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BP's world class pipeline development.

Construction is well under way on BP's billion-dollar Mardi Gras Transportation System in the U.S. Gulf of Mexico. When completed in 2006, it will be the world's largest capacity deepwater pipeline system, capable of transporting more than 1 million bpd of crude and 1.5 Bcf/d of gas.

Background

For more than [bur years, BP has been working on this historic project. The project will traverse 490 miles in the Gulf and transport oil and gas from deepwater field developments in the Southern Green Canyon and Mississippi Canyon leasing areas to markets in the U.S. These developments include the Holstein, Mad Dog, Atlantis and Thunder Horse fields in depths ranging from 4,500 to 7,300 feet. The oil and gas from these fields will be transported to shore by means of the Mardi Gras Transportation System, consisting of Cleopatra, Caesar, Proteus, Endymion and Okeanos pipelines.

Ranging in size from 16 to 28 inches in diameters, these lines will begin at steel catenary risers (SCRs) on the BP host platforms, (two spars and two semi-submersibles) and run to booster platforms located on the continental shelf.

BP's Mardi Gras Transportation System also involves the installation of lateral lines, wye sleds, Pipeline End Terminations (PLETs) and jumpers that connect the lines, together with all their associated components and fittings.

Building a project of this scope is no easy task. At the deepest point of the pipeline system, the water pressure on the pipeline reaches a force of 3,245 psi. The combination of pipe diameter, unprecedented water depth and water pressure is pushing pipeline technology past previous limits and will set new milestones and achievements for deep water developments.

Engineering & Design

BP awarded INTEC Engineering the contract for engineering the entire deep water portion of the Mardi Gras Transportation System. INTEC began the project in May 2000 and successfully completed the definition engineering to BP's satisfaction by July 2001. Once the project had been under way for several months, BP extended INTEC's scope to include procurement, construction and commissioning support. This included the design of all SCRs, pipelines, wye sleds and their specialized fittings. It also involved addressing and resolving issues associated with the wye sleds and PLETS (which will weigh up to 100 tons) and the need for collect connectors, valves, wye blocks, flex joints and other pipeline components.

Another technological feat performed by INTEC was the design of the large-diameter SCRS, which are to be suspended from the spars and semi-submersibles. The major design challenge was fatigue damage due to a combination of vessel motion and vortex induced vibrations. These were solved primarily using and developing design methods and cutting edge software.

The most critical sections in any SCR are the welds that join the individual pipes, since these are subject to fatigue loading. In order to verify that the welds will be suitable for the life of the project, test joints of project pipe are to be welded together by the installation contractor, Heerema, using the welding equipment and procedures to be used in the field. The welded lengths will be subjected to fatigue testing by Stress Engineering in Houston.

Full scale collapse tests have been performed on 28-inch project pipe in order to accurately predict the behavior of large-diameter pipe in deepwater, and specifically, the resistance to collapse under combined external pressure and bending. INTEC's deepwater design was validated through a series of successful tests carried out by C-FER Technologies in Canada. The tests also confirmed that thermal aging, occurring during the external coating process, actually enhances the pipe's resistance to collapse at depth.

INTEC was also charged with dealing with a client requirement to ensure that the entire system could be pigged with both intelligent and conventional pigs. INTEC helped define and develop these pigs which were later manufactured.

Pipe Lay Operations

At this time, pipelay work has progressed to a stage where the 100-mile Okeanos pipeline in Mississippi Canyon is on line. The 70-mile Proteus and 90-mile Endymion oil pipelines are scheduled to come on line in the first quarter of 2005.

In Green Canyon, the 115-mile Cleopatra Gas Gathering System is scheduled to come on line in the third quarter of this year. Also in Green Canyon, work is winding down on the 115-mile Caesar oil pipeline being installed by Heerema Marine Contractors. The J-lay installation of the 24-inch diameter pipe in 7,300 feet of water for the project represents another industry first. Prior to the project start, Heerema Marine Contractors had to make major alterations to its semi-submersible heavy lift vessel, Balder, to accommodate the towering equipment needed to lay the pipe while minimizing kinks.

The J-lay pipeline installation method being used was selected over the more traditional S-lay method because it allows the pipe to come off the vessel vertically, gradually bending until it reaches the bottom.

Since the most critical section in any SCR is the weld that joins the individual pipes, much attention was paid to ensuring that fatigue loading would not be too great. This was accomplished by Heerema testing its welding equipment and procedures it would be using in the field to weld up test joints prior to the project start. The welded lengths were then subjected to fatigue testing and approval by Stress Engineering.

The Balder is one of only two vessels in the world capable of handling this kind of project. Pipelay work basically starts with the Balder's crew, which total 242 persons, supervising the arrival of barge loads of 80 foot pipe joints. On the deck of the Balder, additional welding produces pipe strings measuring 240 feet long. Each welded section is inspected by ultrasound, and then coated with a special powder to seal the welds.

Once pipelay work begins, every aspect of the process is carefully critiqued through the use of an ROV equipped with a camera. The photos taken by the ROV are constantly observed aboard the Balder to ensure that the pipe is kink free when it is laid on the sea floor.

On an average clay, the Balder can lay an estimated 1.5 miles of pipe. Prior to the deepwater pipeline installations on the project, Allseas pipelay vessel Solitaire carried out pipelay operations in intermediate water depths using the S-lay method.

Project Completion

Mardi Gras Transportation System Inc., a BP America subsidiary, expects to complete the project in 2006. Once completed, BP will operate all of the pipelines in the Mardi Gras System. Production from the six deepwater fields under development will have a daily production that will match that of the Trans-Alaska Pipeline.
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Title Annotation:2004 International/Offshore Report; British Petroleum Company PLC
Publication:Pipeline & Gas Journal
Geographic Code:4EUUK
Date:Apr 1, 2004
Words:1097
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