This application claims priority to U.S. Provisional Patent Application Ser. No. 61/247,928 filed Oct. 1, 2009.
1. Field of the Invention
The invention relates generally to systems and methods to form an opening by cutting through an obstruction within a wellbore.
2. Description of the Related Art
In the course of wellbore production operations, objects and devices occasionally become undesirably stuck within a production wellbore and are substantially resistant to removal using fishing devices. Such instances might include, for example, when an object, such as a ball valve ball is locked in the closed position such that it cannot be opened using conventional methods. In such instances, the locked closed object is most often generally oriented such that a transverse hole within the object is generally oriented perpendicular to the wellbore.
The present invention provides a milling tool and a method for using such an apparatus to form an opening in an object, device or other obstruction within a wellbore that includes a transverse hole. The presence of this hole requires the milling tool to bore through curved surfaces at the top and bottom of the hole which presents unique and complex design challenges. The milling tool may be deployed downhole on drill string or on coiled tubing. When deployed on coiled tubing, a mud motor is positioned between the coiled tubing and the milling tool in order to cause the milling tool to rotate.
In a preferred embodiment, the milling tool includes a milling tool body having a sequence of sections of increasing diameter with a nose cutting portion at the distal end, a cutting section, and a shaft portion at the proximal end of the milling tool body. The generally stepped cutting section of the milling tool body preferably presents a series of sections of increased diameters arranged in a step-type fashion. The cutting section presents a plurality of affixed cutters that are designed to contact and bore through an obstruction. In a preferred embodiment, the cutters are secured within cutter pockets that are formed into the milling tool body.
In preferred embodiments, the milling tool includes a plurality of stabilizing wear pads. Preferably, the wear pads are formed of axially extending strips of copper alloy or similar ate al that are located in a specific spaced circumferential relation around the circumference of the milling tool body and are positioned nearly adjacent to the cutters for cutter protection. The pads disposed upon the shaft portion adjacent the cutting portion present a greater engagement diameter along the shaft portion of the milling tool body than the greatest cutting diameter of the cutters. This permits the milling load to be supported and stabilized when the cutters of the final step are completely through the upper solid portion of the obstruction. during cutting operation, these pads wear away.
The milling tool includes an axial fluid flowbore that is in fluid communication with fluid flowing through the running string. Fluid circulation ports extend from the fluid flowbore through the milling tool body. Thus, fluid that is dispersed down through the running string will be circulated out through the circulation ports to flow debris away from the cutters during operation.
In a further feature of the invention, an annular flow through no-go centralizer preferably surrounds a reduced-diameter shaft portion of the milling tool body. The no-go centralizer is preferably rotationally moveable with respect to the milling tool body. The outside diameter of the centralizer as measured around the centralizer ribs is larger than the milling tool body diameter, such that the centralizer ribs present stop shoulders to engage an upper portion of a wellbore obstruction, thereby stopping cutting progress of the milling tool and signaling to an operator that the desired hole has been established.
In operation, the milling tool is used to establish openings through wellbore obstructions and create access to hydrocarbon reservoirs into which access was previously restricted by the obstruction. Though general in intended application, the devices and methods of the present invention are particularly well suited to instances wherein the device must bore through wellbore obstructions, such as closed ball valve balls, which include large diameter holes which are transverse to the boring direction. These applications are particularly challenging as both the top and the bottom of the transverse hole are curved. As this curvature is being bored, the cutters of a given step will bear on the obstruction material during a portion of a given revolution of the milling tool and be unsupported during another portion of the revolution. When the bored hole approaches the transverse hole diameter, the arcs in which the cutters are in contact with the obstruction become small. The cutters must be constantly supported to avoid severe vibration, so an alternative means of supporting the cutters must be provided. In accordance with embodiments of the present invention, when cutters are not supported on the top side of the transverse hole, cutters cutting on the bottom side of the hole are in contact with the obstruction. If the cutters of each step substantially perform their cutting in a plane perpendicular to the milling tool axis, it is not always geometrically possible to keep them supported. Thus, the cutters are angled with respect to the milling tool axis so their contact on the top and bottom of the transverse hole is extended over an appreciable boring distance which enables the milling tool to be designed such that it is supported by the cutters in contact with the obstruction for most of the revolution. Even when the cutters at the top and bottom of the transverse hole are fully supported, angling the cutters provides another important benefit of cutting efficiently with a relatively constant applied cutting load by maintaining an approximately constant cut width. As the cutters at the top enter the transverse hole, their cut width becomes progressively narrower as the boring progresses. Conversely, the cutters engaging the bottom of the hole start with a very narrow cut width at contact, and the width grows progressively as the boring progresses. With proper axial spacing, the width of the bottom cut can increase substantially the same amount as the top cut decreases, providing a substantially constant cut width and milling contact area. In addition, once the cutters have passed entirely through the upper solid portion of the obstruction, the milling tool is stabilized by contact between wear pads and the upper solid portion. Hole cutting devices constructed in accordance with the present invention may be used with through-tubing arrangements. These devices apply an essentially constant cutting load, so designs are provided that will operate effectively at a constant load, thereby offering substantial advantages.
The advantages and further aspects of the invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout the several figures of the drawing and wherein:
Referring first to
The milling tool body 12 has a distal end 20 and a proximal end 21. The distal end 20 of the milling tool body 12 presents a nose cutting portion, generally indicated at 22. In a preferred embodiment, the nose cutting portion 22 includes a pair of cutting prongs 24, 26, which protrude axially in the distal direction from cylindrical base 27. Each cutting prong 24, 26 has a generally semi-circular cross-section and a gap 28 located between the cutting prongs 24, 26. Hardened nose cutters 30, 32 are affixed to each of the cutting prongs 24, 26, respectively. The nose cutters 30, 32 are preferably formed of carbide or a similar suitably hard substance and may be attached to the prongs 24 or 26 by brazing, as is known in the art. Preferably, the nose cutters 30, 32 have an elongated, generally oblong configuration. The nose cutters 30, 32 may be of the type described in U.S. Pat. No. 7,363,992 entitled “Cutters for Downhole Cutting Devices” and issued to Stowe et al. U.S. Pat. No. 7,363,992 is owned by the assignee of the present invention and is hereby incorporated in its entirety by reference Each of the nose cutters 30, 32 presents a wear face 34. As is apparent from
A generally conical cutting section 36 is located adjacent the nose cutting portion 22 on the milling tool body 12 and is preferably integrally formed with the cylindrical section 27 of the nose cutting portion 22. As best shown in
Hardened cutters 44 are affixed within the cutter pockets 42 such that at least three flat sides can be positioned against the cutter pocket walls. The cutters 44 contact the pockets 42 on at least three sides such that their location is fully determined by the pocket 42. The cutters 44 are preferably made of carbide or a similar suitably hard material and may be of the same type as the nose cutters 30, 32 previously described. The cutters 44 may be affixed to the cutter pockets 42 by brazing. As can be seen in
The milling tool body 12 also includes an elongated shaft portion 48 that is located proximally from the conical cutting portion 36. The shaft portion 48 provides a section of maximum diameter for the tool 10. There are no cutters 44 located upon the shaft portion 48.
Multiple stabilizing and wear pads 50 are preferably affixed to the milling tool body 12. It is preferred to use a copper alloy, or another suitable soft and erodable material, to form the pads 50. The wear pads 50 are formed of a material that is softer than the cutters 44. It is also preferred that the wear pads 50 are formed of a material that is softer than the milling tool body 12. The wear pads 50 provide a section of stabilization because they mitigate vibration-induced damage to the cutters 44 and resist motor stalling due to extreme metal-to-metal friction. It is noted that the pads 50 are generally disposed in a longitudinal axial configuration upon the milling tool body 12 including both the cutting section 36 and the shaft portion 48. As can be seen with reference to
As can be seen in
In accordance with a further feature of the present invention, a no-go centralizer sleeve 56 is preferably disposed around a reduced-diameter shaft portion 58 of the shaft portion 48 of the milling tool body 12. An exemplary no-go centralizer sleeve 56 is shown in
In operation, the milling tool 10 is operable to contact a wellbore obstruction and create a hole therein, The configuration of the milling tool 10 permits a small, initial hole or opening to be created in the obstruction which is then enlarged until the milling tool 10 has created a hole that is the desired full gage. Milling through a ball valve ball, such as ball valve ball 62, presents unique challenges due to the geometry of the valve ball and the fact that it is typically fashioned from very hard material. Milling through a ball valve ball requires cutting a hole through an upper solid portion of the valve ball (62a in
The substantially equivalent milling contact area is highly desirable when milling is conducted using a coiled tubing running string.
Referring now to
Those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof.
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