Wax Control

Classification: Internal 2011-03-08

Wax control

Narve Aske, Leading advisor, Multiphase Fluid Control


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.


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

on [m

]

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ture

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Waxdeposition

Fluidtemperature

Wax

Gas hydrates


Multiphase fluid control

PVT / fluid composition

Reservoir Well Pipelines Process

Asphaltenes

Scale

Hydrates

Wax

Rheology

Emulsions

Naphtenates

Foam


Accumulated length of multiphase flow lines [km]

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1970 1980 1990 2000 2010


The future ….

Longer distance

More difficultfluids

Deeper water

Increased fieldcomplexity

Arctic / harshenvironment


Outline






What is wax?

Soft wax Hard wax

Wax consistency range


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


Wax-forming components in crude oils

Non-wax

Mainly n-alkanes

WaxC7

C8C9

C10+

Lab. analysis Pseudo-components


Wax precipitation curve


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


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wax

thic

knes

s (m

m)

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Tem

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ture

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What happens in the pipeline?

Wax after 1 day

Wax after 2 days

Wax after 7 days

Temperature


Wax depositionchallenges

•Stuck pigs

•HSE

•Inspection tools

•Plugged pipelines


Outline






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


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

O

HH

FF

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SiO

O

HH

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SiO

O

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SiO

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SiO

O

SiO2


Outline






Vale

Skirne

Huldra

Vale

Skirne

BraeStatpipe

Vale

Skirne

Vale

Heimdal

Vale

Huldra

Vale

BraeStatpipe

ValeVale

Heimdal

Heimdal – Brae condensate export pipeline


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)


•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


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 again


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!


Thank you

Documents

Wax Control