CROSS-REFERENCE TO RELATED APPLICATIONS
- STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 60/538,745 filed on Jan. 23, 2004, titled “Cutting Structure for Single Roller Cone Drill Bit,” which is now incorporated by reference.
- BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to the field of roller cone (“rock”) bits used to drill wellbores through earth formations. More specifically, the invention is related to the structure of cutting elements used in roller cone bits having a single roller cone.
2. Background Art
Roller cone drill bits are commonly used in the oil and gas industry to drill well bores through earth formations. One example of a conventional drilling system used to drill a well bore is shown in FIG. 1. The drilling system includes a drilling rig 10 used to turn a drill string 12 which extends downward into a wellbore 14. Connected to the end of the drill string 12 is a roller cone drill bit 20.
The most common type of roller cone bit is a three cone bit (illustrated at 20 in FIG. 1). A three cone bit 20 includes a bit body adapted to be coupled to a drilling tool assembly or “drill string” which rotates the bit as it is pressed axially into the formations being drilled. The bit body includes three legs, each having a bearing journal thereon. A generally conical roller cone is rotatably mounted to each bearing journal. During drilling, the roller cones are pressed against a formation and rotate about the respective journals while the bit is rotated under an axial load on the formation. A plurality of cutting elements is disposed on each of the roller cones, typically in rows. The cutting elements extend from the surface of the cones to engage and break up formation as the bit is rotated.
One particular type of roller cone drill bit is a single cone bit, which includes only one leg, one bearing journal and one roller cone rotatably mounted on the bearing journal. The drill diameter of the single roller cone bit is substantially concentric with an axis of rotation of the drill bit. This type of drill bit has been shown to be particularly useful in drilling small diameter wellbores (e.g., less than about 4 to 6 inches [10 to 15 cm]) because the bearing structure can be larger relative to the diameter of the drilled hole when the bit has only one concentric roller. This is in contrast to the typical three cone bit, in which each journal must be smaller relative to the drilled hole diameter. Having a significantly larger radial bearing for the same bit diameter than a comparable three roller cone bit allows for higher loads to be placed on the single cone bit to increase the rate of penetration of the drill bit.
One of the limitations of single cone roller bits is that the cutting elements tend to experience greater wear over time due to shearing action, compared to cutting elements on a two or three cone bits. The cutting elements on the single cone bit undergo as much as an order of magnitude more shear than do the cutting elements on a conventional two or three cone bit. Large amounts of shear on cutting elements of single cone bits become apparent when looking at the bottomhole patterns of each type of bit. Single roller cone bits typically drill out a “bowl” shaped bottomhole geometry. The cutting elements on the single cone bit generally shear the formation creating multiple grooves laid out in hemispherically projected hypotrochoids. In contrast, a two or three cone bit generates a series of individual craters or indentations during drilling. Shearing rock typically causes more wear on a cutting element than impacting the rock to compressively fail it. The cutting elements on single cone bits also go through large changes in their direction of motion during drilling, typically anywhere from 100 to 360 degrees. Such changes require special consideration in design.
The single roller cone drill bit efficiently drills the portion of the wellbore proximate the center of the bottom hole because a large portion of the cutting structure near the center of the hole remains in moving contact with the formation during drilling. However, as a result, the wear of the cutting elements on a single cone bit is typically not uniform. In general, cutting elements in the zone that cuts the bottom of a borehole being drilled typically maintain substantially constant contact with the formation during drilling, and cutting elements in the zone that primarily contacts the side wall of the bore hole have more intermittent contact with the formation. Therefore, the cutting elements near the bottom are worn more quickly. As cutting elements are worn and became dull, the cutting efficiency of the bit significantly declines and the effective life of the bit is unduly limited. This is further discussed in U.S. Pat. No. 6,119,797 entitled “Single Cone Earth Boring Bit”, which is incorporated herein by reference.
Cutting element wear in the zone that primarily contacts the side wall is also an important consideration in bit design because an essential performance aspect of any drill bit is its ability to drill a wellbore having the full nominal diameter of the drill bit from the time the bit is first used to the time it becomes worn and must be replaced. In the case of a single roller cone bit, several of the cutting elements on the single roller cone eventually engage the wellbore wall at the gage diameter. As the cutting structure wears, the drilled diameter of the wellbore may be substantially reduced. The reduction in wellbore diameter can be an intolerable condition and may require reaming with subsequent bits or the use of reamers or other devices designed to enlarge the wellbore diameter. Moreover, the reduced wellbore diameter will decrease the flow area available for the proper circulation of drilling fluids and bit cuttings. The use of bits, reamers, or other devices to ream the wellbore can incur substantial cost if the bottom hole assembly must be tripped in and out of the hole several times to complete the procedure.
Drill bit life and efficiency are of great importance because the rate of penetration (ROP) of the bit through earth formations is related to the wear condition of the bit. Accordingly, various methods have been used to provide abrasion protection for drill bits in general, and specifically for roller cones and cutting elements. For example, roller cones, cutting elements, and other bit surfaces have been coated with hardfacing material to provide more abrasion resistant surfaces. Further, specialized cutting element insert materials have been developed to optimize longevity of the cutting elements. While these methods of protection have met with some success, wear is still a problem for single cone bits.
To address the problems of wear associated with single cone bits, diamond enhanced inserts consisting of a polycrystalline diamond layer bonded to a tungsten carbide/cobalt substrate in a HTHP process have been proposed and used as cutting elements for single cone bits. Examples of diamond enhanced inserts and other super hard inserts are further described in U.S. Pat. Nos. 4,525,178, 4,606,106, 4,797,241, 4,650,776, 5,271,749, 5,326,380 and incorporated herein by reference. Such inserts have been used on the nose portion of a cone as a “bearing surface” or on the entire cone as cutting elements. Due to the prohibitive cost of large diamond enhanced inserts, inserts used on single cone bits have been generally small with very limited extensions from the cone surface. The short extension of diamond enhanced inserts limits penetration of the formation and cuttings removal during drilling. Thus, while bit life has been improved, the rate of penetration of these bits has been unduly limited. To over come this limitation, larger diamond enhanced inserts with longer extensions are desired, but the high cost and fragility associated with these larger diamond enhanced inserts have shown them to be unsuitable and unfeasible for commercial products.
- SUMMARY OF INVENTION
A cutting element structure for a single cone roller bit that provides wear resistance without sacrificing toughness and/or cutter extension is desired.
In one aspect, the present invention relates to single roller cone drill bit. The drill bit includes a single rotatable cone formed from steel and having at least one cutting element disposed at a selected position thereon. The at least one cutting element includes an extending body formed from steel which has a first end coupled to the cone and a distal end extending away from the cone. A super hard element is coupled to the distal end of the extending body to form at least a portion of a cutting surface for the cutting element.
In another aspect, the invention relates to a method for making a drill bit. The method includes rotationally coupling a roller cone to a journal of a single roller cone drill bit body, and providing at a selected position on the cone a cutting element comprising an extending body formed from steel and a super hard element coupled to a distal end of the extending body to form at least a part of an outer surface of the insert.
- BRIEF DESCRIPTION OF DRAWINGS
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.
FIG. 1 shows one example of a conventional drilling system.
FIG. 2 shows a generalized cut away view of a single roller cone drill bit.
FIG. 3 shows a cone of a single cone drill bit having a cutting structure in accordance with one embodiment of the present invention.
FIG. 4 shows a single cone drill bit having a cutting structure in accordance with another embodiment of the present invention.
FIG. 5 shows an enlarged cross-section view of a cutting element in accordance with one embodiment of the present invention shown in FIG. 4.
FIG. 5A shows another example of a super hard element in accordance with an embodiment of the present invention.
- DETAILED DESCRIPTION
FIG. 6 shows another example of a single cone bit in accordance with an embodiment of the present invention.
A general structure for a single cone roller cone drill bit which can be made according to various embodiments of the invention is shown in a cut away view in FIG. 2. The bit 22 includes a body 23 made of steel or other high strength material. The body 23 includes a coupling 24 at one end adapted to join the bit body 23 to a drill string (not shown) for rotating the bit 22 during drilling. The bit body 23 may also include gage protection pads 25 at circumferentially spaced apart positions about the bit body 23. The gage protection pads 25 may include gage protection inserts 26 in some embodiments. The gage protection pads 25 if used, extend to a drill diameter 27 of the bit 22.
Another end of the bit body 23 includes a bearing journal 23A to which a single roller cone 28 is rotatably mounted. In some embodiments, the cone 28 may be locked onto the journal 23A by locking balls 23B disposed in the corresponding grooves on the outer surface of the journal 23A and the interior surface of the cone 28. The means by which the cone 28 is rotatably locked onto the journal 23A is not meant to limit the scope of the invention. The cone 28 is formed from steel or other high strength material and may be covered about its exterior surface with hardfacing or similar material intended to reduce abrasive wear of the cone 28. In some embodiments, the cone 28 will include a seal 29 disposed to exclude fluid and debris from entering the space between the inside of the cone 28 and the journal 23A. Such seals are well known in the art.
The cone 28 includes a plurality of cutting elements 31, 32 thereon at selected positions. The journal 23A depends from the bit body 23 such that it defines an angle α between the rotational axis 33 of the journal 23A and the rotational axis 34 of the bit 22. The size of this angle α will depend on features such as the nature of the earth formation being drilled by the bit. Nonetheless, because the bit body 23 and the cone 28 rotate about different axes, the motion of the cutting elements 31, 32 during drilling can be roughly defined as falling within a wall contacting zone 35, in which cutting elements 32 located therein at least intermittently contact the outer diameter (wall) of the wellbore, and a bottom contacting zone 36, in which cutting elements 31 located therein are in substantially continuous contact with the earth formations, and generally do not contact the outer diameter (wall) of the wellbore during drilling.
The cutting elements 32 in the wall contacting zone 35 define the drill diameter of the bit. Having cutting elements for the wall contacting zone 35 which provide good toughness, minimize axial wear, and maintain suitable cutting action against formation being drilled, can extend the life of the bit, while helping to provide relatively high rates of penetration. The cutting elements 31 in the bottom contacting zone 36 significantly effect on the rate of penetration through formations. Having cutting elements in the bottom contacting zone 36 which minimize axial wear and provide adequate strength and toughness that allows for increase cutting element extension to aggressively cut through formations, can also extend the life of the bit and provide for increased rates of penetration. Issues related to single roller cone drill bits are further described in U.S. application Ser. No. 10/407,922, titled “Single Cone Rock Bit Having Inserts Adapted to Maintain Hole Gage During Drilling” and U.S. patent application Ser. No. 10/498,822, titled “Cutting Element Structure for Single Roller Cone Bit,” which are both assigned to the assignee of the present invention and incorporated herein by reference.
In accordance with one aspect of the present invention, FIG. 3 shows an example cutting structure for a single cone bit. The roller cone 42 of the bit is formed from steel and includes a plurality of cutting elements 43 formed on the outer surface of the cone at selected positions. The cutting elements 43 are generally arranged in rows. At least one of the cutting elements 43 (cutting element 44) comprises a milled steel tooth having a steel extending body 45 formed on the outer surface of the cone 42. The extending body 45 extends outward from the surface of the cone 42 with an axial length (primary extension length), b. The cutting element 44 further includes a super hard element 46 press fit into a socket (not shown separately) formed at a distal end of the extending body 45. The super hard element 46 is positioned to extend from a surface of the extending body 45 by a distance (secondary extension length), t, such that it engages with and cuts through earth formations during drilling. The super hard element 46 is exposed at the distal end of the extending body 45 to provide a super hard and wear resistant cutting face for the cutting element 44.
Also, as shown in FIG. 3, in one or more embodiments of the invention the extending body 45 may be configured to extend substantially from the cone surface to form an aggressive cutting structure for the bit. The distal end of the extending body 45 may truncate to a substantially planar surface. The exposed surface of the super hard element 46 which forms the cutting face of the cutting element 44 may have a convex shape with a truncated, substantially planar tip. The other cutting elements 43 on the cone 42 may have a configuration similar to that of cutting element 44.
The cutting structure shown in FIG. 3 is just one example of a cutting structure for a single cone bit in accordance with the present invention. In other embodiments, the cutting elements may comprise inserts instead of teeth and may have different configurations depending on their position on the cone. The super hard material may be disposed at different selected positions proximal the distal end of the cutting element. Also, in other embodiments, different types of cutting elements may be included at selected locations on the cone. The cutting elements may have different abrasion resistances, such as higher near the nose of the cone than near the gage, to provide for more even wear of the cutting elements during drilling. Having cutting elements comprising an extending body formed from steel with a super hard cutting face, advantageously, provides greater impact toughness than a fully diamond enhanced insert without sacrificing abrasive resistance at the cutting face, and allows for the use of cutting elements having greater extensions.
For example, another embodiment in accordance with aspects of the present invention is shown in FIG. 4. The bit 50 includes a bit body 52 and a roller cone 54 rotatably coupled to the bit body 52. Cutting elements 56, 57, 58 are disposed at selected locations on the cone 54 and generally arranged in circumferential rows. At least one of the cutting elements 56 comprises an insert disposed in a socket formed in the surface of the cone 54. In the example shown, the cutting element 56 and a plurality of other similarly configured cutting elements are disposed in the bottom contacting zone (36 in FIG. 2) of the bit 50. The insert (cutting element 56) includes an extending body 56A formed of steel and having a first end coupled to the cone 54 and a distal end extending in a direction away from the cone 54. A super hard element 56B is embedded, including base and sides, in the distal end of the extending body 56A with an exposed surface to provide a wear resistant cutting tip. An enlarged partial cross-section view of cutting element 56 on the cone 54 is shown in FIG. 5.
Referring to FIG. 5, the extending body 56A of the insert is disposed in the socket formed in the surface of the cone 54. The extending body 56A may be press fit, brazed, or attached to the cone 54 using a method known in the art. The other end of the extending body 56A (hereafter referred to as the distal end) extends away from the surface of the cone 54 an axial length (primary extension length), b. The insert further includes a super hard element 56B that is press fit or otherwise attached to a socket formed at the distal end of the extending body 56A. The super hard element 56B may be formed of any super hard material, such as polycrystalline diamond or polycrystalline cubic boron nitride. The super hard element 56B is configured such that when placed in the socket of the extending body 56A it extends from the surface of the extending body 56A a distance (secondary extension length), t, to form at least a portion of a cutting face for the cutting element. In the example shown, the super hard element 56B forms the tip or crest of the cutting element 56 and is adapted to engage and cut through earth formations during drilling.
As illustrated in FIG. 5A, in accordance with another embodiment of the present invention, the super hard element may comprise a compact of super hard material 59. The super hard compact 59 may comprise a body of super hard material 59A bonded to a substrate 59B. In such case, the substrate 59B is disposed in the socket formed in the extending body (56A in FIGS. 4 and 5) of the cutting element (56 in FIGS. 4 and 5) and the super hard material 59A is exposed proximal the distal end of the extending body (56A in FIG. 4) to form at least part of the cutting face. The super hard element 59 in accordance with one example of an embodiment in accordance with the present invention may comprise a polycrystalline diamond body or layer bonded to a substrate formed of tungsten carbide infiltrated with a binder material.
Super hard elements 59 having substrates 59B may be brazed, press fit, or otherwise attached to the extending body of a cutting element in accordance with embodiments of the present invention. Also, in various embodiments of the invention, the super hard element may comprise any super hard material, such as polycrystalline diamond, cubic boron nitride, natural diamond, carbide or other super hard material. The super hard element may further include a substrate formed from tungsten carbide, other metal carbide and/or other hard materials known in the art for making super hard compacts.
Referring back to the embodiment shown in FIG. 4, in addition to cutting elements 56, the bit 50 also includes cutting elements 57 disposed on the cone 54 which terminate into a substantially planar upper surface. In this example, cutting elements 57 are disposed in the wall contacting zone (35 in FIG. 2) and define the gage diameter of the bit 50. The cutting elements 57 comprise tungsten carbide inserts disposed in sockets formed on the cone 54. In other embodiments, these inserts may be formed from tungsten carbide, other metal carbide, other hard materials, super hard materials, or combinations of hard and super hard materials known in the art, and may be formed as described in U.S. application Ser. No. 10/152,498 (“the '498 application”), titled “Single Cone Rock Bit Having Inserts Adapted to Maintain Hole Gage During Drilling,” which is incorporated by reference. In other embodiments, cutting elements 57 may be teeth formed on the cone and may include hardfacing.
The bit 50 also includes a plurality of cutting elements 58 disposed on the cone 54 which terminate in a generally convex or rounded upper surface. In this example, cutting elements 58 are tungsten carbide inserts press fit into sockets formed on the cone 54. Cutting elements 58 are disposed on an inner row on the cone 54 between bottom contacting cutting elements and wall contacting cutting elements on the cone 54. Similar to cutting elements 57 above, in other embodiments cutting elements 58 may be inserts or teeth formed on the cone and may include hardfacing.
Another embodiment in accordance with the present invention is shown in FIG. 6. In this embodiment, the single roller cone bit 60 includes a single cone 62 rotatably mounted to the bit body 61 and having a plurality of cutting elements 63 mounted thereon. The cone 62 is a milled cone formed of steel. At least one of the cutting elements 63 (cutting element 64) comprises a milled steel tooth 66 formed on the cone 62 and having a super hard element 68 partially embedded in the distal end of the tooth 66. The super hard element 68 has an exposed surface that extends from the end of tooth 66 to form a cutting face or tip for the tooth 66. In this embodiment, the tooth 66 has a box-like form which tapers toward the distal end and has a substantial height (or extension) from the surface of the cone 62 to provide an aggressive cutting structure for the bit 60.
In some embodiments of the invention, the extension lengths of the cutting elements are selected to provide an aggressive cutting structure for the bit and/or to allow for improve cutting structure or hole cleaning. Benefits that may be obtained by providing cutting elements having substantial extensions from the cone surface are also disclosed in the '489 application. Referring to the example shown in FIG. 3, the primary and secondary extension lengths, b and t, of the components of cutting element 44 typically will be selected based on the bit size, the cutting element position on the cone, and the formation to be drilled. The total extension length L (L=b+t) of a cutting element in one or more embodiments may be from 0 to 1 inches (about 0 to 25 mm) or more. In one or more embodiments, the primary extension length b is at least about 0.08 inches (about 2 mm), and a secondary extension length t is at least about 0.04 inches (about 1 mm) for drill bit diameters (27 in FIG. 2) of between about 5 and 9 inches. For larger single roller cone drill bits, the primary and secondary extensions may be larger. For example, the primary extension length b may be at least 0.30 inches (about 8 mm), and the secondary extension length t may be at least about 0.06 inches (about 1.5 mm) when the drill bit has a drill bit diameter (27 in FIG. 2) between about 9 to 18 inches.
For an example in accordance with FIG. 3, the extending body has a primary extension length, b, of about 0.47 inches (about 12 mm) from the surface of the cone, and the super hard element 46 has a secondary extension, t, of about 0.09 inches (about 2 mm) from the surface of the extending body. This cutting structure was for a single cone bit having a bit diameter of about 7.875 inches. In other embodiments, the cutting elements may have a more substantial primary extension, such as 0.60 inches (about 15 mm) or more depending on the type of formation being drilled.
In general, one or more cutting elements in accordance with one or more embodiments of the invention may be disposed in a bottom contacting zone (36 in FIG. 2) of the cone. The cutting element may have a substantial primary extension, such as at least 0.47 inches (about 12 mm) or more, to provide an aggressive bottomhole cutting structure for the bit. Such cutting elements may also or alternatively be disposed in the wall contacting zone (cutting elements 7, in FIG. 2) of the bit to maintain gage. The ratio of secondary extension to primary extension (t/b) for a cutting element in accordance with the present invention may be selected to have a value between 0 (flush mounted) and 1. In various embodiments in accordance with aspects of the invention, the primary extension b of the extending body 45 will typically be between 0.08 to 1 inches (about 2 to 25 mm), and the secondary extension t of the super hard element 46 will typically be between 0 inches (flush mounted) and 0.4 inches (about 10 mm).
The super hard material inserted in the steel extending body of the cutting element in accordance with one or more embodiments of the invention may comprises any super hard material, including diamond, cubic boron nitride, or tungsten carbide. The super hard material selected will typically depend on the particular formation expected to be drilled by the bit. In one embodiment, the super hard element may comprise a small polycrystalline diamond compact press fit into the extending body of the cutting element to form at least a portion of the cutting face for the cutting element. The polycrystalline diamond compact may comprise a mass of polycrystalline diamond bonded to substrate formed of metal carbide or other material. In such case, the substrate may be press fit into the extending body of the cutting element and/or alternatively brazed to the cutting element. Additionally, for embodiments having polycrystalline diamond, the diamond body may also be partially or fully depleted of catalyzing material for increased wear resistance. Also, in other embodiments, other materials may be disposed between the extending body and super hard insert to reduce interface stresses, improve impact resistance, or provide better bonding between the super hard insert to the extending body.
Those skilled in the art will appreciate that cutting elements comprising a hybrid insert including a steel body having super hard element embedded therein, the cone may be formed from any material known in the art, including steel or a matrix material, such as tungsten carbide infiltrated with a cobalt binder. For embodiments wherein the cone is formed of matrix material, the matrix material may be infiltrated with natural diamond, thermally stable polycrystalline diamond (TSP), or other super hard material.
In one or more embodiments, a wear enhanced cutting element as described above may be used in conjunction with other types of cutting elements on a cone. For example, one or more cutting elements as described above may be placed selectively placed in the high wear zones of the cone or intermittently placed in select regions of the cone. Also, in one or more embodiments the cutting elements may be arranged differently than that shown. For example, in one embodiment, the cutting elements may be randomly arranged about the outer surface of the cone or arranged in a configuration other than rows. In one or more embodiments, the cutting elements and/or the bit body may be coated with hardfacing material (not shown) to reduce wear on the cutting elements and/or the surface of the cone during drilling.
In one or more embodiments of the invention, because super hard material is embedded in a softer more fracture resistant material and can be limited to the region near the cutting end of the cutting element 34, a cutting element with a larger extension can be used to allow greater penetration in to the formation. Additionally hardfacing can be applied over the extension material for increased wear resistance. Having cutting elements with larger extensions compared to conventional diamond enhanced inserts available for single cone drill bits, also may allow for better cuttings removal during drilling. Additionally, embodiments of the invention allow for the use of larger inserts with longer extensions without the high cost and fragility associated with conventional diamond enhanced inserts.
A cutting element having a body formed from steel provides greater toughness than a conventional diamond-enhanced insert. Bits formed in accordance with one or more embodiments of the present invention may comprise cutting structures which exhibit enhanced wear resistance without significantly sacrificing toughness.
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.