Decommissioning Index

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Case Studies The following section provides information on some past and present decommissioning projects in the North Sea. Fig: Approximate locations of the North Sea decommissioning projects detailed in this section North West Hutton Fig: a) A schematic view of the entire NW Hutton structure, and b) an aerial view of the topsides   North West Hutton is a large steel platform installed in 1981 comprising drilling, production and accommodation facilities. It was operated by Amoco (U.K.) Exploration Company (now a subsidiary of BP plc.) and is located in the Northern North Sea (block number 211/27a) in a water depth of 143 m. The total topsides weight is around 20 000 tonnes. The jacket consists of an 8 leg, X-braced steel space frame fixed to the sea bed. The total jacket weight is 17 500 tonnes including the weight of the piles. North West Hutton ceased production in July 2002 and since July 2004 has been classified as a “normally unattended installation” whilst the removal and disposal options are prepared. The installation is regularly visited to inspect the structure and perform maintenance duties on essential equipment. The decommissioning programme for the installation was approved in April 2006 by the then DTI. The programme requires that: the topsides and steel jacket down to the top of the footings (the base of the jacket) are completely removed for recycling onshore; the jacket footings are to be left in place, including the piles which fix the structure to the seabed (under an OSPAR derogations ruling); the drill cuttings pile will be left in place to allow the seabed to recover naturally; the oil pipeline to be trenched and buried and the gas pipeline, which is already trenched, will be left in place. The final programme is based on a comprehensive assessment of all options involving a range of external studies. These investigated the key safety, environmental, social, technical and economic aspects of various decommissioning solutions. An Independent Review Group of six environmental experts and engineers from the UK, Norway and Germany verified that the assessment process and studies were comprehensive and objective. A stakeholder consultation process gathered views from a wide range of organisations and individuals and these were taken into consideration in arriving at the programme recommendations. The statutory public consultation on the proposals was completed in March 2005. Consultation on the jacket proposals via the OSPAR process was completed in December 2005. The contract for the removal and onshore disposal and recycling of the installation was awarded to Heerema Marine Contractors in September 2006. Offshore removal work is expected to start in 2008 and be completed by the end of 2009. The topsides and jacket will be removed by heavy lift vessel and taken to the Able yard on Teesside, where it is estimated that 97 % of the material recovered will be recycled. Click here for more detailed information on the decommissioning of North West Hutton from the BP website. Hutton TLP Fig: The Hutton TLP after being floated away from it’s position on the Hutton Field Hutton TLP was the first ever production Tension Leg Platform (TLP) – a floating production platform permanently moored to the sea floor via tethers or tendons (tension legs) at each of the structures corners. Hutton TLP was originally installed in 1984 by Conoco, but at the time of decommissioning it had been bought by Kerr-McGee. It was removed for re-use outside the UK when the platform was purchased by Seymorneftegaz in August 2002, and after having its decommissioning programme accepted by the UK Government. The floating platform was towed to Murmansk in Russia where the topsides facilities and main hull were de-mated. Subsequently the topsides were transported by barge to the Sevmash fabrication yard at Severodvinsk, where they were temporarily stored while undergoing refurbishment and refitting. After completion the topsides were reinstalled onto a new hull structure, and towed into position ready for a new role in the development of the Prirazlomnoye Field, 1200 km north east of Arkhangelsk in the Barents Sea. Brent Spar Fig: a) Aerial view of the Brent Spar installation. b) Brent Spar with Greenpeace protestors The Brent Spar was taken out of operation in 1991 after some 15 years' service in the Shell/Esso Brent field in the Northern North Sea - the UK's largest source of oil and gas. A very large floating oil storage and loading buoy, the Spar had stored oil from the Brent "A" platform and acted as a tanker loading facility for the whole of the Brent field. Detailed studies by several independent companies established that deepwater disposal of the Spar at a site in the deep Northern Atlantic was the Best Practicable Environmental Option (BPEO). The UK Government publicly approved this original plan in February 1995, and also informed the European Union and the twelve countries in continental Europe who were signed up to the Oslo Convention for the protection of the marine environment. However, these scientific and risk evaluations were largely swept aside in the exceptional events of the summer of 1995, when outrage against deepwater disposal of the Spar arose in many people from a deeply-rooted belief in the principle of "clean seas". Shell abandoned the deepwater disposal plan on 20th June. The UK Government accepted this course of action and helped Shell to obtain a licence from the Norwegian authorities allowing the Spar to be anchored in the deep waters of Erfjord. A series of stakeholder dialogue seminars were held across Europe to help find a publicly acceptable solution for the Brent Spar. Following a long and detailed evaluation of contractor bids, in January 1998 Shell announced its choice of solution for Spar - a "one-off" re-use as a Norwegian Ro/Ro ferry quay at Mekjarvik. In August of the same year, the UK Government approved Shell's recommendation and by July 1999, the Mekjarvik quay was completed. Following the controversy over the decommissioning of Brent Spar - international governmental policies were significantly adjusted. The legislative requirements of today have been shaped by the debates which ensued. In addition to Brent Spar installation the Brent Anchor Blocks and Remote Flare structures were successfully decommissioned between 2003 and 2006 as part of the Brent Redundant Facilities Decommissioning Programme. In preparation Shell conducted pre-decommissioning surveys and initiated a stakeholder consultation process in July 2003. The structures were wholly removed to shore for disposal/reuse in July/August 2005. Subsequent removal of any residual debris from the seabed sites took place during summer 2006. As part of the post-decommissioning survey the Scottish Fishermen’s Federation conducted trawler tests in the areas, consequently issuing clean seabed certificates confirming that any seabed debris present had been entirely removed. Shell is currently considering end of field life options for the remaining infrastructure contained within the Brent field. This could mean decommissioning of the present structures - Brent Alpha, Bravo, Charlie and Delta platforms. A preliminary stakeholder consultation exercise has already been initiated in January 2007. This will be followed by a series of stakeholder dialogue sessions before the final programme is decided. Click here for more information about how Brent Spar was decommissioned from the Shell website. Ekofisk Fig: Aerial views of installations on the Ekofisk field: a) the Ekofisk 2-4 A FTP Platform, and b) the Ekofisk Tank In 1994, Phillips Petroleum Norway (now ConocoPhillips Norge) initiated the Ekofisk I Cessation project with the objective of achieving the disposal of the field's varied range of structures in a safe, environmentally friendly and cost-effective manner. In October 1999, the company published an Impact Assessment Report detailing the results of an assessment of the effects on the environment and society estimated to result from the implementation of each of the relevant disposal alternatives for Ekofisk I topsides, substructures, pipelines, drill cuttings and seabed debris. A Cessation Plan was also submitted to the Norwegian Ministry of Petroleum and Energy at that time. The proposals concern the decommissioning of 14 steel platforms and 1 large concrete tank (Ekofisk Tank). The concrete tank, which weighs 1.2 million tonnes, was a candidate for derogation under the OSPAR rules governing decommissioning. In the spring of 2001, a consultation document was sent to all the OSPAR contracting parties. No objections were raised to the proposal to leave the concrete tank substructure as long as it does not harm the environment in the long-term. In June 2002, the Norwegian Parliament also approved the recommendation to leave the tank in place. Decommissioning of the other 14 structures and the Ekofisk Tank topsides at Ekofisk I began in 2005/2006 and are scheduled to continue until 2013. Heerema Marine Contractors were awarded the contract for the removal of bridges, bridge supports and flares using heavy lift vessels. The Ekofisk Tank topsides will be removed by AF Decom. Both companies will cooperate on the onshore disposal part of the work, which is due to be carried out at a new facility at Raunes in Vats, Rogaland, Norway. Click here for more information on the decommissioning of the Ekofisk field from the ConocoPhillips Norge website. Maureen Fig: Maureen Installation being towed to shore Oil production from the Maureen facilities became uneconomic in June 1999 following a rapid decline in production levels. There were no remaining opportunities to increase production levels economically and Cessation of Production (COP) was granted to the operator, ConocoPhillips, by the then DTI on October 7th, 1999. By that time, the plans for decommissioning Maureen were well under way. The Maureen platform was a unique structure since it was a steel gravity base structure which was designed to be re-floated and moved to another location for reuse (the Maureen owners’ preferred solution) or to a suitable inshore location for deconstruction and recycling. The structure weighed 110,000 tonnes and was the first large structure to be decommissioned in the world. The decommissioning programme document, which described the owners’ decommissioning recommendations, was issued for public consultation in June 2000. The UK government approved the proposals in December 2000. In June 2001 the whole platform was successfully re-floated and towed by six tugs to a yard at Stord on the West Coast of Norway. The Maureen loading column, which was also designed for removal, was re-floated shortly after the platform and also towed to Stord. At 10,000 tonnes the concrete column is the second heaviest structure to be removed after the Maureen platform. The Maureen owners continued to seek a buyer for a possible full reuse of the platform until the last possible moment. However, in October 2001 a partial reuse was found for both the platform and column substructures. The base of the platform was cut up and used as part of a deep-water quay at a yard on Stord, while the concrete column was used as a breakwater in a leisure marina nearby. Over 95% of the remaining parts of the structures were reused or recycled. Frigg Fig: a) Concrete drilling platform 1 (CPD1) in the UK sector of the Frigg Field, and b) Drilling Platform 2 (DP2) in the Norwegian sector Gas production at the Frigg Field ceased in October 2004 after 27 years of operation. The field is unique in that it straddles the borders of both the UK and Norwegian continental shelves and the plans for its decommissioning had to be approved by the authorities in both countries. To simplify the matter it was agreed that disposal of facilities on both sides of the border would be coordinated in a single jointly agreed decommissioning programme. Installations present on the Frigg field comprise three steel platforms and three large concrete structures. The size and complexity posed by its decommissioning meant that the operator Total E&P Norge AS, on behalf of the owners, have worked for a number of years with stakeholders to seek the best decommissioning solution for the field. Final approval of the Frigg Field Cessation Plan was obtained in March 2003 from the Norwegian and UK governments. All topside facilities will be removed to shore for disposal, as will the three steel substructures, or jackets. The three concrete substructures, two located in the UK Sector and one in the Norwegian Sector, will be left in place after the removal of the external steel works. Navigation aids will be installed on each substructure. The drill cuttings pile situated around the DP-2 platform will be left in place, at a maximum of 20 cm thickness. The offshore removal work is planned to last four years starting summer 2005, with the main offshore removal activities being carried out during the calmer summer months. Click here for more information on the decommissioning of the Frigg field from the Total E&P Norge website. Manifold Compression Platform (MCP-01) Fig: Manifold Compression Platform 01 (MCP-01) The Manifold Compression Platform MCP-01 was installed in 1976 and sits in 94m of water, 173km north-east of Aberdeen in block number 14/5 in the UK sector. Its concrete gravity structure weighs over 386,000 tonnes. It is operated by Total E&P UK Limited. The original purpose of the platform was to act as a compression and interconnection platform for the Frigg Transportation System (FTS) consisting of a 32” Frigg UK pipeline and a 32” Frigg Norwegian pipeline (known today as the Vesterled pipeline) transporting gas from the Frigg reservoir to the St Fergus Gas Terminal in Scotland. In 1992 MCP-01 was re-configured to allow it to be operated as a “not-normally-manned” platform controlled from the St. Fergus Gas Terminal. Security cameras onboard monitor the platform 24 hours a day. To improve safety and reduce maintenance, the operational equipment used on the platform was kept to a minimum. The two 32” pipelines entering/leaving MCP-01 continue to be in use and therefore required rerouting to allow MCP-01 to be decommissioned. After this process had been completed the topsides were prepared for removal, and following statutory consultation in November 2005 permission was granted for the early removal of the topsides structures. The timing was adjusted to afford synchronisation with the decommissioning work also taking place on the Frigg field, therefore achieving maximum synergy effects. During the topsides removal process a flotel will be located next to MCP-01. The equipment will be removed by use of a heavy lift vessel and by a “piece small” technique where the steel is cut into smaller items for transport in containers to shore. The offshore removal works are planned to be completed by summer 2008. The heavy lift barge will return in the summer of 2009 to remove temporary equipment. Click here for more information on the decommissioning of Manifold Compression Platform 01 from the Total UK website. Indefatigable Fig: The “Juliet” (left) and “Lima” (right) platforms on the Indefatigable field in the southern North Sea The indefatigable gas field is situated around 75 km off the East Anglian coast in the “Norfolk Banks” area of the southern North Sea at a depth of around 31 m. Production came on stream in 1971. The Shell/Esso administered section of the field is located in blocks 49/19 and 49/24 with infrastructure comprising 5 platforms (Juliet, Kilo, Mike, Lima and November) 26 wells and 5 pipelines. The five installations were installed between 1970 and 1988 and are small fixed steel platforms with four six or ten legs and weighing between approximately 1,000 and 4,000 tonnes. Currently all five platforms are designated as “not normally manned” installations. As relatively small installations none of the structures present on the field qualify for derogations under OSPAR 98/3. After all wells have been permanently plugged and decommissioned, and the topsides facilities prepared and cleaned, the installations (both jackets and topsides) will be wholly removed to shore for disposal/recycling, with a presumption that the recycling of materials shall be maximised. It is anticipated that the pipelines (which have a history of stable burial) will be decommissioned in-situ, with appropriate remedial work at ends and crossings. Due to the strong currents in this region of the southern North Sea, together with the fact that no drilling has occurred in the area since 1992 there are no drill cuttings piles under any of he platforms. The decommissioning recommendations formed were based upon open consultations with the public and other interested stakeholders. Current estimates suggest the decommissioning work will be carried out over the period 2008 to 2011. Click here for more information from the Shell website on the decommissioning of the Indefatigable field.