Milling and capturing device

Abstract

A milling system can be used to remove portions of a failed valve that clogs a wellbore. When milling a partially open valve that clogs a wellbore, the target material to be removed can not be present at the center axis of the wellbore, resulting in the target material not completely surrounding the milling bit, which can cause the bit to deviate from the target during milling, thereby reducing milling efficiency. The disclosed milling system can be used to mill and capture a sample of any downhole obstruction that does not have any material near the center axis of the wellbore. A first embodiment of the milling system can be configured to completely mill out the material in the wellbore, while a second embodiment can be used to mill out the material in the wellbore and further capture the milled material or sample.

Description

Technical Field

[0001] The subject matter disclosed in this article relates to milling and capture devices, and more specifically, to milling and capture devices for downhole intervention tools. Background Technology

[0002] Wellbore production may require the use of various valves, including but not limited to ball valves, gate valves, or any other type of movable barrier that can be used to plug the wellbore. Valves or movable barriers may fail in a position between fully open and fully closed. When a valve fails in a partially open or closed position, parts of the valve may block the flow of wellbore fluids and may affect the clearance required to insert and remove equipment from the wellbore. Milling and catching devices will allow the removal of the blocked portion of the faulty valve to clear the wellbore and allow equipment and wellbore fluids to pass through.

[0003] When milling a partially open valve that is blocking a wellbore, the target material to be removed may not be located on the wellbore's central axis, resulting in the target material not completely surrounding the milling bit. This can cause the bit to deviate from the target during milling, thus reducing milling efficiency. For milling rigs deployed on drill pipe or coiled tubing, the system can typically provide sufficient torque and force at the bit to overcome this inefficiency; however, for milling rigs deployed on cables, the available force and torque are smaller, making it difficult to overcome losses caused by bit deviation.

[0004] This section aims to introduce the reader to various aspects of the technology that may be related to the aspects of the present technology described below and / or claimed. This discussion is intended to help provide the reader with background information to facilitate a better understanding of the various aspects of this disclosure. Therefore, it should be understood that these statements should be read in this context and not as an admission of any kind. Attached Figure Description

[0005] These and other features, aspects, and advantages of the invention will become better understood when the following detailed description is read with reference to the accompanying drawings, in which the same reference numerals denote the same parts, in which:

[0006] Figure 1 This is a schematic diagram of an embodiment of an intervention system including a milling system according to embodiments of the present disclosure;

[0007] Figure 2 It is equipped with a tractor-based intervention tool and Figure 1 An overview of the oil field and the transport vehicle of the milling system;

[0008] Figure 3 It is located in the horizontal part of the well. Figure 2 An enlarged view of the milling system;

[0009] Figures 4A-4C Exemplary gate valves and ball valves are depicted when closed, open, and partially open at different levels.

[0010] Figure 4D A ball valve in a partially open configuration is shown, which can partially pass through. Figure 1-3 The milling system was removed;

[0011] Figure 5 It has a milling drill bit. Figure 1-3 A view of an embodiment of a milling system;

[0012] Figure 6 It has a ring cutter and a central body. Figure 5 Detailed view of the milling drill bit;

[0013] Figure 7 yes Figure 6 A schematic diagram of an embodiment of the central body;

[0014] Figure 8 It has a capture device Figure 6 A schematic diagram of an alternative embodiment of the central body;

[0015] Figure 9 This is a schematic diagram of an alternative embodiment of a ring cutter, which includes a spring and a central body with a hole-finding feature;

[0016] Figure 10 This is a schematic diagram of the features of the alternative capture device and the alternative hole finder;

[0017] Figure 11 This is a schematic diagram of an alternative embodiment with a central body having a universal joint;

[0018] Figure 12 This is a schematic diagram of an alternative embodiment of the central body, which is configured to both mill and capture milling chips; and

[0019] Figure 13A and 13B Therefore, it is to unfold ( Figure 13A ) and folding Figure 13B (A schematic diagram of an alternative embodiment of the capture device shown.) Detailed Implementation

[0020] One or more specific embodiments will now be described. To provide a concise description of these embodiments, not all features of the actual implementation are described in the specification. It should be understood that, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which may vary from implementation to implementation. Furthermore, it should be understood that such development efforts can be complex and time-consuming, but remain routine tasks of design, fabrication, and manufacturing for those skilled in the art who benefit from this disclosure.

[0021] The following discussion covers certain examples that are comparable to the scope of the originally claimed subject matter. These examples are not intended to limit the scope of this disclosure. In fact, this disclosure may include various forms that are similar to or different from the examples set forth below.

[0022] When describing elements of various embodiments of this disclosure, the articles “a,” “an,” and “the” are intended to indicate the presence of one or more elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that additional elements may be present in addition to those listed. Furthermore, it should be understood that references to “an embodiment” or “an embodiment” in this disclosure are not intended to be construed as excluding the existence of additional embodiments that also incorporate the described features. Additionally, the phrase “A based on B” is intended to mean that A is at least partially based on B. Furthermore, unless explicitly stated otherwise, the term “or” is intended to be inclusive (e.g., logical “OR”) rather than exclusive (e.g., logical “XOR”). In other words, the phrase “A or B” is intended to mean A, B, or both A and B.

[0023] The oil and gas industry comprises many sub-sectors, such as exploration, drilling, logging, extraction, transportation, refining, and retail. During exploration and drilling, wellbores may be drilled into the ground for reasons including the discovery, observation, and / or extraction of resources. These resources may include oil, natural gas, water, or any other combination of underground elements.

[0024] A wellbore, sometimes called a borehole, can be a straight or curved hole drilled into the surface from which resources can be discovered, observed, and / or extracted. Additionally, a wellbore may have horizontal sections to increase production and / or efficiency. After the wellbore is formed, logging and production can be carried out. Logging may include detailed documentation of the geological structures traversed by the wellbore and can also be performed during the wellbore's formation (e.g., drilling). Production may include extracting resources from within the wellbore.

[0025] Wellbore production may require the use of various valves or movable barriers to isolate different sections of the wellbore. Valve or movable barrier failures in the position between fully open and fully closed can impede the flow of wellbore fluids and may affect the clearance required for inserting and removing equipment from the wellbore. Milling devices will allow the removal of blocked portions of faulty valves to clear the wellbore, allowing for the passage of equipment and wellbore fluids. Additionally, capture devices can be used to collect milled material.

[0026] Now for reference Figure 1 A schematic diagram of an embodiment of the intervention system 100 is shown. System 100 includes a downhole assembly 110 with a milling system 150 for performing milling applications in the well. A communication transmission line 125 is also provided. Line 125 is housed on a spool 117, which is provided to the oilfield 190 as part of a complete surface drive system (e.g., winch system 115). Thus, the milling system 150 can be deployed from the oilfield surface 190 through pulleys 175 and the wellhead 180 into the well for milling operations. The surface drive system 115 includes equipment for controlling the deployment of line 125 and / or generating motion for the deployment of line 125.

[0027] Once the downhole milling application is complete, the aforementioned delivery line 125 allows for convenient tool retrieval. Specifically, line 125 can be unwound from a reel 117 of the surface drive system or winch system 115 to deploy the milling system 150 into the well. The reel 117 is later rewound so that it can be retrieved along with the milling system 150 once the application is complete. While the depicted line 125 can be a cable, coiled tubing or other line types may also be used, and the surface drive system 115 may include an injector or other suitable surface equipment, such as, but not limited to, surface equipment for pumping fluid into the pipe or well to enable the pumped fluid to deliver the milling system 150 into the well.

[0028] The downhole assembly 110 can acquire readings or measurements that lead to deployment adjustments. Specifically, as described above, cable 125 includes communication capabilities. Therefore, sensors 111, 112 of the downhole assembly 110 can be used to acquire data during deployment and milling applications.

[0029] In the illustrated embodiment, the delivery line 125 is deployed through the well along with the winch system 115 and its unwinding spool 117 via the traction machine 114 as described above. In one embodiment, coiled tubing is used instead of the illustrated cable 125, and an injector may be used as part of the winch system 115.

[0030] Now for reference Figure 2 The diagram shows an overview of an oil field with well 280, which includes valve 283 and accommodates... Figure 1The view shows a tractor-driven downhole assembly 110 and its delivery mode (i.e., cable 125). The view also shows the downhole assembly 110 advancing through the horizontal portion 287 of a well 280 towards a valve 283. More specifically, the well 280 includes a vertical portion defined by casing 285 that passes through multiple formations 290, 295, extending several thousand feet below the oilfield surface 190. In the illustrated embodiment, a conventional drilling rig 225 and pressure control equipment 250 are provided to facilitate the tractor-driven cable delivery shown. However, in the case of coiled tubing, an injector can be positioned above the wellhead 180. Furthermore, as mentioned above, alternative types of delivery vehicles, such as slicklines or drill pipe, can also be used.

[0031] Continue to refer to Figure 2 In one embodiment, well 280 transitions to the horizontal portion 287 at a bend 289 where the vertical portion and casing 285 terminate. For example, this type of structure could be designed to extract hydrocarbons from the lower formation 295 at the location of the horizontal portion 287. Therefore, for well completion, maintenance, or monitoring purposes, valve 283 or other movable barriers could be located at other locations within well 280.

[0032] Now for reference Figure 3 And refer to other sources. Figure 2 An enlarged view of the downhole assembly 110 and the conveyor line 125 is depicted as being centered by a centerer 113 within the horizontal portion 287 of the well 280. The centerer 113 assists in centering the milling system 150 and, in other embodiments, can be integrated into the rotary module of the rotary milling system 150. For illustrative purposes, the assembly 110 is depicted moving toward the valve 283 in the downhole direction (arrow 375). As shown, the assembly's traction device 114 is equipped with rollers 314 or wheels to assist downhole advance.

[0033] Now for reference Figures 4A-4D Valve 283 can be any valve known in the prior art, including but not limited to gate valve 283a. Figure 4A ), ball valves 283b, 283c ( Figure 4B , 4C Or any other type of movable barrier that can be used to plug a wellbore; Figure 4A Gate valve 283a is shown in the open position (1), partially open position (2), and closed position (3). If gate valve 283a malfunctions in the partially open position (2) or closed position (3), the portion of gate valve 283a that falls into sleeve 285 may need to be milled off. Figure 4B A ball valve 283b with a seated ball (left) and an empty ball seat (right) is shown. Figure 4CThe diagram illustrates various positions of ball valve 283c from fully closed (left side) to partially open and gradually open to fully open (right side), where the ball valve may malfunction when closed, open, or partially open to any degree. Depending on the extent to which ball valve 283c is open, the amount of material that may need to be ground off or removed from the sleeve 285 will vary. Figure 4D The portion of ball valve 283c that will be removed during milling to clean the casing or wellbore 285 is shown. In this embodiment, the sample or portion or residue of the removed valve 283c is wedge-shaped, but it can be of any shape depending on the amount of material blocking the casing or wellbore 285.

[0034] Figure 5 An embodiment of a milling system 150 is shown, comprising an electronic section 505 for controlling tools and actuators, an anchor and pusher section 510, a rotary tool 520, and a milling bit 530. The anchor and pusher section 510 provides bit pressure on the drill (WOB) for milling through downhole material and reacts with milling torque. The rotary tool 520 rotates the milling bit to generate torque. The milling bit 530 mills through a blockage portion of a fault valve 283. The milling system 150 can be used to mill and capture samples of any downhole blockage that has no material near the centerline of the wellbore.

[0035] Figure 6 It shows Figure 5 The milling drill bit 530 includes a ring cutter 610 and a central body 640 disposed within the ring cutter 610. Figure 7 The first embodiment of the central body 640, shown in further detail, can be configured to completely mill out the material (e.g., valve 283) within the wellbore 285. The central body 640 includes an internal milling device 710. The internal milling device 710 may also include replaceable cutting inserts 720, or may include cutting structures machined directly into the body 640 of the milling device itself.

[0036] The lower end of the internal milling device 710 may also include an end mill 730 for inserting a target 283 with solid material near the drill bit center (i.e., the central axis of the wellbore). Depending on the shape and material of the milled target 283, the specific configuration of the internal milling device 710 may include various shapes and utilize various cutting structures 720. Regardless of the configuration, the radial force generated by cutting on one side of the internal milling device 710 is reacted by an opposing radial force on the annular cutter 610. To facilitate initiating cutting at the center of the target 283, the internal milling device 710 is recessed within the leading edge 615 of the annular cutter 610, thus the annular cutter 610 will machine a pocket before the internal milling device 710 contacts the target 283. For spherical targets, the annular cutter 610 may tend to self-center, such that the radial reaction force on the annular cutter 610 begins with the radial component of the contact force, and then, once the pocket has been milled, transforms into the same behavior as for flat targets. Compared to milling drills without a surrounding annular cutter, this embodiment of the invention increases the force on the cutter and better maintains the initial milling trajectory.

[0037] The internal milling device 710 and the ring cutter 610 can be rigidly connected at 750°, so that they rotate together. Milling drill bit 530 ( Figure 6 ) connected to the rotating part 520 ( Figure 5The connecting feature is located at the upper end of the central body 640. The milling drill bit may also include a hole 770 for capturing milling chips within the internal milling device 710, and a channel or groove for guiding chips into the hole 770. The ring cutter 610 may also include a hole for allowing uncaptured chips to exit the milling drill bit 530. In one or more embodiments, the ring cutter 610 may be arranged as an external centerer or sleeve and may be used to provide centering, target alignment, target milling torque reaction, or a combination thereof. In one or more embodiments, the ring cutter 610 may be connected to the internal milling device 710 such that the internal milling device 710 rotates relative to the ring cutter 610. For example, the internal milling device 710 and the ring cutter 610 may be connected using a bearing joint or other rotary joint known now or in the future. In one or more embodiments, the ring cutter 610 may be configured to move axially as the milling target 283 is milled. In this embodiment, the internal milling device 710 may rotate relative to the ring cutter 610, or the ring cutter 610 and the internal milling device 710 may rotate together. In one or more embodiments, the ring cutter 610 does not rotate relative to the internal milling device 710, and the internal milling device 710 is configured to mill a portion of the ring cutter 610 when the internal milling device 710 moves axially in the milling direction. For example, the ring cutter 610 may be connected to the central body 640 using a joint that provides radial support and allows axial movement, such as a journal bearing. In one embodiment, during operation, the ring cutter 610 will move axially relative to the internal milling device 710.

[0038] Figure 8 It shows Figure 6 A second embodiment of the central body 640, which can be used to mill material (e.g., valve 283) within the wellbore 285 and further capture the milled material or sample 410 (see Figure 4DThe central body 640 includes an internal shaft 810 and a capturing device 830. The internal shaft 810 may be solid or flexible in the radial direction. The internal shaft 810 and the annular cutter 610 may be rigidly attached or coupled to each other to transmit torque while allowing independent axial movement. In this embodiment, the internal shaft 810 is connected to the capturing device 830, which includes a cylindrical brush. The brush 830 includes circumferentially distributed bristles with a certain stiffness. The brush 830 may be positioned or extended beyond the leading edge 615 of the lower end of the annular cutter 610 to facilitate capturing the lower sample material. The bristles of the brush 830 may be biased in the axial and / or tangential directions to provide low stiffness when entering the open valve 283 and high stiffness in the opposite direction. In one embodiment, the bristles of the brush 830 may be biased so that their free ends are axially away from the direction of milling advance and tangentially away from the direction of milling rotation. When the wedge sample 410 ( Figure 4D When the sample 410 is completely cut off from the valve 283 by the annular cutter 610, the bristles of the brush 830 will push the sample 410 against the inner diameter of the annular cutter 610 and prevent the sample 410 from falling back through the center of the annular cutter 610.

[0039] Figure 9 An alternative embodiment of the central body 640 is shown, which also includes a spring 910 on the annular cutter 610 for biasing the relative axial position of the annular cutter 610 and the inner shaft 810. The capturing device 830 can be made of any suitable material and has any suitable configuration that allows the capturing device 830 to pass through the milling target 283 and expand at a large rate of expansion once it has passed through the opposite sides of the milling target 283.

[0040] In this embodiment, the inner shaft 810 also includes a flexible shaft 960 with a capturing device 830 and a hole finder feature 955 located at the lower end of the flexible shaft 960. The hole finder feature 955 assists the capturing device 830 with the flexible shaft 960 into the valve 283 and through the milling target 283, and then expands once it has passed the opposite side of the milling target 283. In this embodiment, the hole finder feature 955 includes an angled tip that rotates with the flexible shaft 960. The flexible shaft 960 can be made of any suitable material and has any suitable configuration that allows the flexible shaft 960 to be biased relative to the annular cutter 610 to a nominal center position. When the angled tip 955 contacts the valve surface 283, the flexible shaft 960 allows the tip 955 to deflect radially while continuing to rotate with the shaft 960 until the tip 955 is aligned with a hole in the partially open valve 283. When the angled tip 955 is aligned with the bore, the biasing behavior causes the angled tip 955 to move rearward toward a nominally centered position and into the bore. Because the inner bore surface is nominally perpendicular to the direction of rotation, the angled tip 955 is prevented from leaving the bore, and the flexible shaft 960 accommodates some rotational bending behavior. In an alternative embodiment, the bore finder feature 955 may include a tapered ring mounted on the flexible shaft 960. The tapered ring bore finder may be well-suited for use with ball valves, where the ball valve generates radial forces when the tapered ring contacts the spherical surface of the ball. The tapered ring bore finder operates in a similar manner to the angled tip bore finder 955.

[0041] Figure 10 An alternative embodiment of the central body 640 is shown, wherein the orifice seeker features include a tapered ring 1055, and the internal shaft 1010 further includes a spring 1075 to provide high stiffness in one axial direction and low stiffness in the opposite axial direction. This embodiment also includes an alternative trapping device 1030, which is connected to a flapper of the tapered ring 1055 via a hinge 1035. The flapper 1030 can be allowed to fold upwards to pass through the valve 283 (…). Figure 4D However, this prevents the baffle 1030 from folding downwards to capture the sample 410. The baffle 1030 can also be biased in the opening direction using at least one spring.

[0042] Figure 11 An alternative embodiment of a central body 640 including a tapered ring hole finder feature 1055 is shown, wherein the inner shaft 1110 further includes a spring 1075. In this embodiment, the inner shaft 1110 is a flexible shaft, which is a segmented solid shaft connected by at least two universal joints 1160. This embodiment also includes a baffle 1030 to catch any milled specimens coupled to the tapered ring 1055 via hinge 1035.

[0043] Figure 12An alternative embodiment is shown, wherein the central body 640 is configured to both mill and capture the sample 410. Figure 4D The hole finder feature is replaced by a milling drill bit 1230 at the lower end of the internal shaft 1210. In this embodiment, the internal shaft 1210 may also include a spring 1075. The milling drill bit 1230 is configured to remove only the valve 283. Figure 4D The material in the center, after which the capturing device 1030 (e.g., a baffle) can pass through the hole created in the valve by the milling drill bit 1230.

[0044] Figure 13A and 13B An alternative embodiment of the capturing device 1330 is shown, which can be used with any of the aforementioned disclosed internal shafts 810, 1010, 1110, 1210. The capturing device 1330 can be a shaped cup configured to fold in one direction but prevent tipping in the opposite direction. The capturing device 1330 can be made of any suitable material, including but not limited to elastomers and sheet metal, when the capturing device 1330 is pushed through such... Figure 13B When the limiting part is shown, the material allows the capturing device 1330 to fold in one direction and then expand again through, as shown. Figure 13A The limiting part is shown. If the metal sheet is used for the capturing device 1330, the metal sheet may be corrugated to allow it to fold.

[0045] During operation, the downhole assembly 110 moves to the appropriate depth within the borehole. Rotating section 520 ( Figure 5 Starting from ground control. Rotary part 520 rotary ring cutter 610 ( Figure 6 The annular cutter 610 includes a central body 640, which has one of the embodiments described herein or a variation thereof. Pusher portion 510 ( Figure 5 The milling drill bit 530 was advanced into target 283. Figure 4D As the material is milled, the downhole assembly 110 moves downhole as the material is removed from the target. For use with a sample 410 (constructed for capturing samples) Figure 4D In embodiments using a central body, the capturing devices 810, 1030, and 1330 are positioned in front of the annular cutter 610, such that the sample is retained before being separated from the target substrate material. In embodiments using a central body configured for full-hole material removal, the annular cutter 610 reacts against the internal milling device 710 (…). Figure 7The radial force generated. After the first milling operation is completed, a subsequent milling operation can be performed, in which the process is repeated, but the subsequent milling chips push the previous milling chips further upward into the internal milling device 710, where the milling chips can be retained inside the milling bit 530 and the downhole assembly 110 can be brought back to the surface.

[0046] In one embodiment, the capture mechanism may be made of any suitable flexible material, including but not limited to elastomers, to achieve the same purpose.

[0047] In one embodiment, the capture mechanism may be used in conjunction with another capture mechanism, or combined into one unit.

[0048] In one embodiment, the capture mechanism can be made of any number of baffle arms.

[0049] In one embodiment, the spring that keeps the baffle arm open can be installed in a variety of ways, including internal or external bow springs.

[0050] In one embodiment, the internal shaft can be long enough that the capture mechanism extends below the valve before milling begins.

[0051] In one embodiment, the capture mechanism may be constructed with intentional weak points, causing the capture mechanism to reverse or otherwise break without leaving any parts in the well, so that the downhole components can be pulled out of the wellbore before the milling operation is completed.

[0052] In one embodiment, the capture mechanism can use more complex linkages to provide structural support for the capture mechanism, while still allowing the capture mechanism to fold inward.

[0053] In one embodiment, the bottom of the capturing mechanism may use an integrated orifice finder feature to increase or maximize the likelihood that the capturing mechanism will advance through a partially open valve.

[0054] In one embodiment, the integrated hole finder feature can operate by slowly rotating the milling drill bit while simultaneously pulling or releasing the transport vehicle.

[0055] In one embodiment, the catch mechanism can be actively opened rather than passively opened by means of an integrated screw or spring-loaded release mechanism that opens only after the milling drill bit has rotated.

[0056] In one embodiment, the end of the catch mechanism baffle arm may have integrated features to minimize the chance of catching on the restraints when pulling out of the wellbore.

[0057] In one embodiment, the capture mechanism can be used for other milling operations besides milling through a partially open valve.

[0058] In one embodiment, in addition to milling, the capture mechanism can also be used for downhole holding / capturing.

[0059] While this disclosure may have various modifications and alternatives, specific embodiments have been illustrated by way of example in the accompanying drawings, and have been described in detail herein. However, it should be understood that this disclosure is not intended to be limited to the specific forms disclosed. For example, while some embodiments described herein include specific combinations of milling and capturing systems, other combinations are also possible. Rather, this disclosure is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure as defined by the appended claims.

[0060] The techniques proposed and claimed herein are referenced and applied to physical objects and concrete examples of practical nature, which significantly improve upon the art and are therefore not abstract, intangible, or purely theoretical. Furthermore, if any claim appended to this specification contains one or more elements designated as "means for [performing] [a function]..." or "steps for [performing] [a function]...", such elements are intended to be interpreted according to 35U.SC112(f). However, for any claim containing elements designated in any other manner, such elements are intended not to be interpreted according to 35U.SC112(f).

[0061] This written description uses examples to disclose the invention, including the best mode, and also enables any person skilled in the art to practice the invention, including making and using any device or system and performing any combined methods. The patent scope of the invention is defined by the claims, but may include other examples that would occur to a person skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that are not different from the literal language of the claims, or if they include equivalent structural elements that are not substantially different from the literal language of the claims.

Claims

1. A milling apparatus, comprising: A ring-shaped cutter constructed to cut milling chips from obstructions; The central body is located within the ring cutter; and An internal milling device is provided in a central body, the central body including an internal shaft and a capturing device provided at one end of the internal shaft; The internal milling device is recessed into the lower end of the annular cutter, and the internal milling device includes a hole for capturing milling chips within the internal milling device.

2. The milling apparatus according to claim 1, wherein the internal milling device and the annular cutter are rigidly connected and rotate together.

3. The milling apparatus of claim 1, wherein the capturing device comprises a brush with distributed bristles biased to provide greater hardness in a first direction and less hardness in an opposite direction.

4. The milling apparatus according to claim 1, wherein the capturing device includes a baffle arm.

5. The milling apparatus according to any one of claims 1-4, wherein the central body comprises a flexible shaft and a hole finder feature disposed at one end of the flexible shaft.

6. The milling apparatus of claim 5, wherein the hole finder feature includes an angled tip that rotates together with the flexible shaft.

7. The milling apparatus according to claim 5, wherein the hole finder features a tapered ring mounted on one end of a flexible shaft.

8. The milling apparatus according to any one of claims 1-4, wherein, The ring cutter is connected to the central body using a connector that allows the central body to rotate relative to the ring cutter.

9. The milling apparatus of claim 8, wherein the annular cutter is configured to move axially.

10. The milling apparatus of claim 8, wherein the annular cutter is used to provide centering, target alignment, target milling torque reaction, or a combination thereof.

11. The milling apparatus of claim 8, wherein the internal milling device is configured to mill a portion of the annular cutter when the internal milling device moves axially in the milling direction.

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