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An operator in Aberdeen needed to cut a section in 9 ⅝ -in. N-80 casing at 3,149 ft (960 m). The casing had perforations at 12 shots per foot (SPF), so cutting the section without damaging the section mill knives would be a challenge.

To cut and mill the section, Baker Hughes, a GE company (BHGE), deployed a Model D™ section mill designed for milling perforated casing in production zones. The knives were dressed with special METAL MUNCHER™ advanced milling technology (AMT) carbide to provide the robustness and enhanced cutting performance needed to mill through the perforated casing.

After conducting a surface test, the BHGE team tripped the bottomhole assembly (BHA) in hole to the cutting depth, then began rotating the string at 80 rpm with 450 gal/min and 3,500 to 5,000 lb (1587.6 to 2268 kg) of torque. The rpm was then increased to 120 and 500 gal/min, and the team observed a 50 psi (3.45 bar) pressure drop at surface, confirming the cut was successfully made.

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Challenges & Results
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Challenges

  • Operator needed to cut a section in 9 ⅝-in. 40# N-80 casing
  • Casing was perforated (12 SPF, 39-in. diameter, 45° spacing)
  • Low yield point for circulating out cuttings

Results

  • Lowered NPT through single-trip operation
  • Increased ROP with rugged cutters
  • Successfully cut the casing at 3,149 ft (960 m)
  • Milled 60 ft of casing in 27.5 hr
  • Used jets sub above tools to help circulate cuttings out of the well
  • Mill showed only ¹⁄16-in. wear
  • Near-bit stabilizer and taper mill maintained full gauge