Excellant Wax PPT

Wax control Arild Stokkenes Leading advisor Multiphase Fluid Control

Outline • Flow Assurance in Statoil • What is wax and what problems may it cause? • How to control wax deposition

• How to monitor wax deposition • Case example: How to not control wax deposition 2/10/2014

Flow Assurance Process Separator Slug catcher

Main deliverables/competence:

Thermohydralic multiphase analysis System design Hydrate- and wax control philosophies Slug control Operational support Multiphase metering

Scale control

Asphaltene control

Wax control

Chemical Injection Package Fluid properties Rheology

Hydrate control

Emulsion control

Corrosion control

Multiphase equipment: Wellbore hydraulics

Transient pipeline thermohydraulics

• Multiphase meter • Multiphase pump

“Flow assurance” = safe, uninterrupted and simultaneous transport of gas, oil and water from reservoirs to processing facilities.

2/10/2014

Fluid control – the problems Gas hydrates Asphaltenes

Wax Kristin-NJ/DR Wye - wax deposition and temperature profile after 600 h

70

50 0.003

40 30

0.002

20 0.001

10 0

0 0

20

40

60

Pipeline length [km]

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Wax deposition

60

0.004

80

100

Temperature [°C]

Wax deposition [m]

0.005

Fluid temperature

The future …. Arctic / harsh environment

Longer distance Deeper water

More difficult fluids

2/10/2014

Increased field complexity

Outline • Flow Assurance in Statoil • What is wax and what problems may it cause? • How to control wax deposition

• How to monitor wax deposition • Case example: How to not control wax deposition 2/10/2014

What is wax?

Wax consistency range

Soft wax

2/10/2014

Hard wax

n-alkane

What 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

2/10/2014

wax crystal

Wax-forming components in crude oils C10+

Mainly n-alkanes Non-wax

Wax

C7 C8 C9

Lab. analysis Pseudo-components • subtype of the saturates (non-polar compunds without double bonds) • Mainly alkanes of > C18 • Can be linear, branched or cyclic

9 - 2/10/2014

Simple questions – difficult to answer ! Steady-state Wax deposition

Shut-down/restart Gelling

• Will wax accumulate on the pipe wall when the oil flows?

• If so, where and how fast? • How often do we have to pig the line? • Is chemical assistance needed (wax inhibitor)?

Key parameters:

2/10/2014

• When we shut down a pipeline, do we have enough power (pressure) to make it flow again?

• How long will it take to reach normal flow rate?

• Is chemical assistance needed (pour point depressant)?

Wax appearance temperature (WAT) Wax content Pour Point

Wax precipitation and wax depositon Wax precipitation is defined as the formation of solid particles out of the liquid, directly related to thermodynamic properties.

Wax deposition is describing the formation and growth of the precipitated solid on a surface, related to flow and transport process.

3 inch 2 inch

Cold finger device

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Flow loop

Wax precipitation curve Norne crude at 1 bar 8

Wt% solid wax

7 6 5 4 3 2 1 0 -20

-10

0

10

20

Temperature (°C)

2/10/2014

30

40

50

Wax diffusion towards cold surface 1. The cold wall removes wax molecules from the oil 2. Give rise to a diffusion of wax molecules toward the wall

n   wax DM n wax DM dC / dr dC / dT dT / dr

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dC dC dT   wax DM dr dT dr

mass flux of dissolved wax molecules towards the pipe wall density of solid wax molecular diffusion coefficient of dissolved wax molecules concentration gradient of dissolved wax in the laminar sub-layer solubility of wax components as a function of the temperature radial temperature gradient close to the wall

Wax deposition by molecular diffusion Laminar boundary layer

Turbulent core Temperature gradient

Heat loss

WAT

dT/dr dC/dr = dC/dT * dT/dr

Dissolved

Pipe wall

wax

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Wax concentration gradient

dC/dr Velocity profile

Wax depositon_Process 1. Transport to pipe wall

2. Inital wax layer formation

sites

3. Growth

or

4. Aging

Thickness

thin gel

Roughness Hardness

Diffusion Dispersion

Fluid-solid interaction

Crystal growth Trapping of oil

Time Shear/hydrodynamics Diffusion/Counter diffusion

Wax deposition process shown by Rønningsen Rønningsen HP, 6th Int. Conference on Phase Behaviour and Fouling, Keynote speech, 2005

15

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What happens in the pipeline? 7

40

Wax after 7 days

35 30

5

25

Wax after 2 days

4

20 3 15 Wax after 1 day

2

Temperature

1

5

0 0

10

20

30

40

50

60

70

Length (km)

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10

80

90

0 100 110 120

Temperature (C)

wax thickness (mm)

6

Wax deposition modelling in Statoil

 Commercial tools like OLGA, PVTsim  Wax precipitation curve tuning developed internally  Mutivariate analysis 3

Wax content [wt%]

2.5

Cold flow cool down section

2

1.5

Subsea separation and multiphase pumps

1

Water injection pumps

0.5

0 0

10

20

30

40

Wax thickness (mm)

Data Power and control Before tuning distribution unit After tuning

Predicted value Measured value

50

o

Temperature [ C]

Wax precipitation curve tuning 17 2/10/2014

Multivariate analysis validation

The wax build-up can be reproduced 30

…….. but is hard to predict !

•

The pressure build-up can also be reproduced by proper tuning of the roughness effect of the wax deposit, i.e.

– Wax roughness factor

Rough. 0.5 - Diff. 7 - Shear C3 0.7 Rough. 1.0 - Diff. 2 - Shear tuning Rough. 0.5 - Diff. 6

3

200 m wax

20 280 m3 wax 15 10

The wax deposition profile can be reproduced by various combinations of model parameters:

– Diffusion coefficient – Wax porosity – Shear stripping •

wax thickness (mm)

The wax build-up profile in a pipeline can be reproduced using the OLGA (RRR) model.

210 m3 wax

5 0 0

10

20

30

40

50

60

70

80

90

100

110

120

Length (km)

220 Field Pressure

210 Heimdal Export Pressure (bara)

•

25

Rough. 0.5 - Diff. 6

200 190 180 170 160 150 140 130 120 110 100

•

Different ongoing JIP and internalt research ongoing for improving the models

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0

50

100

150

200 250 Time (days)

300

350

400

Outline • Flow Assurance in Statoil • What is wax and what problems may it cause? • How to control wax deposition

• How to monitor wax deposition • Case example: How to not control wax deposition 2/10/2014

Wax deposition challenges

• Stuck pigs • HSE • Inspection tools • Plugged pipelines

2/10/2014

The most famous wax illustration ! • Pipeline between Snorre B and Statfjord B platforms (N. Sea)

• 3 m3 of accumulated wax ahead of pig • Nearly stuck non-bypass pig in riser • Now the line is pigged regularly with optimized bypass pig

Ref. SPE 77573 (2002)

2/10/2014

Methods for controlling wax deposition  Pipeline insulation  External insulation coating on single pipes  Pipe-in-pipe systems  Pigging  Chemicals  Inhibitors  Dispersants  Dissolvers PPD treated oil; this work  Heat  Bundles  Electric heating  Hot oil flushing 2/10/2014

PP-Solid PP-Solid PP-Syntactic PP-Solid PP-Adhesive FBE

PP-Foam

1. 2.

3.

Wax control strategies Single phase oil/condensate pipelines:

–

Wax control normally by regular pigging

Medium length multiphase oil and gas condensate pipelines:

– –

Normally insulated (or heated) Prevents wax deposition and hydrate formation

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?

2/10/2014

Outline • Flow Assurance in Statoil • What is wax and what problems may it cause? • How to control wax deposition

• How to monitor wax deposition • Case example: How to not control wax deposition 2/10/2014

Methods for monitoring of wax deposition Method

Features

Pressure drop

Kind of proven Gives no deposit profile

Pressure pulse

Proven for single phase lines Gives axial deposit distribution

Distributed temperature sensing with fiberoptics

Proven for temperature measurements Potential for deposit detection (utilize insulation effect) Local measurement

Heat pulse monitoring

Not fully qualified (WO 2009/051495) Deposit detection by response to heat pulse (utilize insuation effect) Local measurement

25 2/10/2014

Outline • Flow Assurance in Statoil • What is wax and what problems may it cause? • How to control wax deposition

• How to monitor wax deposition • Case example: How to not control wax deposition 2/10/2014

Heimdal – Brae condensate export pipeline Huldra

Vale Vale Skirne

Heimdal

Statpipe Brae

2/10/2014

Introduction of Vale fluids in 2002 Before 2002, no wax and no pigging performed. Then Vale field started up with high wax content.

Normalized pressure drop, bar

80

WAT (°C) WAX in STO (wt%)

70

Volume rate (Sm3/d)

60

50

Heimdal

Vale

3,2 4,2

24,6 7,3

-22,3 0,5

13,1 4,9

1000

700

300

2000

Start-up waxy cond.

40 30 20 10 0 19.4.01

5.11.01

24.5.02

10.12.02

28.6.03

14.1.04

1.8.04

- Build up of line differential pressure was insignificant until 2004

28 2/10/2014

Huldra Mixture

2004 - 2008 - Foam pigging program - Stuck pigs

2008 -

Fill and soak operation Chemical dissolvant Very good effect in laboratory Only minor effect in field

2008 - 2010 - Foam pigging - Stuck pigs

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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.

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2010: Aggressive pigging! Why change strategy? 1. The pipeline NEEDS to become wax free due to inspection requirements 2. Progressive approach with foam pigs does not work

Two Alternatives for consideration: 1.

Hydraulically Activated Power Pig (HAPP) • Limited experience • Assumed best for downstream facilities

2. High Friction Jetting Pig (HFJP) • Well proven technology • New application

Overall risk was evaluated together with our downstream partners, and the HAPP was chosen

2/10/2014

HAPP pigging operation January 2012 Markland tests before and after

Pig stopped 15.01.12 at 8357 m

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Estimated wax removed by HAPP = 80 m3 Remaining wax in pipeline = approx 350 m3

2013 – High Friction Jet Pig Brae

Heimdal

- Launch 1 off pig from Heimdal using condensate - Pig to be tracked through topsides down to riser hang-off - Pigging speed: ca 0.4 m/s

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500m zone

Finally SUCCESS ~10 m3 wax left in the pipeline (+/- 50%) Reduced from ~350 m3 Wax layer of ~1mm Reduced from up to 20mm

Learning • A main learning:

Consequences of changed operating conditions (e.g. new fluid composition) have to be carefully evaluated and wax control philosophy updated accordingly.

– New tie-backs or reservoirs – Retrograde gas condensates may become significantly leaner as reservoir pressure declines

• An original wax problem may in fact disappear !

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WAT (°C) WAX in STO (wt%) Volume rate (Sm3/d)

Heimdal

Vale

Huldra Mixture

3,2 4,2

24,6 7,3

-22,3 0,5

13,1 4,9

1000

700

300

2000

Year

Mole% C1

Mole% C18+

Bottomhole pressure (bar)

Condensateto-gas ratio Sm3/MSm3

Simulated WAT (PVTsim) (deg C)

2 3 4 5 6 7 8 9 10 11

76,91 77,91 78,39 78,76 79,72 79,89 79,53 79,45 79,30 78,65

0,928 0,406 0,280 0,173 0,098 0,036 0,017 0,009 0,007 0,004

485

549 418 346 290 226 189 166 146 132 122

22 16 11 6 -2