Barium sulphate scale removal offshore

  • Location
    Offshore UK
  • Well type
  • Pressure
    <12 kpsi / 830 bar
  • Wellhead temperature
  • Completion type


In a gas well, offshore UK, barium sulphate scale build-up from the tubing hanger prevents removal of the Wireline Retrievable Surface Controlled Sub-Surface Valve (WR-SCSSV) which is failing to close and required changed.

Additionally LMMV bonnet and stem requires changed-out, 2 plugs are required to complete this work scope (1 being set in the downhole safety valve nipple).

It was a Normally Unmanned Installation (NUI) Platform, so there was limited space, and only day shift operations.

Tubing hanger ID restriction limited milling bits (3.9” hanger restriction, WR-SCSSV No-Go 3.86”).


3.88” OD Tapered milling bits were manufactured to comply with well ID restrictions and size of replacement sleeve. The tool strings run included 2 x Release devices.

Tapered milling bit was replaced with the expandable milling bit which cleared the path. The expandable milling bit closed has 3-1/8” OD, and for this well their maximum opening was limited to 4.1” (tubing ID 4.126”).

The WR-SCSSV depth was achieved, this was clearly confirmed on surface by current draw down and milling response.


Successfully milled scale from below the tubing hanger to the WR-SCSSV.

Safety valve and LMMV were changed as planned.

Operator praised success and professionalism of the crew and support received.

The expandable bit was the key to opening up a path through the scale to allow us to pull the safety valve. Just so you know the new valve is installed & tested. It has taken us 3 years to get to this point with numerous unsuccessful interventions, the alternative was coiled tubing or possibly a workover. Needless to say there are a few happy faces in here.

Tools applied

  • Well Miller® with Expandable Bit

    The Well Miller with Expandable Bit for hardware milling provides operators with a better way to repair wells with mechanical obstacles. It can pass through small ID and expand to a larger OD when activated.

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  • Well Tractor®

    The Well Tractor was regarded as a revolution in the industry when it was introduced in the 1990’s. It enables operators to extend the reach of traditional e-line deployment into highly deviated and horizontal wells.

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  • Welltec Release Device®

    Welltec Release Device (WRD®) is a simple tool which adds versatility and risk reduction to the operation. It provides predetermined locations in the toolstring where it can be parted, should it become stuck.

    Read more