Knowledge Centre
Decommissioning
Introduction
The oil and gas industry has brought enormous benefits to society, not only in the areas of transportation and energy for our homes but also as the basis of many other essential everyday products, such as plastics, pharmaceuticals and fibres. However, many of the structures which have been producing oil and gas on the UK continental shelf (UKCS) for almost forty years are coming to the end of the lifespan for which they were designed. Over the next couple of decades or so, we will see a growing number of redundant oil and gas installations taken out of service or, to use the industry term, "decommissioned". It is a process which raises complex issues. There has been much debate in recent years about the impact of these operations on the environment, on the health and safety of workers, the costs involved and the technology required, particularly when removing very large structures from the harsh, deep waters of the Northern North Sea.
The industry needs to develop solutions that balance these factors for the overall benefit of the environment and society. A strict legal framework of national, regional and international regulations governs how disused offshore facilities are decommissioned.
Process
Decommissioning is the process by which options for the physical removal and disposal of structures at the end of their working life are assessed; a plan of action is formulated by the operator, approved by Government and then implemented. The overall timescale for this is several years, as it needs to take into account many diverse factors and involves many organisations.
In the UK, there are approximately 470 offshore oil and gas installations. These are mainly located in the Northern, Central and Southern North Sea, as well as in the waters west of Shetland and in the Irish Sea. The Department of Energy & Climate Change (DECC) produces several overview maps detailing the infrastructure present on the UKCS.
At present, where a structure cannot merely be floated away, the best solution is normally to cut the structure into smaller more manageable sections, lift them onto barges and subsequently bring them back to shore for re-use, re-cycling or disposal. Often this constitutes a lengthy, costly and weather sensitive procedure.
There are four discrete stages involved in a decommissioning project:
1. The available options for decommissioning are developed, assessed and selected, balancing environmental factors, cost, technical feasibility, health and safety, and public acceptability factors;
2. The operator applies to the Government to finish production having proved the reservoir is no longer viable. The Government will then grant a “cessation of production” (COP) permit. At this stage the wells will be securely plugged deep below the surface;
3. The operator gains Government approval to proceed with its recommended decommissioning option and offshore operations begin to remove all or parts of the structure to shore;
4. Sections are removed to shore and then re-used, recycled or disposed of.
