Successful breakthrough milling in the North Sea

Downhole access
Hero UM
  • Well type Oil producer
  • Max deviation 86.1˚
  • Target depth 9186 ft (2800 m)
  • Total depth 14196 ft (4327 m)
  • Pressure 3989 psi (275 bar)
  • Temperature 162˚F (72˚C)


An operator in the North Sea planned a plug and abandonment (P&A) operation for an oil producer. The last operation in the well—a scale-squeezing pump—was performed nearly two years prior. The operator ran a multi-finger caliper (MFC) tool in hole to determine the status of the well before completing the P&A.

During planning, the operator and third-party services knew of the potential for scale buildup in the well but encountered far more scale than initially presumed.

Welltec® was onsite with the Well Tractor® and Well Miller® as a contingency option if substantial scale was discovered. With the contingency option available, the client decided to move forward with milling rather than abandon the well and reschedule with a coiled tubing (CT) operation.


Initially, the Well Tractor twice conveyed an MFC tool in hole, followed by several attempts with mechanical broaching runs. After determining the severity of the scale, the client decided to attempt milling the scale.

Welltec mobilized with the Well Tractor and Well Miller for the milling operation, preparing multiple bit sizes to address the heavy scale buildup within the well.

The Well Miller, conveyed via the Well Tractor, was used in eight of the 16 runs throughout the operation, alternating with MFC runs to check the status of the scale. Early on, milling was conducted with the 3.78” bit and progressed to the 4” bit for three runs. The 5.65” bit was then used for the next three runs before switching to the 5.5” bit for the final run with the Well Miller.

Upon reaching target depth, a dummy plug was installed, followed by HEX plug at 9022 ft (2750 m). Finally, the Well Puncher®, conveyed by the well Tractor, punched holes from 7228 ft (2203 m) to 7213 ft (2195.5 m). The team received good indicators afterwards when they observed a pressure drop. Finally, a shallow plug was installed on the final run.


The client initially believed this level of scale cleanout could only be accomplished via CT operations. Welltec proved that the combination of the Well Tractor and Well Miller solution could be quite effective in these kinds of situations.

With Welltec’s tools onsite as the contingency, the client received high value in saving both time and cost. Wireline operations require less crew, reduced cost, and reduced mobilization time than CT operations. The smaller footprint of wireline operations also reduced HSE risks.

Client Quotes

“CT must be jealous with the progress we are having with the Well Miller.”

“This operation is definitely a breakthrough into what is conventionally though of as CT operation.”