Patent Publication Number: US-9840874-B2

Title: Hybrid rolling cone drill bits and methods for manufacturing same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/679,346 filed Nov. 16, 2012, and entitled “Hybrid Rolling Cone Drill Bits and Methods for Manufacturing Same,” which is incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE TECHNOLOGY 
     Field of the Invention 
     The invention relates generally to earth-boring bits used to drill a borehole for the ultimate recovery of oil, gas or minerals. More particularly, the invention relates to rolling cone rock bits and to an improved cutting structure for such bits. 
     Background Information 
     An earth-boring drill bit is connected to the lower end of a drill string and is rotated by rotating the drill string from the surface, with a downhole motor, or by both. With weight-on-bit (WOB) applied, the rotating drill bit engages the formation and proceeds to form a borehole along a predetermined path toward a target zone. The borehole formed in the drilling process will have a diameter generally equal to the diameter or “gage” of the drill bit. The length of time that a drill bit may be employed before it must be changed depends upon its ability to “hold gage” (meaning its ability to maintain a full gage borehole diameter), its rate of penetration (“ROP”), as well as its durability or ability to maintain an acceptable ROP. 
     In oil and gas drilling operations, costs are generally proportional to the length of time it takes to drill the borehole to the desired depth and location. The time required to drill the well, in turn, is greatly affected by the number of times the drill bit must be changed in order to reach the targeted formation. This is the case because each time the bit is changed, the entire string of drill pipes, which may be miles long, must be retrieved from the borehole, section-by-section. Once the drill string has been retrieved and the new bit installed, the bit must be lowered to the bottom of the borehole on the drill string, which again must be constructed section-by-section. This process, known as a “trip” of the drill string, requires considerable time, effort and expense. Since drilling costs are typically one the order of thousands of dollars per hour, it is desirable to employ drill bits which will drill faster and longer, and which are usable over a wider range of formation hardnesses. 
     One common type of earth-boring bit, referred to as a rolling cone or cutter bit, includes one or more rotatable cone cutters, each provided with a plurality of cutting elements. During drilling with WOB applied, the cone cutters roll and slide upon the bottom of the borehole as the bit is rotated, thereby enabling the cutting elements to engage and disintegrate the formation in its path. The borehole is formed as the cutting elements gouge and scrape or chip and crush the formation. The chips of formation are carried upward and out of the borehole by drilling fluid which is pumped downwardly through the drill pipe and out of the bit. 
     Cutting elements provided on the rolling cone cutters are typically one of two types—inserts formed of a very hard material, such as tungsten carbide, that are press fit into undersized apertures in the cone surface; or teeth that are milled, cast or otherwise integrally formed from the material of the rolling cone. Bits having tungsten carbide inserts are typically referred to as “insert” bits, while those having teeth formed from the cone material are commonly known as “milled tooth bits.” The shape and positioning of the cutting elements (both teeth and inserts) upon the cone cutters greatly impact bit durability and ROP, and thus, are important to the success of a particular bit design. 
     The inserts in insert bits are typically positioned in circumferential rows on the rolling cone cutters. Specifically, most insert bits include a radially outermost heel row of inserts positioned to cut the borehole sidewall, a gage row of inserts radially adjacent the heel row and positioned to cut the corner of the borehole, and multiple inner rows of inserts radially inward of the gage row and positioned to cut the bottom of the borehole. The inserts in the heel row, gage row, and inner rows can have a variety of different geometries. 
     Particular cutting elements may be more well suited in particular types of formations. For example, milled teeth may be more effective in softer formations. However, the relative softness of milled teeth as compared to inserts may cause the teeth to erode and wear rapidly when engaging harder formations. Once the cutting structure is damaged (e.g., teeth worn and/or broken), the rate of penetration may be reduced to an unacceptable rate, the drill string must be removed in order to replace the drill bit. Inserts made of relatively hard materials (e.g., material containing a high percentage of tungsten carbide) are usually more effective in harder formations. However, inserts often have smaller cutting surfaces as compared to milled teeth, reducing their effectiveness in softer formations. Further, formations may contain both relatively hard and soft zones, reducing the effectiveness and drilling efficiency of a rolling cone bit having only either inserts or milled teeth. 
     Accordingly, there remains a need in the art for drill bits that provide a relatively high rate of penetration and footage drilled, yet are durable enough to withstand hard and abrasive formations that may quickly damage milled teeth of a rolling cone bit. Such drill bits and cutting elements would be particularly well received if they offered the potential to improve overall drilling efficiency in formations including both soft and hard zones without the need for tripping the bit out of the hole in order to exchange drill bits. 
     BRIEF SUMMARY OF THE PREFERRED EMBODIMENTS 
     These and other needs in the art are addressed in one embodiment by a rolling cone bit for drilling a borehole in earthen formations. In an embodiment, the rolling cone bit comprises a bit body having a bit axis. In addition, the rolling cone bit comprises a rolling cone cutter mounted on the bit body and having a cone axis of rotation. The cone cutter includes a cone body, a plurality of teeth arranged in a first inner row and a plurality of inserts. Each insert is disposed within one tooth in the first inner row. 
     These and other needs in the art are addressed in another embodiment by a rolling cone drill bit for drilling a borehole in earthen formations. In an embodiment, the rolling cone bit comprises a bit body having a bit axis. In addition, the bit comprises a rolling cone cutter mounted on the bit body and having a cone axis of rotation. The cone cutter includes a cone body, a plurality of teeth arranged in a first inner row and a plurality of inserts disposed in the first inner row. Further, the first inner row is positioned immediately circumferentially adjacent one tooth in the first inner row. Each insert in the first inner row trails the immediately circumferentially adjacent tooth in the first inner row relative to a direction of cone rotation about the cone axis. 
     These and other needs in the art are addressed in another embodiment by a method of forming a drill bit for cutting a borehole. In an embodiment, the method comprises positioning a plurality of inserts in a mold. In addition, the method comprises filling the mold with a metal powder. Further, the method comprises surrounding at least a portion of each insert with the metal powder during the process of filling the mold with a metal powder. Still further, the method comprises sintering the metal powder in the mold to form a cone cutter having a cone body and a plurality of teeth extending from the cone body. Each insert is secured to the cone body. 
     Embodiments described herein comprise a combination of features and advantages intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical advantages of the invention in order that the detailed description of the invention that follows may be better understood. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of an embodiment of an earth-boring bit in accordance with the principles described herein; 
         FIG. 2  is a partial cross-sectional view taken through one leg and one rolling cone cutter of the bit of  FIG. 1 ; 
         FIG. 3  is a perspective view of one of the rolling cone cutters of the bit of  FIG. 1 ; 
         FIG. 4A  is a top view of the rolling cone cutter of  FIG. 3 ; 
         FIG. 4B  is a cross-sectional view taken along line  4 B- 4 B of  FIG. 4A ; 
         FIGS. 5A-5C  are enlarged views of one gage tooth, one inner row tooth and the nose tooth, respectively, of the rolling cone cutter of  FIG. 3 ; 
         FIG. 6  is a perspective view of the insert disposed within each tooth of  FIGS. 5A-5C ; 
         FIG. 7  is a perspective view of an embodiment of a mold assembly for partially preforming one inner row tooth of the bit of  FIG. 3 ; 
         FIG. 8A  is a perspective view of the fixture of  FIG. 7 ; 
         FIG. 8B  is a top view of the fixture of  FIG. 7 ; 
         FIG. 9A  is a top view of the hardened cap of  FIG. 7 ; 
         FIG. 9B  is a perspective view of the insert and the hardened cap of  FIG. 7 ; 
         FIG. 10A  is a top view of the mold assembly of  FIG. 7 ; 
         FIG. 10B  is a cross-sectional view taken along line  10 B- 10 B of  FIG. 10A ; 
         FIG. 11  is a perspective view of a partially preformed inner row tooth of the bit of  FIG. 3 ; 
         FIG. 12  is an embodiment of a method for forming a rolling cone cutter including a plurality of teeth, each with an insert disposed therein, in accordance with the principles described herein; 
         FIG. 13  is a perspective view of an embodiment of an earth-boring bit in accordance with the principles described herein; 
         FIG. 14  is a partial cross-sectional view taken through one leg and one rolling cone cutter of the bit of  FIG. 13 ; 
         FIG. 15  is a perspective view of one of the rolling cone cutters of the bit of  FIG. 13 ; 
         FIG. 16  is an enlarged view of one tooth and associated insert of the bit of  FIG. 13 ; 
         FIG. 17  is a side view of one tooth and associated insert of the bit of  FIG. 13 ; 
         FIG. 18  is a perspective view of a ridge cutter of the bit of  FIG. 13 ; and 
         FIG. 19  is an embodiment of a method for forming a rolling cone cutter including a plurality of teeth and inserts disposed thereon, in accordance with the principles described herein. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following discussion is directed to various exemplary embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment. 
     Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness. 
     In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port, while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. 
     Referring now to  FIG. 1 , an embodiment of a rolling cone drill bit  10  is shown. Bit  10  has a central axis  11  and includes a bit body  12  with an externally threaded pin  13  at its upper end and a plurality of rolling cone cutters  100  rotatably mounted on bearing shafts that depend from the bit body  12 . Pin end  14  is adapted to secure bit  10  to a drill string (not shown). Bit body  12  is formed of three sections or legs  19  welded together and has a predetermined gage diameter defined by the outermost reaches of cone cutters  100 . 
     Bit  10  also includes a plurality of nozzles  18  (one shown in  FIG. 1 ) and lubricant reservoirs  17  (one shown in  FIG. 1 ). Nozzles  18  direct drilling fluid toward the bottom of the borehole and around cone cutters  100 . Reservoirs  17  supply lubricant to the bearings that support each of the cone cutters  100 . Bit legs  19  include a shirttail portion  16  that serves to protect the cone bearings and seals, described in more detail below, from formation cuttings and debris that seek to enter between leg  19  and its respective cone cutter  100  during drilling operations. 
     Referring now to both  FIGS. 1 and 2 , each cone cutter  100  is rotatably mounted on a journal  20  extending radially inward at the lower end of one leg  19 , and has a central axis of rotation  22  oriented generally downwardly and inwardly toward bit axis  11 . Each cutter  100  is secured on its corresponding journal  20  with locking balls  26 . In this embodiment, journal bearings  28 , thrust washer  31 , and thrust plug  32  are provided between each cone cutter  100  and journal  20  to absorb radial and axial thrusts. In other embodiments, roller bearings may be provided between each cone cutter  100  and associated journal pin  20  instead of journal bearings  28 . In both journal bearing and roller bearing bits, lubricant is supplied from reservoir  17  to the bearings by apparatus and passageways that are omitted from the figures for clarity. The lubricant is sealed in the bearing structure, and drilling fluid excluded therefrom, with an annular seal  34 . Drilling fluid is pumped from the surface through fluid passage  24  at pin end  13  and is circulated through an internal passageway (not shown) to nozzles  18  ( FIG. 1 ). As best shown in  FIG. 2 , the borehole created by bit  10  includes sidewall  5 , corner portion  6  and bottom  7 . 
     Referring still to  FIGS. 1 and 2 , each cone cutter  100  includes a body  101 , a plurality of gage teeth  120  and inner teeth  120 ′ extending from body  101 , and a plurality of wear resistant inserts  150  mounted to body  101 . As will be described in more detail below, each insert  150  is disposed within one tooth  120 ,  120 ′, and further, each tooth  120 ,  120 ′ is integral with body  101 . Each cone body  101  includes a generally planar backface  40  and nose  42  opposite backface  40 . Moving axially relative to cone axis  22  from backface  40  to nose  42 , each cone body  101  further includes a generally frustoconical heel surface  44  and a generally convex curved surface  46  extending from heel surface  44  to nose  42 . As best shown in  FIG. 1 , frustoconical heel surface  44  and convex surface  46  intersect at an annular edge or shoulder  50 . 
     Heel surface  44  is adapted to scrape or ream the borehole sidewall  5  of the borehole as the cone cutter  100  rotates about the borehole bottom  7 . Teeth and/or inserts may be provided in heel surface  44  to aid in such scraping or reaming action. It should be appreciated that heel surface  44  may be referred to by others in the art as the “gage” surface of a rolling cone cutter. Surface  46  supports a plurality of cutting elements that gouge or crush the borehole bottom  7  as cone cutters  100  rotate about the borehole. During drilling operations, bit  10  is rotated about axis  11  in a clockwise cutting direction looking downward at pin end  13  along axis  11  and each cone cutter  100  rotates about axis  22  in a counterclockwise cutting direction looking at backface  40  along axis  22 . 
     Referring now to  FIGS. 2-4B , teeth  120 ,  120 ′, and inserts  150  disposed therein, are arranged in a plurality of axially spaced (relative to cone axis  22 ) circumferential rows. More specifically, each cone cutter  100  includes a first or gage circumferential row  70   a  of teeth  120  extending from surface  46  axially adjacent shoulder  50  and a second circumferential row  80   a  of teeth  120 ′ extending from surface  46  and axially disposed between row  70   a  and nose  42 . Teeth  120  in row  70   a  function primarily to cut the corner  6  of the borehole while teeth  120 ′ in row  80   a  function to cut the bottom  7  of the borehole. Rows  70   a  and  80   a  of teeth  120 ,  120 ′, are arranged and spaced on each rolling cone cutter  100  so as not to interfere with teeth  120 ,  120 ′, on the other cone cutters  100  ( FIG. 1 ). Each cone cutter  100  is also provided with a “ridge” cutting element  170  extending from nose  42  and configured to prevent formation build-up between the cutting paths of teeth  120  in row  70   a  and teeth  120 ′ in row  80   a . Element  170  extends along axis  22  ( FIG. 2 ) and includes four circumferentially adjacent teeth  171 . Teeth  171  of each element  170  intersect at axis  22 . Each cone cutter  100  has a gage row  70   a  of teeth  120 , an inner row  80   a  of teeth  120 , and a ridge cutting element  170 , although not identically arranged and positioned. In particular, the arrangement and spacing of teeth  120 ,  120 ′, and elements  170  differs as between the three cone cutters  100  in order to maximize borehole bottom coverage, and also to provide clearance for the teeth  120 ,  120 ′, and elements  170  on the adjacent cone cutters  100 . 
     Each tooth  120 ,  120 ′, and  171  is integral and unitary with the corresponding body  101 . In other words, each tooth  120 ,  120 ′, and  171  is monolithic with the corresponding body  101  such that teeth  120 ,  120 ′,  171  and the body  101  are a single-piece. Thus, as used herein and is common terminology in the art, the terms “tooth” and “teeth” refer to individual and multiple, respectively, cutting structures for engaging the formation that extend from and monolithic (i.e., unitary and integral) with the body of a corresponding rolling cone cutter. 
     Referring now to  FIGS. 3 and 5A , each tooth  120  of row  70   a  extends perpendicularly from body  101  and has a generally chisel-shaped cutting structure for engaging the formation. In particular, each tooth  120  has a central axis  125 , a base  121  at surface  46 , and a cutting surface  122  extending from base  121  to an elongate chisel-crest  123  distal body  101 . In this embodiment, base  121  is generally U-shaped. Cutting surface  122  includes a pair of planar flanking surfaces  124 , and a convex lateral side surface  126 . Surface  122  further includes a planar surface  144  that extends from and is generally coplanar with heel  44 . Surface  144  extends from base  121  to a curved edge  146  that extends between flanking surfaces  124 . Flanking surfaces  124  taper or incline towards one another as they extend from base  121  to chisel crest  123  that extends between edge  146  and crest end or corner  123   c . In this embodiment, crest end  123   c  is a partial sphere, defined by a spherical radius. Lateral side surface  126  extends from base  121  to crest end  123   c  and between flanking surfaces  124 . Surfaces  124 ,  126  intersect at rounded edges  127  that extend from base  121  to corners  123   c  and provide a smooth transition between surfaces  124 ,  126 . A protrusion  128  extends from each flanking surface  124  proximal crest  123 . Each chisel crest  123  extends linearly along a crest median line  129 . Teeth  120  are arranged and positioned such that a projection of each crest median line  129  intersects cone axis  22  of the corresponding cone cutter  100 . As will be described in more detail below, one insert  150  is disposed within each tooth  120 . 
     Referring now to  FIGS. 3 and 5B , each tooth  120 ′ of row  70   a  is configured similarly to teeth  120  of row  70   a , and thus similar features are numbered alike. However, base  121 ′ of tooth  120 ′ has a generally elliptical shape and cutting surface  122 ′ of tooth  120 ′ includes a pair of lateral side surfaces  126  extending from base  121 ′ that intersect a pair of crest ends  123   c  between flanking surfaces  124 . Also, as will be described below, one insert  150  is disposed within each tooth  120 ′. 
     Referring now to  FIGS. 3 and 5C , each element  170  extends perpendicularly from nose  42  of body  101  and has a central axis  175  coincident with cone axis  22 . As previously described, each element  170  comprises four teeth  171  that intersect at axes  22 ,  175 . Similar to teeth  120  previously described, each tooth  171  has a generally chisel-shaped cutting structure for engaging the formation. In particular, each element  170  has a generally circular base  172  at nose  42 , and each tooth  171  has a cutting surface  173  extending from base  172  to an elongate chisel-crest  174  distal body  101 . Each cutting surface  173  includes a pair of planar flanking surfaces  176  and a radially outer (relative to axis  22 ,  175 ) convex lateral side surface  177 . Flanking surfaces  176  taper or incline towards one another as they extend from base  172  to chisel crest  174  that extends from a radially outer crest end or corner  174   c  to axes  22 ,  175  and crests  174  of the other teeth  171 . In this embodiment, crest ends  174   c  are partial spheres, each defined by spherical radii. Lateral side surfaces  177  extend from base  101  to crest end  123   c  and between flanking surfaces  176 . Surfaces  176 ,  177  intersect at rounded edges  178  that extend from base  172  to corner  174   c  and provide a smooth transition between surfaces  176 ,  177 . A protrusion  179  extends from each flanking surface  176  proximal crest  174 . Each chisel crest  174  extends linearly along a crest median line  180 . Teeth  171  are arranged and positioned such that a projection of each crest median line  180  intersects cone axis  22  of the corresponding cone cutter  100 . As will be described in more detail below, one insert  150  is disposed within each tooth  171 . 
     Referring now to  FIGS. 2, and 5A-6 , one insert  150  is disposed inside of each tooth  120 ,  120 ′ and  171 . As best shown in  FIG. 6 , each insert  150  includes a base portion  151  and a cutting portion  152  extending axially therefrom. Cutting portion  152  includes a chisel-shaped cutting surface  153  extending from the reference plane of intersection  154  that divides base  151  and cutting portion  152 . In this embodiment, base portion  151  is generally cylindrical, having a central axis  155  and an outer cylindrical surface  156 . Base portion  151  has an axial height  160 , and cutting portion  152  has an axial height  161 . Collectively, base  151  and cutting portion  152  define the insert&#39;s overall height  162 . 
     Cutting surface  153  includes a pair of planar flanking surfaces  153   a  and a pair of convex lateral side surfaces  157 . Flanking surfaces  153   a  generally taper or incline towards one another and intersect at an elongate chisel crest  158  distal base portion  151 . Crest  158  extends linearly along a crest medial line  159  between crest ends or corners  158   c . In this embodiment, crest ends  158   c  are partial spheres, each defined by spherical radii. In this embodiment, each insert  150  is positioned within one tooth  120 ,  120 ′ and  171  such that a projection of median line  159  intersects axis  22  of the corresponding cone cutter  20 , and a projection of axis  155  intersects and is oriented perpendicular to median line  129 ,  180  of the crest  123 ,  174 , respectively, of the corresponding tooth  120 ,  120 ′ and  171 , respectively. Thus, crest  158  and crest  123 ,  174  of the corresponding tooth  120 ,  120 ′ and  171 , respectively, are oriented parallel to each other, but are spaced apart. Further, axis  155  and axis  125 ,  175  of the corresponding tooth  120 ,  120 ′ and  171 , respectively, are parallel, and more specifically, coincident in this embodiment. 
     Depending upon the type of formation being drilled, it may be beneficial to have a cutting element formed of a harder but less ductile material while in others it may be beneficial to have a cutter formed from a softer, yet more ductile material. Further, a single given formation may have regions of varying hardness, necessitating the swapping of cutting elements having varying configurations and materials of construction during a drilling operation in order to maintain a high ROP over the entire length of the operation. Because the swapping of a cutting element during a drilling operation may be a lengthy and expensive process (i.e., requiring tripping of the drillstring), it would be beneficial to have a cutting structure configured to operate in a formation that includes both soft and hard formation regions. For instance, a “hybrid” bit such as bit  10  including teeth  120 ,  120 ′ and  171  and inserts  150  offers the potential to enable drilling of a formation having both soft and hard regions without the need for swapping the bit in order to maintain a high ROP. Specifically, during drilling operations, softer regions of the formation are often encountered first, followed by harder regions of formation. Thus, by positioning inserts  150  within teeth  120 ,  120 ′ and  171 , teeth  120 ,  120 ′ and  171  can provide the initial cutting structure for engaging softer formations, while inserts  150  can provide a secondary cutting structure for engaging harder formations as teeth  120 ,  120 ′ and  171  erode. In other words, teeth  120 ,  120 ′ and  171  sacrificially erode during the initial stages of drilling operations, thereby exposing inserts  150  for subsequent stages of drilling operations where harder regions of the formation are encountered. 
     A molding method is used to partially preform (a) each tooth  120 ,  120 ′, with one insert  150  disposed therein at a predetermined distance measured between crests  123 ,  158 , and (b) each ridge cutting element  170  with one insert  150  disposed within each tooth  171  at a predetermined distance measured between crests  123 ,  174 . One partially preformed gage tooth  120  of row  70   a  is shown in  FIG. 11  and designated with reference numeral  120 ″. Once partially preformed gage teeth  120 ″ (with insert  150  disposed therein), partially preformed inner teeth  120 ′ (with insert  150  disposed therein) and a partially preformed cutter element  174  (with inserts  150  disposed therein) is made, a subsequent molding method is used to simultaneously form the corresponding cone body  101 , form the remainder of teeth  120 ,  120 ′ and  171 , and monolithically combine teeth  120 ,  120 ′ and  171  with the cone body  101 . These molding methods will now be described with respect to teeth  120 , it being understood that the same molding methods are employed for each cutting element  170 . 
     Referring now to  FIG. 7 , a mold assembly  200  for partially preforming one tooth  120  with an insert  150  disposed therein is shown. In this embodiment, mold assembly  200  includes a fixture  201 , a hard metal inlay or cap  230  disposed within fixture  201 , an insert  150  seated in cap  230 , and filling material  260  disposed within cap  230  and encapsulating cutting portion  152  of insert  150 . Fixture  201  includes a mold recess or negative  202  from an upper or top surface  203  of fixture  201 , and an access channel  204   a  extending from top surface  203  between negative  202  and a front surface  204  of fixture  201 . Cap  230  is disposed partially within mold negative  202  of fixture  201  and forms a portion of cutting surface  122  of tooth  120 . In this embodiment, cap  230  forms chisel crest  123 , a portion of each flanking surface  124  adjacent crest  123 , and planar surface  144  of tooth  120 . 
     Referring now to  FIGS. 8A and 8B , recess  202  defines an inner surface  205  in fixture  201  that is generally the negative of tooth  120 . More specifically, inner surface  205  includes a pair of planar flanking surfaces  206  that taper or incline towards one another moving away from top surface  203 , a chisel crest recess or negative  208  with rounded corners  209  at the intersection of surfaces  206 , and a planar surface  210  extending between surfaces  206 . Flanking surfaces  206  include concave recesses  207 . Recess  202  is sized and shaped to receive and support cap  230  removably disposed therein during the molding process. 
     Referring now to  FIGS. 9A-10B , cap  230  includes a mold portion  231  removably seated in recess  202  of fixture  201  and an elongate tang portion  241  extending from recess  202  and fixture  201 . Mold portion  231  includes flanking portions  232  defining the portions of flanking surfaces  124  adjacent crest  123  and a chisel crest portion  238  defining chisel crest  123 . The outer surface of each flanking portion  232  includes one protrusion  128 . Tang portion  241  of cap  230  forms a portion of elongate surface  144  of tooth  120 . A receptacle  239  is defined by portions  232 ,  238 . As best shown in  FIG. 10B , cutting portion  152  of insert  150  is seated in receptacle  239  with planar flanking surfaces  153   a  disposed parallel with surfaces  232  within receptacle  239 . Because the cutting surface  152  of insert  150  does not physically engage any surface of cap  230 , a positioning tool  235  (shown in  FIG. 10B ) coupled to base portion  151  suspends the cutting surface  152  of insert  150  within receptacle  239  at a predetermined position, angle (relative to axis  155 ) and depth (relative to surface  238  of cap  230 ). Thus, the positioning of the insert via tool  235  determines a spacing distance  240  between crests  123 ,  158  and a gap  243  within receptacle  239  between crest  123  and mold portion  231 . Cap  230  is formed from a hard material such as tungsten carbide (WC). In this embodiment, cap  230  comprises approximately 65-85 WT % WC. However, in other embodiments cap  230  may be formed from other types of hard or ultrahard materials. Also, in other embodiments cap  230  may only include mold portion  231  instead of both mold portion  231  and tang portion  241 . A cap similar to cap  230  may be used in other embodiments in forming inner teeth  120 ′. A cap for forming a tooth  120 ′ may include a tang portion configured to act as a lateral side surface  126  of the tooth  120 . 
     As will be described in more detail below, insert  150  is positioned within receptacle  239  of mold portion  231  as shown in  FIGS. 10A and 10B  via a tool coupled to base portion  151 , and then the remainder of receptacle  239  is filled with filler material  260 , which completely surrounds cutting portion  152  of insert  150  and flows into gap  243  between crest  123  and mold portion  231 . Thus, filler material  260  is disposed below and about insert  150 . The size and shape of flanking portions  232  and crest portion  238  can be varied to increase or reduce the amount of filler material  260  disposed within receptacle  239  around insert  150 . For instance, the width of receptacle  239  within crest portion  238  may be increased to allow insert  150  to sit deeper within mold portion  231 , thereby reducing the distance  240 . Distance  240  may also be varied by manipulating the positioning of the tool coupled to insert  150 . By varying distance  240  and the amount of material disposed between crests  123 ,  158 , the amount of drilling time and associated erosion of tooth  120  before exposure of insert  150  can be varied and controlled. For example, in an application where it is desirable to increase the amount of drilling time before insert  150  is exposed to the formation due to erosion of the corresponding tooth  120 , distance  240  may be increased to increase the amount of material disposed between crests  123 ,  158 . 
     Referring now to  FIGS. 7-11 , in the embodiment shown, partially preformed tooth  120 ′ shown in  FIG. 11  is created by first forming cap  230  using a metal injection molding process. Next, as best shown in  FIGS. 10A and 10B , cap  230  is placed within mating  202  of fixture  201  such that the outer surfaces of cap  230  engage the mating surfaces of mold  202 ; and with cap  230  sufficiently seated in fixture  201 , insert  150  is positioned in receptacle  239  of mold portion  231  with flanking surfaces  153   a  disposed parallel with but not touching flank portion  232 . Moving now to  FIG. 7 , low carbon steel filler material  260  in a paste form is poured into receptacle  239  and allowed to completely surround the portion of insert  150  within receptacle  239 . Alternatively, in other embodiments filler material  260  may comprise iron, a steel alloy, WC powder, etc. Over time, the filler material  260  cures and hardens, thereby securing the position of insert  150  within cap  230  and forming partially preformed tooth  120 ′, which is removed from fixture  201  via passage  204   a . In another embodiment, filler material  260  may be poured into receptacle  239  prior to inserting insert  150 . Thus, once material  260  has cured within receptacle  239  a hole is drilled into material  260  at a predetermined location, angle and depth. Once the hole has been drilled additional material  260  in paste form is poured into the hole followed by the insertion of insert  150  into the hole prior to the curing of material  260 . The additional material  260  is allowed to cure, securing insert  150  into position. 
     Referring now to  FIG. 12 , a method  300  for making one rolling cone cutter  100  using partially preformed teeth  120 ′ with inserts  150  disposed therein and one partially preformed ridge cutting element  170  with inserts  150  disposed therein is schematically shown. In this embodiment, the cone body  101 , the remainder of teeth  120 ,  120 ′ and  171 , and the integration of partially preformed teeth  120 ′ and cutter element  170  is accomplished using cold isostatic pressing (CIP) techniques such as the Ceracon® sintering process. In particular, starting in block  301 , a pliable bag mold having a cavity defined by the negative profile of cone cutter  100  is formed. An adhesive, such as Elmer&#39;s Spray Adhesive or Duro All-Purpose Spray Adhesive, etc., is preferably sprayed into the bag mold to allow adhesion between the bag mold and the materials that will be disposed therein. Moving now to block  302 , the partially preformed teeth  120 ′ previously described, as well as a partially preformed ridge cutting element  170 , are positioned in the bag mold in their appropriate locations. Next, in block  303 , the bag mold is disposed and secured within a high pressure canister for use in a sintering cold isostatic molding process. A mixture of WC is then sprayed evenly on the inner surfaces of the bag mold at block  304  to form a thin layer of WC on the body  101  of cone  100  ( FIG. 1 ) to act as an erosion protecting jacket protecting cone  100 . Following this, a metal powder, such as 4625 steel powder or 4815 steel powder, etc., is poured into the bag mold for forming body  101  and the remainder of teeth  120 ,  120 ′ and  171  at block  205 . Moving now to block  306 , with the bag mold sufficiently filled with the metal powder, the canister is pressurized (e.g., approximately 40,000 psi) at step  306  to form cone cutter  100  by simultaneously forming body  101 , the remainder of teeth  120 ,  120 ′ and  171 , and monolithically integrate partially preformed teeth  120 ′ and ridge cutting element  170  with body  101 . At block  307  cone cutter  100  is removed from the canister and the bag mold, and then heat treated at block  308  at a relatively high temperature (e.g., at approximately 2,100° F.). After removal of cone cutter  100  from the canister and bag mold, cone cutter  100  is at approximately 80% of its final density. However, at block  309 , cone cutter  100  is placed within a forging die containing hot graphite (e.g., at approximately 1,900° F.) and is pressurized at extremely high pressures (e.g., approximately 3.2 million psi) to further increase the density of the element to its final density prior to use in the field. The time duration of the pressurization at block  306  may range from approximately 10 to 25 seconds and the duration of the pressurization at block  309  may range from approximately 15 to 25 seconds, depending upon the size of cone  100 . Following the manufacture of rolling cone cutters  100  using method  300 , cone cutters  100  are rotatably mounted to journals  20  of bit body  11  to form bit  10 . 
     Referring now to  FIGS. 13 and 14 , another embodiment of a rolling cone drill bit  400  is shown. Bit  400  is the same as bit  10  previously described except for the cutting structures of the rolling cone cutters. Accordingly, the same reference numerals are used to designate like-components. In this embodiment, bit  400  includes a bit body  12  as previously described and a plurality of rolling cone cutters  500  rotatably mounted on journals  20  extending from the lower ends of legs  19 . Each cone cutter  500  has a central axis of rotation  22 , which is also the central axis of the corresponding journal  20 . During drilling operations, bit  400  is rotated about axis  11  in a clockwise cutting direction looking downward at pin end  13  along axis  11  and each cone cutter  500  rotates about axis  22  in a counterclockwise cutting direction looking at backface  40  along axis  22 . 
     Referring now to  FIGS. 13-15 , each cone cutter  500  includes a body  501 , a plurality of teeth  520  extending from body  501 , and a plurality of wear resistant inserts  550  mounted to body  501 . As will be described in more detail below, each insert  550  is positioned circumferentially adjacent one tooth  520 , and further, each tooth  520  is integral with body  501 . Thus, unlike cone cutters  100  previously described, in this embodiment, inserts  550  are not disposed inside teeth  520 . 
     Each cone body  501  is the same as cone body  101  previously described. Namely, each cone body  501  includes a generally planar backface  40 , a nose  42  opposite backface  40 , a generally frustoconical heel surface  44  axially adjacent backface  40 , and a generally convex curved surface  46  extending from heel surface  44  to nose  42 . As best shown in  FIG. 14 , frustoconical heel surface  44  and convex surface  46  intersect at an annular edge or shoulder  50 . Heel surface  44  is adapted to scrape or ream the borehole sidewall  5 , and surface  46  supports teeth  520  and inserts  550 , which gouge or crush the borehole bottom  7 . Teeth and/or inserts may be provided in heel surface  44  to aid in such scraping or reaming action. 
     Referring now to Figures still to  FIGS. 13-15 , teeth  520  and inserts  550  are arranged in a plurality of axially spaced (relative to cone axis  22 ) circumferential rows. More specifically, each cone cutter  500  includes a first or gage circumferential row  70   a  of teeth  520  and inserts  550  extending from surface  46  axially adjacent shoulder  50  and a second circumferential row  80   a  of teeth  520  and inserts  550  extending from surface  46  and axially disposed between row  70   a  and nose  42 . In this embodiment, one insert  550  is positioned immediately circumferentially adjacent each tooth  520  within each row  70   a ,  80   a . In addition, each insert  550  trails the corresponding adjacent tooth  520  relative to the counterclockwise cutting direction of cone cutter  500  about axis  22 . Thus, in this embodiment, each tooth  520  leads the associated insert  550  into the formation during drilling operations, and further, within each row  70   a ,  80   a , teeth  520  and inserts  550  are circumferentially arranged in an alternating fashion. Teeth  520  and inserts  550  in row  70   a  function primarily to cut the corner  6  of the borehole while teeth  520  and inserts  550  in row  80   a  function to cut the borehole bottom  7 . Rows  70   a  and  80   a  of teeth  120  and inserts  550  are arranged and axially spaced (relative to axis  22 ) on each rolling cone cutter  500  so as not to interfere with teeth  520  and inserts  550  on the other cone cutters  500  ( FIG. 13 ). 
     As best shown in  FIGS. 14 and 15 , each cone cutter  500  is also provided with a “ridge” cutting element  570  extending from nose  42  and configured to prevent formation build-up between the cutting paths of teeth  520  and inserts  550  in rows  70   a ,  80   a . Element  570  extends along axis  22  ( FIG. 14 ) and includes four circumferentially adjacent teeth  571  that intersect at axis  22 . 
     Each cone cutter  500  has a gage row  70   a  of teeth  520  and inserts  550 , an inner row  80   a  of teeth  520  and inserts  550 , and a ridge cutting element  570 , although not identically arranged and positioned. In particular, the arrangement and spacing of teeth  520 , inserts  550 , and elements  570  differs as between the three cone cutters  500  in order to maximize borehole bottom coverage, and also to provide clearance for the teeth  520 , inserts  550 , and elements  570  on the adjacent cone cutters  500 . 
     Each tooth  520 ,  571  is integral and unitary with the corresponding body  501 . In other words, each tooth  520 ,  571  is monolithic with the corresponding body  501  such that teeth  520 ,  571  and the body  101  are a single-piece. On the other hand, inserts  550  are seated and secured within mating sockets in the corresponding cone body  501 . As will be described in more detail below, during manufacture of each cone cutter  500 , the cone body  501  is formed around inserts  550  to retain them therein. 
     Referring now to  FIGS. 15-17 , each tooth  520  extends perpendicularly from body  501  and has a generally chisel-shaped cutting structure for engaging the formation. In particular, each tooth  520  has a central axis  525 , a base  521  at surface  46 , and a cutting surface  522  extending from base  521  to an elongate chisel-crest  523  distal body  501 . In this embodiment, base  521  is generally C-shaped. Cutting surface  522  includes a pair of flanking surfaces  524  and a pair of convex lateral side surfaces  526 . Flanking surfaces  524  taper or incline towards one another as they extend from base  521  to chisel crest  523  that extends between crest ends or corners  523   c . In this embodiment, crest ends  523   c  are partial spheres, each defined by spherical radii. Lateral side surfaces  526  extend from base  501  to crest ends  523   c  and between flanking surfaces  524 . Surfaces  524 ,  526  intersect at rounded edges  527  that extend from base  501  to corners  523   c  and provide a smooth transition between surfaces  524 ,  526 . 
     Each tooth  520  has a leading flanking surface  524  and a trailing flanking surface  524  relative to the counterclockwise cutting direction of the corresponding cone cutter  500 . For purposes of clarity and further explanation, the leading flanking surface  524  is designated with reference numeral  5241  and the trailing flanking surface  524  is designated with reference numeral  524   t . In this embodiment, each leading flanking surface  5241  is convex or bowed outwardly and each trailing flanking surface  524   t  is concave or bowed inwardly. Consequently, the trailing flanking surface  524   t  of each tooth  520  defines a recess or pocket  529  ( FIG. 17 ) on the trailing side of each tooth  520 . Each insert  550  is seated in the pocket  527  of the associated tooth  520 . 
     Each chisel crest  523  extends along a curved or arcuate crest median line  528 . Teeth  520  are arranged and positioned such that a projection of each crest median line  528  generally extends towards cone axis  22  of the corresponding cone cutter  500 . 
     Referring now to  FIG. 18 , each ridge cutting element  570  extends perpendicularly from nose  42  of body  501  and has a central axis  575  coincident with cone axis  22 . Each element  570  and tooth  571  is the same as element  170  and tooth  171 , respectively, previously described except that no inserts (e.g., inserts  120 ,  520 ) are disposed within elements  570  or teeth  571 , and further, elements  570  and teeth  571  do not include any protrusions (e.g., protrusions  179 ) extending from the flanking surfaces. Thus, in this embodiment, each ridge cutter element  570  comprises four teeth  571  that intersect at axes  22 ,  575 . Similar to teeth  171  previously described, each tooth  571  has a generally chisel-shaped cutting structure for engaging the formation. In particular, each element  570  has a generally circular base  572  at nose  42 , and each tooth  571  has a cutting surface  573  extending from base  572  to an elongate chisel-crest  574  distal body  501 . Each cutting surface  573  includes a pair of planar flanking surfaces  576  and a radially outer (relative to axis  22 ,  575 ) convex lateral side surface  577 . Flanking surfaces  576  taper or incline towards one another as they extend from base  572  to chisel crest  574  that extends from a radially outer crest end or corner  574   c  to axes  22 ,  575  and crests  574  of the other teeth  571 . In this embodiment, crest ends  574   c  are partial spheres, each defined by spherical radii. Lateral side surfaces  577  extend from base  572  to crest end  574   c  and between flanking surfaces  576 . Surfaces  576 ,  577  intersect at rounded edges  578  that extend from base  572  to corner  574   c  and provide a smooth transition between surfaces  576 ,  577 . As previously described, in this embodiment, no protrusion (e.g., protrusion  179 ) extends from flanking surfaces  176 . Each chisel crest  574  extends linearly along a crest median line  580 . Teeth  571  are arranged and positioned such that a projection of each crest median line  580  intersects cone axis  22  of the corresponding cone cutter  500 . 
     Referring now to  FIGS. 15-18 , each insert  550  is seated in a socket  502  in cone body  501  and circumferentially disposed within pocket  529  defined by the concave trailing flanking surface  524   t  of the associated tooth  520 . As best shown in  FIGS. 16 and 17 , each insert  550  includes a base portion  551  and a cutting portion  552  extending axially therefrom. Base portion  551  is disposed within one socket  502  and surrounded by cone body  501 , and cutting portion  552  extends perpendicularly from surface  46  of the corresponding cone body  501 . In this embodiment, base portion  551  is generally cylindrical, having a central axis  555  and an outer cylindrical surface  556 . Each insert  550  is positioned and oriented such that its axis  555  is generally parallel to axis  525  of the associated tooth  520 . 
     Cutting portion  552  has an outer cylindrical surface  553  extending axially from base portion  551  and a semi-spherical or dome-shaped cutting surface  554  extending from cylindrical surface  553  and distal base portion  551 . Base portion  551  has an axial height  560  ( FIG. 17 ), and cutting portion  552  has an axial height  561 . Collectively, base  551  and cutting portion  552  define the insert&#39;s overall height  562 . Although cutting portion  552  has a semi-spherical cutting surface  553  in this embodiment, in other embodiments, the cutting portion of the insert (e.g., cutting portions  552 ) can have other geometries such as conical, hyperbolic or chisel-crested. 
     As previously described, for some drilling applications, it may be beneficial to have a cutting structure configured to operate in a formation that includes both soft and hard formation regions. For instance, a “hybrid” bit such as bit  400  including teeth  520 ,  571  and inserts  550  offers the potential to enable drilling of a formation having both soft and hard regions without the need for swapping the bit in order to maintain a high ROP. Specifically, referring to  FIG. 13 , teeth  520  and inserts  550  are positioned in rows  70   a ,  80   a  such that each tooth  520  leads its associated insert  550  into the formation relative to counterclockwise cutting direction of the corresponding cone cutter  500 . In addition, as best shown in  FIG. 16B , each tooth  520  has an extension height H 520  equal to the distance from cone surface  46  to the outermost point of cutting surface  522  and crest  523  as measured parallel to axis  525  and perpendicular to cone surface  46 , and each insert  550  has an extension height H 550  equal to the distance from cone surface  46  to the outermost point of cutting portion  552  as measured parallel to axis  555  and perpendicular to cone surface  46 . In this embodiment, each tooth  520  has the same extension height H 520  and each insert  550  has the same extension height H 550 . Further, in this embodiment, extension height H 520  of each tooth  520  is greater than the extension height H 550  of the associated insert  550 . Thus, during the initial stages of drilling (i.e., before teeth  520  have been worn down), teeth  520  engage the formation before corresponding inserts  550  and penetrate the formation to a greater degree than corresponding inserts  550 . Further, due to the leading positions of teeth  520 , the differences in extension heights H 520 , H 550 , and the positioning of inserts  550  within pockets  529 , inserts  550  are shielded and protected by teeth  520  during the initial stages of drilling. 
     During drilling operations, softer regions of the formation are often encountered first, followed by harder regions of formation. Thus, by positioning teeth  520  in leading positions relative to the corresponding inserts  550  and protecting inserts  550  with teeth  520 , teeth  520  provide the initial primary cutting structure in softer formations, while inserts  550  provide the initial secondary cutting structure in softer formations; whereas inserts  550  provide the primary cutting structure in harder formations as teeth  520  wear, and teeth  520  provide the secondary cutting structure in harder formations as they are worn. In other words, teeth  520  sacrificially erode during the initial stages of drilling operations, thereby transferring the primary cutting duty to inserts  550  for subsequent stages of drilling operations where harder regions of the formation are encountered. 
     Referring now to  FIG. 18 , a method  600  for making one rolling cone cutter  500  is schematically shown. Method  600  is similar to method  300  previously described except that teeth  520  are not partially preformed to include an insert disposed therein. Namely, in this embodiment, cone body  501 , teeth  520 ,  571 , the integration of teeth  520 ,  571  into cone body  501 , and the securement of inserts  550  to body  501  are accomplished using known isostatic processing techniques such as the Ceracon® sintering process. In particular, starting in block  601 , a pliable bag mold having a cavity defined by the negative profile of cone cutter  500  is formed. An adhesive, such as Elmer&#39;s Spray Adhesive or Duro All-Purpose Spray Adhesive, is preferably sprayed into the bag mold to allow adhesion between the bag mold and the materials that will be disposed therein. Moving now to block  602 , inserts  550  previously described and a hardmetal preformed cap for each tooth  520  are positioned in the bag mold in their appropriate locations. In this embodiment, the hardmetal caps placed in the bag mold define at least a portion of the cutting surface  522  for each tooth  520 . Next, in block  603 , the bag mold is disposed and secured within a high pressure canister for use in a sintering cold isostatic molding process. A mixture of tungsten carbide is then sprayed evenly on the inner surfaces of the bag mold at block  604 , and then a metal powder, such as 4625 or 4815 steel powders, is poured into the bag mold for forming body  501  and teeth  520 ,  571  at block  605 . The metal powder completely surrounds base portions  551  of inserts  550  positioned in the bag mold. Moving now to block  606 , with the bag mold sufficiently filled with the metal powder, the canister is pressurized (e.g., approximately 40,000 psi) at step  606  to form cone cutter  500  by simultaneously forming body  501 , teeth  520 ,  571 , monolithically integrating teeth  520 ,  571  with body  501 , and securing inserts  550  within sockets  502 . At block  607  cone cutter  500  is removed from the canister and the bag mold, and then heat treated at block  608  at a relatively high temperature (e.g., at approximately 2,100° F.). After removal of cone cutter  500  from the canister and bag mold, cone cutter  500  is at approximately 80% of its final density. However, at block  609 , cone cutter  500  is placed within a forging die containing hot graphite (e.g., at approximately 1,900° F.) and is pressurized at extremely high pressures (e.g., approximately 3.2 million psi) to further increase the density of the element to its final density prior to use in the field. The time duration of the pressurization at block  606  may range from approximately 10 to 25 seconds and the duration of the pressurization at block  609  may range from approximately 15 to 25 seconds, depending upon the size of cone  500 . Following the manufacture of rolling cone cutters  500  using method  600 , cone cutters  500  are rotatably mounted to journals  20  of bit body  11  to form bit  400 . In the manner described, inserts  550  are secured within sockets  502  by forming cone body  501  around base portions  521  of inserts  550  in this embodiment. 
     While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.