NO20151636A1

NO20151636A1 - Initiation of pliant wave riser and flexible Products using platform pull in winch wire as initiation method

Info

Publication number: NO20151636A1
Application number: NO20151636A
Authority: NO
Inventors: Håvard Strand
Original assignee: Ocean Installer As
Priority date: 2015-12-01
Filing date: 2015-12-01
Publication date: 2017-06-02
Also published as: WO2017095228A1

Description

PATENT - Initiation of pliant wave risers and flexible products using platform pull in winch wire as initiation method

Pliant wave risers typically have the subsea end of the riser and the static section laying on the seabed underneath the vicinity of the topside/platform. These can be challenging to install as it requires a method of taking the subsea end of the riser from the construction/installation vessel and pulling it towards the seabed underneath the platform. As the platform lies over the top of the area that the static section is being pulled to it makes it difficult for the construction/installation vessel to lowerthe riser into place. Typically a large clump weight (dead mans anchor) is used with either a subsea winch or a sheave connected to a wire from a winch on the platform and this is then used to connect to the subsea end from the vessel and pull the subsea end into position. This typically requires heavy equipment installed on the seabed and there is additional winches required on the platform or subsea which can increase the risk for possible breakdown or damage.

CLAIM: This patent application covers a new method whereby the platform pull-in wire is used to initiate the subsea end of the pliant wave riser in order to avoid the need for large clump weight or additional winch/pulling machine. The pull in wire from the platform is used for the final pull-in of the topside end of the riser into the platform, however this method requires it to be used for both the subsea initiation as well the normal topside pull-in method.

The method to initiate the subsea end of the riser consists of the following steps:

• The subsea end of the riser is deployed from the construction/installation vessel (typically from the moonpool but can also be over the side/end of the vessel). This is shown in Figure 1. • The platform pull-in winch wire is also lowered from the platform. This is shown in Figure 1. • A subsea connection is then made between the platform pull in winch wire rigging and the subsea end of riser. This is shown in Figure 1. • The pull in winch wire from the platform and riser on the vessel are paid in/out either simultaneously or in steps or in a combination to allow the subsea end of the riser to be brought doser to the platform and then the "sag bend" catenary or "belly" that is positioned in the correct position to allow it to be landed down on the seabed in correct

position with the subsea end suspended from the platform.

• The landing of the riser "sag bend" or "belly" can be accurately landed by alternately paying in/out of the platform pull-in winch wire, paying in/out of the riser from the vessel, moving the platform or vessel, or a combination of all operations. This is shown

in Figure 2.

• To ensure accurate landing of the riser, a "belly" clump weight connection can be made between the riser and a pre-installed clump weight or other fixing device or structure on the seabed. This allows the riser to be accurately positioned and fixed to prevent risk of

slippage during further laying of riser. This is shown in Figure 3.

• Once the construction/installation vessel is in position, the platform is then moved in a coordinated pattern (typically using the mooring/winch system) and the platform/topside winch wire is lowered (either simultaneously, in steps, or a combination) to enable the subsea end to be lowered towards the seabed and disconnected. This allows the riser static section towards the subsea end being able to be laid by the platform in a certain configuration based on moving the platform and winch accordingly to lay the riser on the seabed avoiding obstacles and other items on the seabed. This is shown in Figure 4.