Abstract:
Downhole cutting tools such as blade mills comprise a body having an upper end for connection with a rotating component of a drill string and a guide member disposed at lower end. The guide member can comprise a shape that is reciprocal to an engagement member disposed on an object within the well that is to be cut by the cutting mill. In certain embodiments, the guide member comprises a portion that is spherically shaped or an apex formed by two angled cutting elements. The cutting tools can also include one or more blades having cutting elements disposed thereon in a stepped arrangement. In one such embodiment, the cutting elements are disposed to cover one or more steps profiled on a lower end of the blade to lessen wear of the blade caused by the cutting of the object by the blade.

Description:
BACKGROUND 
     1. Field of Invention 
     The invention is directed to downhole cutting tools utilized in oil and gas wells to cut objects within the well and, in particular, to downhole blade mills that are used to cut away, among other objects, stuck tools, bridge plugs, well tubing, well casing, and the like disposed within the well. 
     2. Description of Art 
     In the drilling, completion, and workover of oil and gas wells, it is common to perform work downhole in the wellbore with a tool that has some sort of cutting profile interfacing with a downhole structure. Examples would be milling a downhole metal object with a milling tool, performing a washover operation with a rotary shoe, or cutting through a tubular with a cutting or milling tool. During the performance of these operations, it is common for the tool and/or drill string to which the tool is connected, to vibrate or bounce off of the object disposed within the wellbore that is being cut or abraded, causing inefficiencies in the cutting operations. 
     SUMMARY OF INVENTION 
     Broadly, the invention is directed to downhole cutting tools utilized in cutting (also referred to as abrading or milling) an object disposed within the well. The term “object” encompasses any physical structure that may be disposed within a well, for example, another tool that is stuck within the well, a bridge plug, the well tubing, the well casing, or the like. The downhole cutting tools disclosed herein include cutting elements disposed on a body. The cutting elements can be disposed on an outer wall surface of the body, or on blades disposed along the outer wall surface of the tool. The cutting elements are disposed on the body such that rotation of the body causes rotation of the cutting elements. 
     In one particular embodiment, the downhole cutting tool comprises a guide member disposed at an end of the tool. The guide member facilitates engagement of the tool with an object disposed in a wellbore. By engaging the guide member with the object, the tool rotation will follow a more circular path, thereby reducing the magnitude of lateral motion during cutting operations. 
     In other specific embodiments, the downhole cutting tools comprise cutting elements arranged in a staggered pattern. The cutting elements can be disposed directly on an outer wall surface of the body of the tool, or on one or more blades attached to the body of the tool. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view of one specific embodiment of a downhole cutting tool disclosed herein. 
         FIG. 2  is an enlarged view of the cutting elements shown on the embodiment illustrated in  FIG. 1 . 
         FIG. 3  is a side view of another specific embodiment of a downhole cutting tool disclosed herein. 
         FIG. 4  is a partial cross-sectional view of an object disposed in a wellbore showing the downhole tool of  FIG. 1  being lowered to engage the object. 
         FIG. 5  is a partial cross-sectional view of the object disposed in the wellbore shown in  FIG. 4  showing the downhole tool of  FIG. 1  engaged with the object prior to rotation of the tool and, thus, cutting of the object. 
     
    
    
     While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to these embodiments. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF INVENTION 
     Referring now to  FIGS. 1-3 , downhole cutting tool  20  comprises body  21  having first or upper end  22 , second or lower end  23 , and longitudinal axis  24 . First or upper end  22  is adapted to be connected to a drill or work string  80  ( FIGS. 4-5 ), such as through a threaded connection shown in  FIGS. 1 and 3 . Cutting elements  40  are disposed along outer wall surface  26  of body  21 . In the embodiments of  FIGS. 1-3 , cutting elements  40  are disposed on a plurality of blades  30 . It is to be understood, however, that blades  30  are not required. Instead, cutting elements  40  can be disposed directly on outer wall surface  26  or on any other structure desired or necessary to facilitate cutting of an object disposed in a wellbore. 
     In the embodiments shown in the  FIGS. 1-5 , tool  20  is a blade mill having a plurality of blades  30 . One or more of blades  30  can be a “stepped blade” having a stepped profile along cutting end  31  such as shown in  FIGS. 1 and 3 . As shown in  FIGS. 1 and 3 , the profile along cutting end  31  includes first, second, and third steps  32 ,  33 ,  34 . Thus, in the embodiments of  FIGS. 1-5 , tool  20  is a “stepped blade mill.” 
     Although the cutting elements  40  can be disposed on cutting faces  36  in numerous arrangements, in the embodiments of  FIGS. 1-5 , cutting elements  40  are disposed on cutting faces  36  of blades  30  in three columns. First column  41  is disposed parallel to, and closest to, longitudinal axis  24 . Second column  42  is disposed adjacent first column  41  and parallel to longitudinal axis  24 . Third column  43  is disposed adjacent second column  42  and parallel to longitudinal axis  24 . Third column  43  of cutting elements  40  is the furthest from longitudinal axis  24  and closest to the outer edge of cutting face  36 . 
     In addition to being disposed in columns, cutting elements  40  of first column are disposed in a staggered relationship relative to cutting elements  40  of second column. Similarly, cutting elements of second column  42  are disposed in a staggered relationship relative to cutting elements  40  of third column  43 . As best shown in  FIG. 2 , in one particular embodiment, cutting elements  40  of first column  41  are offset relative to cutting elements  40  of second column  42  such that upper surfaces  61  of one or more of cutting elements  40  of first column  41  is not aligned with upper surface  63  or a lower surface  65  of an adjacent cutting element  40  of the second column  42 . In other words, upper surface  61  of one or more cutting elements  40  of first column  41  is level with a point disposed along height  67  between upper surface  63  and lower surface  65  of at least one cutting element  40  of second column  42 . The point can be disposed half-way between upper surface  63  and the lower surface  65 , i.e., the mid-point (as shown in  FIGS. 1-3 ), or any other point in-between. 
     Additionally, as illustrated in  FIGS. 1 and 3 , the lowermost cutting element  40  of each of first, second, and third columns  41 ,  42 ,  43  is disposed such that cutting elements  40  extend beyond (i.e., away from the cutting end  31 ) the stepped profile along cutting surface  31  that defines first, second, and third steps  32 ,  33 ,  34 . The arrangement of cutting elements  40  in this manner lessens exposure of blades  30 , and cutting surface  36  to the object so that cutting elements  40  can more efficiently cut the object disposed in the well. 
     Disposed at lower end  23  of body  21  is guide member  50 . Guide member  50  extends beyond lower end  23  for engagement with the object disposed in the wellbore. Guide member  50  includes a profile for engaging with the an engagement member disposed on the object to stabilize cutting tool  20  during cutting of the object. The profile of guide member  50  can include at least a partial spherical shape ( FIG. 1 ), or tool apex  55  ( FIG. 3 ) defined by one or more cutting elements  40  being disposed on lower end  23 . In embodiments in which cutting elements  40  define apex  55 , one or more of cutting elements  40  can be disposed at non-right angles relative to lower end  23  as shown in  FIG. 3 . In addition, in embodiments in which at least two cutting elements  40  define apex  55 , at least two of the cutting elements  40  can be disposed facing each other. Inclusion of cutting elements  40  as guide member  50  allows guide member  50  to cut or abrade the object in addition to providing stability to the downhole tool  20  during operation. In other words, during rotation of the work string containing downhole tool  20 , cutting elements  40  of guide member  50  cut an opening in the object into which guide member  50  is inserted so as to stabilize downhole tool  20  during further cutting of the object. Thus, guide member  50  having one or more cutting elements  40  cuts an opening large enough such that guide member can enter and engage the interior surface of the object to provide stabilization. 
     Referring now to  FIGS. 4-5 , downhole cutting tool  20  is secured to drill string  80  and disposed within wellbore  84 . Disposed within wellbore  84  is object  90  having engagement member  91  defining engagement member interior surface  92 . The profile of guide member  50  of tool  20  is shaped to be received by engagement member  91 . As used herein, “received” is understood to have its broadest meaning requiring only that guide member  50  is able to engage with engagement member  91 . It is to be understood that the engagement between guide member  50  and engagement member  91  is not required to have a low tolerance fit. All that is required is that guide member  50  can engage with engagement member  91  such that tool  20  and, thus, drill string  80 , are stabilized during cutting operations thereby preventing tool  20  or string  80  to experience vibration or bounce causing a decrease in the efficiency of the cutting as compared to a tool lacking guide member  50 . In one particular embodiment, engagement member  91  comprises a bore that extends the entire longitudinal length of object  90 . In other embodiments, engagement member  91  comprises a recess reciprocally-shaped to the shape or profile of guide member  50 . For example, engagement member  91  can be a concave-shaped recess to receive spherical-shaped guide member  50  ( FIG. 1 ). 
     In operation, drill string  80  is lowered within wellbore  84  ( FIG. 2 ) until guide member  50  engages with engagement member  91  of object  90  ( FIG. 5 ). Drill string  80  is rotated causing cutting elements  40  to cut or abrade away object  90 . Due to the outer diameter of drill string  80  being smaller than the inner diameter of wellbore  84 , drill string  80  is prone to vibrate or bounce upward off of object  90 . To lessen the likelihood of this happening, the engagement of guide member  50  with engagement member  91  stabilizes tool  20  and, thus, drill string  80 . Drill string  80  continues to rotate and move downward as object  90  is cut or abraded away. The rotation and cutting continues until object  90  is removed from wellbore  84 . Thereafter, drill string  80  is removed from wellbore  84  so that other downhole operations can be performed within wellbore  84 . 
     It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. For example, the materials forming the components, the dimensions of each of the components, and the arrangement of the cutting elements can be modified as desired or necessary effectuate the best device for cutting an object disposed in a well. In addition, the guide member is not required to be spherically-shaped or be composed of angled cutting elements. Other guide members and their equivalents can be included as part of certain of the embodiments disclosed herein. Moreover, the cutting elements are not required to have the shapes and dimensions disclosed herein. Additionally, although the upper surfaces and lower surfaces of the cutting elements of the first and second columns are discussed with respect to specific reference numerals, it is to be understood that all of the cutting elements include an upper surface, a lower surface, and a height in the same manner as those discussed with respect to the cutting elements of the first and second columns. Further, it is to be understood that the term “wellbore” as used herein includes open-hole, cased, or any other type of wellbores. In addition, the use of the term “well” is to be understood to have the same meaning as “wellbore.” Moreover, in all of the embodiments discussed herein, upward, toward the surface of the well ( FIGS. 4-5 ), is toward the top of Figures, and downward or downhole (the direction going away from the surface of the well) is toward the bottom of the Figures. However, it is to be understood that the tools may have their positions rotated in either direction any number of degrees. Accordingly, the tools can be used in any number of orientations easily determinable and adaptable to persons of ordinary skill in the art. In addition, referring to a component as being “upper” or “lower” does not dictate the orientation of the component when placed in a well. Accordingly, the invention is therefore to be limited only by the scope of the appended claims.