Well decommissioning is the permanent isolation of any rock formations with flow potential and the restoration of a seabed to its previous status. There are three phases of well decommissioning:
- PHASE 1: Permanent Isolation of the reservoir
- PHASE 2: Permanent isolation of all intermediate zones with flow potential. This phase is complete when all required barriers are in place
- PHASE 3: A well is considered fully decommissioned after removing the wellhead and conductor, the well origin at surface is removed and the well will never be used or re-entered again.
Well decommissioning is conducted by a team of highly skilled personnel who will engineer specific activities for each well bore and then carry out the decommissioning work scopes. These work scopes are normally carried out using one of the following methods:
- Subsea wells: Using a jack-up or semi-submersible drill rig, or in some instances lightweight well intervention vessels (LWIV)
- Platform wells: Using a jack-up, the existing drilling rig on an installation (which may require upgrades to make it fit for purpose); or using purpose-built, modular equipment installed specifically for well decommissioning
Each well is different and knowledge of the well and a record of previous operations is helpful in ensuring a successful campaign.