GB2153886A

GB2153886A - Method of constructing offshore platform

Info

Publication number: GB2153886A
Application number: GB08503302A
Authority: GB
Inventors: Stuart Komaromy
Original assignee: EARL AND WRIGHT Ltd
Current assignee: EARL AND WRIGHT Ltd
Priority date: 1984-02-10
Filing date: 1985-02-08
Publication date: 1985-08-29
Also published as: GB8403568D0; GB8503302D0

Abstract

A method of constructing an offshore platform on a previously founded subsea template 1 comprises the steps of positioning a further template 2 over the subsea template, driving piles 5 through both templates, and then fixing the further template to the piles so that it acts a plan bracing for the platform so constructed. <IMAGE>

Description

SPECIFICATION Method of constructing offshore platform The invention relates to a method of constructing an offshore platform, and to a platform so constructed.

Conventional piled steel platforms require sophisticated fabrication yards, and need large numbers of highly skilled workers capable of advanced welding and inspection techniques.

Such requirements are necessary for the demanding environment of deep water sites in the North Sea.

For locations where there are less demanding conditions, and the sophisticated yards and skilled personnel are not available, an alternative approach may be desirable.

The invention provides a method of constructing an offshore platform comprising the steps of: (i) Installing a first (subsea drilling) template on the seabed, said first template having at least three pile sleeves; (ii) Positioning a second (guide) template on a floating barge over the first template so that three pile guide slots on the second template correspond with the three pile sleeves on the first template; (iii) Stabbing and driving piles through the pile guide slots on the second template and the pile sleeves on the first template; (iv) Raising the second template off the barge; (v) Removing the barge; (vi) Locating the second template to provide generally horizontal bracing between the piles; (vii) Fixing the second template to the piles to form plan bracing; (viii) Constructing a deck at or near the tops of the piles;; In one preferred embodiment the deck is formed of a third (deck) template, which is carried on the same barge on top of the second (guide) template with three further guide slots (corresponding with the slots on the second template and the sleeves on the first template) and in which, after the piles have been stabbed and driven, the third template is raised on and fixed to the tops of the piles, so to form the deck.

Three (or more) templates may be floated out on the same barge.

Tension bracing members may be installed between the second and third templates.

Such tension bracing members may be used as the means of raising/lowering the second template to its final position.

The piles may be fixed to the second template by grouting or by swaging.

In one preferred form of the invention all the templates are of rectangular plan form, and four piles are stabbed and driven through slots and sleeves disposed towards the corners of the templates.

It may be preferred that a deck having installed thereon facilities for the platform is carried on the same barge as the second template.

In an alternative form of the invention the deck is buoyant and includes three pile slots, and is used instead of the barge and the second template, such that the deck is raised sufficiently far above sea level to support the facilities and to provide plan bracing.

The invention includes A platform when constructed according to the method described above.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing, in which sketches I to V show diagrammatic side elevational views of successive stages in the construction of an offshore platform, e.g. for oil or gas production.

Stage I shows a subsea drilling template 1 installed on the seabed. This template is of square planform, and has a pile sleeve at each of its four corners.

Stage II shows a guide template 2 and a deck template 3 positioned on a barge 4 directly over the drilling template 1. The templates 2 and 3 have pile guide slots which correspond with the sleeves at the corners of template 1. The barge 4 is moored so that large diameter piles 5 (e.g 84" O.D.) can be stabbed and driven through the guide slots in the templates 3 and 2 and sleeves in the template 1. The sleeves have conical receptacles to guide the piles into alignment if the templates are not lined up precisely.

In Stage Ill the piles have all been driven, and have been grouted or swaged into the sleeves in template 1. Templates 2 and 3 are then raised on the piles 5 so that the barge 4 is freed of their weight, and the barge can be towed away. Templates 2 and 3 may be raized or lowered by cables or chains which will later form diagonal tension bracing members between the piles and the template (as seen in Stage V).

Template 3 may be welded off to the tops of the piles so to form a deck for the platform, and, as shown in Stage IV, the template 2 is lowered to provide horizontal bracing between the piles 4 at a level intermediate the sea surface and the seabed. Alternatively the template 2 might be fixed to the piles sufficiently far above sea level (ie. above the highest expected wave crest) to provide a base for a cellar deck. Template 2 is fixed to the piles by grouting or swageing in a manner known per se.

Finally, if required, tension bracing can be set up between the piles where they are connected to the templates as shown in Stage V.

Further templates could be provided to form additional levels of intermediate horizontal bracing.

It will be understood that a deck could be installed on top of the piles without the need for template 3. Indeed for some platforms a deck could be carried out on the barge 4, at the same time as template 2; or could replace both the barge 4 and the template 2.

Claims

1. Method of constructing an offshore platform comprising the steps of: (i) Installing a first (subsea drilling) template on the seabed, said first template having at least three pile sleeves; (ii) Positioning a second (guide) template on a floating barge over the first template so that three pile guide slots on the second template correspond with the three pile sleeves on the first template; (iii) Stabbing and driving piles through the pile guide slots on the second template and the pile sleeves on the first template; (iv) Raising the second template off the barge; (v) Removing the barge; (vi) Locating the second template to provide generally horizontal bracing between the piles; (vii) Fixing the second template to the piles to form plan bracing; (viii) Constructing a deck at or near the tops of the piles;

2.As claimed in Claim 1 in which the deck is formed of a third (deck) template, which is carried on the same barge on top of the second (guide) template with three further guide slots (corresponding with the slots on the second template and the sleeves on the first template) and in which, after the piles have been stabbed and driven, the third template is raised on and fixed to the tops of the piles, so to form the deck.

3. As claimed in Claim 2 in which three (or more) templates are floated out on the same barge.

4. As claimed in Claim 2 or Claim 3 in which tension bracing members are installed between the second and third templates.

5. As claimed in Claim 4 in which the tension bracing members are used as the means of raising/lowering the second template to its final position.

6. As claimed in any of the preceding claims in which the piles are fixed to the second template by grouting.

7. As claimed in any one of Claims 1 to 5 in which the piles are fixed to the second template by swaging.

8. A method as claimed in any one of the preceding claims, in which all the templates are of rectangular plan form, and four piles are stabbed and driven through slots and sleeves disposed towards the corners of the templates.

9. A method as claimed in any one of the preceding claims, in which a deck having installed thereon facilities for the platform is carried on the same barge as the second template.

10. A method as claimed in claim 9 as dependent on claim 1 in which the deck is buoyant and includes three pile slots, and is used instead of the barge and the second template, such that the deck is raised sufficiently far above sea level to support the facilities and to provide plan bracing.

11. A method substantially as hereinbefore described with reference to the accompanying drawing.

1 2. A platform when constructed according to the method of any one of the foregoing claims.