GB2049610A - Off-shore oil installation - Google Patents

Abstract

An off-shore installation for loading oil into or unloading oil from a tanker including a supply pipe-line for carrying oil extending upwardly to the installation from an oil source or oil sink, and a flexible transfer pipe-line 8 rigidly connected without rotating glands to the upper end of the supply pipe-line 11, wherein at least a portion of the transfer pipe-line is coiled horizontally around a winding core 9 on the installation so that when a tanker connected to the installation moves in a circle around the installation the transfer pipe-line is uncoiled from or coiled onto the winding core. <IMAGE>

Description

SPECIFICATION Off-shore oil installation This invention relates to off-shore installations for loading oil into or unloading oil from a tanker.

One of the major restraints on the design of an off-shore oil installation, such as a production tower or a loading or unloading buoy, is the positioning of the connection between the moored tanker and the supply pipe-line passing up through the installation.

Whilst the tanker is free to "weather-vane", the supply pipe-line remains virtually fixed in position. By the term "weather-vaning" as used herein is meant the drifting of a ship, such as a tanker, about a fixed mooring point in accordance with the local tides, currents, and wind.

In one existing arrangement, the installation in the form of an articulated production tower includes, above the high-water line, a mooring ring which is freely rotatable about the vertical axis ofthetower, and at the centre of which is disposed a rotatable, sealed oil connection. The supply pipe-line passes up the centre of the tower and it is connected to the tanker through this rotatable connection via a flexible transfer pipe-line passing into the mooring ring.

Where tanker off-loading is the sole purpose of the articulated tower there is no problem with the engineering of this connection; but when this rotatable connection is of large diameter and the tower is constrained into a neck at this point, which puts severe limitations on the provision of heavy equipment on the tower above, the design ofthis rotatable connection presents serious engineering difficulties.

In an attempt to overcome these difficulties, it has been proposed to moor and connect the tanker to the production platform itself, and to rotate the entire platform to compensate for the weathervaning of the tanker. Again, however, a rotatable seal has to be provided at the connection between the supply pipe-line and the transfer pipe-line and in addition there are problems associated with the transfer of electrical power to the relativelystationary articulated tower equipment. It is usual to provide electrically-driven oil pumps at the top of the tower underneath the platform and to supply these pumps with electrical power from a gas turbine generator provided on the platform. A rotatable electrical connection therefore has to be provided between the generator and the pumps.Although this has been achieved for small pumps with low power requirements, the difficulties associated with the transmission of large amounts of power are apparently insurmountable.

In a further development, it has been suggested that the rotatable portion of the tower should be that which lies above the generators. This would mean that the generators and the oil pumps would be fixed relative to each other. The construction and positioning of the effluent gas outlet from the gas turbines now however possess serious problems. In general, the turbine exhausts should be directed upwardly away from the platform, and when a heliport is provided, the exhaust should leave the platform at a height of some 25 metres above the deck of the heliport. The provision of rotatable, sealed ducting for the exhaust gases of the turbines then becomes a difficult engineering problem.

The present invention seeks to provide an arrangement whereby a connection can be achieved between a tanker and a supply pipe-line in an offshore installation without the need for a rotatable, sealed connection either in the oil pipe-line or in the exhaust ducting of gas turbines, if they are present.

In accordance with the present invention there is provided an off-shore installation for loading oil into or unloading oil from a tanker including a supply pipe-line for carrying oil extending upwardly to the installation from an oil source or oil sink, and a flexible transfer pipe-line rigidly connected to the upper end of the supply pipe-line, wherein at least a portion of the transfer pipe-line is coiled horizontally around a winding core on the installation so that when a tanker connected to the installation moves in a circle around the installation the transfer pipe-line is uncoiled from or coiled up on to the winding core.

Preferably the transfer pipe-line is supported for movement towards or away from the installation by a movable carriage which travels in the path around the winding core; the carriage usually carrying means for mooring a tanker, such as a winch. A boom can usually be provided on the carriage for guiding and supporting the transfer pipe-line away from the installation and at least one roller can be provided on the boom to facilitate relative movement between the boom and the transfer pipe-line.

Either the carriage and boom can free wheel around the installation in accordance with the weathervaning of the tanker, or a pair of driving rollers can be provided on the boom to play out and to draw in the transfer pipe-line. This latter arrangement is particularly useful when replacement transfer pipe-lines have to be loaded on to the winding core.

The length of transfer pipe-line wound on to the core can be varied depending on the degree of weather-vaning to be tolerated. Preferably for open sea operations sufficient transfer pipe-line is provided on the winding core fora connected tanker to encircle the installation at least one and a half times clockwise or anti-clockwise without the transfer pipe-line being permanently distorted. In a preferred embodiment at least three full turns of transfer pipeline are provided on the winding core when the transfer pipe-line is fully coiled up on the winding core. An additional length can also be provided in order to enable the tanker to pick up the end connection of the transfer pipe-line with ease.

In order to minimise the deterioration of the transfer pipe-line through weathering, means are preferably provided above the winding core to cover the coiled transfer pipe-line. When the installation is in the form of an articulated tower, a platform is provided above the winding core and serves as the covering means. Electrical power generation equipment on the platform can then be connected direct to at least one electrically-driven oil pump provided within the articulated tower and supplied by the equipment.

One embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is an elevational view of the upper portion of an articulated tower of the present invention; Figure 2 is a cross-sectional view of the tower of Figure 1 taken on line A-A; and Figure 3 is an enlarged sectional view of the hose winding assembly shown in Figure 2 taken on the line B-B.

In the accompanying drawings, the upper portion of the articulated tower generally indicated as 1 includes a supporting column 2 and a platform 3 rigidly attached thereto. A heliport 4 and a chimney tower 5 are provided on the upper portion of the platform 3.

The tower 1 is shown as connected to a tanker 6 by means of a mooring cable 7 for the purpose of loading oil in to the tanker from a sub-sea oil source (not shown). The oil is transferred from the tower 1 to the tanker 6 by means of a flexible transfer pipe-line 8.

The mooring cable 7 and the transfer pipe-line 8 are connected to the tower 1 at a point which is higherthan the highest level of the sea likely to be encountered by the tower.

The flexible transfer pipe-line is connected to the tower by being coiled around a cylindrical portion 9 of the tower which functions as a winding core. Up to three turns of the transfer pipe-line 8 about the winding core 9 can be accommodated on a supporting platform 10. The innermostturn ofthetransfer pipe-line is rigidly connected to the supply pipe-line 11 ofthe tower through which oil flows from the oil source (not shown).

Positioned beneath the supporting platform 10 is a movable carriage 12 which rolls in a horizontal circular path around the winding core 9 of the tower on the surface of a horizontal, circular race-way 13. A vertical race-way 14 is also provided around the cylindrical winding core 9 to take the horizontal thrust of the mooring cable 7 and the transfer pipeline 8. The transfer pipe-line 8 is fed out from the winding core 9 to the tanker 6 through guiding rollers 15. In order to support the transfer pipe-line 8 away from the tower 1, a boom 16 is provided on the carriage 12; the pipe-line 8 being carried by a further setofguiding rollers 17. Apairofdriving rollers 18 are also provided on the boom 16 to play out and to wind up the transfer pipe-line 8.

The mooring cable 7 is connected to a winding drum 19 on the movable carriage 12, and is so controlled that as the carriage rolls on its race-ways 13 and 14 around the winding core 9 of the tower 1 the mooring cable 7 is played out or wound up in a proportionate amount.

A protecting cover 20 is provided around the wind ing core 9 on the carriage 12 in order to reduce the amount of weathering experienced by the transfer pipe-line 8 when wound up on the winding core 9.

When fully wound up, the transfer pipe-line 8 occupies three full turns around the winding core 9 and, in addition, a small length of approximately 15 to 20 metres of pipe-line are provided to enable the tankerto pick up the end connection of the transfer pipe-line with ease. The arrangement is such that when a tanker is due to take on oil, the flexible transfer pipe-line 8 is played out to approximately midway, i.e. one-and-a-halfturns, depending on the wind direction and a prediction of how the wind will change during the following 36 hours. A tanker can be left for as long as sea conditions permit, but the normal time is based on the size oftanker and the rate of off-loading. For economic reasons this should be as short as possible and is usually less than 36 hours.Once the tanker is attached by mooring line 7 and transfer pipe-line 8 to the tower the pumping of oil can be commenced and the carriage 12 and boom 16 will follow the position of the tanker 6 as it weather-vanes around the tower 1. As the tanker rotates clockwise as shown in Figure 2, the transfer hose will be wound on to the winding core 9 and the ship must be brought in closer to the tower 1 in order to avoid any stresses on the flexible transfer pipeline 8. This is achieved by automatically operating the winding drum 19 to draw in the tanker by the mooring cable 7. Conversely, as the tanker 6 weather-vanes anti-clockwise in Figure 2 more transfer pipe-line 8 is played out and the winding drum 19 is arranged automatically to play out the mooring cable 7 to take up the slack in the transfer pipe-line 8.

It will be seen that by providing at least three turns on the winding core 9, a moored tanker is able to weather-vane more than 360" in either direction in the event that the wind should veer or back. In the tower of the present embodiment, it can be seen that the provision of rotatable, sealed connections in the oil pipe-line is obviated, and since the platform 3 and supporting column 2 do not move relative to each no problems arise in the provision of electrical connections between the two portions. Thus conventional electrical power generation equipment, such as gas turbines, can be provided on the platform 3 in order to power oil pumps and other equipment inside the upper portion of the supporting column 2. Furthermore, since the heliport 4 and the exhaust chimney 5 do not rotate with respect to platform 3, the turbine exhaust can be conventionally discharged above the heliport 4. In the described embodiment the transfer pipe-line when not in use is fully protected from the elements and, even if a transfer pipe-line needs to be changed, the attaching and detaching of a transfer pipe-line from an attendant barge is relatively straightforward and rapid.

Due to the absence of any "neck" section in the column a strong, integral structure is obtainable without any constraints on the loading of the platform. In addition, no equipment is needed to rotate any of the platform structure, and the centre of gravity of the platform can be as low as possible. A reduction in platform weight is also possible with the presently described embodiment.

Claims (12)

1. An off-shore installation for loading oil into or unloading oil from a tanker including a supply pipeline for carrying oil extending upwardly to the instal lation from an oil source or oil sink, and a flexible transfer pipe-line rigidly connected to the upper end of the supply pipe-line, wherein at least a portion of the transfer pipe-line is coiled horizontally around a winding core on the installation so that when a tanker connected to the installation moves in a circle around the installation the transfer pipe-line is uncoiled from or coiled up on the winding core.

2. An installation as claimed in claim 1 wherein the transfer pipe-line is supported for movement towards or away from the installation by a movable carriage which travels in a path around the winding core.

3. An installation claimed in claim 2 wherein the carriage carries means for mooring a tanker.

4. An installation as claimed in claim 3 wherein the mooring means comprises a winch.

5. An installation as claimed in any one of claims 2 to 4 wherein the carriage carries a boom for guiding and supporting the transfer pipe-line away from the installation; at least one roller being provided on the boom to facilitate relative movement between the boom and the transfer pipe-line.

6. An installation as claimed in claim 5 wherein a pair of driving rollers are provided to play out and to draw in the transfer pipe-line.

7. An installation as claimed in any one of the preceding claims wherein sufficient transfer pipeline is provided on the winding core for a connected tankerto encircle the installation at least times clockwise or anti-clockwise without the transfer pipe-line being permanently distorted.

8. An installation as claimed in claim 7 wherein at least three full turns of transfer pipe-line are provided on the winding core when the transfer pipeline is fully coiled up on the winding core.

9. An installation as claimed in any one of the preceding claims wherein the coiled transfer pipeline is covered to protect it from the environment.

10. An installation as claimed in any one of the preceding claims wherein a platform is carried by the installation above the winding core.

11. An installation as claimed in claim 10, when in the form of an articulated tower, wherein the platform carries electrical power generation equipment and wherein at least one electrically-driven oil pump is provided within the articulated tower and is supplied by the said equipment.

12. An off-shore installation for loading oil into or unloading oil from a tanker substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.