flow assurance: gas hydrates and wax · flow assurance: gas hydrate and wax -june 2003 steering...

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

Flow Assurance: Gas Hydrates and Wax

June 2003 Meeting Presentations

• Experimental work: physical properties and hydrate measurements (Rod Burgass)

• Thermodynamic modelling: salts and organic inhibitors (Amir Masoudi)

• Thermodynamic modelling: water content of gases (Amir Hossien Mohammadi)

• Experimental work: wax and wax-hydrate measurements (Rod Burgass)

• Thermodynamic modelling: wax (Hongyan Ji)

• PHYSICAL PROPERTY MEASUREMENTS (methanol/salt)

• HYDRATE DISSOCIATION POINT MEASUREMENTS (methanol/salt)

• HYDRATE DISSOCIATION POINT MEASUREMENTS (high pressure rig)

EXPERIMENTAL WORK: PHYSICAL PROPERTY AND HYDRATE MEASUREMENTS

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

• Boiling point-methanol/sodium chloride

• Freezing point-methanol/sodium chloride

PHYSICAL PROPERTY MEASUREMENTS

Schematic of boiling point apparatus constructed in-house

Heating Mantle

Condenser

Thermocouple

Cottrell Pump

Boiling point elevation for aqueous solutions of sodium chloride

373

375

377

379

381

383

0 5 10 15 20 25 30Sodium chloride concentration/mass%

T/K

This workICT

Boiling point data for aqueous solutions of glycerol

373

378

383

388

393

398

403

0 10 20 30 40 50 60 70 80 90Glycerol concentration/mass%

T/K

This workICT

Boiling point data for aqueous solutions of methanol and sodium chloride

Mass% Methanol

±0.1

Mass% sodium

chloride ±0.1

Boiling point

K ±0.2

9.7 0.0 364.3 30.1 0.0 354.2 5.0 4.9 367.5 7.4 16.5 365.2 10.1 10.3 362.9 14.5 14.6 359.4 16.8 15.8 357.8 25.6 5.1 355.4 28.5 12.4 352.8

Freezing point method schematic of sample temperature probe

Aluminium Tube

Test Sample

PRT

PTFE Sleeve

Example of freezing point measurement data for aqueous solution of sodium chloride

2.4

2.7

3.0

3.3

3.6

-4.0 -3.6 -3.2 -2.8 -2.4 -2.0 -1.6 -1.2Sample Temperature/K

T di

ffere

nce

betw

een

prob

es/K

Freezing point

Freezing point measurements for aqueous solutions of sodium chloride

255

258

261

264

267

270

273

0 5 10 15 20 25Sodium chloride concentration/mass%

T/K

This work

CRC Handbook

Freezing point measurements for aqueous solutions of ethylene glycol

238

243

248

253

258

263

268

273

0 10 20 30 40 50Ethylene glycol concentration/mass%

T/K CRC Handbook

This work

Freezing point data for aqueous solutions of methanol and sodium chloride

Mass% Methanol

±0.1

Mass% sodium

chloride ±0.1

Freezing point

K ±0.2

2.8 3.2 269.0 4.2 4.2 267.1 6.4 7.0 263.0 7.8 8.2 260.4 11.5 7.1 258.0 12.9 6.3 257.5 10.1 10.2 255.9 10.8 12.8 252.1 12.9 12.4 250.1

HYDRATE DISSOCIATION POINT MEASUREMENTS

• Hydrate rig-1 set-up and method of measuring dissociation points

• Measurements made of dissociation points for methane hydrates in the presence of an aqueous solution of methanol and sodium chloride

• New high pressure hydrate rig

• Dissociation points for nitrogen hydrates to high pressure

• Dissociation points for black oil using high pressure rig

Experimental Equipment: Rig-1

CRYOSTATPIVOT

TEST GAS

PRESSURE TRANSDUCER

MERCURY PUMP

BORESCOPE TV & VIDEO

0.0

P

TEMPERATURE PROBE

PC

Hydrate Rig-1: Max pressure = 69 MPa, Volume = 654 cc

Experimental Equipment: Rig-1 Cell

LIGHT SOURCE

TEMPERATUREPROBE

TEMPERATUREPROBE

BORESCOPE

CELL

CELL

QUARTZ TUBE

Experimental: Dissociation point method

3.5

4.0

4.5

5.0

5.5

6.0

250 255 260 265 270 275 280 285

T/K

P/M

Pa

Cooling cycleHeating cycle (non-equilibrium points)Heating cycle (equilibrium points)Dissociation point

C1 - 15 mass% K2CO3

3.5

4.0

4.5

5.0

5.5

6.0

250 255 260 265 270 275 280 285

T/K

P/M

Pa


C1 - 15 mass% K2CO3

3.5

4.0

4.5

5.0

5.5

6.0

250 255 260 265 270 275 280 285

T/K

P/M

Pa


C1 - 15 mass% K2CO3

3.5

4.0

4.5

5.0

5.5

6.0

250 255 260 265 270 275 280 285

T/K

P/M

Pa


C1 - 15 mass% K2CO3

3.5

4.0

4.5

5.0

5.5

6.0

250 255 260 265 270 275 280 285

T/K

P/M

Pa


C1 - 15 mass% K2CO3

Experimental hydrate dissociation point measurements for methane hydrates in the presence of aqueous solution

composed of 5.629 Mass% NaCl and 9.434 Mass% methanol

2

6

10

14

18

22

26

30

34

38

42

270 274 278 282 286 290T/K

P/M

Pa

Heriot-Watt experimental

Jager et al (2002)

Experimental hydrate dissociation point measurements for methane hydrates in the presence of aqueous solution

composed of 10.856 Mass% NaCl and 8.912 Mass% methanol

0

5

10

15

20

25

30

35

40

45

50

260 265 270 275 280 285 290T/K

P/M

Pa

Heriot-Watt experimentalJager et al (2002)

Schematic of new high pressure rig

HIGH PRESSURE CELL

WATER JACKET

PRESSURE TRANSDUCER

CONSTANT TEMPER ATURE BATH PRT

Schematic of new high pressure cell

PRT

Pressure transducer

Heated block

Water jacket

Experimental and predicted hydrate dissociation point measurements for nitrogen hydrates

15

35

55

75

95

115

135

155

175

273 275 277 279 281 283 285 287 289 291 293 295 297 299T/K

P/M

Pa

Heriot-Watt new HP rig

Heriot-Watt (QCM)

Literature Marshall et al(1964)Heriot-Watt prediction

Experimental hydrate dissociation point measurements for black oil. Bubble point 17.23 MPa

at 294K

0102030405060708090

100110120130140

279 284 289 294 299 304 309T/K

P/M

Pa

Example of hydrate dissociation point measurement for black oil. Bubble point 17.23 MPa at 294K

42

43

44

45

46

47

48

49

50

296 297 298 299 300 301T/K

P/M

Pa

Dissociation point


Thermodynamic ModellingSalts and Organic Inhibitors


Outline

• Thermodynamic modelling of NaCl and/or MeOH

• New correlation for estimating gas hydrate inhibition

• Maximum inhibition in the salts and organic inhibitor systems


Thermodynamic modelling

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


Modelling methanolModelling methanol

• Boiling point temperature of aqueous methanol solutions.

335

340

345

350

355

360

365

370

0 0.2 0.4 0.6 0.8 1

MeOH / mole fraction

T /

K

exp., 760 mmHg, ICTPrediction, 760 mmHgexp., 800 mmHg, ICTPrediction, 800 mmHgexp., 700 mmHg, ICTPrediction, 700 mmHg


Modelling Modelling NaClNaCl and methanoland methanol

• Experimental and calculated freezing point temperature (F.P.T) for ternary NaCl/MeOH/water mixtures

NaCl, mass% MeOH, mass% F.P.T / K, exp. F.P.T / K, pred. err%3.16 2.81 268.95 269.35 -0.154.18 4.21 267.05 267.52 -0.186.99 6.39 262.95 263.17 -0.088.17 7.83 260.35 260.59 -0.097.11 11.48 257.95 258.01 -0.026.26 12.90 257.45 257.53 -0.0310.21 10.15 255.85 255.75 0.0412.82 10.77 252.05 251.62 0.1712.45 12.92 250.05 249.33 0.29


Modelling Modelling NaClNaCl and methanoland methanol

• Experimental and calculated boiling point temperature (B.P.T) for ternary NaCl/MeOH/water mixtures

NaCl, mass% MeOH, mass% B.P.T / K, exp. B.P.T / K, pred. err%4.90 4.96 367.45 368.85 -0.3816.46 7.38 365.15 365.12 0.010.00 9.67 364.25 365.86 -0.4410.27 10.10 362.85 363.83 -0.2714.57 14.46 359.35 359.35 0.0015.84 16.84 357.75 357.40 0.105.14 25.57 355.35 356.20 -0.240.00 30.12 354.15 355.91 -0.5012.44 28.51 352.75 352.75 0.00


Modelling salt precipitationModelling salt precipitation

• Solubility of NaCl in aqueous methanol solutions at various concentration of methanol as a function of temperature.

0

5

10

15

20

25

30

35

270 280 290 300 310 320 330

T / K

NaC

l / m

ass%

exp., 0 mass% MeOHexp., 10 mass% MeOHexp., 20 mass% MeOHexp., 40 mass% MeOHPredictions

exp. data: Deepstar data (273.15 K) Pinho S.P. & Macedo E.A., 1996 (298.15, 323.15 K)



• Solubility of NaCl in aqueous methanol solutions at various temperature as a function of methanol concentration.

10

15

20

25

30

0 5 10 15 20 25 30 35 40 45

MeOH / mass%

NaC

l / m

ass%

exp.,273.15 K, Deepstar data

exp., 298.15 K, Pinho S.P. & Macedo E.A. 1996

exp., 323.15 K, Pinho S.P. & Macedo E.A. 1996

Predictions



• Solubility of KCl in aqueous methanol solutions at various concentration of methanol as a function of temperature.

0

5

10

15

20

25

30

35

40

45

50

270 280 290 300 310 320 330

T / K

KC

l / m

ass%

exp., 0 mass% MeOHexp., 10 mass% MeOHexp., 20 mass% MeOHexp., 40 mass% MeOHexp., 50 mass% MeOHPredictions

exp. data: Deepstar data (273.15 K); Pinho S.P. & Macedo E.A., 1996 (298.15, 323.15 K)



• Solubility of KCl in aqueous methanol solutions at various temperature as a function of methanol concentration.

0

5

10

15

20

25

30

0 10 20 30 40 50

MeOH / mass%

KC

l / m

ass%

exp., 273.15 K, Deepstar dataexp., 298.15 K, Pinho & Macedo (1996)exp., 323.15 K, Pinho & Macedo (1996)Predictions


VALIDATION OF THE MODEL FOR GAS HYDRATES


Methane hydrate dissociation point in the presence of methanol aqueous solutions

1

10

100

220 230 240 250 260 270 280 290T / K

P /

MP

a

exp, 10 mass%, Ng, H.-J., Robinson, D.B. (1985)exp, 20 mass%, Ng, H.J., Robinson, D.B. (1985)exp, 35 mass%, Robinson, D.B., Ng, H.-J. (1986)exp., 50 mass%, Robinson, D.B., Ng, H.-J. (1986)exp., 50 mass%, Ng, H.J., et al. (1987b)Predictions


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

1

100

248 252 256 260 264 268 272 276 280 284 288 292

T / K

P /

MP

a

exp., 10 mass% MeOH exp., 20 mass% MeOHexp., 30 mass% MeOHexp., 40 mass% MeOHPredictionsHWUHWU

Exp. data: Jager M.D. et al. (2002)

6.2152 mass% NaCl (MeOH free basis)



1

100

260 264 268 272 276 280 284 288 292

T / K

P /

MP

a

exp., 0.0 mass% NaClexp., 5.6 mass% NaClexp., 10.8 mass% NaClPredictionsHWUHWU

10 mass% MeOH (salt free basis)

Exp. data: 0.0 mass% NaCl, Ng, H.J., Robinson, D.B. (1985) 5.6, 10.8 mass% NaCl, Jager M.D. et al. (2002)


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

1000260 264 268 272 276 280 284

T / K

P /

KP

a

exp., 5 mass% MeOH + 5 mass% NaCl, Dholabhai (1997)exp., 10 mass% MeOH + 10 mass% NaCl, Dholabhai (1997)exp., pure water, Dholabhai (1997)Predictions

80% CH4 + 20% CO2


Outline





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


Effect of the system pressure

0

5

10

15

20

25

30

35

40

268 273 278 283 288 293

T/K

P/M

Pa

Distilled WaterMud AMud BMud CMud D

12 K @ 5.5 MPa

15.5 K @ 15 MPa

Mud C

Mud C


100

1

10

267 272 277 282 287 292

T/K

P/M

Pa

Distilled water & C1Distilled water & NGMud 1 & C1Mud 1 & NG

C1

NG

Effect of composition of reservoir fluid

14.3 K for NG13 K for C1


Effect of type of inhibitor

250

5

10

15

20

25

0 5 10 15 20

mole%

dT/K

Methanol (Ng & Robinson, 1985; Robinson & Ng, 1986)

Ethylene glycol, (Robinson & Ng, 1986)

P = 14.66 MPa

MeOHMEG


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

1000260 265 270 275 280

T / K

P / k

Pa

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

1000

10000

262 264 266 268 270 272 274 276 278 280

T / K

P / K

pa

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


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

1000

10000

100000

258 263 268 273 278 283 288 293 298

T / K

P / K

pa

Pure Water,HWHYD modelExp., 10 mass% KCl + 23 mass% EGExp., 8 mass% KCl + 35 mass% EGNew CorrelationIgnoring Ref. P

exp. data: HWU


Methane hydrate phase boundaries in the presence of CaCl2 and MEG aqueous solutions

1000

10000

100000

255 260 265 270 275 280 285 290 295 300 305

T / K

P /

Kpa

Pure water, in-house modelExp., 10 mass% CaCl2 + 15 mass% EGExp., 18 mass% CaCl2 + 14 mass% EGExp., 14 mass% CaCl2 + 26 mass% EGNew Correlation

exp. data: HWU



1

100

260 264 268 272 276 280 284 288 292

T / K

P /

MP

a

exp., 0.0 mass% NaClexp., 6.2152 mass% NaClexp., 11.9179 mass% NaClin-house model PredictionsNew Correlation





1

10

100

254 259 264 269 274 279 284 289

T / K

P /

MP

a

exp., 0.0 mass% NaCl

exp., 6.2152 mass% NaCl

exp., 11.9179 mass% NaClCorrelation




Outline





Gas hydrate stability zone

• Maximum hydrate suppresstion temperature locus in the presence of saturated KCl and EG aqueous solutions.

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

EG Concentration/ mass%

0

5

10

15

20

25

30

Solubility, T=273.15 K

5000 KPa

10000 KPa

30000 KPa


Gas hydrate stability zone

• Maximum hydrate suppression temperature locus in the presence of saturated NaCl and EG aqueous solutions.

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35

EG Concentration/ mass%

0

5

10

15

20

25

30

Solubility, 273.15 K

Solubility, 298.15 K

10000 KPa, 273.15 K

10000 KPa, 298.15 K


Conclusions• Modelling MeOH and/or NaCl was successfully

implemented.

• Precipitation of NaCl and KCl in the MeOHaqueous solutions was modelled.

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

• A general correlation capable of predicting hydrate inhibition effect of salts and/or organic inhibitors was developed.


Conclusions

• Maximum hydrate suppression temperature locus of the systems including salts and organic inhibitors was predicted.

• In salt + organic inhibitor systems, the degree of inhibition can be improved by increasing the concentration of organic inhibitor.

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

Equilibrium Water Content of Gases


• To investigate the existing data

• To extend the in-house model for predicting the water content of gases

Objective


Why to study the water content of gases?

• Hydrate / Ice formation

• Two phase flow

• Corrosion


Typical phase boundaries

1

10

100

1000

-12 -7 -2 3 8 13 18 23T/C

P/ba

r

Lw-V-H

I-V-H

A

B

A : Up Stream ConditionB: Down Stream Condition

NG Dew Point

Joule-Thomson Curve 230 ppm (mole)

300 ppm (mole)400 ppm (mole)

Water Content = 180 ppm (mole)

795 ppm (mole)

H-V Region

Lw-V Region

I-V Region


Evaluating the existing data

• Inconsistency among the data

• Limitations with respect to extrapolating to other P&T conditions

• GERG (Groupe Europeen de Recherches Gazieres, 2001) data


Model description H

wf = Vwf H-V Equilibrium

L

if = Vif ),1( ni = Lw-V Equilibrium

I

wf = Vwf I-V Equilibrium


Flow-Chart

Input T, P & Compositions

P > PLw-V-H ?

H-V Equil.

T > Ice point ?

Lw-V Equil.

P > PI-V-H ?

H-V Equil. I-V Equil.

P < Pdew ?

YesNo

NoYes Yes No

Yes

No single gas PhaseNo

0

25

240 300T/K

P/M

Pa H-V

H-V

Lw-V

I-VI-V-H

Lw-V-H

I-Lw-V


Predictions Water Content of Methane at 10 MPa

1

10

100

1000

230 240 250 260 270 280 290 300 310 320

T/K

Wat

er c

onte

nt (m

g/N

m3)

GERG (2001)KSEPL WAGA (Supplied by Shell)GPA RR45 by interpolation (Supplied by Shell)Dhima et.al. (2000)Ugrozov + Olds et.al. (1996)GERG model predictionSTFlash predictionSTFlash phase transitions (Supplied by Shell)This prediction


Predictions (Continue)Water Content of 94.69% Methane & 5.31% Propane

1

10

100

1000

230 235 240 245 250 255 260 265 270 275 280

T/K

Wat

er c

onte

nt (m

g/N

m3)

Prediction (2.07 MPa)Experimental (2.07 MPa)Prediction (3.45 MPa)Experimental (3.45 MPa)Prediction (6.89 MPa)Experimental (6.89 MPa)Prediction (10.34 MPa) Experimental (10.34 MPa)


Conclusions• Presence of water in a natural gas can lead

to hydrate and/or ice formation, as well as two phase flow, and corrosion.

• Accurate experimental data, especially at low temperatures are necessary to develop thermodynamic models.

• The in-house thermodynamic model has been extended to predict the equilibrium water content of gases.

• WAX MEASUREMENTS 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 – June 2003 Steering Committee Meeting

• APPARATUS AND METHOD

• MEASUREMENT EXAMPLES

WAX MEASUREMENTS USING QUARTZ CRYSTAL MICROBALANCE

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

4988500

4989000

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

Wax Appearance Temperature (WAT) for a dead crude using QCM

4952500

4953000

4953500

4954000

4954500

4955000

4955500

4956000

4956500

290 295 300 305 310 315 320 325 330 335 340T/K

Res

onan

t fre

quen

cy/H

z

CoolingHeating

WDT 325K

WAT 308K

Wax Appearance Temperature (WDT) for a dead crude using QCM

4956000

4956050

4956100

4956150

315 320 325 330 335 340T/K

Res

onan

t fre

quen

cy/H

z

WDT 325K

Wax and Hydrate measurements on a synthetic mixture of alkanes

• Apparatus and methods

• Test fluid

• Experimental WDT and hydrate dissociation point measurements

Schematic of high pressure (52MPa) visual rig

Composition of synthetic hydrocarbon Mixture (D) for components heavier than C4

Component

Mass%

Mole%

C7 37.50 48.992 C10 47.40 43.615 C13 3.61 2.563 C16 3.54 2.049 C18 0.64 0.331 C22 0.63 0.267 C24 0.64 0.246 C28 4.95 1.641 C30 0.35 0.107 C36 0.68 0.177 C40 0.05 0.012

Composition of synthetic hydrocarbon Mixture (D) with light components (live). Bubble point measured

as 12.62 MPa at 299 K.

Component Mass% Mole%

N2 0.56 1.66 CO2 0.34 0.64 C1 7.19 37.10 C2 0.89 2.45 C3 0.37 0.70 nC4 0.06 0.09 iC4 0.11 0.15 nC5 0.03 0.03 iC5 0.03 0.03 C7 33.93 28.02 C10 42.84 24.91 C13 3.26 1.46 C16 3.20 1.17 C18 0.58 0.19 C22 0.57 0.15 C24 0.58 0.14 C28 4.47 0.94 C30 0.31 0.06 C36 0.62 0.10 C40 0.04 0.01

WDT measurements on synthetic fluid with and without C1-C4

048

121620242832364044

295 297 299 301 303 305 307 309 311 313 315T/K

P/M

Pa

WDT components heavier than C4

WDT live fluid

Experimental and predicted hydrate dissociation point measurements for synthetic fluid

048

121620242832364044

275 279 283 287 291 295T/K

P/M

Pa

Hydrate experimentaldissociation pointsHydrate predicted points

Summary of wax and hydrate measurements on synthetic fluid

048

121620242832364044

275 280 285 290 295 300 305 310 315T/K

P/M

Pa

WDT components heavier thanC4WDT live fluid

Hydrate experimentaldissociation pointsHydrate predicted points


Thermodynamic Modelling -Wax


• Wax blockage is a major problem of flow assurance.

• Many reservoir fluids at subsea pipeline conditions are prone to the formation of both hydrate and wax.

• Wax formation could affect the thermodynamic and kinetics of hydrate formation, and vice versa.

• Integrated study of hydrate and wax is required.

Why Are We Studying Wax?


• Accuracy in measurement and prediction of wax equilibrium is far inferior to that of hydrate.

• Shortcomings of wax measurements in the literature:– Detection of WAT (i.e., cloud point temperature)– Using continuous cooling and heating– Using unreliable experimental techniques

• Shortcomings of wax models in the literature– Based on WAT– Using inaccurate thermodynamic descriptions

Where Did We Start?


• Improving wax measurements– Detection of WDT (i.e.,wax disappearance

temperature)– Using step cooling/heating– Using reliable experimental techniques

(e.g., QCM, visual)

• Improving wax predictions– Developing the Heriot-Watt university WAX

(HWWAX) model based on reliable WDT data

What Do We Do?


Using improved thermodynamic descriptions• Accurate correlations for physical properties

• Modified SRK and PR EoS parameters for heavy hydrocarbons

– Tc and Pc correlations have been selected– Universal BIP has been established

• A new approach for describing wax solids

• Extending to high pressure conditions– With consideration of pressure effects on solid phase

Heriot-Watt University Wax Model (HWWAX)


Heriot-Watt University Wax Model (HWWAX)• Improvements made in HWWAX increase the

prediction accuracy.

• HWWAX has shown reliability in SLE calculations for prediction of– Wax phase boundary at different P– Wax amount and composition at different T and P

• The developed model is capable of wax equilibrium predictions for mixtures containing

5CCn ≥


Work Conducted in This Phase of Project • Background

– Light compounds (e.g., C1 – C4 , CO2 , N2) commonly present as wax problems occur in subsea transfer lines

– It is necessary to predict the effect of light compounds on the wax phase boundary

• Modelling work conducted– HWWAX has been extended to systems consisting

of light compounds, where VLSE calculations are needed


Contents of the Following Presentation • Wax equilibrium modelling used in HWWAX

– Thermodynamic description of phases– Flow chart for calculation of WDT

• Calculation of fluid phase behaviour (Pb)– In order to study the effect of wax formation on Pb

• Comparison of HWWAX predictions to measurements– Model validation– Effect of light compounds on WDT– Effect of wax formation on Pb


HWWAX Modelling Wax EquilibriumThermodynamic description of phases

• (V)LSE

• using SRK EoS and PR EoS independently

•

Vif L

if

= ∫ dP

RTvfsf

P

P

SiOS

iSii

Si

o

expγ

( ) Si

Li

Vi fff ==


HWWAX Modelling Wax Equilibrium

Yes No

bPP >

SLE VLSE

WDT calculation algorithm for mixtures with light compounds


HWWAX Calculation of Bubble Point Pressure

Yes No

WDTT >

VLE VLSE

Pb calculation algorithm for mixtures potentially forming wax


Lumping Compounds into Pseudo-component

285

295

305

315

325

335

345

0 0.2 0.4 0.6 0.8 1

C32 mole fraction

WD

T/K

nC5-nC32nC6-nC32nC7-nC32nC8-nC32nC10-nC32nC12-nC32

285

295

305

315

0 0.025 0.05

Experimental WDTs (Seyer, 1938; Madsen et al., 1976; Roberts et al., 1994) for binaries consisting of n-alkanes


Systems used• Binaries

– C1-C20– C2-C24

• Multi-component mixtures– mixtures with C1

(literature data)– mixtures without and with C1 to C4

(generated in this laboratory)– mixture without and with natural gas

(generated in this laboratory)

HWWAX Predictions


HWWAX Predictions: C1-C20 Binary

0

20

40

60

80

100

120

140

160

300 310 320 330 340 350

T/K

P/M

PaExp. WDT: x(C1)=0.823 Exp. WDT: x(C1)=0.650Exp. WDT: x(C1)=0.384 Exp. WDT: x(C1)=0.152Exp. Tf: n-C20 Exp. Pb: x(C1)=0.823Exp. Pb: x(C1)=0.650 Exp. Pb: x(C1)=0.384Exp. Pb: x(C1)=0.152 WDT predictions, HWWAXPb predictions, HWWAX

Experimental data compared with predictions of Pb and WDT for C1-C20 binary, using HWWAX coupled with SRK EoS


HWWAX Predictions: C2-C24 Binary

0

5

10

15

20

25

290 300 310 320 330 340 350

T/K

P/M

Pa

Exp. WDT: x(C2)=0.967 Exp. WDT: x(C2)=0.608Exp. WDT: x(C2)=0.392 Exp. WDT: x(C2)=0.120Exp. Tf: n-C24, Floter et al. (1997) Exp. Pb: x(C2)=0.967Exp. Pb: x(C2)=0.608 Exp. Pb: x(C2)=0.392Exp. Pb: x(C2)=0.120 WDT predictions, HWWAXPb predictions, HWWAX

Experimental data compared with predictions of Pb and WDT for C2-C24 binary, using HWWAX coupled with SRK EoS


HWWAX Predictions : Mixtures with C1Compositions of mixtures consisting of methane (Daridon et al. 1996)

A B C D Comp. Mole % Mole % Mole % Mole %

C1 43.70 43.80 43.60 44.00 C10 46.10 45.90 46.15 45.80 C18 - 1.65 1.33 6.80 C19 - 1.43 1.27 - C20 3.27 1.25 1.16 - C21 2.24 1.15 1.10 - C22 1.53 0.91 1.04 - C23 1.05 0.78 0.98 - C24 0.72 0.67 0.92 - C25 0.49 0.58 0.87 - C26 0.34 0.50 0.81 - C27 0.23 0.43 0.77 - C28 0.16 0.37 - - C29 0.11 0.31 - - C30 0.07 0.27 - 3.40


HWWAX Predictions: Mixture A (with C1)

0

5

10

15

20

25

30

35

40

45

50

240 260 280 300 320 340 360 380 400 420 440

T/K

P/M

Pa

Exp. Pb in A: Daridon et al. (1996)Predicted Pb in A: HWWAX modelExp. WDT in A: Daridon et al. (1996)Predicted WDT in A: HWWAX model

L

L+V

S+L

S+L+V

Measured (Daridon et al., 1996) and predicted (using HWWAX coupled with SRK EoS) phase boundaries for Mixture A


HWWAX Predictions: Mixture B (with C1)

Measured (Daridon et al., 1996) and predicted (using HWWAX coupled with SRK EoS) phase boundaries for Mixture B

0

5

10

15

20

25

30

35

40

45

50

260 280 300 320 340 360 380 400 420 440

T/K

P/M

Pa

Exp. Pb in B: Daridon et al. (1996)Predicted Pb in B: HWWAX modelExp. WDT in B: Daridon et al. (1996)Predicted WDT in B: HWWAX model

S+L

S+L+V

L

L+V


HWWAX Predictions: Mixtures Without and With C1-C4

Compositions of mixtures B and C (without and with C1 – C4) Mixture B Mixture C Without C1-C4 With C1-C4 Without C1-C4 With C1-C4

Comp. Mole % Mole % Mole % Mole % C1 - 28 - 24.41 C2 - 4.04 - 2.55 C3 - 1.46 - 5.66 C4 - 1.12 - 3.63 C7 - - 47.44 30.24 C10 80.04 52.32 37.76 24.07 C16 - - 6.44 4.11 C18 - - 2.40 1.53 C20 6.43 4.2 3.24 2.06 C21 4.39 2.87 1.81 1.15 C22 2.99 1.96 0.22 0.14 C23 2.06 1.34 0.30 0.19 C24 2.34 1.53 - - C28 1.41 0.92 0.21 0.13 C30 0.34 0.23 0.18 0.12



Tuned BIP and comparisons of calculated Pb to experimental data for mixtures B and C (with C1-C4)

BIP: binary interaction parameter between C1 and the other compounds in the mixture

Experimental Calculations using SRK EoS Mix. T/K Pb/MPa BIP Pb/MPa Rel. Dev. %

B 291.00 9.30 0.12 9.40 1.00 C 284.00 7.60 0.12 7.50 -1.00



Measured (this laboratory) and predicted (using HWWAX with SRK EoS) WDTs for mixtures B and C, with and without C1-C4

0

10

20

30

40

50

280 290 300 310 320 330 340 350 360

T/K

P/M

Pa

Exp.: B without C1-C4, this workPred.: B without C1-C4, HWWAXExp.: B with C1-C4, this workPred.: B with C1-C4, HWWAXExp.: C without C1-C4, this workPred.: C without C1-C4, HWWAXExp.: C with C1-C4, this workPred.: C with C1-C4, HWWAX


HWWAX Predictions: Mixture C With C1-C4

Measured and predicted WDTs for C with C1-C4

Experimental Predictions and Deviations (Dev.) Data Lumping C6-C20 into pseudo-component Without lumping num. Using SRK EoS Using PR EoS Using SRK EoS

P/MPa WDT/K WDT/K Dev./K WDT/K Dev./K WDT/K Dev./K1 1.01 286 288 2 288 2 290 4 2 2.19 286 288 2 288 2 290 4 3 5.26 285 287 2 287 2 289 4 4 7.14 285 287 2 287 2 289 4 5 7.96 286 287 1 287 1 289 3 6 14.6 286 288 2 289 3 291 5 7 22.8 287 290 3 290 3 292 5 8 31.7 289 292 3 292 3 294 5 9 41.6 291 294 3 294 3 296 5


HWWAX Predictions: Mixtures Without and With Natural Gas

Without natural gas With natural gas Comp. Mole % Mole %

N2 - 1.66 CO2 - 0.64 C1 - 37.10 C2 - 2.45 C3 - 0.70

nC4 - 0.09 iC4 - 0.15 nC5 - 0.03 iC5 - 0.03 C7 48.99 28.02 C10 43.62 24.91 C13 2.56 1.46 C16 2.05 1.17 C18 0.33 0.19 C22 0.27 0.15 C24 0.25 0.14 C28 1.64 0.94 C30 0.11 0.06 C36 0.18 0.10 C40 0.01 0.01

Compositions of mixtures D (without and with natural gas)



Tuned BIP and comparisons of calculated Pb to experimental data for D (with natural gas)

BIP(1,j): Binary interaction parameter between C1 and the other compounds in the mixture

Experimental Calculations using SRK EoS T/K Pb/MPa BIP(1,j) Pb/MPa Rel. Dev. % 299 12.6 0.06 12.5 2



0

10

20

30

40

50

290 300 310 320 330 340 350 360

T/K

P/M

Pa

Exp.: D without light ends, this work

Pred.: D without light ends, HWWAX

Exp.: D with light ends, this work

Pred.: D with light ends, HWWAX

Measured (this laboratory) and predicted (using HWWAX coupled with SRK EoS) WDTs for mixture D, excluding and including light ends


• HWWAX model has been extended to mixtures containing light compounds – Predictions are in good agreement with independent

experimental data

• Existence of light compounds leads to WDT reduction compared to the system without light compounds

• Impacts of wax formation on bubble point pressures have been studied using HWWAX

Conclusions

flow assurance: gas hydrates and wax · flow assurance: gas hydrate and wax -june 2003 steering...

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