Removing carbonate scale to ensure wellbore access

Downhole access
JYE133053 Removing carbonate scale - Well Intervention - Welltec
  • Max. deviation 89.72° @ 10,696 ft (3,260m) MD/RT
  • Max. temperature 221°F (105°C)
  • Tubing diameter 4.5" OD
  • Min. restriction 2.75"
  • Location Yemen


A water injector in the Kharir field was experiencing issues with carbonate scale build-ups that led to decreased injectivity. KHA1-51 was completed in 2011, as one of the deepest injectors in the basement rock in an area where the surrounding pressure is sharply decreasing. KHA1-51 has been actively injecting water since November 2011, at a rate of 3,500 BWPD.

On a neighboring injector well, carbonate scale deposits caused six months of down time waiting on a workover rig. Thus Total E&P Yemen, did not want to take any risks when planning a PLT operation on this well.

Communication with one neighboring well had been confirmed by interference in pressure and water-cut evolution and the aim of the upcoming PLT operation was to get the complete injection profile.

To ensure proper access to the open hole, Total E&P Yemen first did an acid pickle on the tubing one week prior to the logging job. However, the acid did not dissolve the accumulated scale; thus, an e-line scale clean out was initiated.


At 8,291 ft (2,527m) the Well Miller® 218 configured for scale removal was deployed and milled 46 ft (14m) down to the Wireline Entry Guide (WEG), where the tool operator switched to logging mode to correlate the CCL in order to confirm the bottom of tubing; then the toolstring was returned to surface.

The Well Miller for scale removal was combined with a Well Tractor® 218 to apply weight-on-bit and counter the reactive torque from the milling bit rotation. The milling operation was performed during water injection to push deposits away from the milling bit while milling to avoiding getting stuck.


This was the industry’s first electric line scale milling operation in the Middle East and North Africa. The scale removal operation increased the water injection by 15% with no well head pressure. This successful scale cleaning was performed in just one run with no downtime or LTIs and took less than half the time as the estimated time for a workover rig.

The well head initial pressure of 90 bar decreased to 1 bar atmospheric pressure because the surface pressure disappeared. The results of the subsequent PLT operation can be read in the case story: “New world record: 46,801 ft tractored in one run in open hole well”.