Characterising Gas-lift Instabilities with OLGA2000

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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
hubin_at_ipt.ntnu.no Telephone [phone] Fax
47 7394 4472
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If gas injection is not critical...

• 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?
Replace the orifice with a venturi
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OLGA2000 simulation settings

• 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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Density wave instability can occur!
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OLGA simulation results PR is 90bara and air
injection rate is about 18000Sm3/D
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OLGA simulation results PR is 90bara and air
injection rate is about 40000Sm3/D
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OLGA simulation results PR is 90bara and air
injection rate is about 54000Sm3/D
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Summary

• Increasing reservoir pressure and gas injection
  rate increases stability.
• Increasing well depth, tubing diameter, PI and
  system pressure decreases stability
• Instability occurs only when

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Production loss due to density wave instability
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Apply feedback control to the well Variation of
choke opening after controller is started
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Variation of Pwf and wellhead production rate
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Manual control at the same choke opening
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Conclusions

• 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.