Efficiently mill and underream multiple sections in offshore well
An operator was planning a P&A operation in the UK sector of the
North Sea. Its objective was section milling two windows of approximately 100
ft in the 13 3/8-in casing—the first across the Frigg Formation and the
second across the Utsira Formation. Each openhole section would then need to be
underreamed—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 helping to decrease the cost and
regulatory concerns inherent to well decommissioning. The solution included a
hybrid ProMILL system cutting structure with WavEdge ridged milling elements
used in combination with 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 7.5 days and USD 1 million across P&A operation
The integrated P&A solution effectively displaced and conditioned
the well as required. In the first window, across the Frigg Formation, the
operator milled and underreamed a record-breaking 109 ft of 13 3/8-in casing in
one trip using performance inserts. In the second window, across the Utsira
Formation, conventional inserts milled and underreamed 100 ft of133/8-in casing
in 27.25 h, achieving the operator's fastest milling time in the formation.
During milling, the operator achieved an ROP of 4.2 ft/h, representing a
40% increase compared with 3 ft/h, the average ROP of the operator's jobs
completed in the field. In this well, the operator recorded an overall cost
reduction of 7.5 days and USD 1 million—the ProMILL system's efficacy
played an integral role in this achievement. Using the ProMILL system in this
well continued the operator's string of zero HSE events during abandonment in
three previous wells.
