Patent Publication Number: US-7210377-B2

Title: Cone erosion protection for roller cone drill bits

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional application of U.S. patent application Ser. No. 09/974,735 entitled “CONE EROSION PROTECTION FOR ROLLER CONE BITS,” filed Oct. 10, 2001 now U.S. Pat. No. 6,698,098. 

   BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The invention relates generally drill bits used to drill wellbores through earth formations. More specifically, the invention relates to hardfacing structures applied to drill bits and methods for applying the same so as to reduce erosion of the drill bit during drilling operations. 
   2. Background Art 
   Drill bits used to drill wellbores through earth formations generally are made within one of two broad categories of bit structures. Drill bits in the first category are generally known as “fixed cutter” or “drag” bits, which usually include a bit body formed from steel or another high strength material and a plurality of cutting elements disposed at selected positions about the bit body. The cutting elements may be formed from any one or combination of hard or superhard materials, including, for example, natural or synthetic diamond, boron nitride, and tungsten carbide. 
   Drill bits of the second category are typically referred to as “roller cone” bits, which usually include a bit body having one or more roller cones rotatably mounted to the bit body. The bit body is typically formed from steel or another high strength material. The roller cones are also typically formed from steel or other high strength material and include a plurality of cutting elements disposed at selected positions about the cones. The cutting elements may be formed from the same base material as is the cone. These bits are typically referred to as “milled tooth” bits. Other roller cone bits include “insert” cutting elements that are press (interference) fit into holes formed and/or machined into the roller cones. The inserts may be formed from, for example, tungsten carbide, natural or synthetic diamond, boron nitride, or any one or combination of hard or superhard materials. 
   Application of hardfacing to the base material from which the cones and drill bit are formed is known in the art. The hardfacing can be applied in the form of special erosion protection inserts used in addition to the cutting elements. See for example, U.S. Pat. No. 3,952,815 issued to Dysart. Another method known in the art that uses hardfacing to protect roller cones is described in U.S. Pat. No. 5,291,807 issued to Dysart. The method in the Dysart &#39;807 patent includes marking the face of a roller cone by masking or etching, applying hardfacing material, such as tungsten carbide, in the form of a powder, and heating the cone to bond the hardfacing powder to the cone. U.S. Pat. Nos. 3,461,983 and 3,513,728 issued to Hudson include disclosure related to drilling holes (sockets) in the cone prior to application of the hardfacing, plugging the holes, and then applying the hardfacing material using a flame application process. After applying the hardfacing material with the flame process, the plugs are removed and the inserts are pressed into the previously drilled sockets. 
   Moreover, U.S. Pat. No. 5,348,770 issued to Sievers discloses a method for applying hardfacing to a cone which uses a high velocity oxygen fuel (HVOF) spray process after the cone is formed. Forming the cone includes drilling the sockets for the inserts. U.S. Pat. No. 4,396,077 issued to Radtke discloses a method for applying hardfacing to a fixed cutter bit. The method includes generating an electric arc and spraying arc-heated hardfacing material onto a substantially completely assembled bit structure. 
   SUMMARY OF INVENTION 
   In one aspect, the invention comprises a method of forming a drill bit structure, the method comprising affixing a plurality of spacers to the drill bit structure at preselected locations on an outer surface of the drill bit structure. A hardfacing material is applied to the drill bit structure. The plurality of spacers are then removed from the drill bit structure and holes are machined in the drill bit structure proximate the preselected locations. Drilling inserts are positioned in each hole. 
   In another aspect, the invention comprises a method of forming a drill bit structure, the method comprising machining a plurality of holes at preselected locations in the drill bit structure. Spacer inserts are positioned in each of the plurality of holes. A hardfacing material is applied to the drill bit structure using an arc hardfacing process, and the plurality of spacer inserts are removed from the plurality of holes. Drilling inserts are positioned in each of the plurality of holes. 
   In another aspect, the invention comprises a method of forming a drill bit structure, the method comprising machining a plurality of holes in preselected locations in the drill bit structure. Spacer insert are positioned in each of the plurality of holes. A hardfacing material is applied to the drill bit structure using an arc hardfacing process, and the plurality of spacer inserts are removed from the plurality of holes. The plurality of machined holes are enlarged to a selected diameter so as to enable disposition of drilling inserts therein, and drilling inserts are positioned in each of the plurality of enlarged holes. 
   In another aspect, the invention comprises a method of forming a drill bit structure, the method comprising machining a plurality of holes in preselected locations in the drill bit structure. Spacer insert are positioned in each of the plurality of holes. A hardfacing material is applied to the drill bit structure using a high velocity oxygen fuel hardfacing process, and the plurality of spacer inserts are removed from the plurality of holes. The plurality of machined holes are enlarged to a selected diameter so as to enable disposition of drilling inserts therein, and drilling inserts are positioned in each of the plurality of enlarged holes. 
   In another aspect, the invention comprises a method of forming a drill bit structure, the method comprising machining a plurality of holes at preselected locations in the drill bit structure. Spacer inserts are positioned in each of the plurality of holes. A hardfacing material is applied to the drill bit structure with a high velocity oxygen fuel hardfacing process, and the plurality of spacer inserts are removed from the plurality of holes. Drilling inserts are positioned in each of the plurality of holes. 
   In another aspect, the invention comprises a method of forming a drill bit structure, the method comprising applying a hardfacing material to selected surfaces of the drill bit structure. The hardfacing material comprises a carbide infiltrated material comprising a plurality of perforations at preselected locations therein and a powder infiltrated material comprising a plurality of perforations therein, the perforations in the powder infiltrated material adapted to correspond to the perforations in the carbide infiltrated material. A plurality of holes are machined in the drill bit structure proximate the plurality of corresponding perforations, and drilling inserts are positioned in each hole. 
   Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 

   
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  shows a typical prior art roller cone drill bit. 
       FIG. 2  shows a cross-sectional view of a leg of the roller cone drill bit of  FIG. 1 . 
       FIG. 3A  shows a cross-sectional view of spacers affixed to a surface of a drill bit structure in accordance with an embodiment of the invention. 
       FIG. 3B  shows a cross-sectional view of a hardfaced drill bit structure in accordance with an embodiment of the invention. 
       FIG. 3C  shows a cross-sectional view of spacer inserts positioned in holes machined in a drill bit structure in accordance with an embodiment of the invention. 
       FIG. 3D  shows a cross-sectional view of a hardfaced drill bit structure in accordance with an embodiment of the invention. 
       FIG. 3E  shows a cross-sectional view of a hardfaced drill bit structure in accordance with an embodiment of the invention. 
       FIG. 3F  shows a cross-sectional view of an embodiment of the invention. 
       FIG. 4A  shows a cross-sectional view of an embodiment of the invention. 
       FIG. 4B  shows a cross-sectional view of an embodiment of the invention. 
       FIG. 4C  shows a perspective view of an embodiment of the invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a typical prior art roller cone bit used for drilling boreholes in earth formations. The drill bit  10  comprises a bit body  20  and threads  14  formed at an upper end and three legs  22  formed at a lower end. The threads  14  are adapted to couple the bit  10  to a drillstring or bottom hole assembly (BHA) (not shown) used to drill a wellbore (not shown). 
   Each of three roller cones  16  is rotatably mounted on a corresponding leg  22  proximate the lower end of the bit body  20 . A plurality of cutting elements, which in this case comprise inserts  18  that are typically formed from cemented tungsten carbide, are press-fit (or interference fit), brazed, or otherwise affixed in holes (not shown separately in  FIG. 1 ) formed in the roller cones  16 . Lubricant for the roller cones  16  is provided to the journals ( 19  in  FIG. 2 ) on which the roller cones  16  are rotatably mounted from grease reservoirs  24  in the bit body  20 . This configuration is generally used for sealed-bearing rock bits. For open-bearing (unsealed) rock bits, such as those typically used in mining applications, there typically are no grease reservoirs  24 . 
   Referring to  FIG. 2 , when in use, the drill bit  10  is threaded onto a lower end of the drillstring (not shown) and lowered into a wellbore or borehole. The drillstring is rotated by, for example, a rig rotary table (not shown) or a top drive (not shown), and the inserts  18  in the cones  16  engage the bottom and side of the borehole  25 . As the bit rotates, the cones  16  rotate on the bearing journals  19  and drill the borehole  25 . Weight on bit (WOB) is applied to the drillstring and to the formation by the inserts  18 , and the formation is generally crushed and chipped (or scraped) by the inserts  18 . A drilling fluid (often referred to as “drilling mud”) is usually pumped through the drillstring to the drill bit ( 10  in  FIG. 1 ) and is ejected through nozzles ( 26  in  FIG. 1 ) disposed in the bit body ( 20  in  FIG. 1 ). The drilling fluid then travels up a borehole annulus (not shown) formed between the exterior of the drillstring and the borehole  25  wall. The drilling fluid transports most of the formation cuttings drilled by the bit to the surface. In addition, the drilling fluid serves to cool and clean the inserts  18  and roller cones  16  as the borehole  25  is being drilled. 
     FIG. 2  also shows a lower portion of the leg  22  that supports a journal bearing  19 . A plurality of cone retention balls  21  (e.g., “locking balls”) and roller bearings  12   a  and  12   b  surround the journal  19 . An O-ring  28 , located within in an O-ring groove  23 , seals the bearing assembly. The type of seal and roller cone retention device are only shown here to illustrate the general structure of a roller cone drill bit and are not intended to limit the invention. 
   The cones  16  include multiple rows of the inserts  18 , and the roller cones  16  generally include a heel portion  17  located between gage row inserts  15  and the O-ring groove  23 . A plurality of heel row inserts  30  are approximately equally spaced about a circumference of the heel  17 . The heel row inserts  30  and the gage row inserts  15  act together to drill a gage diameter of the borehole  25 . The interior row inserts  18  are generally arranged in, for example, concentric rows, and they serve to crush and chip the earth formations being drilled. 
   As used herein, the term “erosion” refers to both erosion and other abrasive wear. Much of the erosion of the roller cones  16  typically occurs between the gage row inserts  15  and heel row inserts  30 . Furthermore, erosion also may occur at lands  27  formed between the gage row inserts  15  and inner row inserts  18 . Generally, a “land” refers to a surface on a roller cone where holes (e.g., “sockets”) are drilled so that inserts  18 ,  15 ,  30  may be disposed therein. Moreover, erosion may occur in grooves  24  formed between successive inner rows of inserts  18 . These areas on a roller cone surface are collectively referred to as “areas susceptible to erosion” and must generally be protected to increase the longevity of the drill bit in both normal and harsh drilling conditions. For example, erosion in these areas may result in damage to the roller cone, loss of the inserts and/or roller cone cracking (particularly between the inserts), and/or a loss of lubrication for the roller cones. In highly erosive environments, the entire cone body may be exposed to severe erosion. 
   Accordingly, embodiments of the present invention relate to methods of applying hardfacing coatings to roller cones and drill bits so that bit longevity and performance may be extended, especially in harsh drilling conditions. In some embodiments of the invention, hardfacing coatings may be applied with an arc process as described in U.S. Pat. No. 6,196,338 issued to Slaughter et al. and assigned to the assignee of the present invention. For example, the hardfacing may be applied with a plasma transferred arc process (PTA), a gas-shielding tungsten arc (also known as “gas tungsten arc”) welding process, a metal inert gas arc (“gas metal arc”) welding process, and similar processes known in the art. 
   In some embodiments, an electric arc such as that formed by the PTA process is preferred because an area of a cone heated for application of hardfacing may be closely controlled. Advantageously, close control of the heated area prevents damage to a large area of the cone that may be produced with, for example, an unshielded chemical flame. 
   The following detailed discussion describes various aspects of the invention. The hardfacing techniques described below may be used to apply a hardfacing coating to any drill bit structure such as, for example, a roller cone or a drill bit shoulder. Accordingly, descriptions related to application of hardfacing coatings to roller cones are not intended to limit the scope of the invention to a single use (e.g., hardfacing roller cones). Further, while some embodiments are described with respect to insertion of cutting elements into machined holes in a drill bit structure, other types of drilling inserts (where the term drilling inserts is intended to include cutting elements), such as gage protection elements, may be used within the scope of the invention. Accordingly, the examples provided in the description below are not intended to be limiting with respect to, for example, a specific type of drilling insert. 
   In one embodiment of the invention shown in  FIG. 3A , spacers  50  are disposed on a surface  52  of a roller cone  54  that is rotatably attached to a drill bit (not shown) in a manner similar to that described above. The spacers  50  may comprise, for example, graphite, oxide ceramics (including porous alumina, porous silica, mullite, and the like), soft metals (including copper and the like), and other suitable materials known in the art. Moreover, coated metals, metallized plastic, heat resistant plastic, and the like may also be used with embodiments of the invention. 
   The spacers  50  may be positioned at selected locations on the surface  52  of the roller cone  54 . The positioning of the spacers  50  is adapted to correspond to, for example, desired locations of cutting element inserts that will be affixed to the roller cone  50  after a hardfacing material has been applied thereto. The spacers  50  enable a hardfacing material to be applied to the entire surface  52  of the roller cone  54  without, for example, omitting hardfacing from the desired locations where cutting element inserts (or drilling inserts) and/or gage protection elements are to be disposed. This aspect of the invention helps ensure that a substantially even coating of hardfacing material is applied to the selected areas of the roller cone  54  and/or drill bit (not shown). Moreover, use of spacers  50  may increase a speed of application of the hardfacing material because an operator does not have to spend as much time avoiding application of the hardfacing material to the locations where cutting element inserts will be disposed. 
   Referring to  FIG. 3B , the spacers  50  may be affixed (e.g., adhesively or mechanically bonded) to the surface  52  of the roller cone  54  in selected locations, the selected locations forming, for example, a number of rows (not shown). Hardfacing material  56  may then be applied to the surface  52  of the roller cone  54  so that the spacers  50  remain substantially exposed (as shown in  FIG. 3B ). After the hardfacing material  56  has been applied, the spacers  50  may be removed by any means known in the art (e.g., by breaking, chipping, and/or drilling out the spacers) so that holes adapted to receive cutting element inserts, gage protections inserts, and the like may be drilled (e.g., machined) in the non-hardfaced portions of the roller cone (formerly occupied by the spacers). Note that, in other embodiments, the spacers may be substantially covered with hardfacing material during the coating process. 
   After hardfacing has been completed, and because the hardfacing material  56  generally does not adhere to the spacers in the same manner as the hardfacing material  56  adheres to a base metal of the roller cone  54  (e.g., because the hardfacing material  56  generally does not form a metallurgical or mechanical bond with the spacers  50 ), the portions of the hardfacing material  56  proximate the spacers  50  may be removed so that cutting element insert holes  58  my be drilled as described above. After the holes  58  have been drilled in the roller cone  54 , cutting element inserts (not shown) may be affixed in the holes  58  by interference fit, brazing, and/or other means known in the art. 
   In another embodiment of the invention shown in  FIG. 3C , cutting element insert holes  60  may be drilled in a roller cone  62  prior to hardfacing. Spacer inserts  64 , such as graphite inserts, may then be inserted into the holes  60 . Note that materials other than graphite may be used in various embodiments of the invention, including the materials described above with respect to spacers. For example, the spacer inserts  64  may comprise oxide ceramics (including porous alumina, porous silica, mullite, and the like), soft metals (including copper and the like), and other suitable materials known in the art. Moreover, coated metals, metallized plastic, heat resistant plastic, and the like may also be used. 
   Referring to  FIG. 3D , hardfacing material  66  may then be applied to a surface  68  of the roller cone  62  and/or other selected portions of the drill bit (not shown), and the inserts  64  may be either substantially exposed or substantially covered after application of the hardfacing material  66  (as in the embodiments described above). As shown in  FIG. 3E , the inserts  64  may be removed from the roller cone  62  after hardfacing material  66  has been applied thereto so that cutting element inserts (not shown) may be affixed in the holes  60  by brazing and/or other means known in the art. 
   In another embodiment of the invention shown in  FIG. 3F , holes  100  having a diameter D 1  may be machined in a roller cone  92  prior to hardfacing. Spacer inserts typically referred to as “mushroom caps”  90  may be inserted into the holes  100 . Hardfacing material  96  may then be applied to a surface  94  of the roller cone  92  and/or other selected portions of the drill bit (not shown), and the mushroom caps  90  may be either substantially exposed or substantially covered after application of the hardfacing material  96  (as in the embodiments described above). The mushroom caps  90  may be removed from the roller cone  92  after hardfacing material  96  has been applied thereto. After removal of the mushroom caps  90 , the holes  100  may be enlarged to a diameter D 2  so as to form cutting element insert holes  98  (shown as the dashed line in  FIG. 3F ) so that cutting element inserts (not shown) may be affixed in the insert holes  98  by brazing and/or other means known in the art. In this manner, the mushroom caps  90  act as both spacers and spacer inserts and enable an insert hole  98  to be enlarged to the desired diameter D 2  after hardfacing material  96  has been applied to the roller cone  92 . 
   The mushroom caps  90  may be formed from any suitable material known in the art. For example, the mushroom caps  90  may be formed from the materials described above with respect to the spacers and spacer inserts of the previous embodiments. 
   The previous embodiments related to the use of, for example, inserts as spacers for the positioning of cutting element inserts generally include application of hardfacing materials using the aforementioned arc processes. Moreover, high velocity oxygen fuel (HVOF) processes may also be used to apply hardfacing in these embodiments of the invention. In a preferred embodiment, the hardfacing material is applied via an electric arc process. The electric arc process enables the hardfacing material application to be closely controlled so that, for example, only selected portions of the roller cone and/or drill bit to be hardfaced are heated to elevated temperatures during the hardfacing process. 
   Advantageously, the above described embodiments of the invention include precise application of a selected pattern of hardfacing material to the roller cone or other surface that is to be coated for erosion protection. In this manner, the invention helps avoid formation of a hardened layer that is difficult to machine when, for example, cutting element inserts holes are later drilled for installation of cutting element inserts. 
   In another embodiment of the invention shown in  FIG. 4A , layers  70 ,  72  of infiltrated material are used to form a coating of hardfacing material  74  over a surface  76  of, for example, a roller cone  78 . The layers  70 ,  72  of infiltrated material may comprise, for example, tungsten carbide infiltrated materials sold under the name “Conforma Clad,” a mark of Conforma Clad, Inc., of New Albany, Ind. Application of the hardfacing material  74  includes, for example, positioning a carbide infiltrated layer  70  over the surface  76  of the roller cone  78 . Note that as used herein the term “infiltrated material” represents a discrete layer of bonded material that may be easily handled and, for example, placed over a surface to be hardfaced in a substantially conformal manner. Typically, in the embodiments described herein, polytetrafluoroethylene (PTFE, which may be, for example, a material sold under the name “Teflon,” a mark of E. I. DuPont de Nemours of Wilmington, Del.) forms a structural component such as a cloth, and is later “burned off” or vaporized during the hardfacing process. Accordingly, the carbide infiltrated layer  70  may comprise, for example, tungsten carbide and PTFE. 
   A powder infiltrated layer  72  may then be placed on top of the carbide infiltrated layer  70 . The powder infiltrated layer  72  may comprise, for example, Nickel, Boron, Cobalt, Silicon, Chromium, PTFE, and combinations thereof. The roller cone  78 , the carbide infiltrated layer  70 , and the powder infiltrated layer  72  are then heated in a controlled environment (e.g., in an enclosed oven (not shown) with a selectively controlled atmosphere) to a relatively low temperature so as to vaporize the PTFE. The temperature is then elevated to approximately 900–1200° C. for a selected period of time. At the elevated temperature, the alloys (e.g., Nickel, Cobalt, etc.) in the powder infiltrated layer  72  liquefy, infiltrate the carbide infiltrated layer  70 , and thereby form a hardfacing material  74  that becomes metallurgically bonded to the surface  76  of the roller cone  78  (see, e.g.,  FIG. 4B ). The composition of the infiltrated layers  70 ,  72  may be varied so that the hardfacing material  74  is adapted for use in specific environments. Such compositions are known in the art, and the materials listed above in the simplified description of the invention are not intended to limit the invention to a specific composition. 
   Heating of the infiltrated layers  70 ,  72  may be performed by any means known in the art. For example, the roller cone  78  and/or other parts of the drill bit (including the entire bit in some embodiments) may be placed in an oven and heated to the selected temperatures. In other embodiments, heating may be performed using spot heating sources including lasers, high intensity light sources, induction heating tools, microwave sources, and the like. Accordingly, the type of heat source used to heat the infiltrated layers  70 ,  72  so as to form the desired metallurgical bond is not intended to be limiting. 
   In embodiment shown in  FIG. 4C , the infiltrated layers  80  typically comprise perforations  82  in selected corresponding locations (e.g., perforations formed in the carbide infiltrated layer are adapted so as to align with perforations formed in the powder infiltrated material) so as to allow for later disposition of cutting element inserts in a roller cone  84 . For example, the infiltrated layers  80  may be perforated in a selected manner so as to form “rows”  86  of perforations  82  when the infiltrated layers  80  are disposed on the roller cone  84 , a gage surface (not shown), or any other part of a drill bit (not shown) that is to be coated with a hardfacing material. In this manner, the roller cone  84  may be hardfaced while selected areas of the roller cone  84  proximate the perforations  82  may remain substantially uncoated so that cutting element holes  88  may be machined in the roller cone  84  surface so as to allow for disposition (e.g., brazing) of cutting element inserts therein. 
   In another embodiment of the invention, the infiltrated layers are selectively infiltrated with hardfacing materials so that selected areas of the infiltrated layers comprise substantially only PTFE (or another suitable material) that may be vaporized at a relatively low temperature. After the PTFE (or other suitable material) is vaporized, “gaps” or preformed perforations are formed in the hardfacing material. The gaps are selectively arranged to correspond to desired locations of insert holes (e.g., in rows) that may be machined in a roller cone or other drill bit structure after the hardfacing process has been completed. Accordingly, specially formed infiltrated layers may be developed to correspond to, for example, selected roller cone cutting element geometries, different size roller cones (e.g., for different sizes of drill bits), and the like. 
   Note that other embodiments may comprise, for example, a carbide infiltrated layer pre-bonded to a powder infiltrated layer (e.g., using a mechanical bond, an adhesive bond, a chemical bond, or similar means known in the art). In these embodiments, perforations in the materials may be pre-aligned so as to ease positioning the materials proximate the surface of the drill bit structure in a desired manner. 
   Advantageously, the infiltrated material hardfacing process forms a strong metallurgical bond with, for example, the surface of the roller cone. The metallurgical bond is typically stronger (e.g., more resistant to wear and erosion) than a traditional mechanical bond formed by other hardfacing processes. The metallurgical bond provides increased wear resistance and longevity when drilling in, for example, harsh downhole and/or other subsurface environments. Further, the perforations in the infiltrated materials may be closely controlled so as to produce, for example, a closely toleranced cutting element arrangement. Finally, application of the infiltrated cloth to the hardfaced areas may be performed relatively quickly (as compared to, for example, traditional welded application hardfacing processes). 
   While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.