes
Kristin-NJ/DR Wye- wax deposition and temperature profile after 600 h
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Pipeline length [km]
Wax
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ositi
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]
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Tem
pera
ture
[°C
]
Waxdeposition
Fluidtemperature
Wax
Gas hydrates
Classification: Internal 2011-03-08
Multiphase fluid control
PVT / fluid composition
Reservoir Well Pipelines Process
Asphaltenes
Scale
Hydrates
Wax
Rheology
Emulsions
Naphtenates
Foam
Classification: Internal 2011-03-08
Accumulated length of multiphase flow lines [km]
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1970 1980 1990 2000 2010
Classification: Internal 2011-03-08
The future ….
Longer distance
More difficultfluids
Deeper water
Increased fieldcomplexity
Arctic / harshenvironment
Classification: Internal 2011-03-08
Outline
•Flow Assurance in Statoil
•What is wax and what problems may it cause?
•How to control wax deposition
•Case example: How to not control wax deposition
Classification: Internal 2011-03-08
What is wax?
Soft wax Hard wax
Wax consistency range
Classification: Internal 2011-03-08
n-alkane
wax crystalWhat is wax?
•Natural constituents of crude oils and most gas condensates
•Typical wax content 1-15 wt%
•Mostly long chain n-alkanes
•Solubility strongly dependent on temperature
•Operational consequences:
–Gelling
–Deposition
Classification: Internal 2011-03-08
Wax-forming components in crude oils
Non-wax
Mainly n-alkanes
WaxC7
C8C9
C10+
Lab. analysis Pseudo-components
Classification: Internal 2011-03-08
Wax precipitation curve
Classification: Internal 2011-03-08
Wax concerns•Wax deposition in the well or pipeline?
–Where, how much and how fast?
•Wax deposition in oil coolers topside
–Requires frequent cleaning and/or wax inhibitor
•Wax accumulation in storage tanks
–Gravity settling
•Gelling in flowlines, storage tankes etc.
•Pressure transducer malfunction etc.
Key parameters: Wax appearance temperature (WAT)Wax content
Classification: Internal 2011-03-08
0
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0 10 20 30 40 50 60 70 80 90 100 110 120Length (km)
wax
thic
knes
s (m
m)
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Tem
pera
ture
(C)
What happens in the pipeline?
Wax after 1 day
Wax after 2 days
Wax after 7 days
Temperature
Classification: Internal 2011-03-08
Wax depositionchallenges
•Stuck pigs
•HSE
•Inspection tools
•Plugged pipelines
Classification: Internal 2011-03-08
Outline
•Flow Assurance in Statoil
•What is wax and what problems may it cause?
•How to control wax deposition
•Case example: How to not control wax deposition
Classification: Internal 2011-03-08
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
Classification: Internal 2011-03-08
Wax control strategies1. Single phase oil/condensate pipelines:
– Wax control normally by regular pigging
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?
HH
FF
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FF F
SiOO
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HH
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SiO
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SiO
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SiO
O
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SiO
O
SiO2
Classification: Internal 2011-03-08
Outline
•Flow Assurance in Statoil
•What is wax and what problems may it cause?
•How to control wax deposition
•Case example: How to not control wax deposition
Classification: Internal 2011-03-08
Vale
Skirne
Huldra
Vale
Skirne
BraeStatpipe
Vale
Skirne
Vale
Heimdal
Vale
Huldra
Vale
BraeStatpipe
ValeVale
Heimdal
Heimdal – Brae condensate export pipeline
Classification: Internal 2011-03-08
Short history 2002 -2008 •2002: Vale on stream
•2003: Pressure increase
•2004: Pigging program
August: 6” pig stuck
32 m3 wax pumped back
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0 50 100 150 200 250 300 350 400Time (days)
Hei
mda
l Exp
ort P
ress
ure
(bar
a)
Classification: Internal 2011-03-08
•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
Short history 2002 -2008
Classification: Internal 2011-03-08
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.
Classification: Internal 2011-03-08
”Fill & soak” wax removal operation
Chemical
Gel
Sea water
Hydrocarbon
Heimdal
Brae
Classification: Internal 2011-03-08
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 again
Classification: Internal 2011-03-08
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!
Classification: Internal 2011-03-08
Thank you