GB2133447A

GB2133447A - Offshore structures

Info

Publication number: GB2133447A
Application number: GB08329547A
Authority: GB
Inventors: N C Bradshaw
Original assignee: BROWN EARL AND WRIGHT Ltd
Current assignee: BROWN EARL AND WRIGHT Ltd
Priority date: 1982-11-04
Filing date: 1983-11-04
Publication date: 1984-07-25
Also published as: GB8329547D0

Abstract

An offshore platform substructure capable of supporting facilities comprises two tubular steel framed tower structures 11 and 12 adapted to be located with their respective bases adjacent each other and to be joined at their respective tops, and to have unconnected lengths between their bases and their tops of more than half the total height of the platform substructure. It is preferred that the tower structures are also adapted to be joined at their respective bases. <IMAGE>

Description

SPECIFICATION Offshore structures The invention relates to substructures for offshore platforms. Such platforms may be used to support facilities for the production of oil and/or gas.

The invention provides an offshore platform substructure capable of supporting facilities, and comprising two tubular steel framed tower structures adapted to be located with their respective bases adjacent each other and to be joined at their respective tops, and to have unconnected lengths between their bases and their tops of mor than half the total height of the platform substructure.

It is preferred that the tower structures are also adapted to be joined at their respective bases.

In one preferred form of the invention the joints at bases and tops of tower structures lie in a single plane between the tower structures.

It is also preferred that a joint between the bases of the tower structures is formed by axially aligned sleeves outstanding from each of the bases through which a pin can be threaded, slotted or dropped, and in which the pin is grouted to one or more sleeves outstanding from each base.

In this form it is preferred that the joints at the top of the tower structure are aligned with the sleeves outstanding from the bases of the tower structure.

In an alternative form of the invention the bases of the tower structures may be spaced apart by and joined to or aligned with one or more subsea templates, either independent of or integrated with the individual tower structures.

In one optionai form the joint at the tops of the tower structures is formed by a deck portion extending between the tower structures.

Preferably one of the tower structures is fabricated on a face opposed to another face of that tower structure which will be joined at its top to the top of the other tower structure.

Fabrication can be on launch rails, as with a barge launched structure, or on plinths as with a self floating structure.

More specifically both tower structures are so fabricated.

Preferably one of the tower structures is of rectangular planform, and tapers from its base to its top, where it is adapted to receive a joint to join it to the other tower structure.

It is further preferred that the two tower structures are substantially identical.

The invention also provides a method of constructing an offshore platform substructure comprising the steps of placing one tower structure with its base adjacent to the base of a second tower structure, and joining the tops of the two tower structures.

Preferably the tower structures are joined at their respective bases before they are joined at their tops.

A specific embodiment of this invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a perspective view, Figure 2 is a side elevation, Figure 3 is a front elevation, Figure 4 is a sectional elevation on the line AA in Figure 3, and Figure 5 shows an assembly sequence of one tower structure.

Figures 6 to 10 correspond generally to Figures 1 to 5, but illustrate a platform substructure comprising two self floating tower structures instead of two barge launched structures.

As shown in Figure 1 a platform substructure 10 comprises two tubular steel framed tower structures 11 and 12 which have their bases 1 2A and 14 located adjacent to each other and joined together. Both structures are fixed to the seabed by piles which are grouted in pile sleeves either within the main framing or, as shown, on separate outrigger frames.

The tops 1 5 and 1 6 of the two tower structures 11 and 12 are joined together by portions 17 and 1 8 which are cantilevered towards each other from the tops of the respective towers, The tops of the tower structures and the tops of the cantilevered portions are arranged in a single plane to form a flat deck capable of supporting facilities (not shown) for oil or gas production.

In one alternative form portions 1 7 and 1 8 may be fabricated as a single bridging section which is lowered into place between the tower tops 1 5 and 16. In another alternative form portions 15, 17, 18 and 16 may be a single deck placed upon the tops of the two towers 11 and 12.

As may be seen from Figures 1 and 3 the tower structures 11 and 12 have unconnected lengths between their bases and their tops, which may be 60% of the total height of the substructure 10. It is a feature of this particular substructure that the unconnected length is more than 50% of its total height.

The tower structures 11 and 12 are joined at their bases 1 2A and 14 by a pin which is threaded through axially aligned sleeves on the two tower structures. The pin (not shown) would be threaded, slotted or dropped down the line 19 shown on Figure 3 through sleeves fixed to the bases 1 2A and 14 of the tower structures. The pin would be fixed to the sleeves by grouting.

Several pins could be used in this way to connect the two tower structures along the plane in which the bases are adjacent to each other.

(This is the plane of the line 19 as seen in Figure 3).

The invention is not limited to pinned connections at the tower bases, and other forms of fixing could be used depending on availability and suitability.

Each of the tower structures can be constructed as shown in Figure 5. (This is a typical fabrication sequence for a barge launched structure. The tower structures are built on launch rails 21 and 22 which may later be used to load out and then to launch the tower structures off a barge. Launch frames 23 and 24 are rolled up and joined together by infill bracing. Outer frames 25 and 26 are then rolled up section by section and connected to the launch frames. Piling steelwork 27 and 28 is then erected and connected to the bases of the outer frames 25 and 26. This piling steelwork could be incorporated in the launch and/or outer frames.

As shown in Figure 6 to 10, an alternative construction sequence is comprehended within the scope of the invention. With particular reference to Figure 10 a tower structure is constructed from rolled up frames 32 on plinths 33 for sideways launch.

As a further alternative the tower structure may be constructed in a dry dock which is subsequently flooded for the tower structure to float out.

Claims

1. An offshore platform substructure capable of supporting facilities, and comprising two tubular steel framed tower structures adapted to be located with their respective bases adjacent each other and to be joined at their respective tops, and to have unconnected lengths between their bases and their tops of more than half the total height of the platform substructure.

2. A substructure as claimed in Claim 1 in which the tower structures are also adapted to be joined at their respective bases.

3. A substructure as claimed in Claim 2 in which joints at bases and tops of tower structures lie in a single plane between the tower structures.

4. A substructure as claimed in Claim 3 in which a joint between the bases of the tower structures is formed by axially aligned sleeves outstanding from each of the bases through which a pin can be threaded, slotted or dropped and in which the pin is grouted to one or more sleeves outstanding from each base.

5. A substructure as claimed in Claim 4 in which the joints at the top of the tower structure are aligned with the sleeves outstanding from the bases of the tower structure.

6. A substructure as claimed in Claim 2 in which the bases of the tower structures are spaced apart by and joined to or aligned with one of more subsea templates, either independent of or integrated with the individual tower structures.

7. A substructure as claimed in Claim 1, Claim 2 or Claim 6 in which the joint at the tops of the tower structures is formed by a deck portion extending between the tower structures.

8. A substructure as claimed in any one of the preceding claims in which one of the tower structures is fabricated on a face opposed to another face of that tower structure which will be jointed at its top to the top of the other tower structure.

9. A substructure as claimed in Claim 8 in which the tower structure is fabricated on launch rails, as with a barge launched structure.

10. A substructure as claimed in Claim 8 in which the tower structure is fabricated on plinths, as with a self floating structure.

1 A substructure as claimed in Claim 9 or Claim 10 in which both tower structures are so fabricated.

12. A substructure as claimed in any one of the preceding claims in which one of the tower structures is of rectangular planform, and tapers from its base to its top, where it is adapted to receive a joint to join it to the other tower structure.

13. A substructure as claimed in any one of the preceding claims in which the two tower structures are substantially identical.

14. A method of constructing an offshire platform substructure comprising the steps of placing one tower structure with its base adjacent to the base of a second tower structure, and joining the tops of the two tower structures.

1 5. A method claimed in Claim 14 in which the tower structures are joined at their respective bases before they are joined at their tops.

16. A substructure substantially as hereinbefore described with relevenace to and as shown in Figure 1 to 5 and 6 to 10 of the accompanying drawings.

1 7. A method of constructing a substructure substantially as hereinbefore described with relevance to Figure 1 to 5 and 6 to 10 of the accompanying drawings.