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, Schlumberger 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.