Mardi Gras Project Pushes Deepwater Pipeline Frontiers

In 2000, BP embarked upon one of history's largest offshore oil and gas field investments by initiating the development of several deepwater prospects in the Southern Green Canyon and Mississippi Canyon areas of the Gulf of Mexico. These developments include the Holstein, Mad Dog, Atlantis and Thunder Horse fields in water 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 the Cleopatra, Caesar, Proteus and Okeanos pipelines.

Ranging in size from 16 to 28 inches in diameter, these lines will begin at Steel Catenary Risers (SCRs) on the BP host platforms (two spars and two semisubmersibles) and run to booster platforms located on the continental shelf. The 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.

The combination of pipe diameter and water depth is pushing pipeline technology past previous limits, and both the engineering and installation of the system will set new milestones and achievements for deepwater projects.

BP awarded INTEC the contract for engineering the entire deepwater portion of the Mardi Gras Transportation system. Once the project had been underway for several months, INTEC's scope was extended to include procurement, construction and commissioning support.

INTEC welcomed the challenge of engineering the largest and deepest subsea oil and gas transportation system ever attempted. To successfully complete this ultra-deepwater large diameter pipeline project, significant advances in deepwater pipeline technology were essential. Early in the project, INTEC established a team tasked with the development of the technologies required for project success. The team was also responsible for standardizing methodologies to ensure design consistency throughout the entire project. An INTEC team of highly qualified, experienced, and motivated engineers was therefore assembled to provide safe, economic, and innovative design solutions.

The scope of the Mardi Gras project included the design of all SCRs, pipelines, wye sleds and their specialized fittings. A particular client requirement was that the entire system should be piggable by both intelligent and conventional pigs. These pigs, which have to be capable of traversing multi-diameter pipelines and asymmetric wyes, were not currently available. INTEC has helped define and develop these pigs, and following extensive trials they are now being manufactured.

Click to Enlarge... BP has specified that they must have the ability to repair any section of the pipeline should any damage occur during installation or operation. It soon became apparent to the team that no single contractor possessed all of the equipment that would be required for a repair in such deep water, especially when required at short notice. INTEC recommended purchasing the required repair equipment for permanent availability to the project in the unfortunate event that a repair was necessary. The responsibility for specifying and procuring this equipment was also part of the scope of the INTEC technology team. These systems are currently being manufactured under INTEC's supervision.

INTEC has been instrumental in the design and procurement of riser monitoring systems being installed on the SCRs. These systems will record data that will be used in validating the tools that are currently being used for SCR design. The systems will monitor the behavior of the risers and the environmental conditions that cause cyclic motions of the supporting vessels and the risers. By measuring riser fatigue life, INTEC has designed systems for BP to effectively manage riser life within safe guidelines.

Heerema's Pipelay Vessel Balder Many challenges were identified during definition engineering due to the large diameters of the pipelines and risers, and the extreme water depths in which they are to be installed. Other issues being addressed and resolved by INTEC are associated with the wye sleds and PLETS (which will weigh up to 100 tons), and the need for collet connectors, valves, wye blocks, flexjoints and other pipeline components. Once again, INTEC Engineering is significantly raising the bar on deepwater technology by meeting and exceeding the stringent design requirements established for the Mardi Gras Transportation System.

Another deepwater 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 technological challenges are being solved by INTEC's riser group which is using and developing design methods and cutting edge software. This project further establishes INTEC's leadership in deepwater SCR design.

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.

Drawing on its previous experience with the Oman-India and Blue Stream (Black Sea) deepwater pipeline projects, INTEC is successfully designing the 350 miles of 16- to 28-inch diameter pipelines making up the Mardi Gras Transportation System under the full range of stringent design issues. These include flow assurance, survey and route selection, coatings, cathodic protection, material selection, span mitigation, buckle arrestors, pipeline crossings, J-lay collars, procurement of all hardware, and construction support. The pipelines are designed to be installed by S-lay in intermediate water depths (less than 3,400 feet) and J-lay in deep water.

The J-lay of 24-inch pipelines in 7,300 feet of water by Heerema will be another industry first. This has led Heerema to make major alterations to the SSIV Balder to allow it to perform the work. The Balder had previously been used as a heavy lift vessel. With the installation of additional thrusters, a pipe handling system, and a Jlay tower, the Balder is now uniquely qualified for installing large diameter, deepwater pipelines.

The Mardi Gras Transportation System involves the use of subsea wye sleds and PLET assemblies. These systems consist of a flat seabed foundation structure supporting a pipeline connection assembly of valves, collet connectors and either an induction bend or a wye. The Mardi Gras system requires the installation of the largest and heaviest wye sleds and PLETs ever attempted. In fact, these sleds and PLETs will be so large that problems are expected in the sagbend of the pipeline during J-lay, causing the limit of the installation vessel's J-lay tower to be approached. INTEC, in close cooperation with Heerema, is developing special measures to keep the sleds within the constraints of the J-lay vessel, thereby reducing the high strains in the sagbend during installation - another technological advance. Engineering of the wye sleds and PLETs has been substantially completed by INTEC and fabrication is well underway.

Of paramount importance to the project is Getting HSE Right (GHSER). In addition to the objective of "no accidents, no harm to people and no damage to the environment", BP's further commitment is "Everybody who works for BP, anywhere, is responsible for Getting HSE Right. Good HSE performance is critical for the success of our business". INTEC has successfully raised the team's level of safety, in terms of awareness and practices, through a program of GHSER training. INTEC's Senior Vice President and the Project Director are also members of the project HSE Steering Committee that meets regularly with BP and other project contractors to facilitate delivery of outstanding HSE performance by providing guidance and demonstrating commitment to Getting HSE Right.

"Failing to plan is planning to fail", another of BP's project mottos, highlights the importance placed on planning and controlling the progress and the delivery of the work. BP expects the base scope, ongoing option evaluations and changes to be satisfactorily delivered on schedule and within pre-established budgets. INTEC's ability to comply with continuing scope changes, while maintaining the required progress on the base scope, further demonstrates our flexibility and technological expertise.

INTEC commenced work on the Mardi Gras Transportation System project in May 2000 and successfully completed the definition engineering to BP's satisfaction by July 2001. The project is currently in the execution phase. Detailed design and procurement are currently more than 50% complete and offshore construction has commenced with preparatory work for the pipeline crossings. The project is progressing satisfactorily towards J-lay, due to commence in February 2003. First production from Holstein is due in mid-2004.

INTEC started the project 2 years ago with an engineering team consisting of just 15 INTEC engineers and 2 BP client representatives. Since that time, the INTEC team has grown to 95 and the number of in-house client representatives has grown to 10. INTEC's engineering team also includes 7 package engineers dedicated to procurement support. In addition to the engineering team, BP has a 9-member construction team in the INTEC offices, responsible for the management of the installation contractors. Seven members of this construction team are secondees from INTEC.

INTEC's project management team consists of the project director, Alvin Alleyne and project managers: Brian McShane, Sharon Rich, Bruce Chandler and Gene Mullee, together with Jim Gilchrist as the interface and procurement manager and Chuck Lewis as project controls manager. In addition, the project is supported by an HSE manager, Peter Carr; a quality assurance manager, Russell Ramsey; and a highly qualified team of project advisors including Dave McKeehan, Vural Dolen, John Shanks, and Chris Tam.