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A customer in the North Sea off the coast of Norway needed to remove a string of 9 ⅝-in. 53.5-lb/ft production casing inside 13 ⅜-in. outer casing. Baker Hughes, a GE company (BHGE), suggested a milling operation using the METAL MUNCHER™ turbo pilot mill dressed with advanced milling technology (AMT) carbide inserts.

The METAL MUNCHER turbo pilot mill is a high-performance mill used for milling washover pipe, casing, and liners. It is designed to produce small cuttings that are easy to circulate out of hole and is efficient when dressed with METAL MUNCHER G3 carbide inserts. These specially designed cutting structures have strong, impact-resistant, ultra-sharp primary cutting edges. They last longer under heavy impact than other conventional tungsten-carbide inserts and work well with the pilot mill assembly to manage rate of penetration (ROP).

After tripping the pilot mill to depth, the BHGE team began milling at 4,707 ft (1435 m) and successfully milled 228 ft (69.5 m) of the production casing in 55 hours, averaging an ROP of 4.19 ft/hr (1.28 m/hr). Once the mill was tripped out of hole, the assembly was inspected and the mill had lost only 1.5 in. (3.81 cm) from the initial 30-in. (76.2-cm) long blade inserts. The same customer had to abandon a cut-and-pull operation on a nearby rig when they were unable to successfully retrieve a 51-ft (15.5-m) section of cut 9 ⅝-in. 53.5-lb/ft casing. They decided to mill the remaining stuck casing, but weather conditions between the rig and the transport center prevented the milling assembly from shipping. Conditions were forecasted to last several hours, meaning the customer’s operation would have to wait a day before they could receive the additional milling assembly.

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Challenges & Results


  • Operator needed to cut a section in 9 ⅝-in. 53.5# casing
  • Stuck casing in second well
  • Inclement weather threatened delays


  • Milled casing in two wells with the same pilot mill without redressing
  • Saved a day of rig time and an estimated USD $300,000
  • Managed ROP to deliver clean mill jobs on both wells