GB2335181A

GB2335181A - Travelling jacking arrangement for offshore platform

Info

Publication number: GB2335181A
Application number: GB9816073A
Authority: GB
Inventors: Peter Bennett
Original assignee: RESOURCE MARGINAL SYSTEMS Ltd
Current assignee: RESOURCE MARGINAL SYSTEMS Ltd
Priority date: 1998-03-13
Filing date: 1998-07-24
Publication date: 1999-09-15
Also published as: GB9816073D0; GB9805287D0

Abstract

A shallow water platform comprises a deck structure 10 and a plurality of support legs 11 where each support leg is provided with a directly engaging jacking device which is also engaged with the deck structure. Each jacking device comprises a through-passage for receiving the leg, a pair of actuator controlled clamps 12, 13 in the through-passage for engaging the leg and a drive means, e.g. a hydraulic piston 14, 15 for moving the clamps relative to one another along the leg. Preferably the legs are circular in cross-section and each clamp comprises a pair of opposed callipers (16, Figure 2) having concave inner surfaces which frictionally engage with the leg. Preferably the clamps are normally biased into engagement with the legs, e.g. by adjustable compression springs (18, Figure 2), and the actuator means, e.g. a hydraulic piston (19, 29 Figure 2), removes the bias when actuated. Preferably roller means, e.g. a pair of opposed spring biased rollers (25, Figure 2), are provided on each clamp to guide its displacement along the leg.

Description

2335181 Shallow Water Platform This invention relates to an offshore

shallow water platform, particularly intended for use in industries associated with the exploration and/or production of oil, gas or other resources.

British Patent No. 1 540 928 discloses a conventional offshore shallow water platform comprising a deck structure and a plurality of support legs for supporting the deck structure above the sea level.

In use, the platform is floated into position with its legs in the raised position, whereupon the legs are lowered onto the sea bed. The deck structure is then raised up the legs to a suitable height above sea level. Finally, the deck structure is clamped firmly to the legs.

Hitherto, the lowering of the legs and the raising of the platform has been achieved using linear winches which are fastened to the deck structure and which drive along cables that extend between opposite ends of each leg.

A disadvantage of using cables is that they are susceptible to corrosion and wear in sea conditions.

Accordingly, there is a risk that a cable may stretch or snap.

Another disadvantage of using cables is that they add significantly to the weight of the platform. We have now devised a shallow water platform which alleviates the above-mentioned problems. 25 In accordance with this invention there is provided a shallow water platform comprising a deck structure, a plurality of support legs slidably mounted to the deck structure and a plurality of jacking devices engaged with the deck structure for directly engaging respective support legs, each jacking device comprising a through-passage for receiving a said leg, first and second clamping means in the through passage for engaging said leg, first and second actuator means for respectively operating said first and second clamping means and drive means extending between said first and second clamping means for moving said first and second clamping means relative to each other along the leg.

2 In use, the jacking devices are operated to move the legs relative to the platform and vice-versa. The jacking devices directly engage the legs and thus the problem associated with conventional cable-type platform winches are 5 alleviated.

Preferably the legs are circular in cross-section, each clamping member comprising a pair of opposed callipers having respective concave inner surfaces which frictionally engage with the leg.

Preferably the clamping means are normally biassed into engagement with the legs, said actuator means being arranged to remove said bias when actuated. Thus, under normal conditions all of the clamping means are engaged with their respective legs, so that the deck structure is securely fastened to the legs. This arrangement has the advantage that the deck structure will not be released from the legs in the event that one or more the actuator means fails.

In conventional shallow water platforms, actuators of the linear winches must be actuated before the cables are gripped. Thus, there is a risk that the deck structure could be released from the leg if the actuator fails. Furthermore, the arrangement of the actuators means that it is not safe to rely on the winches to hold the deck structure permanently in position, once it has been raised up the legs, whereas the arrangement of the present invention can safely be used to permanently clamp the deck structure in position, since the clamping means normally engage the legs.

Preferably the clamping means are biassed into engagement with the legs by springs, such as coil springs, the actuators being arranged to compress the springs when actuated, so that the springs no longer act on the clamping means. Preferably the force exerted by said springs on the clamping means is adjustable. Preferably the actuators are hydraulically operated. 35 Preferably the drive means of each jacking device comprises a hydraulic jack disposed between the first and second clamping means and arranged to displace the first and second clamping means relative to each other along the leg. Preferably the first and second clamping means of each 3 jacking device are connected to the deck structure via respective drive means.

Preferably roller means are provided on each of said clamping means for guiding them along the legs as they are 5 displaced.

Preferably a pair of opposed roller means are provided on each of said clamping means, the roller means preferably being spring biassed against the leg, so as to centralise the leg relative to the through-passage in the jacking device.

An embodiment of this invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 is a side view of a portion of a shallow water platform in accordance with this invention; Figure 2 is a sectional view along the line II-II of Figure 1; and Figure 3 is a longitudinal section through a clamp member actuator of the platform of Figure 1, when actuated.

Referring to Figure 1 of the drawings, there is shown a shallow water production platform comprising a deck structure 10 and a plurality of support legs 11 (one only shown) disposed at respective corners of the deck structure 10. The legs 11 are slidable axially of themselves relative to the deck structure 10.

A jacking device is disposed at each leg 11 for moving the deck struczure 10 and leg 11 relative to each other during installation and removal of the platform. The jacking device comprises an upper clamp assembly 12 and a lower assembly 13, each having a through-passage through which the leg 11 extends.

A plurality of hydraulic rams 14, 15 extend upwardly from the respective clamp assemblies 12, 13, axially of the leg 11, the upper ends of the rams 14, 15 being engaged with the underside of respective portions of the deck structure.

Referring to Figure 2 of the drawings, each clamp assembly e.g. 13 comprises a pair of opposed C-shaped clamping members 16 that extend around the leg 11. The opposed clamping members 16 are held together on opposite sides of the clamp assembly 12 by three vertical ly- stacked actuator assemblies 20.

Referring to Figure 3 of the drawings, each actuator 4 assembly 20 comprises an elongate rod 17, which extends through a pair of parallel radially extending flanges 21 respectively provided on opposed ends of the C-shaped clamping members 16. Opposite ends of the rod 17 also extend through respective second flanges 22 on each clamping member 16, the second flanges 22 being arranged parallel to the first flanges. Opposite ends of the rod 17 also extend axially through the centre of respective telescopic hydraulic actuators having a body 19 and a piston 29. A lip 23 extends around the body 19 of each actuator and a helical compression spring 18 is disposed between the lip 23 on the body 19 of each actuator and the flange 21 at the end of its respective clamping member 16. The outer end of the pistons 29 are secured to the flanges 21 of their respective clamping members 16. A nut 24 is disposed at each end of the rod 17 f or retaining the body 19 of the actuator on the rod 17.

A plurality of opposed roller devices 25 are disposed on respective clamp members 16, as shown in Figure 2 of the drawings. Each roller device 25 comprises a rotatably mounted roller arranged to roll axially along the leg 11 of the platform and a helical spring which biases the roller into contact with the leg 11.

In use, when no hydraulic pressure is applied to the actuator assemblies 20, the two compression springs 18 of each assembly 20 exert equal and opposite forces on the nut 24 at their respective end of the rod 17, via the body 19 of their respective hydraulic actuator. The nuts 24 are not free to move apart and thus the coil springs 18 react against the flanges 21 of their respective clamp members 16, thereby biassing the clamp members 16 together. In this manner, the clamp members 11 are securely clamped against the legs 11 of the platform when no hydraulic pressure is applied to the actuator assemblies 20. In practice, the springs each exert a force of about 90 tons on the leg 11 of the platform.

Referring again to Figure 3 of the drawings, when hydraulic pressure is applied to the actuator assemblies 20, the body 19 of the actuator moves towards its respective flange 21, thereby compressing the spring 18. The body 19 of the actuator is free to slide through the second flange 22 and thus 1 the spring bias is removed from the nuts 24, so that the clamp members 16 are free to move apart, thereby releasing the leg 11.

It will be appreciated that if the hydraulic pressure fails, the clamp members 16 will be reapplied to the legs 11, so that there is no danger of the deck structure 10 separating from the legs 11.

Referring again to Figure 1 of the drawings, in order to raise the deck structure 10 up the legs 11, the hydraulic rams 14, 15 of the upper and lower clamp assemblies 12, 13 are retracted. Hydraulic pressure is then applied to the actuator assemblies 20 of the upper clamp assembly 12, in order to release the clamp members 16 of the upper clamp assembly 12 from the leg 11. The hydraulic rams 15 of the lower clamp assembly 13 are then extended, thereby pushing the deck structure upwardly along the leg 11. A microprocessor controls the operation of each jacking device at each leg, thereby ensuring that all of the devices are operated in synchronism. The roller devices 25 on the lower device centralise the leg 11 in the through passage of the upper clamp assembly 12.

Next, hydraulic pressure is removed from the actuator assemblies 20 of the upper clamp assembly 12, whereupon hydraulic pressure is applied to the actuator assemblies 20 of the lower clamp assembly 13. The rams 14 of the upper clamp assembly 12 are then extended to push the deck structure 10 further up the leg 11. Whilst this is happening, the rams 15 of the lower clamp assembly 13 are retracted, so that the lower clamp assembly 13 is pulled back towards the deck structure, ready for the next stroke: this process then repeats itself in a similar manner until the deck structure 10 is at the desired position, whereupon hydraulic pressure can be removed so that the clamp members 16 safely and securely hold the deck structure permanently in position. However, it is envisaged that an additional locking mechanism could be used as a safety precaution.

A similar jacking process is used to lower the platform and to raise the legs.

The jacking devices of the present invention are simple and inexpensive in constructions and yet safe and easy to use.

6 In another embodiment, either the rams 14, 15 of the upper or lower clamp assembly 12,13 can be omitted in order to save cost at the expense of halving the jacking speed.

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Claims

1) A shallow water platform comprising a deck structure, a plurality of support legs slidably mounted to the deck structure and:,-jluL-lit-y-_of jacking devices engaged with the deck structure for directly engaging respective support legs, each jacking device comprising a through-passage for receiving a said leg, first and second clamping means in the through passage for engaging said leg, first and second actuator means for respectively operating said first and second clamping means and drive means extending between said first and second clamping means for moving said first and second clamping means relative to each other along the leg.

2) A shallow water platform as claimed in claim 1, in which the legs are circular in cross-section, each clamping member comprising a pair of opposed callipers having respective concave inner surfaces which frictionally engage with the leg.

3) A shallow water platform as claimed in claims 1 or 2, in which the clamping means are normally biassed into engagement with the legs, said actuator means being arranged to remove said bias when actuated.

A shallow water platform as claimed in claim 3, in which the clamping means are biassed into engagement with the legs by compression springs, said actuators means being arranged to compress the springs when actuated, so that the springs no longer act on the clamping means.

5) A shallow water platform as claimed in claim 4, in which the force exerted by said springs on the clamping means is adjustable.

6) A shallow water platform as claimed in any preceding claim, in which the actuators are hydraulically operated.

7) A shallow water platform as claimed in any preceding claim, in which the drive mans of each jacking device comprises 8 a hydraulic jack disposed between the first and second clamping means and arranged to displace the first and second clamping means relative to each other along the leg.

8) A shallow water platform as claimed in any preceding 5 claim, in which the first and second clamping means of each jacking device are connected to the deck structure via respective drive means.

9) A shallow water platform as claimed in any preceding claim, in which roller means are provided on each of said clamping means for guiding them along the legs as they are displaced.

10) A shallow water platform as claimed in claim 9, in which a pair of opposed roller means are provided on each of said clamping means, the roller means preferably being spring biassed against the leg, so as to centralise the leg relative to the through-passage in the jacking device.

11) A shallow water platform substantially as herein described with reference to the accompanying drawings.

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