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INSTALLATION METHOD OF LAYING FLEXIBLE RISERS IN ULTRA DEEP WATER

IP.com Disclosure Number: IPCOM000243919D
Publication Date: 2015-Oct-28
Document File: 4 page(s) / 262K

Publishing Venue

The IP.com Prior Art Database

Abstract

An installation method of laying flexible risers or pipes in ultra deep water is disclosed Multiple friction clamps are used to support the riser in stages using cables attached to winches to the required depth One or more pipe laying support vessels PLSVs deploy the riser up to the depth where a tensioner on the vessel gets close to the capacity limit At this point a second friction clamp is deployed off the vessel supporting a second length of riser connected through cables to additional winches to share the top tension from the tensioner and the process continued to the required depth As the PLSV is laying the pipes the tension that winches can share with tensioner starts to decrease once the bottom end of the riser begins to touch the seabed whereupon the clamp and connecting cables may be detached and re deployed A feasible method is provided for laying subsea pipe in ultra deep water which enables even vessels with small tensioner capacity to be used for deep water installation

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INSTALLATION METHOD OF LAYING FLEXIBLE RISERS IN ULTRA-DEEP WATER

BACKGROUND

The invention concerns installation method of laying flexible risers or pipes in ultra-deep water. In recent years, scarcity of resources has driven subsea oil and gas exploitation activities in ultra- deep water. The present flexible riser systems are qualified to deliver services under harsh environmental conditions, and survive the extreme and fatigue requirements. However, installation of risers in deep water can be challenging, since the top tension due to the self-total weight of the riser could reach the capacity limit of the tensioner on the pipe laying support vessels (PLSVs).

In the existing method, the risers are laid using auxiliary buoyancy units, filled with air or foam for example, or air lift bags attached along the pipe during installation. The buoyancy units help to reduce top tension sustained by the tensioner on the pipe laying support vessel. However, this method requires large tensioner capacity for deep water installation, which is also not feasible for laying subsea pipe in ultra-deep water. Therefore, there is a need for a method of laying flexible risers, which is capable of reducing top tension during installation of flexible risers.

BRIEF DESCRIPTION OF DRAWINGS

The invention discloses a method of laying flexible risers or pipes in ultra-deep water, wherein:

FIG. 1 illustrates a schematic of installation method for laying flexible risers in deep water.

FIG. 2 presents a schematic of multiple winches attached to the installation vessel.

FIG. 3 illustrates supporting installation using winches attached to multiple supporting vessels.

DETAILED DESCRIPTION

The invention presents an installation method of laying flexible risers or pipes in ultra-deep water. The proposed procedures for installation of subsea pipes in ultra-deep water are illustrated in FIG. 1, wherein multiple friction clamps are used to support the riser in stages using cables attached to winches, to the required depth. In step 1, one or more pipe laying support vessels (PLSVs) deploy the riser up to the depth where a tensioner on the vessel gets close to the capacity limit. As shown in FIG. 1 step 1, a first friction clamp C1 is placed at such a location that the self-total weight of the pipe below the friction clamp is close to the capacity limit of the


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278801 
tensioner, while the friction clamp is connected to winches through cables. In step 2, a second friction clamp C2 is deployed off the vessel, supporting a second length of the riser connected through cables to additional winches to share the top tension from the tensioner.

In step 3, as the PLSV is laying the pipes, the tension on the winches starts to decrease once the bottom end of the riser begins to touch the seabed. Further friction clamps C3, C4, etc. could be used as ne...