David Knott
Senior Editor
Now some of the first fields developed are near the end of their lives. So operators and governments are making plans to decommission giant platforms, which present problems just as challenging as their original development.
U.K. and Norwegian waters hold the biggest North Sea platforms. The U.K. government is expected to set out abandonment guidelines for operators this year, and Norway will follow soon after.
The U.K. Department of Trade & Industry (DTI) has approved eight abandonment programs. These were relatively straightforward, mainly involving floating production units or subsea facilities that require complete removal.
Heading the DTI's abandonment unit, based in Aberdeen, is Peter Holt.
Holt lists approved field abandonments to date as Crawford, Argyll-Duncan-Innes, Blair, Forbes, Angus, Fulmar's single anchor leg mooring (SALM) buoy, and Brent's spar loading buoy, as well as part of the Staffa pipeline.
Crawford, Argyll-Duncan-Innes, Blair, and Angus were all floating production systems with subsea wellheads. Forbes abandonment required complete removal of a small southern North Sea platform. The Fulmar buoy is still on site, while the Brent spar is scheduled for dumping at sea this year.
In 1978, BP Exploration Operating Co. Ltd. removed a small steel platform in the U.K. southern North Sea gas basin. This was similar to many platform removals carried out in the Gulf of Mexico.
EXPERIENCE
"Compared with the challenges ahead of us, these have been relatively straightforward cases involving in the main complete removal of facilities from the seabed," Holt said.
"However, we have also gained valuable experience from dealing with these early programs. They have done much to highlight the contentious areas. We have had to consider how to deal with drill cuttings, debris clearance and post-abandonment monitoring, the approach to deep sea disposal, and particular problems that pipelines present."
Only three fields off Norway have ceased production, and Oslo has not decided how they should be abandoned. Legislation is expected to be debated in Storting (parliament) this year.
Industry has abandoned four platforms off Netherlands. They were small structures in shallow water and so had to be completely removed.
In 1988, Winter-shall Noordzee BY removed the K13-D gas field satellite platform and a year later removed the K13-C wellhead and production/compression platforms.
In 1989, Unocal Netherlands BY removed a satellite monotower plat-form from Helder oil field on Block Q1.
Denmark has seen no platform abandonments. A Department of Energy official said one platform may come up for removal within 2-3 years. "It has been a candidate for removal before, but we have managed to keep it alive."
PEAK PERIOD
Holt reckons about 15 U.K. North Sea production units will be abandoned in the next 5 years, including the first fixed steel structures. He expects a peak for U.K. abandonment during 2005-2010, when as many as 100 plat-forms may be decommissioned.
Paul Dymond, chairman of the abandonment committee of U.K. Offshore Operators Association (Ukooa), said the U.K. now has 149 structures in shallow water, 53 in deep water, and a further 17 floating production units.
Total abandonment of the shallow water platforms is required, while floating unit removal is straightforward. This leaves only about 25% of U.K. platforms for which partial removal and dumping are issues.
Dymond expects 50 U.K. installations to be decommissioned during the next 10 years, involving 15 of Britain's 20 operators. In this period, U.K. abandonment spending will amount to an estimated Fl.5 billion ($2.25 billion).
Dymond said there will be two to four abandonments/year to 2000. The rate will rise to nine or 10/year after 2000.
Holt predicted there will be about 15 abandonments during the next 5 years, including the U.K.'s first fixed steel structure. The abandonment rate is expected to reach a peak in 2005-2010, when as many as 100 structures are expected to be abandoned.
U.K. Industry & Energy Minister Tim Eggar told a recent conference U.K. operators have shown that advances in reservoir management and efforts to reduce operating costs can repeatedly delay field abandonments.
U.K. CANDIDATES
"Take for example Unocal's Heather field," Eggar said. "It was confidently expected to be the first abandonment on the U.K. continental shelf of a major fixed steel installation. Production was predicted to cease in 1995. It might still be the first, but not in 1995."
He said innovative well stimulation techniques and an operating philosophy in touch with the times have focused on practical issues such as equipment reliability and sharing certain facilities with other operators. Such measures have reduced costs and delayed the end of field life at least another year.
Eggar also cited Beatrice field, operated by BE The company was said to have trimmed operating costs 20% during 1994, deferring the end of production by at least 2 years to early 1997.
DTI has approved a plan by Shell U.K. Exploration & Production to dump its Brent spar loading buoy this summer in more than 2,000 m of water about 200 miles off Northwest Britain.
A Shell official said the company surveyed a number of sites and is awaiting government's decision on the prefer-red option. The dump site is on the U.K. abyssal plain, beyond reach of today's trawl nets.
Wood Mackenzie Consultants Ltd., Edinburgh, said several U.K. oil fields are approaching the end of their producing life, but abandonment dates are highly sensitive to oil price and short term outlook.
Emerald field, a semisubmersible development by Midland & Scottish Resources plc, Aberdeen, was intended to finish producing in 1994. However, Wood Mackenzie pointed out, the field was producing 10,000 b/d of oil at the end of 1994, but production could cease in 1995.
Heather field was producing 7,000 b/d of oil at the end of last year and is expected to cease producing in 1996. Amoco also postponed its first platform closure, on Northwest Hutton.
Wood Mackenzie said, "Northwest Hutton field, forecast by many as the first large platform abandonment, appears to have been reprieved. Abandonment initially was scheduled for 1993 but has since been postponed and may not take place now for several years."
A Unocal U.K. Ltd. official confirmed that Heather was now thought likely to stop producing at the end of 1996, with abandonment slated for 1997.
Unocal was said to be discussing the abandonment method with DTI and has informally proposed partial removal of the platform. Work on a safety program for abandonment is to be started in the next few months.
"However, there is still potential to defer abandonment of Heather still further," the Unocal official said. "End of production is a constantly moving target."
An Amoco spokesman said decommissioning of Northwest Hutton is now expected in 2-3 years time but may be pushed back still further: "Minds get focused on fields economics when a deadline is fixed.
NORWAY'S CLOSURES
North Sea Platforms by Country and Type (13899 bytes)
Northeast Frigg field off Norway was shut down in May 1993 by operator Elf Petroleum Norge AS. The field was developed with a six wellhead subsea manifold and a control platform, which is an articulated column placed 150 m away from the wellheads.
Cost of Northeast Frigg abandonment is an estimated 120 million kroner 18.5 million), not including plugging and abandonment of wells.
Elf has proposed dumping of the Northeast Frigg control column in the deepwater Nedstrand fjord.
The plan is said to be strongly opposed by Norway's Ministry of the Environment. Authorities view the proposal as a test case, unfairly in the company's view because the tower is not a full platform.
Dag Erlend Henriksen, legal adviser in the oil and gas department of Norway's Ministry of Industry & Energy, said the abandonment plan for Northeast Frigg will be presented to Storting by mid-April, with a decision expected early in May.
Henriksen said operator Norsk Hydro AS shut down Mime field in November 1993. "Since that came as a surprise to the licensees, no solutions for abandonment have yet been presented to the ministry. As far as I know, licensees are trying to sell the production equipment."
Block 7/11 Mime field was developed with a single subsea production tree controlled from the Cod field platform.
Odin field on Block 30/10 stopped producing in August 1994. Operator Esso Norge AS is expected to submit an abandonment plan this month, with a decision from government due later this year. Odin was developed using a steel platform in 100 m of water.
Another five or six Norwegian fields are expected to stop producing over the next 5 years, and a number of platforms in the Ekofisk complex will be shut down as the field is redeveloped.
A Phillips Petroleum Co. Norway official said West Ekofisk and Albuskjell F platforms in the Ekofisk complex have recently ceased production, along with the Odin satellite operated by Esso.
Other platforms are expected to be closed down as the field is redeveloped away from the complex center, where seabed subsidence has raised platform safety fears (OGJ, Dec. 19, 1994, p. 146).
Phillips is evaluating which platforms will be required as Ekofisk liquids are rerouted through a new transportation and processing platform due to be installed in 1998.
Phillips is to present its plan for closure of Ekofisk platforms to government by the end of this month. The company hopes it will be allowed to mothball the idle units and postpone abandonment.
Because of state owned working interests, Norway's government faces the problem of paying 70-80% of Norway's expected total 50 billion kroner abandonment costs ($7.7 billion).
"Abandonment spending will be competing with hospitals and social welfare in government budgets," a government official said. "The issue is politically loaded, so authorities will be keen to look at alternatives to complete removal."
GOVERNMENT VIEWS
U.K.'s DTI expects to approach abandonments case by case and views early projects as test cases. Eggar is also keen to keep costs down to minimize the call on the British treasury.
"Very large sums of money are involved, and there are likely to be significant cost differences between abandonment options in any particular case," Eggar said.
"Nor is it free money or even simply money that belongs to the private sector. Much of the cost will be offset against tax, and up to 60% of the burden will fall on the taxpayer. We must therefore take a balanced and proportionate approach."
The U.K. government is firm in its view that responsibility for platforms remains with operators long after production ceases.
Ukooa has proposed that government accept the military risk of abandoned installations, specifically the risk of submarines hitting platform stumps.
But government has decided regulations should not be changed since the military risk is not great.
"Residual liability has been a prominent issue for some time," Holt said. "Government remains of the view that residual liability rests firmly with the owners of the facilities.
"However, we recognize that perpetuity may present difficulties, and we will undertake further work to assess whether any long term post-abandonment safeguards are needed."
Norway's ministry is mirroring the U.K. government approach of taking abandonments on case by case, Henriksen said. Beyond meeting international maritime regulations, every possible option is open, he said.
"This case by case approach is based on a recognition that each installation has its own specification," Henriksen said. "You have to acknowledge that the best solution for Northeast Frigg field installations, weighing 6,000-7,000 metric tons, may not be the best solution for the gigantic Troll platform, weighing more than I million metric tons."
As in the U.K., costs to government underlie Oslo's planning.
"Someone has said that we have only 5% of the world platform population," Henriksen said. "But if total removal should be carried out, we would account for 80-90% of the costs."
Because the state is the largest owner of Norwegian offshore assets, it shares operators' interest in cost effective abandonment, Henriksen said.
GUIDELINES
Officials from a number of government departments are drafting guidelines for U.K. platform abandonments. Eggar said a consultative document on the guidelines will be sent to oil companies by mid-April.
The guidelines are being prepared by government's Abandonment Policy Review Committee led by Alex Wilson, head of DTI's oil and gas office in Aberdeen.
Abandonment was brought into U.K. petroleum legislation through the Petroleum Act of 1987. This act requires U.K. operators to submit an abandonment plan to DTI when required. The plan is separate from the abandonment safety case required by Health & Safety Executive.
The review committee expects to report to ministers soon. The report will form the basis of guidelines that will be issued to operators for comment.
Holt hinted at what some of the committee's recommendations will be: "We obviously want to avoid premature abandonment. It would be folly to remove valuable infrastructure which might still play an important role in development of the U.K. continental shelf.
"Mr. Eggar has stressed the importance he attaches to sharing of abandonment information and experiences, and it is fairly certain we will be taking steps to encourage pooling of experience."
LIKELY OPTIONS
Water Depths of all Structures by Country (11508 bytes)
DTI has decided a key feature of each abandonment program should be a cost benefit analysis of the options. An essential part of the analysis will be a "best practicable environmental option" (BPEO) assessment.
Holt said, "It is possible that, when we apply cost benefit analysis techniques and BPEO assessment to structures in the central and northern North Sea that partial removal, including toppling, will be the optimum solution. Work undertaken during the review has demonstrated clearly that partial removal should remain an acceptable abandonment option."
Holt said the jury is still out on several aspects of abandonment. More work is needed to see if there is an optimum way to dispose of topsides under any set of circumstances and on how best to deal with drill cuttings piles.
"Concrete structures present special problems," Holt said. "Some say concrete structures should just be left in place, but we believe further study is needed.
"Abandonment of any concrete structure on the U.K. continental shelf is some way off, so there is time for such studies to be done. Any proposal to leave such a structure in place would need to persuade us that other options are not practicable in cost and technology terms and, most important, that long term arrangements could be put in place to safeguard navigation."
Holt said there is a strong case for establishing safety zones around the remnants of installations and having them marked on shipping charts. But safety zones that prevent passage by surface vessels would contradict International Maritime Organization guidelines, which say a 55 m clearance would allow overhead traffic.
Holt said, "I believe what we are seeking is a solution along the lines of that proposed in Norway in which surface navigation is allowed but fishing within safety zones is not. Discussions are continuing within government on that."
Pipeline disposal is also viewed by DTI as an unsolved problem. Cost benefit analysis leads DTI to believe leaving rigid pipelines in place is an option, given post-abandonment inspection programs and lack of effect on fishing.
Unburied flexible flow lines and umbilicals will need to be removed, Holt said. "To leave them behind would be to leave litter on the seabed, and that is unacceptable."
Complete removal of platforms in the shallow southern North Sea is the only option, Holt said, because of the 55 m clearance required under maritime law.
"It is likely that the bulk of materials removed during abandonment will be disposed of onshore," Holt said, "and that applies to areas outside the southern basin as well. The extent of the likely impact and the capacity of existing disposal facilities is still unclear."
REMOVAL FLEET
North Sea Steel Jackets by Weight and Country (12578 bytes)
North Sea Steel Platform Topsides by Weight and Country. (13170 bytes)
Hugh Williams, business development manager for Heerema U.K. Ltd., Aberdeen, points out that the marine construction fleet has grown in line with platform developments since the West Sole platform was installed in the U.K. southern North Sea in 1966.
Capacity of the crane vessel fleet has increased to match design weight of modules and jackets to be lifted. Recent integrated deck lifts have been almost 11,000 metric tons.
Williams said, "Offshore construction has almost exclusively been completed by assembling the largest components possible onshore. Finished components are transported offshore in the form of modules and jackets, where they are installed and hooked up."
He said today's construction vessels can remove any structure currently in place in the North Sea, and for the foreseeable future these vessels are under-utilized.
Williams cited two examples of small steel platform removals in the U.K. southern gas basin to prove his case: removals of a West Sole field platform in 1978 and Forbes platform in 1993.
The DB102 crane barge operated by McDermott Marine Construction, London, is under contract to remove three steel platforms from the Esmond complex centered on Block 43/13a.
Total weight of Esmond structures to be removed in 1995-96 is 15,000 metric tons, and this is expected to include the largest North Sea structure removed to date.
"For topsides and jackets, the lift and removal operation is similar to lift and installation," Williams said. "It will be necessary to cut the larger, heavier jackets into a few discreet lifts. But there are no structures the current fleet cannot lift and remove."
Williams said a number of abandonments of the North Sea are under discussion. For the U.K., he listed Northwest Hutton, Heather, Esmond, Beatrice, Leman BK, Brent spar, Fulmar SALM, Murchison, and Emerald. Off Norway, he cited Odin, the Northeast Frigg column, and Ekofisk complex structures.
DISPOSAL OPTIONS
Williams said it almost always will be cheaper to remove and transport topsides in large sections to shore for scrapping. Barge transport, used to carry many structures out to installation sites, will be feasible in every case.
"However," Williams said, "transport on the deck of a semisubmersible construction vessel (SSVC) has many advantages.
"First, at the offshore location it is easier to lift a module onto the deck of the SSCV than to lift it onto a cargo barge. Second, smaller grillage and sea fastening is required. Third, SSCV motion characteristics induce less stress into the module structure than barge transport, and therefore structural analysis and specific strengthening for transport may be avoided."
Williams argues against partial removal and dumping.
Dumping a structure requires three operations not needed with removal to shore for scrapping: The structure must be cleaned of all restricted materials, it must be prepared for dumping, and the operator will be held liable for the structure's remnants after removal and will be responsible for regular inspections.
Williams reckons the immediate cost of removing any jacket that could be left below the statutory 55 m clearance depth may be smaller long term than the cost of marking, maintaining, inspecting, monitoring, and insuring the remaining portions.
'Should regulations change,' Williams said, "removal of a further corroded structure would be more difficult. The clean solution to the operator for himself and the image of the industry is to remove the complete structure to clean seabed level."
Copyright 1995 Oil & Gas Journal. All Rights Reserved.
