GB1580790A - Underwater drilling apparatus and method - Google Patents

Description

(54) UNDERWATER DRILLING APPARATUS AND METHOD (71) We, ROBERT MARK GOODEN, a British subject and JOSEPH VINCENT DUNNE, an Australian subject, both of Trelease Mill, St. Martin, Helston, Cornwall, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to the drilling of holes in underwater beds and has particular, but not exclusive application to socalled core drilling to obtain rod-like samples of said beds for geological evaluation. It will be appreciated from the following description that the invention has numerous applications in which holes are required to be drilled in underwater beds in addition to core drilling.

The invention provides an improved method for underwater drilling and apparatus for carrying out the method.

There has been a substantial increase in recent years in exploiting underwater, especially undersea, resources of, for example, minerals and hence a corresponding increase in demand for core samples from underwater beds. Several drilling techniques of widely varying cost, performance and type are available or have been proposed for obtaining such samples. However, none are entirely satisfactory. Vibrocorers, which are successfully employed for forming holes of up to about 70 feet in soft material do not penetrate even soft rock. Diver-operated bed-mounted drilling rigs can only be used in shallow waters to permit of reasonable operating time by the diver. Automatic bed-mounted drilling rigs can be used in deeper waters but lack of degree of fine control and adaptability to varying conditions which can only be obtained with an operator.Moreover, said automatic rigs are costly and generally unreliable in that drilling difficulties are not readily overcome without constant manual supervision on the rig. Barge-mounted or other floating drilling rigs except expensive drilling ships are difficult to operate in tidal areas and cannot be used during adverse weather or water conditions. Finally, jack-ups are very limited by water depth and frequently are too large for the required use thereby unnecessarily adding to the cost of drilling.

It is an object of this invention to provide a method and apparatus for drilling holes in underwater beds which is particularly suited for drilling holes to a depth of up to about 2000 feet below water level, which is relatively inexpensive, which is less vulnerable to adverse weather and water conditions than the aforementioned known floating rigs, and which permits of lengthy operator presence at the drill head.

According to a first aspect of the present invention, there is provided a method of underwater drilling, especially core sampling, which comprises attaching a buoyant totally submerged drilling rig to an underwater bed by a tubular drill casing and drilling into the underwater bed by a drill string passing through said casing whilst the casing is maintained in tension by the buoyancy of the rig.

According to a second aspect of the present invention, there is provided apparatus for performing the method of the invention, which apparatus comprises a buoyant totally submersible drilling rig; a tubular drill casing adapted to depend from said rig; means for attaching said casing to an underwater bed; and a drill string adapted to extend through said casing to be operated from the rig to drill into the underwater bed.

It is preferred that the drilling rig should be submerged to the shallowest depth to allow operation in the prevailing weather and water conditions. Usually, said depth will be 30 to 40 feet below water level but other depths can be used if and when required.

Suitably, the tubular drill casing is anchored to the underwater bed by means of a weighted locating member deposited on the bed and to which the distal end of the casing is anchored. This member can be attached to the drilling rig for lowering and raising the member from the bed. The weight of said member is preferably twice as heavy as the weight necessary to submerge the drilling rig.

Guide means advantageously are provided between the rig and the locating member to g:idc the distal end of the tubular drill casing into engagement with said member.

The tubular drill casing usually will be constructed of a plurality of interconnectable tubular sections to facilitate assembly and to permit of ready variation of casing length to compensate for different bed depths. It is preferred that the casing is connected to the rig and the anchoring means by respective gimbal couplings.

It is also preferred that the apparatus should be capable of adopting a floating configuration in which it can be towed to a desired drilling location. To this end, the rig conveniently comprises one or more at least partially floodable buoyancy tanks and winch means are provided on the rig to lower and raise the anchoring means. Said winch means can also serve to pull the rig from a floating to a submerged position when the anchoring means is in position at the underwater bed.

Power for the apparatus and in particular for the drill conveniently is supplied by, for example, flexible hydraulic or pneumatic hoses, from a prime mover on board an accompanying support vessel floating on the water surface.

As mentioned previously, the invention has particular application to the taking of core samples. However, it also has application to other underwater drilling requirements such as, for example, providing holes for the insertion of ground anchors, measuring instruments or explosives.

The following is a description by way of example only and with reference to the accompanying drawings of apparatus in accordance with a preferred embodiment of the present invention and of the operation thereof. In the drawings: Figure 1 is a perspective view of the apparatus in an operative position; Figure 2 is a side view partially in section and on an enlarged scale of the drilling rig of the apparatus of Figure 1 and Figure 3 is a series of four side views showing how the apparatus of Figure 1 is manoeuvred from a floating to a drilling attitude.

Referring to the drawings, drilling apparatus in accordance with a preferred embodiment of the present invention comprises a drilling rig generally indicated at 1 and a locating member generally indicated at 2. The rig comprises a central working capsule 3 connected by a framework 4 to four equidistant cylindrical floats 5. The capsule 3 has an upper working chamber 6 separated from a lower drill rod store 7 by watertight hatches 8. An entrance hatch 9 is provided in the capsule to permit diver entrance and exit. In the working chamber 6 the necessary controls for operation of the rig are provided together with a hydraulic drill head 10. A drill well 11 extends from the working chamber 6 through the store 7 and has at its lower end a gimbal clamp assembly 12 to releasably receive the upper end of a tubular drill casing 13.

Each float 5 comprises an upper pressurized buoyancy tank 14 and a lower floodable buoyancy tank 15. Hydraulically operated winches 16 and 17 are located at the head and foot respectively of each float and are enclosed by domed covers 18. These covers 18 suitably are formed of glass-reinforced plastics whilst the buoyancy tanks 14, 15 and working capsule 3 are formed of steel.

The tubular drill casing 13 is formed of interconnectable tubular steel sections and in the operative configuration shown in Figure 1 is threadably received in a gimbal coupling (not visible in Figure 1) surmounted by an inverted frustoconincal guide 19. Said coupling is mounted on a bridge 20 of the locating member 2, which bridge connects a pair of weights 21. The total weight of the locating member 2 is approximately twice that required to submerge the drilling rig when the tanks 15 are flooded.

In the drilling configuration shown in Figure 1, cables 22 extend between winches 17 and respective corners of the locating member 2. Said cables are under tension in said configuration and also serve, as hereinafter described, to lower and raise the locating member. A guide 23 for the casing 13 extends between cables 22 and is movable longi tudinally with respect thereto to guide the casing to the locating member.

If required the top winches 16 can be attached to side anchor lines (not shown) to apply tension to such lines in a prevailing tidal current. These winches 16 are also used in the manoeuvring of the assembly from its floating to its drilling attitude as described hereinafter.

Hydraulic power, life support and other systems are supplied to the rig 1 by means of an umbilical line 24 extending to a terminal buoy 25 and thence to a support vessel 26.

The buoy 25 is anchored by cable 27 to a buoy anchor 28.

In the floating configuration shown in Figure 3A, the rig 1 is disposed with the longitudinal axes of the capsule 3 and floats 5 horizontal and the locating member 2 (shown digrammatically in Figure 3) is suspended immediately below the rig by means of a pair of cables 22 connected to winches 17 of the respective uppermost floats 5 and a pair of cables 29 connected to winches 16 of the respective lowermost floats 5. The sections of casing 13 are stored in the capsule 3.

In use the apparatus is towed to the desired location in its floating configuration shown in Figure 3A and the umbilical line 24 connected to support vessel 26. Winches 16 are then operated to extend cables 29 to allow the attitude shown in Figure 3B to be adopted.

Winches 17 are subsequently operated to winch in cables 22 to draw the capsule 3 and floats 5 to a substantially vertical attitude as shown in Figure 3C. The remaining pair of cables 22 are then connected to the locating member 2 and the cables 29 slackened off and detached as shown in Figure 3D. From the configuration shown in Figure 3D, the locating member 2 is lowered by cables 22 to the bed 30 (see Figure 1). Water is then admitted to tank 15 to decrease the buoyancy of the rig 1 and the rig is winched down cables 22 to a submerged location 30 to 40 feet below water level. The casing 13 is then assembled and lowered with the aid of guides 23 and 19 into the coupling on locating member 2. The casing is rotated from means provided in the rig to threadably engage the locating member coupling and is then clamped in coupling 12. Cables 22 are then eased to tension casing 13 and adjusted to counteract any tendency for locating member 2 to tilt. A drill string 31 is assembled from drill rods in the store 7 and lowered through the casing 13 to the bed 30. The drill string 31 is rotated by drill head 10 to drill into the bed 30 a hole 32 to collect core samples or for other purposes. The buoyancy of the rig and/or tension in the cables 22 can be adjusted to maintain the desired tension in casing 13 during the drilling operation.

The apparatus is returned to its floating configuration for removal to another drilling station by reversing the procedure described above.

It will be appreciated that the invention is not restricted to the details described above but that numerous modifications and variations can be made without departing from the scope of the invention as defined in the follow

Claims (16)

ing claims. WHAT WE CLAIM IS:-

1. A method of underwater drilling which comprises attaching a buoyant totally submerged drilling rig to an underwater bed by a tubular drill casing and drilling into the underwater bed by a drill string passing through said casing whilst the casing is maintained in tension by the buoyancy of the rig.

2. A method as claimed in Claim 1 wherein the rig is submerged to a depth of 30 to 40 feet below the water surface.

3. A method as claimed in any one of the preceding Claims wherein the drill casing is anchored in a weighted locating member deposited on the underwater bed.

4. A method as claimed in any one of the preceding Claims in which core samples are drilled from the underwater bed.

5. A method of underwater drilling sub stantially as hereinbefore described with reference to the accompanying drawings.

6. Apparatus for performing the method of Claim 1, said apparatus comprising a buoyant totally submersible drilling rig; a tubular casing adapted to depend from said rig; means for attaching said casing to an underwater bed; and a drill string adapted to extend through said casing to be operated from the rig to drill into the underwater bed.

7. Apparatus as claimed in Claim 6 wherein said means for attaching comprises a weighted locating member adapted to be deposited on the underwater bed and to anchor the distal end of the casing.

8. Apparatus as claimed in Claim 7 wherein said weighted locating member is attached to the drilling rig for lowering and raising said member from the underwater bed.

9. Apparatus as claimed in either of Claims 7 and 8 wherein guide means are provided between the rig and the locating member to guide the distal end of the tubular drill casing into engagement with said member.

10. Apparatus as claimed in any one of Claims 7 to 9 wherein the locating member is about twice as heavy as the weight necessary to submerge the drilling rig.

11. Apparatus as claimed in any one of Claims 6 to 10 wherein the tubular drill casing consists of a plurality of interconnectable tubular sections.

12. Apparatus as claimed in any one of Claims 6 to 11 wherein the tubular drill casing is connected to the rig and to the anchoring means by respective gimbal couplings.

13. Apparatus as claimed in any one of Claims 6 to 12 capable of adopting a floating configuration for towing to a desired drilling location.

14. Apparatus as claimed in any one of Claims 6 to 13 wherein the drilling rig comprises one or more at least partially floodable buoyancy tanks.

15. Apparatus as claimed in any one of Claims 6 to 14 wherein winch means are provided on the rig to lower and raise the anchoring means.

16. Apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.