Thermodynamic modelling of systems
containing water and hydrate inhibitors
application to flow assurance and gas
processing
Antonin Chapoy
Hydrates, Flow Assurance & Phase Equilibria Research Group
Institute of Petroleum Engineering, Heriot-Watt University, Edinburgh, UK
Outline
•
•
•
•
Presentation of the research group
I t d ti
Introduction
Thermodynamic Modelling
Results – Discussions
– HSZ in The Presence of High Concentration of
Inhibitor(S) or Salt(S)
– HSZ of Oil/Condensate in the Presence of Produced
Water and Inhibitors
– Hydrate Inhibitor Distribution in Multiphase Systems
– Gas Hydrate in Low Water Content Gases
• Remarks and Conclusions
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Hydrates, Flow Assurance & Phase Equilibria Research Group
• Background
– PVT and Phase Behaviour of Petroleum Reservoir
Fluids research started in 1978
– Gas hydrate
y
research started in 1986
– Centre for Gas Hydrate Research Established in Feb
2001
– Centre
C
ffor Flow
Fl
A
Assurance R
Research
h (C
(C-FAR)
FAR) started
d in
i
2007
• Areas
A
off Activities
A ti iti
– Research
– Consultancy
– Training (open and in-house courses)
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Hydrates, Flow Assurance & Phase Equilibria Research Group
Research Interests
• PVT andd Phase
Ph
B
Behaviour
h i
off R
Reservoir
i Fl
Fluids
id and
d CO2Rich Systems
• Flow Assurance
–
–
–
–
Gas Hydrates
W
Wax
Salt (halite)
Asphaltene
• Gas Hydrates
– Flow Assurance
– Gas Hydrates in Sediments
– Positive/other Applications
pp
of Gas Hydrates
y
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
What are gas hydrates ?
• Gas hydrates or clathrate
hydrates are:
– Ice-like crystalline
compounds
– Co
Composed
posed o
of water
a e + gas
(e.g. methane, CO2)
– Formed under low
temperatures and elevated
pressures
– Stable
St bl wellll above
b
th
the iicepoint of water
Methane hydrate: the
b
i snowball
b ll
burning
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Hydrate Structures and Stability Zone
• The
Th necessary conditions:
diti
– Presence of water or ice
– Suitably sized gas/liquid
molecules (such as C1, C2, C3,
C4, CO2, N2, H2S, etc.)
– Suitable
S
temperature and
pressure conditions
P
Hydrates
• T and P conditions is a function
of gas/liquid and water
compositions.
• Can form anywhere that the
above conditions are met
No Hydrates
T
Hydrate
y
phase
p
boundaryy
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Gas Hydrate Formation
• Not necessary:
–Presence of a gas phase
–Presence of a free water phase
p
–Very low temperature conditions
–Very
V
hi h pressure conditions
high
diti
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Gas Hydrate Formation
• The extent of hydrate formation and the
resulting problems depends on:
– The
ea
amount
ou o
of water
ae a
and
d hydrate
yd a e forming
o
g
compounds
– Pressure and temperature
p
conditions
– Amount of thermodynamic or kinetic inhibitors
– Presence of natural inhibitors
– Other factors, such as, growth modifiers, local
restriction, fluid type, pipe wall characteristics,
etc.
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Where Can They Form?
• They can form anywhere, such as:
– Pipelines (offshore and onshore)
– Processing facilities (separators, valves, etc)
– Heat exchangers
– Sediments (permafrost regions and subsea
sediments)
– Offshore drilling operations
– Etc
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Interesting Properties
–
–
–
–
–
–
–
–
–
–
–
Capture large amounts of gas (up to 15 mole%)
Remove light components from oil and gas
Form at temperatures well above 0 °C
Generallyy lighter
g
than water
Need relatively large latent heat to decompose
Non-stochiometric
More than 85 mole% water in their structure
Exclude salts and other impurities
Result from physical combination of water and gas
Hydrate composition is different from the HC phase
Large
g amounts of methane hydrates
y
exist in nature
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Hydrate Structures
6
Methane, ethane,
carbon dioxide….
2
51262
8
16
+
Structure 1
Structure 2
Propane, iso-butane,
natural gas….
P T and
suitable
guests
512
51264
3
2
1
Structure H
Methane + neohexane,
methane + mch….
435663
51268
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Hydrate former in Natural Gas
• Methane
– sII former
f
– Both small and large cages of SI
• Ethane
– sI former
– Only large cages of SI
• Propane
– sII former
– Only large cages of SII
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Hydrate Formers in Natural Gas
• i-butane
– sII former
– Only large cages of sII
• n-butane
– Does not form hydrate on its own
– Form
F
in
i the
th presence off another
th
hydrate former, i.e. methane
– Only large cages of sII
• Cyclo-propane
– sI or sII former depending on T and P
– Only large cages
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Hydrate Formers in Natural Gas: Non
Hydrocarbons
• Nitrogen
– sII former
– Small and large cages of sII
• Carbon dioxide
– sI former
– Only large cages of sI
• Hydrogen Sulphide
– sI former
– Small and large cages
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Other Hydrate Formers
• Freons
• Halogens (fluorine and chlorine)
• Noble gases (argon
(argon, krypton
krypton, xenon
xenon, radon not
helium)
– Very stable compound →good indication that no
chemical bonding exist between the host and the guest
• Ai
Air (N2 + O2)
• SO2 (very
( y soluble in water)) and small mercaptans
p
(methanethiol, ethanthiol and propanethiol)
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Avoiding Hydrate Problems - Current practice
•
•
•
•
•
•
Increasing the system temperature
- Insulation
- Heating
Hydrates
Reducing the system pressure
Injection of thermodynamic inhibitors
- Methanol, ethylene glycol, ethanol
Using Low Dosage Hydrate Inhibitors
- Kinetic Inhibitors (KHI)
- Anti-Aggglomerants
ggg
((AA))
Wellhead
conditions
P
•
No Hydrates
Water removal (dehydratation)
Combinations of the above
New Approach: Cold Flow
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Flow Assurance- Hydrates: The problems
• Hydrate blockages are major flow assurance
p
problems
in
operations.
offshore
and
deep
p
water
• Currently the most common flow assurance
strategy
t t
i to
is
t rely
l upon injection
i j ti off inhibitors
i hibit
in order to inhibit hydrate formation.
• It is crucial for accurate knowledge of
hydrate phase equilibrium in the presence of
inhibitors to avoid gas hydrate formation
problems
problems.
• Lack of experimental data, especially for real
reservoir fluids.
• Capability to accurately predict the hydrate
stability zone is therefore essential to plan
potential flow assurance issues
issues.
Gas hydrates
G
h d t removed
d ffrom
a subsea transfer line
(Courtesy of Petrobras)
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Thermodynamic Modelling
f f
•Thermodynamic
For VLE or VHE, we have:
Modelling
• CPA E
EoS:
S
V
P
L
or
fV  fH

RT
a (T )
1 RT 
 ln( g ) 
1  
 xi  1  X Ai


Vm  b Vm (Vm  b) 2 Vm 
  i
Ai
f  f
V
SRK part
radial distribution function
H
Association part

B AB 
X Ai   1    x j X j  i j 
j BJ


site fractions
the association strength


Ai B j
1
   AB   Ai B j
  1  b
 g (d ) exp
  RT  
1
simp
i .
g(d )

1  1.9
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Thermodynamic Modelling
• For Hydrate:
Solid solution theory of van der Waals and Platteeuw
 H




fwH  fw exp
p  w 
RT 

where
 H
w


 w    RT  v m ln 1   C mj f j 
m
j



H
w
• Modeling of electrolyte solutions:
Combining the EoS with the Debye Hückel electrostatic contribution
lni  lniEoS  ln  iEL
i  1, 2,..., n
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Thermodynamic Modelling
• BIPs between self-associating compounds using solubility data:
1 n x i , exp  x i ,cal
FOB  
N 1
x i , exp
400
0.004
0.003
Culberson et al. (1951)
Duffy et al. (1961)
Yokoyama et al. (1988)
Wang et al
al. (1995)
Yang et al. (2001)
Kim et al. (2003)
Chapoy et al. (2004)
0.002
0.001
0
0
100
200
300
400
P / bar
Solubility of methane in water at 25 oC.
5600
350
4900
300
4200
250
3500
200
2800
150
2100
100
1400
50
700
0
0.0001
P / Psia
o
25 C
P / bar
CH4 Solubility / mole frract.
• methane-water:
0
0.001
0.01
0.1
Water content / mole fraction
Water content of methane in equilibrium with
liquid water 0, 10, 25, 40 and 75oC.
Haghighi H., Chapoy A., Tohidi B., 2009, J. Oil Gas Sci. Technol., 64, 141.
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Thermodynamic Modelling
• methane-MEG:
• methane-methanol:
0.03
0.35
o
CH4 S
Solubility / mole fract.
50 C
0.25
0.2
0.15
0.1
Schneider, 1978
Francesconi, 1978
Brunner, 1987
0.05
0
0
100
200
300
400
500
50 C
0.025
0.02
0.015
0.01
0.005
0
600
0
P / bar
300
100
150
200
250
300
350
400
450
Solubility of methane in MEG at 50 oC.
4350
200
3850
180
250
3350
2350
150
1850
100
2800
160
2400
140
2000
120
1600
100
80
1200
1350
60
800
850
40
350
20
50
-150
0.1
P / bar
2850
P / Psia
200
0.01
50
P / bar
S l bilit off methane
Solubility
th
iin methanol
th
l att 50 oC.
C
0
0.001
Jou et al., 1994
Zheng et al., 1999
1
MeOH content / mole fraction
Water content of methane in equilibrium with
liquid methanol 10, 25, 50 and 75oC.
P / Psia
0.3
P / bar
CH4 Solubility / mole ffract.
o
400
0
0.1
1
10
100
1000
0
10000
MEG content / ppm (mol.)
Water content of methane in equilibrium with
liquid MEG 5, 10, 40, 50 and 65oC.
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Thermodynamic Modelling
• BIPs between cross-associating compounds (e.g. watermethanol and water-MEG) adjusted using VLE (bubble and
dew point data) or SLE (freezing point depression data) :
n
xi , exp  xi ,cal
1
FOB 
N

1
xi , exp
1
FOB 
N
n
Ti ,exp  Ti ,calc
For SLE data
Objective Function:

1
Ti ,exp
For VLE data
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Thermodynamic Modelling
• SLE for water-methanol:
280
• SLE for water-MEG:
280
270
270
260
250
T/K
T/K
260
Pushin and Glagoleva (1922)
ICT (1926)
Feldman and Dahlstrom ((1936))
Frank et al. (1940)
Ross (1954)
Ott et al. (1979)
CRC Handbook (2004)
Haghighi et al. (2009a)
240
230
220
10
ICT (1930)
Olsen et al. (1930)
Conrad et al. (1940)
Spangler and Davies (1943)
Ross (1954)
Cordray et al. (1996)
CRC Handbook (2004)
240
230
220
210
0
250
20
30
0
40
5
10
20
25
30
35
40
45
50
55
MEG
G / mass%
ass%
M OH / mass%
MeOH
%
• VLE for water-MEG:
• VLE for water-methanol:
80
90
Kurihara et al. (1995) T = 333 K
Kurihara et al. (1995) T = 328 K
80
Saturated Liquid (Bubble point) T=343.15 K
Saturated Vapour (Dew point) T=343.15 K
Saturated Liquid
q
((Bubble p
point)) T=363.15 K
Saturated Vapour (Dew point) T=363.15 K
Predictions: This work
70
0
70
60
60
50
P / kPa
P / kPa
15
50
40
40
30
30
20
20
Bubble line predictions: This work
Dew line predictions: This work
10
10
0
0
0
20
40
60
80
100
MeOH / mol%
Haghighi H., Chapoy A., Burgess R., Mazloum S., Tohidi B.,
2009, J. Fluid Phase Equilibr., 278, 109-116.
0
20
40
60
80
100
MEG / mole%
Haghighi H., Chapoy A., Tohidi B., 2009, J. Fluid Phase Equilibr.,
276, 24-30.
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Thermodynamic Modelling
MEG / wt%
0
10
20
30
40
50
60
70
80
90
0
Pure MEG: T= -12.4 oC ((=+/-0.8oC))
-10
10
T/oC
-20
-30
-40
-50
50
CRC Handbook
Conrad et al. ((1940))
Spangler and Davies (1943)
Cordray et al. (1996):lab1
Cordray et al. (1996):lab2
Cordray et al
al. (1996):metastale
Ross (1954)
Zinchenko (2001)
Gjertsen et al. (2001)
GPA RR205
This work
Thermodynamic
Modelling
-60
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
100
Avoiding Hydrate Problems - Current practice
•
Increasing the system temperature
- Insulation
- Heating
•
•
Reducing the system pressure
•
Using Low Dosage Hydrate Inhibitors
- Kinetic Inhibitors (KHI)
Injection of thermodynamic inhibitors
- Methanol, ethylene glycol, ethanol
- Anti-Aggglomerants
Anti Aggglomerants (AA)
•
•
•
Water removal (dehydratation)
Combinations
off th
the above
C bi ti
b
New Approach: Cold Flow
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Experimental Equipment
• Materials:
M t i l
– Distilled water
– North Sea natural gas
– Inhibitors
• Equipments:
–
–
–
–
Autoclave cells
V = 300 to 2000 ml
Max P = 400 – 2000 bar
-80 < T < 50 oC
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Typical Experimental Procedures
• Cell loaded with starting fluids at T = 20 C or higher
– Depending
D
di on experiment:
i
water ± salts
l ±
Thermodynamic inhibitor (MEG, methanol)
– Headspace left for further fluid injections: gas (G)
(G),
live oil…
• To form hydrates,
hydrates temperature reduced,
reduced their presence
being confirmed by pressure drop
• Hydrate dissociation point is found by stepwise increase
of T
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014
Hydrates: Experimental Methods
6.0
P/MPa
a
5.5
Cooling cycle
Heating cycle (non-equilibrium points)
Heating cycle (equilibrium points)
Dissociation point
5.0
4.5
4.0
C1 - 15 mass% K2CO3
3.5
250
255
260
265
T 270
275
280
285
T/K
SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014