Subsea 7 Norway As

Christian Linde Olsen

Stylianos Panayides

Christian Wathne

Pavlos Vardoulakis

Fartein Thorkildsen

A subsea pipeline () has a friction-reducing outer coating, treatment or finish () that extends along discrete regions mutually spaced along the length of the pipeline. During laying, curvature is imparted to the pipeline () along its length, for example by the residual curvature method or by snake-lay, to create expansion loops () of increased curvature relative to intermediate portions () of the pipeline () that join those loops (). Each of the loops () is coincident with a respective one of the regions that bear the friction-reducing outer coating, treatment or finish (). This facilitates lateral movement of the loops () relative to the seabed () to mitigate and control buckling in use of the pipeline ().

Mitigation of buckling in subsea pipelines

A method of constructing a sliding subsea foundation includes embedding at least one mass of rocks in seabed soil and placing a sliding mudmat on the seabed over the or each mass of rocks. The rocks can be lowered into a cavity in the seabed by dumping the rocks into the cavity or when contained within a gabion that is inserted into the cavity. Alternatively, a gabion containing the rocks can penetrate the seabed soil, driven by self-weight or additionally by a deadweight bearing on the gabion. The gabion can be lowered toward the seabed suspended from the deadweight. The deadweight can be removed and recovered after the gabion has been embedded in the seabed. The mass of rocks is embedded within an area of excursion of the mudmat to ensure that the mudmat will lie directly above the mass of rocks at any position within the area of excursion.

Subsea foundations

A method of installing an upright elongate hollow subsea foundation that is higher than it is wide, such as a suction pile. The foundation is at least partially embedded in seabed soil. A partition layer is placed within the foundation, for example by injecting a grout, supported by a plug of soil that is surrounded by the foundation. The partition layer is placed on the plug of soil at a level that is spaced from the top of the foundation by at least 20% of the height of the foundation. Above the partition layer, the interior of the foundation may be filled with water and/or a rigid body, such as a solid mass or a hollow liquid-filled tank.

Hollow subsea foundations

A bearing surface of a subsea foundation has a low-resistance coating such as an aerogel, an aero-clay or a polymeric film. When the foundation is installed, the bearing surface is embedded in the seabed soil using the low-resistance coating to reduce resistance movement of the bearing surface relative to the seabed soil. The coating may then dissolve or fragment away from the bearing surface or transform into a higher-resistance state while remaining on the bearing surface. These mechanisms degrade a resistance-reducing property of the coating to increase resistance to movement of the embedded bearing surface relative to the seabed soil. Suction may be applied to the foundation before or after the resistance-reducing property of the coating has substantially degraded.

Installation of embedded subsea foundations

A protective cover for a subsea elongate element, such as a pipeline, has an open end and a barrier attached to a cover to extend across and close an open end. The barrier is flexible to conform to and surround an elongate element extending from under the cover and protruding through the barrier. This prevents rocks of a rock berm from getting under the cover through the open end.

Growing community of inventors

Stavanger, Norway

Christian Linde Olsen