Patent Publication Number: US-10781640-B2

Title: Rotary cutting tool

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present document is based on and claims priority to GB Non-Provisional Application Serial No.: 1509607.6, filed Jun. 3, 2015, which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     In the context of drilling and working within an underground borehole, a reaming tool for enlarging the borehole may incorporate blocks which extend axially, face generally radially outwardly towards the wall of the borehole and carry cutters for removing material from the borehole wall to increase the diameter of the hole. Some reamers have blocks which are expandable outwardly from the tool body, enabling the reamer to be inserted into the borehole to a desired depth, and then expanded to enlarge the hole from that depth onwards. Expandable reamers are illustrated by U.S. Pat. Nos. 6,732,817 and 7,954,564. In other reamers the blocks are fixed to the central body of the tool but project outwardly from it. An illustration of a block which is integral to the body and projects from it is seen in U.S. Pat. No. 6,386,302. 
     Whether expandable from the tool body or fixed at positions projecting from it, there may be a plurality of cutter blocks distributed azimuthally around the tool axis. 
     It is normal practice that a rotary cutting tool such as a reamer can be incorporated in a drill string extending from surface or alternatively attached to coiled tubing extending from the surface. Drilling fluid is pumped down the drilling string or coiled tubing to the reamer tool and returns to the surface outside tubing with cuttings entrained in the returning fluid. 
     As is shown by U.S. Pat. Nos. 6,732,817 and 7,954,564, it is known for the outwardly facing parts of a cutter block to incorporate a channel which extends in the axial direction over part or all of the axial length of a cutter block. Such a channel can provide a pathway for the flow of drilling fluid returning towards the surface from below the cutter block. Flow along such a channel in the outer face of a block can enhance cooling of the block by the drilling fluid (because flow along the channel is additional to flow past the sides of the block) and can assist the removal of cuttings which have been formed at the leading edge of the block. Since such a channel provides a pathway for cuttings, it is sometimes referred to as a “junk slot”. 
     As shown by U.S. Pat. Nos. 6,732,817 and 7,954,564, such a channel may also provide space for the insertion of a second row of cutters, behind a row of cutters which are at the leading edge as the tool rotates. 
     A desirable characteristic for a reamer, and indeed for many rotary cutting tools used in a borehole, is smooth rotation with the tool in its intended position centred on the borehole axis. In practice there can be unwanted vibration and a phenomenon referred to as “whirling” which is an undesirable motion in which tool axis does not remain centred within the hole but instead moves around the hole axis while the periphery of the tool makes repeated impacts against the wall of the hole. 
     SUMMARY 
     This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. 
     One aspect of the present disclosure provides a downhole cutting tool for enlarging the diameter of a hole, comprising a rotary tool body with at least one support member which carries cutters and which projects or is extensible from the tool body, wherein a radially outward facing part of the support member includes a channel for fluid flow which runs generally axially along the support member and wherein at least a rotationally trailing edge of the channel extends along the support member in a direction or succession of directions which are inclined relative to the tool axis. 
     Setting part or all of the channel at an angle inclined to the tool axis is a measure to mitigate vibration and whirling as the tool rotates. It reduces the amount of straight channel edge which is parallel to the tool axis. We have recognised that if a straight edge parallel to the tool axis strikes or snags on the borehole wall as the tool is rotating, it can transiently become a pivot axis around which the tool turns bodily, thereby initiating or perpetuating a whirling motion of the tool and/or increasing vibration. 
     The channel may be implemented so that the rotationally leading and trailing edges of parts of the channel are both inclined relative to the tool axis. However, the rotationally trailing edge of the channel is of course a leading edge of those parts of the support member which follow the channel and this edge presents more significant risk of impact to the borehole wall than does the leading edge of the channel. Consequently, the channel may be implemented such that some or all parts of the rotationally trailing edge are inclined relative to the tool axis while the corresponding parts of the leading edge are parallel to the tool axis or inclined at a smaller angle. Such an arrangement may give a channel which varies in width whereas in other embodiments parts of the channel which have the trailing edge inclined relative to the tool axis are constant width so that the leading edge is similarly inclined relative to the tool axis. 
     The trailing edge, or both edges, of the channel may comprise one or more straight sections inclined to the tool axis, one or more curved sections in which at least part of the curved section is inclined to the tool axis, or some combination of these. It is possible that the trailing edge, or both edges, of the channel will include one or more portions which do run parallel to the tool axis but these may be sufficiently short that at least 75% of the overall length of the trailing edge, or both edges, of the channel is inclined relative to the tool axis. The angle of inclination to the tool axis may be no more than 45° possibly not more than 35°. More specifically, at least 75% of the length of the trailing edge, or both edges, of the channel may be inclined at an angle of at least 10° and possibly at least 15° up to 35° or 45° relative to the tool axis. 
     In many embodiments the channel will extend from one axial end of the support member to the other axial end of the support member and will change inclination one or more times so that the channel keeps within the width of the support member. The support member for cutters may include one or more surfaces positioned to contact the borehole wall which has been cut by the cutters and the channel may extend across such surfaces, where its edges will also be edges of surfaces intended to contact the borehole wall. The support member may take the form of a block to which cutters are attached. 
     In some embodiments the rotary tool is a reamer which can be used to enlarge a borehole by cutting formation rock from a borehole wall. Such a tool may have cutters with polycrystalline diamond at the hard cutting surface. In other embodiments the rotary tool is a mill to remove metal from the interior wall of tubing secured in a borehole, possibly removing the entire thickness of the tubing wall from the interior so as to destroy the tubing. A mill may have cutters of tungsten carbide or other hard material which is not diamond. 
     In another aspect, there is disclosed here a method of enlarging a borehole or removing tubing secured in a borehole, comprising attaching a tool as stated above to tubing, inserting the tool and attached tubing into the hole, and rotating the tool to enlarge the diameter of the borehole or comminute the tubing fixed in the borehole, while flowing fluid from the surface to the tool and returning fluid from the tool to the surface while at least part of the fluid flow travels along the channel of the at least one support member. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic, cross-sectional view of a drilling assembly in a borehole; 
         FIG. 2  is a cross-sectional elevation view of one embodiment of expandable reamer, showing its expandable blades in collapsed position; 
         FIG. 3  is a cross-sectional elevation view of the expandable reamer of  FIG. 2 , showing the blades in expanded position; 
         FIG. 4  is a perspective view of a cutter block for the expandable reamer of  FIGS. 2 and 3 ; 
         FIG. 5  is a side view of the cutter block of  FIG. 4 , shown in operation in a borehole; 
         FIG. 6  is a view in the direction shown by arrow VI in  FIG. 5 , looking on to the radially outer face of the cutter block of  FIGS. 4 and 5 ; 
         FIG. 7  is a cross-section on the line VII-VII of  FIG. 6 ; 
         FIG. 8  is a similar cross-section to  FIG. 7  showing a modification; 
         FIG. 9  is a similar view to  FIG. 6 , showing modifications; 
         FIG. 10  is a view onto the upper part of the radially outer face of a cutter block similar to that in  FIG. 6 , showing another modification; 
         FIG. 11  is a side view onto the upper part of a cutter block, showing another possible modification; 
         FIG. 12  is a view onto the upper part of the radially outer face of the cutter block of  FIG. 11 ; 
         FIG. 13  is a view onto the radially outer face of another embodiment of cutter block; and 
         FIG. 14  shows the radially outward faces of three cutter blocks of a reamer, illustrating a further possibility. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an exemplary drilling assembly which includes an expandable under-reamer  22 . A drill string  12  extends from a drilling rig  10  into a borehole. An upper part of the borehole has already been lined with casing and cemented as indicated at  14 . The drill string  12  is connected to a bottomhole assembly  18  which includes a drill bit  20  and an under-reamer  22  which has been expanded beneath the cased section  14 . As the drill string  12  and bottomhole assembly  14  are rotated, the drill bit  20  extends a pilot hole  24  downwards while the reamer  22  simultaneously opens the pilot hole  24  to a larger diameter borehole  26 . 
     The drilling rig is provided with a system  28  for pumping drilling fluid from a supply  30  down the drill string  2  to the reamer  22  and the drill bit  20 . Some of this drilling fluid flows through passages in the reamer  22  and flows back up the annulus around the drill string  12  to the surface. The rest of the drilling fluid flows out through passages in the drill bit  20  and also flows back up the annulus around the drill string  12  to the surface. 
     As shown, the distance between the reamer  22  and the drillbit  20  at the foot of the bottom hole assembly is fixed so that the pilot hole  24  and the enlarged borehole  26  are extended downwardly simultaneously. It would be possible to use the same reamer  22  attached to drillstring  12  (but without the drill bit  20  and the part of the bottom hole assembly  18  below the reamer  22 ) in similar manner to enlarge an existing borehole. 
     Referring now to  FIGS. 2 and 3 , one embodiment of expandable reaming tool is shown in a collapsed position in  FIG. 2  and in an expanded position in  FIG. 3 . 
     This expandable tool comprises a generally cylindrical tool body  106  with a central flowbore  108  for drilling fluid. The tool body  106  includes upper  110  and lower  112  connection portions for connecting the tool into a drilling assembly. Intermediately between these connection portions  110 ,  112  there are three recesses  116  formed in the body  106  and spaced apart at 120° intervals azimuthally around the axis of the tool. 
     Each recess  116  accommodates a cutter block  122  in its retracted position. The three cutter blocks are similar in construction and dimensions. The outer face  129  of the cutter block  122  is indicated without detail in  FIGS. 2 and 3 . 
     The cutter block  122  has side faces with protruding ribs  117  which extend at an angle to the tool axis. These ribs  117  engage in channels  118  at the sides of a recess  116  and this arrangement provides a pathway which constrains motion of each cutter block such that when each block  122  is pushed upwardly relative to the tool body  106 , it also moves radially outwardly from the position shown in  FIG. 2  to an expanded position shown in  FIG. 3  in which the blocks  122  project outwardly from the tool body  106 . It will be appreciated that each cutter block is constrained by the ribs  117  in channels  118  to move bodily upwardly and outwardly without changing its orientation (i.e. without changing its angular position) relative to the tool axis. 
     A spring  136  biases the blocks  122  downwards to the retracted position seen in  FIG. 2 . The biasing spring  136  is disposed within a spring cavity  138  and covered by a spring retainer  140  which is locked in position by an upper cap  142 . A stop ring  144  is provided at the lower end of spring  136  to keep the spring in position. 
     Below the moveable blocks  122 , a drive ring  146  is provided that includes one or more nozzles  148 . An actuating piston  130  that forms a piston cavity  132  is attached to the drive ring  146 . The piston  130  is able to move axially within the tool. An inner mandrel  150  is the innermost component within the tool, and it slidingly engages a lower retainer  170  at  172 . The lower retainer  170  includes ports  174  that allow drilling fluid to flow from the flowbore  108  into the piston chamber  132  to actuate the piston  130 . 
     The piston  130  sealingly engages the inner mandrel  150  at  152 , and sealingly engages the body  106  at  134 . A lower cap  180  provides a stop for the downward axial movement of piston  130 . This cap  180  is threadedly connected to the body  106  and to the lower retainer  170  at  182 ,  184 , respectively. Sealing engagement is provided at  586  between the lower cap  180  and the body  106 . 
     A threaded connection is provided at  156  between the upper cap  142  and the inner mandrel  150  and at  158  between the upper cap  142  and body  106 . The upper cap  142  sealingly engages the body  106  at  160 , and sealingly engages the inner mandrel  150  at  162  and  164 . 
     In operation, drilling fluid flows downwards in flowbore  108  along path  190 , through ports  174  in the lower retainer  170  and along path  192  into the piston chamber  132 . The differential pressure between the fluid in the flowbore  108  and the fluid in the borehole annulus surrounding tool causes the piston  130  to move axially upwardly from the position shown in  FIG. 2  to the position shown in  FIG. 3 . A portion of the flow can pass through the piston chamber  132  and through nozzles  148  to the annulus as the cutter blocks start to expand. As the piston  130  moves axially upwardly, it urges the drive ring  146  axially upwardly against the blocks  122 . The drive ring pushes on all the blocks  122  simultaneously and moves them all axially upwardly in recesses  116  and also radially outwardly as the ribs  150  slide in the channels  118 . The blocks  122  are thus driven upwardly and outwardly in unison towards the expanded position shown in  FIG. 3 . 
     The movement of the blocks  122  is eventually limited by contact with the spring retainer  140 . When the spring  136  is fully compressed against the retainer  140 , it acts as a stop and the blocks can travel no further. There is provision for adjustment of the maximum travel of the blocks  122 . This adjustment is carried out at the surface before the tool is put into the borehole. The spring retainer  140  connects to the body  106  via a screwthread at  186 . A wrench slot  188  is provided between the upper cap  142  and the spring retainer  140 , which provides room for a wrench to be inserted to adjust the position of the screwthreaded spring retainer  140  in the body  106 . This allows the maximum expanded diameter of the reamer to be set at the surface. The upper cap  142  is also a screwthreaded component and it is used to lock the spring retainer  140  once it has been positioned. 
       FIGS. 4 to 7  show a cutter block in more detail. The side face shown by  FIG. 5  is the leading face in the direction of rotation of the tool. As already mentioned, the cutter block is a steel block with inclined ribs  117  on each side face. Ends  124  of ribs  117  are seen in  FIG. 6 . The inclined ribs are not seen in  FIG. 7 . Part of the wall of the tool body  106  is seen in  FIG. 5 . 
     The outer part of the block  122  has upper  201  and lower  203  cutting regions provided with cutters  205 ,  207 . The upper and lower cutting regions  201 ,  203  are curved as shown by  FIG. 5  so that the cutters  205 ,  207  in these regions are positioned radially outwards from the tool axis by amounts which are least at the top and bottom ends of the block  122  and greatest adjacent the middle section which includes stabilising pad  211 . This stabilising pad  211  has a generally smooth, part-cylindrical outward surface positioned to face and slide over the borehole wall. To increase its resistance to wear, the stabilising pad may have pieces of harder material embedded in it and lying flush with the outward facing surface of the pad  211 . 
     The cutters  205 ,  207  are polycrystalline diamond cutters (abbreviated to PDC cutters) which have a disc of diamond particles embedded in a binder matrix at one end of a cylindrical body of hard material which may be a mass of tungsten carbide particles embedded in a binder material. The cutters are secured in pockets formed in the steel block  122  so that the disc of diamond particles is exposed as a hard cutting surface. Securing the cutters  205 ,  207  in the pockets in the block  122  may be done by brazing although it is also possible for cutters to be secured mechanically in a way which allows them to rotate around their own axis thereby distributing wear. It has been normal practice for the hard disc of diamond crystals to provide a flat cutting surface as shown in the drawings. However, other shapes including cones can be used for the hard surface of a cutter. 
     When the reamer is advanced downwardly within a hole to enlarge the hole, it is the curved lower cutting regions  203  of its blocks  122  which do the work of cutting through formation rock. This takes place in  FIG. 1  as the drill string  12  is advanced downwardly. It is normal practice for most of the work done by reamer to be done as the reamer is advanced downwardly. However, the enlarged portion of the borehole can also be extended upwardly if required, using the upper cutting regions  201  on the blocks  122  to remove formation rock while pulling upwardly on the drill string  12 . 
     In the upper cutting region  201 , the PDC cutters  205  are mounted so as to be partially embedded in the steel block  122  and project radially outwardly from the curved face  213  of the block. 
     In the lower cutting region, a radially outer margin of the side face is inclined as a bevel  204  along the outer face of the block. The hard faces of the PDC cutters  207  are exposed within the area of this bevel  204 . The block  122  is also formed with a succession of radially outward-facing surfaces  217  each located circumferentially behind and extending axially above a cutter  207 . As best seen from  FIG. 4  and  FIG. 7 , each surface  217  is at the same radial distance from the tool axis as the radially outer extremity  209  of its associated cutter  207  and so as indicated by  FIG. 7  each surface  217  slides over the formation rock which has been cut by its associated cutter  207 . The stabilising pad  211  is at the same radial distance from the tool axis as the extremities of the topmost three cutters  207 . 
     The cutting action of the reamer as it rotates and advances downwardly is illustrated in  FIG. 5  in which the downward direction is indicated by arrow D. The original borehole wall is indicated at  214 . The cutters  207  cut material from the borehole wall, progressively increasing the borehole diameter to the finished enlarged diameter defined by the topmost three of the cutters  207 . The stabilising pad  211  makes sliding contact with the enlarged borehole wall at this diameter. 
     It can be seen that the upper cutting region  201  curves away from the enlarged borehole wall  215  so that the upper cutters  205  do not contact the borehole wall while the reamer is advancing downwardly and there is a space  219  between the upper cutting region  201  and the borehole wall  215 . 
     The block  122  has a channel  220  which runs along the length of the block from an inlet opening  222  at the lower end of the block  122  to an outlet opening  224  at the upper end of the block. While the reamer is in operation, some of the drilling fluid travelling upwardly around the drill string enters the channel  220  at its lower opening  222  and flows along this channel towards the upper outlet  224 , cooling the block  122  as it does so. The position of the floor of this channel is indicated in  FIG. 5  by broken line  226 . As shown by  FIG. 7 , the channel intersects each surface  217 , and likewise the stabilising pad  211 , at a leading edge  228  and trailing edge  229 . 
     Although this channel  220  extends generally axially along the block  122 , most of it is made up by three portions  230  which are inclined at an angle of approximately 25° to the tool axis. The inclined portions  230  are connected by portions  232  which are parallel to the tool axis but are much shorter than the inclined portions  230 . Consequently, the length of channel  220  which is parallel to the tool axis is small. This reduces the risk that an edge of the channel, parallel to the tool axis, will snag on the wall of the bore hole and become a pivot axis, thereby initiating or sustaining a whirling motion of the rotating tool. 
       FIG. 8  shows a modification. The trailing edge  229  where the channel intersects the outer surfaces  217  and stabilising pad  211  is formed with a radius rather than with the right angle shown in  FIG. 7 . This further reduces any possibility for the edge  229  to snag on the rock formation. Possible further variations, not used in  FIG. 8 , would be for the leading edge  228  of the channel, and/or the trailing edges  218  of the outer surfaces  217  to be formed with a radius rather than a right angle. 
       FIG. 9  shows a channel  240  with different geometry. In place of inclined straight portions  230  and  232 , the channel  240  is made up of a sequence of curved portions. A large part of each of these curved portions is at an angle of 15° or more to the tool axis. 
       FIG. 9  also shows the cutters  207  of the lower cutting region  203  with differences in circumferential position on the block  122  so that they are not aligned in a straight row. Their cutting faces therefore do not provide a single common line parallel to the tool axis. Of course this arrangement of the cutters  207  could also be used with a channel composed of straight portions  230  and  232  as shown in  FIG. 6 . 
       FIG. 10  shows another possible modification to the cutter block of  FIGS. 4 to 7 . In the lower cutting region  203 , the channel  220  is just the same as shown in  FIG. 6 . The modification shown by  FIG. 10  is that the channel does not extend over the upper cutting region  201 . Instead one of the inclined portions  230  leads across the stabilising pad  211  to an outlet opening  244  at the rotationally trailing face of the cutter block. When the reamer is in use, drilling fluid will enter the channel through the inlet opening  222  at the lower end of the block and flow up to the outlet opening  244 , thus cooling the lower cutting region  203  and the stabilising pad  211  which are the parts of the block where heat is generated while the reamer is being advanced axially downwardly. 
       FIGS. 11 and 12  show another possible modification to the cutter block of  FIGS. 4 to 7 . In the lower cutting region  203  the channel is just the same as shown in  FIG. 6  with the floor  226  of the channel at approximately constant distance radially inwardly from the outer face of the cutter block as shown by the broken line  226  in  FIG. 5 . The channel runs through the stabilising pad  211  with the floor  226  of the channel parallel to the surface of the stabilising pad  211  and so also parallel to the tool axis as is the case in the block of  FIGS. 4 to 7 . However, in the modification shown by  FIGS. 11 and 12 , the floor  226  (shown as a broken line) of the channel  220  continues parallel to the tool axis in the region above the stabilising pad  211 , as indicated at  246 , until it intersects the curved surface  213  of the upper cutting region  201 . The channel thus finishes before it reaches the upper end of the block  122 . Drilling fluid flowing along the channel comes out into the space  219  between the wall  215  of the enlarged borehole and the upper cutting region  201 . 
     An optional further detail shown in  FIG. 12  is that in the area  238  where the channel extends into the upper cutting region  201 , its side walls are no longer at a constant distance apart but diverge as shown. 
       FIG. 13  shows a further embodiment of cutter block. The upper and lower cutting regions  201  and  203  both have PDC cutters which are partially embedded and project radially outwardly from the block surface. The upper cutting region  201  is largely the same as shown in  FIGS. 4 to 6  with four cutters  205 . The PDC cutters in the lower cutting region  203  are arranged in a leading row of cutters  250  and a following row of cutters  252 . Neither of these rows is precisely aligned, so that, as explained above with reference to  FIG. 9 , neither of them creates a straight axial line parallel to the tool axis. The cutters  252  are positioned axially so as to face gaps between the cutters  250  in the leading row. In this construction, the extremities of cutters  250  and  252  contact the borehole wall as they cut it, but the only other area which contacts the borehole wall is the stabilising pad  211 . 
     A channel runs along the axial length of the block from an inlet opening  222  at the lower end of the block to an outlet opening  224  at the upper end of the block. Where this channel crosses the stabilising pad  211 , it is formed by sections  254  which have trailing edges inclined at approximately 25° angles to the tool axis and leading edges inclined at lesser angles. The two sections  254  are connected by a short section  256  in which the leading and trailing edges are parallel to the tool axis but are shorter than the inclined sections  254 . In the lower cutting region  203  there is a section  260  of the channel which runs between the leading row of cutters  250  and the following row of cutters  252 . Here, where there is no direct contact between the channel edges and the borehole wall, the leading edge is straight and parallel to the tool axis and the trailing edge is a succession of edges arranged so that the hard faces of the cutters  252  coincide with the trailing edge of the channel. This allows insertion of these cutters  252 . In a section  258  of the upper cutting region  201 , the channel edges again do not contact the borehole wall and both edges are parallel to the tool axis. 
       FIG. 14  illustrates a further possibility. This drawing shows the radially outward faces of the three cutter blocks which are distributed azimuthally around the body of a reamer and are extendable from the body of the reamer by the mechanism shown in  FIGS. 2 and 3 . 
     Each block is similar to the blocks shown by  FIGS. 4 to 7 . However, in order to further reduce symmetry the three channels  220  are not positioned identically. The channel  220  on block  270  is the same is in  FIG. 6 . The channels in blocks  272  and  274  are offset in the axial direction of the reamer, with addition of changes of direction at axial portions  232  as required to keep the channels  220  within the width available. In the event that the trailing edge of the channel in one of the axial portions  232  did snag on a feature of the formation as the reamer rotates, the other two blocks are less likely to snag on the same feature because their channels have axial portions  232  at different axial positions. 
     For the purpose of explanation the three blocks  270 ,  272 ,  274  have been shown with cutters  205 ,  207  and stabilising pads  211  which are identical. However, this need not be the case: these features may also show some variation between the three blocks. 
     Modifications to the embodiments illustrated and described above are possible, and features shown in the drawings may be used separately or in any combination. The arrangements of stabilising pads and cutters could also be used in a reamer which does not expand and instead has cutter blocks at a fixed distance from the reamer axis. Other mechanisms for expanding a reamer are known and may be used.