GB2395510A

GB2395510A - Self piling reusable offshore platform

Info

Publication number: GB2395510A
Application number: GB0327213A
Authority: GB
Inventors: David Bone
Original assignee: Tamacrest Ltd
Current assignee: Tamacrest Ltd
Priority date: 2002-11-23
Filing date: 2003-11-24
Publication date: 2004-05-26
Anticipated expiration: 2023-11-24
Also published as: GB0227367D0; GB0327213D0; GB2395510B

Abstract

An offshore platform comprises a deck structure 1, a plurality of support legs 2 slidably mounted to the deck structure, foundation footpads 3 and pile sleeves inserted through said footpads 4.The platform also comprises a pile driver support rail 5 attached to the deck structure, to provide positional control for a pile driving mechanism 6. The pile driving mechanism is powered by an appropriate power source 7, while the support rail has means for lowering piles 8 into the pile sleeves. The footpads are fixed rigidly to said legs or attached using a locking mechanism 11 and 12 located inside the support legs. The offshore structure may be provided with fluid storage and retrieval means. A method for the installation of the structure is also disclosed.

Description

23955 1 0

SELF PILING REUSABLE OFFSHORE PLATFORM

This invention relates to offshore shallow water platforms, particularly intended for use in industries associated with exploration and/or production of oil, gas or other resources.

Conventional offshore shallow water platforms comprise a deck structure and a plurality of trussed support legs for supporting the deck structure above sea level. These platforms remain on site during field life and are then removed for decommissioning or possible use elsewhere.

The support legs are generally fixed either into a gravity base structure or with piles to the seabed. The majority of platforms are anchored by piles which are connected by a complex system of steelwork. The piled type of platform is installed concurrently with the piles, which are either inserted through the legs or using specific pile guides. This necessarily involves high costs for structural steel and specialist installation equipment. Consequential disadvantages are time involved, costs, dedicated equipment, and limited installation procedure.

In use one form of the gravity base type platform is floated into position with its legs in the raised position, whereupon the legs are lowered onto the seabed by ballasting the gravity base.

The deck structure is then raised out of the water to a suitable height above sea level. Finally the deck structure is clamped firmly to the legs. Removal is achieved by reversing the above procedure. A disadvantage of the gravity base type platform is that the gravity base structure is very large and attracts large wave and current loads both during installation and when in place.

Additionally, the gravity base structure is not suitable for use in all types of soil conditions.

We have now devised a platform and a means of installing and supporting the same, which alleviates the above problems.

According to the present invention there is provided an offshore platform comprising a deck structure, a plurality of support legs slidably mounted to the deck structure, foundation and installation guide footpads, pile sleeves inserted through said footpads, a pile driver support rail attached to the structure, said support rail providing positional control for a pile driving mechanism slidably mounted thereto, said pile driving mechanism being powered by a pneumatic or hydraulic compressor or other appropriate power source, said support rail having means for lowering piles, said footpads being fixed rigidly to said legs or attached using a locking mechanism located inside the support legs with drive mechanism such that said locking mechanism can be inserted through the support legs into the footpads thereby connecting said legs and said footpads.

Preferably the deck structure is fitted with slots to allow deployment of the piles.

Preferably the power source is deck mounted. However, in an alternative embodiment the power source could be located on a support vessel or other suitable location.

Preferably the pile driver support rail is attached to the underside and perimeter of the deck structure. Preferably the pile driver support rail provides a pivoted cantilever at the corners of the platform to aid location of the pile driving mechanism.

In an alternative embodiment support for the pile driving mechanism is provided using small platforms or rails located at the top of each leg. In this case a winch or crane would be required to move the pile driving mechanism from one leg to the next.

Preferably the support legs have expanded feet at the lower end. Ilowever, in an alternative embodiment the support legs have uniform cross-section.

Preferably the locking mechanism consists of securing pins or wedges.

Preferably the securing pins or wedges are hydraulically operated. However, in an alternative embodiment the pins are operated by a nonhydraulic mechanism.

Preferably the pins are wedge shaped, though they could be used in other suitable forms e.g. uniform cross section. Alternatively another type of locking mechanism may be employed.

In a further embodiment means is provided for storage of oil/ fluid after drilling and optionally processing. A container fabricated from neoprene or other suitable elastic material is located close to the structure legs, and is used to store processed or unprocessed oil from the drilling operations. The oil is held in the container by use of a control valve, which can be located at deck height of the structure for ease of access. The container is linked to the valve by one or more pipes that can be located inside one or more of the structure legs. The oil can then be retrieved to the surface by releasing the control valve, thereby enabling hydrostatic pressure to force the oil up through the pipes.

In an alternative embodiment, when soil conditions permit, a gravity base type structure can be used to anchor the structure legs to the seabed. This can be a reduced size tubular gravity base and can be used in combination with reduced size piles. With this option a bi-steel construction of the tubular base parts provides structural stiffness and strength. This obviates the need for reinforcement and eases the fabrication process. Also, the base can be used without piles and associated equipment and facilities, and can be used with or without footpads.

Also in accordance with this invention, there is provided a method of installing an offshore platform comprising a deck structure, a plurality of support legs slidably mounted to the deck structure, foundation and installation guide footpads, pile sleeves inserted through said footpads, a pile driver support rail attached to the structure, said support rail providing positional control for a pile driving mechanism slidably mounted thereto, said pile driving mechanism being powered by a pneumatic or hydraulic compressor or other appropriate power source, said support rail having means tor lowering piles, said footpads being fixed rigidly to said legs or attached using a locking mechanism located inside the support legs with drive mechanism such that said locking mechanism can be inserted through the support legs into the footpads thereby connecting said legs and said footpads, the method comprising towing the deck structure and footpads to location, either lowering the legs and rigidly attached footpads to the seabed and connecting said footpads thereto with piles or by the addition of ballast, or lowering the detachable footpads to the seabed and connecting said footpads thereto with piles or by the addition of ballast, then lowering the support legs into guides located at the top of the footpads, connecting the support legs to the footpads by inserting the locking mechanism between the legs and said footpads, and then inserting piles through the pile sleeves using the rail mounted pile driving mechanism.

Removal is facilitated by lowering the platform deck assembly either into the water if buoyant, or down onto an installation barge, then withdrawing the locking mechanism if the footpads are

detachable or cutting the piles if the footpads are attached rigidly, and raising the support legs to the deck structure.

The deck structure can be self-buoyant or can be supported by a barge during tow out and installation or removal.

The footpads can be pre-installed using temporary or permanent piles or ballast, or can be installed concurrently with the platform. In the latter case the footpads will preferably be connected by framing to ensure accurate spacing, and the frame may also be fitted with conductor guides for production drilling operations.

A specific embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 shows a side view of the offshore platform in accordance with this invention; Figure 2 is a cross section of the expanded feet and footpads showing pile locations; Figure 3 is a cross section showing the pile driver support rail.

Referring to the drawings, there is shown an offshore platform comprising a deck structure 1, a plurality of support legs 2, foundation and installation guide footpads 3, pile sleeves 4, a pile driver support rail 5, a pile driver 6, and a compressor 7. Additional stiffening beams 9 are shown between the footpads 3. Expanded feet 10 are shown at the bottom of the legs 2. These are secured to the footpads using securing pins 11. A riser 12 is shown located in one of the support legs 2.

During piling the pile driver 6 is moved into position above a pile 8, and powered using the compressor 7.

The support legs 2 are slidable axially of themselves relative to the deck structure 1. The deck structure l and legs 2 are moved relative to each other during installation using a jacking system or strand jacks (not shown).

During installation the deck structure 1 is floated into position using a barge or using excess buoyancy, with the legs 2 raised. Then, the footpads 3 are lowered to the seabed and secured.

The legs 2 are lowered into the footpads 3 and secured using the pins 11. The deck structure I is raised and secured. The piles 8 are then secured using the pile driver 6.

The pile driver 6 is guided along the support rail 5 using a wheeled trolley (or some other suitable mechanism) to which it is secured. Once in the correct location the pile driver 6 is lowered and fixed to the pile 8. Each pile 8 is inserted through a slot in the support rail 5 into each pile sleeve 4.

The structure 1 can be removed by cutting off the piles 8, releasing the securing pins 11, lowering the deck structure 1, and raising the support legs 2. The footpads 3 can be removed subsequently.

Claims

1. An offshore platform comprising a deck structure, a plurality of support legs slidably mounted to the deck structure, foundation and installation guide footpads, pile sleeves inserted through said footpads, a pile driver support rail attached to the structure, said support rail providing positional control for a pile driving mechanism slidably mounted thereto, said pile driving mechanism being powered by a pneumatic or hydraulic compressor or other appropriate power source, said support rail having means for lowering piles, said footpads being fixed rigidly to said legs or attached using a locking mechanism located inside the support legs with drive mechanism such that said locking mechanism can be inserted through the support legs into the footpads thereby connecting said legs and said footpads..

2. An offshore platform as claimed in Claim 1, wherein the deck structure is fitted with slots to

allow deployment of the piles.

3. An offshore platform as claimed in Claim 1 or Claim 2, wherein the power source is deck mounted.

4. An offshore platform as claimed in any preceding claim, wherein the power source is located on a support vessel or other external location.

5. An offshore platform as claimed in any preceding claim, wherein the pile driver support rail is attached to the underside and perimeter of the deck structure.

6. An offshore platform as claimed in any preceding claim, wherein the pile driver support rail provides a pivoted cantilever at the corners of the platform to aid location of the pile driving mechanism.

7. An offshore platform as claimed in any of claims 1 to 5, wherein support for the pile driving mechanism is provided using small platforms or rails located at the top of each leg.

8. An offshore platform as claimed in any preceding claim, wherein the support legs have expanded feet at the lower end.

9. An offshore platform as claimed in any of claims I to 7, wherein the support legs have uniform cross-section.

10. An offshore platform as claimed in any preceding claim, wherein the locking mechanism consists of securing pins or wedges.

11. An offshore platform as claimed in Claim 10, wherein the securing pins or wedges are hydraulically operated.

12. An offshore platform as claimed in Claim 10 or Claim 11, wherein the securing pins or wedges are operated by a non-hydraulic mechanism.

13. An offshore platform as claimed in any of claims 10 to 12, wherein the pins are wedge shaped.

14. An offshore platform as claimed in any of claims 10 to 12, wherein the pins are non-wedge shaped (e.g. uniform cross section).

15. An offshore platform as claimed in any preceding claim, wherein a gravity base is used to anchor the structure legs to the seabed, said base being of tubular construction and fabricated from bi-steel components, said base being arranged such that it can be used in combination with reduced size piles, or such that it can be used without piles and associated piling equipment and facilities, and also can be arranged so that it can be used with or without said footpads.

16. An offshore platform as claimed in any preceding claim, wherein means is provided for oil/ fluid storage, said means comprising a container fabricated from neoprene or other suitable elastic material, a control valve used to provide a pressure lock mechanism, and pipework providing a passage between said container and said control valve, such that release of the control valve allows fluid flow up through the pipework.

17. A method of installing an offshore platform comprising a deck structure, a plurality of support legs slidably mounted to the deck structure, foundation and installation guide footpads, pile sleeves inserted through said footpads, a pile driver support rail attached to the structure, said support rail providing positional control for a pile driving mechanism slidably mounted thereto, said pile driving mechanism being powered by a pneumatic or hydraulic compressor or other appropriate power source, said support rail having means for lowering piles, said footpads being fixed rigidly to said legs or attached using a locking mechanism located inside the support legs with drive mechanism such that said locking mechanism can be inserted through the support legs into the footpads thereby connecting said legs and said footpads, the method comprising towing the deck structure and footpads to location, either lowering the legs and rigidly attached footpads to the seabed and connecting said footpads thereto with piles or by the addition of ballast, or lowering the detachable footpads to the seabed and connecting said footpads thereto with piles or by the addition of ballast, then lowering the support legs into guides located at the top of the footpads, connecting the support legs to the footpads by inserting the locking mechanism between the legs and said footpads, and then inserting piles through the pile sleeves using the rail mounted pile driving mechanism.

18. A method of installing an offshore platform as claimed in Claim 17, wherein the deck structure is self-buoyant.

19. A method of installing an ofl.shore platform as claimed in Claim 17, wherein the deck structure is supported by a barge during tow out and installation or removal

20. An offshore platform substantially as herein described and illustrated in the accompanying drawings.