GB2436320A

GB2436320A - Deep water remote drilled anchoring system

Info

Publication number: GB2436320A
Application number: GB0604999A
Authority: GB
Inventors: John Richard Carew Armstrong
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-03-13
Filing date: 2006-03-13
Publication date: 2007-09-26
Also published as: GB0604999D0

Abstract

This invention relates to a vessel or equipment anchor device that is lowered to the seabed and under remote instruction from the surface or other control facility drills and fixes the device in place. The device comprises a load-carrying frame 1 with attachment point for the equipment to be anchored and a tether cable 2 for lowering it to the seabed, drill bits 16 that also serve to attach the frame to the underlying seabed, and a removable arm-mounted drill arrangement 12,13,14,15 for inserting the bits, powered and controlled from the surface. The device may also comprise a system for ensuring that the frame is suitably level. A grouting system 17, for grouting the drill bits in place in the seabed may also be provided. A power supply 11 may be provided to supply hydraulic power to operate a slew motor 9 of a drill arm 6 and a drill motor 12 of the drill arrangement.

Description

DEEP WATER REMOTE ANCHORING SYSTEM

This invention relates to permanent deep water anchoring arrangements for loaded structures needing to be fixed into seabed rock or hard ground where it may be impractical or too costly to arrange for a surface ship, jack-up, barge or semi-submersible or for divers to provide direct drilling or support services.

Most offshore structures need to be anchored to the seabed. This typically involves drilling into the seabed for the insertion of piles for soft ground conditions, or mechanical or grouted-in anchorages for hard or rocky ground conditions. The drilling equipment for these procedures is usually mounted on a jack-up platform, barge or workboat for shallow water conditions, or on a semi-submersible platform or dynamically positioned ship for deep water. In either case, the drilling and anchoring operation may be assisted by the use of divers.

Sometimes it may happen that a fixing is required in conditions that are too hostile for these methods to be used. For instance, anchorages for the tethering of offshore wind or wave energy devices or tidal stream turbine systems may need to be sited in deep, fast-flowing current streams where the seabed is rock or hard ground, and where there may be practical difficulties in siting a fixed or floating surface platform for the drilling and installation operation, and where conditions are too hazardous for the use of divers.

In order to make possible such secure anchorages, this invention relates to a device that is lowered to the seabed and, under remote instruction from the surface or other control facility, drills and fixes the anchorages in place.

According to the main aspect of the invention there is provided an underwater anchoring system comprising: a. a frame, lowered to the seabed by a tether which may also carry a power cable, and adapted to mount one or more drill elements and supports b. an arm that can be lowered down the tether cable on to a bearing spindle, said arm then being able to rotate to attach to each drill element in turn c. a drill motor mounted to the arm so that it can cause to rotate the drill element in either direction and also apply force to drive the element into the seabed as it turns d. means to slew the arm about the bearing spindle, for instance a slew motor driving a gear e. a power supply, eg supplying hydraulic power, to operate the slew motor and drill motor f. alternatively to b-e above, an arm fitted with as many drill motors as there are drill elements on the frame g. the means to apply pre-tension to the fixing points to provide long term stability Such a mounting may be deployed from a surface vessel holding station in a fast-running stream, or anchored in slack water. It is also possible that control and power signals are led away to a more convenient shore or shelter-based facility once the equipment has been lowered, so that the anchoring process can be carried out at leisure.

Other features of the invention will be apparent from the following description of preferred embodiments illustrated by way of example only in the accompanying drawings.

Figure 1 is a schematic view of an embodiment of a deepwater remote anchoring system incorporating the invention. This embodiment is specialised as an anchorage for a tidal stream turbine that is able to swing to operate in different tidal directions: other applications will lead to other specialised embodiments of the invention.

With reference to FIgure 1, an underwater assembly 100 comprises a frame 1 that is lowered by its tether cable 2 to rest on the seabed on three blocks 3. Feet 4 are mounted on cylindrical legs 5 that can be screwed down in frame 1 so as to adjust the height of the feet so that the frame rests level on the seabed with all feet in contact.

An arm 6 is lowered down the tether cable over a bearing spigot 7 by a power-carrying cable S until a slew drive motor and pinion 9 engages with gear 10 fixed to frame 1. A power pack 11 provides hydraulic power to motor 9 so that arm 6 can be driven around the frame to each drill position in turn, means being provided to index each position precisely.

A drill motor 12 is mounted on a slide base 13 so that said motor 12 can be driven up and down byahydraulic jack 14.

In operation, drill motor 12 is indexed to be directly over one drill leg 5 and lowered until drill chuck 15 engages the shaped head of drill bit 16. Drill bit 16 is mounted inside leg 5 in such a way that in its initial position it is held within leg 5 by a friction collar so that when drill bit 16 is rotated, leg 5 is screwed into frame 1 until foot 4 is in finn contact with the seabed and the frame rests level. When drill motor 12 and slide base 13 are driven downwards, drill bit 16 disengages from the friction collar so that it no longer engages leg 5, and with rotation from drill motor 12 can be driven into the seabed. Further explanation of this stage is given in the text below in relation to Figure 3.

once drill bit 16 is driven fully into the seabed, a grout or setting mixture from reservoir 17 is injected under pressure through ports and internal passages to emerge adjacent to the drill tip. The grout or setting mixture then fills the void between drill bit 16 and the surrounding seabed structure such that on setting it forms a strong bond locking drill bit 16 to the sides and crevices of the drilled hole.

Drill base 13 and motor 11 are then raised, arm 6 re-indexed over the next drill bit and the process repeated. Once the drill bits are all in place and the grout is set, drill motor 11 may be used to apply pre-tension between frame 1 and each grouted drill bit in turn.

When it is required for the frame to be mounted so that it sits level on the seabed, a level sensor mounted on the arm may be used to determine which leg to engage first and how far down to screw it, so that the frame sits level with all feet engaged.

After all the anchorages are made and properly tensioned, arm 6 may be removed to the sea surface.

To remove frame 1, a cutting torch or wheel may be mounted to the frame and positioned so as to cut through either each drill bit 16, or through leg 5, releasing the frame for lift to the surface.

Underwater lights and cameras may be mounted on to frame 1 or arm 6 to help an operator observe what is happening during the anchorage or removal process.

In an alternative embodiment of the invention, the arm that is lowered down has not just one drill station, but as many as there are legs and drill bits. Referring to FIgure 2 below showing assembly 101, the arm 6 now carries five drill bases 13, jacks 14 and motors 12. As the arm is lowered down and engages spigot 6, a register is engaged and aligns drill motors chucks 15 with the drill bits 16.

Once drill chucks 15 are engaged with drill bits 16, legs 5 may be screwed into frame 1 so that feet 4 all come into contact with the seabed such that the frame rests level. Then bits 16 may be driven into the seabed and grouted in place.

To remove the anchorages, a separate frame in the style of assembly 100 may be lowered down to cut off bits 16 or feet 5.

With refererence now to the means of drill bit fixing for either assembly 100 or 101, Figures 3 and 4 show sectional views of the drill bit respectively in its starting position, and fully driven home into a rock or hard sea-bed, again intended to be illustrative of a particular embodiment of the invention claimed.

In Figure 3, frame 1 has been lowered to the seabed and is sitting on blocks 3 (not shown). Drill bit 16 is tightly held in leg 5 by such as friction collar 19. When drill collar 6 engages with the head of drill bit 16, rotation of said collar and head causes leg to screw down into the frame until foot 4 is in contact with the seabed. This may be done in conjunction with level sensors mounted on frame 1 so that the feet are screwed down until the frame is levelled as required.

Once frame 1 rests level with feet 4 all in contact with the seabed, drilling may commence. Each drill bit is pushed downwards by hydraulic jack 14 until it is no longer held by friction collar 19. Drilling proceeds by rotation of drill bit 16 in conjunction with downward pressure from jack 14. The main shank 20 of drill bit 16 is waisted to allow debris to be displaced up the hole, and spiral flutings serve to locate the drill bit within the lower bearing of leg 5, and also to act as a former for the grout that is inserted later to form a grip for the drill bit.

Having drilled to the full extent of the reach of drill bit 16 (referring now to the position shown in Figure 4), grout is injected under pressure to provide a permanent locking mechanism between the drill bit and the seabed structure as previously indicated.

Once the grout is set, the bond may be tested by applying full torque to the hydraulic motor, up to the point where a retaining pin 22 shears. At this point, the threaded nut 23 forming the head of drill bit 16 is no longer locked to it, and continued rotation of nut 23 serves to apply pretension to drill bit 16, up to the point where the alternating loads on the structure will not cause fatigue to the anchorage components.

In an alternative embodiment, a mechanical rock anchor may be used just behind the tip of the drill so that on reverse rotation of drill bit 16, wedges are forced into the rock, providing pretension for the anchor. This mechanical anchor may be used with or without a subsequent grouting stage. (p

Claims

CLAIMS

1. A deep water remote anchoring system comprising a load-canying frame with attachment pointforthe equipmentto be anchored, ameansof loweringittothe seabed, drillbitstbat also serve to attach the frame to the underlying seabed, and a removable drill arrangement powered and controlled from the surface for inserting the bits.

2. An anchor according to claim I in which the drill arrangement comprises an arm that can be lowered down a guidance cable on to a bearing spigot, said arm being able to engage and drive the drill bits and rotate about said bearing spigot to drive each drill bit in turn.

3. An anchor according to claim 2, in which a drill motor is mounted to the arm so that it can cause to engage and rotate the drill bit in either direction and also apply a force driving the drill bit into the seabed as it turns.

4. An anchor according to claim 1, in which there is in addition a system for ensuring the base is suitably level.

5. An anchor according to any of the preceding claims, in which there is in addition a grouting system for grouting the drill bits in place in the seabed.

6. An anchor according to any of the preceding claims, in which the power cable providing power to the drill system forms part of the means of lowering the arm and drill system to the seabed.

7. An anchor according to any of the preceding claims, in which a power supply supplies such as hydraulic power to operate a slew motor and or drill motor.

8. An anchor according to any of the preceding claims, in which applying reverse rotation to the each drill bit once grouted or otherwise fixed in place, serves to apply pretension to the drill bit anchoring the frame to the seabed.

9. An anchor according to any of the preceding claims, in which each drill bit is initially held clear of the seabed in a friction collar, so that rotation by the drill motor without downward force causes a concentric cylindrical leg to wind up or down so as to level the frame.

10. An anchor according to claim 9 in which once the frame is level, downward force on each drill bit causes it to be pushed clear of the friction collar and into contact with the seabed.

11. An anchor according to any of the preceding claims, in which each leg and drill bit has its own individual drill motor for driving the drill bit into the seabed and, if means of levelling are provided, for levelling the frame.

12. An anchor according to any of the preceding claims, in which a mechanical rock anchor is used above the tip of the drill bit such that on reverse rotation of the drill bit, wedges are forced into the seabed providing pretension of the drill bit.

13. An anchor according to any of the preceding claims, in which a separate arm mounted with equipment for removing the drill bits anchoring the frame, for instance by cutting them close to the seabed, is lowered down the guide wire. f

AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS

DEEP WATER REMOTE ANCHORING SYSTEM

Amended Claims 1. A deep water remote anchoring system suited in particular for deep, fast flowing current streams, comprising a load-carrying frame with attachment point for the equipment to be anchored, a means of lowering it to the seabed, drill bits that also serve to attach the frame to the underlying seabed thus eliminating the need for separate piling operations, and a removable drill operating arrangement powered and controlled from the surface that also negates the need for such as jack-up barges, drill ships, or divers to provide direct drilling or support services.

2. An anchor according to claim i in which the drill arrangement comprises an arm that can be lowered down a guidance cable on to a bearing spigot, said arm being able to engage and drive the drill bits and rotate about said bearing spigot to drive each drill bit in turn.

3. An anchor according to claim 2, in which a drill motor is mounted to the arm so that it can cause to engage and rotate the drill bit in either direction and also apply a force driving the drill bit into the seabed as it turns.

:. 4. An anchor according to claim i, in which there is in addition a system for ensuring the base can be made suitably level.

5. An anchor according to any of the preceding claims, in which there is in addition a grouting system for grouting the drill bits in place in the seabed.

6. An anchor according to any of the preceding claims, in which applying reverse rotation to the each drill bit once grouted or otherwise fixed in place, serves to apply pretension to : the drill bit anchoring the frame to the seabed.

I S..

* 7. An anchor according to any of the preceding claims, in which each drill bit is initially held clear of the seabed in a friction collar, so that rotation by the drill motor without downward force causes a concentric cylindrical leg to wind up or down so as to level The frame.

8. An anchor according to claim 9 in which once the frame is level, downward force on each drill bit causes it to be pushed clear of the friction collar and into contact with the seabed.

9. An anchor according to any of the preceding claims, in which each leg and drill bit has its own individual drill motor for driving the drill bit into the seabed and, ii means of levelling are provided, for levelling the frame.

10. An anchor according to any of the preceding claims, in which a mechanical rock anchor is used above the tip of the drill bit such that on reverse rotation of the drill bit, wedges are forced into the seabed providing pretension of the drill bit.

AnchoragePatentAppkcationl 30306 and Amended Claims 11. An anchor according to any of the preceding claims, ir which a separate arm mounted with equipment for removing the drill bits anchoring tle frame, for instance by cutting them close to the seabed, is lowered down the guide wire. S. * * S. S

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AnchoragePatentAppkcationl3O3O6 and Mended CIaEns