1. 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
Telephone:
Fax:

2. If gas injection is not critical...
Casing heading may happen
To thoroughly eliminate casing heading, make the gas injection critical

3. Replace the orifice with a venturi
Is the well unconditionally stable if gas injection is critical?
Replace the orifice with a venturi

4. 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

5. Density wave instability can occur!

6. OLGA simulation results
PR is 90bara and air injection rate is about 18000Sm3/D

7. OLGA simulation results
PR is 90bara and air injection rate is about 40000Sm3/D

8. OLGA simulation results
PR is 90bara and air injection rate is about 54000Sm3/D

14. 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

15. Production loss due to density wave instability

16. Apply feedback control to the well
Variation of choke opening after controller is started

17. Variation of Pwf and wellhead production rate

18. Manual control at the same choke opening

19. 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.