Abstract:
A method and apparatus for milling an item in a wellbore. The method and apparatus including providing a milling tool having one or more blades which are geometrically configured to resist deflection by distributing cutting forces in multiple directions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Patent Application Ser. No. 60/821,757, filed Aug. 8, 2006, which application is incorporated herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments described herein generally relate to a milling tool. More particularly, the embodiments relate to a milling tool having a blade configured for increased stiffness. More particularly still, embodiments relate to an angled or bent blade adapted to increase the life span of the tool. 
     2. Description of the Related Art 
     During the drilling and production of oil and gas wells, a wellbore is formed in the earth and typically lined with a tubular that is cemented into place to prevent cave ins and to facilitate isolation of certain areas of the wellbore for collection of hydrocarbons. During drilling and production, a number of items may become stuck in the wellbore. Those items may be cemented in place in the wellbore and/or lodged in the wellbore. Such stuck items may prevent further operations in the wellbore both below and above the location of the item. Those items may include drill pipe or downhole tools. In order to remove the item milling tools are used to cut or drill the item from the wellbore. 
     Typical milling tools have blades which extend from the milling tool. The blades often extend from a face of the mill. Such blades are limited in length because the low torsional rigidity and low resistance to deflection when lengthened. The blades typically have a cutting surface which is coated or covered with a cutting material such as crushed tungsten carbide in a nickel silver matrix. Typically a blade provides a support structure for the cutting material. As the milling tool is rotated, the cutting surface will cut through the stuck item while also wearing through the cutting material and the blade. Because the blades are substantially flat and extend from the face in a cantilevered fashion, there are substantial limits on the length and life of the milling tool. As the length of the blade is increased the blades resistance to deflection decreases. This deflection can cause the bond between the cutting material and the blade to fail, thereby increasing the wearing of the blade. The blade will wear out at a rapid rate or break as the deflection increases. Typical blades extend one and a half inches, or less, from the face of the milling tool. When the blade is lengthened beyond one and a half inches the blade deflection increases causing rapid wear and damage to the blade. The life and rate of penetration of a milling tool will directly affect increase the rig time and the wellbore will remain inaccessible until the stuck item is removed. 
     While milling an item downhole, a phenomenon called coring can occur. Coring occurs when blades at the center of the milling tool are worn down at an increased rate which causes an inversed cone shaped formation in the center of the mill. The blades are worn down at an increased rate toward the center of the blade due to the slower surface speed of the mill at the center than at the edges. The slower speed causes increased friction and wear of the blades. Coring leaves a circular area without a cutting device in the center of the mill face. As the mill cuts deeper into the stuck item, some items in contact with the circular area of the mill bit center are not cut and thus creates a core. The core pushes on the mill and may prevent the mill from cutting deeper into the item, or penetrate the milling tool. Reducing coring can increase the life span and effectiveness of a mill. 
     There is a need for a method and apparatus to increase the longevity and the effectiveness of downhole mill bits. Therefore, there is a need for a milling tool with an increased resistance to deflection. 
     SUMMARY OF THE INVENTION 
     In accordance with the embodiments herein there is provided generally a milling tool for use in a wellbore. The milling tool has a body having a connector end and a milling end. The connector end is configured to couple the body to a conveyance. The milling end has a face, one or more blades coupled to the face, at least one of the blades having a height dimension which extends beyond the face and a length dimension, wherein at least a portion of the length dimension couples to the face in a non-planar configuration along one side of the blade. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  illustrates a schematic of a wellbore with a milling tool according to one embodiment of the present invention. 
         FIG. 2  is a perspective view of a milling tool according to one embodiment of the present invention. 
         FIG. 3  is a cross sectional view of a milling tool according to one embodiment of the present invention. 
         FIG. 4  is a perspective view of a milling end of the milling tool according to one embodiment of the present invention. 
         FIGS. 5A-5E  are views of cutting structures of the milling tool according to one embodiment of the present invention. 
         FIGS. 6A-6C  illustrate a schematic of the cutting structure of the milling tool according to one embodiment of the present invention. 
         FIG. 7  is an end view of the milling tool according to one embodiment of the present invention. 
         FIG. 8  is an end view of the milling tool according to one embodiment of the present invention. 
         FIG. 9  is an end view of the milling tool according to one embodiment of the present invention. 
         FIG. 10  is an end view of the milling tool according to one embodiment of the present invention. 
         FIG. 11  is an end view of the milling tool according to one embodiment of the present invention. 
         FIG. 12  is an end view of the milling tool according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of apparatus and methods for milling an item in a wellbore are provided. In one embodiment, a milling tool is configured to have blades that are geometrically designed to increase the life and penetration of the mill. The milling tool is coupled to a conveyance, such as a drill pipe or coiled tubing, and lowered into a wellbore. The milling tool is lowered until it reaches an item that is stuck in the wellbore, such as a drill pipe. The item in the wellbore may prevent use of the wellbore below the item. The milling tool then engages the item while the milling tool is rotated. The geometric configuration of the milling tool has an increased resistance to deflection and torsion. The increased resistance to deflection and torsion allows the blades to be longer than those of conventional milling tools. The increased length increases the life and penetration achieved by the milling tool. The milling tool continues to mill through the item until access to the wellbore has been regained. The milling tool is then removed from the wellbore, and drilling and/or production operations may proceed in the wellbore. 
       FIG. 1  shows a wellbore  100  with a casing  102  cemented in place, a drill rig  104 , a conveyance  108 , a milling tool  110 , and an item  112  stuck in the wellbore  100 . The conveyance  108  may be a drill string which may be rotated and axially translated from the drill rig  104 ; however, it should be appreciated that the conveyance could be any conveyance such as a co-rod, a wire line, a slick line, coiled tubing, casing. The milling tool  110  may be coupled to a drilling motor (not shown) in order to rotate the milling tool in a manner independent from the conveyance. The conveyance  108  is connected to the milling tool  110  at its lower end. The milling tool  110 , as will be described in more detail below, is lowered into the wellbore  100  until it engages the item  112  that is stuck in the wellbore. The item  112 , as shown, is a drill pipe which has been cemented into place; however, the item  112  could be any suitable item stuck in the wellbore  100  including, but not limited to: casing, production tubing, liner, centralizers, whipstocks, packers, valves, drill bits, drill shoes. Optionally, the item  112  may be cemented in place in the wellbore  100 . Preferably, the milling tool  110  engages the item  112  while the milling tool  110  rotates. A milling end  114  of the milling tool  110  then mills away the item  112  and any cement attached to the item  112 . The milling tool  110  may have one or more blades which may be geometrically configured to resist deflection. The milling tool  110  is lowered while rotating and milling until the item  112  is no longer obstructing the wellbore  100 . 
       FIG. 2  is a perspective view of the milling tool  110 . The milling tool  110  has a body  200  with a connector end  202  and a milling end  204 . The connector  202 , as shown, is simply a threaded connection member to coupling the milling tool to the conveyance  108 . The body  200 , as shown, is a cylindrical member adapted for transferring rotation from the conveyance  108  to the milling end  204 . The body  200  may be of any suitable length or shape so long as it is capable of transferring rotation and axial force to the milling end  204  of the body  200 . The body  200  may optionally include one or more stabilizers  206  for centering and stabilizing the milling tool  100  during milling. 
     The milling end  204 , as shown, has a face  208 , one or more blades  210 , one or more cutting structures which may include any combination of one or more inserts  212 , an amorphous structure  214 , and a reinforcing member  216 . The face  208  may be a substantially flat end of the body  200  adapted to couple one or more blades  210 , the amorphous structure  214 , and other members, (not shown), to the body  200 . The one or more blades  210  have a height H which extends beyond the face  208  of the milling tool  110 . The one or more blades  210  may be geometrically configured to resist deflection, as will be described in more detail below. The amorphous structure  214  may be arranged to increase the one or more blades&#39;  210  resistance to deflection and torsion, while increasing the rate of penetration of the milling tool  100 , as will be described in more detail below. 
       FIG. 3  shows a cross sectional view of the milling tool  110 . The body  200  is shown having a flow path  300  for conveying fluid from the conveyance  108  to the face  208 . As shown, the flow path  300  splits into two paths near the face  208 ; however, it should be appreciated that there could be any suitable number of paths at the face  208 . The flow path  300  may convey fluids, such as drilling mud, to the milling end  204  of the milling tool  110  in order to lubricate and cool the milling tool  110  and wash away any cuttings that are created during milling. The flow path  300  delivers the fluid to the side of the one or more blades  210  having the inserts  212 . 
     The one or more blades  210  may be embedded into the face  208 . This may be accomplished by creating a groove (not shown) in the face  208  to correspond with the geometry of a coupling end  302  of the corresponding blade  210 . The coupling end  302  of the blade  210  may be located in the groove and secured to the face  208  by welding or other suitable connection methods. The coupling end  302  of the blade may also be welded directly to the face and not embedded. 
     In an alternative embodiment, the one or more blades  210  may be integral with the milling end  204  of the milling tool  110 . In this embodiment, one or more of the blades  210  may be constructed from the milling tool  110 . For example, the blade  210  may be milled from a piece of metal when forming the milling tool  110 , or cast with the milling tool  110 . In this embodiment, the one or more blades  210  are all form one piece of the milling tool  110 . 
       FIG. 4  shows a perspective view of milling end  204  of the milling tool. The one or more blades  210  are embedded in the face  208  as described above. The one or more blades  210  may extend radially beyond the face  208 , as shown. When the one or more blades  210  extend beyond the face  208 , the reinforcing member  216  may be included to structurally reinforce one or more outer edges  400  on the blades  210 . The reinforcing members  216  may extend beyond the outer diameter of the body  200  and may be coupled to the coupling end  302  of the blades  210 . As shown, the coupling end  302  of the blades  210  are flush with the reinforcing members  216 ; however, it should be appreciated that the coupling end  302  may be embedded into the reinforcing members  216 . 
     The amorphous cutting structure  214  may be used to enhance mill life. The amorphous cutting structure  214  may comprise a crushed carbide with a support structure, such as brass, silver, nickel, plastic, fiber glass, etc, which is brazed onto the milling end  204  of the milling tool  110 , in addition or alternatively the amorphous structure  214  may comprise inserts, PDC, a diamond impregnated matrix, or any suitable cutting structure or combination thereof. The amorphous structure  214  is shown attached to the face  208  and filling a space between created by the one or more blades  210 . The amorphous structure  214 , as shown, is filled to a height that is greater than the height of the blades  210 ; however, it should be appreciated that it could have any height. The amorphous structure  214  may also be placed on the cutting edge of the blades  210  in addition, or as an alternative, to the inserts  212 . The amorphous structure  214  and the inserts  212  may mill the item  112 . 
     The inserts  212 , as shown in  FIG. 4 , include one or more shaped structures  402  for containing the cutting structure coupled to the one or more blades  210 . The shaped structures  402  may be in any configuration depending on the operation.  FIGS. 5A-5E  show embodiments of insert  212  configurations. The shaped structures  402  may have a variety of widths and shapes that may be placed in a staggered configuration. Further, the shaped structures  402  may include a variety of cutting structures in order to increase the life of the mill. In one embodiment, the cutting structure of the inserts  212  includes a layered carbide impregnated insert. The layered carbide impregnated insert includes one layer of a relatively harder tungsten carbide ball fill in a tungsten carbide matrix. For example the hard tungsten carbide ball fill may include a relatively low cobalt content (13% or less) and the tungsten carbide matrix may include a relatively high cobalt content (13%-20%). The second layer is a wear grade tungsten carbide. The carbide may be microwave sintered or applied using any known technique.  FIG. 6A  depicts the layered carbide impregnated insert  600 . The layered carbide impregnated insert  200  may comprise an impregnated carbide layer  602  and a wear grade carbide layer  604 . In an alternative embodiment, the insert  212  may be a layered diamond impregnated insert  606 , as shown in  FIG. 6B . The diamond impregnated insert  606  includes at least two layers. One of the layers is a diamond fill in a tungsten carbide matrix  608 . The second layer is a wear grade tungsten carbide  610 . The carbide may be microwave sintered or applied using any known technique. In yet another alternative embodiment, the insert  212  may be a full diamond impregnated insert  612 , shown in  FIG. 6C . This insert includes diamonds impregnated in tungsten. The carbide may be microwave sintered or applied using any known technique. Further, any suitable insert may be used. Any of these inserts may be used in combination. 
     In general, a minimum number of blades, typically 4 or more, are needed to provide smooth milling. By structurally joining two blades at an apex or bend, the blades provide for smooth milling and have an added stiffness. The increase in stiffness allows for the blades to increase in height thereby increasing the life of the milling tool  110 .  FIG. 7  shows an end view of the milling end  204 . The one or more blades  210  are bent in a manner that gives the blades  210  a self supporting rigidity. The one or more blades  210  have a length L and a width W. The one or more blades  210  have a bend  700  formed in the blades  210 . The bend  700  creates two blade legs  702 A and  702 B which extend from the bend at an angle θ. In one example the optimal angle is 50-60 degrees. The angle θ may be any suitable angle that gives the blades  210  self supporting rigidity. The length of each of the legs  702 A and  702 B may be equal or not equal depending on the milling operation. Deflection may be calculated using the following: 
               y   A     :=         -   W       6   ·   E   ·   I       ·     (       2   ·     L   3       -     3   ·     L   2     ·   a     +     a   3       )             
Area moment of inertia=I (in^4)
 
Length of beam=L (ft)
 
Distance from left edge to load=a (ft)
 
Modulus of elasticity=E (lbf/in^2)
 
Load=W (lbf)
 
Increasing area moment of inertia [I] decreases deflection [y(a)]
 
     
       
         
               
               
               
               
             
               
               
               
             
               
               
             
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 Radius: Angle: 
                 R ≡ 6 · in α ≡ 60 · deg 
               
               
                   
                   
               
             
          
           
               
                   
                 
                   
                     
                       
                         
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                 I 2  = 128.848 in 4   
               
               
                   
                   
               
             
          
           
               
                   
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     The legs  702 A and  702 B are shown as extending beyond the reinforcing structure  216 ; however, the legs  702 A and  702 B may be arranged to not extend beyond the reinforcing structure  216  or the face  208 . Although the bend  700  is shown as having a constant radius, it should be appreciated that the angle θ may be created in any manner, for example two plates may be welded at a point thus having no bend, or the radius of curvature could vary between the legs  702 A and  702 B. Further, each blade may have more than two legs  702  all at various angles relative to one another. This geometry of the blades  210  allows the height of the blades to increase well beyond 2″. In one embodiment, the height of the blades  210  is 4″ beyond the face of the milling tool  110 . As shown, there are two blades  210 ; however, any number of blades  210  may be arranged on the face  208  of the milling tool  110 . 
     A center void  704  between the one or more blades  210  in the center of the face  208  may be filled with the amorphous structure  214 , and/or one or more inserts. Further, a space  706  between the legs  702 A and  702 B may be filled with the amorphous structure  214 . As discussed above, the cutting side of the blades  210  may have one or more cutting inserts  212 . The face  208  may further include a compact cutting inserts  800 , shown in  FIGS. 8-11  located between the blades. The compact insert may be located in the center void  704  to alleviate the effects of coring during milling. The compact insert in the center void  704  allows the coring mechanism to enter the void  704  and then deflect toward the edge of the face  208  after contacting the compact insert. 
       FIGS. 8-12  show end views of the milling tool  110  having multiple blade configurations.  FIG. 8  shows two L shaped blades with an optional compact insert located in the center void.  FIG. 9  shows two V shaped blades with an optional compact insert located in the center void.  FIG. 10  shows three V shaped blades with an optional compact insert located in the center void.  FIG. 11  shows two J shaped blades with two straight blades.  FIG. 12  shows, the bends of the blades be continuous along the length of the blade and having an S shape, or wave shape. Further, the blades  210  could have any suitable shape and/or include a number of patterns. 
     Although not show, it should be appreciated that the bend  700  of the blades may be positioned toward a radial exterior of the milling tool  110 . In this embodiment, the legs  702 A and  702 B may extend from the bend toward the interior of the face, and/or toward another location on the radial exterior of the face. Further, there may be multiple blades  210  having bends  700  on the radial exterior of the face. These, multiple blades may have legs  702 A and  702 B which terminate adjacent to one another, or overlap one another. 
     In an alternative embodiment, the each of the blades  210  could have a different height H, or the height H of the blade  210  could vary along blade. Further, the milling tool  110  may be designed as a milling and drilling tool. For example the blades  210  may be designed for milling and drilling members may be located at a lower height than the height H of the blades  210 . This allows for milling until the blades  210  wear down to the height of the drilling members at which time drilling may begin. 
     The contact area (the L multiplied by the W) of any of the blades  210  described above has a direct effect on the cutting speed and life of the blade  210 . As the contact area is increased, the life of the milling tool  110  will increase however the speed at which the milling tool  110  mills is decreased. A contact pressure is created at the blades  210  by putting weight on the milling tool  110 . The contact pressure is the weight divided by the contact area. When the weight is constant any loss of the contact area due to wear will increase the contact pressure of the blades. The increased contact pressure wears the blades at a greater rate, thus, affecting the life of the milling tool. Thus, optimal results occur when little or no contact area is lost during milling. The blades  210  are designed to expose the same amount of carbide as the height H of the blades  210  is worn down. Therefore, as the blades  210  are worn down the contact area remains substantially the same allowing the milling tool  110  to perform the same as milling continues. 
     In operation the milling tool  110  is coupled to the conveyance  108 , such as a section of drill pipe at the surface. The milling tool  110  is run into the wellbore  100  as additional pipe joints are couple to the conveyance  108 . The milling tool  110  is lowered until it is adjacent the stuck item  112  in the wellbore  100 . The milling tool  110  may then be rotated in a cutting direction either by a downhole motor, and/or by rotating the conveyance  108  at the surface. Preferably the milling tool  110  is rotated as it is lowered into contact with the item  112  in order to commence the milling operation. An operator controls the amount of weight placed on the milling tool  110  and the rotational speed of the milling tool  110 . The weight may be increased or decreased. While milling fluid flows through flow path  300  and out the face  208 . The fluid lubricates the milling end  204  of the tool and pushes the cuttings toward the wellbore surface. 
     With the milling tool  110  rotating and in contact with the item  112 , the one or more cutting structures, the inserts  212  and the amorphous structure  214  begin to mill away the item  112 . When the amorphous structure  214  is placed above the height H of the blades  210 , the amorphous structure  214  begins the milling. The amorphous structure  214  mills and wears down as it mills. It wears down until it is close to the blades  210  at which point both the inserts  212  and the amorphous structure  214  mill away at the item. With the inserts  212  milling, a cutting force may be exerted on the one or more blades  210 . The cutting force will wear away the blades  210 , the inserts  212  and the amorphous structure  214  while milling. The geometry of the blades  210  resists the cutting force, thereby decreasing the deflection of the blades  210 . As the cutting force transfers to the blades, the cutting force will be dispersed along the legs  702 A and  702 B and through the bend  700 . The bend  700  and the legs  702  create multi-directional resistance to the cutting force. The geometry allows a 4″ blade to deflect less than 0.02″ at the lower end, and/or the deflection per inch of the blade height is less than 0.01″. The resistance to deflection may be increased by increasing the distance the blade  210  is embedded into the face  208  of the milling tool. Further, the amorphous structure  214  in the center void  204  and the space  706  increase the blades  210  resistance to deflection. 
     The milling tool  110  continues to rotate while the cutting structures are worn down. The configuration of the tool allows the milling tool  100  to operate up to 5 times longer than traditional milling tools. Therefore, the amount of rig time used to change milling tools  110  is reduced. When the milling operation is complete the milling tool  110  is run out of the wellbore  100 . The wellbore  100  may then be accessed for continued production and drilling operations. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.