Abstract

Towed Pipeline production systems (Pipeline Bundles) are currently fabricated and installed in the North Sea and Norweigian Sea regions from the fabrication facility of a major subsea contractor in Wick, Scotland. The site is located approximately 6 miles north of Wick and extends from the shoreline at Sinclairs Bay landward for approximately 7.8km in an east-west orientation. The current limit for the fabrication of a single Pipeline Bundle is 7.7km.

The company has undertaken a Research and Development study on Pipeline Bundle Extended Lengths (Pipeline Bundle lengths up to 15km) to investigate a means to connect several Pipeline Bundle sections together in order to be able to satisfy the requirements of fields where long tie-backs may be required. Pipeline Bundle length extension can be achieved by onshore tie-in through mechanical connection, Golden welds or fabricated at a different site with a suitable length capacity.

The key benefit of the extended Pipeline Bundle length is to reduce the overall cost of field development by eliminating the requirement for:

  • Interconnecting towheads (Pipeline Bundle end structures),

  • Tie-In spools,

  • Extended hire of tow vessels,

  • Additional Diver/ROV support vessel time for the tie-in of interconnecting towheads.

As a consequence of this length increase, this paper asseses the feasibility of Extended Pipeline Bundle length in the following areas;

  • Pipeline Bundle Tie-in,

  • Pipeline Bundle Pre-commissioning,

  • Required weather window launch - to DNV-OS-H01 Ref.[3],

  • Launch force requirement,

  • Control Depth Tow Method (CDTM) Tow Fatigue,

  • Pipeline Bundle manoeuvring during tow,

  • Application for HT fields – Design Temperature of up to 160°C,

  • Pipeline Bundle Installation - Venting and Flooding

The paper will also demonstrate the commercial advantage of towing longer Pipeline Bundles as against multiple Pipeline Bundle tows.

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