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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)
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• 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
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• Boiling point-methanol/sodium chloride
• Freezing point-methanol/sodium chloride
PHYSICAL PROPERTY MEASUREMENTS
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Schematic of boiling point apparatus constructed in-house
Heating Mantle
Condenser
Thermocouple
Cottrell Pump
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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
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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
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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
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Freezing point method schematic of sample temperature probe
Aluminium Tube
Test Sample
PRT
PTFE Sleeve
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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
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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
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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
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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
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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
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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
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Experimental Equipment: Rig-1 Cell
LIGHT SOURCE
TEMPERATUREPROBE
TEMPERATUREPROBE
BORESCOPE
CELL
CELL
QUARTZ TUBE
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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
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
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
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
Cooling cycleHeating cycle (non-equilibrium points)Heating cycle (equilibrium points)Dissociation point
C1 - 15 mass% K2CO3
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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)
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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)
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Schematic of new high pressure rig
HIGH PRESSURE CELL
WATER JACKET
PRESSURE TRANSDUCER
CONSTANT TEMPER ATURE BATH PRT
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Schematic of new high pressure cell
PRT
Pressure transducer
Heated block
Water jacket
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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
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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
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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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
Thermodynamic ModellingSalts and Organic Inhibitors
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
Outline
• Thermodynamic modelling of NaCl and/or MeOH
• New correlation for estimating gas hydrate inhibition
• Maximum inhibition in the salts and organic inhibitor systems
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
Thermodynamic modelling
• 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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
Thermodynamic modelling
• Binary Interaction Parameters (BIPs) OptimisationWater-SaltSalt-SaltSalt-Organic InhibitorGas-Salt
• NaCl, KCl and CaCl2 as well as MEG have already been modelled.
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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)
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
Modelling salt precipitationModelling salt precipitation
• 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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
Modelling salt precipitationModelling salt precipitation
• 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)
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
Modelling salt precipitationModelling salt precipitation
• 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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
VALIDATION OF THE MODEL FOR GAS HYDRATES
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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)
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
Methane hydrate phase boundaries in the presence of NaCl and MeOH aqueous solutions
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)
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
Outline
• Thermodynamic modelling of NaCl and/or MeOH
• New correlation for estimating gas hydrate inhibition
• Maximum inhibition in the salts and organic inhibitor systems
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
Methane hydrate phase boundaries in the presence of NaCl and MeOH aqueous solutions
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
Exp. data: 0.0 mass% NaCl, Ng, H.J., Robinson, D.B. (1985) 6.2152, 11.9179 mass% NaCl, Jager M.D. et al. (2002)
10 mass% MeOH (salt free basis)
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
Methane hydrate phase boundaries in the presence of NaCl and MeOH aqueous solutions
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
20 mass% MeOH (salt free basis)
Exp. data: 0.0 mass% NaCl, Ng, H.J., Robinson, D.B. (1985) 6.2152, 11.9179 mass% NaCl, Jager M.D. et al. (2002)
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
Outline
• Thermodynamic modelling of NaCl and/or MeOH
• New correlation for estimating gas hydrate inhibition
• Maximum inhibition in the salts and organic inhibitor systems
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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.
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Flow Assurance: Gas Hydrate and Wax - June 2003 Steering Committee Meeting
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.
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
Equilibrium Water Content of Gases
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
• To investigate the existing data
• To extend the in-house model for predicting the water content of gases
Objective
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
Why to study the water content of gases?
• Hydrate / Ice formation
• Two phase flow
• Corrosion
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
Model description H
wf = Vwf H-V Equilibrium
L
if = Vif ),1( ni = Lw-V Equilibrium
I
wf = Vwf I-V Equilibrium
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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)
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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.
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• 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
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• APPARATUS AND METHOD
• MEASUREMENT EXAMPLES
WAX MEASUREMENTS USING QUARTZ CRYSTAL MICROBALANCE
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Schematic of Quartz Crystal Microbalance (QCM)
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Schematic of QCM rig for measurement on dead fluids
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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
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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
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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
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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
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Wax and Hydrate measurements on a synthetic mixture of alkanes
• Apparatus and methods
• Test fluid
• Experimental WDT and hydrate dissociation point measurements
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Schematic of high pressure (52MPa) visual rig
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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
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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
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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
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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
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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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
Thermodynamic Modelling -Wax
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
• 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?
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
• 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?
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
• 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?
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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)
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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 ≥
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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 ==
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
HWWAX Modelling Wax Equilibrium
Yes No
bPP >
SLE VLSE
WDT calculation algorithm for mixtures with light compounds
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
HWWAX Calculation of Bubble Point Pressure
Yes No
WDTT >
VLE VLSE
Pb calculation algorithm for mixtures potentially forming wax
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
HWWAX Predictions: Mixtures Without and With C1-C4
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
HWWAX Predictions: Mixtures Without and With C1-C4
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
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)
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
HWWAX Predictions: Mixtures 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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
HWWAX Predictions: Mixtures Without and With Natural Gas
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
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Flow Assurance: Gas Hydrates and Wax - June 2003 Steering Committee Meeting
• 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