SCOPE OF THE INVENTION

The present invention relates to a drill pipe wrench assembly, and more particularly a wrench assembly which includes a wrench head having hydraulically actuable upper pipe gripping and lower pipe clamping units which are moveable relative to each other to couple and uncouple drill pipe, as part of a drill string.

BACKGROUND OF THE INVENTION

Drill pipe wrenches used in connecting and disconnecting lengths of drill pipes as part of a drill string are well known. Conventional drill string wrenches employ pairs of hydraulically actuable tongs which are provided with a gripping chain configured to circumferentially engage and grip a respective drill pipe. To connect or make-up, or disconnect or break-out lengths of drill pipe as part of a drill string the tongs are rotated in opposing directions to tighten or loosen lengths of drill pipe together.

As a result of the significant torque forces employed during the drilling operation itself, it is not uncommon to require separate sets of clamping tongs for make-up and break-out operations, with the break-out tongs employed being comparatively larger to compensate for increase torque forces necessary for performing break-out operations.

The applicant has appreciated that conventional drill pipes present disadvantages in that the rotary movement of the tongs in making up and breaking out the drill string presents a significant impact and safety hazard to rig workers.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a drill string wrench assembly which includes a wrench head having upper pipe gripping and lower pipe clamping units which are activatable to releasably grip the end portions of aligned lengths of drill pipe in the make-up and break-out of a drill string. The gripping and clamping units are preferably coupled to an indexing assembly which maintains their positioning relative to each other, and which allows the gripping unit to be rotated relative to the clamping unit to provide the wrench torque necessary for the coupling and uncoupling of successive lengths of drill pipe. Electric, pneumatic, or more preferably hydraulic drives or actuators are provided which are operable to selectively reciprocally rotate the gripping and clamping units relative to each other to achieve make-up and break-out operation.

In one possible construction, the indexing assembly is provided with a plurality of interlocked stacked plates and/or tracks. The plates/tracks are optionally provided to translate load forces between the gripping and clamping units, whilst permitting sliding movement relative to each other in movement about the drill string axis.

In another embodiment, the indexing assembly is movably coupled to a shuttle frame. The shuttle frame is operable to selectively move the wrench head to and from an operating position, where the pipe gripping and clamping units are in general alignment with the drill string axis and may be operable to engage the adjacent ends of connected drill/drill pipes. In one simplified construction, the shuttle frame may include extendible support arms configured to support and laterally move the wrench head between the operating position and storage position moved a lateral distance spaced therefrom, in a cantilevered manner.

Accordingly, in one aspect the present invention resides in a drill string wrench assembly operable to couple and or uncouple adjacent ends of drill pipe aligned with a longitudinal axis as part of a drill string, the wrench assembly including, an upper gripper unit activatable to releasably grip an end of a first said drill pipe, a pipe clamping unit activatable to releasably retain an end of a second said drill pipe, and an indexing assembly operable to selectively rotate said upper gripper unit relative to said clamping unit in coupling and/or uncoupling said first and second drill pipes, said indexing assembly including an upper mounting plate, a lower mounting plate and a bearing plate at least partially interposed between and engaged by said upper mounting plate and said lower mounting plate, the lower mounting plate mounting the lower clamping unit and for positioning said lower clamping unit in a clamping position engageable with said end of said second drill pipe, the upper mounting plate mounting the upper gripper unit and for positioning the upper gripper unit in a gripping position engageable with said end of said first drill pipe, the upper mounting plate being movable relative said bearing plate to rotate said upper gripper unit radially about said axis along a first radial path of movement, the bearing plate being rotatable relative to said lower mounting plate to move said upper gripper unit radially about said axis along a second radial path of movement, and an actuator assembly operable to selectively rotate the upper mounting plate relative to said bearing plate and the bearing plate relative to said lower mounting plate when said upper gripper unit and said pipe clamping unit are activated.

In another aspect the present invention resides in a drill string wrench assembly for coupling and/or uncoupling a pair of drill pipes coaxially aligned with a drill string axis, the wrench assembly comprising, a gripper unit activatable to selectively engage and grip an end portion of a first said drill pipe, a pipe clamping unit activatable to selectively engage and grip a generally adjacent end portion of the second other drill pipe, and an indexing carriage assembly for positioning each of the gripper unit and the clamping unit in an operating position whereby the first and second drill pipes are engageable respectively by the gripper unit and clamping unit, in the operating position the indexing carriage assembly being further operable to selectively rotate the gripper unit about the axis relative to said clamping unit to assist coupling and or uncoupling of the first and second drill pipes, said indexing assembly including, a lower mounting plate for mounting said lower clamping unit, a bearing plate rotatable relative to said lower mounting plate along a first arcuate path of movement, and an upper mounting plate mounting the upper gripper unit, the upper mounting plate being rotatable relative to the bearing plate along a second arcuate path of movement, and an actuator assembly operable to selectively rotate the upper mounting plate relative to said bearing plate and the bearing plate relative to said lower mounting plate when said upper gripper unit and said pipe clamping unit are activated.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference may now be had to the following detailed description taken together with the accompanying drawings, in which:

Figure 1 shows a perspective view of a drill string wrench assembly in accordance with a preferred embodiment of the invention; Figure 2 shows a schematic side view of the drill string assembly shown in Figure 1 in an operating position in the connection of aligned lengths of drill pipe in the make-up of a drill string;

Figure 3 shows an enlarged perspective view of the wrench head gripping and clamping assemblies used in the drill string wrench assembly of Figure l ;

Figure 4 shows a perspective front view of the gripping and clamping assemblies shown in Figure 3 with protective covers removed;

Figure 5 shows a perspective rear view of the gripping and clamping assemblies shown in Figure 4;

Figures 6A and 6B show a schematic perspective view and exploded view of a gripping unit used in the gripping assembly shown in Figure 4;

Figure 7 shows a horizontal top sectional view of the gripping unit shown in Figure 6A;

Figure 8 shows a breakout perspective view of a clamping unit used in the clamping assembly shown in Figure 4;

Figure 9 shows a sectional view of a spring compensating assembly used in the clamping unit of Figure 8;

Figures 10A and 10B show a sectional and exploded views of an indexing assembly used in the drill string wrench assembly of Figure 1 ;

Figure 1 1 A illustrates schematically the positioning of the gripping assembly relative to the clamping assembly at a home loading position in the make-up of the drill string. Figure 1 1 B shows an enlarged view of the wrench head throat shown in Figure 1 1 A;

Figure 12A illustrates schematically the initial movement of the gripping assembly relative to the clamping assembly in the break-out or make up of the drill string. Figure 12B shows an enlarged view of the wrench head throat shown in Figure 12A;

Figure 13 shows schematically the engagement of the spinner rollers of the gripping assembly with the upper pipe end in threading coupling and decoupling of pipe ends;

Figure 14 shows schematically the relative positioning of the indexing assembly plates in the home position;

Figure 15 shows schematically the relative positioning of the indexing assembly plates in an initial torque staging position;

Figure 16 shows schematically the relative positioning of the indexing assembly plates in following retraction of the primary cylinder to effect torque tightening of drill string pipe ends;

Figure 17 shows schematically the relative positioning of the indexing assembly plates following retraction of the secondary cylinder to effect secondary torque tightening of the drill pipe ends.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference may be had to Figures 1 and 2 which illustrate a drill string wrench assembly 10 in accordance with a preferred embodiment of the invention. As will described, the drill string wrench assembly 10 is used in the connection and disassembly of the adjacent threaded ends 8a, 8b (Figure 3) of successive axially aligned lengths of drill pipe in the make-up and break-out of a drill string 6.

The drill string wrench assembly 10 includes a wrench head 12 which, as will be described, is used to rotatably couple and decouple the pipe ends 8a, 8b, and a frame shuttle 14 which is used to moveably support and selectively move the wrench head 12 between a storage position and an operating position adjacent to and engageable with the drill string 6. In a simplified construction, the support shuttle 14 is provided with a pair of hingely connected, extendible support arms 16a, 16b which are pivotally connected to and slideable along a base support 18. The support arms 16a, 16b mount and suspend the wrench head 12 in a cantilevered arrangement and are moveable between an extended and retracted folded configurations. Hydraulic cylinders (not shown_ are provided to selectively extend or retract the support arms 16a, 16b, moving the wrench head 12 therewith, to or from the operating position during drill string make-up and/or break-out. The pivot connection of the support arms 16a, 16b may further be provided as a vertical slide 24 moveable relative to the base 18 to permit vertical positioning of the wrench head 12 relative to the adjacent drill pipe ends 8a, 8b which are to be coupled/uncoupled.

It is to be appreciated that in a preferred construction, the support arm 16a, 16b are configured to allow the wrench head 12 to be retracted when not in use to the storage position safely or distance spaced from the drill string 6, to minimize interference with rig workers.

Reference may be had to Figures 3 to 5 which illustrate the wrench head 12 used in the coupling and uncoupling the adjacent ends 8a, 8b of axially aligned lengths of drill pipe. Figure 3 shows the wrench head 12 as including an upper pipe spinning and gripping assembly 30, a lower pipe clamping assembly 60 and indexing assembly 100. As will be described, the indexing assembly 100 is used to mount and couple the gripping assembly 30 for movement relative to the clamping assembly 60 about the drill string axis A-Ai. Figure 3 shows each of the gripping assembly 30 and clamping assembly 60 as being provided with a protective cover 32, 62 for substantially shielding drill rig workers from the moving components of the gripping and clamping assemblies 30, 60 for enhanced worker safety. Figures 4 and 5 show the gripping assembly 30 and clamping assembly 60 with the respective safety covers 32, 62 removed for clarity. As shown best in Figures 3 and 5, the gripping assembly 30, clamping assembly 60 and indexing assembly 100 each define a respective forward channel 34a, 34b, 34c which, in an initial pipe loading/unloading positions, each generally align. When so aligned, the channels each form a vertically open U- shaped throat or recess 34 sized to receive the drill pipe ends 8a, 8b to be joined therein, when the wrench head 12 is provided to the operating position.

Figure 5 shows the spinner and gripping assembly 30 as further including a rigid steel frame 36 which defines the upper-most channel 34a, and on which each lateral side of which are mounted a pipe spinner/gripper unit 38a, 38b. Figures 4 and 5 show best each gripper unit 38a, 38b as being formed as modular constructions, and each disposed in a mirror arrangement on opposing sides of the channel 34a. Each gripper unit 38a, 38b includes a pipe spinner drive 40 (Figure 6A) which is in turn mounted for lateral sliding movement relative to an associated slide module 42. Each pipe spinner drive 40 includes a pair of radially spaced toothed spinner rollers 44a, 44b, an electric or servo-electric or hydraulic worm gear drive 46, and a gear transmission 48 for selectively transmitting rotary power from the drive 46, to each of the spinner rollers 44a, 44b. Preferably, with the wrench head 12 in operation position the drive 46 and gear transmission 48 are configured to allow the rotation of the spinner rollers 44a, 44b about respective axis generally parallel to the drill string axis A-Ai at rotations of between about 40 and 125 rpm, depending upon the diameter of the pipe ends 8a, 8b, and more preferably provide a rotational torque capacity of up to 2000 ft-lbs.

The spinner rollers 44a, 44b are preferably provided as a pair of axially mounted gear fluted rollers which are rotatably affixed to a respective bearing mounted shaft 45 (Figure 6B). The upper end of the shaft 45 includes suitable gearing, such as a spur gear, provided in meshing engagement with the gear transmission 48. Most preferably, the gear transmission 48 is configured to translate motor horsepower at a selected ratio. Although not essential, the gear transmission 48 may be provided with a suitable braking unit (not shown), or more preferably the drive 46, due to its mechanical worm gear operation, is operable as a braking unit and to prevent back driving of the spinner rollers 44a, 44b. The braking operation of the drive 46 or braking unit is operable to allow the locking of the spinner rollers 44a, 44b in place relative to the pipe end 8a during pipe torqueing operations. In another possible configuration, the spinner rollers 44a, 44b may be provided with an

electromagnetic lock mechanism that prevents roller rotation during operation of the wrench head 12 in performing final pipe torque wrenching and unwrenching operations. It is to be appreciated however, that a variety of braking systems may alternatively be used.

As shown best in Figures 6A, 6B and 7, the pipe spinner drive 40 of each spinner gripper unit 38 is slideably mounted on the end of a piston 48 of a hydraulic cylinder 50 by way of a spring compensating assembly 52 which is slideably received within the slide module 42.

The spring compensating assembly 52 is shown best in Figure 6B as including a series of resiliently compressible helical springs 56 which may be aligned in series. The springs 56 are positioned to resiliently bias the pipe spinner drive 40 within the slide module 42 forwardly in a lateral direction towards the drill string axis A-Ai and into contact with the upper most drill pipe end 8a. In this manner, with the wrench head 12 in the operating position and the pipe ends 8a, 8b received in the recess 34, the activation of the hydraulic cylinders 50, advance the associated pipe spinner rollers 44a, 44b towards the axis A-Ai. As piston 48 moves forwardly, the associated rollers 44a, 44b engage the radial sides of the pipe end 8a on each side of the pipe. The spring compensating assembly 52 allows for rearward sliding displacement of the pipe spinner drive 40 relative to the slide frame 42 to compensate for any over lateral pressures supplied by the hydraulic cylinder 50.

It is to be appreciated that the gripper units 38a, 38b and slide modules 42 are provided in an opposing, trapped linear guide arrangement. As a result, the forward movement of the pipe spinner drives 40 of the respective gripper units 38a, 38b advantageously traps the targeted pipe end 8a between the associated pairs of rollers 44a, 44b of each gripper unit 38a, 38b. The helical springs 56 are further selected with a compression strength selected to resiliently bias the rollers 44a, 44b into frictional contact with the pipe end 8a. In this manner, once so engaged, the spinner drive 40 may be actuated in a forward or reverse direction to rotate the pipe end 8a about the drill string axis A-Ai to achieve the initial threaded coupling and final threaded uncoupling of the pipe ends 8a, 8b.

In a preferred construction, the compensating assembly 52 is provided with series of aligned helical springs 56 are secured by way of a collar 57 to the piston 48. Although not essential, most preferably the springs 56 are provided to allow for the spinner rollers 44a, 44b to contact and engage the drill pipe end 8a with at least about 5,000 lbs roller pressure, and preferably at about 10,000 to 12,000 lbs roller pressure. Optionally, a sensor (not shown) may be provided to provide a user with a linear measurement of the roller 44/pipe end 8a compression force. Figure 6B further shows the each gripper units 38 as including a laterally displaceable gripping ram 58. The gripping ram 58 is slidably received in the slide frame 42 and is selectively actuable by the pressurization of the piston 48 into frictional contact with the pipe end 8a to effect full clamping of the gripper unit 38 and pipe 8 through slide frame 42 into frame 36.

Figures 4 illustrates best the clamping assembly 60 used with the presenting invention. The clamping assembly 60 includes a rigid steel clamping assembly frame 63 which defines the lowermost channel 34b forming the bottom portion of the U- shaped recess 34, and a pair of pipe clamping units 64a, 64b. Each of the pipe clamping units 64a, 64b shown best in Figures 8 and 9 are provided as modularly constructed units which are arranged in an opposing mirror orientation on each side of the channel 34b. Each pipe clamping unit 64 includes a V-shaped clamping block 66 which is secured to the end of a piston 68 of a hydraulic cylinder 70 for sliding lateral movement towards or from the axis A-Ai within a slide frame 72. The clamping block 66 is in turn mounted for vertical movement as a unit relative to the slide frame 72 within a vertical compensating frame 74. As shown best in Figure 9, the vertical compensating frame 74 includes pairs of resiliently compressible springs 76a, 76b which resiliently bias the clamping block 66 to a centred position within the slide frame 72. In a simplified construction, the clamping block 66 is mounted to a float block 78. The springs 76 are provided as pairs of disks on the top and bottom of the float block 78 and are slip-fit mounted on respective keeper shafts 80. More preferably, the springs 76 are provided as a number of series mounted disk spring washers which allow for vertical floating movement of the float block 78 relative to a centered rest position of between about 0.5 and 1 inches, and preferably about .75 inches, during drill string make-up and break-out connection processes.

Reference may be had to Figures 10A and 10B which illustrate the indexing assembly 100 in accordance with a preferred embodiment of the invention. The indexing assembly 100 is shown best in Figure 10B as including a rotary carousel 102 which is formed having a three plate construction, and which includes an upper plate 104, a lower plate 108 and a bearing plate 106 which is interposed between the plates 104, 108 for transmitting load forces therebetween. Figures 10A and 10B further show best the indexing assembly 100 as having a primary hydraulic cylinder 1 10 and a secondary hydraulic cylinder 1 12 which, as will be described, are operable to selectively rotate the plates 104, 106, 108 relative to each other to effect the torque wrenching the drill pipe ends 8a, 8b in breakdown and final assembly of the drill string 6.

As shown best in Figure 4 the upper and lower carousel plates 104, 108 are used to respectively mount the gripper and clamping assemblies 30, 60. The plates 104, 106, 108 each respectively define a forward recess which, when the plates 104, 106, 108 are moved to an initial loading/unloading position shown in Figures 1 1A and 1 IB, align with each other as the channel 34c, and the channels 34a, 34b to define the mid-portion of the U-shaped recess 34.

The bottom-most bottom plate 108 is used to mount the wrench head 12 to the ends of the support arms 16a, 16b for movement into and from the operating position. The clamping assembly 60 is fixedly mounted to the underside of the lower plate 108 of the rotary carousel 102. It is to be appreciated, that the vertical compensating frame 74 of each clamping unit 64a, 64b allows for vertical movement of the clamping blocks 66 relative to the clamping assembly frame 63. In use, the clamping blocks 66 remain stationary once clamped to the drill string 8, and the remainder of the wrench head 12 thus moves vertically up or down. This furthermore allows the clamping blocks 66 to move vertically up or down relative to the spinner gripper units 38a, 38b as the drill pipe ends 8a, 8b move relative to each other as they are threadedly coupled and decoupled. In particular, the pair of springs 76a, 76b compensate for the relative change in position between the gripped drill pipe ends 8a, 8b, as the pipe end 8a is threadedly engaged with or disengaged from the end 8b as it is rotated by the spinner drives 40 of the gripper units 36a, 36b when lengths of pipes are connected/disconnected.

Most preferably, in the three plate carousel construction the upper and lower plates 104, 108 are provided as cavity plates which define opposing arcuately extending recesses 1 18a, 1 18b therebetween, and which is sized and configured to receive and retain the bearing plate 106 therebetween. The plates 104, 106, 108 are movably coupled to each other by a series of arcuate interlocking stabilizer plates 104a/b, 106a/b, 108a/b which are arranged for concentric positioning about the axis A-Ai . The plates 104, 106, 108 are constructed whereby in the sandwiched plate arrangement shown in Figure 10, the plates 104, 106, 108 form a generally planar bearing surface in both a radial (1 18a, 1 18b) and thrust 106a, 106b directions. The plates 104, 106, 108 are further slideably connected so as to be actuable in movement to rotate the upper plate 104 relative to the lower plate 108 radially relative to each other. Most preferably, when the wrench head 12 is in the operating positon, the upper plate 104 is movable relative to the lower plate 108 radially about the axis A-Ai through between 0° and 90° movement, or more, and preferably about 72° movement.

Figure 5 shows best the secondary servo-electric or hydraulic cylinder 112 as connecting the upper plate 104 to the bearing plate 106 to permit its relative rotary movement thereabout. Similarly, the primary servo-electric or hydraulic cylinder 1 10 is fixed to the lower plate 108 and moveably connects the bearing plate 106, and with it the upper plate 104 to effect pivotal movement of the bearing place 106 relative to the fixed lower plate 108. Most preferably, each of the servo-electric or hydraulic cylinders 1 10, 1 12 are individually controlled whereby movement between extended and retracted position effects 0° through 36° rotational movement of each of the upper plate 104 and bearing plate 108, for a total wrenching torque of 72°. By the use of the primary and secondary hydraulic cylinders 1 10, 1 12, the wrench head 12 preferably provides a drill string make-up torque capability of between about 3,000 to 163,000 ft-lbs, and a break-out torque of up to 198,000 ft-lbs, at nominal hydraulic pressures of up to 3,000 psi.

The use of the drill string wrenching assembly 10 in performing make-up operations is shown best with reference to Figures 11 to 17, and which illustrate the positioning of the apparatus in achieving a final torque tightening or connecting motion.

With the gripping assembly 30, clamping assembly 60 and index assembly 100 oriented in an initial home load/unload position such that the U-shaped channels 34a, 34b, 34c each align in the manner shown in Figure 1 1A, the support frame shuttle 14 is activated. The support arms 16a, 16b are extended to position the drill string wrench head 12 in the operating position shown in Figure 2, so that the pipe end 8b is moved into alignment with the drill string axis A-Ai, with the lower pipe end 8b of the drill string 6 received in the throat of the U-shaped recess 34 generally interposed between the opposing clamping blocks 66.

An overhead gantry crane (not shown) is used to move the lower end 8a of a next pipe to be joined to the drill string 6 into the throat of the recess 34, in co-axial alignment the pipe end 8b and axis A-Ai, and interposed between the gripper units 36a, 36b as shown in Figures 1 1 A and 1 IB.

With the drill pipe ends 8a, 8b so positioned, the servo-electric or hydraulic cylinders 70 of the clamping units 64a, 64b are each simultaneously activated to move the clamping blocks 66 inwardly towards each other into engaging contact with the radially opposing slides of the drill pipe end 8b as shown in Figures 12A and 12B. The servo-electric or hydraulic cylinders 70 are actuated to advance the V-shaped clamping blocks 66 of each clamping unit 64a, 64b simultaneously towards and against the pipe 8b. The activation of the servo-electric or hydraulic cylinders 70 and extension of the clamping blocks 66 towards the drill string axis A-Ai centres and traps the targeted lower pipe end 8b in axial alignment relative to the drill string axis

The servo-electric or hydraulic cylinders 50 of each of gripper units 38a, 38b are next concurrently activated to move the drive rollers 44a, 44b of each pipe spinner drive 40 laterally towards the axis A-Ai, and into engaging contact with the radially opposing sides of the pipe end 8a as shown in Figure 13. The drives 46 are then activated to rotate each pipe spinner drive 40 whereby engagement with the spinner rollers 44a, 44b spins the pipe end 8a about the axis A-Ai to effect its initial threaded coupling with the pipe end 8b. As the drill pipe end 8a threadedly moves into the pipe end 8b, the entire gripping assembly 30 and clamping assembly frame 63 moves downwardly relative to the V-shaped clamping blocks 66 against the bias of the compensating assembly 74. As the pipe end 8a is rotated, the primary cylinder 1 10 is extended to rotate the upper plate 104 and bearing plate 106 in reverse counter clockwise movement about the axis A-Ai to an initial staging position for torqueing shown in Figure 15. Preferably, the drives 46 rotate the spinner rollers 44a, 44b until a predetermined stall condition is achieved, signalling the initial tightening. Once in the initial staging position, the piston 48 is fully extended to move the gripping ram 58 of each gripper unit 38 into engagement with the pipe end 8a.

To make pipe connection, the primary cylinder 1 10 retracts to rotate the bearing plate 106 and upper plate 104 together up to 36° rotational movement from the position shown in Figure 15 towards the home position as shown in Figure 16. If torque forces are sensed and determined to meet preselected pipe torque requirements, then the cycle is complete and the cylinder rod 48 retracts fully. The spinner rollers 44a, 44b and gripping ram 58 are removed from engagement with the drill string 6 and the wrench head 12 is returned to the home position by the retraction of cylinder 1 10.

If the sensed required torque has not been reached, the secondary cylinder 1 12 retracts, moving the upper plate 104 relative to the bearing plate 106 and lower plate 108 about the axis A-Ai to the position shown in Figure 17. The upper plate 104 is rotated about the axis A-Ai up to a maximum of 36°, or until the predetermined tightening torque is sensed.

The wrench head 12 is then undamped from the drill string 8 and returned to the home position.

The break-out of drill pipes from the drill string 6 is achieved in the opposite manner. To loosen or separate connected drill pipe ends 8a, 8b, the lower clamping assembly 60 is activated to simultaneously move the V-shaped clamping blocks 66 of · each of clamping unit 64a, 64b into engagement with the drill pipe end 8b. The secondary cylinder 1 12 is retracted to mover the upper gripping units 38a, 38b to the position shown in Figure 17. The gripper units 38a, 38b are activated to concurrently move the spinner drive rollers 44a, 44b of each spinner drive 40 into engagement with radial sides of the adjacent next upper pipe end 8a, and the rollers 44a, 44b are locked in place with the gripper ram 58 is laterally moved against the pipe end 8a.

To effect the wrench torque necessary to decouple the drill pipe end 8a from the drill pipe end 8b, the secondary cylinder 1 12 is extended, and most preferably, both the primary and secondary cylinders 1 10, 1 12 are extended in unison moving the plates 104, 106 relative to the plate 108 in the opposite direction radially about the axis A-Ai to at least the position of Figure 12, and preferably to the position of Figure 15.

Following initial decoupling, the worm gear drive 46 of each spinner drive 40 are activated to rotate the rollers 44a, 44b in the uncoupling direction, to complete disengagement of the connected pipe ends 8a, 8b.

The applicant has appreciated that the configuration of the drill string wrench assembly 10 provides various advantages. In particular, the use of the self-centring V-shaped clamping blocks 66 and radially separated pairs of gripping rollers 44a, 44b of the clamping assembly 60 and gripping assembly 30 allow the wrench head 12 to be safely used with drill pipes having a variety of different diameters.

Although the detailed description describes and illustrates various preferred embodiments, the invention is not strictly limited thereto. Many modifications and variations will occur to persons skilled in the art. For a definition of the invention, reference may be had to the appended claims.