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Dry Tree Semisubmersibles: The Next Deepwater Option

Photo courtesy of Moss Maritime.
The Octabuoy dry tree semisubmersible, shown at a shipyard in Qidong, China, is the first of a new type of floating drilling and production platform under construction and is owned by ATP Oil and Gas.

To commercialize some of the world’s most challenging deepwater fields, offshore engineering companies are developing a new class of drilling and production platform known as the dry tree semisubmersible (DTS). The challenge involves taking existing technologies and lessons learned from previous floater designs to create an alternative platform for waters too deep to cost-justify the use of tension-leg platforms (TLPs) and fields too large for spar platforms.

Dry trees, also known as Christmas trees, are wellhead devices installed during the completion stage of a well’s life and give the operator control over production. Used on onshore wells, dry trees have been used extensively on shallow water fixed platforms, TLPs, and spars, but never on a deepwater semisubmersible because that platform’s motions are too extreme to support a dry tree system.

As the DTS concept awaits introduction into the deepwater market, multiple designs are under evaluation by major offshore oil companies and the Norwegian classification society Det Norske Veritas (DNV).

The chief advantages of using a DTS are that operators can drill, complete, and carry out intervention operations on multiple wells from the same platform in depths below 6,000 ft. This saves the operator significant resources that otherwise would be spent over the life of the field on contracting mobile offshore drilling units or purpose-built, well-intervention semisubmersibles.

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Dry Tree Semisubmersibles: The Next Deepwater Option

01 September 2013

Volume: 65 | Issue: 9

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