The activities that are to be carried out while the field is still in production encompass planning, scheduling, information gathering, decommissioning engineering, approvals, and preparation for dismantling. Access to the collective knowledge of all technical and support disciplines from the operations team is a key determinant of success as they have the operational history and are likely to be able to red-flag issues pertaining to particular pieces of equipment.

The relevant physical, operational, environment and safety information is collated into a Basis of Abandonment document (analogous to the Basis of Design in Project Phase) that provides the strategy, goals, budget, KPIs, and basic details required to begin developing detailed procedures.

The decommissioning phase begins after cessation of production and involves the permitting and approvals in which the well P&A and physical dismantling of the equipment occurs. The most efficient initial state of the equipment is that it is de-energised, cleaned and hydrocarbon free. The end state of this phase is the wells permanently isolated, equipment to be left in field disposed of in accordance with approvals, and all other equipment cut, lifted, and transported to shore for reuse, recycling or discarded as waste.

During decommissioning phase, the preparatory engineering work that is conducted results in a detailed set of project documentation including procedures, task plans, logistics and transport plans, and waste plans.

Following completion of the physical dismantling activities, the documents delivered will include well abandonment schematics, completed task lists, inspection and test plans, survey maps, waste and recycling tracking records, certificates, and lessons learned.

During the abandonment phase, the key activity is to monitor the decommissioned assets remaining in-situ and to prepare and submit the requisite reports to the regulator that allow the operator to surrender the title to the field and any equipment remaining therein.

The documentation produced at the end of dismantling is a key input for minimising the scope of work in abandonment phase while assuring a smooth hand-back of the title to the regulator.