Milling glass plug in high pressure condensate well

Hostile environment
JNO161954 Milling glass plug in high pressure condensate well - Well Intervention - Welltec


To eliminate the risk of damage to the formation, surface and down-hole equipment (740 bar, 143°C reservoir pressure and temperature, gas condensate), a North Sea client required Welltec® to mill open a glass plug in the intermediate completion rather than cycling open the glass plug with the use of pressure cycles.

Challenges with this operation were:
- cresence of approx. 20m of cesium formate 2.3 s.g column above the glass plug.

- completion ID changes above the glass plug and presence of debris above the glass plug

- intermediate completion large OD’s vs. fishing small wireline tools (i.e. cable head and the electrical - release device) in case of getting stuck with the BHA during the glass plug milling.


Welltec proposed to use the 318 Well Cleaner® Reverse Circulation Bit (RCB) with 3.8” Ellipse mill bit.

The BHA design was optimized to cover all the risks associated with the milling operation. In the first run HUD was tagged approx. 4m above the glass plug and frequent stalling on the bit gave an early indication of metal debris presence, which was later confirmed by the bailers content.

In the second run, the RCB was fitted with a 4.00” mud paddle also successful in debris collection and gaining depth progress. The 3rd run the RCB was fitted back with the 3.8” Ellipse Mill Bit and was used to mill the glass plug.

The downhole gauge indicated a 0.5 bar drop in pressure while milling confirming the glass plug is milled through. The glass plug area was then drifted.


Completed in 3 runs due to the presence of the debris. A total recovery of 34 kg of debris above the glass plug including: calcium carbonate, aluminum pieces (biggest 45x20x3mm), copper, “coal like” substance and also broken glass from the glass plug itself.

Client decided to use both RCB and the Well Cleaner (PST) in combination to do further clean out below the glass plug, for which further five runs were conducted, resulting in an extra 364 kg settled mud debris collection, with 100% bailer recovery on runs and no NPT. And method for the upcoming high pressure gas condensate wells clean ups in the same field.