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A North Sea operator needed to plug and abandon (P&A) a well. The plan was to section mill 9⅝-in casing in open hole. NORSOK regulations stipulate that a 165-ft (50-m) window for a cement plug is required for each hydrocarbon zone in the wellbore. To meet this regulation, two cement plugs were planned, one from 12,078 to 12,243 ft (3660 to 3710 m) measeured depth (MD), and one from 13,140 to 13,305 ft (3982 to 4032 m) MD, with maximum inclinations of 76º and 83.5º, respectively.

The deeper window took two runs because the knives on the section mill wore out on the first run after milling 40.92 ft (12.4 m). On both of these runs, the only tool in the bottom-hole assembly (BHA) was an extended-reach section mill, without the benefit of a performance sub and with no way to monitor downhole operational parameters.

Due to mud losses, slow progress, loss of weight, high torque peaks (up to 40 kNm), and no indication of changes in the pressure when outside the window, the decision was made to pull the first BHA out of hole. A second extended-reach BHA was then run in hole to complete the deeper window.

For the shallower window, the solution was to use xSight™ smart intervention services to improve section milling efficiency by observing downhole data such as weight, torque, equivalent circulating density (ECD), vibration, and differential pressure in real time.

Download the PDF to read the full case study.

Challenges & Results
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Challenges

  • Deep section mill a 165-ft (50-m) window in 9⅝-in. casing
  • Section mill the window with maximum inclination of 76º inclination

Results

  • Saved a full day of rig time
  • Cut and section milled 148.50 ft (45 m) of 9-in. casing in an openhole wellbore
  • Monitored ECD to reduce risk of mud loss and avoid debris packoff
  • Maximized cuttings removal