thermodynamic modelling of systemsthermodynamic … · · 2015-01-20thermodynamic modelling of...

Thermodynamic modelling of systemsThermodynamic modelling of systems containing water and hydrate inhibitors application to flow assurance and gasapplication to flow assurance and gas processing

Antonin ChapoyHydrates, Flow Assurance & Phase Equilibria Research GroupHydrates, Flow Assurance & Phase Equilibria Research GroupInstitute 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 InhibitorsWater and Inhibitors– Hydrate Inhibitor Distribution in Multiphase Systems– Gas Hydrate in Low Water Content GasesGas 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

• BackgroundPVT and Phase Behaviour of Petroleum Reservoir– PVT and Phase Behaviour of Petroleum Reservoir Fluids research started in 1978

– Gas hydrate research started in 1986y– Centre for Gas Hydrate Research Established in Feb

2001C f Fl A R h (C FAR) d i– Centre for Flow Assurance Research (C-FAR) started in 2007

A f A ti iti• Areas of Activities– Research

Consultancy– Consultancy– Training (open and in-house courses)


Hydrates, Flow Assurance & Phase Equilibria Research Group

Research InterestsPVT d Ph B h i f R i Fl id d CO• PVT and Phase Behaviour of Reservoir Fluids and CO2-Rich Systems

• Flow Assurance– Gas Hydrates

W– Wax– Salt (halite)– AsphalteneAsphaltene

• Gas HydratesFlow Assurance– Flow Assurance

– Gas Hydrates in Sediments– Positive/other Applications of Gas Hydrates


pp y

What are gas hydrates ?

• Gas hydrates or clathrate

• Gas hydrates or clathratehydrates are:– Ice-like crystalline– Ice-like crystalline

compounds– Composed of water + gas Co posed o a e gas

(e.g. methane, CO2)– Formed under low

temperatures and elevated pressuresSt bl ll b th i– Stable well above the ice-point of water Methane hydrate: the

b i b llSFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014

burning snowball

Hydrate Structures and Stability Zone

Th diti• The necessary conditions:– Presence of water or ice– Suitably sized gas/liquid– Suitably sized gas/liquid

molecules (such as C1, C2, C3, C4, CO2, N2, H2S, etc.)S

P– Suitable temperature and

pressure conditions

• T and P conditions is a functionHydrates

• T and P conditions is a function of gas/liquid and water compositions.

No Hydrates

• Can form anywhere that the above conditions are met Hydrate phase boundary

T


y p y

Gas Hydrate Formation

• Not necessary:–Presence of a gas phase–Presence of a free water phasep–Very low temperature conditions

V hi h diti–Very high pressure conditions


Gas Hydrate Formation

• The extent of hydrate formation and the resulting problems depends on:resulting problems depends on:

– The amount of water and hydrate forming e a ou o a e a d yd a e o gcompounds

– Pressure and temperature conditionsp– Amount of thermodynamic or kinetic inhibitors– Presence of natural inhibitors– Other factors, such as, growth modifiers, local

restriction, fluid type, pipe wall characteristics, etc.


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– Offshore drilling operations

– Etc


Interesting Properties

– Capture large amounts of gas (up to 15 mole%)Remove light components from oil and gas– Remove light components from oil and gas

– Form at temperatures well above 0 °C– Generally lighter than watery g– 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– Result from physical combination of water and gas– Hydrate composition is different from the HC phase– Large amounts of methane hydrates exist in natureg y


Hydrate Structures

2 Methane, ethane, carbon dioxide….

6 Structure 1

51262

16 8 Structure 2

51262

3

Propane, iso-butane, natural gas….

51264512

+P T and 3

2 1 Structure H

512645suitable guests

2Methane + neohexane, methane + mch….

1 Structure H


51268435663

Hydrate former in Natural Gas

• MethaneI f– sI former

– Both small and large cages of SI

• Ethane – sI former– Only large cages of SI

• PropanePropane – sII former– Only large cages of SIIOnly large cages of SII


Hydrate Formers in Natural Gas

• i-butane– sII former– Only large cages of sII

• n-butane– Does not form hydrate on its own

F i th f th– Form in the presence of another hydrate former, i.e. methane

– Only large cages of sIIOnly large cages of sII

• Cyclo-propane – sI or sII former depending on T and P– sI or sII former depending on T and P– Only large cages


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• Hydrogen Sulphide– sI former

Small and large cages– Small and large cages


Other Hydrate Formers

• Freons

• Halogens (fluorine and chlorine)

• Noble gases (argon krypton xenon radon not• Noble gases (argon, krypton, xenon, radon not helium)

Very stable compound →good indication that no– Very stable compound →good indication that no chemical bonding exist between the host and the guest

Ai (N O )• Air (N2 + O2)

• SO2 (very soluble in water) and small mercaptans2 ( y ) p(methanethiol, ethanthiol and propanethiol)


Avoiding Hydrate Problems - Current practice

• Increasing the system temperature- InsulationInsulation- Heating

• Reducing the system pressureHydrates

Wellhead conditionsHydratesWellhead conditionsHydratesWellhead conditionsHydratesWellhead conditions

• Injection of thermodynamic inhibitors- Methanol, ethylene glycol, ethanol PPPP

• Using Low Dosage Hydrate Inhibitors- Kinetic Inhibitors (KHI)- Anti-Aggglomerants (AA)

No HydratesNo HydratesNo HydratesNo Hydratesggg ( )

• Water removal (dehydratation)• Combinations of the aboveCombinations of the above

• New Approach: Cold Flow


Flow Assurance- Hydrates: The problems

• Hydrate blockages are major flow assuranceproblems in offshore and deep waterp poperations.

• Currently the most common flow assurancet t i t l i j ti f i hibitstrategy is to rely upon injection of inhibitors

in order to inhibit hydrate formation.

• It is crucial for accurate knowledge ofIt is crucial for accurate knowledge ofhydrate phase equilibrium in the presence ofinhibitors to avoid gas hydrate formationproblems

G h d t d f

problems.

• Lack of experimental data, especially for realreservoir fluids.

Gas hydrates removed from a subsea transfer line

(Courtesy of Petrobras)• Capability to accurately predict the hydrate

stability zone is therefore essential to plan potential flow assurance issues


potential flow assurance issues.

Thermodynamic Modelling

Thermodynamic Modelling• For VLE or VHE, we have:

CPA E S

LV ff or HV ff • CPA EoS:

iA

i XxgVRT

bVVTa

bVRTP 1)ln(1

21

)()(

HV ff

iAimmmm VbVVbV 2)(

SRK part Association partSRK part Association part

site fractions1

1

BAB

jA jiji XxX

bdg jiji BA

ABBA

1exp)(the association strength

j B

jJ

1i

bRT

dg jiji

1exp)(the association strength

SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 20149.11

1)( .

simpdgradial distribution function


• For Hydrate: Solid solution theory of van der Waals and PlatteeuwSolid solution theory of van der Waals and Platteeuw

ffH

ww

Hw

exp

RT

ff ww p

mHH fCvRT 1ln where

• Modeling of electrolyte solutions:

m jjmjmwww fCvRT 1lnwhere

Combining the EoS with the Debye Hückel electrostatic contribution

niELi

EoSii ...,,2,1lnlnln



• BIPs between self-associating compounds using solubility data:

1 n

exp,

,exp,

1

1

i

caliin

xxx

NFOB

• methane-water:

350

400

4900

56000.004

ract

. 25oC

150

200

250

300

P / b

ar

2100

2800

3500

4200

P / P

sia

0.002

0.003

ubili

ty /

mol

e fr

Culberson et al. (1951)Duffy et al. (1961)Yokoyama et al. (1988)Wang et al (1995)

0

50

100

0.0001 0.001 0.01 0.10

700

1400

0

0.001

0 100 200 300 400

CH

4 Sol Wang et al. (1995)

Yang et al. (2001)Kim et al. (2003)Chapoy et al. (2004)

Water content / mole fraction

Water content of methane in equilibrium with liquid water 0, 10, 25, 40 and 75oC.

P / bar

Solubility of methane in water at 25 oC.

SFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014Haghighi H., Chapoy A., Tohidi B., 2009, J. Oil Gas Sci. Technol., 64, 141.


0.3

0.35

fract

. 50oC

• methane-methanol: • methane-MEG:0.025

0.03

fract

. 50oC

0.1

0.15

0.2

0.25

Sol

ubili

ty /

mol

e f

0.01

0.015

0.02

Sol

ubili

ty /

mol

e

0

0.05

0 100 200 300 400 500 600P / bar

CH

4 Schneider, 1978Francesconi, 1978Brunner, 1987

0

0.005

0 50 100 150 200 250 300 350 400 450P / bar

CH

4 S

Jou et al., 1994Zheng et al., 1999

S l bilit f th i th l t 50 C

140

160

180

200

2000

2400

2800

200

250

300

2850

3350

3850

4350

Solubility of methane in methanol at 50 oC. Solubility of methane in MEG at 50 oC.

40

60

80

100

120

P /

bar

800

1200

1600

P /

Psia

100

150

200

P /

bar

850

1350

1850

2350

2850

P /

Psi

a

0

20

40

0.1 1 10 100 1000 10000

MEG content / ppm (mol.)

0

400

0

50

0.001 0.01 0.1 1

MeOH content / mole fraction

-150

350

850

Water content of methane in equilibrium withWater content of methane in equilibrium with


Water content of methane in equilibrium with liquid MEG 5, 10, 40, 50 and 65oC.

Water content of methane in equilibrium with liquid methanol 10, 25, 50 and 75oC.


• BIPs between cross-associating compounds (e.g. water-methanol and water-MEG) adjusted using VLE (bubble and dew point data) or SLE (freezing point depression data) :

,exp,

1

1 caliin

xxx

NFOB

For SLE data

exp,1 ixN

Objective Function:

exp,

,exp,

1

1

i

calciin

TTT

NFOB

For VLE data



• SLE for water-methanol: • SLE for water-MEG:270

280

270

280

240

250

260

270

T / K

ICT (1930)Olsen et al. (1930)Conrad et al. (1940)

240

250

260

T / K Pushin and Glagoleva (1922)

ICT (1926)Feldman and Dahlstrom (1936)

220

230

0 5 10 15 20 25 30 35 40 45 50 55

MEG / mass%

Conrad et al. (1940)Spangler and Davies (1943)Ross (1954)Cordray et al. (1996)CRC Handbook (2004)

210

220

230

0 10 20 30 40

M OH / %

( )Frank et al. (1940)Ross (1954)Ott et al. (1979)CRC Handbook (2004)Haghighi et al. (2009a)

G / ass%

70

80Saturated Liquid (Bubble point) T=343.15 KSaturated Vapour (Dew point) T=343.15 KSaturated Liquid (Bubble point) T=363.15 K

0

80

90Kurihara et al. (1995)Kurihara et al. (1995)

T = 333 KT = 328 K

• VLE for water-methanol: • VLE for water-MEG:MeOH / mass%

30

40

50

60

P / k

Pa

q ( p )Saturated Vapour (Dew point) T=363.15 KPredictions: This work

30

40

50

60

70

P /

kPa

0

10

20

0 20 40 60 80 100

MEG / mole%

0

10

20

0 20 40 60 80 100

MeOH / mol%

Bubble line predictions: This work Dew line predictions: This work


Haghighi H., Chapoy A., Burgess R., Mazloum S., Tohidi B., 2009, J. Fluid Phase Equilibr., 278, 109-116.

Haghighi H., Chapoy A., Tohidi B., 2009, J. Fluid Phase Equilibr., 276, 24-30.


0 10 20 30 40 50 60 70 80 90 100MEG / wt%

10

00 10 20 30 40 50 60 70 80 90 100

Pure MEG: T= -12.4 oC (=+/-0.8oC)

Thermodynamic -20

-10

CRC HandbookConrad et al. (1940)

( )

Modelling-30

T/o C

( )Spangler and Davies (1943)Cordray et al. (1996):lab1Cordray et al. (1996):lab2Cordray et al (1996):metastale

50

-40Cordray et al. (1996):metastaleRoss (1954)Zinchenko (2001)Gjertsen et al. (2001)GPA RR205

-60

-50 GPA RR205This work


Avoiding Hydrate Problems - Current practice

• Increasing the system temperature- InsulationInsulation- Heating

• Reducing the system pressure

• Injection of thermodynamic inhibitors- Methanol, ethylene glycol, ethanol

• Using Low Dosage Hydrate Inhibitors- Kinetic Inhibitors (KHI)Anti Aggglomerants (AA)- Anti-Aggglomerants (AA)

• Water removal (dehydratation)

C bi ti f th b• Combinations of the above

• New Approach: Cold Flow


Experimental Equipment

M t i l• Materials:– Distilled water

North Sea natural gas– North Sea natural gas– Inhibitors

• Equipments:• Equipments:– Autoclave cells – V = 300 to 2000 ml– Max P = 400 – 2000 bar– -80 < T < 50 oC


Typical Experimental Procedures

• Cell loaded with starting fluids at T = 20 C or higherD di i l– Depending on experiment: water ± salts ±Thermodynamic inhibitor (MEG, methanol)Headspace left for further fluid injections: gas (G)– Headspace left for further fluid injections: gas (G), live oil…

• To form hydrates temperature reduced their presence• To form hydrates, temperature reduced, their presence being confirmed by pressure drop

• Hydrate dissociation point is found by stepwise increase• Hydrate dissociation point is found by stepwise increase of T


Hydrates: Experimental Methods

6.0Cooling cycleHeating cycle (non-equilibrium points)Heating cycle (equilibrium points)





5.0

5.5

a

Heating cycle (equilibrium points)Dissociation point

5.0

5.5

a


5.0

5.5

a


5.0

5.5

a


5.0

5.5

a


4.5

5.0

P/M

Pa

4.5

5.0

P/M

Pa

4.5

5.0

P/M

Pa

4.5

5.0

P/M

Pa

4.5

5.0

P/M

Pa

4.0

C1 15 mass% K CO

4.0

C1 15 mass% K CO

4.0

C1 15 mass% K CO

4.0

C1 15 mass% K CO

4.0

C1 15 mass% K CO3.5

250 255 260 265 270 275 280 285

C1 - 15 mass% K2CO3

3.5250 255 260 265 270 275 280 285

C1 - 15 mass% K2CO3

3.5250 255 260 265 270 275 280 285

C1 - 15 mass% K2CO3

3.5250 255 260 265 270 275 280 285

C1 - 15 mass% K2CO3

3.5250 255 260 265 270 275 280 285

C1 - 15 mass% K2CO3

TSFGP Seminar - La Thermodynamique des phases solides- Paris, December, 2014

T/KT/KT/KT/KT/KT

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