US20100186653A1

US20100186653A1 - Extended-deck jack-up

Info

Publication number: US20100186653A1
Application number: US12/322,154
Authority: US
Inventors: Robert Clague
Original assignee: Friede and Goldman Ltd
Current assignee: Friede and Goldman Ltd
Priority date: 2009-01-29
Filing date: 2009-01-29
Publication date: 2010-07-29

Abstract

An offshore structure has stabilizing deck extension members formed as watertight bodies and extending along a port peripheral wall and starboard peripheral wall of the hull. The stabilizing members add stability without substantially increasing weight of the structure. Each of the stabilizing members has an inverted triangle cross-sectional configuration wherein the water plane area of the stabilizing members increases from a lower portion toward an upper portion.

Description

BACKGROUND OF THE INVENTION

This invention relates to offshore structures and more particularly to a leg-supported structure suitable for use as a drilling and production facility for oil and gas mineral reserves.
In the course of offshore operations, a large number of fixed platforms have been used in the oil and gas industry for exploration and production of natural resources. The wells are drilled and pipelines laid for connection to the wells to extract the valuable hydrocarbon fuel from offshore locations, often at a considerable cost to the developer. These types of offshore structures can be delivered to a designated site using a buoyant hull. The structure is deployed by lowering the legs to the sea bottom and then raising the hull to an operational height above expected wave action. The legs are fixed in the designated location to provide stability to the structure, while drilling and production operations are conducted from the deck or decks of the platform hull.
The size of the platform decks is extremely limited due to the weight considerations of the entire structure. Some jack-up designs use a cantilever drill floor that extends over the fixed platform with existing wells to support deeper drilling and stimulate production from the old wells. In order to continue drilling and production using the existing wells, additional process equipment is required for pre-treating of the produced fluids while utilizing the existing process train. If such equipment is to be installed on the old platforms, it will utilize any remaining topsides capacity of these platforms.
Conventional solutions heretofore have been to either make the hull wider, similar to making a larger box, which necessarily adds the weight, or to use a deck extension that comprises a horizontal beam extending from the main deck with an under-deck strut supporting the beam, which is also problematic because of the high maintenance requirements. Besides, the under-deck open extensions add weight without increasing stability.
The present invention contemplates elimination of drawbacks associated with the conventional designs and provision of an extended deck structure that adds platform space, while also adding buoyancy and stability to the hull when it is required for transport.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an offshore platform structure having extended surface area and increased stability.
It is another object of the invention to provide an offshore platform structure that uses watertight stability members of reduced weight and low maintenance requirements. These and other objects of the invention are achieved through a provision of a platform apparatus for an offshore structure having hull with a deck, a bottom plate, a port peripheral wall and a starboard peripheral wall. The platform apparatus according to this invention comprises a stabilizing member secured along the port peripheral wall and a stabilizing member secured along the starboard peripheral wall, each of said stabilizing members comprising a watertight body having a lower portion and an upper portion, a top plate, and a bottom wall extending at an angle in relation to a vertical axis of the hull. Each of the stabilizing members follows the configuration of the respective peripheral wall, while the water plane area of the watertight body increases toward the upper portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the drawings, wherein like parts are designated by like numerals, and wherein

FIG. 1 is a plan view of a main deck of a jack-up platform structure in accordance with the present invention.

FIG. 2 is a cross-section view taken along lines A-A of FIG. 1.

DETAIL DESCRIPTION OF THE INVENTION

Turning now to the drawings in more detail, numeral 10 designates a platform structure in accordance with the present invention. A typical jack-up unit is provided with a plurality of truss legs 12, which extend through leg wells 14 in a floatable hull 16 of the jack-up unit. Although any number of legs may be used to support the hull 16, for illustration purposes, the jack-up unit shown in FIG. 1 has three such legs 12.
Each leg 12 is provided with the jacking assemblies 18 for moving the leg vertically with respect to the hull 16. The legs 12 move from a raised position, when the jack-up unit is in transit and the legs 12 are supported by the hull 16, to a lowered position, when the legs 12 support the hull 16. As the legs 12 are “jacked,” the hull 16 is elevated above an anticipated wave action to support the offshore exploration and/or production operations. Conventional offshore platforms, such as the jack-up unit, comprise a hull shell 20 which defines the peripheral boundaries of a main deck 30.
As can be seen in FIGS. 1 and 2, the hull 16 has a main deck 30, a stern portion 32, a port peripheral wall 34, a bow portion 36, and starboard peripheral wall 38. The side shell of the hull 16 comprises the port peripheral wall 34 and the starboard peripheral wall 38, which extend perpendicularly to the main deck 30 and have a predetermined height. The bottom of the hull 16 is defined by a bottom plate 40.
An extension or stabilizing member 50 is secured to extend along the port peripheral wall 34, and a mirror-image extension or stabilizing member 52 is secured to extend along the starboard peripheral wall 38. Each of the extension members 50 and 52 comprises a horizontal top plate 54, 56, a bow plate 58, 60, a stern plate 62, 64, and angularly oriented (sloped) bottom wall 66, 68, respectively. The plates 54, 58, 62, and 66 are secured to the port peripheral wall 34 in a watertight manner to form the extension member 50. Similarly, the plates 56, 60, 64, and 68 are secured in a watertight manner to the starboard peripheral wall 38 to form the extension member 52. The extension members 50 and 52 are shown to have an inverted-triangle cross-section, although other shapes can be used by persons skilled in the art.
Each extension member 50, 52 define an enclosed compartment. If desired, the extension members 50 and 52 can be formed with a plurality of inner compartments divided by reinforcing bulkheads. The extension members add stability through increased water plane area as well as buoyancy to the platform hull 16 during transit of the platform 10 to the designated site. At the same time, the overall weight of the platform 10 is not significantly increased.
Imaginary waterlines A and B shown in phantom lines in FIG. 2, illustrate the increased water plane area and buoyancy of the hull 16 as the jack-up unit moves in water; shallow draft at waterline A and a deep draft at waterline B. The drawing demonstrates the advantages of extending the deck area using the extension members 50 and 52—as the vessel increases its draft the water plane area increases as well, which is a considerable advantage with regards to the vessel's stability. For a traditional box-shaped hull, which would be limited by the vertical walls 34 and 38, the water plane area remains the same as the draft increases.
Compared to the conventional grating walkways used on the offshore rigs, the top plates 54, 56 are formed as solid plates. Where conventional deck extensions use diagonal struts for supporting the top plates and leaving open spaces between the grating plate and the strut, the present invention provides for enclosed buoyant compartments that are not open to the wave action. Conventional open-area under-deck structure provides no additional stability to the vessel. An additional problem with the conventional design solutions is maintenance, since the under-deck structure is open and corrodes easily. Therefore, the rig operators do not favor such open-area designs. The watertight stabilizing members 50, 52 eliminate these problems.
As can be seen in FIG. 1, the configuration of the extension members 50, 52 follows the configuration of the port peripheral wall 34 and starboard peripheral wall 38. The increased usable deck surface provided by the top plates 54, 56 may be used for installation of the equipment, as walkways for rig personnel, storage, and other objectives. Also importantly, the additional buoyant members add stability to the platform 10.
The inclined bottom walls 66, 68 can be oriented at about 45 degrees in relation to the vertical walls 34, 38 of the hull 16. The weight of the extension members 50, 52 is therefore one-half of the conventional box-shaped hull extensions. As the platform 10 is lowered into water, more surface area of the bottom walls 66, 68 comes into contact with water. Since the surface area of the extension members 50, 52 increase from the points of attachment 70, 72 of the bottom walls 66, 68 with the bottom plate 40 the water plane area of the extension members increase from the lower portion toward the upper portion where the bottom walls 66, 68 are attached to the top plates 54, 56. With the increase in water plane area of the extension members 50, 52, the buoyancy and stability increases. As a as result, the overall stability and buoyancy characteristics of the platform 10 is improved.
It will be apparent that the use of extension deck members is not limited to jack-up rigs. Other offshore structures, such as semi-submersibles, MODU, spars and others can benefit from the aspects of this invention.
Many changes and modifications can be made in the present invention without departing from the spirit thereof I therefore pray that my rights to the present invention be limited only by the scope of the appended claims.

Claims

1. A platform apparatus for an offshore structure having a port peripheral wall and a starboard peripheral wall, the platform comprising:

an extension member secured along the port peripheral wall and an extension member secured along the starboard peripheral wall, each of said extension members comprising a watertight body having a lower portion and an upper portion, and wherein water plane area of said watertight body increases as vessel draft increases

2. The apparatus of claim 1, wherein said platform apparatus further comprises a top deck, and wherein each of said extension members comprises a top plate secured for extension in a generally co-planar relationship to the top deck.

3. The apparatus of claim 2, wherein said platform apparatus further comprises a bottom plate, and wherein each of said extension members comprises a bottom wall extending at an angle between the bottom plate and the top plate.

4. The apparatus of claim 1, wherein said watertight body has a generally triangular cross-section.

5. The apparatus of claim 1, wherein each of said extension members follows configuration aspect of a respective peripheral wall.

6. A platform apparatus for an offshore structure having hull with a deck, a bottom plate, a port peripheral wall and a starboard peripheral wall, the platform comprising:

a stabilizing member secured along the port peripheral wall and a stabilizing member secured along the starboard peripheral wall, each of said stabilizing members comprising a watertight body having a lower portion and an upper portion, and wherein water plane area of said watertight body increases as vessel draft increases.

7. The apparatus of claim 6, wherein each of said stabilizing members has a generally triangular cross-sectional configuration.

8. The apparatus of claim 6, wherein each of said stabilizing members comprises a top plate oriented in a generally co-planar relationship to the deck of the hull and a bottom wall extending at an angle in relation to the top plate and the bottom plate of the hull.

9. The apparatus of claim 6, wherein said stabilizing members facilitate buoyancy of the hull without significantly affecting weight of the platform structure.

10. A platform apparatus for an offshore structure having hull with a deck, a bottom plate, a port peripheral wall and a starboard peripheral wall, the platform comprising:

a stabilizing member secured along the port peripheral wall and a stabilizing member secured along the starboard peripheral wall, each of said stabilizing members comprising a watertight body having a lower portion and an upper portion, a top plate, and a bottom wall extending at an angle in relation to a vertical axis of the hull, and wherein water plane area of said watertight body increases as vessel draft increases.

11. The apparatus of claim 10, wherein each of said stabilizing members has an inverted triangular configuration.

12. The apparatus of claim 10, wherein each of the stabilizing members follows configuration aspect of a respective peripheral wall.