flow assurance: gas hydrates and wax...flow assurance: gas hydrates and wax – december 2003...

Flow Assurance: Gas Hydrates and Wax – December 2003 Steering Committee Meeting

Flow Assurance:Gas Hydrates and Wax

December 2002-November 2005 Programme


Objectives• Hydrate formation in low water content gases

• Hydrate inhibition, inhibitor loss and/or salt precipitation in methanol, glycol, and salt systems

• Hydrate stability zone of oil systems at high pressure conditions

• Gas hydrates in water-oil emulsions

• Hydrates in high water cut (50-90%) oil systems

• Wax phase boundary, and effect of wax on hydrates (and vice versa)


Hydrates in low water content gases• Water content in gas systems

– Experimental measurements (gas, water, ice, hydrates)– Reliability of the measurements

– Extension to other conditions– Reliability of the assumptions

• Hydrate phase equilibria in low water content gasesProgress in the last six months• Theoretical

– Thermodynamic modelling (Lw-V, H-V, I-V regions)– Semi-empirical correlation and comparison with an existing model

• Experimental– Methane solubility in EG aqueous solutions– Water dew point measurement using QCM


Hydrate inhibition in methanol, glycol, and salt systems• Salts and organic inhibitor systems

– Hydrate inhibition– Salting-out– Inhibitor distribution

Progress in the last six months• Thermodynamic modelling of EtOH, NaCl-EtOH and

KCl-MeOH• Hydrate phase boundary measurements (MeOH-NaCl,

MeOH-KCl, EtOH, EtOH-NaCl)• Correlation for estimating gas hydrate inhibition,

extension to MeOH-KCl


Hydrate stability zone of oil systems at high pressure conditions• Deepwater operations and long tiebacks• Limited available data• Measurement challenges

– Visual techniques– P vs T techniques

Progress so far• Construction and commissioning of the very high

pressure hydrate cell (2,000 bar, 30,000 psia)• Nitrogen hydrate phase boundary measurements• Oil with distilled water and aqueous ethanol solutions


Wax-hydrate combinations• Wax and hydrates in subsea pipelines• Wax phase boundary determination

– Experimental (WAT vs WDT, step-heating)– Thermodynamic modelling

Progress in the last six months• Experimental

– QCM in measuring WAT and WDT for a gas condensate and synthetic mixtures

– Effect of light components– Hydrates and wax

• Modelling– Developing a new wax semi-empirical correlation


Gas hydrates in water-oil emulsions• Flow assurance in oil systems

– Water-oil emulsions– Natural inhibition– Effect of water cut, turbulence, etc.

Progress in the last six months

• Simulating various production scenarios in a Brazilian oil with 50% water cut

• Micromodel studies

• Visual rig results

Experimental Work:

HYDRATE MEASUREMENTS

Ross AndersonRod Burgass

Hydrates: Outline

Hydrate dissociation points measured for:

• Single inhibitors– Methane with Ethanol

• Mixed salt-organic inhibitor systems (480 bar)– Methane with Methanol / NaCl– Methane with Methanol / KCl– Methane with Ethanol / NaCl

• Oil systems – High pressure (1500 bar)– Crude with distilled water and with ethanol

Hydrates: Experimental Methods

• Single/mixed inhibitors with methane– Rig-1– Isochoric step-heating techniques

• Oil systems– Very High Pressure Rig– Isochoric step-heating techniques

• Experimental methods detailed in March 2003 Progress Report

Hydrates: Methane with Ethanol

10

100

1000

-10 -5 0 5 10 15 20 25 30

T / C

P / b

ar

15 mass% Ethanol, Kobayashi et al (1951)15 mass% Ethanol, Previous Project30 mass% Ethanol, This workC1, bulk

C1 bulk data:Deaton and Frost (1946)Mcleod and Campbell (1961)Jhaveri and Robinson (1965)

Hydrates: Methane with Methanol / NaCl

10

100

1000

-25 -20 -15 -10 -5 0 5 10 15 20 25 30

T / C

P / b

ar

5.63% NaCl / 9.43% MeOH4.44% NaCl / 28.64% MeOH10.56% NaCl / 8.91 % MeOHC1, bulk


Triangles = Jager and Sloan (2002)

Hydrates: Methane with Methanol / KCl

10

100

1000

-15 -10 -5 0 5 10 15 20 25 30

T / C

P / b

ar

10 mass% KCl / 15 mass% MeOH7 mass% KCl / 25 mass% MeOHC1, bulk


Hydrates: Methane with Ethanol / NaCl

10

100

1000

-20 -15 -10 -5 0 5 10 15 20 25 30

T / C

P / b

ar

10 mass% NaCl / 10 mass% Ethanol7 mass% NaCl / 30 mass% EthanolC1, bulk


Hydrates: High Pressure Oil Data

• Dead North Sea Crude

• Known composition (from Reservoir Fluids project)

• Added light components to make ‘live’

• Bubble point measured

• Hydrate dissociation points measured (to 1500 bar) for:– Distilled water– 16 mass% ethanol

CO

2 N2

C1

C2

C3

iC4

nC4

iC5

nC5

C6 C7 C8

C9

C10

C11

C12 C13

C14

C15

C16

C17

C18

C19

C20

C21

+

0

10

20

30

40

50

60

CO2 C1 C3

nC4

nC5 C7 C9

C11 C13 C15 C17 C19C21

+

Mol

e%High Pressure Hydrate Tests: Oil Composition

Component

High Pressure Hydrate Tests: Hydrate Stability Zone

0

500

1000

1500

0 5 10 15 20 25 30 35

T / C

P / b

ar

Distilled water16 mass% ethanolBubble Point (21C, 165.5 bar)

Abovebubble point

Flow Assurance: Gas Hydrate and Wax - December 2003 Steering Committee Meeting

Thermodynamic ModellingSalts and Organic Inhibitors

Rahim (Amir) Masoudi


Outline• Thermodynamic modelling of EtOH,

NaCl-EtOH, and KCl-MeOH

• Validation of the model for gas hydrate

• Validation of the newly developed correlation for KCl-MeOH

• Conclusions


Thermodynamic modelling

• Scenarios for Salt Precipitation:Temperature reductions as fluids are transported from the reservoir to the surface.Concentration of the brine downhole increases as produced gas strips water, leaving the salt behind.Reduction in CO2 Concentration in the aqueous phase can result in the deposition of bicarbonate as carbonates.The addition of organic hydrate inhibitors reduces salt solubility in the aqueous phase.

Formation Water

Organic Inhibitors

Salt deposition



• The new thermodynamic approachSalt is treated as a pseudo component while its critical properties and acentric factor are optimised.Valderrama-Patel-Teja (VPT) EoSNon-Density Dependent (NDD) Mixing RulesSolid solution theory of van der Waals and Platteeuw

• Data requirements:Initial guess for Critical properties of salt (TC, PC, VC,ZC)Experimental data

Freezing point of salt aqueous solutionsBoiling point of salt aqueous solutionsSalt solubility



• Binary Interaction Parameters (BIPs) OptimisationWater-SaltSalt-SaltSalt-Organic InhibitorGas-Salt

• NaCl, KCl and CaCl2 as well as MEG have already been modelled.


Summarising the capabilities of the modelSummarising the capabilities of the model

• Salt precipitation

• Hydrate stability zone

• Maximum hydrate inhibition effect

• Gas solubility

• Freezing point prediction

• Boiling point prediction

• Vapour pressure prediction

• Composition of all present equilibrium phases


Modelling ethanolModelling ethanol

• Freezing point temperature of aqueous ethanol solutions.

-40.00

-30.00

-20.00

-10.00

0.00

0 10 20 30 40 50

EtOH / mass%

T / C

Exp., CRC

Exp., ICT

Predictions, this work


Modelling ethanolModelling ethanol

• T-x diagram of the binary ethanol/water.

72

77

82

87

92

97

102

0 20 40 60 80 100

EtOH / mass%

T / C

Exp., 640 mmHg, ICTPrediction, 640 mmHgExp., 700 mmHg, ICTPrediction, 700 mmHgExp., 760 mmHg, ICTPrediction, 760 mmHgExp., 800 mmHg, ICTPrediction, 800 mmHg


Modelling KCl and methanolModelling KCl and methanol

• Experimental and calculated freezing point temperature for ternary KCl/MeOH/water mixtures

KCl MeOH Experimental Calculated AD(mass%) (mass%) (C ± 0.2) ( C ) ( C )

3.0 2.7 -3.4 -3.2 0.24.9 5.2 -6.1 -6.3 0.27.1 7.7 -9.9 -9.9 0.09.7 10.2 -14.2 -14.6 0.4

Freezing Point temperature


Modelling KCl and methanolModelling KCl and methanol

• Experimental and calculated boiling point temperature for ternary KCl/MeOH/water mixtures

KCl MeOH Experimental Calculated AD(mass%) (mass%) (C ± 0.2) ( C ) ( C )

2.6 3.6 96.2 97.0 0.819.2 4.3 94.9 94.9 0.04.9 4.5 94.9 96.0 1.19.6 10.2 89.6 90.5 0.913.8 16.4 84.0 84.4 0.46.1 27.9 81.0 81.3 0.3

Boiling Point temperature


Modelling salt precipitationModelling salt precipitation

• Solubility of KCl in aqueous methanol solutions as a function oftemperature.

0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50

T / C

KCl /

mas

s%

Exp., 0 mass% MeOHExp., 10 mass% MeOHExp., 20 mass% MeOHExp., 40 mass% MeOHExp., 50 mass% MeOHPredictions

exp. data: Deepstar data (0.0 ºC); Pinho S.P. & Macedo E.A., 1996 (25, 50 ºC)



• Solubility of KCl in aqueous methanol solutions as a function ofmethanol concentration.

0

5

10

15

20

25

30

0 10 20 30 40 50

MeOH / mass%

KCl /

mas

s%

exp., 0 deg C, Deepstar dataexp., 25 deg C, Pinho & Macedo (1996)exp., 50 deg C, Pinho & Macedo (1996)Predictions


Modelling NaCl and ethanolModelling NaCl and ethanol

• Experimental and calculated freezing point temperature for ternary NaCl/EeOH/water mixtures

NaCl EtOH Experimental Calculated AD(mass%) (mass%) (C ± 0.2) ( C ) ( C )

2.6 3.5 -3.5 -3.3 0.25.0 5.3 -6.4 -6.2 0.28.3 7.5 -11.1 -10.9 0.2

10.1 9.9 -14.8 -15.1 0.312.7 12.7 -21.7 -21.6 0.1

Freezing Point temperature


Modelling NaCl and ethanolModelling NaCl and ethanol

• Experimental and calculated boiling point temperature for ternary NaCl/EeOH/water mixtures

NaCl EtOH Experimental Calculated AD(mass%) (mass%) (C ± 0.2) ( C ) ( C )

2.6 3.5 95.5 95.8 0.35.0 5.3 92.5 93.5 1.0

21.0 4.1 92.0 91.6 0.410.1 9.9 87.4 88.4 0.915.1 15.9 82.8 82.8 0.06.4 33.2 81.8 82.2 0.4

Boiling Point temperature



• Solubility of NaCl in aqueous ethanol solutions as a function oftemperature.

0

5

10

15

20

25

30

25 35 45 55 65 75

T / C

NaC

l / m

ass%

Exp., 0.0 mass% EtOHExp., 10 mass% EtOHExp., 20 mass% EtOHExp., 40 mass% EtOHExp., 50 mass% EtOHPredictions, this work

Exp. data: Pinho & Macedo , 1996



• Solubility of NaCl in aqueous ethanol solutions as a function ofethanol concentration.

0

5

10

15

20

25

30

0 10 20 30 40 50

EtOH / mass%

NaC

l / m

ass%

Exp., 25 deg C

Exp., 50 deg C

Exp., 75 deg C


Exp. data: Pinho & Macedo , 1996






• Conclusions


Methane hydrate dissociation point in the presence of ethanol aqueous solutions

10

1000

-8 -3 2 7 12 17 22 27

T / C

P /

bar

Exp., distilled waterExp., 15 mass% EtOH, Kobayashi (1951)Exp., 15 mass% EtOH, this workExp., 30 mass% EtOH, this workPredictions

C1-distilled water data:Deaton and Frost (1946)Mcleod and Campbell (1961)Jhaveri and Robinson (1965)


Carbon dioxide hydrate phase boundaries in the presence of KCl and MeOH aqueous solutions

1

10

100

-8 -6 -4 -2 0 2 4 6 8

T / C

P /

bar

Exp., Pure water

Exp., 5 mass% MeOH + 10 mass% KCl

Exp., 10 mass% MeOH + 10 mass% KCl


Exp. data: Dholabhai, 1996CO2 Hydrate


80% CH4 + 20% CO2 hydrate phase boundaries in the presence of KCl and MeOH aqueous solutions

10

100

-7 -2 3 8 13

T / C

P /

bar

Exp., Pure water Exp., 5 mass% MeOH + 10 mass% KClPredictions, this work

Exp. data: Dholabhai, 1997 & 1994

80% CH4 + 20% CO2


Methane hydrate phase boundaries in the presence of KCl and MeOH aqueous solutions

10

1000

-21 -17 -13 -9 -5 -1 3 7 11 15 19 23

T / C

P /

bar

Exp., distilled waterExp., 10 mass% KCl + 15 mass% MeOHExp., 7 mass% KCl + 25 mass% MeOHPredictions



Methane hydrate phase boundaries in the presence of NaCl and EtOH aqueous solutions

10

1000

-21 -17 -13 -9 -5 -1 3 7 11 15 19 23

T / C

P / b

ar

Exp., distilled waterExp., 10 mass% NaCl + 10 mass% EtOHExp., 7 mass% NaCl + 30 mass% EtOHPredictions







• Conclusions


Existing correlations• No general correlation for a combination

of salts and/or organic inhibitors

• Shortcomings:

Effect of the system pressure

Effect of the gas/oil composition

Effect of the type of the inhibitor


New CorrelationNew Correlation

- P: Pressure of the system (kPa)- W: Concentration in the solution (mass%)- P0: Dissociation pressure in the presence of

distilled water at 273.15 K (kPa)- Ci and D1: Constants

PDPWW

TPWW

WT

WPWW

T ISI

IS

IS

IS

SSI *

*021.0*

**

* 1

+

+∆+

+∆+

=∆

orST∆ ( )( )( )1)1000()ln( 06543

32

21 +−+++=∆ PCCPCWCWCWCT IIII


Methane hydrate phase boundaries in the presence of NaCl aqueous solutions

10

100

1000

-13 -8 -3 2 7

T / C

P /

bar

Exp., 11.8 mass% NaClExp., 21.5 mass% NaClNew CorrelationHammerschmidt CorrelationYousif & Young Correlation

Exp. data: de Roo et al. 1983


Methane hydrate phase boundaries in the presence of NaCl and KCl aqueous solutions

10

100

-11 -6 -1 4 9

T / C

P / b

ar

Exp., 3 mass % NaCl + 3 mass% KClExp., 5 mass% NaCl + 10 mass% KClExp., 5 mass% NaCl + 15 mass% KClNew CorrelationYousif & Young CorrelationPure water, HWHYD model

CH4 Hydrate

exp. data: Dholabhai, 1991


Carbon dioxide hydrate phase boundaries in the presence of KCl and MeOH aqueous solutions

1

10

100

-9 -7 -5 -3 -1 1 3 5 7 9

T / C

P /

bar

Pure Water, HWHYDExp., distilled water Exp., 5 mass% MeOH + 10 mass% KClExp., 10 mass% MeOH + 10 mass% KClNew Correlation

CO2 Hydrate exp. data: Dholabhai, 1996


Methane hydrate phase boundaries in the presence of KCl and MeOH aqueous solutions

10

1000

-21 -17 -13 -9 -5 -1 3 7 11 15 19 23

T / C

P /

bar

Exp., distilled waterHWHYDExp., 10 mass% KCl + 15 mass% MeOHExp., 7 mass% KCl + 25 mass% MeOHNew Correlation



Conclusions• Modelling EtOH, KCl-MeOH, and NaCl-EtOH

was successfully implemented.

• Precipitation of NaCl in EtOH and KCl in the MeOH aqueous solutions was modelled.

• Comparison with the independent experimental data, has demonstrated the reliability of the developed model.

• Newly developed correlation capable of predicting hydrate inhibition effect of salts and/or organic inhibitors was validated for KCl-MeOHsystems.

EXPERIMENTAL WORK GAS/WATER EQUILIBRIA

Ross Anderson, Antonin Chopy, Rod Burgass

• Measurements of methane solubility in aqueous solutions of ethylene glycol

• Discussion on possible methodology for measurement of amount of water in gas phase in equilibrium with water/hydrates/ice

• Initial measurements of water dew point in methane water mixtures

EXPERIMENTAL WORK GAS/WATER EQUILIBRIA

Flow Assurance: Gas Hydrate and Wax – December 2003 Steering Committee Meeting

Gas Solubility: Experimental Equipment

Measured methane solubility in 20 mass% aqueous EG solutions as a function of P and T. Mole% methane is

relative to moles of the liquid phase

0.00

0.05

0.10

0.15

0.20

0.25

0 20 40 60 80 100

P / bar

Mol

e% C

H 4

0.15.09.924.849.6

Isotherms / C

20 mass% Ethylene Glycol

Measured methane solubility in 40 mass% aqueous EG solutions as a function of P and T. Mole% methane is

relative to moles of the liquid phase

0.00

0.05

0.10

0.15

0.20

0.25

0 20 40 60 80 100

P / bar

Mol

e% C

H 4

0.1524.849.6

Isotherms / C

40 mass% Ethylene Glycol

Experimental data (this work and literature data) showing the effect of EG on methane solubility. Mole% methane

data for EG solutions are plotted on an EG-free basis

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 20 40 60 80 100

P / bar

Mol

e% C

H 4

40 mass% EG, This work

20 mass% EG, This work

Distilled H2O, Culberson andMcKetta (1951)Distilled H2O, Yang et al. (2001)

Distilled H2O, Wang et al. (2001)

Temperature = 25 C

Methods used to make measurements of water in gasDirect methods• The gravimetric hygrometer• The dew point mirror (Chilled mirror)• Karl-Fischer titrationIndirect methods• Spectroscopic• Chromatographic • Hygroscopic methods

Water dew-point measurements using a QCM

• Importance of measurement

• Difficulty of measurement

• Conventional method for measuring amount of water in gas using QCM

• Proposed method

Plot of temperature vs resonant frequency for tests with dry methane and with methane equilibrated with water at

laboratory temperature

4975450

4975500

4975550

4975600

4975650

4975700

4975750

12 15 18 21 24 27 30 33 36 39 42 45T/C

QC

M re

sona

nt fr

eque

ncy/

Hz DRY METHANE

METHANE/WATER

Plot of temperature vs resonant frequency for test with methane equilibrated with water at laboratory temperature

4975450

4975470

4975490

4975510

4975530

4975550

13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45T/C

QC

M re

sona

nt fr

eque

ncy/

Hz

ADSORPTION

Peak of test with methane equilibrated with water at laboratory temperature

4975520

4975522

4975524

4975526

4975528

4975530

17 18 19 20 21 22 23 24 25 26 27 28 29T/C

QC

M re

sona

nt fr

eque

ncy/

Hz

LABORATORY TEMPERATURE

Plot of temperature vs resonant frequency for sample of laboratory air

4975460

4975480

4975500

4975520

4975540

4975560

4975580

4975600

4975620

4975640

0 5 10 15 20 25 30 35 40 45

T/C

QC

M re

sona

nt fr

eque

ncy/

Hz

ADSORPTION

DEW POINT MEASURED VISUALLY

Further work required to fully evaluate proposed method

• What type of QCM surface is best, polished, non-polished or roughened?

• Should the measurement be made with the temperature being changed step-wise or continuously?

• Should the measurement be made on cooling or heating or both?

• What is the accuracy and repeatability of the data?• Can the method be used for measurements at low

moisture contents, low temperature-high pressure?• Would a combination of methods give more reliable

results?


Water Content of Gases


• Collecting the existing VLE data

• Tuning the BIPs in the model for predicting the water content of gases at low temperature conditions

• Developing a semi – empirical approach

Outline


A Typical P-T Diagram for Water – Hydrocarbon System

T

log

(P)

H - LHC

H-V

HC Vapour Pressure

I-V

LW - V

Q 2

Q 1I-H-V Water Vapour Pressure

H-V

H - LHC

L W-H-V

L W-H-L HC

Water Sublimation Pressure


Typical Methane Solubility in Water at 25 oC

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0 20 40 60 80 100 120 140 160 180

P/bar

mol

e fra

ctio

n

Chapoy et al. (2003)aKim et al. (2003)Yang et al. (2001)Wang et al. (1995)Yokoyama et al. (1988)Duffy et al. (1961)Culberson and McKetta (1951)Culberson et al. (1950)Michels et al. (1936)


Typical Water Content of Methane at 100 bar

1

10

100

1000

-40 -30 -20 -10 0 10 20 30 40 50

T/ °C

mg/

Nm3

Chapoy et al. (2003)cGERG (2000)KSEPL WAGA (Supplied by Shell)GPA RR45 by interpolation (Supplied by Shell)Dhima et.al. (2000)Ugrozov (1996) + Olds et.al. (1942)Yarym - Agaev et al. (1985)Kosyakov et al. (1982)STFlash phase transitions (Supplied by Shell)

H-V region

Lw- V region


Which Data?

• Vapour-Liquid Equilibria– Gas solubility in the water rich– Water mole fraction in the gas phase

• Gas Solubility Data for Tuning the BIPs at low temperature conditions.


Model Description

• fwH = fw

V H-V Equilibrium

• fiLw= fi

V (i = 1, N) Lw-V Equilibrium

• fwI = fw

V I-V Equilibrium


Predictions (Water Content of Methane at 100 bar)

1

10

100

1000

-40 -30 -20 -10 0 10 20 30 40 50

T/ °C

mg/

Nm3

Chapoy et al. (2003)cGERG (2000)KSEPL WAGA (Supplied by Shell)GPA RR45 by interpolation (Supplied by Shell)Dhima et.al. (2000)Ugrozov (1996) + Olds et.al. (1942)Yarym - Agaev et al. (1985)Kosyakov et al. (1982)GERG model predictionSTFlash predictionSTFlash phase transitions (Supplied by Shell)This prediction

H-V region

Lw- V region


Results (Water Content of Methane in the H-V Region)

Experimental data from Aoyagi et al. (1980)

1

10

100

1000

-35 -30 -25 -20 -15 -10 -5 0

T/ °C

mg/

Nm3

Experimental (34.5 bar)

Experimental (69 bar)

Experimental (103.4 bar)

This Prediction


Results (Water Content of CO2)

900

1900

2900

3900

4900

5900

6900

7900

10 100 1000

P/bar

mg/

Nm3

Nakayama et al. (1987); 25 °CCoan and King (1971); 25 °CWiebe and Gaddy (1941); 25 °CThis Prediction; 25 °CDohrn et al. (1993); 50 °CD'Souza et al. (1988); 50 °CBriones et al. (1987); 50 °CCoan and King (1971); 50 °CSidorov et al. (1953); 50 °CWiebe and Gaddy (1941); 50 °CThis Prediction; 50 °C


Estimation of Water Dew Point Temperature (oC) of Methane

Using Bukacek Correlation and HWHYD Model.Pressure

/ barWater Content /

mg/Nm3Bukacek

correlationHWHYD model ∆T

150 319.97 25 26.15 1.15

100 404.99 25 26.33 1.33

50 660.14 25 26.07 1.07

20 1426.58 25 25.56 0.56

130 211.82 16 17.51 1.51

90 261.81 16 17.62 1.62

40 464.99 16 17.14 1.14

20 830.96 16 16.68 0.68


Semi – Empirical Approach

• fiLw= fi

V (i = 1, N) :VLE

• yw=

• yw=

• φw= exp(BP + CP 2)

• B = a + & C = c + Tb

Td

))(exp()1(

RTPPv

PPx sat

wLw

w

satwwg −−

φγ

))(exp(RT

PPvP

P satw

Lw

w

satw −

φ


Composition of a Sweet Natural Gas

Component Mole % Helium 0.028

Nitrogen 1.938 Carbon Dioxide 0.851

Methane 93.216 Ethane 2.915

Propane 0.715 i-Butane 0.093 n-Butane 0.135

C5 0.058 C6+ 0.049


A Comparison Between the Predictions of This Approachand Bukacek Correlation for Water Content (mole fraction)

of Natural Gas

T /K P /MPa SGg Water Content

Experimental data

Estimated Water Content (This

Approach) AD %

Estimated Water Content

(Bukacek) AD %

293.15 6 0.598 4.65E-04 4.74E-04 1.85 5.39E-04 15.81

293.15 10 0.598 3.26E-04 3.33E-04 2.23 3.83E-04 17.47

288.15 1.5 0.598 1.16E-03 1.19E-03 2.22 1.25E-03 7.73

288.15 4 0.598 4.68E-04 4.84E-04 3.53 5.44E-04 16.38

288.15 6 0.598 3.56E-04 3.47E-04 2.56 4.02E-04 12.92

288.15 8 0.598 2.72E-04 2.82E-04 3.45 3.31E-04 21.58

283.15 1.5 0.598 8.42E-04 8.57E-04 1.78 9.11E-04 8.13

283.15 6 0.598 2.51E-04 2.51E-04 0.09 2.97E-04 18.31

278.15 0.5 0.598 1.68E-03 1.77E-03 5.7 1.82E-03 8.21

278.15 1.5 0.598 6.05E-04 6.09E-04 0.72 6.53E-04 7.98

278.15 4 0.598 2.58E-04 2.49E-04 3.81 2.90E-04 12.17


Comparison of the Results in Diagram

0

0.0004

0.0008

0.0012

0.0016

0 5 10 15 20 25

T/C

mol

frac

tion

Experimental (GERG)This approachBukacek correlation

60 bar

15 bar


Conclusions (1)

• A comprehensive literature survey was made on the existing VLE data.

• BIPs between Methane – Water and CO2 –Water systems were tuned using gas solubility data.

• VLE data on other components of natural gases (C2, C3, N2, etc) at low temperatures conditions are necessary to further develop the thermodynamic model.


Conclusions (2)

• The results of water content / water dew point are comparable with the recommended predictive methods.

• A semi – empirical approach was developed to predict the water content of gases in the Lw – V and I – V regions. The results are in very good agreement with experimental data.

EXPERIMENTAL WORK: WAX AND HYDRATE MEASUREMENTS

Rod Burgass

• WAX MEASUREMENTS FOR SYNTHETIC MIXTURES OF ALKANES USING QUARTZ CRYSTAL MICROBALANCE

• WAX AND HYDRATE MEASUREMENTS ON A SYNTHETIC MIXTURE OF ALKANES

EXPERIMENTAL WORK: WAX AND HYDRATE MEASUREMENTS

Flow Assurance: Gas Hydrate and Wax – December 2003 Steering Committee Meeting

Schematic of Quartz Crystal Microbalance (QCM)

Schematic of QCM rig for measurement on dead fluids

Wax Appearance Temperature (WAT) for a separator condensate using QCM

4987500

4988000

4988500

4989000

4989500

4990000

293 298 303 308 313 318 323 328T/K

Res

onan

t fre

quen

cy/H

z

COOLING 10 MINUTES PER TEMPERATURE STEP

WAT 299K

Wax Disappearance Temperature (WDT) for a separator condensate using QCM

4987500

4988000

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4989500

4990000

293 298 303 308 313 318 323 328T/K

Res

onan

t fre

quen

cy/H

z

HEATING 2 HOURS PER TEMPERATURE STEP

WDT 313KVISUAL WDT 309K

Example of WAT measurement for a synthetic hydrocarbon mixture using a QCM with a roughened

surface

-800

200

1200

2200

3200

4200

5200

0 1 2 3 4 5 6 7 8

T/C

Cha

nge

in re

sona

nt fr

eque

ncy/

Hz

WAT

Composition of synthetic hydrocarbon Mixture for components heavier than C4

Component

Mass%

Mole%

C10 94.61 97.52 C21 1.71 0.84 C22 1.25 0.59 C23 0.92 0.41 C24 0.67 0.29 C25 0.49 0.20 C26 0.36 0.14

WAT measurements, using QCM, at different pressures for synthetic hydrocarbon mixture (components heavier

than C4)

0

100

200

300

400

0 1 2 3 4 5 6 7 8 9 10

T/C

P/ba

r

Composition of synthetic hydrocarbon Mixture with light components (live). Bubble point measured as 119.7 bar

at OoC.

Component

Mass%

Mole%

CO2 0.46 1.46

C1 7.13 39.42 N2 0.30 0.61 C2 0.87 2.56 C3 0.38 0.76 iC4 0.07 0.10 nC4 0.12 0.18 iC5 0.04 0.05 C10 85.76 53.49 C21 1.55 0.46 C22 1.14 0.32 C23 0.83 0.23 C24 0.61 0.16 C25 0.44 0.11 C26 0.32 0.08

WAT measurements, using QCM, at different pressures for synthetic hydrocarbon mixture without and with light

(C1-C4) components

0

100

200

300

400

0 1 2 3 4 5 6 7 8 9 10

T/C

P/ba

r

Live fluid

Summary of wax and hydrate measurements for synthetic hydrocarbon mixture

0

100

200

300

400

0 2 4 6 8 10 12 14 16 18 20

T/C

P/ba

r

Hydrate dissociation points

Flow Assurance: Gas Hydrates and Wax - December 2003 Steering Committee Meeting

Thermodynamic Modelling -Wax

Hongyan Ji


Predictive mathematic models for wax

WAX MODELConventional thermodynamic model

Empirical model

Thermodynamic descriptionEoS &/ activity coefficient equationNumerical iterationSpecific software package?Composition data required

DetailedBothMulti-stepYesAll compounds

SimplifiedThe latterFewNoFew compounds


• Conventional thermodynamic model: Heriot-Watt WAX (HWWAX) model – It has been developed in previous studies.– Its reliability has been validated against independent

experimental data (WDT, precipitated wax amount and composition).

• Empirical model– It is developed in this work.

Predictive mathematic models for wax


The empirical model developed in this work

• Thermodynamic basis

• Necessary parameters

• Applications of the empirical model

• Conclusions

Outline


• The activity coefficient equation is used to both the liquid and the solid phases.

Thermodynamic basis

∫= dPRTvexpfγxf P

P

S/LiOS/OL

iS/L

iiS/L

i O


• For the reciprocal of SLE temperature

• For WDT

Thermodynamic basis

i,mSii

i

i,m Tsx

lnHR

T11

+

∆

−=γ i,m

i HRa

∆−=

i,mi Tb 1=

( )1201−×+

+

= P.

bsx

lnaWDT

kSkk

kk γ

Necessary parametersNecessary parameters

aa and and bb

γγ

ss


Values of a and b

C28: (1/T)*1000 = -0.0904*ln(xk) + 2.9938 R2 = 0.994

C32: (1/T)*1000 = -0.0797*ln(xk) + 2.9346 R2 = 0.999

C36: (1/T)*1000 = -0.0677*ln(xk) + 2.8818 R2 = 0.998

2.0

2.5

3.0

3.5

4.0

-10 -8 -6 -4 -2 0

ln (xk)

(1/T

*100

0)/K

-1

C5-C28, C7-C28, C12-C28C5-C32, C7-C32, C12-C32C5-C36, C7-C36

points for several binaries (based on experimental data))xln(T k−1


Values of a and b

points for binaries (based on data generated by HWWAX))xln(T k−1

C40: (1/T)*1000 = -0.0619*ln(xk) + 2.8321 R2 = 0.9998C50: (1/T)*1000 = -0.0471*ln(xk) + 2.7315 R2 = 0.9985C60: (1/T)*1000 = -0.0355*ln(xk) + 2.6692 R2 = 0.9928

2.0

2.5

3.0

3.5

4.0

-20 -16 -12 -8 -4 0

Ln (xk)

(1/T

*100

0)/K

-1

C10-C40C10-C50C10-C60


Values of a and b

Values of a and b for C21 – C80

-13.0

-11.0

-9.0

-7.0

-5.0

-3.0

-1.0

1.0

3.0

20 30 40 50 60 70 80

carbon number

a*1

05

2.5

2.6

2.7

2.8

2.9

3.0

3.1

3.2

3.3

b*1

03


Value of γ (solid activity coefficient)

Experimental and estimated SLE data for C18-C19 binaries

10

15

20

25

30

35

0 0.2 0.4 0.6 0.8 1

C19 mole fraction

WD

T/o C

exp. data, Robles et al. (1996)T1: est. data, assuming pure C18 solidT2: est. data, assuming pure C19 solidT: est. data, solid mixture and gama=1T: est. data, solid mixture and gama=1.1


Correlation for s (solid composition)

y = 0.0248x3 - 0.1691x2 + 1.1443x

0.0

0.2

0.4

0.6

0.8

1.0

0 0.2 0.4 0.6 0.8 1

X2

S 2

C29-C30C39-C40C59-C60

Solid concentration as a function of liquid concentration


Correlation for s (solid composition)• When applying the s equation to multi-component

systems, normalized xk values are used.

( ) ( ) *k

*k

*kk x.x.x.s ×+×−×= 144311691002480 23

xk*: normalized liquid mole fraction for the heaviest compound.

1−+=

kk

k*k xx

xx

sk: solid mole fraction for the heaviest compound.


Application 1: WDT estimation

( )1201−×+

+

= P.

bsx

lnaWDT

kSkk

kk γ

•Input data–Liquid compositions for the two heaviest compounds.

–Operation pressure (P).

•Output data–WDT.


• This is shown using synthetic multi-component mixtures.

• Mixtures contain hydrocarbons between C1 and C30.

• Molar concentrations for Cn>C20 follow exponential decay functions ( ), representing highly simplified crude oil.

• q values are between 0.68 and 0.95.


1−×= ii xqx



Component and composition Exp. data Est. data

P WDT WDT Dev.

Mix. Cmax-1 x(Cmax-1) Cmax x(Cmax) /bar /°C /°C /°C

A C29 0.0021 C30 0.0014 1 20 18 -2

B C29 0.0101 C30 0.0087 1 26 30 4

C C26 0.0164 C27 0.0156 1 24 26 2

Experimental data (Pauly et al., 1998) and estimated WDT in this work



Experimental data (Daridon et al., 1996) and estimated WDT in this work

0

50

100

150

200

250

300

350

400

450

500

15 20 25 30 35 40

T/oC

P/ba

r

A: exp. data, Daridon et al. (1996)A: estimated data, this workB: exp. data, Daridon et al. (1996)B: estimated data, this work

-2 oC 2 oC


Experimental composition data and WDT estimation deviations (dev.)

Pauly et al. (1998) Daridon et al. (1996) A B C A' B' C' C1 43.70 43.80 43.60 C10 80.02 66.59 80.29 46.10 45.90 46.15 C18 0.00 5.59 2.45 0.00 1.65 1.33 C19 0.00 4.74 2.32 0.00 1.43 1.27 C20 6.41 4.03 2.21 3.27 1.25 1.16 C21 4.39 3.45 2.10 2.24 1.15 1.10 C22 3.00 2.96 2.00 1.53 0.91 1.04 C23 2.05 2.54 1.90 1.05 0.78 0.98 C24 1.40 2.18 1.81 0.72 0.67 0.92 C25 0.96 1.87 1.72 0.49 0.58 0.87 C26 0.66 1.61 1.64 0.34 0.50 0.81 C27 0.45 1.38 1.56 0.23 0.43 0.77 C28 0.31 1.20 0.16 0.37 0.00 C29 0.21 1.01 0.11 0.31 0.00 C30 0.14 0.87 0.07 0.27 0.00 C20+ 19.98 23.09 14.93 10.20 7.22 7.66

q 0.68 0.86 0.95 0.68 0.86 0.94 Dev./oC -2 4 2 -2 2 2


Application 2: estimation of increased/reduced WDT• For a system which WDT is available (referred as

basic system)– Input data

– WDT and P.– Output data

– Liquid compositions for the heaviest two compounds.

• For systems obtained by concentrating/diluting the basic system (referred as related systems) – Input data

– Increased/reduced liquid compositions that are calculated using– The basic system composition data.– The concentration/dilution ratio.

– Pressure (P).– Output data

– increased/decreased WDT.

( )1201−×+

+

= P.

bsx

lnaWDT

kSkk

kk γ


Application 2: estimation of increased/reduced WDTBasic system

• Distillate fractions are obtained from crude oil.

• WDTs are measured for these distillate fractions.

Experimental data: Srivastava et al. (2001)

• xk for the basic system is estimated using the empirical model.

Fraction 4 Fraction 5Boiling Temperature

range/oC 325 - 350 350 - 375

n-Cn up to n-C25 n-C26

WDT/oC 34 44


Application 2: estimation of increased/reduced WDTRelated systems• Sub-fractions of n-paraffin, iso- & cyclo- paraffin, and

aromatic are separated from the distillate fractions.• WDTs are measured for these sub-fractions.

• WDTs for n-paraffin sub-fractions are estimated using the empirical model, and compared with experimental data.

sub-fraction Experimental WDT/oC Fra. 4 Fra. 5

n-paraffin 45 53 iso-&cyclo- paraffin -4 -4

aromatic 10


Application 2: estimation of increased/reduced WDTRelated systems• Mixtures are prepared by mixing different proportions of

sub-fractions.• WDTs are measured for these mixtures.

– These data are used for validating the model.

• WDTs are estimated using the empirical model, and compared with experimental data.


Application 2: estimation of increased/reduced WDT

Experimental (Srivastava et al., 2002) and estimated WDT data for mixtures based on the fraction 4

-5

5

15

25

35

45

55

0 10 20 30 40 50 60 70 80 90 100

n-paraffins concentration /mass%

WD

T/C

Exp. data, mixtures consisiting of n-, iso-, & cyclo-paraffinsExp. data, fraction 4 distillated from crude oil Estimated data, this work

Trendline of exp. data


Application 2: estimation of increased/reduced WDT

Experimental (Srivastava et al., 2002) and estimated WDT data for mixtures based on the fraction 5

-5

5

15

25

35

45

55

0 10 20 30 40 50 60 70 80 90 100

n-paraffins concentration/mass%

WD

T/C

Exp. data, mixtures consisiting of n-, iso-, & cyclo-paraffinsExp. data, mixtures consisiting of n-paraffins and aromaticsExp. data, fraction 5 distillated from crude oil Estimated data, this work

Trendline of exp. data


• An empirical wax model based on simplified thermodynamic formula and empirically determined parameters has been developed in this work.

• The model capability for estimating WDT has been shown by comparing its predictions with independent experimental WDT data. A general agreement is obtained.

• The empirical model developed at this stage also shows a limitation. Further investigation and improvement are in progress.

Conclusions


GAS HYDRATES IN MULTIPHASE TRANSPORTATION

Shaoran Ren


Well head

Well

Tie-back pipeline Seabed

Subsea multiphase transportation: a tie-back pipeline


Gas/oil/water/hydrate

Flowing, Shut-in & Restart

Viscosity increaseDeposition ?Blockage ?

Pump Pressure Increase


Experimental System• Oil : Brazilian Offshore Oil• Water Content : 50 % vol. (5% NaCl)• Fluid Hydraulics : 1) Flow (Stirring) Conditions

2)Shut-in (no stirring) - Restart • Fluid Emulsification State:

without pre-mixing (600 rpm)pre-mixed at 14,000 rpm before charging to the rig, in order to simulate the shearing effect after fluid passing through subsea equipment


Hydrate Kinetics Rig-1: Modified stirrer blade

Magnetic MotorTorque Measurement

PC

Samplein & out

gas

P

T


TestHigh speed Pre-mixing (14K rpm)

Hydrate formed at P/T, bar/oC

Pressure drop due

to hydrate∆P

Torque increase

Induction time

1 no 79/4 23 18% 5 hours

2 yes 86/7 26 38% 0

3 no 129/7.5 31 49% 0

4 yes 129/10 24 49% 0

Experimental results for Brazilian oil with 50% water cut (5% NaCl), Flowing (or mixing at 600 rpm in Kinetics Rig-1)


Brazilian oil, 50% water, without high speed mixing, tested at a low pressure (9 oC subcooling)

time/hr.0 5 10 15 20

P/ba

r

50

60

70

80

90

100

110

T/o C

0

5

10

15

20

25

30

35

40

45

50

Torq

ue/N

.cm

30

35

40

45

50

55

60PTTorque

Flow Assurance: Gas Hydrates and Wax – December 2003 Steering Committee Meetingtime/hr.

0 5 10 15 20 25

P/ba

r

60

70

80

90

100

110

120

130

140

150

160

T/o C

0

5

10

15

20

25

30

35

40

45

50

Torq

ue/N

.cm

30

35

40

45

50

55

60

PTTorque

Brazilian oil, 50% water, without high speed mixing, tested at a high pressure (10-11 oC subcooling)


Brazilian oil, 50% water, without High Speed pre-mixing, tested at low and high pressures

tim e/hr.0 5 10 15 20 25 30

P/ba

r

405060708090

100110120130140150160

Torq

ue/N

.cm

20

30

40

50

60

70∆P=23 bar, LP∆P=31 bar, HPTorque, LPTorque, HP

28% water to hydrate

21% water to hydrate


Brazilian oil, 50% water, High Speed pre-mixed, tested at low and high pressures

tim e/hr.0 2 4 6 8 10 12

P/ba

r

405060708090

100110120130140150160

Torq

ue/N

.cm

20

30

40

50

60

70∆P=26 bar, LP∆P=24 bar, H PTorque, LPTorque, HP

22% w ater to hydrate

23% w ater to hydrate


Test High speed pre-mixing (14,000rpm)

Shut-in at P/T, bar/oC

Hydrateformed

Blockage at re-start

Remarks

1 no 79/4 undetectable

no Torque 40% up

2 yes 83/4 small yes --

3 no 118/4 small yes --

4 yes 118/4 small yes --

Experimental results for Brazilian oil with 50% water cut(5% NaCl), Shut-in and Restart


Shut-In Restart, Low Pressure, without Pre-mixing,Subcooling 9 oC, not blocked

time/hr.0 10 20 30 40 50

P/ba

r

50

60

70

80

90

100

T/o C

0

5

10

15

20

25

30

35

40

45

50

Torq

ue/N

.cm

0

10

20

30

40

50

60PTTorque

Restart


Shut-In Restart , Low Pressure, with Pre-mixing,Subcooling 9.2 oC, blocked

time/hr.0 5 10 15 20 25

P/ba

r

50

60

70

80

90

100

110

T/o C

0

5

10

15

20

25

30

35

40

45

50

Torq

ue/N

.cm

0

10

20

30

40

50

60PTTorque restart-blocked


High Pressure Visual Rig Observation

• Oil emulsion with 50% water pre-mixed at 10K rpm

• At static condition (shut-in), P=120 bar, T=4 oC. Pressure drops only 3 bar

• An solid-like gel was formed


Glass Micromodel


Micromodel Experimental Rig Set-up

TV / VCR PC

CAMERA

MODEL

TEST GAS / LIQUID TEST GAS / LIQUID

PRESSURE TRANSDUCER

TEMPERATUREPROBEBATH


Original Oil (without added water) in the Micromodel

45 bar, 30 oC 50 bar, 0.3 oC


Formation of hydrate in the Micromodel: Brazilian oil, 20% water, Natural gas, 60 bar (Pre-mixed at 14K rpm)

Hydrates Gas

0.6 oC 17 oC 17 oC, after 130 hours


Conclusions• With 50% water cut, hydrate can readily form at over

70 bar (< 9 oC subcooling). There will be a significant torque or fluid viscosity increase (over 50%). However this may not cause a blockage because of dispersion of hydrate particles in oil.

• Stirrer blockage was observed during shut in –restarts. This may be attributed to the agglomeration of hydrate (and other solid) particles formed during static conditions.

• For the oil/water emulsion with 50% water content, high degree of emulsification (pre-mixed at high speed) did not appear to improve the rheology of the hydrate dispersion.


Helical Tube Stirrer


Brazilian oil, 50% Water cut (5% NaCl), Lab-NG, 650 ml oil inKinetics Rig-1: Helical Tube (stirrer)

time/hr.0 2 4 6 8 10 12 14 16

P/ba

r

404550556065707580859095

100105110115120125

T/o C

0

5

10

15

20

25

30

35

40To

rque

/N.c

m

0

10

20

30

40

50

60

PTTorque


Brazilian oil, 50% Water (5% NaCl), at a low Presssure650 ml oil. Kinetics Rig-1: Helical Tube (stirrer)

time/hr.0 2 4 6 8 10 12 14

P/ba

r

40

50

60

70

80

90

100

110

120

130

140

T/o C

0

4

8

12

16

20

24

28

32

36

40To

rque

/N.c

m

0

10

20

30

40

50

60

PTTorque

flow assurance: gas hydrates and wax...flow assurance: gas hydrates and wax – december 2003...

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