Drilling rig hoisting system

Abstract

A hoisting system for a drilling rig, which has a crown block for attaching to a derrick, the crown block comprising a plurality of sheaves; a travelling block suspended from the crown block via a hoisting cable, the travelling block comprising a plurality of sheaves and being connectable with a payload, the travelling block being arranged to move along a workpath; the hoisting system further comprising: a floating block comprising a plurality of sheaves reeved on the hoisting cable; wherein the floating block is configured to move between: a first arrangement in which the floating block is fixed relative to the crown block; and a second arrangement in which the floating block is fixed relative to the travelling block; wherein the hoisting system is arranged such that, when the floating block is in one of the first or second arrangement, the sheaves of the floating block overlap a sheave of the crown block or travelling block in a direction of the workpath.

Claims

1. A hoisting system for a drilling rig, the hoisting system comprising: a crown block for attaching to a derrick, the crown block comprising a plurality of sheaves; a travelling block suspended from the crown block via a hoisting cable, the travelling block comprising a plurality of sheaves and being connectable with a payload, the travelling block being arranged to move along a workpath; the hoisting system further comprising: a floating block comprising a plurality of sheaves reeved on the hoisting cable; wherein the floating block is configured to move between: a first arrangement in which the floating block is fixed relative to the crown block; and a second arrangement in which the floating block is fixed relative to the travelling block; wherein the hoisting system is arranged such that, when the floating block is in one of the first or second arrangement, the sheaves of the floating block overlap a sheave of the crown block or travelling block in a direction of the work path, and wherein the plurality of sheaves of at least one of the crown block and the travelling block are axially separated into two sheave groups, and the floating block is arranged to be located at least partially between the two sheave groups when the floating block is in one of the first and second arrangements.

2. A hoisting system according to claim 1, wherein the floating block is arranged to overlap a sheave of the crown block or travelling block in such a way that it is nested or nestled amongst the sheaves of the crown block or the travelling block.

3. A hoisting system according to claim 1, wherein the floating block is arranged to overlap a sheave of the crown block or travelling block in such a way that it is nested or nestled amongst the sheaves of the crown block or the travelling block.

4. A hoisting system according to claim 1, wherein the hoisting system is arranged such that, when the floating block is in one of the first or second arrangement, the sheaves of the floating block totally overlap a sheave of the crown block or travelling block.

5. A hoisting system according to claim 1, wherein the plurality of sheaves of the floating block are axially separated into two sheave groups, and at least one sheave of the crown block or travelling block is arranged to be located at least partially between the two sheave groups when the floating block is in one of the first and second arrangements.

6. A hoisting system according to claim 1 wherein the hoisting system comprises a single attachment device for attaching a plurality of the sheaves of the floating block to at least one of the crown block and the travelling block.

7. A hoisting system according to claim 6, wherein the attachment device is arranged such that when the floating block is attached to the at least one of the crown block and the travelling block by means of the attachment device, the sheaves of the floating block totally overlap a sheave of the crown block or travelling block.

8. A hoisting system according to claim 1, wherein the hoisting system further comprises a winch engaged with the hoisting cable at a first end and comprising an anchor engaged with the hoisting cable at a second end.

9. A hoisting system according to claim 8, wherein the hoisting cable is reeved such that a portion of the hoisting cable reeved around a sheave of the floating block forms part of a deadline when the floating block is in one of the first and second arrangements.

10. A hoisting system according to claim 9, wherein the hoisting cable is reeved with a sheave of the floating block arranged closer than the sheaves of at least one of the crown block and the travelling block, to the anchor, such that the portion of the hoisting cable reeved around the sheave of the floating block forms part of the deadline when the floating block is in one of the first and second arrangements.

11. A hoisting system according to claim 1, further comprising a crossover sheave assembly, the crossover sheave assembly comprising at least one crossover sheave and being arranged such that the sheaves of the crown block, travelling block and/or floating block can be reeved onto the hoisting cable in an order which is different to the order in which they are attached to the respective block.

12. A hoisting system according to claim 11, wherein the crossover sheave is reeved on the hoisting cable between a first sheave of one of the crown block, travelling block or floating block and a second sheave of one of the crown block, travelling block or floating block; wherein the crossover sheave is arranged perpendicularly or obliquely to the first and second sheave.

13. A hoisting system according to claim 1, wherein the travelling block comprises the floating block and the floating block forms a detachable module of the travelling block, such that the floating block is suspended from the crown block via the hoisting cable.

14. A hoisting system according to claim 13, wherein the plurality of sheaves of the travelling block are axially separated into two sheave groups, and the floating block is attachable to the travelling block between the two sheave groups, with the sheaves of the floating block substantially axially aligned with the sheaves of the travelling block when the floating block is in the second arrangement.

15. A hoisting system according to claim 13, comprising: a winch engaged with the hoisting cable at a first end; an anchor engaged with the hoisting cable at a second end; and a crossover sheave arrangement; wherein the crossover sheave arrangement comprises a crossover sheave and is arranged such that a sheave of the floating block is arranged on the hoisting cable at a location closer than a sheave of the travelling block, to the anchor.

16. A hoisting system according to claim 13, wherein the travelling block comprises an even number of sheaves separated into two axially separated sheave groups of equal number, and the floating block comprises an attachment device and is arranged to be attached to the travelling block between the two sheave groups such that the sheaves of the floating block totally overlap the sheaves of the travelling block.

17. A hoisting system according to claim 1, wherein the hoisting system is arranged to provide two lifting ratios, a first lifting ratio when the floating block is fixed relative to the crown block, and a second lifting ratio when the floating block is fixed relative to the travelling block.

18. A hoisting system according to claim 1, further comprising a heave compensator configured to compensate for motion.

19. A hoisting system according to claim 18, wherein the heave compensator is associated with a winch of the hoisting system which is configured to provide heave compensation by controlling the spooling rate to compensate for motion.

20. A hoisting system according to claim 18, wherein the heave compensator comprises a crown compensator arranged to facilitate movement of the crown block to compensate for motion wherein the crown compensator comprises a supporting frame which defines an opening for receiving at least part of the crown block or a crossover sheave when the crown block is at its uppermost position in the crown compensator.

21. A method for changing the lifting ratio of a hoisting system according to claim 1, the method comprising: moving a floating block comprising a plurality of sheaves between a first arrangement, in which it is fixed relative to a crown block, and a second arrangement, in which it is fixed relative to the travelling block.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a side elevation view of an example hoisting system;

(2) FIG. 2A is a diagrammatic view of the hoisting system of FIG. 1, shown with a first lifting ratio;

(3) FIG. 2B is a schematic illustration of an overlap of the floating block and the travelling block;

(4) FIG. 3A is a diagrammatic view of the hoisting system of FIG. 1, shown with a second lifting ratio;

(5) FIG. 3B is a schematic illustration of no overlap of the floating block and the crown block;

(6) FIG. 4 is a top view of the hoisting system of FIG. 1;

(7) FIG. 5 is a diagrammatic view of a second example hoisting system;

(8) FIG. 6 is a diagrammatic view of a third example hoisting system;

(9) FIG. 7 is a diagrammatic view of a fourth example hoisting system, shown with a first lifting ratio;

(10) FIG. 8 is a diagrammatic view of the hoisting system of FIG. 7, shown with a second lifting ratio;

(11) FIG. 9 is a diagrammatic view of a fifth example hoisting system;

(12) FIG. 10 is a diagrammatic view of a sixth example hoisting system, shown with a first lifting ratio;

(13) FIG. 11 is a diagrammatic view of the hoisting system of FIG. 10, shown with a second lifting ratio;

(14) FIG. 12 is a diagrammatic view of a seventh example hoisting system, shown with a first lifting ratio;

(15) FIG. 13 is a diagrammatic view of the hoisting system of FIG. 12, shown with a second lifting ratio;

(16) FIG. 14 is a side elevation view of an example hoisting system comprising a crown compensator; and

(17) FIG. 15 is a side elevation view of the hoisting system of FIG. 14.

(18) FIG. 1 illustrates part of a derrick and an example hoisting system 10. FIG. 2A is a diagrammatic representation of the same hoisting system 10. The derrick and hoisting system 10 are suitable for use on a drilling ship, for example. The hoisting system 10 is associated with a work centre. The hoisting system 10 comprises a crown block 12 which is restrained relative to the derrick and a travelling block 14 which is suspended from the crown block 12 by a hoisting cable 16. Each of the crown block 12 and the travelling block 14 comprises a plurality of sheaves.

(19) The travelling block 14 has connectors such that a payload (e.g. a top-drive) can be attached, and thus suspended, from the travelling block 14. One end of the hoisting cable 16 is associated with a winch 18 for drawing the hoisting cable 16 in, and the other end of the hoisting cable is attached to an anchor 20, for fixing that end of the hoisting cable 16. In some examples, the anchor 20 may be replaced with a second winch.

(20) As the winch 18 draws in the hoisting cable 16, the travelling block 14 moves towards the crown block 12 along the workpath. In this manner, any payload attached to the travelling block 14 is also lifted vertically along the workpath.

(21) The hoisting system 10 also comprises a winch sheave 26 and an anchor sheave 28 for assisting in introducing the hoisting cable 16 into the crown block 12, travelling block 14 or floating block 22 from the winch 18 and anchor 20, respectively.

(22) In accordance with known systems, the portion of the hoisting cable 16 extending from the anchor 20 which does not move over the surface of a sheave during the movement of the travelling block 14 is referred to as the deadline 16a. The portion of the hoisting cable 16 which does move over a sheave during movement of the travelling block is referred to as the fastline 16b. In the diagrammatic figures the deadline 16a is illustrated with a broken line.

(23) The hoisting system 10 also comprises a floating block 22. The floating block 22 comprises a plurality of sheaves 23a-c. The floating block 22 is arranged to move between a first and second arrangement. In the first arrangement the floating block 22 is in a first position—fixed relative to the crown block 12. This means that the floating block 22 does not move relative to the crown block 12 with the travelling block 14. In this example, the floating block 22 is located at the top of the workpath and is parked adjacent the crown block 12. This configuration is illustrated by the broken lines in FIG. 1 and in FIG. 3. Since in this arrangement the floating block does not move relative to the crown block, the sheaves 23a-c of the floating block 22 do not contribute to the force/displacement magnification effect of the hoisting system 10. Accordingly, the force amplification is determined by the number of sheaves of the travelling block 14.

(24) In the second arrangement (shown in solid lines in FIG. 1 and in FIG. 2A), the floating block 22 is in a second position—fixed relative to the travelling block 14. This means that the floating block 22 moves as one with the travelling block 14. In this example, the floating block 22 is located between two symmetric groups of travelling block sheaves 15a-f. Since the sheaves 23a-c of the floating block 22 now move relative to the sheaves 13a-f of the crown block 12, the sheaves 23a-c of the floating block 22 now contribute to the force/displacement magnification effect of the hoisting system 10. Accordingly, the force amplification is determined by the combined number of sheaves of the travelling block 14 and floating block 22. This provides a different gearing/lifting ratio compared to that when the floating block 22 is fixed relative to the crown block.

(25) In the example of FIGS. 1 to 3, the floating block 22 has 3 sheaves. The floating block 22 having a plurality of sheaves results in a bigger difference between the two lifting ratios of the hoisting system 10. A single attachment device 24 is provided to attach the whole of the floating block 22 to the travelling block 14. A further, or the same, attachment device may be provided for attaching the floating block 22 to the crown block 12.

(26) The arrangement of the hoisting system 10 of FIGS. 1 to 3 is such that the sheaves 15a-f of the travelling block 14 are arranged in two groups. The two groups of sheaves are axially separated and the hoisting system 10 is arranged such that in the second arrangement the floating block is located between the two groups of sheaves, such that the sheaves 23a-c of the travelling block 22 are substantially coaxial with the sheaves 15a-f of the travelling block 14, i.e. there is a total overlap. The two groups of travelling block sheaves comprise the same number of sheaves and are substantially symmetric (i.e. equally spaced from a centreline of the workpath). This means that the lift provide by the hoisting system is even and the centre of lift acts through the centreline of the workpath 11.

(27) The workpath 11 is illustrated in FIG. 3A and is the up and down travel of the travelling block.

(28) The above arrangement ensures that the length of the workpath is not reduced by the inclusion of the floating block 22. Since the floating block 22 is arranged to nest amongst the sheaves 15a-f of the travelling block, it does not block or inhibit the movement of the travelling block 14 along any portion of the workpath, regardless of whether the floating block 22 is in the first or the second arrangement. This maximises the length of the workpath for a given distance between the crown block 12 and the travelling block 14.

(29) FIGS. 2B and 3B illustrate the concept of sheaves of the floating block overlapping a, or all, of the sheaves of the crown block or the travelling block in the direction of the workpath 11. FIG. 2B schematically illustrates the positions of the travelling block 14A and floating block 22A with respect to the direction of the workpath 11 (illustrated by the arrow). As can be seen, the totality of the sheaves of the floating block 22A overlap those of the travelling block 14a in a direction of the workpath 11. The extent of the overlap is illustrated by the double ended arrow 19. This is a total overlap.

(30) Turning now to FIG. 3B, it can be seen that in the direction of the workpath 11 (illustrated by the arrow), there is no overlap of the floating block 22a and the crown block 12a.

(31) The hoisting system 10 also comprises a crossover sheave assembly 30 (as seen in FIGS. 2 and 3). The crossover sheave assembly is arranged to extend the deadline 16a when the floating block 22 is in the first arrangement. This results in the part of the hoisting cable 16 which is reeved around the sheaves 23a-c of the floating block 22 forms part of the deadline 16a. This means that the sheaves 23a-c of the floating block 22 and the associated sheaves 13c-e of the crown block 12 do not rotate in response to movement of the hoisting cable 16 by the winch 18. This provides the advantages of reduced wear on this section of the hoisting cable 16a and reduced friction opposing the movement of the hoisting cable 16, travelling block 14 and thus payload.

(32) In order to achieve this in the present example, the sheaves 23a-c of the floating block 22 need to be reeved onto the hoisting cable 16 at a location on the hoisting cable 16 which is closer to the anchor 20 than the sheaves 15a-15f of the travelling block. In the present example the crossover sheave assembly comprises a primary crossover sheave 32 and a secondary crossover sheave 34. The primary crossover sheave 32 connects the two groups of sheaves of the travelling block, and so is a large-diameter sheave which extends across the gap formed between the two groups of sheaves. The secondary crossover sheave 34 is located adjacent the anchor sheave 28 on the hoisting cable 16, and facilitates the reeving of the floating block 22 before the travelling block 14, despite the floating block 22 being physically located in the middle of the travelling block 14.

(33) FIG. 4 depicts the hoisting system 10 of FIG. 1 from above.

(34) Turning now to FIG. 5, a schematic view of a second example of a hoisting system is shown. In this example, the winch 18, winch sheave 26, crown block 12, crossover assembly 30, anchor sheave 28 and anchor 20 are the same as in the first example. In this embodiment, the travelling block 14 now comprises three sheaves 15g-i and the floating block 22 is split into two parts 22a, 22b each of which comprises three sheaves 23d-i. The travelling block 14 is located centrally with respect to the workpath and the floating block parts 22a,b are located symmetrically to either side of the travelling block 14.

(35) As before, this example provides two gears, since the two floating block parts 22a,b will be connected and disconnected in tandem in order to ensure a lifting force through the centreline of the workpath. The example of FIG. 5 provides a higher maximum lifting speed than the example of FIGS. 1 to 4, since the payload can be lifted with the hoisting cable 16 reeved through only 3 active sheaves on the travelling block, rather than the minimum of 6 in the previous example.

(36) In the example of FIG. 4, the deadline only extends to the secondary crossover sheave 34.

(37) FIG. 6 schematically depicts an example with an identical crown block 12, travelling block 14 and floating block 22 as the previous example, although with a different crossover sheave arrangement 30. In the example of FIG. 6, the winch sheave 26 and the secondary crossover sheave 34 are arranged such that the sheaves 15g-i of the travelling block are reeved on the hoisting cable 16 closer to the winch 18 than the sheaves of the floating block 23d-i. The primary crossover sheave 32 is arranged to span the portion of the workpath occupied by the travelling block such that the sheaves of both parts of the floating block 23d-i can be reeved on the hoisting cable 16 closer to the anchor 20 than the sheaves of the travelling block 14. This results in the deadline extending through all of the sheaves of the floating block 23d-i when the floating block 22 is fixed relative to the crown block 12.

(38) FIGS. 7 and 8 schematically illustrate an example with the same crown block 12, travelling block 14 and floating block 22 as the example of FIGS. 1 to 4, but with no crossover sheave assembly 30. As such, the hoisting system 10 comprises fewer sheaves, but the deadline is made shorter (as illustrated by the broken line in the figures).

(39) FIG. 9 schematically illustrates the example of FIGS. 5 and 6, although with the crossover sheave arrangement removed.

(40) In the example of FIG. 10, the sheaves 23j-l of the floating block 22 can be separated from the floating block 22 and independently moved between an arrangement in which the sheave is fixed relative to the crown block 12 and an arrangement in which the sheave is fixed relative to the travelling block 14. In FIG. 10, a central sheave 23k of three is moved to a position where it is fixed relative to the crown block 12. In FIG. 11, two outer sheaves 23j,l of the three floating block sheaves 23j-l are moved to a position in which they are fixed relative to the crown block 12.

(41) In the example of FIGS. 12 and 13, the hoisting system 10 is arranged such that the sheaves of the floating block are reeved on the hoisting cable 16 such that they intersperse sheaves of the travelling block 14, rather than the crown block 12 as in the other examples. As such, the floating block 22 is not suspended from the crown block 12. The principle of this example is, however, identical to preceding examples. In a first arrangement (as shown in FIG. 12), the floating block 22 is arranged in a fixed relationship with respect to the crown block 12 and the lifting/movement ratio is determined by the number of sheaves of the crown block 12 combined with the number of sheaves of the floating block 22. In a second arrangement (as shown in FIG. 13), the floating block 22 is arranged in a fixed relationship with respect to the travelling block 14, and the lifting/movement ratio is determined by the number of sheaves of the crown block 12 alone.

(42) FIGS. 14 and 15 show an example hoisting system comprising a heave compensator for compensating for wave motion. The heave compensator comprises a crown compensator 36. The crown compensator 36 comprises a support frame comprising two masts 38 arranged to flank the crown block 12 and crossover sheave assembly. The masts 38 comprise tracks along which the crown block 12 and crossover assembly can be driven. The masts and tracks are arranged vertically such that the crown block and crossover sheave assembly can be raised and lowered. Raising and lowering the crown block to oppose the wave motion can minimise the movement of the payload with respect to the seabed.

(43) In the present example, the crown compensator 36 provides passive heave compensation; although in other embodiments it may also/alternatively provide active heave compensation.

(44) The masts 38 define a spacing thereinbetween 40 which will be discussed later.

(45) When the crown compensator 36 is in a deactivated, or parked, state, as shown in FIG. 14, the crown block 12 is locked with respect to the support frame and is unable to move with respect to the rig/derrick on which it is installed. This may be the case when the hoisting system is in a heavy lift mode, at which time the winch may be configured to provide heave compensation by controlling the spooling of the hoisting cable. As the hoisting system is in a heavy lift mode, the travelling block of the system of FIG. 14 is in the second position—locked with respect to the travelling block (although it is to be noted that the activation state of the crown compensator is not directly linked to the arrangement of the travelling block).

(46) FIG. 15 shows the same hoisting system, albeit with the crown compensator 36 activated. In this example, the winch is parked when the crown compensator is providing heave compensation. When the crown compensator 36 of the hoisting system of FIG. 15 is activated, the crown block and crossover sheave assembly are raised and lowered in response to wave motion. In FIG. 15, the crown block 12 and crossover sheave assembly are at a high position within the crown compensator 36, which is likely to correspond to the rig or derrick being located at the trough of a wave.

(47) The opening 40 defined by the support frame is located directly above the crown block 12 and the crossover sheave 32. As such, the crossover sheave 32 can be received in the opening when the crown compensator moves the crown block 12 and crossover sheave assembly into a high position. This provides a more compact arrangement than may otherwise be the case.

(48) The present invention has been described above purely by way of example. Modifications in detail may be made to the present invention within the scope of the claims as appended hereto.