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- Improving well performance and integrity
Case studies



Key info

  • Region: UK North Sea
  • Customer: Premier Oil
  • Field: Brenda
  • Well Type: Subsea
  • Well head type: Subsea


Case benefits

Retrofit Gas lift design to aviod a costly workover. Prior to intervention there was no production. Without the design work carried out by PTC petroluem engineers straddles could have been set at the incorect depth.



Key capabilities


  • Gas lift for wells without side pocket mandrels or mandrels set at incorrect depths.


Typical applications


  • Retrofit Gas lift to increase oil production
  • Retrofit Gas lift for gas well dewatering
  • Retrofit annulus to tubing bleed off

Gas Lift Straddle

GoLift Straddle
GoLift Straddle
GoLift Straddle
GoLift Straddle
GoLift Straddle

Retrofit Gas lift system, Premier Oil, Brenda, D3


An existing subsea gas lifted oil well in the Central North Sea stopped producing. The existing third party gas-lift system was comprised of 2 x IPO unloading valves and an operating valve. Due to an error in the gas lift design continuous gas injection could only be achieved via the the uppermost IPO unloading valve. The uppermost IPO unloading valve eventually failed and it was no longer possible to inject lift gas into the well, stopping production. PTC designed, built and installed a retrofit (straddle based) system using an intervention vessel. The intervention operation was completed as planned and the well was successfully brought back online . 




  • Existing subsea well Brenda D3 (block15/25b)
    • 3 x gas-lift mandrels in 5-½” tubing in 9-⅝” casing
    • 2 x IPO unloading valves, 1 x operating valve
    • Mandrels set too deep for well conditions and existing Gas Lift Valves (GLVs) could not be pulled.
  • Well historically lifting from uppermost (IPO unloading) valve only
    • Deeper valves unused
    • Uppermost IPO unloading valve failed, as it was not designed for constant injection (3rd Party, non PTC valve)
    • Gas injection not possible
  • Well unable to flow without gas lift and as a result production stopped




  • PTC performed a gas lift design for D3 and discovered that only one unloading valve and one operating valve would be required over the life of field.
    • Holes were punched in the tubing at the PTC specified depths
    • Interwell staddles packers were used in conjunction with PTC’s GoLift Gas Lift straddle and GLVs.




The intervention operation took aproximatly 7 days. PTC was provided production data after restart the 29th of November, which showed that the well was now averaging 1685stb/d. The well is still successfully producing today. It was estimated that the costs for the entire intervention operation, including all equipment, personnel and the intervention vessel were recoverd after 68 days of production.