Page 72: of Offshore Engineer Magazine (Apr/May 2014)

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Pipelines

Mobile foundation technology could ofer an economic solution to some stranded ofshore hydrocarbon reserves.

Professor Susan

Gourvenec looks at the issues.

Mobilizing subsea foundations

The Prelude FLNG subsea architecture, atest statistics show Australia’s which transport oil or gas from wells to supported by traditional mudmats. total petroleum output has an processing facilities.

Image from Shell.

L annual export sales value of more Mudmats are typically 5-15m in edge than A$25 billion (US$22.8 billion) and length, but can be more than 40m in brought to site (to install these structures) annual taxation payments by the indus- some cases. The purpose of the mudmats adds considerable expense – pushing try of more than A$8 billion (US$7.3 is to transfer the weight of the structure projects further up the cost curve.

billion). it supports over a suffciently large area

Mobile foundations ofer a solution

One of the challenges the industry of the seabed so as to avoid unacceptable faces is unlocking the huge hydrocarbon settlements and resist the lateral loads The term “mobile foundation” may reserves offshore Australia, and else- applied by the connected pipelines. seem an oxymoron—we typically expect where, that are currently unreachable. Offshore pipelines undergo cycles of foundations, and the structures they

Australian research and development thermal expansion and contraction over support, to remain stationary. It would be into mobile foundation technology is one the lifetime of a feld through cycles alarming if our homes or offce buildings piece of the jigsaw. of start-up and shutdown. In service started to wander, but we accept that pipelines expand as hot oil or gas passes ocean-going vessels experience stability

Existing foundations through them and contract when they and mobility concurrently.

Subsea developments involve a number cool due to a shutdown. The thermal The concept of a mobile foundation is of wells across a feld connected by a expansion of the pipelines transmits lat- similar to a sleigh or ski on snow. It’s a network of pipelines, so-called infeld eral loads to the mudmats supporting the foundation that is engineered to slide or fowlines. A variety of pipeline infra- structures attached to the pipelines. glide across the seabed to absorb some structure supports the fowlines, such as Increasingly, as developments move of the applied loads, rather than simply pipeline end terminations (PLETs), pipe- into deeper water, where seabed soils being engineered to be big enough to line end manifolds (PLEMs) and in-line can be extremely soft, and as conditions resist the loads and remain stationary.

tee structures (ILTs). such as operating temperature become A mobile subsea foundation might look

This seabed infrastructure is typically more onerous, these foundations can be much like a conventional mudmat foun- supported on shallow mat-type founda- too large or heavy to be installed by the dation, at least at the seabed—comprising tions, so-called mudmats, that are ideally pipelaying vessel. a rectangular plate resting on the seabed. small enough to be installed by the same The requirement of a specialized Traditional mudmats are typically vessel that lays the subsea pipelines, heavy-lift installation vessel to be equipped with short skirts that penetrate

April 2014 | OE oedigital.com 74 000_OE0414_Pipelines3_MobileFoundations.indd 74 3/23/14 12:22 PM