GB2344121A

GB2344121A - Top drive having drive shaft concentric with the rotor

Info

Publication number: GB2344121A
Application number: GB9825690A
Authority: GB
Inventors: Gordon Pearson Campion
Original assignee: MACTAGGART SCOTT
Current assignee: MACTAGGART SCOTT
Priority date: 1998-11-25
Filing date: 1998-11-25
Publication date: 2000-05-31
Also published as: GB9825690D0

Abstract

A top drive assembly (10, Fig 1) comprises, a motor assembly (12, Fig 1) having a rotor 28, a drive shaft (14, Fig 1) for connection to a drill string, said drive shaft extending through the motor assembly and being concentric with said rotor, and means 38 and 39 for releasably retaining the drive shaft in the rotor, such that the drive shaft may be withdrawn from the motor assembly. The motor may be a radial piston, multi-lobed cam hydraulic motor, wherein the running speed may be adjustable and the running direction reversible. The means for releasably retaining the drive shaft may be in the form of split collars or clamps, for location on lower and upper shaft portions 40 and 44, to limit axial shaft movement. In a second aspect of the invention a disc brake assembly 46, 47 and 48 is provided, to restrain the rotor and shaft, relative to a housing 26 of the top drive.

Description

TOP DRIVE This invention relates to a top drive.

In the oil and gas exploration and extraction industries, bores are drilled to gain access to subsurface hydrocarbon-bearing formations. Drilling is typically accomplished using a drill bit mounted on the lower end of a rotating drill string formed of drill pipe lengths; as the drill bit progresses and the length of the drilled bore increases additional drill pipe lengths are added to the string at the surface. Drive for the drill string may be provided by a rotary table and kelly on the drilling floor cf a rig, and through which the drill string passes, or by a motor assembly, known as a top drive, coupled to the upper end of the drill string and suspended from the rig derrick.

A top drive assembly typically comprises one or more hydraulic or electric motors coupled to a gearbox. An output shaft from the gearbox includes a threaded coupling for engaging a"saver sub"or the like coupled to the upper end of the drill string. The top drive assembly is suspended from the derrick via a block and is fixed against rotation. The top drive is mounted on a vertically extending guide, such that the assembly may move downwardly as the drill bit advances and the length of the drilled bore increases.

The vertical range of movement of a top drive is limited by the working height of the derrick, which typically equates to three lengths of drill pipe; for use with a top drive, drill pipe is typically stored as "stands", each stand comprising three nine metre sections of drill pipe. Thus, the drill string length may be increased by three lengths of drill pipe at a time, and the drilling operation will be interrupted at appropriate intervals to add a drill pipe stand to the existing string.

A similar situation arises during"tripping"operations, that is when a drill string is being retrieved from or run into an existing well; during tripping operations the drill pipe stands will be handled by the top drive assembly but will not normally be connected to the top drive output shaft.

In some rigs, and in particular in portable rigs, the derricks tend to be smaller, and the reduced working height may reduce the number of lengths of drill pipe that may be added to the drill string at one time. As a result, the drilling operation must be interrupted more frequently and the average drilling speed drops considerably.

Accordingly, a bulky top drive assembly, which reduces the working height still further, may have a considerable effect on the efficiency of a drilling operation, and the advantages normally available due to the presence of the top drive may be lost.

Examples of various top drive assemblies and configurations are described in GB-A-2 079 819, GB-A-2 091 788, EP-A-0 162 001, US-A-4,529,045 (Varco International Inc), EP-A-0 196 284 (Maritime Hydraulics A. S.) and US-A5,433,279 (Tessari et al).

According to the present invention there is provided a top drive assembly comprising a motor having a rotor and a drive shaft for connection to a drill string, the rotor being concentric with the drive shaft.

This arrangement will tend to be more compact than conventional top drives, in which the motor axis is parallel to but offset from the drill string. Also, the alignment of the motor axis and drill string facilitates support of the top drive and the drill string suspended therefrom.

According to another aspect of the present invention there is provided a top drive assembly comprising a motor having a rotor for coupling to a drill string whereby, in use, the drill string is rotated at the same speed as the rotor.

The top drive of this aspect of the invention does not require a gearbox, and thus may be relatively compact.

Also, one of the primary reasons for breakdowns in existing top drives is gearbox failure, such that top drives in accordance with the invention are likely to be more reliable than existing arrangements.

Preferably, the motor is a hydraulic motor.

Conventional top drives utilise one or more electric motors, having rotors which rotate at relatively high speed, such that a reduction gearbox must be provided.

However, an appropriate hydraulic motor may provide a low speed, high torque output and thus be coupled directly to the drill string. The hydraulic motor may take any appropriate form, but is preferably a radial piston, multilobed cam motor, such as manufactured and supplied by MacTaggart Scott & Co Ltd of Loanhead, Midlothian, Scotland. Such motors comprise a rotating shaft unit mounted within a stationary housing. A rotor assembly mounted on the motor shaft contains an even number of radially displaced pistons and crosshead assemblies. The pistons push the crosshead assemblies against the slope of a cam ring to provide the motor driving torque.

Preferably also, the motor running speed is adjustable.

Preferably also, the motor running direction is reversible.

According to a further aspect of the present invention there is provided a top drive comprising: a motor assembly; a drive shaft for connection to a drill string, the drive shaft extending through the motor assembly and being concentric with a rotating part thereof; and means for releasably retaining the drive shaft in said rotating part, such that the drive shaft may be withdrawn from the motor assembly on release of said means.

In use, the drive shaft will typically be connected to a saver sub or the like which is itself connected to the top of the drill string. During drilling or tripping operations, involving adding or removing drill pipe lengths to or from the drill string, the drive shaft may suffer wear and damage and will require repair or replacement from time to time. In conventional top drives this is likely to require dismantling of the top drive. However, in this aspect of the invention all that is required is that the means for retaining the drive shaft in the motor assembly be released, and the drive shaft withdrawn.

Preferably, the means for releasably retaining the drive shaft in the rotating part is in the form of one or more split collars or clamps, conveniently half clamps, for location on one or both of upper and lower portions of the drive shaft, which clamps limit the axial movement of the shaft relative to the rotating part.

Preferably also, the rotating part of the motor assembly is a rotor.

Preferably also, the drive shaft is splined to the rotating part.

According to a still further aspect of the present t invention there is provided a top drive assembly comprising a housing fixed against rotation and a rotating portion for coupling to a drill string, a disc brake assembly being provided for restraining the rotating portion relative to the housing.

In conventional top drives, rotating portions of the top drive assembly may be held against rotation by extendable keys engaging toothed gears. However, this arrangement does not permit fine control of the degree of rotation of the drill string, as is desirable during directional drilling. With the provision of the disc brake assembly of this aspect of the present invention it is possible to closely control the rotation of the drill string.

Preferably, the disc brake assembly is a multi-plate assembly.

Preferably also, the brake assembly is normally on, most preferably the brake assembly being spring applied and hydraulically released.

Preferably also, the brake assembly is mounted on the motor housing and the disc or discs mounted on a rotor.

According to another aspect of the present invention there is provided a top drive comprising a housing fixed against rotation, a rotor assembly, a drive shaft coupled to the rotor assembly and having a threaded end portion for connection to a drill string element, and a clamp restrainable against rotation and for releasably engaging a drill string element, whereby a drill string element held by the clamp may be made up to the drive shaft by rotating the drive shaft relative to the clamp.

This aspect of the present invention obviates the need to provide a separate torque wrench assembly for use in making up drill string elements to the drive shaft, as is provided in conventional top drives. Clearly, the omission of such an assembly in the present invention facilitates provision of a relatively simple and compact top drive assembly.

Preferably, the clamp is selectively rotatable relative to the housing and may be selectively coupled to the housing to prevent such rotation.

Preferably, the clamp is hydraulically actuated.

According to a still further aspect of the present invention there is provided a top drive comprising: a housing fixed against rotation; a rotor assembly; a drive shaft coupled to the rotor assembly and having a lower end for connection to a drill string element ; a rotary joint having a first part mounted to the housing and a second part which is selectively rotatable relative to the first part; a drill string elevator support coupled to the joint; a drill string element engaging clamp coupled to the joint; and one or more guide rods coupled to the second part of the rotary joint for supporting the elevator support and the clamp.

In this aspect of the present invention, torsional loads applied to the clamp may be transferred via the guide rods and the rotary joint to the housing. In existing top drives, transfer of such torsional forces is achieved by an external member extending between the clamp and the housing, which member increases the space required to accommodate the top drive and which is also vulnerable to damage.

Preferably, the pipe handling assembly is coupled to the housing via a rotary joint. Most preferably, the joint may be selectively restrained to prevent relative rotation between the housing and assembly. The joint may be in two parts, one part fixed relative to the housing and the other part fixed against rotation relative to the assembly. The assembly may be rotatably coupled to said other parts via one or more guide rods.

These and other aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a top drive assembly in accordance with a preferred embodiment of the present invention; Figure 2 is a sectional view of the hydraulic motor and drive shaft of the assembly of Figure 1; Figure 3 is a side view of the top drive assembly of Figure 1; Figure 4 is an end view of the top drive assembly of Figure 1; and Figure 5 is a sectional view on line 5-5 of Figure 4.

Reference is first made to Figure 1 of the drawings, which illustrates a top drive 10 in accordance with a preferred embodiment of the present invention. The top drive 10 comprises a motor 12, a main shaft 14 extending through the motor, and a pipe handling assembly 16 coupled to the motor 12 via a rotary joint 18. The pipe handling assembly 16 includes a link hanger 20 with two links 22,23 suspended therefrom for supporting an elevator (not shown), and also a torque cylinder 24.

The motor 12 includes a housing 26 and, in use, the housing 26 is mounted to vertical guide rails (not shown).

In use, the housing 26 is fixed against rotation but may be moved vertically up or down the guide rails. The top drive is suspended from an appropriate main block, not shown, via a swivel (not shown) which is coupled to the upper end of the hollow main shaft 14. The swivel includes a bail suspended from a hook on the main block. In addition, the housing 26 is suspended from the main hook by a chain and a pair of counterbalance cylinders (not shown) which may be utilise to allow for limited vertical movement of the top drive without requiring corresponding movement of the main block, as will be described.

Reference is now made to Figure 2 of the drawings, which illustrates the top drive motor 12 in section. In this embodiment the motor 12 is a hydraulic motor, and in particular a radial piston, multi-lobed cam motor, such as manufactured and supplied by MacTaggart Scott & Co Ltd of Loanhead, Midlothian, Scotland. A rotor assembly 28 mounted on the main shaft 14 contains an even number of radially displaced pistons 30 and cross-head assemblies 32.

The pistons 30 push the cross-head assemblies 32 against the slope of a cam ring 34 to provide the motor driving torque. The main shaft 14 is splined to the rotor assembly 28 at 36 and is retained within the rotor assembly 28 by upper and lower split collars 38,39. The lower split collar 39 co-operates with a shaft shoulder 40 located directly below the splines 36, and is retained in position around the shaft 14 by lifting the shaft relative to the rotor 28, such that the collar 39 is contained within an annular recess 42 in the lower end of the assembly 28. The upper split collar 38 is bolted together, and engages an annular groove in the shaft 44 at the upper end of the rotor assembly 28. Thus, to remove the shaft 14 from the motor 12 all that is required is for the upper split collar 38 to be removed from the shaft 14, and the shaft may then be dropped through the rotor assembly 28.

Figure 2 also illustrates the braking arrangement for the motor 12, which includes brake actuators 46,47 (only two shown). A set of floating discs 48 are mounted on the rotor assembly 28 and are interleaved with discs 50 mounted to the motor housing 26. Each brake actuator 46,47 includes a pin 52 biased to push the discs 48,50 into braking contact by belville springs 54. Each pin 52 also define a piston 56 in communication with a hydraulic fluid source, and by pressurising the hydraulic fluid the pins 52 may be retracted and the brake released.

Reference is now also made to Figures 3,4 and 5 of the drawings which illustrate details of the rotary joint 18, link hanger 20 and the torque cylinder 24. The rotary joint 18 includes two principal parts, an upper part 58 being fixed relative to the housing 26, and a lower part 60 being rotatably mounted thereon, with appropriate bearings 62 between the two parts 58,60. If desired, the parts 58, 60 may be configured to rotate freely relative to one another, or a catch 64 may be actuated to lock the parts 50,60 relative to one another. The lower rotary joint part 60 supports a pair of guide rods 66,67, the lower ends of which are fixed to the torque cylinder 24.

As may be seen in Figure 5 of the drawings, the torque cylinder 24 defines a pair of opposing cylinders 68 each accommodating a piston 70 (only one shown) on the end of which is provided a clamp 72 for engaging a saver-sub 74 mounted on the lower end of the main shaft 14 ; in use, the pin connection on the lower end of the saver-sub 74 will engage with a corresponding box connection on the upper end of the drill string.

When actuated, the clamps 72 engage the saver-sub 74 to prevent relative rotation between the saver-sub 74 and the main shaft 14, as will be described.

Between the lower part of the rotary joint 60 and the torque cylinder 24, the guide rods 66, 67 pass through the e link hanger 20. The link hanger 20 is suspended on the guide rods 66,67 via respective belville spring stacks 76 which normally lift a face of the link hanger 78 clear of a shoulder 80 defined by the lower end of the main shaft 14. However, when any significant load is applied to the link hanger 20, as, for example, when the drill string is suspended from an elevator (not shown) mounted between the lower ends of the links 22,23, the springs 76 are compressed, such that the majority of the load is transferred from the link hanger 20 to the shaft 14, and thus to the main swivel and block.

The links 22,23 are illustrated in the drawings extending vertically downwards from the link hanger 20 however the links may be pivoted, and thus the elevator suspended between the ends of the links moved laterally away from the drilling axis, by operation of respective link tilt mechanisms 82. Each mechanism comprises a piston and cylinder arrangement 84, an arm 86 pivotally mounted on the link hanger 28 and a pivot link 88 between the arm 86 and the respective link 22,23. The piston and cylinder arrangements 84 are double acting such that the elevator may be moved to either side of the drill string axis.

In use, during a drilling operation, the pin at the lower end of the saver-sub 74 is engaged with the box at the upper end of a drill string (not shown). Hydraulic fluid is then supplied to the motor 12 at the appropriate rate and pressure, to drive the rotor assembly 28 clockwise. The rotation of the rotor assembly 28 is transferred directly to the main shaft 14 and the drill string. During normal drilling operations, the upper and lower parts of the rotary joint 58,60 are fixed relative to one another, such that the link hanger 20 and torque cylinder 24 remains stationary relative to the rotating drill string. Also, the link tilt mechanisms 82 are actuated to pivot the links 22,23"backwards"by 30 from the vertical such that the elevator is moved clear of the drill string.

As the drill bit on the lower end of the drill string advances, the top drive 10 will itself move downwardly on the derrick guides. On approaching the lower end of the guides and the drill floor, a mechanical stop in the link tilt mechanism may be released to allow the links 22,23 to be tilted by up to 70 from the vertical, thus allowing the top drive 10 to be moved closer towards the drill floor.

On reaching the drill floor, the fluid pump supplying hydraulic fluid to the motor 12 is shut off. The upper end of the drill string is then set in slips in the drill floor, which support the weight of the drill string.

Pressurised fluid is then supplied to the counterbalance cylinders to lift the bail of the main swivel off the main hook and such that the weight of the top drive 10 is supported by the counter-balance cylinders. The motor 12 is then turned anticlockwise to break-out the saver-sub 74 from the upper end of the drill string. As the connection unscrews, the top drive 10 is lifted on the counterbalance cylinders. The main hook is then raised slightly to engage the swivel bail, and the pressure in the counterbalance cylinders released.

The top drive assembly 10 is then lifted until it is adjacent to the upper end of the drill stands as stored in the drill stand rack. The link tilt mechanism is then actuated to tilt the links 22,23 forwards to allow a derrickman to latch the next drill stand in the elevator.

The top drive 10 is then lifted to bring the weight of the stand onto the elevator and under this additional load the link tilt mechanism allows the elevator to swing back to the drill centre.

The top drive is lifted until the lower end of the stand is level with the upper end of the drill string adjacent the drill floor. The rig floor crew then stab the bottom of the stand into the drill string and make up the connection at the drill floor.

To make up the connection between the top drive and the stand, the top drive 10 is first raised on the counterbalance cylinders to lift the swivel bail off the derrick hook. The top drive is then lowered to stab the pin of the saver sub 74 into the box on the upper end of the stand. A back up tong is attached to the drill pipe held in the slips. The makeup torque is then set on the driller's console and the top drive motor 12 rotated clockwise at slow speed to torque up both the connection between the stand and the drill string and the connection between the stand and the top drive. As the connections are made up, the top drive is pulled down on the counterbalance cylinders. The main hook is then raised to take up the load on the swivel bail and the pressure released from the counterbalance cylinders. The elevator is then tilted backwards, clear of the stand, the slips are released, and drilling may commence once more.

If it should prove necessary to replace the saver-sub 74, sufficient pressure is supplied to the counterbalance cylinders to lift the swivel bail off the main hook.

Hydraulic fluid is then supplied to the piston and cylinder arrangement 68,70 to actuate the clamps 72. By reversing the motor 12, it is then possible to break out the main shaft 14 from the saver-sub 74. As the connection unscrews, the top drive is lifted on the counterbalance cylinders. The hook is then raised to engage the swivel bail and the pressure in the counterbalance cylinders released.

To fit a new saver-sub 74, the sub is first manually lightly made up to the main shaft 14. The clamps 72 are then actuated to grip the sub 74, and the makeup torque set on the driller's console. The motor 12 is then turned slowly clockwise to make up the connection. The clamps 72 may then be released.

During use of the clamps 72, torsional loads experienced by the clamps 72 are transferred through the rods 66,67 to the rotary joint 60 and the motor housing 26.

During tripping out of and into the hole, that is when a drill string is being retrieved from a well or run into an existing well, the operation is similar to that described above, however there is no requirement to makeup the drill string or stands to the top drive, and thus the drill string and stands are solely supported by the elevator and links 22,23 during the operation.

While the drill string or pipe stands are supported by the elevator, the weight of the string or stands must of course be supported by the top drive 10. When there is no load applied to the link hanger 20, the weight of the link hanger is supported by the rotary joint 18, and thus by the motor housing 26: the link hanger 20 is supported on the spring stacks 76 on the guide rods 66,67, which are suspended from the lower part of the rotary joint 60.

However, on experiencing an increased load, the spring stacks 76 compress, such that the link hanger face 78 comes to rest on the drive shaft shoulder 80. Thus, the weight of the drill string or a pipe stand is then supported by the main shaft 14, rather than the motor housing 26.

It will be apparent to those of skill in the art that the above-described embodiment offers numerous avantages over conventional top drives. Notably, the absence of a gear box in the top drive 10 simplifies the construction of the top drive and it is believed that the absence of a gear box will also lead to improved reliability. Further, the absence of a gear box, and also numerous other features of the invention, result in a more compact arrangement which is of particular advantage in portable rigs, in which the working height between the drill floor and the upper end of the derrick may be restricted.

It will also be apparent to those of skill in the art that the above-described embodiment is merely exemplary of the present invention, and that various modifications and improvements may be made thereto without departing from the scope of the present invention.

Claims

CLAIMS 1. A top drive assembly comprising a motor having a rotor and a drive shaft for connection to a drill string, the rotor being concentric with the drive shaft.
2. A top drive assembly comprising a motor having a rotor for coupling to a drill string whereby, in use, the drill string is rotated at the same speed as the rotor.
3. The top drive of claim 1 or 2, wherein the motor is a hydraulic motor.
4. The top drive of claim 3, wherein the motor provides a low speed, high torque output and is coupled directly to the drill string.
5. The top drive of claim 3 or 4, wherein the hydraulic motor is a radial piston, multi-lobed cam motor.
6. The top drive of any of the preceding claims, wherein the motor running speed is adjustable.
7. The top drive of any of the preceding claims, wherein the motor running direction is reversible.
8. A top drive comprising: a motor assembly; a drive shaft for connection to a drill string, the drive shaft extending through the motor assembly and being concentric with a rotating part thereof; and means for releasably retaining the drive shaft in said rotating part, such that the drive shaft may be withdrawn from the motor assembly on release of said means.
9. The top drive of claim 8, wherein the means for releasably retaining the drive shaft in the rotating part is in the form of one or more split collars or clamps for location on one or both of upper and lower portions of the drive shaft, which clamps limit the axial movement of the shaft relative to the rotating part.
10. The top drive of claim 8 or 9, wherein the rotating part of the motor assembly is a rotor.
11. The top drive of any of claims 8 to 10, wherein the drive shaft is splined to the rotating part.
12. A top drive assembly comprising a housing fixed against rotation and a rotating portion for coupling to a drill string, a disc brake assembly being provided for restraining the rotating portion relative to the housing.
13. The top drive of claim 12, wherein the disc brake assembly is a multi-plate assembly.
14. The top drive of claim 12 or 13, wherein the brake assembly is normally on.
15. The top drive of claim 14, wherein the brake assembly is spring applied and hydraulically released.
16. The top drive of any of claims 12 to 15, wherein the brake assembly is mounted on the motor housing and the disc or discs mounted on a rotor.
17. A top drive comprising a housing fixed against rotation, a rotor assembly, a drive shaft coupled to the rotor assembly and having a threaded end portion for connection to a drill string element, and a clamp restrainable against rotation and for releasably engaging a drill string element, whereby a drill string element held by the clamp may be made up to the drive shaft by rotating the drive shaft relative to the clamp.
18. The top drive of claim 17, wherein the clamp s selectively rotatable relative to the housing and may be selectively coupled to the housing to prevent such rotation.
19. The top drive of claim 17 or 18, wherein the clamp is hydraulically actuated.
20. A top drive comprising: a housing fixed against rotation; a rotor assembly; a drive shaft coupled to the rotor assembly and having a lower end for connection to a drill string element; a rotary joint having a first part mounted to the housing and a second part which is selectively rotatable relative to the first part; a drill string elevator support coupled to the joint; a drill string element engaging clamp coupled to the joint; and one or more guide rods coupled to the second part of the rotary joint for supporting the elevator support and the clamp.
21. The top drive of claim 20, wherein the pipe handling assembly is coupled to the housing via a rotary joint.
22. The top drive of claim 21, wherein the joint may be selectively restrained to prevent relative rotation between the housing and assembly.
23. The top drive of claim 21 or 22, wherein the joint is in at least two parts, one part fixed relative to the housing and the other part fixed against rotation relative to the assembly.
24. The top drive of claim 23, wherein the assembly is rotatably coupled to said other parts via one or more guide rods.