Transcript Document

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Characterising Gas-lift Instabilities with OLGA2000
ASME/API/ISO Fall 2003 Gas-Lift Workshop
21-22 October 2003, Kuala Lumpur
Bin Hu
Ph.D Candidate
Department of Petroleum Engineering and Applied Geophysics
Norwegian University of Science and Technology
E-mail: [email protected]
Telephone: +47 7359 4975
Fax: +47 7394 4472
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If gas injection is not critical...
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• Casing heading may
happen
• To thoroughly eliminate
casing heading, make the
gas injection critical
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Is the well unconditionally stable if gas
injection is critical?
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Replace the orifice
with a venturi
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OLGA2000 simulation settings
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•
•
•
•
•
Vertical air/water two-phase flow
No slug tracking
Iso-thermal
Initiated from steady-state
Boundary conditions
– Static IPR
– Psep is constant
– Constant gas source is given near the bottom of the well
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Gas injection rate (kg/s)
Stability map (L=2500m, PI=4e-6kg/s/Pa, Psep=10bara, 100% choke opening, ID=0.125m)
1,25
1,20
1,15
1,10
1,05
1,00
0,95
0,90
0,85
0,80
0,75
0,70
0,65
0,60
0,55
0,50
0,45
0,40
0,35
0,30
0,25
0,20
0,15
0,10
0,05
0,00
Density wave instability can occur!
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40 50
60
70 80
90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310
PR-Psep (bar)
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OLGA simulation results
350
9.E+06
300
8.E+06
250
7.E+06
200
6.E+06
150
5.E+06
Bottomehole flowing pressure
Production rate at wellhead
100
4.E+06
3.E+06
0.E+00
3
1.E+07
Production rate at wellhead (m /D)
Pwf (Pa)
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PR is 90bara and air injection rate is about 18000Sm3/D
50
1.E+04
2.E+04
3.E+04
4.E+04
5.E+04
0
6.E+04
Time (s)
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OLGA simulation results
1.E+07
2100
9.E+06
1800
8.E+06
1500
7.E+06
1200
6.E+06
900
Bottomhole flowing pressure
Production rate at wellhead
5.E+06
600
4.E+06
300
3.E+06
0.E+00
1.E+04
2.E+04
3.E+04
4.E+04
5.E+04
Production rate at wellhead (m 3/D)
Pwf (Pa)
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PR is 90bara and air injection rate is about 40000Sm3/D
0
6.E+04
Time (s)
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OLGA simulation results
1.E+07
1400
9.E+06
1200
8.E+06
1000
7.E+06
800
6.E+06
Bottomhole flowing pressure
Production rate at wellhead
600
5.E+06
400
4.E+06
200
3.E+06
0.E+00
1.E+04
2.E+04
3.E+04
4.E+04
5.E+04
Production rate at wellhead (m 3/D)
Pwf (Pa)
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PR is 90bara and air injection rate is about 54000Sm3/D
0
6.E+04
Time (s)
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Stability map for different well depth
1,1
0,9
Gas injection rate (kg/s)
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1,0
0,8
0,7
2000m
2500m
3000m
0,6
0,5
0,4
0,3
0,2
0,1
0,0
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
(PR-Psep)/ρlgL
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Stability map for different system pressure
1,3
1,1
1,0
Gas injection rate (kg/s)
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1,2
0,9
0,8
0,7
10bara
0,6
20bara
5bara
0,5
0,4
0,3
0,2
0,1
0,0
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
(PR-Psep)/ρlgL
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Stability map for different Productivity Index
1,0
0,8
Gas injection rate (kg/s)
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0,9
0,7
0,6
4e-6kg/s/Pa
0,5
8e-6kg/s/Pa
2e-6kg/s/Pa
0,4
0,3
0,2
0,1
0,0
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
(PR-Psep)/ρlgL
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Stability map for different choke opening
0,9
0,7
Gas injection rate (kg/s)
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0,8
0,6
0,5
100 %
0,4
50 %
10 %
0,3
0,2
0,1
0,0
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
(PR-Psep)/ρlgL
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Stability map for different tubing diameter
1,3
1,1
1,0
Gas injection rate (kg/s)
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1,2
0,9
0,8
0,7
ID=0.125m
0,6
ID=0.10m
ID=0.15m
0,5
0,4
0,3
0,2
0,1
0,0
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
(PR-Psep)/ρlgL
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Summary
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• Increasing reservoir pressure and gas
injection rate increases stability.
• Increasing well depth, tubing diameter,
PI and system pressure decreases
stability
• Instability occurs only when
PR  Psep
 l gL
1
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Production loss due to density wave instability
1.8
1.6
Normalized production rate
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2.0
1.4
Open loop dynamical simulation results
With feedback control
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.0E+04
1.5E+04
2.0E+04
2.5E+04
3.0E+04
3.5E+04
4.0E+04
4.5E+04
5.0E+04
5.5E+04
6.0E+04
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Gas injection rate (Sm /D)
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Apply feedback control to the well
Variation of choke opening after controller is started
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1.2
1.0
Choke opening (-)
0.8
0.6
0.4
0.2
0.0
0.E+00
1.E+04
2.E+04
3.E+04
4.E+04
5.E+04
Time (s)
6.E+04
7.E+04
8.E+04
9.E+04
1.E+05
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Pwf (Pa)
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1.E+07
2000
9.E+06
1800
8.E+06
1600
7.E+06
1400
6.E+06
1200
5.E+06
1000
Bottomhole flowing pressure
Production rate at wellhead
4.E+06
800
3.E+06
600
2.E+06
400
1.E+06
200
0.E+00
0.E+00
1.E+04
2.E+04
3.E+04
4.E+04
5.E+04
6.E+04
7.E+04
8.E+04
9.E+04
Production rate at wellhead (m 3/D)
Variation of Pwf and wellhead production rate
0
1.E+05
Time (s)
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Pwf (Pa)
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1.E+07
1500
9.E+06
1350
8.E+06
1200
7.E+06
1050
6.E+06
900
5.E+06
Bottomhole flowing pressure
Production rate at wellhead
750
4.E+06
600
3.E+06
450
2.E+06
300
1.E+06
150
0.E+00
0.0E+00
5.0E+03
1.0E+04
1.5E+04
2.0E+04
2.5E+04
3.0E+04
3.5E+04
Production rate at wellhead (m 3/D)
Manual control at the same choke opening
0
4.0E+04
Time (s)
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Conclusions
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• Density wave instability can occur in
deep depleted gas-lift wells.
• The instability not only causes operating
problem, but also reduces production.
• Active feedback control is an effective
method for both stabilising and avoiding
production loss.
• OLGA is at least capable of qualitatively
capturing the instability dynamics.
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