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Gaslift as Back-Up for a Subsea ESP Lifted Well

Gaslift as Back-Up for a Subsea ESP Lifted Well Philip Holweg - Shell Expro Eric Lovie - Schlumberger API Gaslift Workshop Woodbank, Aberdeen 12 November 2001. Gaslift as Back-Up for a Subsea ESP Lifted Well. Outline Justification for installing gaslift on an ESP lifted well

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Gaslift as Back-Up for a Subsea ESP Lifted Well

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  1. Gaslift as Back-Up for a Subsea ESP Lifted Well Philip Holweg - Shell ExproEric Lovie - Schlumberger API Gaslift WorkshopWoodbank, Aberdeen12 November 2001

  2. Gaslift as Back-Up for a Subsea ESP Lifted Well Outline • Justification for installing gaslift on an ESP lifted well • Gaslift orifice selection • ESP and gaslift performance to date

  3. Introduction to Gannet E Reservoir characteristics • API = 20.8 • Viscosity = 12 cP • GOR = 113 scf/bbl • Reservoir pressure = 2,400 psi • Reservoir depth = 5,700 ft • Strong aquifer support • High permeability sands 1 - 2 Darcy

  4. Gannet E - Subsea ESP Development

  5. Justification for ESP & Gaslift • Reservoir fluids very heavy and viscous • Well productivity proved to be high (58 bbl/day/psi) • confirmed by dedicated well test before ESP was designed • High flowline backpressure • 1,200 psi with 2 ESPs flowing • Expected flow rates: • Natural 0 • Gaslift 1x 6,000 bbl/day • ESP 3x 18,000 bbl/day • Therefore ESP is preferred artificial lift method

  6. Justification for ESP & Gaslift • Uncertainty around ESP runlife • one of the first subsea ESP installations worldwide • require at least 6 - 12 months runlife to break even due tohigh ESP change-out cost subsea • Infrastructure synergy with GF • only needed 7 km additional gaslift line • Therefore, a dedicated gaslift line was justified to GE • minimises economic exposure in case of ESP failure

  7. Benefits of Gaslift Back-Up • Production optimisation • minimise oil deferment upon ESP failure • scheduling time for workover rig is 4 - 12 weeks • Maximising value • later in field life it is more economic to gaslift than to perform ESP change-out • Cost of ESP change-out (4 - 5 M£)

  8. Gaslift Valve Selection Gaslift has to be compatible with ESP lift • Main objective is to protect ESP cable • prevent gas migration into ESP cable elastomers(risk of explosive decompression of cable) • allow bleed-off of annulus in a controlled manner(maintain <5 bar above THP) • ensure annulus fluid does not change(control pressure fluctuations due to unwanted fluid effects) • Therefore annulus requires to be a closed volume • install a draw bar in gaslift valve • employ a single point injection system

  9. Gannet E - Completion Diagramme 5-1/2” Tubing 4-1/2” Side Pocket Mandrel @ 4,400 ft TVSS 10-3/4” ESP Packer ESP system 3,000 ft Sand Screens

  10. Gaslift Valve with Draw Bar Draw Bar(shear pressure 1,000 psi)

  11. 2,500 2,000 1,500 Pressure (Psi) 1,000 500 0 140 Temp (F) 90 40 20,000 Flow (bbl/d) 10,000 0 18:00 00:00 06:00 12:00 18:00 00:00 06:00 Time (hours) Gaslift Activation gaslift PDG annulus Drawdown Startpressurisingannulus Well unloaded 1,000 psi(gradientcorrected) THP riser separator Draw bar shear THT Export line unloading separator gross Well unloading

  12. 25,000 Waterbreakthrough Water Oil ESP #1failure 20,000 15,000 Gaslift Rate (bbl/d) 10,000 5,000 ESP #2 ESP #1 0 Jan-98 Apr-98 Jul-98 Oct-98 Jan-99 Apr-99 Jul-99 Oct-99 Jan-00 ESP vs Gaslift Performance #1

  13. 25,000 ESPfrequencyincrease Water Oil ESP #2failure 20,000 15,000 Rate (bbl/d) Gaslift 10,000 5,000 ESP #2 0 Feb-00 May-00 Aug-00 Nov-00 Feb-01 May-01 Aug-01 Nov-01 ESP vs Gaslift Performance #2

  14. Gaslift and ESP Production Rates • GE-01 Production performance to date • ESP #1: 17 months runlife @ 15,000 - 18,000 bbl/day • Gaslift: 2 months @ 5,000 - 8,000 bbl/day • ESP #2: 23 months runlife @ 15,000 - 18,000 bbl/day • Gaslift: 4 months @ 5,000 - 6,000 bbl/day • More gaslift at higher watercut & tail end production • less priority to work over well - availability of mobile rig • well will be put on gaslift permanently end of field • workover costs 4 M £ - 5 M£

  15. Conclusions • Business case: • good insurance on development risk • reduces oil deferment in case of ESP failure • optimises tail-end of field life economics • Performance: • valve operation demonstrated • ESP versus gaslift rates as predicted

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