Well Plug & Abandonment using HWU - Balance Point Control

Background

The Platform was located in the Dutch North Sea. Due to reservoir depletion, production was shut down and the gas processing facilities were removed. Most wells were drilled in the period from 1981 to 1989 with well depths ranging from 1740 to 4300 m. The objective was to Plug & Abandon (P&A) 11 wells and to cut casings and conductors at 6 m below the sea-floor.

Execution

Hydraulic workover was identified as the most efficient way to conduct all P&A work including the casing and conductor cutting operations.
A skidframe was used to support the HWU and enable quick skidding from well to well.
Cement Bond Logs (CBL) were performed to prove cement integrity behind the casings and to prove zonal isolation.
Each well was plugged with 4 cement plugs.
Casings and conductors were cut using a mechanical tubing conveyed rotating cutting tool.
A special pre-tensioning system was used to pull pretension on the casings and conductors while cutting.
After cutting the casing and conductors were left behind for a heavy lift vessel to pick them up together with the jacket.

Results

All wells were successfully plugged and abandoned. All cement plugs were successfully tested during the first test
Cement integrity behind the casings was achieved. No special intervention was required.
No support vessel was required during the entire operation.
Average time to abandon one well was 13 days (inclusive casing and conductor cutting).
All casings and conductors were successfully cut.
Zero incidents and accidents.