Integrated P&A BHA Helps Set Bridge Plug and Mill and Underream 150-ft Window in a Single Run | Schlumberger
Case Study
North Sea, United Kingdom, Europe, Offshore

Challenge: Efficiently section mill 150-ft [46-m] window and then underream the open hole to enable placing an abandonment cement plug.

Solution: Deploy the ProMILL trip-saving milling and underreaming system with performance inserts and efficiently manage cuttings removal using the WELL COMMANDER ball-activated drilling circulating valve from M-I SWACO, a Schlumberger company.


  • Set 9 5/8-in bridge plug from a taper mill, displaced and conditioned well, milled and underreamed 150-ft section, and completed window in a single run
  • Milled at an ROP of 4.5 ft/h [1.4 m/h], a 50% increase compared with the average for the field, 3 ft/h [0.9 m/h]
  • Observed cutter wear of only 30% after milling the 150-ft window
  • Completed window in 50 h, saving 3.5 rig days and USD 600,000
Products Used

Integrated P&A BHA Helps Set Bridge Plug and Mill and Underream 150-ft Window in a Single Run

Efficient performance saves operator 3.5 drilling days and USD 600,000 in decommissioning operation in the UK sector of the North Sea

Efficiently mill and underream section in offshore well

An operator was planning a P&A operation in the UK sector of the North Sea. Its objective was section milling a 150-ft window in the 9 5/8-in casing then underreaming the open hole—all in a single trip— to enable placing a rock-to-rock abandonment cement plug against the original formation.

Use integrated, single-run solution to achieve objectives

Schlumberger collaborated with the operator on an integrated solution that would meet the P&A objectives while decreasing the cost and regulatory concerns inherent to well decommissioning. The BHA solution included the ProMILL system with new performance milling inserts that feature a concave shape. The performance milling inserts were used in combination with the conventional inserts to enhance cutter durability and improve swarf quality. Additionally, the WELL COMMANDER valve was run to boost circulation by removing cuttings at high flow rates, which eliminated a dedicated trip for conditioning the wellbore fluids for the milling program.

The ProMILL system would eradicate all potential leak paths from the abandonment barrier which is not possible to ensure when using perf-and-squeeze methods.

Saved 3.5 days and USD 600,000 with single-trip solution

The integrated P&A solution performed the following operations in a single run:

  • displaced and conditioned the well
  • set the 9⅝-in bridge plug on the taper mill
  • milled a 150-ft section
  • underreamed the exposed formation to prepare the wellbore for a rock-to-rock abandonment plug

During milling, the operator achieved an ROP of 4.5 ft/h, representing a 50% increase compared with 3 ft/h, the average ROP of the operator's jobs completed in the field. The knife wear on the ProMILL system was 30%–35%, which was lower than has been previously seen in similar operations.

The window was completed in 50 h, saving the operator 3.5 days and USD 600,000. This operation set Schlumberger records for the longest single-run window milling, section underreaming, and bridge plug setting as well as the longest single-run milled window.

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The ProMILL system saved an operator multiple trips in a North Sea decommissioning project.
Products Used

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