The acTeon cusTomer magazine

V.6 6-09

PeTrobras awards exclusiVe TorPedo Pile Technology righTs To inTermoor

aquaTic’s innoVaTiVe mooring line recoVery ProjecT brings success for deePocean

claxTon’s new TilTing Tension deck Pushes The boundaries in The norTh sea

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Paul AlcockT: +44 1603 227019 F: +44 1603 774175W: www.acteon.comE: paul.alcock@acteon.com

© Acteon Group Ltd 2009

8–11 September Tern Place office opening to coincide with Offshore Europe 2009, Aberdeen, UK

14–16 September European Offshore Wind 2009 Conference & Exhibition, Stockholm, Sweden

1–2 October Offshore Decommissioning Summit, Kuala Lumpur, Malaysia

For further information please contact DiAry

06 FAST, EFFECTivE AnD SAFE

08 bLUEviEW ThinKinG

09 ChAin OF SUCCESS

10 rEEL vALUE FOr MOOrinGS

12 hAnDLinG ThE TEnSiOn

14 ASSET inTEGriTy MAnAGEMEnT

15 riGLESS AbAnDOnMEnT

riCHArD HiGHAMGROUP CHIEF EXECUTIVE, ACTEON

COmmENT

KEViN BUrTONVICE PRESIDENT, TECHNOLOGY, ACTEON

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This edition of S2S contains several articles on decommissioning, always a pertinent theme when the oil price has taken a downward swing. One story relates to issues surrounding the rigless decommissioning of wells in the North Sea; another reports on a new and effective way of recovering mooring systems by reeling them back onto a boat.

By combining the knowledge and skills that exist across Acteon, we can offer extraordinary overall capabilities in this area. Through working closely with our customers, we devise decommissioning and abandonment solutions that offer genuine cost, safety and environmental benefits, and enhance company reputations within the industry and beyond. We see decommissioning as an exciting area; it is our view that even at the very end of the oilfield development cycle it is still possible to create significant shareholder value.

Despite the concerns surrounding carbon dioxide emissions from fossil fuels, oil and gas are going to feature in the energy equation for some time to come. Therefore, it is equally important to develop and produce these resources in the safest and most efficient ways possible, and there are two articles in this issue that resonate with this notion. The tilting tension deck designed for BG Group by Claxton to handle unusually high drilling riser loads is a great example of inventive offshore engineering. And the risk-based integrity management system we are applying for BP in the Gulf of mexico is a beacon for the industry in terms of ensuring the safety of critical items of equipment in hostile environments.

At every stage in the oilfield life cycle, there are going to be challenges to overcome – and there will be opportunities to grasp. It is our aim at Acteon to help you rise to the occasion, whatever the circumstances.

much has changed since the last edition of S2S. The world economy has suffered financial turmoil, credit is difficult to come by and oil prices have retracted to around $60 per barrel.

After many years of effort building our team, we are keen to retain our capacity and ability to support our clients. The prospect of reduced revenues, pricing pressures and lower utilisation has led us to look carefully at all the aspects of our business. We are focusing on making our operations more cost-effective and efficient, while looking for more ways to deploy our skills and resources.

A changing environment provides new opportunities to use our technology and know-how to do things differently. Our ambition is to provide increasingly cost-effective solutions for our clients’ projects.

We are continuing to judiciously invest in our geographic expansion, equipment, skills and technology.

Commitment, fresh thinking and teamwork are attributes that we have fostered at Acteon for several years. They have never been more important than they are today. Applying them in the areas I have just outlined will be vital to our continuing success in difficult times and will enable us to make a real contribution to the future of our industry and our customers.

Intermoor has anchored a mobile offshore drilling unit and installed preset anchors for a tender-assist drilling vessel for Chevron subsidiary Cabinda Gulf Oil Company Ltd (CABGOC) offshore Angola. Intermoor provided design, engineering, procurement and installation services for the permanent preset moorings at the Tombua–Landana site and the Tombua South drill centre. The company also handled the fabrication of an 18-m suction follower and the various installation aids that were required for installing the suction-embedded plate anchors (SEPLA) at the Tombua–Landana site. This project was the first time SEPLAs have been used offshore Angola for CABGOC.

Eight mooring anchors were installed at both locations. At Tombua–Landana, installing the eight SEPLAs at a water depth of 380 m took, on average, just over a day per anchor to complete.

LDD has successfully completed a project to drill a 1950-mm, 17-m long discharge riser shaft for the Rosedale Wastewater Treatment Plant in Auckland, New Zealand.

The company used its PBA 408 pile-top drill rig, which is usually used for sockets up to 1300 mm in diameter owing to the limited clearance through the base of the rig. To facilitate the larger diameter of the drill bit and the stabilisers, a false deck was flange-bolted to the bottom of the drill rig. The larger-diameter equipment was run inside the conductor and then suspended from the false deck; finally, the drillstring was run from above.

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new equiPmenT reduces fluke engenharia cosTsNew equipment that provides steel tension relief through heat balancing during the manufacture of Fluke Engenharia’s torpedo anchors has been developed in-house.

Previously, the company was hiring equipment from a supplier with a limited availability in Brazil and that could thus command extremely high rental charges.

Fluke Engenharia currently has three of the units in operation and has already recovered the cost of the development and manufacturing programme. The units boast 98% local content.

The engineering team is now designing a unit that can work with multiple torpedo piles simultaneously.

LDD PrOViDEs sOLUTiONs iN NEw ZEALANDLDD ExCEEDED

THE CLiENT’s ExPECTATiONs By COMPLETiNG THE sHAfT ONE AND A HALf DAys AHEAD

Of sCHEDULE.

NEWS

LDD worked closely with the installation vessel company throughout the project and exceeded the client’s expectations by completing the shaft one and a half days ahead of schedule, despite having to drill entirely through rock. Local environmental sensitivities were managed without any difficulties: notably the ability of the drilling rig to meet the tight noise limitations imposed by the local authorities.

inTErMOOr COMPLETES MOOrinG OPErATiOnS in AnGOLA

Polyester lines specifically designed and fabricated for the Tombua–Landana site will be attached to the preset SEPLAs and the anchor chain using subsea mooring connectors in mid-2009. The preset system will then be used to hook up and moor the tender-assist drilling vessel. This polyester preset will be yet another offshore first for CABGOC in Angola.

“Successful installation of the SEPLAs is an important milestone for Intermoor on a project that has included several challenges, including vessel availability, the investigation of various installation methods, the fabrication requirements and the limited installation windows,” said Intermoor project manager michael O’Driscoll.

Intermoor is now the exclusive licensee of torpedo pile technology in the USA. Petróleo Brasileiro SA (Petrobras) granted the rights to Intermoor in November 2008. In the last eight years, Petrobras has successfully installed more than 1000 torpedo piles (gravity-embedded cylindrical projectiles) for anchoring deepwater flowlines and facilities offshore Brazil.

Torpedo piles typically range in size from 24 to 98 t. The largest torpedo pile can provide an anchor-holding capacity of up to 1000 t.

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PETrObrAS AWArDS ExCLUSivE TOrPEDO PiLE TEChnOLOGy riGhTS TO inTErMOOr

“Petrobras’s extensive experience in the use of torpedo piles has shown them to be both economical and less time-consuming to install than the alternatives, such as suction piles or drag-embedded plate anchors,” said Intermoor chief engineer Bob Wilde. “Intermoor looks forward to extending this remarkable technology to the Gulf of mexico and other US waters.”

“sUCCEssfUL iNsTALLATiON Of THE sEPLAs is AN iMPOrTANT MiLEsTONE fOr iNTErMOOr.”

SRP is carrying out tests to confirm the performance of one of its latest products, Quick-Flange, before its commercial launch in the coming months. Quick-Flange is a lightweight marine drilling riser connector designed to be made up much more quickly than conventional flange connectors. The principal aim behind the development has been to reduce the time taken to run marine drilling risers in deep water.

Quick-Flange uses breached bolts that can be closed in a fraction of a turn and do not require to be preloaded by torquing them up. SRP is hopeful of being able to machine existing flanges to accept the new fasteners, thus providing rig owners with a simple, cost-effective way of upgrading their existing marine drilling riser systems.

A recent rig-moving trial for Petrobras in the Campos basin, Brazil, demonstrated perfectly the value of Trident’s new Wi-Fi-enhanced TriADS+ portable tug-management system. The Brazilian operator has roughly 30 drilling rigs on contract, and conducts four to eight moves a month using a combination of in-house tug-management systems and individual positioning units on the rig and each of the anchor-handling vessels.

The addition of Wi-Fi to the Trident system creates extra bandwidth, which enables the units on the anchor handlers to be remotely controlled from the rig at distances of up to 3000 m. Crucially, navigation experts on the rig can troubleshoot the anchor handlers’ navigation systems, a process that in the past often involved bringing the rig and the vessel together, and hours of expensive downtime. Furthermore, at the end of a project, the anchor handlers can have their navigation units reprogrammed for the next project via the Wi-Fi link. So, instead of them having to return to shore, they can sail straight from one job to the next.

The Petrobras representatives, who it is believed are looking to outsource some of their rig-moving activities, expressed their complete satisfaction with the trial, which pitched the Trident technology directly against the operator’s existing rig-moving system. The new system has already attracted much attention from clients in the North Sea.

wi-fi TriAL sUCCEss

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No two subsea well decommissioning projects are exactly alike – each provides its own distinct set of challenges. Yet there is a common thread running through most of them, and that is the requirement for strong project management and coordination. Nexen Petroleum U.K. in Aberdeen, UK, was well aware of this when it approached Acteon company OIS, which has recently taken over from WellCut Decommissioning Services, to help with a survey and four-well abandonment programme in the North Sea Scott field. One of Nexen’s main concerns was to establish a skilled and focused group of service providers capable of working together as an effective team.

OIS has considerable experience of conducting decommissioning projects, from site assessment through to final reporting, and was tasked with, first, planning the programme, which was to be based on a previously undertaken well categorisation study, and, second, directing the work. This included assembling all the necessary players, defining their roles and responsibilities, and performing a thorough risk assessment of the entire operation.

well surveyThe project commenced with a 10-well survey using a DP2 vessel and a work-class remotely operated vehicle (ROV). At this point, the opportunity was taken to remove entangled fishing nets from the wells before the four-well abandonment phase of the offshore programme got under way.

For the well survey activities, OIS used sister Acteon companies Trident and UWG plus four other specialist contractors. Trident provided the survey equipment for the vessel and marine support services during the works and mobilisation phases. The survey activities were managed by OIS using the Island Offshore vessel the Island Vanguard and Oceaneering International ROVs. UWG took care of wellhead cap removal, drifting the wells and net clearance.

decommissioningThe team of subcontractors assembled by OIS for the main decommissioning works included Acteon companies UWG, InterAct, Claxton and Trident. Norse Cutting & Abandonment (NCA) provided the abrasive cutting services; eight other companies were also involved. For the abandonment operation, OIS used a suspended well abandonment tool (SWAT®) supplied and refurbished by UWG, and abrasive cutting equipment from NCA to abandon four of the wells. Two of these were category 1; the others were 2.1 and 2.2.

Trident supplied the necessary survey equipment and marine support services, subcontracting the supply of transponders and subsea positioning equipment to Seatronics. UWG provided offshore operations personnel, and Claxton provided SWAT-tooling and offshore-operations personnel. InterAct delivered the well classification, the preliminary procedures and the health, safety and environment submittals.

It was the record of more than 130 successful suspended well abandonments by Acteon companies that convinced Nexen of the value of choosing OIS.

Once the project was under way, Nexen added to the work scope by asking for assistance in severing another well in the field, one that had been recently suspended using a semisubmersible after encountering equipment problems during the abandonment phase. After an engineering review, and with Nexen’s agreement, the rig was moved off location, and OIS’s chartered vessel was brought in to carry out the intervention and severance. The operation was completed, with considerable overall cost savings, within eight hours of the rig leaving the location.

When the wells had been cut, the wellheads were recovered to the back deck of the vessel ready for component recycling and environmentally friendly disposal, which fulfilled the agreement to return the seabed to its original condition.

key challengesThe project presented several challenges. One of them was managing and optimising the performance of new abrasive severance technology. The NCA abrasive cutting system had to interface with equipment from other subcontractors and had not been used at the water depth in this case. OIS arranged a series of interface engineering meetings and managed them on behalf of Nexen. In addition, the vessel used at Scott field was new, so there was a shakedown period during which minor problems were addressed and overcome. Finally, and not least, the team of subcontractors that OIS selected were all based in different places, so effective communications were vital to optimise the overall performance.

The result, according to Nexen, was a smooth operational process in which all personnel and equipment reached the vessel in good time and worked together as planned.

fasT, effecTiVe and safeCOOrDiNATiON is THE KEy TO sUCCEssfUL wELL DECOMMissiONiNG PrOjECT

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swAT’s THE BENEfiT?

A SWAT unit can be deployed from the back deck of a vessel or through a moon pool. After any fishing nets and debris have been cleared, the cap has been removed and the well has been drifted, the SWAT unit is landed on the wellhead where it is used to perforate the casing and place a cement plug in the well. Engineers can then sever the wellhead using an explosive charge or an abrasive severance method.

Using the SWAT system removes the need for expensive drilling rigs and diver intervention, and can save field operators up to £400,000 per day: savings that are made up of drill rig costs and the anchor-handling vessel charges incurred when moving a rig to a new location.

PerformanceEffective well decommissioning of this sort requires precise planning, careful project and contract management, and a positive working environment where the emphasis is on safety and teamwork. Interface engineering and project and operations management logic were vital to the smooth running of the operation. OIS handled specific key contracts, and provided risk management supervision to keep all parties working to the highest standards of offshore safety and to ensure that the quality of the work delivered was maintained throughout.

Over the course of the operation, an excellent working relationship developed between Nexen and OIS, one that is expected to progress and mature through an agreement for further work in 2009 and 2010. The success of the well-abandonment campaign at Scott field required skills and technology drawn from across the Acteon group of companies and beyond. Contributions from all the subcontractors were necessary for achieving Nexen’s aims, but underpinning the team’s success was effective project, contract and operations management.

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Seatronics, the Acteon specialist marine electronics company, has reached an agreement with BlueView Technologies under which the two companies will work together to market BlueView’s miniature multibeam sonar systems in countries outside the USA.

BlueView, based in Seattle, USA, introduced the novel systems, also called 2D forward-looking sonars, in 2005. Until now, the company has focused most of its sales efforts within the USA, particularly targeting the US Navy, the US Customs and several port authorities. Approximately 200 commercial systems have been sold for use on remotely operated vehicles (ROV), underwater vessels, surface boats and fixed surveillance platforms. The objective now is to exploit Seatronics’ global marketing network, plus its excellent reputation in the marine electronics sales and rental field, to promote the product for a greater range of applications and in more countries.

Using between 256 and 512 separate sonar beams, the units provide a constant, real-time sonar image of what is in front of them; an image that is not degraded by the motion of the platform on which they are mounted. Often referred to as acoustic cameras, they form a perfect complement to optical cameras, as they can to “see” through murky water. Currently, there are four different units to choose from, which, depending on their technical specifications, offer imaging over a range of distances and at various resolutions.

The basic P450E-15 model operates at 450 kHz, can resolve two objects 5 cm apart and, although it can detect strong targets up to 140 m away, works best over a distance range of 5–50 m. Its principal application is for wide-area searching and open-water navigation. Operating at a maximum frequency of 2.25 mHz, the DF900-2250 model can resolve two objects 1 cm apart at a range of between 0.3 and 3.0 m. With this performance, it provides an effective replacement for a normal optical camera in zero-visibility conditions and may be used to navigate in cluttered surroundings or within complex structures.

From a practical standpoint, all the units are small, light and compact, and consume very little power (10–15 W). Hence, they are easy to mount on the smallest ROV or they can be used manually by divers. All the units can be used in water depths to 300 m; most are suitable for 1000 m, and one model, the DP900-90, is good for 4000 m.

The units have been used extensively by the US Navy and counter-terrorism organisations to check ships’ hulls and berths for the presence of explosive devices. Customs authorities have also used them to counter the smuggling of illegal substances under water.

Seatronics managing director David Currie is looking forward to the prospect of marketing the BlueView units. He expects them to become essential items for ROV operators in the oil and gas industry

blueView ThinkingseaTronics and blueView Technologies To markeT miniaTure mulTibeam sonar sysTems ouTside The usa

working in water with visibility problems. “They have a lot to offer users involved in structural inspection tasks,” he says, adding, “One interesting application is the identification of pipeline leaks, as both gas and nonaqueous liquids strongly attenuate the sonar beam and so show up well on the sonar image.”

Currie believes that the BlueView products are significantly ahead of the field in terms of imaging performance and practicality. He describes them as based on “winning technology,” and points out that, even though thoroughly proven, they are still the subject of substantial research and development effort on BlueView’s part.

“With the support that Seatronics can provide for the units in the field, I am confident we will see a rapid uptake of the BlueView products,” Currie says. “Seatronics already has units available for demonstration, sale or rental in all of their bases.”

“They haVe a loT To offer users inVolVed in sTrucTural insPecTion Tasks. one inTeresTing aPPlicaTion is The idenTificaTion of PiPeline leaks.”

The BlueView units are easily fitted to ROVs or may be used manually by divers.

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chain of successVasT exPerience and The laTesT Technology ensure ThaT chainco is cerTainly noT The weakesT link for oPeraTors and rig owners requiring a raPid and Thorough chain insPecTion serVice

The addition to ChainCo’s equipment inventory in recent months of three new mobile chain inspection units and a mobile stud press unit has significantly boosted the company’s service capabilities and reinforced its position as the world leader in mooring chain inspection, repair and maintenance.

The company now has seven mobile units strategically located around the world, which is part of the reason behind the company’s success, according to managing director Alan Duncan. “ChainCo’s reputation is based on its ability to respond rapidly to requests for help from clients, and to supply them with highly experienced people and sufficient inspection capacity to carry out work within tight time frames,” he says. “A good example of this is the way we recently mobilised two complete inspection spreads and four inspection squads to malta at short notice to inspect 8500 m of chain for a customer. We were able to complete the job in just five days.”

floating production and storage vesselsChainCo’s mobile stud press unit, the only one of its kind in the industry, was built with floating production and storage vessel mooring chains in mind. In the past, these have been designed for the life of the vessel, perhaps as long as 25 years. As these moorings are often oversized to allow for some wear and corrosion, there has not been much emphasis on inspecting them. However, the position is changing and there are increasing calls for regular inspection of these mooring systems. The reason is the growing number of failures that are coming to light; there have been numerous reports of single chain failures in the North Sea alone over the past two years.

Ideally, chain inspection would be carried out offshore, which presents quite a challenge. Fly-by camera inspections using remotely operated vehicles are possible, but magnetic particle inspection requires the chain to be taken out of the water and placed on the back of a boat. Even then, pressing loose studs in chain that may be up to 140 mm in diameter has hitherto been impossible. In the past, this was outside the range of existing mobile chain inspection units.

The new mobile stud press unit changes all this. It has been designed to press the largest chains on the market, and can be easily transported offshore in a standard open-top shipping container. Now, operators can inspect and repress the studs of the largest chains offshore on the deck of an anchor-handling vessel, thus saving huge amounts of time and money.

In the short time that the unit has been available, it has been used offshore to repress the studs on chains belonging to two permanently moored production facilities in the North Sea.

chainco inspected approximately 21,000 m of chain during 2008 in 11 countries around the world using mobile inspection units. most of the chain belonged to semisubmersible drilling rigs, which commonly have eight moorings, each typically around 1400 m long. The diameter of the steel bar used to form the links is normally between 76 and 84 mm.

The shipping and offshore industry classification societies require that the chains used to moor structures of this kind are normally inspected every five years. This is largely because of the wear and tear on the chain caused by the frequent relocation of these structures, and the critical nature of the drilling operations that they support.

The inspection process begins by laying out the chain on the ground or the back deck of a boat for cleaning using ultra-high-pressure water jets. it is then closely visually examined before being fed through the chainco unit, where it undergoes dimensional checks and magnetic particle inspection to detect any cracks or weld defects. any loose studs are also picked up at this stage. The chain is then passed through a press where the offending studs are tightened.

chainco currently has inspection units in angola, canada, namibia, singapore, south africa, the uk and the usa: though this is a situation that could change rapidly. a team of three or four experienced operators and dnV-certified inspectors man the units, which have their own power generators and can, therefore, work independently.

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Decommissioning a redundant loading buoy in the North Sea was probably never going to make the headlines. However, the unusual way that Aquatic managed to recover the buoy’s eight mooring lines is certainly worth reporting. Quick, efficient, cost-effective and safe, it is a method that could well become commonplace in future.

Aquatic was asked to become involved in decommissioning Venture Production’s Kittiwake loading buoy in 2008 by the project’s lead contractor, the Norwegian service provider DeepOcean. The question was whether it would be possible to recover the eight mooring lines, each made up of 765 m of wire rope terminated top and bottom by 265 and 82.5 m, respectively, of 3¼-in. chain, using one of Aquatic’s powered reel systems.

reel Value for moorings

mike Gaskin, Aquatic vice president, projects, takes up the story: “Our reel systems are primarily designed to handle flexible flowlines, mooring wires, umbilicals and power cables. We knew that the chain would require more torque than usual to spool it, especially at the outer limit of the reel, and that for the recovery scenario it would generate high compression forces on the reel’s hub.

“Following a design review, we took our standard AQSR-50 reel and reinforced the hub to increase its spooling-on load rating from 10 to the 30 t we calculated would be necessary for this application. We also upgraded one of our AQPR-02 tower drive systems to provide up to 150 t.m of torque: a level that we judged would provide the unit with a reasonable degree of contingency.”

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Both components of the new system were assembled in Aquatic’s Peterhead workshops. Like other Aquatic systems, the reel and the drive tower are designed to be compact and easily dismantled so that they can be readily transported by road in standard containers.

In this case, the system was destined for Teesside, UK, where it was fitted aboard the Volantis, a DP2 class vessel normally used for jet trenching operations.

The recovery operation went very smoothly. A remotely operated vehicle was used to cut each of the mooring lines 50 m from the touchdown point on the seabed, and rigging was attached to secure them. They were then cut away from the buoy and spooled onto the

Venture Production’s Kittiwake field lies in 85 m of water in the North Sea, 135 km east of Peterhead, UK. Oil from the field was initially exported via an exposed-location, single-buoy mooring system – the Kittiwake loading buoy. In 2005, this was replaced by a less weather-dependent, submerged anchor loading system. more recently, a pipeline was run from the field to the BP Unity platform 32 km away to render the Kittiwake loading buoy well and truly redundant.

reel. Dealing with the last two of the eight chains was slightly more involved, as their recovery had to be carefully coordinated with the movements of two tugs employed to restrain the buoy once it was free from its moorings. In addition to the mooring lines, Aquatic also recovered a 3-in. umbilical consisting of four 3/8-in. hydraulic hoses that had been used to power the valves on a pipeline end manifold during loading operations.

The Volantis needed to make only two trips to the field. Four moorings and the umbilical were recovered to the reel on the first trip and four moorings on the second. Once ashore, the lines were easily removed from the reel for further cutting and disposal.

“This exercise would normally have called for a more expensive anchor-handling vessel,” says Gaskin. “The lines would have been winched up and stored in chain lockers or on deck for transport to shore: an operation that would probably have involved a good deal more offshore manpower than in this case.

“We are proud to have engineered an elegant alternative solution for recovering the moorings and, equally, to have managed the project offshore without incident.”

The next step for Aquatic is to modify the system used for this project to enable greater lengths of mooring chain to be reeled. In future, Gaskin sees mooring recovery as a standard Aquatic offering.

But perhaps the last word for now should go to the customer. Ottar mæland, senior engineer, DeepOcean, says, “This was a highly successful operation for Venture Production. Although it was Aquatic’s first project of this kind, everything proceeded to plan; it is testament not only to the company’s expertise but also to the flexibility of its equipment.”

or convex bearing plates: the four on the deck floor are convex and the four on the underside of the loading plate are concave. During operation, the wave and current forces acting on the conductor are sensed and transmitted to the power unit that governs the movement of the individual hydraulic cylinders. By this means, the angle between the deck and the tension plate adjusts (tilts, gimbals and squats) to reduce the effective localised bending moment seen at surface by the riser. This reduces stress and therefore increases fatigue life.

Before the tensioning system was installed on the rig, it underwent tests in Claxton’s workshops in Great Yarmouth, UK. The tilting mechanism was thoroughly checked, and the system was subjected to a 750-t test load. In October 2007, two Claxton engineers and a rig crew went out to the Rowan Gorilla VI, where they ran the conductor and installed the tensioning system. First, the hydraulic cylinders were fitted to the tension deck. These were then connected to their power pack and extended by 4–6 in. before the tension plate was added on top. The conductor, with its pre-installed rack section, was run through the centre of the tension plate via the rotary table; then, once the correct space-out had been achieved, the two-piece adjustable nut was attached to the rack.

“The system was installed within budget and on time, and subsequently performed exactly as we expected,” says Kyson. “BG Group must have been impressed because it has recommended the system to Canadian Natural Resources (CNR), which is down to use the rig next.”

Lockart Campbell, senior subsea engineer with BG Group, confirmed satisfaction with the system: “Our partnership with Claxton has worked well. I am confident in their ability, both to provide well-executed engineering solutions and to react to arising needs in a helpful and professional manner.”

The tilting tensioning system is now back in Claxton’s workshops being serviced before being reinstalled on the rig for CNR. Beyond this contract, maersk has also expressed an interest in using it. Kyson concedes that this is not the first tilting tensioning system on the market, although he is not aware of another system that can also generate a tension of 400 t. Furthermore, he is proud of the fact that Claxton was able to provide the ideas, the engineering expertise and the people to devise and then quickly deliver a highly practical and reliable solution to its latest challenge.

handling The Tension claxTon’s new TilTing Tensioning sysTem Pushes The boundaries of whaT can be done To helP drillers in The norTh sea

Although from a production perspective the North Sea’s best days may now be in the past, the province still generates great examples of offshore engineering innovation, as this drilling riser project for BG Group plc illustrates.

About two years ago, BG Group plc approached Claxton to provide a conductor tensioning system to meet some unusually demanding requirements. The company wanted to drill in water depths of 78 m in the Jackdaw field using the Rowan Gorilla VI jackup drilling rig – nothing too out of the ordinary so far. However, as Chris Kyson, project engineering team leader, explains: “A combination of the way the rig was configured, the environmental conditions in the area and the fact that BG Group wanted the system to be capable of withstanding the sort of seas normally associated with a 50-year storm resulted in the need for a conductor tensioning system that could generate up to 400 t of load.”

A more common rating for conductor tensioning systems in the North Sea is 300 t, which can easily be achieved using Claxton’s positive-grip tension-ring systems. Presented with this challenge, Claxton went back to the drawing board and came up with a new tensioning system: one that would not only provide the required tensile loads but also tilt to reduce the bending stresses and wave-shock loading affecting the conductor.

“We were reluctant to resort to a welded tension ring in place of our positive-grip system because this would have meant having to set a precise space-out distance between the ring and the tension deck,” says Kyson. “It is easy to get this wrong and create knock-on effects that compromise the integrity of the other elements of the conductor system. Instead, we opted to insert a machined rack, 37-in. long, into the conductor tension joint, which, with its outside diameter of 34 in., can pass through the rig’s rotary table. In place of the ring, we have a two-piece adjustable nut that engages on the teeth of the rack and enables the space-out distance to be readily altered during the conductor installation process.”

Perhaps more unusual than the tension rack was the tilting mechanism that was also incorporated into the conductor tensioning system to alleviate the wave- and current-induced stresses experienced by the conductor. To understand how this works, it is necessary to know that the tension in the system is generated by a series of four hydraulic cylinders acting against the floor of the tension deck upwards onto a tension plate. The four cylinders are connected between the deck and the tension plate via either concave

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Ensuring the structural integrity of offshore facilities and equipment has always been paramount – unfortunately, it does not get any easier. The development of new oil and gas reserves in extreme situations; existing infrastructure that is closer to the end of its design life than the beginning; and an intense focus on health, safety and environmental performance are all putting pressure on operators to do more on the integrity front. But as Peter Falconer, head of 2H Offshore’s global integrity management business, points out, it is not simply more effort that is required but action of a more structured kind. “Companies are increasingly recognising the value of taking a risk-based approach to integrity management (Im) because it focuses attention on the parts of the operation where problems are most likely to occur. The benefit arises from being able to identify potential problems before they escalate and cause equipment or system failures that compromise operations.”

integrity loopEffective Im involves a series of distinct steps, beginning with the gathering of information about the equipment under review. The creation of an efficient database from the available design reports, as-built records and operational logs is fundamental to the Im process. Using this information, plus expert knowledge and experience of the behaviour of the equipment, a risk-based analysis of the threats to the equipment and possible failure modes is carried out. This forms the basis for a strategy

asseT inTegriTy managemenTTaking a sTrucTured aPProach and focusing on risk

risK-BAsED AssEssMENT

At the heart of the iM process lies a risk-based assessment that follows a set course. Expert knowledge and experience of the equipment under review are vital, especially during the first part of the assessment:1. identify the main threats to specific items of equipment and the possible modes of failure.2. Assess the probability of failure occurring.3. Estimate the consequences of failure and rate their severity according to predefined criteria. 4. Combine the probability and the consequences of failure to obtain a criticality rating.5. Assess the predictability of the failure based on how well the failure mode is understood and the reliability of the usual inspection,

monitoring and mitigation measures. Use this to generate a confidence rating. 6. Combine the criticality assessment with the confidence rating to generate an inspection, monitoring and mitigation strategy,

particularly with regard to the minimum inspection interval, for the particular item of equipment.

2H Offshore has been working with BP in the Gulf of mexico since 2005 to manage the integrity of around 100 deepwater risers and the in-field flowlines associated with the oil company’s eight production facilities in the region: seven floating units, including the Thunder Horse semisubmersible (shown here), and the Pompano fixed platform. The scope of the contract was extended in 2007 to include subsea production equipment. Currently, our Im team has 20 people from 2H and another Acteon company, InterAct, working closely with BP’s central Im organisation in Houston, USA. The success of the contract has been influential in the recent award of Im contracts in Asia Pacific to carry out risk-based inspection of deepwater risers for a leading international operator, and in the middle East, where the scope includes more than 400 well conductors in four shallow-water fields.

covering inspection, monitoring and any relevant failure mitigation measures. It is then a question of implementing the strategy and collecting the new data generated. “The data are used in two ways,” says Falconer. “ Any data that are outside the boundaries of what was expected will trigger remedial action or changes to the maintenance regime or the way the equipment is operated. Just as importantly, the information is used to update and refine the Im strategy. This feedback mechanism, the creation of an integrity loop, is very powerful, as, in time, it raises your understanding of the critical issues and enables you to adopt a much more proactive stance on the integrity of your key assets.”

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According to a report issued in march by Oil & Gas UK1, there are 4635 exploration, appraisal or development wells in the UK sector of the North Sea. Of these, it is thought that 2749 (roughly 60%) could be decommissioned using existing technology and, crucially, without resorting to a drilling rig. That leaves 1886 wells that are likely to cost a good deal more to decommission – unless the industry can come up with new rigless ways of dealing with at least some of them.

Phil Chandler, senior petroleum engineer with Acteon company InterAct Activity management Ltd, was instrumental in the preparation of the report on behalf of the well abandonment work group at Oil & Gas UK. He says, “The study has put the spotlight firmly on rigless decommissioning technology. For platform wells, it is the areas of well control and long-string tubular recovery where there needs to be some fresh thinking. Additionally, the lack of accommodation, platform cranes and deck space often poses considerable challenges to rigless well decommissioning in the southern North Sea. There also needs to be greater focus on planning and logistics to tackle the large stock of wells in this sector.

“Rigless subsea well abandonment has received considerable attention in recent years, and there has been lots of interest in new-generation well intervention vessels. A DP2 classification, the ability to run a subsea lubricator for wireline operations, and mud and cement pumping are essential. Better vessels will possess DP3 classification; a pipe handling tower, with active heave compensation, capable of running or pulling complete work or completion strings; a pipe-picking machine; mud and brine tanks; cement storage; aqueous fluid processing facilities; slickline, electric-line and coiled-tubing capabilities; and, not least, lots of deck space. However, I believe that, in the near term, limited well control capability will probably remain the major shortcoming of these vessels. Pulling a tubing hanger through a riser and blowout preventer will require a very stiff riser and a heavy blowout preventer, and therefore result in costs similar to those of a drillship. The important conclusion is that, given the existing technology, rigless abandonment will be restricted to those subsea wells where control can be achieved downhole before pulling the completion.”

Chandler feels there are many other areas where technical advances could lead to significant benefits when decommissioning both platform and subsea wells. He cites, for example, the ability to deal with leak paths caused by deeply set control lines and cables; better plugging technology; more advanced cutting tools for use at extended depths; logging tools to provide better information about annular conditions; methods for determining the location and the extent of leaks in compromised completions; improved remedial cementing technology; and ways of centralising completions and tubing in high-angle wells.

rigless abandonmenTinTeracT has ProVided major inPuT To The recenT oil & gas uk well abandonmenT sTudy

Chandler believes the findings of the report will act as a spur to investment in new technology and innovative services but stresses that it is not just simply about new technology. He says, “We have to think about how we can use existing technology in smarter ways. Acteon companies have been working in this area for several years and have undertaken scores of rigless abandonment projects in the North Sea and the Gulf of mexico. Critical to their success has been the effort put in before going offshore to understand the way particular wells were constructed and their status at the time production ceased. Within Acteon, we have undertaken over 1300 such well reviews. They are a vital insight into the well and indispensable when it comes to engineering and planning the abandonment exercise.”

1UK North Sea Well Abandonment Study, march 2009, issued by Oil & Gas UK

acteon offers an outstanding portfolio of interlocking products and services targeting the subsea arena. we can align our knowledge, skills and experience in a variety of ways to provide inventive solutions to the complex challenges faced by subsea developers and operators.

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