GB2039575A

GB2039575A - Underwater drilling

Info

Publication number: GB2039575A
Application number: GB8000706A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-01-09
Filing date: 1980-01-09
Publication date: 1980-08-13
Also published as: GB2039575B

Abstract

Underwater drilling apparatus comprises a barge (10) having a movable working platform (12) on which are mounted a pair of gantries (16). A mast (20) can be moved in each gantry (16) to the sea bed and a kelly (30) extends the length of each mast (20). The kelly (30) mounts a selected extension at its lower end, and receives through its length a selected drill tool which is lowered by means of flexible tubing (42), the latter passing compressed air to the tool if required, and facilitating change of the drill tool. The tool and kelly are rotated by a rotating table 32 which by hydraulic motors which enables the apparatus to be used in greater depths of water than conventional drilling rigs. <IMAGE>

Description

SPECIFICATION Improvements in or relating to a method of and apparatus for underwater drilling This invention is concerned with improvements in or relating to a method of, and apparatus for underwater drilling.

In a known apparatus a barge with a working platform is floated to a desired location above the sea bed and has a substantially vertically extending fixed gantry relative to which a drill assembly is movable by winches such that the drill assembly can be lowered to the sea bed. The drill assembly comprises a drill tube mounted on an elongate mast structure. To accommodate different depths in which the apparatus can be used the tube is formed in sections which are coupled together. A selected drill tool, such as a diamond core bit or a percussion hammer is fitted with appropriate sections of rod to enable the tool to be lowered through the tube to the drilling location, and be operated from the upper end of the tube. Additional tube sections will be required depending on the depth of hole required.The tube is rotatably driven in the drill assembly by means of a compressed air motor located on the gantry.

The rating of the compressed air motor limits the depth to which the tube can be driven into the sea bed and thus limits the type of sea bed which can be drilled and blasted at any one time. Also when it is necessary to change the drill tool the rod sections have to be uncoupled to enable the drill to be raised to the working platform for the change to be made, this being extremely time consuming and therefore costly. Further because the drill assembly is retained in its lowered position by means of gravity only, the vertical wave motion can create problems and thus limit the depth of water in which apparatus can be used.

According to the present invention there is provided apparatus for drilling the sea bed, said apparatus comprising a working platform, a drill support arrangement fixedly mounted thereon, a drill assembly including a drive member having a through bore, means for moving the drill assembly relative to the drill support arrangement such that drill assembly can be lowered to the sea bed when the working platform floats on the surface of the sea, means for effecting rotation of the drive member, adaptor means for mounting a selective extension at a lower end of the drive member, and means for positioning a selected drill tool through the drive member to a drilling location at a free end of the extension.

Preferably the means for positioning the drill tool comprises a flexible conduit which is connected at one end to a location on the working platform and releasably connected at the other end to the selected drill tool.

The selected drill tool may be a percussion tool, and means may be provided for supplying com pressed airthrough the flexible conduit.

Preferably also the drive member is a kelly, and the means for effecting rotation of the kelly compris es a pair of hydraulic motors.

Advantageously means is provided for holding the drill assembly on the sea bed, and the holding means may comprise a pull down chain system.

According to the present invention there is also provided a method of drilling the sea bed, comprising the steps of positioning a working platform at a location where the sea bed is to be drilled, the working platform having a drill support arrangement fixedly mounted thereon and a drill assembly movably mounted on the drill support arrangement, mounting a selected extension at the lower end of a drive member which has a through bore, moving the drill assembly relative to the drill support arrangement to the sea bed, positioning a selected drill tool through the drive memberto a drilling location at the lower end of the drive member, and rotatably driving the drive member for drilling of the sea bed.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which Figure 1 is an elevation of a drilling rig in a non-drilling condition; Figure2 is an elevation of the drilling rig of Figure 1 in a drilling condition; Figure 3 is a plan view of the working platform of the rig of Figures 1 and 2; Figure 4 is a section through the gantry and mast of the rig of Figures 1 and 2; Figures 5to 7 illustrate examples of different extensions and tools used with the drive member; and Figure 8 is a diagrammatic view of a stabiliser arrangement for the mast.

Reffering to the drawings, a drilling rig comprises a barge 10 which movably mounts a working platform 12 on a track 14. The platform 12 is substantially U-shaped and is fitted around one side of the barge 10, the latter having its tracks 14 on upper and lower horizontally extending faces. On its vertically extending face the platform 12 mounts a pair of vertically extending gantries 16, each of which extends beyond the upper and lower faces of the platform 12 and is supported by stabilising arms 18 extending between each of the upper and lower faces of the platform 12 and the gantry itself.

Each gantry comprises a framework which is open at the side remote from the platform 12 and receives therein the framework of a mast 20 which is movably mounted relative to the gantry 16 and extends through an access platform 22 at the level of the upper face of the working platform 12. The mast 20 is preferably formed in sections of three metres in length to a length of 30 metres and the gantry 16 is preferably 20 metres in length. The mast 20 can be raised and lowered relative to the gantry 16 by means of a four drum cable winch arrangement 24 driven by an hydraulic power unit 26, both the winch arrangement 24 and the power unit 26 being mounted on the upper face of the working platform 12, the latter also mounting a counter balance weight 28.

The mast 20 forms part of a drill assembly which also includes a drive member or kelly 30 of a rectangular configuration and extending the length of the mast 20. The kelly 30 has a through bore of square cross section and is rotatably mounted on a turntable 32 fixed substantially midway along the length of the mast 20, the turntable 32 mounting a pair of hydraulic motors 34 for providing rotation of the kelly 30 relative to the mast 20. The motors 34 can be used selectively so as to vary the torque and speed of the kelly 30, the torque available being in the region of 600 ft. Ibs. to 15000 ft. Ibs. or more and the speed available being in the region of 35 r.p.m. to 600 r.p.m.

At the lower end of the kelly 30 an adaptor 36 is mounted on the kelly by means of retaining studs 37 and mounts a selected drill casing extension 38 (Figures 5 to 7). The choice of extension 38 depends on the type of operation which is to be carried out.

For example Figures 5 and 6 show a kelly extension of 1.5 metres in length threaded into the adaptor 36, the extension having a saw tooth bit at its lower end for bedding into rock. Figure 7 shows an extension of 8.5 metres in length threaded into the adaptor 36 and having a saw tooth bit at its lower end for drilling into a sea bed comprising layers of rock and sand and boulders.

Selected drill tool can be positioned at the lower end of the kelly 30 and the extension 38 by lowering the tool through the kelly 30 from the upper end thereof, i.e. from the working platform 12, by means of a winch 40 mounted on the upper surface of the platform 12. The winch 40 has a flexible tubing 42 extending over pulleys on a pulley arm 44 and releasably coupling to the upper end of the tool through a swivel or ball joint. The pulley arm 44 is pivotally mounted on the gantry 16 and is movable between an operative position across the location of the mast 20 as shown in Figure 2, and an inoperative position clear of the mast 20 as shown in Figure 1.

For a percussion tool, compressed air is passed through the pipe 42. Each tool has a square sectioned upper part 46 which is axially fixed relative to the kelly, such that the tool is driven by the kelly 30.

Figure 5 shows a tool used for drilling and soil sampling and comprising a barrel 48 having a diamond core bit 50 at its lower end. Figures 6 and 7 show compression hammers 52, 54 respectively of different lengths. The hammer 52 extends beyond the lower end of the kelly extension 38, with the latter bedding into the rock of the sea bed and enabling the hammer to proceed, while the hammer 54 is retained within its kelly extension 38 to enable drilling through the different layers of the sea bed.

In use, the drilling rig is floated to the drilling location in the condition shown in Figure 1 i.e. with the mast 20 raised to the level of the upper face of the platform 12. When the rig is in position, the mast 20 is lowered by means of the winch arrangement 24, after an appropriate kelly extension 38, depending on the depth and type of hole required, has been fixed to the lower end of the kelly 30 by means of the adaptor 34. It is advisable that at least 10 metres of mast remain in the gantry at any one time. The selected tool is lowered into the kelly 30 by means of the winch 40 and drilling is commenced by means of the hydraulic motors 34 on the turntable 32. A stabiliser arrangement 56 (Figure 8) is fixed to the lower end of the mast 20 on the inside thereof and comprises a steel spike 58 resiliently mounted within a guide tube arrangement 60 by means of a coil spring 62.When the mast 20 is in position, with the spike 58 buried into the sea bed to stop movement, the cables of the winch arrangement 24 are slackened to enable the barge 10 and the platform 12 to move with the waves relative to the mast 20.

If it is desired to change the drilling tool, the tool can be lifted through the kelly 30 by means of the winch 40 and then the newly selected tool lowered into position. Also explosives necessary for blasting of the sea bed can be lowered through the kelly 30 after drilling has been completed and the tool has been removed.

To retain the drill assembly in position a pull down chain system (not shown) is provided on the mast 20 below the turntable 32 and is preferably hydraulically operated. It is desirable that the chain system can provide a 22000 Ibs pull down force.

It will be appreciated that such a drilling rig requires much less labour and time consuming tasks during operation than conventional rigs and is therefore much less costly to operate. The drilling operation advantageously takes place at the sea bed.

Also the use of hydraulic motors for the drive of the kelly instead of compressed air motors enables the apparatus to be used in greater depths of water than conventional rigs and it is possible to drill large holes economically even in deep water. In existing rigs gravity feed is too slow to enable acceptable drilling holes of more than 21/2 inches in diameter, and also the components of the drill assemblies required for drilling such holes would be extremely heavy and the apparatus would be uneconomic.

Also in existing rigs the length of mast is limited to the depth of the sea bed at high tide in order to give access to the upper end of the tube for coupling rod extensions to the drill tool. At low tide therefore the mast and tube projects above sea level and there has to be provided an arrangement for raising the operator and equipment to the upper end of the tube. In the rig described herein this is not a problem because of the coupling of the tool to the flexible tubing. Also it is envisaged that the kelly will be formed on a telescopic arrangement to enable the upper end to be at sea level even in depths greater than the unextended length of the kelly.

Various modifications can of course be made without departing from the scope of the invention.

For example although the working platform as shown in the drawings mounts two gantries connected together by a stabilising bar and each having one drilling assembly, additional drilling assemblies may be provided if desired.

Claims

1. Apparatus for drilling the sea bed, said apparatus comprising a working platform, a drill support arrangement fixedly mounted thereon, a drill assembly including a drive member having a through bore, means for moving the drill assembly relative to the drill support arrangement such that drill assembly can be lowered to the sea bed when the working platform floats on the surface of the sea, means for effecting rotation of the drive member, adaptor means for mounting a selective extension at a lower end of the drive member, and means for positioning a selected drill tool through the drive member to a drilling location at a free end of the extension.

2. Apparatus according to claim 1, wherein the means for positioning the drill tool comprises a flexible conduit which is connected at one end to a location on the working platform and releasably connected at the other end to the selected drill tool.

3. Apparatus according to claim 2, wherein said one end of the flexible conduit is attached to a winch on the working platform and said other end of the flexible conduit is releasably coupled to the tool by means of a swivel joint.

4. Apparatus according to claim 2 or 3, wherein the flexible conduit passes over a pulley arrangemenu which is movable between an operative position over an upper end of the drill assembly and an inoperative position clear of the drill assembly.

5. Apparatus according to any of claims 2 to 4, wherein the selected drill tool is a percussion tool, and means are provided for supplying compressed air through the flexible conduit.

6. Apparatus according to any of the preceding claims, wherein the drive member is a kelly, and the means for effecting rotation of the kelly comprises a pair of hydraulic motors.

7. Apparatus according to claim 6, wherein the hydraulic motors are located on a turntable which is mounted on the drill assembly and through which the kelly extends for rotation relative thereto.

8. Apparatus according to any of the preceding claims, wherein the drive member has at least a telescopic part.

9. Apparatus according to any of the preceding claims, wherein means are provided for holding the drill assembly on the sea bed.

10. Apparatus according to claim 9, wherein the holding means comprises a pull down chain system provided on the drill assembly.

11. Apparatus according to claim 10, wherein the pull down chain system is hydraulically operated.

12. Apparatus according to any of the preceding claims, wherein a stabiliser arrangement is provided at a lower end of the drill assembly.

13. Apparatus according to claim 12, wherein the stabiliser arrangement comprises a spike resiliently mounted within a guide tube, the spike normally extending beyond the lower end of the drill assembly.

14. A method of drilling the sea bed, comprising the steps of positioning a working platform at a location where the sea bed is to be drilled, the working platform having a drill support arrangement fixedly mounted thereon and a drill assembly movably mounted on the drill support arrangement, mounting a selected extension at the lower end of a drive member which has a through bore, moving the drill assembly relative to the drill support arrangemenu to the sea bed, positioning a selected drill tool through the drive member to a drilling location at the lower end of the drive member, and rotatably driving the drive member for drilling of the sea bed.

15. Apparatus for drilling the sea bed substantially as herein before described with reference to the accompanying drawings.

16. A method of drilling the sea bed substantially as hereinbefore described with reference to the accompanying drawings.

17. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.