Abstract:
An insert for an earth boring drill bit, such as a PDC rock bit or a roller cone rock bit, is provided. The insert includes a base integrally joined to a top section, the top section having a first flank that curves in a substantially helical manner about a longitudinal axis of the insert to join a crest.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/833,174 filed Jul. 25, 2006. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates in general to earth boring devices used in oil field applications, and, more particularly, to inserts for earth boring rotary cone rock bits. 
       BACKGROUND 
       [0003]    Conventional earth boring rotary cone rock bits are commonly used in oil field applications. Rotational energy and weight applied to the bit by the drill pipe force the rotary cutters into earth formations. The borehole is formed as the punching and scraping action of the rotary cutters remove chips of formation. The rate at which borehole is formed is largely a result of the design of the rotary cutters. One main category of rotary cutters is tungsten carbide insert (TCI) cutters. The teeth on TCI cutters are made of tungsten carbide and are press fit (inserted) into undersize apertures on the cone. The teeth on the cutters functionally break up the formation to form new borehole by punching into it vertically and scraping horizontally. The amount of punching action is governed primarily by the weight on the bit. The horizontal scraping motion is a resultant of the position and shape of the cone cutter. 
         [0004]    Medium and soft formation bits usually drill through varied formations in a single well. Recording devices which show instantaneous rates of penetration will often show rates as high as four feet per minute and rates as slow as one foot in ten minutes on the same bit run. As a rule, the formations tend to become harder as depth increases but there are large variations in hardness at all depths. 
         [0005]    Bits having long inserts are typically most efficient for fast drilling in soft formations. Long inserts are relatively weak though, and are subject to breakage in the slower drilling hard formations. Short blunt inserts are better suited for the harder formations because they are less subject to breakage, but they limit a bit&#39;s penetration rate in soft formations. 
         [0006]    Accordingly, there is a need for wear resistant inserts for drilling bits that provide a high rate of penetration in both soft and hard formations while providing resistance to insert breakage. 
       SUMMARY OF THE INVENTION 
       [0007]    An insert for an earth boring drill bit is provided. The insert includes a base integrally joined to a top section, the top section having a first flank that curves in a substantially helical manner about a longitudinal axis of the insert to join a crest. 
         [0008]    A drill bit for boring an earth formation is provided. The drill bit includes a plurality of helical chisel inserts. 
         [0009]    A method for drilling an earth formation is provided. The method includes the steps of providing a rotary cone cutter having a plurality of cutters, wherein each cutter has an axis of rotation for plowing the formation in a direction, and comprises an outermost heel row and a second row, positioning a first set of helical chisel inserts on the heel row, and positioning a second set of helical chisel inserts on the second row. The helical chisel inserts each include a base integrally joined to a top section, the top section having a leading flank and a trailing flank that curve in a substantially helical manner about a longitudinal axis of the insert to join an elongated crest. 
         [0010]    The foregoing has outlined rather generally the features and technical advantages of one or more embodiments of the present invention in order that the detailed description of the present invention that follows may be better understood. Additional features and advantages of the present invention will be described hereinafter which may form the subject of the claims of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    A better understanding of the present invention can be obtained when the following detailed description is considered in conjunction with the following drawings, in which: 
           [0012]      FIG. 1  is a cross-sectional view of a portion of an embodiment of a TCI tri-cone rock drill bit of the present invention, showing one cone cutter rotatably mounted on a bearing pin shaft; 
           [0013]      FIG. 2  is a front elevational view of an embodiment of the rock drill bit insert of the present invention; 
           [0014]      FIG. 3  is a top view of the insert of  FIG. 2 ; 
           [0015]      FIG. 4  is a front elevational view of another embodiment of the rock drill bit insert of the present invention; 
           [0016]      FIG. 5  is a schematic view of a bore hole bottom showing insert tracks left by an embodiment of the roller cone cutter, wherein the helical chisel inserts have been positioned for reducing insert breakage; and 
           [0017]      FIG. 6  is a schematic view of a bore hole bottom showing insert tracks left by an embodiment of the roller cone cutter, wherein the helical chisel inserts have been positioned for increasing penetration rate. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. 
         [0019]    As used herein, the terms “up” and “down”; “upper” and “lower”; “uphole” and “downhole” and other like terms indicating relative positions to a given point or element are utilized to more clearly describe some elements of the embodiments of the invention. Commonly, these terms relate to a reference point as the surface from which drilling operations are initiated as being the top point and the total depth of the well being the lowest point. 
         [0020]    The present invention is directed to a helical chisel insert for a drill bit, such as a roller cone bit. The helical design of the insert provides an aggressive shape for increased penetration during drilling. In addition, the helical chisel insert is suitable for positioning the inserts in a vectored manner on the drill bit to achieve an orientation that provides increased resistance to insert breakage and/or and increased rate of penetration. 
         [0021]      FIG. 1  shows a drill bit in accordance with an embodiment of the present invention, indicated by  2 . Drill bit  2  has a threaded section  4  on its upper end for securing to the drill string (not shown). A frusto-conical roller cone cutter  8  is rotatably mounted and secured on the bearing pin shaft  16  which extends downward and inward, from the bottom of the journal segment arm  6 . Cone cutter  8  has a cutting structure consisting of helical chisel inserts  22 . Helical chisel inserts  22  are mounted on either heel row  10 , second row  12 , inner row  14 , or any combination thereof Helical chisel inserts  22  may be press fit into hole  9  or otherwise positioned on cone cutter  8 . Helical chisel inserts  22  may be made from any suitable material including tungsten carbide, diamond enhanced tungsten carbide, diamond or polycrystalline diamond compact (PDC). Cone cutter  8  may include conventional inserts on those rows where helical chisel inserts  22  are not mounted. The cone cutters  8  are rotatably mounted on journals with sliding bearing surfaces. The axis of rotation  18  of the cone cutter  8  extends inwardly through the center of the bearing pin shaft  16  toward and offset from the axis of rotation  20  of the drill bit  2 . Although  FIG. 1  depicts drill bit  2  as a roller cone bit, it will be understood by those of ordinary skill in the art that the helical chisel insert of the present invention may be used in PDC bits and other types of drill bits. 
         [0022]      FIGS. 2 and 3  show front and top views, respectively, of an embodiment of the helical chisel insert  22   a  of the present invention.  FIG. 4  shows the front view of another embodiment of helical chisel insert  22   b  of the present invention. As shown in  FIGS. 2-4 , helical chisel insert  22  has a cylindrical base  24  which may be inserted in hole  9  with its longitudinal axis  26  being normal to the surface  21  of cutter  8  (hole  9  and surface  21  shown in  FIG. 1 ). A top portion  50 , which is connected to cylindrical base  24 , includes a cutting tip  28  and an elongated crest  36  having a length  52  along its broad side and a width  53 . Top portion  50  has two faces or flanks, leading flank  30  and trailing flank  32 . Flanks  30  and  32  commence at the joinder of the top portion  50  and cylindrical base  24 , shown as corners  42  and  44 , respectively, and curve upwards in a substantially helical manner about longitudinal axis  26 , to join crest  36  at corners  38  and  40 , respectively. Flanks  30  and  32  define substantially concave surfaces  46  and  48 . As is apparent from  FIGS. 2-4 , flanks  30  and  32  define a contoured surface that is continuously twisted from the top of base  24  to the crest  36  such that iterative cross sections of top portion  50  will describe a helix at their outermost points. 
         [0023]    The contoured surface of helical chisel insert  22  provides a more aggressive cutting surface than convention chisel inserts and may provide a greater rate of penetration than conventional chisel inserts. The shape of helical chisel insert  22  may allow insert  22  to plow through the formation, as opposed to merely striking the formation. As a result, helical chisel insert  22  may remove more rock for a given position in the drill bit than a conventional insert. For example, helical chisel inserts  22  may provide a more aggressive insert in soft formation drilling by orientating the elongated crest  36  of the cutting tip  28  preferentially with the cutting or plowing action of the drilled formation relative to the chisel rolling direction. The result may be faster rates of penetration for the drill bit  2  as a whole. Helical chisel inserts  22  may add improved plowing action to the insert over conventional inserts as helical chisel insert  22  describes its arc into, through and out of the formation being drilled. 
         [0024]    Helical chisel insert  22  has a degree of twist θ, measured from the longest axis of the bottom cross section to the longest axis of the elongated crest  36 . The degree of twist θ may be selected based on the desired characteristics including, for example, penetration rate and resistance to breakage. The embodiment of helical chisel insert  22   a  shown in  FIGS. 2 and 3  has a degree of twist θ of about 90°, for example. The embodiment of helical chisel insert  22   b  shown in  FIG. 4 , has a degree of twist θ of about 15°, for example. Flanks  30  and  32  may curve either substantially clockwise or substantially counterclockwise. Flanks  30  and  32  may have a twist from about 90° clockwise to about 90° counterclockwise, thus describing the entire 360° radius. Flanks  30  and  32  may be selectively shaped to provide different crest  36  geometries that describe the degree of twist in variations of an “s” shape, but within the same insert diameter. Helical chisel insert  22  may incorporate timing mark  54  to assist a user with positioning helical chisel inserts  22  on drill bit  2  in a precise manner. 
         [0025]    Although  FIGS. 2-4  depict helical chisel bit  22  with two flanks, it will be understood by those of ordinary skill in the art that other embodiments of the helical chisel insert of the present invention may include only one flank, or may include more than two flanks. Similarly, while  FIGS. 2-4  depict helical chisel bit  22  with an substantially elongated crest, it will be understood by those of ordinary skill in the art that other embodiments of the helical chisel insert of the present invention may include different crest formations depending on the number of flanks and the selected contour geometry, among other factors. 
         [0026]    Helical chisel inserts  22  may be positioned on rolling cone cutter  8  in a vectored manner such that the elongated crests  36  are selectively oriented with respect to the direction of plowing action. By vectoring helical chisel inserts  22  in this manner, a drill bit  2  may be selectively configured to provide a greater rate of penetration, improved resistance to breakage, or a combination thereof. Embodiments of this vectored positioning are shown in  FIGS. 5 and 6 . 
         [0027]      FIG. 5  is a schematic view of a borehole bottom showing the impression left by helical chisel inserts  22  on the two outer rows of a cone cutter, selected and positioned thereon to reduce insert breakage. The direction of bit rotation is indicated by arrow  56 . By orienting (vectoring) the elongated crests  36  of the inserts  22  in line with the insert movement a helical chisel insert  22  presents a very small face to the formation. The insert  22  can withstand higher forces (or harder formations) in this situation. The helical chisel inserts  22  on the outermost heel row have a selected angle of twist θ such that crests  36  are oriented at an angle from about 30° to about 60° from the axis of rotation of the cone toward the leading side of the cone. The helical chisel inserts  22  on the second row have a selected angle of twist θ such that crests  36  are oriented at an angle from 30° to 60° from the axis of the cone toward the trailing side of the cone. Stated another way, the elongated crests on the heel row are oriented at an azimuth direction ranging from 300° to 330° from the axis of rotation of the cone with the axis being equal to 360°. The elongated crests on the second row are oriented at an azimuth direction of 30° to 60° from the axis of the cone. 
         [0028]    With such an orientation, the insert  22  moves in formation in a direction in line with the elongated crest  36  so that a relatively small area, about width  53  of the insert  22 , contacts the formation and relatively small chips are formed. The relatively thick section of tungsten carbide, for example, along the length  54  of the crest  36  provides a very high resistance to insert breakages. This type of insert orientation provides a cone cutter with much higher resistance to breakage than a similar cutter with conventional insert orientation. 
         [0029]    The direction of bit rotation is indicated by arrow  56 . The initial engagement of the elongated crests of the heel row inserts is indicated by  58 . The disengagement of the elongated crests of the heel row inserts is indicated by  66  with the direction of the plowing of formation represented by arrow  62 . The elongated crests of the second row inserts engage  60  and disengage  68  the formation in the direction indicated by arrow  64 . 
         [0030]    Alternatively, the angle of twist θ may be selected to orient or vector the crest  36  so that the broad side  52  of the insert crest  36  faces the direction of the plowing action. In this case, each insert  22  removes more formation, resulting in a faster penetration rate. This configuration is illustrated in  FIG. 6 , which is a schematic view of a borehole bottom showing insert tracks left by inserts  22  on the two outer rows of a cone cutter, where the inserts are oriented for increasing penetration rate. As shown in  FIG. 6 , the elongated crests  36  of the helical chisel inserts  22  are relatively perpendicular to the direction of the plowing action, indicated by arrow  88 . The elongated crests  36  of the inserts  22  positioned on heel row  10  are oriented at an angle of 30° to 60° toward the trailing side of the cone. The elongated crests  36  of the inserts  22  on second row  12  are oriented at an angle of 30° to 60° toward the leading side of the cone. Stated another way, the elongated crests of the heel row inserts are oriented at an azimuth direction ranging from about 30° to 60° from the axis of rotation of the cone. The elongated crests of the second row inserts are oriented at an azimuth direction of 300° to 330° from the axis of rotation of the cone with the axis being equal to 360°. This orientation may break formation along a wider path, making more chips and larger chips than orientation of standard TCI bits, resulting in an increase penetration rate. 
         [0031]    The direction of bit rotation is indicated by arrow  82 . The initial engagement of the elongated crests of the heel row inserts is indicated by  84 . The disengagement of the elongated crests of the heel row inserts is indicated by  86  with the direction of the plowing of formation represented by arrow  88 . The elongated crests of the second row inserts engage  90  and disengage  92  the formation in the direction indicated by arrow  94 . 
         [0032]    The embodiments shown in  FIGS. 5 and 6  show an angle of twist θ of about ±30°. Other embodiments of the helical chisel inserts of the present invention, however, may have a twist from about 90° clockwise to about 90° counterclockwise, thus describing a greater range. As a result, the helical chisel inserts allow for an increased degree of freedom in configuring the drill bit to improve resistance to insert breakage, rate of penetration, or a balance of both. 
         [0033]    The helical chisel inserts of the present invention may provide a more aggressive cutting surface than convention chisel inserts and may provide a greater rate of penetration than conventional chisel inserts. The helical chisel inserts may add improved plowing action to the insert over conventional inserts as the helical chisel insert describes its arc into, through and out of the formation being drilled. If the insert life is given priority over the rate of penetration, the helical chisel insert may be described in reverse rotation. The helical chisel inserts also provide an insert designer with another degree of freedom to optimize chisel contour geometries to accommodate the particular stresses and wear patterns observed downhole. 
         [0034]    From the foregoing detailed description of specific embodiments of the invention, it should be apparent that a helical chisel insert for rock bits that is novel has been disclosed. Although specific embodiments of the invention have been disclosed herein in some detail, this has been done solely for the purposes of describing various features and aspects of the invention, and is not intended to be limiting with respect to the scope of the invention. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the disclosed embodiments without departing from the spirit and scope of the invention as defined by the appended claims which follow.