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

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2/10/2014

Flow Assurance

Wellbore hydraulics Transient pipeline

thermohydraulics

Chemical Injection Package

Fluid properties

Rheology

Multiphase equipment:

Multiphase meter

Process

Separator

Slug catcher

Scale control Asphaltene control

Wax control Hydrate control

Emulsion 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 = safe, uninterrupted and simultaneous transport of gas, oil and water from reservoirs to processing facilities.

Fluid control the problems

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Asphaltenes

Kristin-NJ/DR Wye

- wax deposition and temperature profile after 600 h

0

0.001

0.002

0.003

0.004

0.005

0 20 40 60 80 100

Pipeline length [km]

Wa

x d

ep

os

itio

n [

m]

0

10

20

30

40

50

60

70

Te

mp

era

ture

[C

]

Wax

deposition

Fluid

temperature

Wax

Gas hydrates

The future .

2/10/2014

Longer distance

More difficult

fluids

Deeper

water

Increased field

complexity

Arctic / harsh

environment

Outline






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What is wax?

2/10/2014

Soft wax Hard wax

Wax consistency

range

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

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n-alkane

wax

crystal

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Wax-forming components in crude oils

Non-wax

Mainly n-alkanes

Wax

C7 C8

C9

C10+

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 -

Simple questions difficult to answer !

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)?

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)?

Steady-state

Wax deposition

Shut-down/restart

Gelling

Key parameters: Wax appearance temperature (WAT)

Wax content

Pour Point

2/10/2014

11

Wax precipitation and wax depositon

3 inch

2 inch

Flow loop Cold finger device

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.

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Wax precipitation curve

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Norne crude at 1 bar

0

1

2

3

4

5

6

7

8

-20 -10 0 10 20 30 40 50

Temperature (C)

Wt%

so

lid

wax

13 - 2/10/2014

Wax diffusion towards cold surface

dr

dT

dT

dCD

dr

dCDn MwaxMwax

n mass flux of dissolved wax molecules towards the pipe wall

wax density of solid wax

DM molecular diffusion coefficient of dissolved wax molecules

dC / dr concentration gradient of dissolved wax in the laminar sub-layer

dC / dT solubility of wax components as a function of the temperature

dT / dr radial temperature gradient close to the wall

1. The cold wall removes wax molecules from the oil

2. Give rise to a diffusion of wax molecules toward the wall

14 - 2/10/2014

Wax deposition by molecular diffusion

Wax concentration gradient

Dissolved

wax

WAT

Temperature gradient

Velocity profilePip

e w

all

Heat loss

Turbulent coreLaminar boundary

layer

dT/dr

dC/dr

dC/dr = dC/dT * dT/dr

15

Wax depositon_Process

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Wax deposition process shown by Rnningsen

Rnningsen HP, 6th Int. Conference on Phase Behaviour and

Fouling, Keynote speech, 2005

1. Transport

to pipe wall

2. Inital wax

layer formation 3. Growth 4. Aging

Thickness

Roughness

Hardness

sites

Fluid-solid

interaction

Crystal growth

Trapping of oil Time

Shear/hydrodynamics

Diffusion/Counter diffusion

Diffusion

Dispersion

or

thin gel

What happens in the pipeline?

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0

1

2

3

4

5

6

7

0 10 20 30 40 50 60 70 80 90 100 110 120

Length (km)

wax

th

ick

ne

ss (

mm

)

0

5

10

15

20

25

30

35

40

Te

mp

era

ture

(C

)

Wax after 1 day

Wax after 2 days

Wax after 7 days

Temperature

Wax deposition modelling in Statoil

17

Power and control

distribution unit

Cold flow cool

down section

Subsea separation and

multiphase pumps

Water injection

pumps

Commercial tools like OLGA, PVTsim Wax precipitation curve tuning developed internally

Mutivariate analysis

Temperature [oC]

Wax c

on

ten

t [w

t%]

0 10 20 30 40 500

0.5

1

1.5

2

2.5

3

Data

Before tuning

After tuning

Wax precipitation curve tuning

Predicted value

Measured value

Wax th

ickn

ess (

mm

)

Multivariate analysis validation

2/10/2014

The wax build-up can be reproduced

18

100

110

120

130

140

150

160

170

180

190

200

210

220

0 50 100 150 200 250 300 350 400

Time (days)

He

imd

al

Ex

po

rt P

res

su

re (

ba

ra)

Field Pressure

Rough. 0.5 - Diff. 6

0

5

10

15

20

25

30

0 10 20 30 40 50 60 70 80 90 100 110 120

Length (km)

wa

x t

hic

kn

es

s (

mm

)

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

280 m3 wax

210 m3 wax

200 m3 wax The wax build-up profile in a pipeline can be

reproduced using the OLGA (RRR) model.

.. but is hard to predict !

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

Diffusion coefficient

Wax porosity

Shear stripping

The pressure build-up can also be reproduced by proper tuning of the roughness effect of the wax

deposit, i.e.

Wax roughness factor

Different ongoing JIP and internalt research ongoing for improving the models

2/10/2014

Outline






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Wax deposition

challenges

Stuck pigs

HSE

Inspection tools

Plugged pipelines

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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

Heat Bundles

Electric heating

Hot oil flushing

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FBE

PP-Adhesive

PP-Solid

PP-Syntactic

PP-SolidPP-Foam

PP-Solid

FBE

PP-Adhesive

PP-Solid

PP-Syntactic

PP-SolidPP-Foam

PP-Solid

PPD treated oil; this workPPD treated oil; this work

Wax control strategies 1. 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 (Snhvit):

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






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

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Outline






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Vale

Skirne

Huldra

Vale

Skirne

Brae Statpipe

Vale

Skirne

Vale

Heimdal

Vale

Huldra

Vale

Brae Statpipe

Vale Vale

Heimdal

Heimdal Brae condensate export pipeline

Introduction of Vale fluids in 2002

- Build up of line differential pressure was insignificant until 2004

Before 2002, no wax and no pigging performed. Then Vale field started up with

high wax content.

0

10

20

30

40

50

60

70

80

19.4.01 5.11.01 24.5.02 10.12.02 28.6.03 14.1.04 1.8.04

No

rmal

ize

d p

ress

ure

dro

p, b

ar

Start-up waxy cond.

28

Heimdal Vale Huldra Mixture

WAT (C) 3,2 24,6 -22,3 13,1

WAX in STO (wt%) 4,2 7,3 0,5 4,9

Volume rate (Sm3/d) 1000 700 300 2000

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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

2/10/2

014

29

30 - 2/10/2014

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.

2010: Aggressive pigging!

Two Alternatives for consideration:

1. Hydraulically Activated Power Pig (HAPP)

Limited experience Assumed best for downstream facilities

Why change strategy?

1. The pipeline NEEDS to become wax free due to inspection requirements

2. Progressive approach with foam pigs does not work

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

Estimated wax removed by HAPP = 80 m3

Remaining wax in pipeline = approx 350 m3 Pig stopped 15.01.12 at 8357 m

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2013 High Friction Jet Pig

2/10/2014

500m

zone

Heimdal Brae

- 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

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 !

34

Year Mole% C1 Mole%

C18+

Bottomhole

pressure

(bar)

Condensate-

to-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

65

549

418

346

290

226

189

166

146

132

122

22

16

11

6

-2

2/10/2014

Thank you

Documents

Excellant Wax PPT