US 5,421,676 AGranted

Tension leg platform and method of instalation therefor

AssigneeSea Engineering Associates, Inc.

InventorsPieter G. Wybro, David N. Dunlop

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Abstract

A compact offshore tension leg platform having a deck, a hull, and a plurality of elongate tendons securing the hull to an ocean floor foundation provides full well workover and production capabilities for autonomous operation and can be installed and operated in any waterdepth and sustain any environmential loading conditions. The hull supports the well risers of well trees located below the water surface at an elevation in close proximity to the connections of the tendons to the hull. Alternatively the risers and trees may be supported by the deck. A well workover platform, supported by a circular perimeter trackway on the deck may be positioned over any of the well risers for workover operations. Liquid products may be exported from the platform via a seabed pipeline or to a floating tanker moored to a mobile offtake on the deck support column. The hull is configured to minimize loadings in the tendons. All components, except the deck, are installed by a drilling vessel without the need for specialist installation vessels and equipment. The tendons are arranged in groups offset from the hull body to resist platform overturning loadings, and to reduce the tendons pretension required to prevent platform pitch and roll motions. The wells are drilled prior to installation of the hull using a drilling vessel. After installation of the platform, all operations required on the wells are performed autonomously from the platform without the need for another drilling vessel or equipment.

Claims15

Dependent claims

An offshore tension leg platform comprising:

(a) a hull having a bottom portion and an upper portion including a slender column adapted at its upper end to receive and support deck means and after said deck means is supported thereon, said column being disposed partially above the surface of the water and partially below, and said hull having a plurality of internal ballast/buoyancy compartments for varying its buoyancy such that it may be towed floating to the installation site, ballasted in stages until tendons are connected thereto, then deballasted until it has a predetermined installed draft;
(b) structural support elements connected with said hull extending a predetermined distance outwardly therefrom and having vertical-entry tendon connection sleeves at their outer ends which are positioned in laterally outward spaced relation to said hull a predetermined distance and each having an open bottom end to receive the upper end of a tubular tendon;
(c) a plurality of elongate tubular tendons each of which is connected at a lower end to a foundation pile on the seabed and having an upper end vertically received within said tendon connection sleeves by lowering said hull by ballasting and thereafter connected to said tendon connection sleeves, said tendons disposed in outwardly spaced relation to said hull means a predetermined distance sufficient to reduce loadings in said tendons caused by horizontal loadings imposed on said platform;
and
(d) deck means supported at the upper end of said slender column for supporting well production equipment and well workover equipment.

2 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/014,690Filed 8 Feb 1993
Granted: 6 Jun 1995
Term ends: Not estimatedThe source records don’t support an estimate.

Classification13 codes

E21B 19/004
Specially adapted for underwater drilling: supporting a riser from a drilling or production platform
B63B 21/502
Anchoring arrangements or methods for special vessels, e.g. for floating drilling platforms or dredgers: by means of tension legs
B63B 77/00
Transporting or installing offshore structures on site using buoyancy forces
E21B 17/01
Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings: risers