Page 40: of Offshore Engineer Magazine (Nov/Dec 2013)

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the respective pressures of the touchdown region and the main and fortifed zones preventing it from being could be fully strength- dragged from the vessel tested onshore. This could under the harsh current

Subsea not have been done with a conditions met offshore the single fowline laid in-feld. Shetlands. It enabled longer

Bundle expansion reduces lengths of umbilical to be laid the build-up of axial forces, in higher sea-states and stron- and allows feld develop- ger currents for longer dura- ment without a cooling tions. As a result, the SDD is spool. System weight and now the primary option for tensile forces on the sleeve this kind of installation.

and carrier prevent the In the event of a storm, bundle from global lateral a through contingency buckling. procedure was planned to

The 5.1km bundle for BG secure the umbilical in a

Knarr project will be the lazy S-wave confguration;

Subsea 7’s autonomous inspection vehicle (AIV) designed in deepest bundle installed to however, due to clement collaboration with SeeByte. Photo: Subsea 7.

date at 410m. It will tie back meteorological conditions, the Knarr production mani- it was never required to be fold to the foating production, storage two-way fber optic communication, high deployed. and offoading (FPSO) unit. The inte- voltage electricity supply, chemical sup- grated design of the bundle fowlines and ply and hydraulic power.

structures (cooling spool length) allows The installation was particularly chal-

AIV will be commercially the system to be tuned to BG’s specifc lenging as it consisted of laying a low- available later this year fow assurance requirements. The bundle density product (127mm diameter, 10.6

Subsea 7, in collaboration with SeeByte, will be installed under the drill rig kg/m submerged weight) along a route software solutions provider for while on site, reducing the development with particularly high currents and a unmanned underwater vehicles, has timescale, and the increased fexibility large range of water depths (20 to 600m). developed an autonomous inspection of bundle installation method again As a result, large umbilical defections vehicle (AIV), which will be commer- de-risked the schedule impact of other were expected, and a subsea depressor cially available later this year from the on-site operations. device (SDD) was devised to aid instal- company’s life-of-feld division. With

The bundle for Shell Fram was the lation and act as a ballast to weigh down its ability to recognise and respond to frst bundle designed with two-midline the catenary and oppose current. structures, tying two drill centers back to The SDD was made of a weight ele- its surroundings, instinctively correct- a single FPSO. Unfortunately, due to poor ment with a bellmouth funnel opening ing its trajectory in real time based on drilling results, the Fram development on each side through which the umbili- information it gathers from its on-board in its current confguration has been cal ran and was suspended from a deck sensors, the AIV is set to become a cost- cancelled. Using bundles would have winch. The original unit weighed 2.5 efective, low-risk inspection tool to aid reduced the number of risers. tons, but was ballasted with steel blocks feld survey and integrity management

Goodlad’s Subsea 7 colleagues Renaud to reach a weight of 4.6 tons to handle and intervention activities. Subsea 7

Gueret and Subhajit Lahiri presented a the unusually high currents. The wire says that the AIV, which can be oper- paper in the same session on last sum- length was tuned to control the SDD ated directly from a host facility such mer’s installation of the 127km umbili- height above the seabed.

as an FPSO or platform, or from infeld cal between the landfall at the Shetland Gueret and Lahiri’s paper concluded support vessels or mobile rigs, will

Islands and the Laggan manifold. It con- that the use of the SDD has been success- transform life-of-feld projects. sisted of a bundle arrangement, including ful in stabilizing the umbilical motion in •

A vessel towing out a bundle, with the towhead in the

The fring line in fabrication hall’s at the Wick facility. foreground, at Wick, Scotland. Photo: Subsea 7.

Photo: Subsea 7.

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