Norway's Ekofisk field area and Total's Frigg complex in the North Sea are driving development of new decommissioning solutions. Overall, the Frigg field abandonment project was priced at US $417 million in 2000 - the least cost option preferred by Total - with work scheduled between 2006 and 2009.
In June 2004, Norway's Petroleum Safety Authority (PSA) approved partial removal of some structures under the first phase of the Frigg field decommissioning plan submitted by Total, which applied to the treatment and compression platform (TCP 2) drilling platform 2 (DP2) and treatment platform
1 (TP 1) in the Norwegian sector and the quarters Platform (QP) and concrete drilling platform (CDP 1) in the United Kingdom. Decommissioning at Ekofisk involves 11 major platforms. Phase 1 involves smaller items, bridges, flare stacks and tripods. Pre-qualification is underway for Phase 2, involving larger structures including jackets and topsides, said Steve Preston, director of sales and business development, Heerema Marine Contractors, and currently president of the International Marine Contractors Association. He describes Ekofisk phase one work as "...relatively small, straight-forward reverse installation," which solution providers are considering but doubts it will interest single lift specialists.
The global decommissioning market has been estimated to be worth between $50 billion and $80 billion with over 7,000 platforms eventually due for removal worldwide and 650 are on the North West European Continental Shelf (NWECS).
Britain's Department of Trade and Industry has separately estimated the decommissioning market on the NWECS at $26.9 billion over the next 30 years.
Legislation approved in Portugal in 1998 during an Oslo and Paris Commission meeting dictated that most North Sea structures should be pulled out, thus creating the removal market that exists today.
Three major groups have emerged to bid for this work, Heerema in alliance with Technip, Saipem with Aker Kværner and Amec with Zenocean, an industry source indicated.
Attention has narrowed on the North Sea because of the size of structures due for removal and the hostile environment in which work will have to be performed. Several solutions are single-lift approaches, in the belief that this enhances offshore safety at a lower cost with less vessel mobilization and fewer hazards than multiple offshore heavy lifts. But few concepts have gone much beyond drawings and model tests, and most will only commit to construction once abandonment contracts are confirmed.
In the United Kingdom Amec is working with Zenocean and Mentor Subsea on developing the single-lift vessel (SLV) - featured in E&P in August 2004 - for which negotiations over construction are underway with a Chinese shipyard. Technip has halted development on a solution based on its TPG 500 jackup pedigree. Instead it is working with Heerema.
Excalibur Engineering has promoted its Pieter Schelte concept, involving turning two tankers into a catamaran. Aker Kværner has developed a design based on buoyancy tanks. Other solutions are out there. And Heerema and Saipem can both offer heavy lift crane barges.
"The main challenges for single lift are twofold. Firstly, finding a technical solution that fits and works for a wide variety of platforms - almost every platform in the North Sea is different," said Preston.
"The geometry of some of the platforms is very difficult for some of these concepts to work with."
He pointed out some platforms were built with modules skidded on using module support frames. "They do not lend themselves to single piece heavy lift-off solutions."
Heerema's H851 barge is capable of carrying 50,000 tonnes and it has been used in float-over studies for West Africa. "There are quite some challenges doing float-overs with 25,000 tonnes, and we think that is technically very difficult," Preston added. He believes a reverse float-over is possible for decommissioning facilities while the huge front-end cost for single lift solutions is off-putting. "I am sure there are some cases where it might work but the second issue is the economics. It is just difficult to build up a company to invest in these vessels. Our sector has been suffering over-investment compared with the revenue it has been able to achieve for the work it does. It is very capital intensive business."
Uncertainty about the timing of the decommissioning market hasn't helped. "The problem with decommissioning is that it is continually being pushed back. In the end it will come. But you need continuity or at least some volume certainty to make it work."
Technip temporarily halted development of its installation and decommissioning vessel (IDV), based on its Technip GeoProduction 500 (TGP500) design, used twice before on the North Sea Harding and Elgin/Franklin projects operated by BP and Total, and again by BP for its Caspian Sea Shah Deniz gas project. The IDV offers a fixed working platform with retractable legs on the seabed. It is designed to raise 14,000 tonnes topsides in a single lift, and between 6,000 and 8,000 tonnes jackets. It features a gated front access and offers all-year-round operation in water depth up to 344 ft (105 m). Two lifting systems operate on the concept: One comprises up to four beams which slide below a topsides which are then raised up with electro-hydraulic jacking. The IDV itself can then be raised further on its own legs.
One IDV design featured a 2000 tonne pedestal crane, but this has been dropped. Currently Technip is working with Heerema on the Frigg decommissioning contract bid - which will entail using Heerema's Thialf crane barge. However, Cathrine Bjaarstad, study and facilities manager for Technip responsible for front end engineering and design at Technip for the Frigg bid, said the IDV is well matured. "We went to fabrication yards before developing that far, and for pricing in the steel market. We did not bid the IDV for Frigg but we have not stopped our development work," she said. "It is much more suitable for Ekofisk which is a little more shallow. It will be more suitable and less expensive . . . we can be more efficient with more single lifts . . ."
Model basin tests have been done, the main scantling has been through but uncertainty surrounding the timing and value of decommissioning projects prevents Technip investing in the IDV, which requires 18 months and $150 million - to build it.
Excalibur Engineering has been touting the Pieter Schelte for some years. The catamaran concept from Excalibur - part of the Allseas Group owned by Edward Heerema - was originally based on converting two 300,000-deadweight tonnes tankers to provide a SLV for jackets and topsides. With a projected cost around $300 million, the concept has evolved into using newbuild hulls and could raise topsides up to 48,000 tonnes and jackets up to 25,000 tonnes (28,000 short tons) by hoisting them over the stern on huge lifting frames. It is envisaged the Pieter Schelte would be 1,110 ft (245 m) long, and 387 ft (118 m) wide. Its huge size is intended to provide stability offshore in severe sea conditions, supplemented by hydraulic motion compensation equipment. Its principal benefits include single piece lifting, minimizing offshore cutting, preparation and cleaning of separation equipment and minimization of risk-exposure during offshore operations.
Aker Kværner's solution for jacket lifting adapts technology used to refloat the Phillips Maureen gravity-based platform 3 years ago using buoyancy.
Aker Kværner Offshore Partner (AKOP) based in Bergen is proposing to build buoyancy tanks which can attach to jacket legs and be used to float the jackets up once they have been severed at the seabed.
Each tank is 164 ft (50 m) long, and 20 ft (6 m) in diameter and can be used alone or in pairs, Engineering Manager Rolf Eide said. "They could lift up to 11,000 tonnes."
Tanks would be floated out horizontally to the field location and then attached to each jacket leg using winches and tractor tugs with eight tanks in all for a four-leg jacket. All vertical loads will be transferred to the jacket through specially engineered brackets fastened to the jacket by remotely operated vehicles (ROVs). These brackets then withstand the full lifting force as the tanks are de-ballasted, thus raising the jacket. After lifting, the combined unit would be raised 32.8 ft (10 m) above the mud line, and towed ashore vertically.
AKOP is liaising with Saipem on a bid for the Frigg removal work - using Saipem's S7000 crane barge for topsides removal.
"We are also doing studies for both the Thistle and Miller platforms, and it can be used for North West Hutton," Eide said.
While figures for construction costs for some single lift solutions have been quoted between $150 million to $300 million, Eide said the AKOP offering will be much less. "The costs for these tanks is next to nothing," he said. "The fabrication of them is simple steel work. If we got a contract say in March, we could remove the jacket the following summer."
No diving would be involved - clamps would be engineered for ROV attachment.
And since no two jackets are identical, new buoyancy tanks could be custom-built if necessary. "The cost is so small we could make them for each jacket," he said.
MPU's Heavy Lifter is a concrete-four column design featuring three pontoons arranged in a U-shape configuration and it is aimed at topsides and jacket removal in two separate operations. It is designed to float into position against a platform, then adjustable steel lifting beams attach to either topsides or jackets for removal, and de-ballasting provides the necessary uplift force to remove a structure from the sea. A flexible jacking system has been developed for jacket removal either as a supplement or alternative to lifting frames.
MPU maintains its concept can be used both for platform removal and installation. "The MPU Heavy Lifter is designed to lift 15,000 tonnes topsides with an air gap of 82 ft (25 m) although the frame can take 25,000 tonnes," explained Trond Labo, technical director at MPU Enterprise AS, the company behind the concept. "We have done all the engineering to actually place an order for it," he said. "But we will not build it until we have a contract."
That decision depends on Frigg and Ekofisk field owners choosing the concept or concepts they prefer for their respective decommissioning projects.
Various solutions have been developed for lifting jackets and for transferring topsides weight onto the vehicle. MPU Enterprise AS has patented designs for the overall unit as well as the lifting frames; a lifting and rotating bracket system and for a lifting/rotating cradle. Model tests have been conducted on the concept at Marintek in Trondheim, Norway, and joint industry studies during 2001 and 2002 were carried out using the unit for removing topsides on the Norwegian Albuskjell 2/4 F platform on the Ekofisk field, and on Shell's Gannet and Kerr-McGee's North Ninian jackets, with the same unit. Extensive technical work was also carried out for the Ekofisk Booster Removal Project, which was terminated in September 2003.
Heavy lift capacity between 14,500 and 40,000 tonnes is suggested and MPU has also developed a smaller, steel vessel, the MPU Lifter, with lifting capacity 5,000 tonnes. This is aimed at the Southern North Sea installation, removal and transport market for smaller topsides and jackets plus subsea installations, and for installation of offshore wind turbines and services to offshore wind parks.
"The feasibility of removing these structures have been successfully documented," MPU said. Also Det Norske Veritas has surveyed and approved the operational feasibility of the concept, while model testing and numerical analysis of has been done again at Marintek in Trondheim.
The company is 30% owned by conceptual engineers Dr. Olav Olsen with which Aker Kværner is designing concrete structures for the Piltun and Lunskoye developments in the Sakhalin II project off western Russia.
SeaMetric's Twin Marine Lifter (TML) was one of the most innovative concepts unveiled a few years ago by SeaMetric International in Stavanger, for tackling North Sea decommissioning. It uses two barges 394 ft by 150 ft by 30 ft (120 m by 46 m by 9 m) mounted with between three and six cantilevered lifting arms on each barge to raise structures. At one the end of the lifting arms are ballast tanks and buoyancy tanks on the other. Used in combination, these would provide uplift force. Each lift arm would be skidded across to reach below the "candidate" structure. The TML features heave compensation, which SeaMetric has said would allow mating and load transfer in up to sea state 8.2 ft (2.5 m). It could lift up to 18,000 tonnes in a single wave period using air to push a 300-tonne water column down and out through the bottom of the high-pressure water tanks. Seametric claims the device can swiftly generate the uplift for a quick lift-off in a normal wave period - often only a few seconds. Also the rocker lift arms would be configurable to handle variations in the center of gravity in the candidate structure.
Tested at Marintek in Norway, the TML could operate in up to sea state 15 ft (5 m).
"Marintek has verified with model tests that the TML system to have less than 10% vertical dynamic load when 95% of the total lift object's weight has been transferred to the barges," SeaMetric claimed. In October 2002 Total sponsored studies using the TML for removing the Frigg QP jacket supported by BP and SND - Norway's Industrial and Regional development fund.
Between May and June 2003, a TML 12,000 concept underwent a third phase of model tests at Marintek to study jacket lifts.
Master Marine of Norway combines the principals of jackup rigs with a skidding system for topsides and a boat-shaped hull to offer lifting and a transport barge in a single entity called the Happy Jack. Oslo-based Master Marine's concept would maneuver to within close proximity of a platform and would then be jacked up. Skid beams would then be rolled out from the vessel's stern, underneath topsides, and attach to strong points on the topsides. Once separated from the jacket, hydraulic jacks on the roller beams would lift the topsides and this load would then be skidded back across on to the hull. Two stern-mounted boom cranes would then be used to lift jackets in single or several pieces on to the rear of the vessel. Discharging the loads at an onshore site would involve a reversal of these processes. Again, it is a novel concept, and the lifting capacity is 14,000 tonnes.
One of the cheaper concepts is the $30 million Delta Lifter with a jacket lift capacity of 8,000 tonnes which offers a lifting time of only 6 hours even in a 10-year summer storm scenario.
Steinar Draegebo, managing partner of Marine Technology Corporation in London and a major owner in Delta Lifting, said the concept is aimed purely at jacket removal and could cover 80% of those in the North Sea. "It is purely designed for jackets. We are not trying to do something with topsides," Draegebo said.
It is an unmanned steel-barge, equipped with ballasting and de-ballasting only. Supply vessels would provide power for ballast pumps and control operations. During towing ashore, the vehicle would also be semi-submerged, reducing wave and weather vulnerability. "It is purely a dumb barge, it is not an oilfield vessel," added Draegebo. He told E&P from the design work to date, a unit could be built and operational within 27 months.
Other contenders include the Versatruss system, again using a two-barge arrangement and strain jacks which have been successfully used both offshore Venezuela, and offshore California, lifting 6,300 tonnes. Doris Engineering has touted its 20,000 lift capacity semisubmersible Archipose 2000 and Stavanger-based Marine Shuttle Operations has previously promoted its Offshore Shuttle, another semisubmersible with large-diameter steel tubulars and a topsides lift capacity of 22,000 tonnes and 18,000 tonnes for jackets.
Preston said some areas of technology are not mature enough, including undersea cutting and handling of seabed drill cuttings. And while there are disposal sites for platforms around the North Sea there is a related issue about reputation management. "Operators are really nervous about pieces of their kit turning up in another part of the world. The reputation management over this issue is enormous," Preston said. Some joint industry projects between operators and contractors have been established to tackle decommissioning issues, and Preston applauds this. Also the 240-member IMCA is developing guidelines over key technical and operational issues.