Recent technological advances and investment have seen a surge of new activity in the North Sea region. The development of new techniques and technologies means reservoirs that were previously considered inaccessible and uneconomical are now viable. In 2012 the UK sector saw record levels of investment, while Oil and Gas UK reported that companies looking to capitalize on these new advances spent US $14 billion on further exploration and development.

Schiehallion is one example of this. The field is located 282 km (175 miles) west of Shetland and was discovered by BP in the early 1990s. In 1998 the operator installed an FPSO vessel that currently processes the output from four subsea centers.

Extended field life

Originally engineered to support a field life of 20 years, the current infrastructure has produced an estimated 300 MMbbl since its installation.

However, since first oil the understanding of Schiehallion and other fields has evolved significantly. Recent appraisal wells have indicated that there might be more than double the amount of recoverable reserves previously thought.

The redevelopment, BP’s Quad 204 project, will enable the potential recovery of an additional 450 MMbbl of resources and extend production to 2035.

To maximize this potential, up to 25 new field wells will be drilled, bringing the total to 52 wells. Achieving these targets will require an estimated $5 billion investment by BP.

This investment will see the current subsea infrastructure undergo a full redevelopment as well as the replacement of the current FPSO vessel with a purpose-built unit equipped to deal with both the forecast production and the North Atlantic’s harsh environment.

The 25 additional wells will join the existing infrastructure along with 17 km (10.6 miles) of new rigid pipeline, needed to connect each drillsite to the replacement FPSO unit. The changes also will see new manifolds, flowline termination assemblies, umbilical termination assemblies, and flowlines and umbilicals installed at each drillsite to create what will become one of the world’s largest subsea systems.

The redevelopment is expected to greatly increase output from each drillsite, with the field expected to eventually produce 130,000 b/d of oil and 623 Mcm/d (22 MMcf/d) of gas.

Given the project’s scale and the many changes required to maximize the field’s potential, success will rely on the seamless integration of many smaller projects carried out by a range of subsea and oil service companies.

Project integration

Technip, as a subsea engineering specialist, is playing a major role in Schiehallion’s redevelopment. The company’s Quad 204 team has been tasked with disconnecting the existing FPSO unit, installing the new unit when it arrives on site, and mooring it securely in the existing location. The remit also encompasses recovering the old moorings from the site.

In addition, Technip has been commissioned to completely replace the riser and mooring system now in place. The project will necessitate the recovery of all flexible and umbilical risers. This will be followed by replacing the system with the installation of 21 custom flexible risers that eventually will be connected to the new FPSO unit as well as numerous jumpers being installed on the seabed. The project scope also includes the installation of 15 additional rigid pipelines along with umbilicals and subsea structures.

In addition to the technical challenges that make this project unique from a Technip perspective, the environmental conditions mean the riser and mooring system must be able to cope with 30-m (98-ft) waves and up to 80 m (262 ft) of lateral movement of the FPSO vessel with no adverse effects.

While the company regularly carries out projects providing vessel support, engineering expertise, pipe lay and manufacturing, ROVs, and personnel, it is now being asked by clients to provide a service that encompasses all of its capabilities.

A brownfield site, Quad 204 is different mainly because of its scale. The scope of work doesn’t encompass anything that Technip hasn’t undertaken before; rather, it brings together the company’s vertically integrated subsea business and capabilities. It draws, and will continue to draw, on Technip’s subsea experience for the delivery of the entire project scope.

Operationally, this project has required the company to adapt its regular team structure significantly to cope with the demands Quad 204 has presented. The company’s teams are typically quite small, but the many components of Quad 204 have led to the adoption of a matrix structure to coordinate all aspects of the workscope. Consequently, Technip has more than 100 people currently working directly on the project.

Longer timescale

Another differentiating aspect of the project is the timescale. Typically, Technip works on shorter projects. For example, a typical North Atlantic tieback usually takes between 12 and 18 months.

The vast scope of the Quad 204 project, as well as the many companies involved, means that the total operation is expected to take several years from the initial contract award in 2012, with the operator aiming to have the field onstream by 2016.

This may sound like a relatively long time, but during the winter season the weather and sea state can combine to considerably reduce workable weather windows, which gives a small insight into the logistical challenges faced by Technip’s project team. Even with the window it has, hitting each stage of the project timeline will be crucial to overall success.

Technology and logistics

The components being used by Technip are based on established technology. The challenge will be one of logistics. Ensuring the timely fabrication, disconnection, and installation of the equipment will be one of the most demanding aspects of the project from Technip’s perspective.

This timescale and the number of Technip personnel involved means that the Quad 204 project is a significant focus for the company and will use a large proportion of its resources, including its Lerwick base, which was set up to support Technip’s work offshore the Shetlands.

The first vessel mobilized in April 2013, and each year will see three to five major construction spreads working in the field. The vessels will work during a 6- to 8-month period, until October/November each year. For a brownfield project, where there may have been significant historical operations, it is crucial that the project team ensures that all existing infrastructure is removed correctly so it has the best possible foundation from which to enter the next stage of the project during 2014.

Last year saw the design and start of fabrication of the 21 bespoke risers that will connect the newly redeveloped subsea centers to the FPSO unit. The rigid pipelines that are designed using a corrosive resistant alloy lining have been coated and will be fabricated into 1-km (.62-mile) stalks at Technip’s spoolbase in Evanton, Scotland.

A significant number of Technip’s vessels will be involved in various forms at some stage, including the newest addition to the company’s fleet, the Deep Energy – one of the largest pipelay vessels ever built. It is at this stage that the field’s subsea structures will be installed along with the first of the newly fabricated jumpers and risers.

D-MaC system

The installation of these components will involve the use of a Diverless-Maintained Cluster (D-MaC), a proprietary set of subsea tie-in tools used by BP across all its Shetland operations. Two new sets of D-MaC tooling have been procured for the Quad 204 project and have been successfully integrated with the ROVs onboard the Olympic Challenger vessel for use throughout the project.

The culmination of Technip’s involvement will see the new FPSO unit towed to the site before being connected to the redeveloped subsea infrastructure.

Quad 204 represents a significant milestone for Tech-nip as the first time the company will integrate and carry out a brownfield project of this size that will use the majority of its subsea services. Regionally, the project is also highly significant with the investment made by BP and its partners and highlights the renewed confidence the industry has in the UK Continental Shelf as a producing region.

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