CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of, and priority to, U.K. Patent Application No. 1519329.5, filed November 2, 2015, and titled "Rotary Milling Tool," which application is expressly incorporated herein by this reference in its entirety.

BACKGROUND

At times, it may be desired to remove a length of tubing that has been fixed in place in a wellbore.

This tubing may be wellbore casing that is surrounded by cement. Sometimes, such removal of a length of tubing is done in preparation for setting a cement plug when a well is being abandoned. Removing a length of tubing that has been fixed within a wellbore is customarily done with a rotary milling tool, customarily referred to as a section mill or casing mill, which comminutes the tubing to swarf.

In the case of a section mill, expandable blades are activated downhole and cut into the casing. By rotating the section mill and moving the section mill axially within the wellbore, a section of casing can be milled away. A difficulty can arise, however, from couplings on the exterior of lengths of casing tubulars. Standard couplings have an internal thread that engages external threads on end portions of mating casings. It is possible that the milling tool will cut into the casing string within such a coupling before completely milling the coupling. The result is that part of the coupling becomes detached during milling and produces a ring encircling, but no longer attached to, the casing tubulars. Such a ring can slide axially along the tubing and can rotate relative to the tubing. Eventually, such a ring is pushed against an obstacle— possibly the next coupling— which restrains further axial movement. It may then block the further advancement of the tool. As the rotary tool continues to turn, the ring itself is not cut because it rotates within the wellbore and with the milling tool. The freely rotating ring also may restrict the milling tool's cutters from contacting casing tubulars that are fixed in the wellbore, so the milling tool may rotate but may not cut anything, or may cut with reduced efficiency.

SUMMARY

Some aspects of the present disclosure relate to tools and methods for removing tubing within a wellbore.

According to some aspects of the present disclosure, a rotary milling tool for comminuting tubing in a wellbore includes a tool body and a plurality of cutting assemblies projecting from or extensible from the tool body and distributed azimuthally around a longitudinal axis of the tool body. At least one cutting assembly may include a supporting structure and a plurality of hard-surfaced cutters attached thereto, with the shape of the supporting structure and the positions of the cutters thereon being such that a first cutter or group of cutters provide cutting surfaces at positions whose distance from an axially leading end of the rotary tool decreases as radial distance from the tool axis increases. According to one or more aspects that may be combined with any one or more other aspects, a cutter or cutters with cutting positions arranged in this way can mill a coupling or other item projecting from tubing progressively from its outside in an inwardly direction, toward the tubing. This avoids creating a separate ring generated when the attachment to the tubing is destroyed before the ring to which it is attached.

According to one or more aspects that may be combined with any one or more other aspects disclosed herein, a method of removing tubing in a wellbore includes comminuting the tubing with a rotary tool that includes a tool body and a plurality of cutter assemblies projecting from or extensible from the tool body and distributed azimuthally around a longitudinal axis of the tool body. At least one cutting assembly may include a supporting structure and a plurality of hard-surfaced cutters attached thereto. A first cutter or group of cutters may be positioned to cut into material projecting outwardly beyond the exterior of the tubing at cutting positions arranged so that distance from an axially leading end of the rotary tool decreases as radial distance from the tool axis increases. As a result, removal of projecting material may progress radially inwardly toward the tubing as the tool advances.

The statements above may refer to cutters and/or structure of a cutting assembly or tool in an "as new" configuration in which it is manufactured, before use. Some milling tools change shape as they wear, but the change of shape and the timing have been unpredictable. A cutting assembly as set out above may have the stated features when it is inserted into the wellbore, and so will reliably have these features when milling through couplings begins. The cutters that are used may be sufficiently durable that there is no significant change in shape during use, or over prolonged periods of use.

In addition to the cutter or group of cutters that can remove material projecting outwardly from tubing, a cutting assembly may also have a second cutter or group of cutters that provide cutting surfaces for milling the tubing itself. The second cutter or group of cutters may be located radially inwardly from the cutting surfaces of the first cutter or group of cutters. This second cutter or group of cutters may have cutting positions whose distance from an axially leading end of the rotary tool increases as radial distance from the tool axis increases, so that removal of tubing may progress outwardly from the inside wall of the tubing as the tool advances.

For the tools and methods described herein, it is possible that some or even each of the cutting assemblies could be fixed to the tool body and project from it. A tool with fixed cutting assemblies could be used to mill tubing where it is possible to begin at an end of the tubing (e.g., a casing mill beginning milling at the surface). In some forms of a tool, however, the cutting assemblies are extensible from the tool body by operation of a drive mechanism. The tool may then be inserted into tubing with the cutting assemblies retracted and when the tool is at the position where milling or other cutting is to start, the cutting assemblies are extended by operation of the drive mechanism and cut outwardly through the tubing as they are extended. According to one or more aspects that may be combined with any one or more aspects herein, an extensible cutting assembly may have a third cutter or group of cutters that provides cutting surfaces radially outwardly from the cutting surfaces of the first cutter or group of cutters and serve for cutting outwardly through the tubing as the cutting assemblies are extended from the tool body.

The supporting structure of a cutting assembly may have (and may have been manufactured with) one or more edges arranged so that distance from an axially leading end of the rotary tool decreases as radial distance from the tool axis increases and the first cutter or group of cutters may be adjacent such an edge or edges. Such an edge may lie at one side of a recess in the support structure. A cutting assembly may be shaped to extend radially outwardly across the upper end of the tubing that is to be milled while also including a region that projects axially into an end portion of the uncut tubing and a region that projects axially forward outside the end portion of the uncut tubing. These portions that project axially forwardly will then lie at either side of a recess extending axially back from the leading edge of the cutting assembly. The uncut end of the tubing will project into this recess and the cutting positions for cutter(s) milling couplings from the outside and cutter(s) milling tubing from the inside may be located at either side of the recess.

In accordance with one or more aspects that may be combined with any one or more other aspects herein, the rotary tool may have at least three cutting assemblies distributed azimuthally around it at the same axial position. For instance, there may be three cutting assemblies at 120° azimuthal intervals around the tool body, four at 90° intervals, six at 60° intervals, or the like. In some embodiments, cutting assemblies may be distributed azimuthally at unequal intervals.

According to some aspects, when a tool has expandable cutting assemblies, the drive mechanism controlling expansion may be powered hydraulically by fluid pumped from the surface. The drive may be arranged to expand a single cutting assembly or a plurality of cutting assemblies, distributed azimuthally around the tool body, in unison. The travel of the cutting assemblies as they are expanded may be motion around a pivotal attachment to the tool body or it may be a motion in which the cutting assemblies move outwardly without changing their orientation relative to the tool body. The latter may be brought about by constraining each cutting assembly to be movable along a pathway (e.g., sliding along a linear path). More specifically pathways may be angled relative to the tool axis and configured so that when the cutting assemblies are moved axially they also move outwardly in unison.

Cutters according to aspects of the present disclosure may have hard faces and may be bodies of a hard material. Tungsten carbide is an example material that may be used for cutters due to its high hardness and toughness, and its good thermal stability. Other hard materials that may be used are carbides of other transition metals, such as vanadium, chromium, titanium, tantalum, and niobium. Silicon, boron, and aluminum carbides are also hard carbides. Some other hard materials are boron nitride, aluminum boride, polycrystalline diamond, polycrystalline boron nitride, and various carbonates. A hard material may have a Knoop hardness of 1,300, 1,600, 1,800, or even more. One or more of the cutters of aspects of the present disclosure may have a shape of cutting surface and a position on the tool such that at least part of the cutting surface is at a positive back rake. In the context of the present application, a positive back rake means that the part of the cutting surface is inclined relative to the direction of rotation such that an edge where the cutting surface cuts furthest into the tubing, coupling, or other outward projection is a trailing edge of the cutting surface relative to the direction of rotation and extends from such an edge with a back rake angle (e.g., between 15° to 70° or possibly between 30° and 60°), and such an edge has an angle (e.g., greater than 90°) included between the cutting surface and the surface of the cutter body following the cutting surface. When there is a back rake angle in a range from 15° to 70° between at least part of the cutting surface and perpendicular to the direction of traverse relative to the workpiece, the angle between the cutting surface or part thereof and the direction of rotation may lie in a range from 20° to 75°.

As disclosed in a currently unpublished GB patent application, the inventors have found that a cutting surface with a large back rake angle leads to the formation of swarf with less rigidity. It may be in the form of short pieces weakly connected together, or sometimes not connected at all. Changing the nature of the swarf reduces the risk of entangled swarf forming a "birds nest" blockage in the wellbore. A significant back rake may cause the cutter to be pressed against the tubing with more force than would be used with less back rake or none. In a machine-shop context, increased force between a cutting tool and workpiece would be a disadvantage, but we have recognized that when operating a cutting tool in a wellbore, a greater force may be beneficial. More force can be provided by increasing the weight on the tool and control of the cutting speed by varying the weight on the tool becomes easier. Increasing the included angle between the cutting surface and a surface of the body behind the cutter surface makes the cutter more robust and reduces the risk of the cutter being chipped or broken.

The cutter body of any one or more aspects herein may be dimensioned such that the at least part of a back-raked cutting surface extends at least 2 mm from the edge where the cutting surface cuts furthest into the tubing. The cutter body's surface trailing back from such an edge may extend at least 2 mm (and possibly at least 3 mm or at least 5 mm) back from the edge.

The length of tubing removed by a tool or method as disclosed in any one or more aspects herein may be considerable. It may, for example, be a length that is many times (for instance more than 10 times) greater than the axial length taken up by the cutters and guide surfaces of the tool itself. The length of tubing removed may be 5 meters, 10 meters, 25 meters, 50 meters, or more. The removal of tubing may be carried out for various reasons, but in some instances it may be done before plugging and abandoning a wellbore, for slot recovery, for wellbore departure, or for other reasons.

This summary is provided to introduce a selection of concepts that are further described below. This summary is not intended to be used as an aid in limiting the scope of the subject matter claimed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic axial view of a rotary milling tool with fixed cutting assemblies, positioned to mill tubing from one end, according to one or more aspects of the present disclosure;

FIG. 2 shows a rotationally leading face of one cutting assembly of the tool of FIG. 1 when the tool is milling tubing;

FIG. 3 is a cross-sectional view taken on line B-B of FIG. 2;

FIG. 4 shows the rotationally leading face seen in FIG. 2 when the rotary milling tool is milling a tubing coupling;

FIG. 5 is a face view of the leading end of a cutter, according to one or more aspects of the present disclosure;

FIG. 6 is a side view of a cutter in contact with a workpiece;

FIG. 7 is a perspective view of another rotary milling tool, according to one or more aspects of the present disclosure;

FIG. 8 is a sectional elevation view of the tool of FIG. 7, with the extensible cutting assemblies retracted;

FIG. 9 is a sectional elevation view of part of the tool of FIG. 7 with a cutting assembly partially extended;

FIG. 10 is a sectional elevation view of part of the tool of FIG. 7 with a cutting assembly fully extended and milling tubing;

FIG. 11 is a perspective view of one cutting assembly, according to one or more aspects of the present disclosure;

FIG. 12 is an enlarged underneath view of the cutting region of a cutting assembly, according to one or more aspects of the present disclosure;

FIG. 13 diagrammatically shows the radial and axial layout of cutters of a cutting assembly of FIGS. 7 to 12; and

FIG. 14 is a side view of parts of a cutter block used in another rotary tool, according to one or more aspects of the present disclosure.

DETAILED DESCRIPTION FIGS. 1 to 6 show a rotary milling tool with fixed cutting assemblies used for milling tubing when it is possible to access an upper end of the tubing. For example, casing section milling downwardly from the top of a wellbore may be carried out when it a sealing plug is to be placed at a depth below the surface (e.g., at a modest depth such as within 700 meters of the surface as part of the process of abandoning a well).

As shown, an existing wellbore may be lined with lengths of tubing 12 (wellbore casing) that can be screw-threaded at each end and joined end-to-end by correspondingly threaded couplings 14 (seen in FIGS. 2 and 4). Although standard couplings have an internal thread to engage an external thread on the end portions of casing tubulars, that thread may not extend fully to each end of a coupling. Cement 15 can be placed in the annular region between the casing and the surrounding rock formation to hold the tubing 12 within the formation. The tubing 12, couplings 14, and cement 15 may have been in place for some years before operations are undertaken to cut or remove portions of the tubing 12.

FIG. 1 schematically illustrates the tool and wellbore looking axially from above. The tubing 12 is shown with hatching. The tool has a central hollow cylindrical body 16 that can be attached to the bottom end of a drill string. This body 16 defines a bore or through passage 17 for drilling fluid pumped down the drill string. The fluid flows out of the bottom end of the tubing and can return up the annulus around the drill string. The direction of rotation is indicated by arrow A.

In the illustrated aspect, six cutting assemblies 18 are rigidly attached to the central body 16 and project radially out from it at 60° intervals azimuthally around the axis of the body. FIGS. 2 and 4 show the rotationally leading face of one cutting assembly 18. Each cutting assembly 18 may include a supporting structure and cutters attached thereto. The supporting structure may be a block 20 rigidly coupled to the body 16, although the blocks 20 may be expandable in other aspects (see FIGS. 7-14). The cutters 22-28 may be generally cylindrical and secured in pockets or other cavities in the block 20 so that they are partially embedded in block 20 with leading ends exposed and facing the direction of rotation. In some aspects, the cutters may not be cylindrical and may instead have other configurations. The cutters of the various aspects of the present disclosure may be made of a hard material such as, but not limited to, tungsten carbide. This hard material may be provided as a powder. The powder may then be compacted into the shape of the cutter and sintered giving a desired hardness. Manufacturers of sintered tungsten carbide cutters include Cutting and Wear Resistant Developments Ltd, Sheffield, England and Hallamshire Hard Metal Products Ltd, Rotherham, England.

Tungsten carbide is a material may be used for cutters 22-28 because it is very hard and also has good thermal stability. Other hard materials that may be used are carbides of other transition metals, such as vanadium, chromium, titanium, tantalum, and niobium. Silicon, boron, and aluminum carbides are also hard carbides. Some other hard materials are boron nitride, aluminum boride, polycrystalline diamond, and polycrystalline boron nitride. A hard material may have a hardness of at least 1,300, or at least 1,600, and possibly at least 1,800 or more on the Knoop scale. By contrast, steel, other metals or metal alloys, or other materials used for the block 20 are likely to have a Knoop hardness below 1,000.

The cutters 22-28 may be secured in pockets in the block 20 by brazing, but other methods of securing cutters may be used if desired. For instance, mechanical interlocks, welding, adhesives, frictional fits, or other securement methods may be used.

As shown in FIG. 2, the block 20 may have an upper part that extends radially outwardly of the tubing 12 (e.g., after extended) and an outer part 30 that extends downwardly at, around, or along the exterior of the tubing 12. Thus, there may be a recess in the block 20 that extends axially upwardly into the block 20 between its inner part 31 and outer part 30. One or more cutters 27 may be located at the upper end of this recess and one or more cutters 24-26 may be attached to the outer part 30 at the radially outer edge of the recess, which outer edge is optionally angled such that the distance from an axially leading end of the rotary tool decreases as the radial distance from the tool axis increases (e.g., tapered outward in a downhole direction).

FIG. 2 shows action of the tool while it is cutting tubing 12, but has not yet reached a coupling 15. A radially outwardly facing surface 32 on the inner block part 31 may be a partially-cylindrical outwardly facing surface 32, with a radius such that the surface 32 is centered on the tool axis. The cutter 22 may be positioned so that its radially outer extremity is at or near the same distance from the tool axis as the surface 32. Thus, the radial extremity of the cutter 22 may be aligned with the surface

32 as shown by FIG. 3. There is also a part-cylindrical outwardly facing surface 33 that may be centered on the tool axis at a larger radius from the tool axis as compared to the surface 32. The extremity of cutter 23 may be at or near the same distance from the tool axis as the surface 33, and may thus be aligned with the surface 33.

The rotating tool may advance axially in the downward direction shown by arrow D in FIGS. 2 and 4. The tubing 12 may have some corrosion and deposited material on its inside surface as depicted schematically at 36. The axially leading cutter 22 on each block 20 may be positioned to remove this material 36 and optionally to also remove some material from the inside wall of the tubing 12, thus creating a new inwardly facing surface on the tubing 12. This surface is indicated 42 in FIG. 3.

Because the part-cylindrical outwardly facing surfaces 32 are centered on the tool axis and aligned at the same radial distance from the tool axis as the extremities of the leading cutters 22, they may also be a close fit to the inward facing surface 42 created on the tubing by the cutters 22 as is shown in FIG.

3, and may slide over this new inwardly facing surface 42 as the tool rotates. The cutters 23 may remove a further thickness of tubing 12, creating a fresh inwardly facing surface on which the surfaces

33 slide. This close fit of surfaces 32, 33 to surfaces created on the tubing 12 may position the tool axis accurately relative to the tubing 12, and can stabilize the tool to reduce vibrations encountered by the tool.

As the tool progresses downwardly, the cutter 26 (or some combination of cutters 26-28) may remove some thickness from the exterior of the tubing 12 and any remainder may be cut by the cutter 27. One or both of cutters 24 and 25 may cut through cement 15 around the tubing 12. The cutters 24- 26 optionally cut through cement, and the radially outermost cutter 28 may also cut through cement 15.

FIG. 4 shows the function of the tool when it comes to coupling 14. The cutters 22, 23 continue to cut tubing 12 as described herein. The cutter 24 may be the first cutter to contact the coupling 14, and it may remove part of the thickness from the exterior of the coupling 14. As the tool advances, the cutter 25 may remove a further thickness and finally the cutter 26 may remove the remaining thickness of the coupling 14, as well potentially a portion of the thickness from the exterior of the tubing 12. Thus, the coupling 14 may be milled to swarf by working radially inwardly from the exterior of the coupling, greatly reducing opportunity for part of the coupling 14 to become a detached ring. FIGS. 5 and 6 show the example shape of cutters 22, 23, 24, 25, and 27. Each of these cutters may have a cylindrical body 44 and a shaped leading end in which a front face 46 with smaller diameter than the body 44 is surrounded by a tapered annular surface 48 that is inclined at an angle of 45° to the front face 46. The angle included between the side wall of the cutter body 44 and the annular surface 48, as shown, is 135°, although the angle may be varied. For instance, in other embodiments, the angel included between the side wall of the cutter body 44 and the annular surface 48 may be within a range having an upper limit, a lower limit, or both upper and lower limits including any of 90°, 105°, 120°, 135°, 150°, 165°, or 180°. In other embodiments, the angle may be less than 90° or greater than 180°. When the cutter is mounted on a tool, part of the annular surface 48 may act as a cutting surface. With this geometry, for instance, the positive back rake angle between the cutting surface 48 and line perpendicular to the workpiece 52 (tubing or coupling) being cut is approximately 45°. The inventors of the present application have discovered that cutting with a substantial back rake angle leads to swarf with much less mechanical strength and rigidity than swarf produced by cutters without any back rake. This cutting action first makes the material more brittle, so that when swarf separates from the workpiece, the pieces are smaller. As a result, there is a reduced risk that pieces of the swarf will hook together in so-called "bird-nesting" and clog the path of flow back to the surface.

Each of the cutters may be the same, or one or more different types, shapes, or other configurations of cutters may be used. For instance, in FIGS. 2 and 4, the cutter 26 is slightly different. The cutter 26 may also be cylindrical with a shaped leading end including an annular cutting surface; however, the angle of this cutting surface may be different. For instance, instead of a 45° back rake, the back rake angle may be greater (e.g., approximately 60°). With such a large back rake angle, the remnant of coupling 14 that is being cut is also pushed inwardly with a force greater than the cutting force. This pushes the remnant of the coupling 14 forcefully against the partially cut tubing 12 and friction and plastic deformation can act to hold the uncut remnant of the partially milled coupling 14 in place while the coupling 14 is being milled.

The cutter 28 may, in some aspects, be provided to assist with cutting cement in the path of the outer part 30 of the cutting assembly. Optionally, the cutter 28 may not cut the metal or other material of the tubing and couplings, and optionally has a different shape than the cutters 22-27. For instance, the cutter 28 may have a flat leading face as its cutting surface (or a flat cutting surface with a small bevel). In some aspects, this cutter 28 could be a polycrystalline diamond cutter which has sintered diamond at its leading surface.

The six projecting cutting assemblies 18 shown in FIG. 1 may all be identical to each other and constructed as described above with reference to FIGS. 2 to 6. In some aspects, however, one or more of the cutting assemblies 18 may differ from one another, or from each other. By way of example, the cutting assemblies 18 may each have blocks 20 and cutters 22-28 with the general configuration shown in FIGS. 2 and 4, but with slight differences in the axial and radial positions of cutters so that corresponding cutters on successive assemblies cut to progressively increasing radii. In such an aspect, each cutter 22-28 may be at a unique radial and axial position relative to each other cutter on a different cutting assembly 18. In other aspects, however, there may be redundancy in the radial and axial position of one or more cutters (and potentially each cutter may have redundancy). Where a cutter is at a different radial/axial position relative to each other cutter, the cutter can be considered to be a "single set" cutter. Where at least two cutters share a particular radial/axial position, the cutters can be considered to be "plural set" cutters. Each cutting assembly 18 may include single set cutters, plural set cutters, or a combination of single and plural set cutters.

In another aspect, one or more of the cutting assemblies 18 (e.g., three of the six cutting assemblies) may extend radially outwardly beyond tubing and have cutters 24, 25, 26 for cutting the couplings, while one or more other of the cutting assemblies 18 (e.g., the other three of the six cutting assemblies) may have cutters such as 22, 23, and 27 for cutting tubing from the inside, but do not extend radially outwardly beyond the tubing (e.g., the casing or coupling).

FIGS. 7-14 show an example tool that uses the same principles for milling tubing but is expandable downhole. This allows the tool to be inserted to a chosen depth through existing tubing, and then expanded to cut outwardly through the tubing before being made to advance axially to remove a length of tubing. Thus, the tool may pass through casing that is going to remain in the wellbore, to reach casing or other tubing that will be removed. One circumstance in which an expandable tool may be used is when removing tubing and exposing the rock formation around a wellbore in preparation for setting a cement plug for a wellbore abandonment operation.

FIGS. 7 to 10 show the general layout and function of the expansion mechanism of an example embodiment of a rotary milling tool. As seen in the perspective view in FIG. 7, the tool may include a tubular main body 60 with upper end 62 and lower end 64. In a central section there may be three longitudinal slots 66 distributed at 120° intervals around the tool axis, although any number of slots 66 at any of various equal or unequal angular intervals may be used.

The tool can be incorporated into a drill string in some aspects. As show in FIG. 8, the upper and lower end regions may include portions 68 (e.g., box tool joints) that can include threads to enable a threaded connection to a drill pipe, drill collar, or other component of a drill string.

A central tube 70 may have a sliding fit within the main body 60. Axial movement of the tube 70 relative to the main body 60 may be guided by the body 60 and one or more optional sleeves 71 coupled to the body 70. This tube 70 may be urged upwardly by a return spring 72. Each slot 66 may houses an arm 74 that can be used as a cutting assembly. In some embodiments, the arms 74 can swing around pivot 75 from the retracted position shown in FIG. 8 to the extended position shown in FIG. 10. Each arm 74 may pivot about 90°, although an arm 74 may pivot more or less than 90° in other aspects. In the illustrated embodiment, the inner end of each arm 74 may be formed with projections 76, that can function as gear teeth and allow the arms 74 to act as pinions. These mesh with projections 78 from the tube 70, which can act as a pinion. When the tool is in its retracted condition as shown in FIG. 8, drilling fluid pumped down the drill string can flow downwardly through the tube 70 and out of the lower end 64 of the main body 60. When the tool— included within a drill string— has been lowered to the desired depth, fluid pressure may be used to activate the tool. In some aspects, this may include increasing the fluid pressure. The fluid flowing through the restriction 80 may create a pressure increase that causes the tube 70 to overcome the bias of the return spring 72 and slide or otherwise move axially downward within the body 60. In another aspect, a ball, dart, or other obstruction device may be dropped down the drill string. This ball may be dimensioned to block the tube 70 at the restriction 80. Pressure of the drilling fluid then acts on the ball and the tube 70 to force the tube 70 to slide downward against the biasing force of return spring 72, thereby compressing the return spring 72. Regardless of the activation mechanism, as the tube 70 moves downwardly, the projections 78 on the tube 70 meshing with the teeth 76 on the arms 74, urge the arms 74 to rotate around their pivots 75 toward their extended positions as shown in FIG. 10. In some embodiments, outer surfaces 81 of the arms 74 may abut stop blocks 82 bolted or otherwise coupled to the main body 60 when the arms 74 are in the fully extended position. Downward movement of tube 70 may also allow some drilling fluid to flow out through an opening 84 in the tube 70, into a chamber 85 radially between the body 60 and the tube 70, and out of the body 60 through nozzles 86 in the body.

While activation of the tool may be controlled hydraulically, in other embodiments other activation mechanisms may be used. For instance, a downhole motor and power source may be used to allow electric activation. In some embodiments, a signal (e.g., a wireless signal such a series of pressure or flow pulses) may be sent to the tool. The signal may be recognized as an instruction to activate or deactivate the tool. A processor, controller, or other electronic device may then activate the motor to move the tube 70. Other signals may also include instructions sent through the drilling fluid in other manners (e.g., changes in drilling fluid type or density, an RFID tag, etc.). Any other activation device used in connection with expandable downhole tools may also be used in connection with some aspects of the present disclosure.

In some aspects, each arm 74 may carry a number of cutters that each optionally have the general configuration shown by FIGS. 5 and 6. A generally cylindrical body may be partially embedded in the arm 74 and an exposed leading end shaped so that an annular cutting surface is at a positive back rake angle. These cutters may be sintered tungsten carbide or made from additional or other materials as discussed herein. The cutters are shown in FIGS. 7 and 8, but some example positions of the cutters are shown in more detail in FIGS. 9 to 12.

As shown in FIG. 10, each arm 74 may extend radially outwardly beyond the tubing 12 that is being milled or otherwise cut. An outer portion 87 of the arm projects axially forward (i.e., downward in FIG. 10) at the exterior of the tubing and a recess 88 extends into the arm 74 between this outer portion 87 and the remainder of the arm 74 which is within the tubing 12. The radially outer edge of this recess 88— which may also be an inner edge of the outer portion 87— may be tapered, inclined, or otherwise configured such that the distance from the axially leading end (e.g., downhole end) of the rotary tool generally decreases as the radial distance from the tool axis increases. Any taper on the inner edge of the outer portion 87 may be linear, curved, step-wise, or otherwise configured. In some aspects, the inner edge may be undulating or contoured such that the radial distance from the tool axis may increase and decrease when moving toward the axially leading end of the rotary tool.

The axial extent of an arm 74 may be limited by the space available for it within the slot 66 in the body 60. Consequently, in some embodiments, less than all of the cutters on each arm may be exposed at the rotationally leading face of the arm 74. This is shown by the perspective view FIG. 11 and by FIG. 12, which is an enlarged view of the outer part of an arm seen from below. The radially outward end face of the arm 74 (e.g., adjacent cutters 98, 100, 102 in FIG. 11) may incorporate a channel 89. The channel 89 optionally intersects and continues into a channel 90 extending radially inwardly some distance along the underside of the arm 74 (e.g., from the outward end face toward the cutters 91, 92). Cutters 92, 94, 96, 98, 100, and 102 may have their leading ends exposed at the rotationally leading face 77 of the arm 74. Cutters 91, 93, 95, and 97 may have their leading ends exposed in the channel 90. The radial and axial positions of the cutters are shown diagrammatic ally in the profile view of FIG. 13, in which the cutters are each shown aggregated in a single plane, without differing circumferential positions.

In use, a tool according to aspects of the present disclosure may be attached to a drill string and lowered to the depth at which milling out of section of casing tubing 12 is to begin. The drill string and tool may be rotated while their axial positions are at least temporarily kept about constant. Drilling fluid is pumped down the drill string and the tool is activated (e.g., a ball is dropped to lodge at restriction 80) to start expansion of the arms 74. Initially each arm extends until the cutter 102 on the arm begins to cut into the tubing 12 as shown in FIG. 9. In some embodiments, a downhole motor may be used to rotate the tool, rather than by rotating the tool from surface.

As the arm 74 cuts into the tubing 12, the arm 74 can expand radially farther. After the cutter 102 cuts through the tubing 12, expansion continues with cutter 100 and then cutter 98 cutting the tubing 12. When the fully extended position is reached (see FIG. 10), weight or additional weight can be applied to the tool so that axial advance of the tool begins. The cutting action at this stage may be generally analogous to that shown by FIGS. 2 and 4. Tubing 12 is progressively cut from the interior working outwards, and by the cutter 94 at the upper edge of the tubing 12. The first cut is made by cutter 91, the second by cutter 92 which is exposed at the leading face 77 and then additional cuts by cutters 93 and 94. It is noted that cutter 94 is optionally positioned slightly differently from cutter 27 in that the center of cutter 94 may be slightly radially inward from the exterior of the tubing 12, although the cutter 94 may be centered with the exterior of the tubing 12 or slightly radially outward from the exterior of the tubing 12 in other aspects.

The steel or other structure of arm 74 may include surfaces 111, 112, and 113, seen as edges in FIG. 12. The surfaces 111-113 may be generally aligned with extremities of cutters 91-93 in some aspects, so that these surfaces can slide on or along new metal surfaces cut on the tubing by the cutters 91-93, respectively, and thereby position the tool at a desired position within the tubing 12. As can be seen from FIG. 13, when the tool reaches a coupling 14, the coupling may initially be cut from a radially outward surface toward a radially inward surface by cutter 95, then by cutter 96, followed by cutter 97. One or more of the cutters 95-97 may have a back rake as discussed herein. For instance, the cutter 97 may have a back rake of 60° like the cutter 26 described earlier. This large back rake enables the cutter 97 to push the remnant of the coupling 14 hard against tubing 12. The remnants of the coupling and tubing are finally removed by cutter 94. Cutters 94-97 constitute a group of cutters for cutting the couplings 14, and are adjacent the outer edge of recess 88, which may be such that the distance from an axially leading end of the rotary tool decreases as radial distance from the tool axis increases. Thus, these cutters are also optionally arranged such that distance from the axially leading end of the rotary tool decreases as radial distance from the tool axis increases, the couplings 14 are milled progressively inwardly from the outside and are comminuted to swarf without becoming detached from the tubing 12.

The arms 74 that are optionally distributed at 120° intervals around the body 60 may be similar to each other in the number and layout of cutters. The arms 74 may, however, vary slightly in the axial and radial positioning of cutters. For instance the cutters 91-93 on one arm 74 may be positioned at slightly greater radius and axially slightly above (e.g., uphole of) the corresponding cutters on the preceding arm 74. Cutters on the next arm 74 may be at a still greater radius and still farther axially above the corresponding cutters on the first arm 74. With such an arrangement, the cutters 91-93 on the three arms 74 can each cut helices as they rotate and advance so that the work of cutting tubing is shared by each of the cutters on each of the arms. In such an arrangement, each cutting element 91- 93 may be a single-set cutter.

Other mechanisms may be used to expand cutters to mill tubing, and concepts disclosed here may be used with such mechanisms. U.S. Patent Publication No. 2003/0155155 Al, which is incorporated herein by this reference in its entirety, is one of several documents in which the expansion of cutting assemblies from a cylindrical tool body is brought about by a mechanism that uses the pressure of drilling fluid to drive cutter blocks upwardly. The cutter blocks have protruding splines that are at an angle to the tool axis and fit into matching channels that are part of the cutter body around a central mandrel. Consequently, when the blocks are pushed upwardly in unison, the splines slide in the matching channels and guide the blocks to expand radially in unison.

FIG. 14 illustrates use of an example cutter block that can use a mechanism similar to that described in U.S. Patent Publication No. 2003/0155155 Al in a section mill. A cutter block has an inner part 120 with angled splines 122 and an outer part 124 including cutters 22-27, 126. This block may be one of three blocks distributed azimuthally around the body of a rotary tool, and the splines 122 correspond to those shown at 650 in FIGS. 7 and 8 of U.S. Patent Publication No. 2003/0155155 Al. The mechanism shown and described in that document may be used in connection with the block shown in FIG. 14 to push the blocks upwardly and outwardly while the tool is rotating within tubing that is to be removed. The outer part 124 of each block may be largely the same as a cutting assembly shown in FIG. 2, with hard cutters 22-27, whose function is the same as described with reference to FIGS. 2-4. The outer part 124 of the block in FIG. 14 may, however, also have a row of cutters 126 for cutting outwardly through tubing as the block is expanded outwardly from the tool body.

It will be appreciated that the embodiments and examples described in detail herein can be modified and varied within the scope of the concepts which they exemplify. Proportions of the drawings are to scale for some embodiments, but may be varied and are therefore schematic for other aspects and embodiments. Features referred to herein or shown in individual embodiments may be used together in any combination as well as those which have been shown and described specifically. More particularly, where features were mentioned above in combinations, details of a feature used in one combination may be used in another combination where the same feature is mentioned. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the claims that follow.