GB2152977A

GB2152977A - Deep water oil/gas drilling or production apparatus

Info

Publication number: GB2152977A
Application number: GB08432723A
Authority: GB
Inventors: Jack George Brown
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-12-29
Filing date: 1984-12-28
Publication date: 1985-08-14
Also published as: GB8432723D0; GB8334510D0

Abstract

Apparatus for drilling for or production of oil or gas comprises a normally vertical tower 10 of length to extend above sea level, means (15) extending throughout the length of the tower 10 to receive a drilling mechanism therein, and at least an upper and a lower thruster unit 22, 24 located externally of the tower 10 and adjustable in position along the length thereof, said thruster units being operable to effect dynamic positioning of the tower. <IMAGE>

Description

SPECIFICATION Apparatus for drilling for or the production of oil, gas or the like This invention relates to drilling apparatus for oil, gas or the like.

When drilling for or producing oil or gas in under sea or deep water conditions, e.g. of the order of 300 to 400 metres, it has been previously pro posed to provide a tower within which a drill string can be located. The tower is customarily sur mounted by a platform at its upper end and the tower is supported in a vertical position by various means e,g, three outwardly diverging support legs or cables which are fixedly anchored to the sea bed. It will be appreciated that such previously proposed structures are of a relatively permanent nature suitable for production only and cannot eas ily be moved from one location to another.

An object of the present invention is to provide apparatus for drilling or production in deep water conditions and which can relatively easily be re-lo cated.

In a preferred embodiment there is provided ap paratus for drilling for or production of oil, gas or the like comprising a normally vertical tower of length to extend above sea level, means adapted to extend throughout the length of the tower to receive a drilling mechanism therein, and at least an upper and a lower thruster unit located externally of the tower and adjustable in position along the length thereof, said thruster units being operable to effect dynamic positioning of the tower.

An embodiment of the present invention will now be described, by way of example, with refer ence to the accompanying drawings in which: Figure 1 is a diagrammatic illustration of apparatus in accordance with the present invention; and Figure 2 is a plan view of the apparatus.

Referring to the drawings, apparatus particularly for use in deep water drilling for or production of oil or gas comprises a vertical elongated cylindrical tower 10 consisting of spaced inner and outer con centric skins 11, 12. The external diameter of the tower 10 can be of the order of 20 metres. The in ner and outer skins 11, 12 are interconnected by radial partitions 13 which serve to divide the space between the inner and outer skins 11,12 into a lab yrinth of tanks and buoyancy chambers 14. Within a space 15 defined by the inner skin 12 a drill string (not shown) is adapted to be located.

At the upper end of the tower 10 there is posi tioned a control block 16 which can incorporate a helicopter platform as well as constituting an ac commodation and control module by means of which dtilling operations can be controlled.

A semi-submersible propelled dynamically positionable platform 17, having a substantially 'U' shaped deck as can be seen from Figure 2, is pro vided with a notch or indent 18 whereby the plat form 17 can be positioned around the tower 10 and hydraulically-operated clamps 19 operated in order to flexibly secure the platform 17 around the tower. Shock absorbers for example pneumatic wheel fenders 20 are provided between the surface of the indent 18 and the outer surface of the tower 10.

Adjacent the upper end of the tower 10 but below sea-level there is provided an upper thruster unit 21 consisting of four thrusters 22 spaced equidistantly around the tower on the same horizontal plane. A second thruster unit 23, also having four similarly disposed thrusters 24, is positioned adjacent the lower end of the tower. The thruster units 21 and 23 are mounted on tracks 25 and 26 respectively extending along the length of the tower whereby the vertical position of the thruster units 21 and 23 can be varied therealong and which will allow each thruster unit to be manoeuvred on its tracks up to the platform 15 for maintenance.It will be noted that the thrusters 22 of the upper thruster unit 21 are angularly displaced by 45" relative to the thrusters 24 of the lower unit 23 in order to permit movement of the lower thruster unit past the upper unit should this be required.

The lower end of the tower 10 is provided with cutting edges 26 to enable the tower to cut into the sea bed by suitable loading of the tower. Alternatively, all the thrusters 22 and 24 can be operated in the same direction so that the tower can be rotatably drilled into the sea bed to enable it to be retained in position therein.

Furthermore towards the bottom of the tower 10 there is provided a chamber 27 which is capable of being blown or evacuated in order to provide a diving bell. Hyperbaric accommodation 28 is provided above the chamber 27.

A trackway 29 which is clear of the thruster units is provided to allow supply of items, e.g. blow-out prevention apparatus from the deck of the semisubmersible rig 17 to the diving bell chamber 27 through a suitable closeable aperture in the outer wall 12 of the tower 10. Alternatively a sea bed production module can also be fed down the trackway and fixedly secured in position by pile driving equipment (not shown) integral in the tower.

A crown block (also not shown) can be mounted high inside the tower 10 at a distance apart from a rotating table of a drilling platform at a distance apart of say 200 metres. This permits tripping of drill strings in relatively long lengths as the drill string does not have to be split at every joint, it only being required to split the drill string say every seven or eight joints. In addition, the customary drill bit can be withdrawn into the diving bell chamber 27 for renewal or maintenance. Drill strings can be stored within the tower chamber 15.

If desired, a secondary generator can be housed within the tower in case the customary hotel services provided by the semi-submersible platform are lost on disengagement of the semi-submersible platform from the tower under emergency conditions.

The apparatus for the present invention can be used for prosepctive drilling or production drilling and can eventually be used as a production platform. It will be appreciated that the tower of the invention because of the provision of the thruster units 21 and 23, can easily be moved from one lo cation to another in vertical position. Also, by varying the direction of application of the thruster units 21 and 23 the loading imposed by the tower on the sea bed can be controlled as desired. This is particularly important when the apparatus is being employed on soft sea beds.

If it is desired to conduct major repair and maintenance on the apparatus, the tower can be brought to the surface and disposed horizontally thereby allowing access to all surfaces thereof by rotation of the tower.

Prior to such manoeuvre the accommodation control block 16 can be lowered on to the deck of the semi-submersible platform with the U-shaped notch of control block 16 registering with the notch in the deck of the semi-submersible platform.

It will be appreciated that the air pressure in the chamber 27 equates to water pressure at that depth. Pressure seals on the drill string separate that high pressure from atmospheric pressure in chamber 15 of the tower.

When the drill bit is approaching oil-bearing formations, it may be prudent to change from atmospheric pressure air to atmospheric pressure carbon dioxide or other non-combustible gas, thus requiring all operators in chamber 15 to wear breathing apparatus.

Tracks 29 run externally down the tower wall 12, from a point well above the deck of platform 17 to a point approximately level with, or below, the floor of chamber 27. A three-stage articulated loading arm 31 is power-driven up and down these tracks 29 as required. A large, possibly semi-circumferential, watertight door 32 let into the wall 12 of the tower gives access to chamber 27, after flooding and pressure equalisation, and the positioning of tracks 29 adjacent this door 32 enables arm 31 to load BOPstacks, already carried by arm 31 down from the deck of platform 17, directly onto any selected one of a ring of wellheads within chamber 27.

Arm 31 can also reach, and bring up to platform 17, any of the thrusters for servicing or repair.

Claims

1. Apparatus for drilling for or production of oil, gas or the like, comprising a normally vertical tower of length to extend above sea level, means extending throughout the length of the tower to receive a drilling mechanism therein, and at least an upper and a lower thruster unit located externally of the tower and adjustable in position along the length thereof, said thruster units being operable to effect dynamic positioning of the tower.

2. Apparatus according to Claim 1, in which, the lower edge of the tower includes a cutting edge.

3. Apparatus according to Claim 2 in which the thruster units are operable to effect rotation of the tower to drill the tower into the sea bed.

4. Apparatus according to any one of the preceding Claims, further including, at or near the lower edge of the tower, a chamber capable of being blown or evacuated to form a diving bell.

5. Apparatus according to Claim 4, further including above the chamber, hyperbaric accommodation.

6. Apparatus according to any one of the preceding Claims, further including a three-stage articulated loading arm adjustable in position along the length of the tower.

7. Apparatus according to Claim 6 when dependant upon Claim 4 or 5, in which the tower includes a door to allow access into the chamber, and in which the loading arm is operable to carry an item from an upper region of the tower, downwards to the region of the chamber, and to carry said item directly into the chamber through the door.

8. Apparatus for drilling for or production of oil, gas or the like arranged substantially as described herein with reference to the drawings.