Barium sulphate scale removal offshore

Downhole safety valves
JABZ171004 Barium sulphate scale removal - Well Intervention - Welltec
  • Location Offshore UK
  • Well type Gas
  • Pressure <12 kpsi / 830 bar
  • Wellhead temperature 300°F
  • Completion type Cased


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.