An operator in the North Sea planned to mill a window in a 9⅝-in casing and underream an open hole to enable rock-to-rock barrier placement in a single trip P&A operation. SLB recommended the ProMILL™ trip-saving milling and underreaming system to eliminate the need for a dedicated trip to the surface. They successfully milled and reamed an 85-ft window at MD of 9,000 ft with a single assembly. They repeated the operation on three wells and saved more than 24-h on each well.

Reduce dedicated BHAs for each run

In a P&A campaign in the UK Continental Shelf, an operator planned to create permanent rock-to-rock barriers by placing cement across the impermeable shale formations. If the operator found poor cement behind the casing, then it would performing milling and underreaming to allow setting a cement-rock barrier. In offset wells, the milling and underreaming operations required dedicated BHAs, resulting in a 24-hour trip.

Combine multiple runs into a single trip system

To save rig time, SLB recommended running the ProMILL system, which combines an underreamer and a section mill in one efficient tool. The operation began by cutting and milling the casing windows with the section mill. Then, an activation ball was dropped and pressure was applied to shear the retaining pins. This action activated the underreamer by allowing an internal piston to move down, forcing the underreamer arms outward. The open hole is then underreamed to virgin formation during the same trip.

Eliminated a trip and saved 24 hours per well

The ProMILL system enabled milling and underreaming 85-ft windows at 9,000-ft MD in three wells in one trip each. The efficient system allowed reducing openhole exposure time, manual handling, and personnel exposure on the drill floor. By eliminating the extra trips, the operator saved at least 24 hours of rig time per well.