Abstract:
A method and apparatus for milling and/or broaching within a wellbore. A flexible broach runs into the wellbore and is located adjacent a portion of the wellbore to be broached. The broach reciprocates axially within the wellbore and removes at least part of the portion to be broached. Weight may be coupled to the broach, thereby applying a resultant side load for broaching an offset portion of the wellbore. The broach comprises a flexible member that may be a bare cable. When an abrasive material is disposed on an outer surface of the flexible member, the flexible member may be a cable, a continuous rod, or pressurized coiled tubing. Alternatively, sleeves positioned on the flexible member may have an abrasive material on their outer surface. A rotational mill that is either coupled to the broach or run in separately from the broach can further mill the wellbore.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims benefit of U.S. provisional Patent Application Ser. No. 60/536,946, filed Jan. 16, 2004, which is herein incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   Embodiments of the invention generally relate to milling within a wellbore. More particularly, the invention relates to straightening a shifted or restricted wellbore by reciprocating a flexible broach axially within the wellbore. 
   2. Description of the Related Art 
   Hydrocarbon wells typically begin by drilling a borehole from the earth&#39;s surface to a selected depth in order to intersect a formation. Steel casing lines the borehole formed in the earth during the drilling process. This creates an annular area between the casing and the borehole that is filled with cement to further support and form the wellbore. Thereafter, the borehole is drilled to a greater depth using a smaller diameter drill than the diameter of the surface casing. A liner may be suspended adjacent the lower end of the previously suspended and cemented casing. In general, the diameter, location, and function of the tubular that is placed in the wellbore determines whether it is known as casing, liner, or tubing. However, the general term tubular or tubing encompasses all of the applications. 
   Shifting of the wellbore caused by pressure changes in the wellbore, swelling of surrounding formations, subsidence, earth movements, and formation changes can deform, bend, partially collapse, or pinch downhole tubulars. Therefore, a cross section of downhole tubulars becomes more irregular and non-round over time. Further, the path through the wellbore may become crooked, offset, or bent at an abrupt angle due to the shifting. Bends in the wellbore and deformed tubulars that define the bore can obstruct passage through the bore of tubing, equipment, and tools used in various exploration and production operations. For example, the bend may prevent a sucker rod from functioning and cause production to cease. Even if the tool can pass through the bore, these obstructions often cause wear and damage to the tubing, equipment, and tools that pass through the obstructed bore. 
   Current remediation operations to correct bends in the wellbore utilize rotational mills. The rotational mills have cutting surfaces thereon that rotate along the shifted section of the wellbore to remove casing and surrounding materials, thereby reducing the severity or abruptness of the angle. The mill provides a straighter path through the wellbore and reestablishes a bore that a round tubular can pass through. A liner secures in place across the milled portion in order to complete the remediation operation. 
   However, there exist several problems with using rotational mills for shifted wellbore remediation. In operation, one end of a rigid mill contacts an opposite side of the casing at the shift in the wellbore and places large side loads on the mill along the area being milled. The side loads cause rigid mills to fail prematurely resulting in the expense of replacement and repeated trips downhole to complete the milling process. Further, the mill can sidetrack away from the wellbore if the mill is not kept within the portions of the wellbore on either side of the shifted area during the milling procedure. Recently, rotating mills disposed on flexible members such as cable have been used to initiate the milling process at the shifted portion of the wellbore, thereby permitting a second mill that is run in separately to complete the milling process. Milling by rotation of a flexible mill is described in detail in U.S. Pat. No. 6,155,349, which is hereby incorporated by reference in its entirety. Requiring two trips downhole to complete the milling of the shifted section of the wellbore requires additional time at an added expense. Further, the flexible member may prematurely fatigue due to the stresses caused by the rotation during the milling. 
   Mills are used in various other wellbore remediation and completion operations. Generally, mills may remove ledges and debris left on the inside diameter of the tubulars such as excess cement, equipment remnants, burrs on the tubular itself, or metal burrs on the inside of the casing around a milled window. Well tubulars may become plugged or coated during production from corrosion products, sediments, hydrocarbon deposits such as paraffin, and scum such as silicates, sulphates, sulphides, carbonates, calcium, and organic growth. Thus, milling operations can remove the debris that collects on the inside surface of the tubular in order to prevent obstruction of the passage of equipment and tools through the bore of the tubulars. Further, mills can be used to elongate windows and straighten the angle into a lateral wellbore. 
   Therefore, there exists a need for an improved tool and method of milling within a wellbore that reduces stress and fatigue from rotation. There exists a further need for an improved method for remediation of a shifted section of wellbore with a single trip downhole. 
   SUMMARY OF THE INVENTION 
   The present invention generally relates to methods and apparatus for milling and/or broaching within a wellbore. A flexible broach runs into the wellbore and is located adjacent a portion of the wellbore to be broached. The broach reciprocates axially within the wellbore and removes at least part of the portion to be broached. Weight may be coupled to the broach, thereby applying a resultant side load for broaching an offset portion of the wellbore. The broach comprises a flexible member that may be a bare cable. When an abrasive material is disposed on an outer surface of the flexible member, the flexible member may be a cable, a continuous rod, or pressurized coiled tubing. Alternatively, sleeves positioned on the flexible member may have an abrasive material on their outer surface. A rotational mill that is either coupled to the broach or run in separately from the broach can further mill the wellbore. 

   
     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  is a sectional view of a wellbore illustrating a flexible broach reciprocating axially adjacent a shifted or bent section of the wellbore. 
       FIG. 2  is a view of a milling tool having a flexible broach portion coupled to a rotational mill portion. 
       FIG. 3  is a view of a cylinder of the flexible broach portion of the milling tool shown in  FIG. 2 . 
       FIG. 4  is a view of the milling tool shown in  FIG. 2  during a broaching operation within a wellbore. 
       FIG. 5  is a view of the milling tool shown in  FIG. 2  during a milling operation within the wellbore. 
       FIG. 6  is a view of an elliptical cylinder for coupling to adjacent elliptical cylinders to form a flexible broaching tool. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The invention generally relates to milling in a wellbore using a flexible broach.  FIG. 1  illustrates a wellbore  100  having casing  102  and a flexible broach  104  positioned in the wellbore  100  adjacent a shifted or bent section of the wellbore  100 . A downhole camera (not shown) may be run in on the broach  104  or milling tool to establish proper position within the wellbore  100  prior to milling or broaching. Other known locating techniques or devices may be used for locating the broach  104  at the bent section. The broach  104  may be lowered to the bent section using any known conveyance member  108 . All of the mills and broaches described herein are run into a wellbore on a conveyance member and located therein. In certain embodiments, the broach  104  may be an integral portion of the conveyance member  108  as will be apparent for embodiments wherein the broach  104  is a cable, a continuous rod, or coiled tubing. As indicated by arrow  106 , the broach  104  reciprocates axially within the wellbore  100  to cut or broach a slot  110  in the casing and/or the surrounding formation or cement. The broach  104  may be reciprocated axially by any known method such as by axially moving the conveyance member  108  at the surface of the wellbore  100 . In this manner, elimination of rotational torque to the broach  104  prevents fatigue and failure of the broach  104 . 
   The broach  104  shown in  FIG. 1  includes a flexible elongated body  112  and a weight  114  attached at a lower end of the elongated flexible body  112 . The weight  114  provides tension to the body  112  such that the body  112  frictionally contacts the bent section of the wellbore  100  where the slot  110  is formed. In one embodiment, the body  112  is a bare cable or wire rope that abrades or saws the slot  110  as the broach  104  reciprocates within the wellbore  100 . In an alternative embodiment, the body  112  is a cable, a portion of a continuous rod, or a portion of pressurized coiled tubing that is coated with an abrasive material  116  such as crushed tungsten carbide. The abrasive material  116  is shown spaced axially along the body  112 . However, the abrasive material  116  may be disposed along the entire length of the body  112 . The broach  104  permits cutting of the slot  110  at a high rate since the entire length of the broach  104  cuts the slot  110  using multiple blades formed by the abrasive material  116 . 
   With the broach  104  shown in  FIG. 1 , it may be necessary to remove the broach from the wellbore  100  and further mill the slot  110  using a rotational mill (not shown) in order to open up the slot  110  to full gage. However, the slot  110  effectively reduces the angle of the bend, the amount of rotational milling required and the stress on the rotational mill. An exemplary rotational mill is illustrated by a rotational milling portion  201  of a milling tool  200  shown in  FIG. 2 . However, any known rotational mill may be run into the wellbore  100  to open up the slot  110 . As explained with the milling tool  200  in  FIG. 2 , the rotational mill may include a stinger section that guides the rotational mill into the slot  110 . 
     FIG. 2  shows a milling tool  200  having a flexible broach portion  202  coupled to a rotational mill portion  201 . The rotational mill portion  201  has a connector end such as box end  203  for connecting to a conveyance member and a stinger  205  opposite the box end  203 . Since the stinger  205  is integral with a shaft  207  of the rotational mill portion  201 , the rotational mill portion is long, preferably approximately twenty five feet. The length of the rotational mill portion  201  permits the rotational mill portion to flex, thereby aiding in relieving stress. Further, the length of the rotational mill portion  201  initially spaces the box end  203  from the sharp bend in the wellbore in order to prevent the connection at the box end  203  from breaking or failing. The stinger  205  preferably increases in outer diameter towards the box end  203 . As shown, the rotational mill portion  201  has five blade sections  204  axially spaced and located between the box end  203  and the stinger  205 . However, the rotational mill portion may include any number of blade sections  204 . Each blade section  204  has milling inserts (not shown) positioned along the blades directed to cut both down and sideways such that the rotational mill portion  201  relieves some of the side load by milling sideways as well as down. 
   Between the rotational mill portion  201  and the flexible broach portion  202  is a swivel  208  or knuckle joint that isolates rotational torque applied to the rotational mill portion  201  from the flexible broach portion  202 . Additionally, a cable connector such as a cable slip  209  may be used to couple a cable  212  (e.g., a left-hand wound cable) of the flexible broach portion  202  to the rotational mill portion  201 . In some embodiments, the cable  212  is fixed to a box connection or other connection in order to couple the cable  212  to the rotational mill portion  201  and does not require use of the cable slip  209 . 
   The flexible broach portion  202  includes the cable slipped through an internal longitudinal bore of a series of cylinders  210  coated with an abrasive such as crushed tungsten carbide. As shown in more detail in  FIG. 3 , each cylinder  210  has the longitudinal bore  303  and a cutting helix  300  on an outside surface that is oriented such that the leading edge of the helix  300  is perpendicular to the area being cut. Thus, helix  300  provides a cutting surface on the cylinder  210  that is perpendicular to the area cut when the cylinder  210  reciprocates axially and not rotationally. The helixes can be offset or at alternating angles (e.g., clockwise and counter clockwise). A convex ball nose  301  of the cylinder  210  mates with a concave socket end  302  of an adjacent cylinder. The ball  301  and socket  302  mating of adjacent cylinders provides flexibility to the flexible broach portion  202 . Referring back to  FIG. 2 , weights  213  are attached to the cable  212  below the cylinders  210  in order to supply tension to the flexible broach portion  202  during a broaching operation. Weights  213  and cylinders  210  may be attached together using tool joints that are babbitted to the cable ends. For example, connections such as between the cable  212  and the rotational mill portion  201  may be formed by positioning a tool joint over an end of the cable  212 , fraying the end of the cable and pouring a babbitt or epoxy resin into a socket of the tool joint as is known in the industry. 
     FIG. 4  shows the milling tool  200  shown in  FIG. 2  during a broaching operation within a wellbore  400 . As indicated by arrow  406 , the milling tool  200  reciprocates axially to cut a slot  410  into a casing  402  at a bend in the wellbore  400 . During the broaching operation, the flexible broaching portion  202  is located adjacent the bend in the wellbore  400 . Thus, the reciprocation of the cylinders  210  having abrasive outer surfaces in contact with the casing  402  at the bend broaches the slot  410 . 
     FIG. 5  illustrates the milling tool  200  during a milling operation after forming the slot  410  in the casing  402  with the broaching operation. The stinger  205  enters the slot formed by the flexible broach portion  202  to guide the rotational mill portion  201  during the milling operation. Further, the stinger deflects in order to provide a side force so that the rotational mill portion  201  located adjacent the bend mills sideways to relieve its own stress. As indicated by arrow  506 , the milling tool  200  rotates to mill the wellbore  400  at the bend using the rotational mill portion  201 . The swivel  208  prevents transferring rotation to the flexible broach portion  202 . Even if rotation is transferred to the flexible broach portion  202 , the flexible broach portion  202  is not stressed during the rotation from the milling operation. 
   Any flexible broach  104  embodiment described in  FIG. 1  may replace the flexible broach portion  202  of the milling tool  200  shown in  FIG. 2 . Further, while  FIGS. 2 ,  4  and  5  are shown having the rotational mill portion  201  coupled to the flexible broach portion  202 , the flexible broach portion  202  may be used independently of the rotational mill portion  201  in a manner similar to the flexible broach  104  shown in  FIG. 1 . In this instance, it may be necessary to have cylinders  210  that increase in outer diameter toward the surface of the wellbore. The cylinders  210  with a smaller diameter can enter a deformed portion of the casing that would not permit passage of the cylinders having a larger diameter. Once the smaller diameter cylinders broach the wellbore, the larger diameter cylinders can be lowered to broach the wellbore to full gage. 
     FIG. 6  illustrates an elliptical cylinder  610  with an abrasive material such as crushed tungsten carbide  600  on an outside surface thereof. The elliptical cylinder  610  slips onto a cable next to adjacent elliptical cylinders to form a flexible broaching tool similar to the flexible broach portion  202  shown in  FIG. 2 . The elliptical cylinder  610  has a major axis that orients within casing that has been deformed by a shifted wellbore to also have a major axis. In this manner, the elliptical cylinder  610  orients in a predetermined direction and the major axis is large enough to create a full gage slot by broaching as described herein. 
   While the foregoing is directed to embodiments of the 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.