Abstract:
A rotating tool for milling or drilling in a well bore, having one or more rotating cutting structures, with each cutting structure rotating about its own axis, and with the cutting structures rotating about the axis of the tool. The rotational axis of the tool is offset from the axis of at least one cutting structure, with the axis of the tool passing through that cutting structure. This ensures that the cutting structure which spans the axis of the tool rotates independently of the tool, to prevent the existence of a zero velocity point on the cutting face of the tool.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is in the field of rotating cutting tools used for milling downhole metal members in a well bore, and rotating cutting tools used for drilling a well bore through an earth formation. 
     2. Background Information 
     Various milling applications and drilling applications have, over the years, suffered from the problem of a “dead” spot in the center of the mill or drill bit. As the mill or drill bit rotates, it revolves around a central axis. At the point where that central axis passes through the cutting face of the mill or drill bit, the cutting structure is degraded and quickly becomes ineffective. Ultimately, a core, or depression, is worn into the cutting matrix. As the core wears further into the matrix, fluid circulation in the area is reduced, and cuttings resulting from the milling or drilling operation are no longer effectively removed. The reason for this problem is that on the cutting face, at the point where the central axis passes through the cutting face, the cutting elements have essentially a zero cutting surface speed. 
     In a typical milling situation, for instance, a segment of metal tubing may be stuck in the well bore. The tubing will usually be bent and leaning against the sides of the casing or well bore. In this situation, a rotating metal milling tool will typically be run downhole to mill away the bent metal tubing. As the milling tool progresses downwardly, milling away the bent tubing, there will be a number of times when the wall of the bent tubing is positioned against the center of the face of the milling tool. This results in a zero relative speed of the cutting elements across the bent tubing at the center point, with little effective cutting taking place. This generates considerable heat at the center point, which can soften the cutting matrix, leading to rapid deterioration of the matrix at the center point. Ultimately, this can create a deep depression or cone in the center of the face of the milling tool. When the depression deepens to the point of reaching the body of the milling tool, which is typically made of steel, no further milling progress can be made. 
     A similar problem can occur in the drilling of a well bore through an earth formation. Coning of the drill bit can occur at the center point, resulting in slowing or even stalling of drilling progress, requiring the drilling operation to be stopped until a new bit is installed. It is the object of the present invention to provide a design, which can be incorporated into either a milling tool or a drill bit, which will not have a zero cutting speed anywhere on the cutting face of the tool, thereby eliminating the coning problem and allowing a full depth milling or drilling operation to be accomplished. 
     BRIEF SUMMARY OF THE INVENTION 
     Whether embodied in a milling tool or a drill bit, the tool of the present invention has a cutting assembly consisting of one or two cutting structures, with at least one of the cutting structures being rotated about an axis offset from the axis of the borehole. The tool is connectable to the lower end of a drill string or coiled tubing, for positioning in a well bore. Use of the term “drill string” herein is intended to include all types of tubular strings, including coiled tubing, where the context allows. The cutting assembly as a whole rotates about its longitudinal axis. Further, each of the cutting structures rotates about its own longitudinal axis. The longitudinal axis of at least one cutting structure is offset from, but parallel to the longitudinal axis of the cutting assembly, and this cutting structure spans the longitudinal axis of the cutting assembly. Therefore, as the cutting assembly rotates, the offset cutting structure rotates independently, insuring that the center point of the cutting assembly does not have a zero cutting surface speed. This prevents coning of the cutting structures at the center point. Where a second cutting structure is present in the cutting assembly, it can also have an offset axis, or its axis can coincide with the axis of the cutting assembly. 
     In one embodiment, the cutting assembly can be mounted on the lower end of a housing connected to a drill string or coiled tubing, with a first cutting structure being fixedly mounted to the housing and a second cutting structure rotatably mounted to the housing. The rotational axis of the first cutting structure coincides with the axis of the housing, while the rotational axis of the second cutting structure is offset from the axis of the housing. In this embodiment, the first cutting structure is rotated by rotation of the housing, while the second cutting structure is independently rotated by a drill motor mounted within the housing. Rotation of the cutting assembly as a whole is accomplished by rotating the drill string to rotate the housing and cutting assembly, or by rotation of the housing and cutting assembly with a drill motor. The cutting assembly can be centered on the axis of the well bore or casing within which the apparatus is positioned. 
     In a second embodiment, the cutting assembly can be mounted on the lower end of a drill motor connected to a drill string or coiled tubing, with each of two cutting structures being independently rotated by the drill motor. Independent rotation of the cutting structures with a single drill motor can be accomplished by use of a single input, dual output transmission. Rotation of the cutting assembly as a whole is accomplished by rotating the drill string to rotate the drill motor and cutting assembly, or by rotation of the drill motor and cutting assembly with a drill motor. As with the first embodiment, the cutting assembly can be centered on the axis of the well bore or casing within which the apparatus is positioned. 
     In a third embodiment, a drill motor is fitted with clamp-on eccentric stabilizers which offset the axis of the drill motor from the axis of the borehole or casing. The drill motor is connected to a drill string or coiled tubing. Where the drill motor is connected to a rotatable drill string, the eccentric stabilizers contact the walls of the borehole or casing. Where the drill motor is connected to coiled tubing, the motor and stabilizers can be located within a rotatable housing which essentially aligns with the borehole or casing axis. In either case, the cutting assembly consists of a single cutting structure driven by the drill motor. This cutting structure can be aligned with the axis of the drill motor, with the result that the cutting assembly is offset from the axis of the well bore or casing. In this embodiment, the single cutting structure is rotated by the drill motor, while rotation of the motor and cutting assembly as a whole is accomplished by rotating the drill string, or by rotating the motor and cutting assembly with a drill motor. 
     In any of the embodiments where rotation of the apparatus is accomplished by a drill motor, a second drill motor may be used, or a secondary drive off a single drill motor may rotate the apparatus. 
     The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which: 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a schematic longitudinal section view of a first embodiment of the apparatus of the present invention; 
     FIG. 2 is a schematic end view of the cutting assembly mounted on the lower end of the apparatus shown in FIG. 1; 
     FIG. 3 is a schematic longitudinal section view of a second embodiment of the apparatus of the present invention; 
     FIG. 4 is a schematic end view of the cutting assembly mounted on the lower end of the apparatus shown in FIG. 3; 
     FIG. 5 is a schematic longitudinal section view of a third embodiment of the apparatus of the present invention; and 
     FIG. 6 is a schematic end view of the cutting assembly mounted on the lower end of the apparatus shown in FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIG. 1, a first embodiment of the tool  10  of the present invention includes a housing  12 , a drill motor  14 , and a cutting assembly  18 . The housing  12  is connectable to the lower end of a drill string or coiled tubing DS. The housing  12  is rotatable about its longitudinal axis  26 , either by rotation of the drill string DS, or by being driven by a separate drill motor (not shown), above the housing  12  on the drill string DS. Alternatively, the housing  12  can be rotated by a secondary drive (not shown) off the drill motor  14 . The drill motor  14  can be driven by drilling fluid, or by compressed air, or by any other suitable means. The drill motor  14  can be mounted, and centered if desired, in the housing  12  by means of one or more mounts or centralizers  16 . 
     The cutting assembly  18  is mounted on the lower end of the housing  12 , for rotation by means of rotation of the housing  12 . The longitudinal axis of rotation  26  of the housing  12  is also the longitudinal axis of rotation  26  of the cutting assembly  18 . The cutting assembly  18  comprises a first cutting structure  19 , which is fixedly mounted to the lower end of the housing  12 , and a second cutting structure  20 , which is rotatably mounted to the lower end of the housing  12 . The longitudinal axis of rotation  26  of the housing  12  and the cutting assembly  18  is also the longitudinal axis of rotation  26  of the first cutting structure  19 . The second cutting structure  20  is independently rotatable about its longitudinal axis  28 , which is parallel to, but laterally offset from, the longitudinal axis  26  of the cutting assembly  18 . The second cutting structure  20  is driven by the drill motor  14 , via one or more coupling mechanisms or universal joints  22 ,  24  if required. The second cutting structure  20  spans the longitudinal axis  26  of the cutting assembly  18 , since the longitudinal axis  26  of the cutting assembly  1   8  passes through the second cutting structure  20 . 
     As shown in FIG. 2, the first cutting structure  19  can incorporate a plurality of blades, or it could be a crescent shaped structure with a flat lower face similar to the lower face shown on the second cutting structure  20 . In either case, the first cutting structure  19  is dressed with cutting elements. The axis of rotation  26  of the housing  12 , the cutting assembly  18 , and the first cutting structure  19  passes through the center point  30  of the lower face of the cutting assembly  18 . The second cutting structure  20  can be a circular structure with a flat lower face as shown, or it could incorporate blades similar to the blades shown on the first cutting structure  19 . In either case, the second cutting structure  20  is dressed with cutting elements. The axis of rotation  28  of the second cutting structure  20  is parallel to, but laterally offset from, the axis of rotation  26  of the cutting assembly  18 . Therefore, although the second cutting structure  20  spans the longitudinal axis  26  of the cutting assembly  18 , the axis of rotation  28  of the second cutting structure  20  does not pass through the center point  30  of the lower face of the cutting assembly  18 . Instead, as the second cutting structure  20  independently rotates about its axis  28 , the cutting elements on the second cutting structure  20  continually sweep the center point  30 . It can be seen, therefore, that there is no point on the lower face of the cutting assembly  18  which has a zero cutting speed at any time. 
     As shown in FIG. 3, a second embodiment of the tool  110  of the present invention includes a drill motor  114 , and a cutting assembly  118 . The drill motor  114  is connectable to the lower end of a drill string or coiled tubing DS. The drill motor  114  is rotatable about its longitudinal axis  126 , either by rotation of the drill string DS, or by being driven by a separate drill motor (not shown), above the drill motor  114  on the drill string DS. Alternatively, the drill motor  114  can be rotated by a secondary drive (not shown) off the drill motor  114 . The drill motor  114  can be driven by drilling fluid, or by compressed air, or by any other suitable means. 
     The cutting assembly  118  is mounted on the lower end of the tool  110 , for rotation as a unit, by means of rotation of the entire drill motor  114 , as described above. The longitudinal axis of rotation  126  of the drill motor  114  is also the longitudinal axis of rotation  126  of the entire cutting assembly  118 . The cutting assembly  118  comprises a first cutting structure  119 , which is independently rotatably mounted to the lower end of the tool  110 , and a second cutting structure  120 , which is also independently rotatably mounted to the lower end of the tool  110 . The first cutting structure  119  is independently rotatable about its longitudinal axis  129 , which is parallel to, but laterally offset from, the longitudinal axis  126  of the cutting assembly  118 . The first cutting structure  119  is driven by the drill motor  114 , via one output of a single input, dual output transmission  122 . The second cutting structure  120  is independently rotatable about its longitudinal axis  128 , which is parallel to, but laterally offset from, the longitudinal axis  126  of the cutting assembly  118 . The second cutting structure  120  is also driven by the drill motor  114 , via a second output of the single input, dual output transmission  122 . Alternatively, each cutting structure  119 ,  120  could be independently driven by a separate drill motor or air motor. The second cutting structure  120  spans the longitudinal axis  126  of the cutting assembly  118 , since the longitudinal axis  126  of the cutting assembly  118  passes through the second cutting structure  120 . 
     As shown in FIG. 4, the first cutting structure  119  can be a circular structure with a flat lower face as shown, or it could incorporate blades similar to the blades shown on the first cutting structure  19  in FIG.  2 . In either case, the first cutting structure  119  is dressed with cutting elements. The axis of rotation  126  of the drill motor  114  and the cutting assembly  118  passes through the center point  130  of the lower face of the cutting assembly  118 . The axis of rotation  129  of the first cutting structure  119  is parallel to, but laterally offset from, the axis of rotation  126  of the cutting assembly  118 . The second cutting structure  120  also can be a circular structure with a flat lower face as shown, or it could incorporate blades similar to the blades shown on the first cutting structure  19  in FIG.  2 . In either case, the second cutting structure  120  is dressed with cutting elements. The axis of rotation  128  of the second cutting structure  120  is parallel to, but laterally offset from, the axis of rotation  126  of the cutting assembly  118 . Therefore, although the second cutting structure  120  spans the longitudinal axis  126  of the cutting assembly  118 , the axis of rotation  128  of the second cutting structure  120  does not pass through the center point  130  of the lower face of the cutting assembly  118 . Instead, as the second cutting structure  120  independently rotates about its axis  128 , the cutting elements on the second cutting structure  120  continually sweep the center point  130 . It can be seen, therefore, that there is no point on the lower face of the cutting assembly  118  which has a zero cutting speed at any time. 
     As shown in FIG. 5, a third embodiment of the tool  210  of the present invention includes a drill motor  214 , and a cutting assembly  218 . It can also include a housing which essentially aligns with the borehole or casing BH within which the apparatus is positioned. The housing or drill motor  214  is connectable to the lower end of a drill string or coiled tubing DS. The tool  210  is rotatable about its longitudinal axis  226 , either by rotation of the drill string DS. or by being driven by a separate drill motor (not shown), above the tool  210  on the drill string DS. Alternatively, the tool  210  can be rotated by a secondary drive (not shown) off the drill motor  214 . The drill motor  214  can be driven by drilling fluid, or by compressed air, or by any other suitable means. Whether or not the housing is present, the drill motor  214  is held in a position laterally offset from the longitudinal axis of the tool  210  by one or more eccentric stabilizers  216 , which can be the clamp-on type. 
     The cutting assembly  218  comprises a single cutting structure which is rotatable about its longitudinal axis  228 , which is parallel to, but laterally offset from, the longitudinal axis  226  of the tool  210 . The cutting structure  218  is driven about its axis  228  by the drill motor  214 . Further, the cutting structure  218  is rotated about the axis  226  of the tool  210  by rotation of the tool  210 , either by turning of the drill string DS, by use of a second drill motor (not shown), or by means of a secondary drive (not shown) off the drill motor  214 . The cutting structure  218  spans the longitudinal axis  226  of the tool  210 , since the longitudinal axis  226  of the tool  210  passes through the cutting structure  218 . 
     As shown in FIGS. 5 and 6, the cutting structure  218  can incorporate a plurality of blades, or it could have a flat lower face similar to the lower face shown on the second cutting structure  20  in FIG.  2 . In either case, the cutting structure  218  is dressed with cutting elements. The axis of rotation  228  of the cutting structure  218  is parallel to, but laterally offset from, the axis of rotation  226  of the tool  210 . Therefore, although the cutting structure  218  spans the longitudinal axis  226  of the tool  210 , the axis of rotation  228  of the cutting structure  218  does not pass through the center point  230  of the lower face of the tool  210 . Instead, as the cutting structure  218  independently rotates about its axis  228 , the cutting elements on the cutting structure  218  continually sweep the center point  230 . It can be seen. therefore, that there is no point on the lower face of the cutting assembly  218  which has a zero cutting speed at any time. 
     Any of these embodiments, by preventing the occurrence of a zero speed point anywhere on the lower face of the cutting assembly  18 ,  118 ,  218 , prevents coning of the matrix material and deterioration of the central portion of the face of the cutting assembly  18 ,  118 ,  218 . 
     While the particular invention as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages hereinbefore stated, it is to be understood that this disclosure is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended other than as described in the appended claims.