Abstract:
A cutting element, or insert, is provided for use with drills used in the drilling and boring of subterranean formations. This new insert has improved wear characteristics while maximizing the manufacturability and cost effectiveness of the insert. This invention accomplishes these objectives by employing a superabrasive diamond layer of increased depth and by making use of diamond layer surface shape that is generally convex.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to devices for drilling and boring through subterranean formations. More specifically, this invention relates to polycrystalline diamond compacts (“PDCs”), also known as cutting elements or diamond inserts, which are intended to be installed as the cutting element of a drill bit to be used for boring through rock in any application, such as oil, gas, mining, and/or geothermal exploration, requiring drilling through geological formations. Still more specifically, this invention relates to polycrystalline diamond inserts which have a surface topography formed integral to an otherwise spherical, conical, or other uniform geometric shape, to increase stress at the insert/rock interface, thereby inducing the rock to fail while requiring the expenditure of less overall energy and introducing little, if any, additional internal stresses to the insert.  
           [0003]    2. Description of Related Art  
           [0004]    Three types of drill bits are most commonly used for penetrating geologic formations. These are: (1) percussion bits; (2) rolling cone bits, also referred to as rock bits; and (3) drag bits, or fixed cutter rotary bits. Each type of bits may employ polycrystalline diamond inserts as the primary cutting device.  
           [0005]    In addition to the drill bits discussed above, polycrystalline diamond inserts may also be used with other down hole tools, including but not limited to: reamers, stabilizers, and tool joints. Similar devices used in the mining industry may also use this invention.  
           [0006]    Percussion bits penetrate through subterranean geologic formations by an extremely rapid series of impacts. The impacts may be combined with a simultaneous rotations of the bit. An exemplary percussion bit is shown in FIG. 1 b . The reader is directed to the following list of related art patents for further discussion of percussion bits.  
           [0007]    Rolling cone bits currently make up the largest number of bits used in drilling geologic formations. Rolling cone bits have as their primary advantage the ability to penetrate hard geologic formations while being generally available at a relatively low cost. Typically, rolling cone bits operate by rotating three cones, each oriented substantially transverse to the bits axis and in a triangular arrangement, with the narrow end of each cone facing a point in the direct center of the bit. An exemplary rolling cone bit is shown in FIG. 1 a.    
           [0008]    A rolling cone bit cuts through rock by the crushing and scraping action of the abrasive inserts embedded in the surface of the rotating cone. These abrasive inserts are generally composed of cemented tungsten carbide, but may also include polycrystalline diamond coated cemented tungsten carbide, where increased wear performance is required.  
           [0009]    The primary application of this PDC invention is currently believed to be in connection with percussion and rolling cone bits, although alternative embodiments of this invention may find application in connection with other drilling tools.  
           [0010]    A third type of bit is the drag bit, also known as the fixed cutter bit. An example of a drag bit is shown in FIG. 2. The drag bit is designed to be rotated about its longitudinal axis. Most drag bits employ PDCs which are brazed into the cutting blade of the bit. The PDCs then shear the rock as the bit is rotated about its longitudinal axis.  
           [0011]    While it is expected that this invention will find primary application in percussion and rolling cone bits, some use in drag bits may also be feasible.  
           [0012]    A polycrystalline diamond compact (“PDC”), or cutting element, is typically fabricated by placing a cemented tungsten carbide substrate into a refactory metal container (“can”) with a layer of diamond crystal powder placed into the can adjacent to one face of the substrate. The can is then covered. A number of such can assemblies are loaded into a high pressure cell made from a soft ductile solid material such as pyrophyllite or talc. The loaded high pressure cell is then placed in an ultra-high pressure press. The entire assembly is compressed under ultra-high pressure and temperature conditions. This causes the metal binder from the cemented carbide substrate to become liquid and to “sweep” from the substrate face through the diamond grains and to act as a reactive liquid phase to promote the sintering of the diamond grains. The sintering of the diamond grains causes the formation of a polycrystalline diamond structure. As a result the diamond grains become mutually bonded to form a diamond mass over the substrate face. The metal binder may remain in the diamond layer within the pores of the polycrystalline structure or, alternatively, it may be removed via acid leeching and optionally replaced by another material forming so-called thermally stable diamond (“TSD”). Variations of this general process exist and are described in the related art. This detail is provided so the reader may become familiar with the concept of sintering a diamond layer onto a substrate to form a PDC insert. For more information concerning this process, the reader is directed to U.S. Pat. No. 3,745,623, issued to Wentorf Jr. et al., on Jul. 7, 1973.  
           [0013]    Existing PDCs often exhibit durability problems in cutting through tough geologic formations, where the diamond working surface may experience high but transient stress loads. Under such conditions, existing PDCs have a general tendency to crack, spall, and break. Similarly, existing PDCs are relatively weak when placed under high loads from a variety of angles. These problems of existing PDCs are further exacerbated by the dynamic nature of both normal and torsional loading during the drilling process, during which the bit face moves into and out of contact with the uncut material forming the bottom of the well bore.  
           [0014]    For optimal performance, the interface between the diamond layer and the tungsten carbide substrate must be capable of sustaining the high residual stresses that arise from thermal expansion and bulk modulus mismatches between the two materials. These differences create high residual stress at the interface as the materials are cooled from the high temperature and pressure process. Residual stress can be deleterious to the life of the PDC cutting elements, or inserts, during drilling operations, when high tensile stresses in the substrate or diamond layer may cause fracture, spalling, or complete delamination of the diamond layer from the substrate.  
           [0015]    Typical prior PDCs have a relatively thin diamond layer, generally between 0.020 and 0.040 inches in thickness. The cylinder of carbide to which the diamond layer is attached is generally at least three times thicker than the diamond layer.  
           [0016]    Diamond is used as a drilling material primarily because of its extreme hardness and abrasion resistance. However, diamond also has a major drawback. Diamond, as a cutting material, has very poor toughness, that is, it is very brittle. Therefore, anything that further contributes to reducing the toughness of the diamond, substantially degrades its durability.  
           [0017]    A number of other approaches and applications of PDCs are well established in related art. The applicant includes the following references to related art patents for the reader&#39;s general familiarization with this technology.  
           [0018]    U.S. Pat. No. 4,109,737 describes a rotary drill bit for rock drilling comprising a plurality of cutting elements mounted by interference-fit in recesses in the crown of the drill bit.  
           [0019]    U.S. Pat. No. 4,604,106 reveals a composite polycrystalline diamond compact comprising at least one layer of diamond crystals and precemented carbide pieces which have been pressed under sufficient heat and pressure to create a composite polycrystalline material wherein polycrystalline diamond and the precemented carbide pieces are interspersed in one another.  
           [0020]    U.S. Pat. No. 4,694,918 describes an insert that has a tungsten carbide body and at least two layers at the protruding drilling portion of the insert. The outermost layer contains polycrystalline diamond and the remaining layers adjacent to the polycrystalline diamond layer are transition layers containing a composite of diamond crystals and precemented tungsten carbide, the composite having a higher diamond crystal content adjacent to the polycrystalline diamond layer and a higher precemented tungsten carbide content adjacent to the tungsten carbide layer.  
           [0021]    U.S. Pat. No. 4,858,707 describes a diamond insert for a rotary drag bit consists of an insert stud body that forms a first base end and a second cutter end.  
           [0022]    U.S. Pat. No. 4,997,049 describes a tool insert having a cemented carbide substrate with a recess formed in one end of the substrate and having abrasive compacts located in the recesses and bonded to the substrate.  
           [0023]    U.S. Pat. No. 5,154,245 relates to a rock bit insert of cemented carbide for percussive or rotary crushing rock drilling. The button insert is provided with one or more bodies of polycrystalline diamond in the surface produced by high pressure and high temperature in the diamond stable area. Each diamond body is completely surrounded by cemented carbide except the top surface.  
           [0024]    U.S. Pat. No. 5,217,081 relates to a rock bit insert of cemented carbide provided with one or more bodies or layers of diamond and/or cubic boron nitride produced at high pressure and high temperature in the diamond or cubic boron nitride stable area. The body of cemented carbide has a multi-structure containing eta-phase surrounded by a surface zone of cemented carbide free of eta-phase and having a low content of cobalt in the surface and a higher content of cobalt next to the eta-phase zone.  
           [0025]    U.S. Pat. No. 5,264,283 relates to buttons, inserts and bodies that comprise cemented carbide provided with bodies and/or layers of CVD- or PVD-fabricated diamond and then high pressure/high temperature treated in the diamond stable area.  
           [0026]    U.S. Pat. No. 5,304,342 describes a sintered product useful for abrasion- and impact-resistant tools and the like, comprising an iron-group metal binder and refractory metal carbide particles.  
           [0027]    U.S. Pat. No. 5,335,738 relates to a button of cemented carbide. The button is provided with a layer of diamond produced at high pressure and high temperature in the diamond stable area. The cemented carbide has a multi-phase structure having a core that contains eta-phase surrounded by a surface zone of cemented carbide free of eta-phase.  
           [0028]    U.S. Pat. No. 5,370,195 describes a drill bit having a means for connecting the bit to a drill string and a plurality of inserts at the other end for crushing the rock to be drilled, where the inserts have a cemented tungsten carbide body partially embedded in the drill bit and at least two layers at the protruding drilling portion of the insert. The outermost layer contains polycrystalline diamond and particles of carbide or carbonitride.  
           [0029]    U.S. Pat. No. 5,379,854 discloses a cutting element which has a metal carbide stud with a plurality of ridges formed in a reduced or full diameter hemispherical outer end portion of said metal carbide stud. The ridges extend outwardly beyond the outer end portion of the metal carbide stud. A layer of polycrystalline material, resistant to corrosive and abrasive materials, is disposed over the ridges and the outer end portion of the metal carbide stud to form a hemispherical cap.  
           [0030]    U.S. Pat. No. 5,544,713 discloses a cutting element with a metal carbide stud that has a conic tip formed with a reduced diameter hemispherical outer tip end portion of said metal carbide stud. A corrosive and abrasive resistant polycrystalline material layer is also disposed over the outer end portion of the metal carbide stud to form a cap, and an alternate conic form has a flat tip face. A chisel insert has a transecting edge and opposing flat faces, which chisel insert is also covered with a polycrystalline diamond compact layer.  
           [0031]    U.S. Pat. No. 5,624,068 describes buttons, inserts and bodies for rock drilling, rock cutting, metal cutting and wear part applications, where the buttons or inserts or bodies comprise cemented carbide provided with bodies and/or layers of CVD- or PVD-fabricated diamond and then HP/HT treated in a diamond stable area.  
           [0032]    Each of the aforementioned patents and elements of related art is hereby incorporated by referenced in its entirety for the material disclosed therein.  
         SUMMARY OF THE INVENTION  
         [0033]    In drill bits which are used to bore through subterranean geologic formations, it is desirable to provide an insert which has increased durability. This invention provides this increased durability by increasing the diamond layer thickness to decrease the spalling failure of the diamond layer from the non-planar upper surface of the insert and to reduce the residual stresses within the insert, thereby permitting the insert to withstand greater service loads.  
           [0034]    Therefore, it is an object of this invention to improve cutter durability by increasing the thickness of the diamond layer.  
           [0035]    It is a further object of this invention to improve cutter durability by providing a diamond layer which provides full cutter surface coverage.  
           [0036]    It is a further object of this invention to provide a cutter with improved ability to resist spalling failure of the diamond layer.  
           [0037]    It is a further object of this invention to provide a cutter which is capable of withstanding greater service loads.  
           [0038]    These and other objectives, features and advantages of this invention, which will be readily apparent to those of ordinary skill in the art upon review of the following drawings, specification, and claims, are achieved by the invention as described in this application.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0039]    [0039]FIG. 1 a  depicts an exemplary related art roller cone earth boring bit.  
         [0040]    [0040]FIG. 1 b  depicts an exemplary related art percussion bit.  
         [0041]    [0041]FIG. 2 depicts an exemplary related art drag or fixed cutter bit.  
         [0042]    [0042]FIG. 3 depicts a preferred embodiment of the invention showing a full diamond cap.  
         [0043]    [0043]FIG. 4 depicts a preferred embodiment of the invention showing an increased diamond layer thickness.  
         [0044]    [0044]FIG. 5 depicts a preferred embodiment of the invention showing an increased diamond layer thickness in the center of the insert.  
         [0045]    [0045]FIG. 6 depicts a preferred embodiment of the invention showing an increased diamond layer thickness in the periphery of the insert.  
         [0046]    [0046]FIG. 7 depicts a preferred embodiment of the invention showing a full diamond cap on a generally conically shaped insert.  
         [0047]    [0047]FIG. 8 depicts a preferred embodiment of the invention showing an increased diamond layer thickness on a generally conically shaped insert.  
         [0048]    [0048]FIG. 9 depicts a preferred embodiment of the invention showing an increased diamond layer thickness in the center of a generally conically shaped insert.  
         [0049]    [0049]FIG. 10 depicts a preferred embodiment of the invention showing an increased diamond layer thickness in the periphery of a generally conically shaped insert.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0050]    This invention is intended for use in cutting tools, most typically roller cone bits, as shown in FIG. 1 a , and percussion bits, as shown in FIG. 1 b . The typical rolling cone bit  101  includes three rotating cones  102 ,  103 ,  104 . Each rotating cone  102 ,  103 ,  104  has a plurality of cutting teeth  107 . Each insert (also known as a drill insert, compact or PDC) is pressed into the drill bit such that the diamond surface is exposed outside the bit. FIG. 1 b  shows a standard percussion bit  109  with cemented carbide button drill inserts  108 , for percussion rock drilling. The diamond coated inserts of this invention can be substituted for the carbide button inserts  108  shown in FIG. 1 b.    
         [0051]    [0051]FIG. 2 depicts the top view of an example of a typical drag bit  201 . A number of inserts, which also could be of the type described in this invention are shown  201   a - t  arranged in rows emanating in a generally radial fashion from the approximate center  205  of the bit. It is expected by the inventor that the inserts of this invention could be used on rolling cone, percussion and drag bits of virtually any configuration.  
         [0052]    In each embodiment of this invention the insert is composed of essentially two materials: polycrystalline diamond, which covers the cutting surface of the insert; and tungsten carbide. The tungsten carbide region is the area of the insert that is brazed or pressed into the bit body, while the polycrystalline diamond region is the area of the insert that comes in contact with the geologic formation during the drilling operation. In the present invention, the quantity of diamond in the polycrystalline diamond layer is significantly greater than used in prior art inserts. The present invention also has a non-linear, hemispherical or conical shape and is designed to cover the entire cutting surface of the insert. In some embodiments of the invention the polycrystalline diamond layer interfaces with the tungsten carbide region using a generally flat interface, a generally convex interface, an extension of diamond into the tungsten carbide region, and/or an extension of the tungsten carbide into the diamond region. Each interface has its own advantages and applications. Although the interfaces between the diamond region and the substrate regions are shown as generally smooth, it would also be possible to include in the interface a variety of mechanical modifications (e.g., ridges, undulations or dimples, or chemical modifications to enhance both the adhesion between the regions, as well as the transfer of stress between the diamond region and the substrate region. The polycrystalline diamond regions of the present invention are thicker than typically used because a thicker diamond layer provides a greater insert life. As the drill is operated the diamond region of the insert comes into direct physical contact with hard rock. The polycrystalline diamond regions of the various embodiments of the present invention are all essentially symmetrical around the center axis of the insert. This symmetry permits the installation of the insert without regard to the bit face.  
         [0053]    The inserts, as described in this invention, although typically constructed with polycrystalline diamond on a tungsten carbide substrate, can, alternatively, use other materials, such as cubic boron nitride or some other superabrasive material in place of the polycrystalline diamond. Similarly, titanium carbide, tantalum carbide, vandium carbide, niobium carbide, hafnium carbide, or zirconium carbide can be used in place of the tungsten carbide for the substrate. Such superabrasive materials and substrate materials suitable for use in inserts are well known in the art.  
         [0054]    Typically, the inserts of this invention are formed by sintering the diamond layer under high temperature and high pressure conditions to the substrate, using a metal binder or reactive liquid phase such as cobalt. The substrate may be brazed or otherwise joined to an attachment member such as a stud or to a cylindrical backing element to enhance its affixation to the bit face. The cutting element may be mounted to a drill bit either by press-fitting or otherwise locking the insert into a receptacle on a steel-body drag bit, percussion bit or roller cone bit, or by brazing the insert substrate (with or without cylindrical backing) directly into a preformed pocket, socket or other receptacle on the face of a bit body, as on a matrix-type bit.  
         [0055]    An insert, as described in this invention, is preferably fabricated by placing a preformed cemented carbide substrate into a container or cartridge with a layer of diamond crystals or grains loaded into the cartridge adjacent to one face of the substrate. A number of such cartridges are then loaded into an ultra-high pressure press simultaneously. Next, the substrates and adjacent diamond crystal layers are subjected to ultra-high temperature and ultra-high pressure conditions. Such ultra-high pressure and ultra-high temperature conditions cause the metal binder from the substrate body to become liquid and to sweep from the region behind the substrate face next to the diamond layer, through the diamond grains and then to act as a reactive liquid phase to promote a sintering of the diamond grains thereby forming the polycrystalline diamond structure. As a result, the diamond grains become mutually bonded together forming a diamond mass over the substrate face. This diamond mass is also bonded to the substrate face. Alternatively, the diamond layer may be formed as above, but separately from the substrate, and may be subsequently bonded to the substrate material by brazing with a tungsten or titanium-base braze. Yet another alternative method is to deposit the diamond layer on the substrate by chemical vapor deposition (CVD) processing. The metal binder may remain in the diamond layer within the pores existing between the diamond grains or may be removed and optionally replaced by another material, as known in the art, to form a so-called thermally stable diamond. Where the binder is removed by leaching a diamond table is formed with silicon, or alternatively another material having a coefficient of thermal expansion similar to that of diamond. Variations of this general process exist in the art, but this detail is provided so that the reader will understand the concept of sintering a diamond layer onto a substrate on order to form a cutter or insert.  
         [0056]    In a case of the present invention, the desired surface shape of the diamond layer is achieved by utilizing preformed cans. Alternatively, the surface shape can be formed by grinding or even through the use of etching, EOM, EDG, etc.  
         [0057]    Eight examples of the inventive insert design are now described. Further modifications may be made without departing from the essential nature of the invention and such modifications should be considered to fall within the scope of this patent.  
         [0058]    [0058]FIG. 3 depicts the top  301  and section  302  view of a single preferred embodiment of the invention. It can be seen that inserts of this invention are generally cylindrical in shape, with a generally hemispherical diamond surface  306 , the apex of which is at the center axis  307  of the insert. This diamond insert is composed of a layer of polycrystalline diamond  303  bonded to a tungsten carbide substrate  304 . The polycrystalline diamond layer  303  serves as the cutting surface. The interface region  305  is shown where the polycrystalline diamond layer  303  is joined to the substrate  304 . In this embodiment of the invention the interface region  305  is essentially flat. Alternatively, the interface region can have an irregular geometry imposed on it.  
         [0059]    [0059]FIG. 4 depicts the top  401  and section  402  view of a second embodiment of the invention. Again, the insert is generally cylindrical in shape, with a generally hemispherical diamond surface  406 . Alternatively, the apex of the hemisphere could be offset from the center of the insert. This diamond insert is composed of a layer of polycrystalline diamond  403  bonded to a tungsten carbide substrate  404 . The polycrystalline diamond layer  403  serves as the cutting surface. The interface region  405  is shown where the polycrystalline diamond layer  403  is joined to the substrate  404 . In this embodiment of the invention the interface region  405  is curved with the apex  407  of the curve at the center axis  408  of the insert. Alternatively, the interface region  405  may be positioned such that the diamond layer is relatively thinner or relatively thicker.  
         [0060]    [0060]FIG. 5 depicts the top  501  and the section  502  view of another embodiment of the invention. Again, the insert is generally cylindrical in shape, with a generally hemispherical diamond surface  506 . This diamond insert is composed of a layer of polycrystalline diamond  503  bonded to a tungsten carbide substrate  504 . The polycrystalline diamond layer  503  serves as the cutting surface. The interface region  505  is shown as the region where the polycrystalline diamond layer  503  is joined to the substrate  504 . In this embodiment of the invention the interface region  505  includes a trough  507  in the substrate  504  in which the diamond layer  503  extends. This trough  507  intersects and runs perpendicular to the center axis  508  of the insert. Alternatively, the trough  507  can be revolved about the center axis  508  of the insert.  
         [0061]    [0061]FIG. 6 depicts the top  601  and the section  602  view of another embodiment of the invention. Again, the insert is generally cylindrical in shape, with a generally hemispherical diamond surface  606 . This diamond insert is composed of a layer of polycrystalline diamond  603  bonded to a tungsten carbide substrate  604 . The polycrystalline diamond layer  603  serves as the cutting surface. The interface region  605  is shown as where the polycrystalline diamond layer  603  is joined to the substrate  604 . In this embodiment of the invention, the interface region  605  includes a protrusion  607  of the substrate  604  into the polycrystalline diamond  603  layer. This protrusion  607  intersects and runs perpendicular to the center axis  608  of the insert. Alternatively, the protrusion  607  can be revolved about the center axis  608  of the insert.  
         [0062]    [0062]FIG. 7 depicts the section  701  view of an alternative embodiment of the invention. In this embodiment the insert has a generally conic shaped polycrystalline diamond region  702  bonded to a cylinder which is the tungsten carbide substrate  703 . The polycrystalline diamond region  702  serves as the cutting surface. The interface region  704  is shown where the polycrystalline diamond region  702  is joined to the substrate  703 . In this embodiment of the invention the interface region  704  is generally flat. Alternatively, the interface region  704  may have irregularities imposed upon it. The apex of the cone  705  is formed along the center axis  706  of the insert.  
         [0063]    [0063]FIG. 8 depicts the section  801  view of an alternative embodiment of the invention. In this embodiment the insert has a generally conic shaped polycrystalline diamond region  802  bonded to a generally conic shaped tungsten carbide substrate region  803 . The polycrystalline diamond region  802  serves as the cutting surface. The interface region  804  is shown where the polycrystalline diamond region  802  is joined to the substrate  803 . In this embodiment of the invention, the interface region  804  is of a generally conical shape. The apex of both the diamond region cone  805  and the interface region cone  806  is formed along the center axis  807  of the insert.  
         [0064]    [0064]FIG. 9 depicts the section  901  view of an alternative embodiment of the invention. In this embodiment, the insert also has a generally conic shaped polycrystalline diamond region  902  bonded to a generally cylindrically shaped tungsten carbide substrate region  903 . The polycrystalline diamond region  902  serves as the cutting surface. The interface region  904  is shown as the area where the polycrystalline diamond region  902  is joined to the substrate  903 . In this embodiment of the invention, the interface region  904  includes a trough  905  in the substrate  903  in which the diamond region  902  extends. This trough  905  intersects and runs perpendicular to the center axis  906  of the insert. Alternatively, the trough  905  can be revolved about the center axis  906  of the insert.  
         [0065]    [0065]FIG. 10 depicts the section  1001  view of an alternative embodiment of the invention. In this embodiment, the insert also has a generally conic shaped polycrystalline diamond region  1002  bonded to a generally cylindrically shaped tungsten carbide substrate region  1003 . The polycrystalline diamond region  1002  serves as the cutting surface. The interface region  1004  is shown where the polycrystalline diamond region  1002  is joined to the substrate  1003 . In this embodiment of the invention, the interface region  1004  includes a protrusion  1005  of the substrate  1003  into the polycrystalline diamond  1002  layer. This protrusion  1005  intersects and runs perpendicular to the center axis  1006  of the insert. Alternatively, the protrusion  1005  can be revolved about the center axis  1006  of the insert.  
         [0066]    Alternative embodiments of the invention employing a combination of one or more of the features of the foregoing inserts should be considered within the scope of this invention.  
         [0067]    The described embodiments are to be considered in all respects only as illustrative of the current best mode of the invention known to the inventor at the time of filing the patent application, and not as restrictive. Although several of the embodiments shown here include a trough or protrusion in the interface region, interface region geometry is not intended to be limited to a single trough or protrusion or to a particular interface region shape. The scope of this invention is, therefore, indicated by the appended claims rather than by the foregoing description. All devices which come within the meaning and range of equivalency of the claims are to be embraced as within the scope of this patent.