Decommissioning Index

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Introduction 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. Fig: Schematic showing a typical fixed steel platform Please click on the image below to see a larger view: 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. Fig: Overview map showing the oil and gas fields and pipelines on the UKCS. Source: Wood Mackenzie   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 dangerous, 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 he structure to shore; 4. Sections are removed to shore and then re-used, recycled or disposed of. Historical context Most of the global oil and gas industry’s experiences of decommissioning offshore infrastructure comes from the US Gulf of Mexico, where around 1,000 small structures have been removed. However the relatively shallow (30 - 50 m) water depths, and weather conditions differ greatly from the northern North Sea, where weather conditions are harsher and water depths can reach up to 200 m. The first platform to be decommissioned in the North Sea was in 1978. Since then about 30 structures have been removed or approved for removal. Nearly half of these are floating or sub-sea structures and all removals to-date have been to a clean sea-bed. However, approval has recently been given to the “North West Hutton” and “Frigg” structures, which under OSPAR 98/3 qualify for partial removal, leaving a steel stump and the concrete sub-structure respectively. The decommissioning issue therefore will continue with the effective management of this legacy. In the early 1990s, when the oil price dipped below $10/barrel, the prospect of a significant increase in decommissioning activity fired predictions of over 50 installations and costs of £1.5 billion in the ten years to 2005. This led to much speculation that a lucrative new business would result. However, studies have since shown that the economic activity from extending oil and gas developments is far more beneficial. Assisted by the rise in oil prices and renewed interest in the UKCS, this has been the predominant driver for investment in recent years. decommissioning activity levels have turned out to be less than a third of those predicted and some field lives have been extended beyond 15 years. This also illustrates the uncertain nature of planning for contract service capacity into the decommissioning market. In 1995, the decision to dispose of the Brent Spar was reversed by the actions of Greenpeace and the subsequent public interest that was roused. International governmental policies were significantly adjusted. The legislative requirements of today have been shaped by the debates which ensued.