Instrumented cutter

Abstract

A rotary cutting tool for use in a wellbore has an instrumented cutter disposed in a cavity in a tool body. The instrumented cutter body has an outer end exposed at an open end of the cavity and is connected to the cutter body by at least one connecting portion having a smaller cross-section and greater flexibility than the outer end portion. The outer end portion and the connecting portion are movable slightly within the cavity, but the cavity sufficiently closely surrounds at least a portion of the outer end to limit lateral movement to elastic strain of the flexible connection portion. One or more sensors, which may be strain gauges, are used to measure forces on the outer end in a plurality of directions transverse to the cavity and cause elastic strain of at least one connecting portion.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit and priority of U.S. Patent Application No. 62 / 827,549, filed on April 1, 2019. This application also relates to U.S. Patent Application No. 62 / 827,516, filed on April 1, 2019 and U.S. Patent Application No. 62 / 827,373, filed on April 1, 2019. Each of the foregoing is hereby expressly incorporated by reference in its entirety. Background of the Invention

[0003] Reamers and drill bits are typically constructed with a cutting structure that includes a block or blade defining a plurality of cavities, sometimes referred to as pockets, into which cutters are assembled. The tool body can be incorporated into a drill string or attached to a downhole motor to rotate the tool.

[0004] Example cutters used in drill bits or reamers include polycrystalline diamond (PDC) cutters, which include a polycrystalline diamond cutting face bonded to a substrate made of tungsten carbide. The polycrystalline diamond cutting face is made of diamond grains sintered integrally with the substrate using a binder. Cutters for milling tools used to remove metal from the inside of a metal tube can be attached to pockets of a milling blade or directly bonded to the surface of the blade and can be made of sintered tungsten carbide.

[0005] Cutters for drill bits, reamers, and milling cutters can be fixed in the pockets using brazing techniques that attach the cutters within the respective pockets or to the surface of the cutting tool. Summary of the Invention

[0006] This Summary of the Invention is provided to introduce some concepts that will be further described in the Detailed Description below. This Summary of the Invention is not intended to be used to limit the scope of the claimed subject matter.

[0007] Embodiments of the present disclosure relate to a rotary cutting tool for forming or enlarging a subterranean conduit, including a tool body defining a plurality of cavities each having an open end and a plurality of cutters assembled into the cavities and attached to the tool body.

[0008] The cutting tool has at least one cutter with a cutter body including an outer end portion that is exposed at the open end of the cavity and is connected to the cutter body within the cavity by at least one connecting portion that is rigidly connected to the outer end portion but has a smaller cross - sectional area than the outer end portion, and thus has greater flexibility than the outer end portion. The total cross - sectional area of one or more connecting portions transverse to the connection can be less than the cross - sectional area of the outer end portion. The tool includes at least one sensor so as to be able to measure the force acting on the outer end portion of the cutter in any one of a plurality of directions transverse to the cavity and the cutter therein.

[0009] The cutter body may further include an inner end fixed to the cutter body within the cavity, at least one connecting portion extending between the inner end and the outer end and rigidly connected to the inner end and the outer end, and the cross-sectional area of at least one connecting portion being smaller than that of the inner end and the outer end, thereby having greater flexibility than the inner end and the outer end. With this structure, the outer end and the connecting portion are not directly attached to the tool body, but are attached by being fixed to the inner end of the tool body. Both the interior and the exterior of the cutter body are rigidly connected to the connecting portion, such that the force acting on the outer end can be transmitted to the connecting portion and also from there to the inner end and forward to the tool body. When a force is applied to a hard surface on the outer end of the cutter, strain is caused. This strain mainly consists of the deformation of the connecting portion, since the cross-sectional area of the or each connecting portion is smaller than that of the outer end and is thus more flexible.

[0010] The cavity wall may closely surround at least a portion of the outer end, but with a spacing small enough to allow limited movement of the outer end transverse to the cavity. This causes strain in the connecting portion. However, the cavity wall may be close enough to the outer end of the cutter such that the limited range of movement of the outer end does not cause deformation of the connecting portion beyond the elastic deformation, that is, it does not cause deformation beyond the elastic limit.

[0011] The spacing between the connecting portion and the surrounding cavity wall may be greater than the spacing between the outer end and the cavity wall. This can ensure that the force transmitted to the connecting portion comes only from the outer end, since the tool body cannot directly contact the connecting portion and transmit force to them.

[0012] The connecting portion may be a plurality of separate connecting portions, which are spaced apart and the total cross-sectional area is smaller than the cross-sectional area of the outer end and any inner end. As an alternative to this structure, there may be only a single connecting portion, which may be a single hollow cylinder.

[0013] Providing a more flexible connecting portion allows the force on the hard surface of the cutter to cause deformation of the cutter body, and this deformation can enable the measurement of the force acting on the cutter body. There are various possibilities for sensors to measure the force. A position sensor may be used to observe the change in position of the exterior relative to the tool body, possibly by measuring the change in position of the exterior relative to the inner end. Another method is to measure the strain (which is of course deformation) of the connecting portion. This can be done by strain sensors attached to the connecting portion.

[0014] In a second aspect, the present invention provides a rotary cutting tool for forming or enlarging a subterranean conduit, comprising a tool body defining a plurality of cavities each having an open end, and a plurality of cutters assembled into the cavities and attached to the tool body, wherein: at least one cutter assembled into the cavity has a cutter body including an outer end portion that is exposed at the open end of the cavity and is connected to the cutter body within the cavity by at least one connecting portion that is rigidly connected to the outer end portion but has a smaller cross-sectional area than the outer end portion, and thus has a greater flexibility than the outer end portion; at least one connecting portion of the tool body and the surrounding cavity are sized such that the spacing between at least one connecting portion and the cavity wall is greater than the spacing between the outer end portion and the cavity wall; and the tool includes at least one sensor for measuring forces acting on the outer end portion in a plurality of directions.

[0015] The total cross-sectional area of the connecting portion transverse to the cutter axis may not be greater than 50% of the cross-sectional area of the outer end portion transverse to the same axis. It may be in the range of 15% or 20% to 40% of the cross-sectional area of the outer end portion.

[0016] A third aspect of the present disclosure provides a rotary cutting tool for forming or enlarging a subterranean conduit, comprising a tool body defining a plurality of cavities and a plurality of cutters assembled into the cavities and attached to the tool body, wherein: at least one cutter assembled into the cavity has a cutter body including an outer end portion that is exposed at the open end of the cavity and is connected to the cutter body within the cavity by at least one connecting portion that is rigidly connected to the outer end portion but has a smaller cross-sectional area than the outer end portion, and thus has a greater flexibility than the outer end portion; and the cross-sectional area of at least one connecting portion does not exceed 50% of the cross-sectional area of the outer end portion, and thus has a greater flexibility than the outer end portion, and the tool includes at least one sensor for measuring forces acting on the outer end portion in a plurality of directions.

[0017] As already mentioned, the cutter body may further include an inner end portion fixed to the cutter body within the cavity, at least one connecting portion extending between the inner end portion and the outer end portion and being rigidly connected to the inner end portion and the outer end portion, and the cross-sectional area of at least one connecting portion is smaller than that of the inner end portion and the outer end portion, and thus has a greater flexibility than the inner end portion and the outer end portion.

[0018] The inner end portion of the cutter body may have a shape different from a cylindrical shape and engage a mating shape of the cavity to limit rotation of the cutter body relative to the tool body.

[0019] The cutter can have a hard cutting surface exposed at the open end of the cavity. Such a hard surface may be harder than steel and may have a Knoop hardness of at least 1300, 1600, 1800 or even higher. Tungsten carbide is a well-known hard material with good thermal stability. Other hard carbides are carbides of other transition metals such as vanadium, chromium, titanium, tantalum and niobium. Silicon, boron and aluminum carbides are also hard carbides. Other hard materials are boron nitride and aluminum boride. These hard materials can be used to provide a hard surface on the outer end of the body, especially if the cutter is used in a tool for milling tubing. For drill bits and reamers, the outer end of the cutter can have a hard polycrystalline diamond face, which will provide very superior diamond hardness.

[0020] The sensor can measure the strain of the connection part, and embodiments of the present disclosure include a strain sensor attached to the connection part. The strain sensor can be a resistance strain gauge and can include conductive tracks adhered to an electrically insulating carrier on the connection part (or one of the connection parts) such that the strain of the connection part changes the length and resistance of the conductive tracks. A plurality of strain gauges can be constructed and electrically connected to measure a component of the force separately. The strain gauges on one or more connection parts can be constructed and connected to measure the strain of the force components that shear on the outer end of the cutter body from each of two directions that are perpendicular to each other and also perpendicular to the axes of the body and the cavity. The strain gauges can also be constructed and connected to measure the strain generated by the axial load on the outer end of the cutter body.

[0021] In another aspect, a method of observing the forces on the cutter of a rotary cutting tool is now disclosed, the method including providing a rotary cutting tool having one or more cutters as described above and observing or recording data from the sensor while operating the tool within a conduit. Description of the Drawings

[0022] Figure 1 is a schematic cross-sectional view of a drilling assembly in a borehole;

[0023] Figure 2 is a perspective view showing the general arrangement of a fixed cutter drill bit;

[0024] Figure 3 is a perspective view of a part of a drill bit body before assembling the cutter according to an embodiment of the present disclosure;

[0025] Figure 4 and 5 show the characteristics of two forms of resistance strain gauges according to some embodiments of the present disclosure;

[0026] Figure 6 is a top view of a set of interconnected strain gauges on a carrier according to some embodiments of the present disclosure;

[0027] Figure 7 is an enlarged side view of an instrumented cutter according to an embodiment of the present disclosure;

[0028] Figure 8 is along Figure 7 an enlarged cross-sectional view of the instrumented cutter taken along line 8-8;

[0029] Figure 9 is along Figure 7 taken in the direction of arrow C of Figure 7 an end view of the instrumented cutter;

[0030] Figures 10 to 15 is a longitudinal cross-sectional view of the cutter, showing an example stage in cutter manufacture;

[0031] Figure 16 is a cross-sectional view of a drill bit blade, showing a cavity for receiving the cutter;

[0032] Figure 17 is Figure 16 a cross-sectional view of the blade, with the cutter seated in the cavity in the blade;

[0033] Figure 18 is a top view of a carrier such as Figure 6 showing only the Poisson gauge;

[0034] Figure 19 is Figure 18 an example circuit diagram of the gauge shown;

[0035] Figure 20 and 22 is a top view of a carrier such as Figure 6 showing only a pair of connected chevron gauges;

[0036] Figure 21 and 23 are Figure 20 and 22 example circuit diagrams of the gauges shown in;

[0037] Figure 24 is a schematic axial view of multiple chevron gauges according to an embodiment of the present disclosure when they can be positioned on an instrumented cutter;

[0038] Figure 25 is a perspective view of a cutter block for an expandable reamer;

[0039] Figure 26 is according to an embodiment of the present disclosure Figure 25 a longitudinal cross-sectional view of the cutter block, showing an instrumented cutter in a cavity in the cutter block;

[0040] Figure 27 is a side view of a cutter block of a section or casing mill according to an embodiment of the present disclosure, for milling and removing a portion of a wellbore casing;

[0041] Figure 28 is according to an embodiment of the present disclosure Figure 27 longitudinal cross - sectional view of the cutter on line 28 - 28;

[0042] Figure 29 is an enlarged side view of an instrumented cutter according to another embodiment of the present disclosure;

[0043] Figure 30 is at Figure 29 cross - sectional view of the instrumented cutter on line 30 - 30;

[0044] Figure 31 and 32 are example circuit diagrams of strain gauges for use in an embodiment of Figure 29 and 30 according to another embodiment of the present disclosure;

[0045] Figure 33 is a cross - sectional view similar to the view shown in Figure 30 showing another embodiment of the cutter;

[0046] Figure 34 are example circuit diagrams of strain gauges for use in an embodiment of Figure 33 according to an embodiment of the present disclosure;

[0047] Figure 35 is a top view of a set of fiber Bragg sensors on a carrier according to an embodiment of the present disclosure;

[0048] Figure 36 is can be used in Figure 35 enlarged top view of two fiber Bragg sensors on the carrier;

[0049] Figure 37 and 38 are longitudinal cross - sectional views of two parts of a cutter incorporating a capacitance sensor according to an embodiment of the present disclosure;

[0050] Figure 39 is Figure 37 and 38 longitudinal cross - sectional view of the cutter after connecting the two parts; and

[0051] Figure 40 and 41 is Figure 37 and 38 front views of two parts of the capacitance sensor shown in Detailed Description

[0052] Example embodiments of the present disclosure relate to providing instrumentation in a rotary cutting tool for creating, extending, or enlarging a subterranean conduit. The conduit may be a borehole drilled through a geological formation, and the tool may be a drill bit or reamer, the purpose of which is to create, extend, or widen the borehole. The tool may also include a mill for removing material from a casing or other pipe within the conduit. In patent publication GB2535787A, which is incorporated herein by reference in its entirety, an example milling tool for removing metal from the interior of a pipe within a borehole is disclosed, wherein the tool also has a body defining a cavity for receiving hardfacing cutters.

[0053] Figure 1 A borehole assembly including a drill bit 20 and a cutting tool 18 is shown by way of example. The cutting tool 18 may include a reamer or a milling tool. A drill string 12 extends from a rig 10 into the borehole. The upper portion of the borehole has been lined with a casing 15 and cemented as shown at 14. The drill string 12 is connected to the cutting tool 18, and the cutting tool 18 is connected to the drill bit 20 by an additional drill string 12. In the illustrated embodiment, the cutting tool 18 may operate as an expandable reamer that has expanded below the casing section 14. When the drill string 12 is rotated and a drilling pressure is applied, the drill bit 20 extends downwardly into a pilot hole 22 while the reamer opens the pilot hole 22 to a larger diameter borehole 24. In an embodiment where a portion of the casing 15 is to be removed, the cutting tool 18 represents a casing or section mill having fixed or expandable blades or cutter blocks that are arranged and designed to remove the casing. The cutting tool 18—whether operating as a reamer to enlarge the borehole or as a casing or section mill to remove the casing—may operate with or without the drill bit 20.

[0054] The rig is provided with a system 26 for pumping drilling fluid from a supply source 28 along the drill string 12 to the cutting tool 18 and the drill bit 20. Some of the drilling fluid flows through channels in the cutting tool 18 and returns to the surface upwardly along the annular space around the drill string 12. Other portions of the drilling fluid flow from the cutting tool 18 to the drill bit 20, out of nozzles or ports in the drill bit 20, and also return to the surface upwardly along the annular space around the drill string 12. The distance between the cutting tool 18 and the drill bit 20 at the bottom of the bottom hole assembly is optionally fixed. For example, when the cutting tool 18 is a reamer, as the pilot hole 22 is drilled or extended, the enlarged borehole 24 may also extend downwardly simultaneously.

[0055] Of course, it is understood that it is possible to drill a borehole without the cutting tool 18, such that the drill bit 20 attached to the drill string 12 forms a borehole having the diameter of the drill bit 20 and does not widen the borehole or remove the casing. The same cutting tool 18 attached to the drill string 12 may also be used, although without Figure 1The drill bit 20 and a portion of the drill string 12 shown below the mid-cutting tool 18 to enlarge a previously drilled borehole or to remove a casing previously installed in the borehole.

[0056] Reference will be made to the Figures 2 to 23 description of the drill string with instrumented cutters embodying the present disclosure. Although described with respect to a drill bit, one of ordinary skill in the art will understand, in view of the present disclosure, that the described instrumented cutters can be used in other tools, including reamers, milling tools (such as section mills, casing mills, pilot mills, follow mills, finishing mills, watermelon mills, junk mills, etc.), stabilizers, etc. In addition, other types of instrumented cutters can be included, including instrumented cutters having sensors for one or more physical properties. By way of example, U.S. Patent Publication No. 2012 / 0312599 (which is hereby incorporated by reference in its entirety) discloses a cutter with an instrument for monitoring cutter wear during use, and the cutter can include strain gauges.

[0057] Exemplary cutting tools and cutters of the present disclosure can have multiple components. To facilitate understanding of some embodiments of the present disclosure, the following discussion will include the following descriptions: (a) a drill bit body and PDC cutters, which can be made by the prior art or include drill bit shape features dedicated to the instrumented cutters described herein; (b) the structural portion of the instrumented cutter; and (c) the electrical connections between the strain gauges and multiple strain gauges used in the instrumented cutter.

[0058] Drill Bit Body and Layout

[0059] Figure 2 Features of an exemplary fixed cutter drill bit fitted with PDC cutters for drilling through a rock formation to form a borehole are shown. The drill bit has a drill bit body 30 rigidly connected to a central shank 31 that terminates in a threaded connection 32 for connecting the drill bit to the drill string to rotate the drill bit and thereby drill the borehole. The drill bit has a central axis 33 about which the drill bit rotates in a cutting direction as shown by arrow 34.

[0060] The cutting structure provided on the drill bit includes three main blades 36 spaced apart at an angle and alternating with three sub-blades 38. These blades each project from the drill bit body and extend radially outward from the axis 33. The main blades 36 start closer to the axis 33 than the sub-blades 38. These main blades 36 and sub-blades 38 are separated by channels 40, which are sometimes referred to as chip removal grooves or flow channels. The channels 40 allow the supplied drilling fluid to flow downward along the drill string and be delivered through holes 42, which can be referred to as nozzles or ports. The drilling fluid flow cools the PDC cutters and, as the flow moves towards the wellhead, carries the drill cuttings away from the drill bit surface.

[0061] Blades 36, 38 have recesses or other types of cavities extending inwardly from the open ends facing the direction of rotation. The PDC cutters 44 are fixed in these cavities formed in the main blade 36 and the sub - blade 38 by brazing so as to be rotationally guided and project from the blades, which exposes the diamond cutting faces of the PDC cutters, as shown in the figure. The three main blades 36 are similar to each other, but can be different in various ways, such as the number and position of the cutters 44 attached to the blades. Similarly, the sub - blades 38 can be similar, but can also be slightly different in the number and position of the cutters 44 or otherwise. In addition, although the blades 36, 38 can be evenly spaced around the axis 33, the drill bit can also have some unevenly spaced blades to provide an asymmetric blade design.

[0062] Figure 3 A portion of the drill bit body of the drill bit is shown, which can be fitted with the instrumented cutters disclosed herein. This embodiment of the drill bit body can include many features similar to those described in the reference Figure 2 or shown in Figure 2 . The body of the drill bit is connected to a central shank that terminates in an internal or external threaded connection (see Figure 2 ) for connecting the drill bit to the drill string. Figure 3 The drill bit body of Figure 2 also includes main blades and sub - blades separated by channels, as shown in Figure 3 . A front surface 46 of one sub - blade 38, a front surface 46 of one main blade 36, and a rear surface 48 of another main blade are shown. Nozzles for delivering drilling fluid can be provided, but are not shown in Figure 3 . In this embodiment, each cavity 50 on the sub - blade 38 and the radially inward cavity 52 on the main blade 36 are sized to receive PDC cutters fixed in these cavities 50, 52 by brazing. The cavity 54 is radially away from the drill bit axis and is located on the main blade 36 in this embodiment, optionally having a longer length (e.g., measured circumferentially), and can accommodate an instrumented cutter, which will be described in more detail herein.

[0063] The drill bit body can be made of a variety of materials. For example, the drill bit body can be machined from steel, additively manufactured from any of a variety of materials (such as steel, titanium, inconel, etc.), cast by placing molten metal in a mold, or formed from particulate hard material such as tungsten carbide, which is placed in a mold and infiltrated with a molten metal binder. An example of the disclosure related to the drill bit material is U.S. Patent No. 8211203, which is incorporated herein by reference. Here in Figure 2 and 3The drill bit shown can have a body formed in any of these ways or using any suitable material. When the drill bit is formed by infiltrating particulate hard material, the shank having connection 32 is optionally a steel component that is embedded in the hard particles prior to infiltration. When the drill bit body is molded in this way, the mold can be made of graphite. The internal channels within the drill bit can be formed by placing graphite rods in the cavity defined by the mold and then wrapping particulate material around these rods.

[0064] As described above, the drill bit body can also be manufactured in other ways, including by using computer-aided additive manufacturing methods that deposit the particulate material of the drill bit body as successive layers. In accordance with a digital design, the particulate material is bonded together and bonded to the previous layer where needed. An article initially made of particulate material in this way can subsequently be infiltrated with a metal binder or can be formed without subsequent infiltration.

[0065] Strain gauge

[0066] An example resistance strain gauge consistent with embodiments of the present disclosure observes strain through a conductive but somewhat resistive path deposited on a sheet (such as an electrically insulating polymer), which sheet is referred to herein as the carrier. The carrier is adhered or otherwise coupled to the substrate to be observed. If stress on the substrate causes it to elongate slightly, the carrier and the conductive path also elongate, and the resistance of the conductive path increases. Conversely, if there is a stress that compresses the substrate and shortens the conductive path, the resistance decreases. This type of strain gauge is available from many manufacturers and component suppliers, including HBM Inc. of Marlborough, Massachusetts, USA, HBM UK Ltd. of Harrow, UK, and National Instruments of Newbury, UK or Austin, Texas, USA.

[0067] Strain gauges can be formed as pairs that are close to each other on the same carrier, where the conductive path of one individual strain gauge extends at a different angle (such as perpendicular to the conductive path of the neighboring strain gauge) from the conductive path of the neighboring strain gauge. Such paired gauges can allow compensation for temperature variations or can allow one of the gauges in the pair to be measured for strain while both are exposed to the surrounding temperature. Multiple strain gauges can also be used in combination so that one strain in the system (such as a strain in one direction) can be measured separately from another.

[0068] Figure 4An enlarged view of a pair of strain gauges is shown. The conductive paths are deposited or otherwise formed on a carrier 60. In region 62c, the strain gauge is provided by a conductive path that extends back and forth multiple times in a direction parallel to that indicated by the double arrow 63. This provides a section of the conductive path that is strained when the underlying substrate is strained in a direction parallel to arrow 63. If the strain elongates or shortens the carrier 60 in the direction of arrow 63, the conductive path will elongate or shorten accordingly in that direction, resulting in an increase or decrease in the resistance of the conductive path. As shown, the reverse turns 64 are thickened to reduce the resistance of those portions of the path that are transverse to the direction of arrow 63.

[0069] In region 62t, a second gauge is provided by a conductive path that extends back and forth transverse / perpendicular to arrow 63. The resistance of the conductive path in this region 62t is not affected by strain parallel to arrow 63. As explained in more detail herein, the conductive path in region 62t can be used to compensate for the effect of temperature. The conductive paths in regions 62c and 62t are interconnected and connected to a tab 66 on the support carrier. The other ends of these two conductive paths are connected to separate tabs 67. A pair of electrically connected gauges having the layout as Figure 4 shown can be referred to as a Poisson gauge.

[0070] Figure 5 Another example of a pair of strain gauges provided by conductive paths on a single carrier 60 is shown. Again here, each strain gauge is also provided by a conductive path that extends back and forth multiple times in one direction. In region 68, and in region 69, the conductive paths are at 45° to the direction of arrow 63, but the conductive path in region 69 extends perpendicular to the conductive path in region 68. As before, the two gauges are connected together and connected to a common tab 66, while the other ends of the two conductive paths are connected to their respective tabs 67. A pair of gauges having Figure 5 the configuration shown can be referred to as a chevron gauge.

[0071] Figure 6 A set of strain gauges on a single rectangular carrier 70 is schematically shown for some embodiments of the instrumented cutter described herein. At each of the positions 71, 72, 73, and 74 there are Figure 5 chevron gauges of the type shown. At each of the positions 75, 76, 77, and 78 there are Poisson gauges that include one gauge having a conductive path parallel to the length of the carrier and one gauge having a conductive portion transverse to the length of the carrier. The connections from tab 79 and the connections between the gauges are also deposited or otherwise formed on the rectangular carrier 70.

[0072] Instrumented cutter

[0073] Figure 7is a side view of an exemplary instrumented cutter having a body with an outer end 80, an inner end 82, and a connecting portion 84 extending between the outer end 80 and the inner end 82. In this embodiment, the outer end 80 includes a solid cylinder centered on the axis 87 of the instrumented cutter. The outer end 80 may include a cylinder 86 attached to a PDC cutter, which has the same diameter as the PDC cutter. The cylinder 86 may be formed of the material that serves as the substrate of the PDC cutter or may include other materials (such as steel). The PDC cutter includes a polycrystalline diamond cutting face 88 that is integrally formed with or otherwise attached to a substrate 90. The diamond cutting face 88 may be formed of diamond crystals or grains stacked together and sintered with a binder, while the substrate 90 may include tungsten carbide grains also sintered with a binder. Although the diamond cutting face 88 is shown as having a flat outer end face, in some embodiments, the diamond cutting face 88 may be non-flat. For example, the diamond cutting face may be pointed (such as conical, frustoconical, ridged, chisel-shaped, etc.), concave, have serrated features, etc.

[0074] In this embodiment, the inner end 82 is also cylindrical but may be integral with or otherwise attached to another part 92. In some embodiments, the other part 92 has a square, rectangular, or other polygonal cross-sectional shape, although it may also be circular. As Figure 9 shown, the other part 92 is shown in an illustrative square cross-sectional shape. The connecting portion 84 extending between the inner end 82 and the outer end 80 may be solid or, as Figure 8 shown in the cross-section taken along Figure 7 line 8-8, may be hollow or have an internal cavity therein.

[0075] In some embodiments, a carrier 70 carrying strain gauges (such as Figure 6 strain gauges 71-78) may be adhered or otherwise coupled to the inner surface of the connecting portion 84. As Figure 8 schematically shown, the length of the carrier may be selected such that it extends completely around the interior of the cylindrical connecting portion 84 with only a small gap 94 (such as less than 20%, less than 10%, less than 5%, or less than 2% of the inner surface perimeter) or no gap at all between its ends. The length of the carrier 70 and the positions of the gauges 71-78 on the carrier 70 may be arranged and designed such that when the carrier 70 is in place within the cylindrical portion 84, certain gauges may be diametrically opposed. For example, the chevron gauges 71 and 73 may be diametrically opposed to each other, and other or additional pairs of gauges (such as chevron gauges 72 and 74, Poisson gauges 75 and 77, or Poisson gauges 76 and 78) may be diametrically opposed to each other.

[0076] Manufacture

[0077] Figures 10 to 15 is a cross-sectional view of an instrumented cutter to show an example manufacturing process for fabricating the cutter into two component parts that are subsequently joined together. In the first step shown in Figures 7 to 9 , the substrate 90 of the PDC cutter is attached to a solid cylinder 96 of the same diameter to obtain the article shown in Figure 10 (e.g., by brazing). For some embodiments, the embodiments shown in Figure 10 may generally be drawn to scale, but for other embodiments, they are not drawn to scale. For example, the substrate 90 may be longer compared to the cutting face 88. As described above, the solid cylinder 96 may be formed of any suitable material, including any different grades of steel. Figure 10 As shown in

[0078] As Figure 11 shown, the cylinder 96 may be machined (e.g., on a lathe) along a partial length thereof, as shown at 98, to reduce the diameter of the partial length of the cylinder 96 to the outer diameter of the connecting portion 84. Thereafter, as shown in Figure 12 , a blind hole may be drilled or formed in the cylinder 96. In this particular embodiment, the length of the hole is approximately equal to the length of the machined portion 98 of the outer diameter of the cylinder 96. As the hole is formed, the machined portion defines the connecting portion 84 and has a reduced diameter and is a hollow cylinder integral with the outer end 80.

[0079] Figure 14 The second component part shown in Figure 9 may be fabricated by machining a cylinder (e.g., steel or other material) to form a square end 92 at one end. The remaining portion of the cylinder then forms the inner end 82. Threaded holes 102 are optionally made along all or part of the length of the second component part and are optionally made along the axis. In some embodiments, small holes 104 are drilled through the inner end (see also Figure 14 ). The small holes 104 may be angled, as shown in

[0080] As Figure 13 shown, a carrier 70 with attached connecting wires 106 (only two of which are shown) is adhered or otherwise coupled to the interior of the cylindrical connecting portion 84. Adhesives for attaching strain gauges to steel and similar materials are available from strain gauge manufacturers and may include two-part epoxy adhesives. Next, Figure 13 and 14The two parts shown are joined together, and the connecting wire 106 is passed through the hole 104. Then, the connecting portion 84 can be welded, brazed, or otherwise joined to the inner end 82. For example, electron beam welding can be used to fabricate Figure 15 the instrumented cutter shown.

[0081] In view of the disclosure herein, it should be understood that Figures 10 - 15 the method shown in is merely illustrative. In other embodiments, the order or process can be varied or combined. For example, the cylinder 96 can be molded or machined into a certain shape (e.g., having holes and a reduced outer diameter) before being attached to the substrate 90. Similarly, another component 82 can be attached to the cylinder 96 before being attached to the substrate 90.

[0082] Figure 16 A cross-section through the cavity 54 in the main blade 36 of the drill bit is shown. At the inner end of the cavity, the drill bit body has a square recess 110 to accommodate the square end 92. There are through-holes 112 for bolts and a channel 114 from the inner end of the cavity to the rear surface 48 of the blade. This channel 114 leads along the rear surface of the blade to the channel 116, as seen more clearly in Figure 3 . The openings 118 of the three channels 114 are shown in Figure 3 .

[0083] As Figure 15 shown, the cutter is inserted into the cavity 54 to the Figure 17 position shown, while passing the wire 106 from the strain gauge through the channel 114. The angle of the cavity positions the cutter at an angle to the central axis of the drill bit relative to the axis of the drill bit body, so that the cutter projects from the blade, as shown. The PDC disk 88 is exposed, and more of the outer end 80 is also exposed, as shown at 91. The remainder of the outer end 80, the connecting portion 84, and the inner end 82 are located within the cylindrical cavity 54 of the drill bit blade 36. When the cutter is inserted into the cavity, the square portion 92 fits into the corresponding recess 110 at the inner end of the cavity and prevents any rotation of the cutter within the cavity. When the cutter is fully inserted, it is fixed in place by bolts 119 into its threaded holes 102.

[0084] The inner end 82 of the cutter is dimensioned for an interference fit at the inner end of the cavity 54. The outer end 80 is dimensioned for a sliding fit within the cavity, with only a small clearance between the outer end 80 and the surrounding wall of the cavity. Due to this arrangement, the force applied to the PDC disk 88 in the axial direction of the cutter (i.e., the axial load on the cutter) is transmitted through the connecting portion 84 to the inner end 82 and from there to the blade 36 of the drill bit. This stress causes strain, which is an elastic compression of the connecting portion 84.

[0085] The force component on the PDC disk 88 that is not in the axial direction of the cutter will also be transmitted to the connection portion 84 and will cause a strain that bends the connection portion 84. This is restricted by the outer end portion 80 that abuts against the wall of the cavity 56, so the bending deformation of the connection portion 84 will not exceed its elastic limit.

[0086] The wire 106 is guided along the channel 116 at the rear surface 48 of the blade 36 and from there is guided to an electronic instrument assembly that is contained within a bottomhole assembly located at the well bottom end of the drill string 12 and that operates strain gauges and records the measured data, or using a known form of telemetry technology from downhole tools to the surface, such as mud pulse telemetry or by using wired drill pipe, it is sent forward to the surface. Such an electronic instrument assembly can for example be contained within a measurement while drilling (MWD) device in the drill string located near the bit. Before the signal is sent to the surface, the electronic instrument assembly may perform some signal processing. The wire 106 may also lead to some electronic devices housed within the bit itself, which then send the signal forward to the MWD device for further processing and / or transmission to the surface. The electronic devices within the bit itself may also have the ability to transmit to the surface.

[0087] When the cutter and the wire 106 have been placed in position, the channels 114 and 106 are filled with an electrically insulating flexible filling material, which is an organic polymer. This can be a silicone polymer or a polyurethane polymer, and it can be introduced as a liquid and then cured in place. Such a filling material can be a continuous polymer block or a closed-cell foam. In either case, the flexible filler is used to exclude drilling fluid and protect the wires.

[0088] In the embodiment shown here, the inner end portion 82 is fixed in position by bolts that hold the square end portion 92 in the corresponding recesses 110. Other attachment methods are possible, such as welding or adhesives.

[0089] Another type of sensor can also be inserted into the space within the connection portion 84. This is shown in Figure 17 where there is a temperature sensor 108 in this connection portion. The electrical connection 109 to this sensor is shown in Figure 17 as incomplete but will lead out through the channel 114.

[0090] The function of the strain gauge

[0091] Four Poisson gauges 75–78 are used to measure the axial force at the outer end of the cutter, separated from any force component transverse to the axial direction. The chevron gauges 71 and 73 are radially opposite each other in the connecting portion 84. The chevron gauges 72 and 74 are also diametrically opposite each other. The nominal diameter between gauges 72 and 74 is orthogonal to the nominal diameter between gauges 71 and 73. These pairs of radially opposite chevron gauges are used to measure the strain caused by the shear force components in each of two directions that are perpendicular to each other and also perpendicular to the axis of the cutter. Thus, the forces measured by the gauges can be resolved into axial and shear components in these two perpendicular directions that are perpendicular to the axis of the cutter.

[0092] It is well known to use a Wheatstone bridge circuit to measure the change in resistance of a strain gauge. It is well known to use multiple gauges in a Wheatstone bridge to separate the strain and the force causing the strain into different components. However, the measuring device for this embodiment incorporates unique features that will now be described.

[0093] The four Poisson gauges 75-78 on the carrier 70 are interconnected but not connected to any of the chevron gauges 71-74. They are connected in a Wheatstone bridge with two gauges on each arm of the bridge. This is shown by Figure 18 and 19 shown.

[0094] Figure 18 Shown is Figure 6 the carrier which has the Poisson gauges 75-78 and their electrical connections, but the chevron gauges 71-74 and the connections to these gauges are not shown. As Figure 4 shown, each Poisson gauge consists of two separate strain gauges whose conductive paths are perpendicular to each other. The individual strain gauges designated 75c–78c have conductive paths parallel to arrow 63 which is parallel to the axis of the cutter. The individual strain gauges designated 75t–78t have conductive paths perpendicular to arrow 63.

[0095] Figure 18 includes the connections to the Poisson gauges and is also shown as a circuit diagram by Figure 19 shown, Figure 19 showing how the individual strain gauges are connected in the Wheatstone bridge. The ground connection and the fixed power supply voltage are designated 0V and V+ respectively. Connections 121 and 122 are the outputs of the Wheatstone bridge and they are connected as inputs to the differential amplifier 130.

[0096] The axial load applied to the outer end 80 of the cutter compresses the connecting portion 84 and the carrier 70 in the axial direction shown by arrow 63, thereby shortening the conductive paths of the gauges 75c - 78c and reducing their resistance. The gauges 75t–78t are not affected. As a result, the potential at 121 increases and the potential at 122 decreases. The final change in the potential difference between 121 and 122 is amplified by the differential amplifier 130 and is a measure of axial strain and thus of axial load.

[0097] The resistance of the strain gauges may vary with temperature, but as long as this affects all gauges equally, the changes in all four arms of the Wheatstone bridge will be the same and thus will not significantly change the potential difference between 121 and 122.

[0098] Shearing forces on the outer end 80 of the cutter will stretch one or both of the gauges 75c - 78c while compressing the diametrically opposite gauges by an equal amount. The net result is no change in the output. For example, if one strain stretches 75c and compresses the opposite gauge 77c while keeping everything else the same, the potential at 121 will drop due to the increased resistance of gauge 75c. The potential at 122 will also drop by a substantially equal amount due to the decreased resistance of gauge 77c, so the potential difference between 121 and 122 will remain substantially unchanged. More generally, when strain stretches any one gauge and compresses the diametrically opposite gauge, Figure 19 the resistance changes in the two arms of the shown Wheatstone bridge will substantially compensate. In this way, the four Poisson gauges in the Wheatstone bridge and their connections are able to separate axial load from shearing forces and measure only axial load.

[0099] Figure 20 is shown Figure 6 a portion of the carrier, with diametrically opposite chevron gauges 71 and 73 and their electrical connections. The Poisson gauges 75–78, the chevron gauges 72 and 74, and their electrical connections are omitted. Figure 20 Each of the chevron gauges 71 and 73 shown in Figure 5 is composed of two separate gauges as shown in Figure 21 The conductive paths are orthogonal to each other and at 45° to the axial direction shown by arrow 63. These are here designated 71a, 71b, 73a, and 73b. Figure 21 A circuit diagram is shown. The outputs 123 and 124 of the Wheatstone bridge are inputs to the differential amplifier 132.

[0100] Figure 22 and 23 are directly analogous to Figure 20 and 21 but show the chevron gauges 72 and 74 and their connections. The individual gauges are again connected as a Wheatstone bridge and the outputs 125 and 126 are connected as inputs to the differential amplifier 134.

[0101] An axial load on the outside 80 of the cutter will compress its connecting portion 84 and the chevron strain gauges. However, all of the individual gauges will be compressed equally, so the potential differences between 123 and 124 and also between 125 and 126 will not change. The same will be true for any change in temperature. Thus, the chevron gauges separate and ignore the axial load on the cutter.

[0102] Figure 24 is a schematic view showing the position of the chevron gauges in an axial view. For purposes of explanation, assume that the shear force acts in the direction of the arrow, parallel to the diameter between gauges 71 and 73. This will produce strains where the conductive paths of gauges 71a and 71b are equally stretched while the conductive paths of gauges 73a and 73b are equally compressed. From Figure 21 it can be seen that the change in resistance will cause an equal change in potential at 79c and 79d, so the potential difference between 123 and 124 will not change. See again Figure 24 , the strain also stretches gauges 72a and 74b while compressing 74a and 72b. From Figure 23 it can be seen that this will lower the potential at 125 while raising the potential at 126. This produces a change in the potential difference between these two points which is amplified by differential amplifier 134. Thus, the effect of the shear force on the diameter between gauges 71 and 73 is measured by gauges 72 and 74 and ignored by gauges 71 and 73. Correspondingly, any shear force along the diameter between gauges 72 and 74 is measured only by gauges 71 and 73.

[0103] The overall result is that the output of the chevron gauges excludes the axial load on the cutter and provides separate measurements of the shear force components in directions perpendicular to each other and perpendicular to any axial load. Since the potential difference changes in the Wheatstone bridge are small, they are amplified downhole by a differential amplifier or other electronic circuitry. As described above, this can be located in a compartment within the bit or in a measurement sub in the drill string near the bit.

[0104] When the rotary tool (a drill bit in this embodiment) is downhole in a well, the downhole fluid pressure will apply an axial force to the cutter and thus a constant compressive stress to the connecting portion 84. This can be observed as a baseline value which deviates from this value when the bit is at the surface. If this baseline is measured with the bit not rotating, then the measurement of the compressive axial strain of the connecting portion 84 and thus the axial load on the cutter will provide a measurement of the downhole pressure. However, since it may not be convenient to stop drilling for such a measurement, a pressure sensor can be provided on the outside of the bit.

[0105] In the above circuit, each Wheatstone bridge is supplied with a fixed voltage, and the voltage difference across the bridge is connected to a differential amplifier or other electronic circuit that amplifies the voltage change caused by the strain and thus the corresponding change in the resistance of the strain gauge in the Wheatstone bridge. However, electronic circuits that rely on maintaining a constant current rather than a constant supply voltage are also known and can be used.

[0106] Reamer

[0107] The above reference Figures 7 to 24 The cutter described above can be used for other rotary cutting tools. Figure 25 and 26 shows incorporation into a reamer block. WO2015 / 085288 (which is incorporated herein by reference) is one of a number of documents describing a rotary tool that is a reamer for enlarging a borehole. In such a tool, the expansion of three cutter blocks from a cylindrical tool body is achieved by a mechanism that drives the cutter blocks upward using the pressure of the drilling fluid. The cutter blocks have projecting splines that are angled with respect to the cutter axis and fit into mating channels that are part of the cutter body. Thus, when the blocks are uniformly pushed upward, the splines slide in the mating channels and guide the blocks to expand radially uniformly.

[0108] Figure 25 is very similar to that shown in Figure 4 A perspective view of cutter block 140 which is similar to the cutter blocks shown in WO2015 / 085288. The block is one of three blocks that are circumferentially distributed around the rotary tool body. The block 140 has an upper cutting region 144 and a lower cutting region 146 on which hard surface cutters are mounted in a front row of cutters 148 and a rear row of cutters 150. There is an axial intermediate portion between these regions where the cutters are only in the front row and includes a stabilizer pad 152. The stabilizer pad does not include cutters but has a generally smooth front surface that is positioned to face the borehole wall and slide on the borehole wall. Most of these cutters are conventional PDC cutters brazed into cavities in the steel block 140. As described in WO2015 / 08528, the splines 154 on the block 140 guide it to travel upward and outward.

[0109] Figure 25 The cutter 156 within the front row of cutters 148 in Figure 26 is a cross-section through the cutter and the upper part of the block 140. It can be seen that the arrangement is very similar to Figure 17The arrangement shown. The cutter is held in place in the cavity by long bolts 158 inserted through the rear surface of the cutter block 142. The diamond disk 88 is exposed, and more of the exterior 80 is exposed, as shown at 120. The wire 106 is routed through the block 140 and connected to electronics located in a compartment within the tool.

[0110] Milling cutter

[0111] A tool having the structure described in WO2015 / 085288 can be used as a section milling cutter for removing a section of a drill casing by assembling the tool with a cutter block for this purpose. This is shown by Figure 27 As shown in the figure, the existing drill hole is lined with multiple sections of pipe 160 (drill casing) connected end to end. Cement 162 has been placed between the pipes 160 and the surrounding rock formation. The pipes 160 and the cement 162 may have been in place for many years.

[0112] As disclosed in WO2015 / 085288, the cutter block assembled to the tool has an inner part 164 which has angled splines 154 to guide travel to the block as the block expands. The inner part 164 is attached to the outer part 166. The block is one of three blocks distributed azimuthally around the rotating tool body and can extend outwardly through a slot in the tool body. The edge of the slot is visible at 168.

[0113] The outer part 166 of each block is steel and has cutters 172, 173, and 174 fixed in cavities therein such that they are partially embedded in the outer block part 126, with their front ends exposed and facing the direction of rotation. Cutters 172 and 176 are cylinders of sintered tungsten carbide powder. Cutter 174 is an instrumented cutter, very similar to the Figures 10 to 15 cutter shown, except that its outer end is composed of a steel cylinder 86 brazed to a cylinder 176 of sintered tungsten carbide powder which has a hard cutting face. It is held in place in the outer block part 166 by bolts 178. The wire 106 from the strain gauge in the connecting part 84 passes down through the outer block part 166 and the inner block part 164 and is connected to electronics located in a compartment within the tool body.

[0114] The radially outward surfaces 182 and 183 on the outer block part 166 are partially cylindrical, with a radius such that when the block has extended from the tool body, these surfaces are centered on the tool axis. As Figure 28 shown, the surface 183 is at the same distance from the tool axis as the radially outer end of the cutter 173. The surface 182 is similarly aligned with the radial end of the cutter 172.

[0115] In use, the tool is attached to the drill string and lowered to the desired position within the borehole. The mechanism within the tool body as shown and described in WO2015 / 085288 serves to push the cutter blocks upward and outward when the tool rotates within the pipe to be removed. The hard cutters 172, 173, 174 cut through the surrounding pipe outwardly. When the cutter blocks are fully extended, weight is applied to the tool, which pushes the outer block portion 122 downward onto the pipe that has been cut.

[0116] When the rotating tool axially advances in the downhole direction as shown by arrow D, the hard cutters 172, 173, 174 of the tool now continuously mill away the pipe 160. The axial guiding cutter 172 on each block 20 is positioned to remove some material from the inner wall of the pipe 120, thereby creating a new inward-facing surface on the pipe 162. The partially cylindrical surface 182 slides on this newly formed inner surface of the pipe. The cutter 173 removes a further thickness of the pipe 160, creating a new inward-facing surface on which the surface 183 slides. The tight fit of the surfaces 182, 183 with the inner surface formed on the pipe 160 precisely positions the axis of the rotating tool relative to the pipe 160. As the tool advances downward, the cutter 174 removes the remaining thickness of the pipe 160.

[0117] Other cutter embodiments

[0118] Figure 29 and 30 shows another form of cutter that can be inserted into the cavity 28 of the drill bit body as shown in Figure 3 or into the cutter blocks of a reamer or Figure 25 a milling cutter as shown in Figure 27 . Similar to the cutter shown in Figure 7 , the outer end portion 204 includes a diamond disk 88 that is integral with a sintered tungsten carbide disk 90 brazed to a steel cylinder 86. The inner end portion is also a cylinder 82 on which a square end 92 is located. The inner and outer end portions are connected by four connecting portions 206 and 208. As can be seen from the enlarged cross-sectional view in Figure 30 , the connecting portions 206, 208 are spaced 90° apart about the cutter axis such that two of the connecting portions 206 are diametrically opposite each other, while the other two connecting portions 208 are also opposite each other. As shown in Figure 30 , each of these connecting portions 206, 208 has a rectangular cross-section. Figure 5 Herringbone shear gauges 211, 212, 213 and 214 of the type shown in Figure 4Poisson gauges 215, 216, 217, and 218 of the type shown are attached to the other wide faces. The wiring connecting these strain gauges 211 - 218 to the electronic instrument assembly located within the rotary tool is carried out through holes 220 in the inner end 82.

[0119] The cylinder 86, the inner end 82, the square end on the cylinder 92, and all four connecting portions 206, 208 are made as a single-piece article by selectively laser sintering steel powder. The tungsten carbide disc 90 of the PDC cutter is then attached by brazing, and thereafter the strain gauges 211 - 218 are adhered to the connecting portions 206, 208.

[0120] Although these strain gauges 211 - 218 are attached to surfaces that extend radially rather than circumferentially with respect to the cutter axis, they are connected in a Wheatstone bridge circuit that is similar to the circuit described above. The chevron shear gauges 211 and 213 on the two connecting portions 206 are connected in the Wheatstone bridge as Figure 31 shown. This has the same function as the circuit Figure 21 shown. The shear gauges 212 and 214 on the other two connecting portions 208 are connected in a similar circuit. The Poisson gauges 215–218 are connected in the Figure 32 shown circuit, which has the same function as the circuit Figure 19 shown.

[0121] Figure 33 A cutter similar to Figure 29 and 30 is shown, except that there are three connecting portions 226 instead of four connecting portions 206, 208. These connecting portions 226 respectively carry Figure 5 and 4 the chevron shear gauges 211, 212, and 213 and the Poisson gauges 215, 216, and 217 of the type shown. The two parts of each chevron shear gauge are connected in a Wheatstone bridge circuit with two fixed resistors Rf as Figure 34 shown, where the resistors Ra and Rb represent Figure 5 the two mutually perpendicular gauges of the chevron gauge shown. The two parts of each Poisson gauge are connected in a similar circuit. Then there are a total of six Wheatstone bridge circuits and six differential amplifiers 228.

[0122] Each Wheatstone bridge will eliminate the effect of temperature changes in the same manner as described previously. The chevron gauges in such a Wheatstone bridge will eliminate fully axial strain, since this will have the same effect on the two separate gauges of the chevron gauge.

[0123] Because the gauges are located on three connecting portions 226 at different azimuthal positions around the cutter axis, the degree to which each gauge is stretched or shortened by the shear force on the disk 88 of the cutter depends on the direction of the shear force. However, strain gauges and Wheatstone bridge circuits cannot resolve the force into an axial load and a shear force in the perpendicular direction. Instead, the analog output from the differential amplifier 228 is digitized and recorded. The recorded signal is then computationally processed to separate the axial force from the shear force and to resolve the shear force in two mutually perpendicular directions.

[0124] Figure 35 and 36 shows different forms of strain sensors that can be used to replace the above-mentioned resistance strain gauges. These are optical sensors based on fiber Bragg gratings. By creating a systematic variation in the refractive index within a short length of the optical fiber, a Bragg grating is formed in the optical fiber. The grating selectively reflects light at a specific wavelength that depends on the grating pitch. The strain in the optical fiber changes the grating pitch and thus changes the wavelength at which the grating reflects maximally because there is maximum constructive interference.

[0125] Patent literature regarding the generation of Bragg gratings in photosensitive optical fibers by ultraviolet light irradiation includes U.S. Patents 5,956,442 and 5,309,260 and the literature cited therein. Strain sensors based on fiber Bragg gratings are available from many suppliers, including HBM and National Instruments.

[0126] Figure 35 shows a carrier 250 to which eight individual sensors 251 - 258 formed in an optical fiber 260 are adhered. Two of these sensors 252 and 256 are shown in Figure 35 in greater proportion. Each sensor contains a Bragg grating, which is a short length of optical fiber 262 with a systematic refractive index variation. For use, the optical fiber 260 is connected to an interrogation device schematically represented by 264, which directs light at different wavelengths along the common optical fiber 260, receives the reflections, and determines the wavelength at which the reflectivity is maximum. When a portion of the optical fiber 260 containing the grating is compressed or stretched, the wavelength at which the reflectivity is maximum changes. The observed wavelength change is proportional to the strain and thus to the force causing the strain. The gratings of the eight sensors 251 - 258 are all made with different pitches and thus they reflect different wavelengths. Thus, all of these can be interrogated by the same device 264 that sends and receives light along the common optical fiber 260.

[0127] The carrier 250 is adhered to Figures 10 to 15inside the cylindrical connection portion 84 of a cutter of the type shown, such that four sensors 251 - 254 extend in the axial direction, while sensors 255 - 258 extend in the circumferential direction. The optical fiber 260 is led out through the channel 84. Sensors 251 - 254 are formed in the axially extending portion of the optical fiber, and these observe the axial force on the outer end portion 80 of the cutter, but are not affected by shear forces. Sensors 255 - 259 are not affected by axial forces, but are affected by shear forces. Sensors 255 and 257 are diametrically opposite each other and observe the shear force components parallel to that diameter. Sensors 256 and 258 are also diametrically opposite each other radially along a diameter perpendicular to the diameter connecting sensors 255 and 257. Thus, sensors 256 and 258 observe shear force components perpendicular to those affecting sensors 255 and 257.

[0128] The output from the interrogation device 264 can be in digital form and can be processed by a computer to give measurements of the strain in the connection portion 84 and the forces on the exterior 22 of the cutter. The Bragg gratings are sensitive to both temperature and strain. Therefore, a thermistor or other temperature sensor is attached to the carrier 250, as shown at 266, and processing the output from the interrogation device 264 includes correction for temperature effects.

[0129] Another technique that may be used for strain sensors within the connection portion 84 is the piezoresistive sensor, also known as a "semiconductor strain gauge". Such a sensor has a conductive path that includes a semiconductor material. The resistance of such a material is affected by the strain of the material, resulting in a change in the atomic spacing within the semiconductor. The change in resistance in response to strain is greater than that of a resistive sensor. Suppliers of such gauges include Micron Instruments of Simi Valley, California, USA and Kulite Semiconductor Products of New Jersey, USA.

[0130] Figures 37 - 41 The cutter shown has the same shape and dimensions as the Figures 7 - 15 cutter, but it utilizes a capacitive position sensor to observe the displacement of the outer end portion 80 relative to the inner end portion 82. Figure 37 Similar to Figure 12 . A solid cylinder attached to the disc-shaped body 90 of the PDC cutter has been machined to form a cylindrical connection portion 84 and a central strut 270, both of which extend from the solid cylindrical portion 272 of the body 90 attached to the PDC cutter. Figure 38 The portion shown is generally the same as Figure 14 in. It consists of an inner end portion 82 and a square end portion 92, but the hole 82 does not extend completely through the inner end portion 82.

[0131] The capacitive sensor consists of an electrically insulating material disk 274 adhered to the strut 270 and a larger disk 276 of insulating material adhered to the inner end 82. The facing surfaces of disks 274 and 276 have electrodes disposed therein. As shown in FIG. 70, the inserted electrode in portion 274 is a square conductive plate 280. FIG. 71 shows five square conductive plates 281 - 285 inserted into disk 276.

[0132] The axial force on the outer end 80 pushes the plate 210 closer to the conductive plates on portion 276, and the increase in capacitance of the capacitor formed by plates 280 and 285 can be measured. The shear force on the outer end 80 causes the cutter to deform such that the end of the strut 270 is slightly displaced from the axis of the inner end, and this can be measured as a change in capacitance between plate 280 and two or more of the plates 281 - 284. These capacitance measurements are made by an electronic instrument assembly that repeatedly measures the capacitance using an alternating potential applied successively to plate 280 and each of the plates 281 - 285. Since plates 281 and 283 are located on one diameter and plates 282 and 284 are located on a perpendicular diameter, the shear force can be resolved into components along these diameters.

[0133] Another possibility is structurally similar to Figures 37 - 41 the arrangement in, where portion 274 is omitted from the end of the strut 270 and inductive sensors are provided in the positions of plates 280 - 285. The force on the outer end that causes the connecting portion 84 to deform causes a change in the position of the strut 270 and thus a change in the inductive coupling between the inductive sensor and the strut 270. These changes are observed and measured as changes in the output of the inductive sensors at positions 280–285.

[0134] It should be understood that the embodiments and examples described in detail above can be modified and varied within the scope of the concepts they illustrate. The proportions can vary and may not be as shown in the drawings, which are schematic and intended to explain the layout and function of the embodiments. The features mentioned above or shown in a single embodiment above can be used in any combination and together with combinations that have been specifically shown and described. More specifically, in cases where features are mentioned in the above combinations, the details of the features used in one combination can be used in another combination where the same feature is mentioned. Thus, all such modifications are intended to be included within the scope of the present disclosure as defined by the following claims.

Claims

1. A rotary cutting tool for forming or enlarging an underground conduit, comprising: A tool body defining a cavity having an open front end; And A cutter assembled into the cavity and attached to the tool body, the axis of the cutter extending from the open front end into the cavity, the cutter having: A cutter body, an outer end portion of which is exposed at the open front end of the cavity; And At least one connecting portion connecting the cutter to the tool body, the cross-section of the at least one connecting portion being smaller than the cross-section of the outer end portion, and the at least one connecting portion also having greater flexibility than the outer end portion, Wherein the outer end portion and the at least one connecting portion are sufficiently movable within the cavity such that lateral movement of the outer end portion relative to the cavity causes strain in the at least one connecting portion, but the cavity sufficiently closely surrounds at least a portion of the outer end portion to limit such lateral movement and limit deformation of the at least one connecting portion; At least three sensors attached to the at least one connecting portion at different azimuthal positions around the axis and arranged to measure forces acting on the outer end portion in a plurality of directions transverse to the axis, the forces causing strain in the at least one connecting portion; and At least three sensors attached to the at least one connecting portion at different azimuthal positions around the axis and arranged to measure forces acting on the outer end portion in the direction of the axis, the forces causing strain in the at least one connecting portion, The at least one cutter body includes an inner end portion located in the cavity and fixed to the tool body, wherein the at least one connecting portion extends between the inner end portion and the outer end portion and is rigidly connected to the inner end portion and the outer end portion, and the at least one connecting portion has a cross-section smaller than the cross-sections of the inner end portion and the outer end portion and has greater flexibility than the inner end portion and the outer end portion, Wherein the at least one connecting portion is provided with an inner cavity, and the at least three sensors are disposed on an inner surface of the inner cavity.

2. The rotary cutting tool according to claim 1, wherein, The outer end portion of the cutter body is cylindrical, and at least a portion of the inner end portion is non-cylindrical and engages a mating portion of the cavity, the mating portion having a shape that restricts rotation of the inner end portion.

3. The rotary cutting tool according to claim 1, wherein, The cavity sufficiently closely surrounds at least a portion of the outer end portion of the at least one cutter to prevent the at least one connecting portion from deforming beyond elastic strain.

4. The rotary cutting tool according to claim 1, wherein, The dimensions of the at least one connecting portion and the surrounding cavity of the tool body are designed such that the spacing between the at least one connecting portion and the wall of the cavity is greater than the spacing between the outer end portion and the wall of the cavity.

5. The rotary cutting tool according to claim 1, wherein the at least one connecting portion includes a plurality of connecting portions that extend between an inner body portion and an outer body portion and are rigidly connected to the inner body portion and the outer body portion.

6. The rotary cutting tool according to claim 1, wherein the at least one connecting portion includes a single connecting portion that defines a cylinder extending between an inner body portion and an outer body portion and is rigidly connected to the inner body portion and the outer body portion.

7. The rotary cutting tool according to claim 1, wherein, The outer end portion has a cutting surface exposed at the open front end of the cavity, and the cutting surface has a Knoop hardness of at least 1600.

8. The rotary cutting tool according to claim 1, wherein, The outer end portion is integral with the at least one connecting portion.

9. The rotary cutting tool according to claim 1, wherein, The inner end portion, at least a part of the outer end portion, and at least one connecting portion of the cutter body are made by an additive manufacturing technique.

10. The rotary cutting tool according to claim 9, wherein, The inner end portion, at least a part of the outer end portion, and at least one connecting portion of the cutter body are made by selective laser sintering or electron beam melting of metal powder.

11. The rotary cutting tool according to any one of the preceding claims 1-10, wherein, The sensor includes at least one capacitive or inductive sensor for sensing the position of the outer end portion relative to the tool body.

12. The rotary cutting tool according to any one of claims 1 to 10, wherein the at least one connecting portion includes a single connecting portion that defines a cylinder extending between and rigidly connected to the inner body portion and the outer body portion, and the sensor includes a plurality of strain sensors attached to the inner wall of the cylinder.

13. The rotary cutting tool according to claim 12, wherein, The strain sensors attached to the connecting portion include one or more of a resistance strain gauge, a fiber Bragg grating sensor, or a piezoresistive strain sensor.

14. The rotary cutting tool according to any one of claims 1 to 10, wherein, The tool body is a drill bit body.

15. The rotary cutting tool according to any one of claims 1 to 10, wherein, The tool body is a reamer or a reamer block body.

16. A method of observing forces on a cutter of a rotary cutting tool, comprising: Positioning the rotary cutting tool according to any one of the preceding claims in a wellbore; and Observing or recording data from one or more of its sensors when operating the tool within a conduit.

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