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Use of Transient Simulators to Assess Gas Lift Viability for Offshore Angola

Use of Transient Simulators to Assess Gas Lift Viability for Offshore Angola. 2002 North American Gas Lift Workshop. SHAUNA NOONAN / FRED BROWNLEE. Actually a better title would be:. Produce 40,000 BWPD from 23,000 ft MD (8800 ft TVD) via Gas Lift Fact or Fiction?. Presentation Outline.

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Use of Transient Simulators to Assess Gas Lift Viability for Offshore Angola

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  1. Use of Transient Simulators to Assess Gas Lift Viability for Offshore Angola 2002 North American Gas Lift Workshop SHAUNA NOONAN / FRED BROWNLEE

  2. Actually a better title would be: Produce 40,000 BWPD from 23,000 ft MD (8800 ft TVD) via Gas Lift Fact or Fiction?

  3. Presentation Outline • Operating Parameters • Discussion on software (transient and static programs) • Work scope • Some of the results • What did we learn? • Questions

  4. Parameters • 4500 psi injection pressure at wellhead • Target production of 40,000 bwpd / well • 0.68 gravity injection gas • Up to 30 MMscfd source gas available / well • 1.06 gravity water • Wellhead pressure of 250 psi • Reservoir Pressure of 3500 psi • Dry Tree (offshore in 1200 ft water)

  5. Deviation Profile

  6. From previous nodal analysis... • The target rate may be reached via conventional gas lift for a flow area equivalent to 8 5/8” tubing. • This would require gas lift rates of approximately 20 MMscfd. BUT…..

  7. We have the following concerns: • Strategic importance of this well for project development • Static nodal program cannot predict whether the well could be unloaded. • Transient program can predict unloading conditions, but uses flow correlations that are not valid for large tubing sizes (greater than 5.5”) • Existing transient flow program is not capable of reverse flow completions analysis. • At the high injection pressures required, is the gas actually in a gaseous state at the orifice?

  8. OLGA 2000 “OLGA 2000 is the market-leading simulator for transient multiphase flow of oil, water and gas in well and pipelines with process equipment. “ • Over 10,000 experiments were run in eight years on the SINTEF Two-Phase Flow Laboratory near Trondheim, Norway • The tests were run in both steady state and transient modes • The resultant data / correlations reside within OLGA 2000 • ChevronTexaco has been using this program for many years to assess flow assurance issues in pipelines and risers. It has not been used for downhole analysis applications • Limited to single point gas lift configurations

  9. The Plan • Evaluate various completion options for high rate water wells using three different flow analysis software packages: • Well Evaluation Manager (WEM) using OLGAs • Dynalift • OLGA2000 • Evaluate Dynalift when used for large tubing completions • Develop & validate the well unloading sequence • Confirm importance of surface controlled downhole choke

  10. Scope of Study The following scenarios were evaluated: • Case WA1: Lift gas injection down 11¾” casing with 8⅝” tubing. • Case WA2: Lift gas injection down 11¾” casing with IPC 7” tubing • Case WA3: Lift gas injection down 11¾” casing with IPC 8⅝” tubing • Case WB1: Lift gas injection down 3½” tubing with 9⅝” casing • Case WB2: Lift gas injection down 2⅞” tubing, with 9⅝” casing

  11. Results

  12. Case WA1 - Steady State

  13. Case WA1 - Steady State

  14. Case WA1 • Notes: • Separation between WEM & OLGA2000 not fully explained; (possibility - OLGA2000 starting with transient flow first) • Dynalift example uses 0.5” orifice - significant at higher flow rates (problems with 1”) • OLGA2000 & WEM assume a fixed pressure differential not a fixed choke

  15. Note the 180,000 bwpd slug OLGA predicted during the unloading cycle.

  16. Case WA1 - Unloading

  17. Case WA2

  18. Case WA1 versus Case WA3

  19. Effect of IPC Roughness Difference Case WA1: 0.0018 Case WA3: 0.00006

  20. Case WB1 OLGA2000 & WEM include pressure loss from casing connections in annulus; Dynalift uses equivalent area

  21. WHAT DID WE LEARN? • Have a higher degree of confidence that this well could be unloaded. • Question of conventional versus reverse gas lift must include drilling feasibility and operational safety concerns • WEM OLGAs works well for assessing well performance but does not answer unloading questions • For higher rate / pressure single point gas lift systems, surface controlled downhole gas lift valves are mandatory to reduce upsets while unloading the well

  22. QUESTIONS?

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