Well Miller CVF® enables highly complex gate valve milling operation from RLWI vessel

Downhole hardware
HERO 1712 X 963 Case Story CVF Congo
  • Well type: Producer
  • Water depth: 682 meters
  • Challenge: 3" subsea gate valve - Incoloy 925
  • Client feedback: "We can be extremely proud of this achievement!"


Since late 2019, TotalEnergies had faced a highly challenging situation offshore of Congo, where the necessary replacement of a subsea Christmas tree was being prevented by a gate valve that was stuck in a partially open position (55%).

With complete access to the well restricted, the gate valve needed to be fully opened/milled through in order to enable the Christmas tree to be replaced and re-establish production from the well.

Faced with the possibility of having to arrange for a full workover rig, an alternative plan was developed, utilizing brand new hardware milling technology developed by Welltec which would allow the operation to be carried out from a Riserless Light Well Intervention (RLWI) vessel. With the added difficulty of the valve being made of a three-inch plate of high-strength Incoloy, there was a demand for a robust but precise solution capable of milling through it while simultaneously ensuring the milled section could be retrieved to surface and not lost downhole.

This successful and complete milling operation represents an industry first, and is testimony to the capabilities of the Well Miller CVF (Continuous Variable Force) platform which brings CNC-like machining precision to downhole environments.


The operation was split into two main phases:

Design - The design phase of the operation began with an extensive process to develop a custom locating bit to match the exact profile of the partially opened gate valve; this custom manufactured ‘key’ needed to allow the milling bit to function without restriction while simultaneously locking into place with the section to be milled in order to prevent the loss of any material downhole. A replica of the stuck valve was made, and multiple surface integration tests (SIT) were performed on the valve with the trial milling operations being conducted both horizontally and vertically. These tests were made to ensure the milled section could be successfully recovered before the verified solution was mobilized along with multiple contingency options.

Execution - The Well Miller CVF was run in hole, providing dynamic weight on bit and indications of piston movement, enabling Welltec and TotalEnergies to closely monitor progress at all times. Once the custom key had landed in the exact position required to mill the valve, the gate valve was then milled through in 17 hours, with the coupon recovered to surface.


A customized solution was combined with a brand-new hardware milling system to reinstate a valuable asset for TotalEnergies.

Utilizing controlled force, accurate piston reading and bi-directional stroking capability, the Well Miller CVF system was able to mill through the Incoloy gate valve, subsequently facilitating the replacement of the Christmas tree utilizing a RLWI vessel as opposed to a Drillship – a significant cost-saving.

Furthermore, new CVF technology has made an immediate impact by meeting client needs on a task with a high degree of complexity, enabling the operation to be performed in a cost-effective way which would otherwise not have been possible.

Client feedback

"Congratulations to you all! We did it! We can be extremely proud of this achievement! I am speechless!"