PDC BITS HAVING ROLLING CUTTERS AND USING MIXED CHAMFERS

Abstract

A cutting tool cutting tool may include a tool body having a plurality of blades extending radially therefrom, a plurality of rotatable cutting elements having a first chamfer mounted on at least one of the plurality of blades, and a plurality of non-rotatable cutting elements having a second, distinct chamfer mounted on at least one the plurality of blades.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. §119, this application claims the benefit of U.S. Provisional Application No. 61/783,428, filed on Mar. 14, 2013, and U.S. Provisional Application No. 61/721,908, filed on Nov. 2, 2012, both of which are incorporated by reference in their entirety.

BACKGROUND

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 “roller cone” bits, which 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.

Drill bits of the second category are typically referred to as “fixed cutter” or “drag” bits. This category of bits has no moving elements but rather have a bit body formed from steel or another high strength material and cutters (sometimes referred to as cutter elements, cutting elements or inserts) attached at selected positions to the bit body. For example, the cutters may be formed having a substrate or support stud made of carbide, for example tungsten carbide, and an ultra hard cutting surface layer or “table” made of a polycrystalline diamond material or a polycrystalline boron nitride material deposited onto or otherwise bonded to the substrate at an interface surface.

An example of a prior art drag bit having a plurality of cutters with ultra hard working surfaces is shown in FIG. 1A. A drill bit 10 includes a bit body 12 and a plurality of blades 14 that are formed on the bit body 12. The blades 14 are separated by channels or gaps 16 that enable drilling fluid to flow between and both clean and cool the blades 14 and cutters 18. Cutters 18 are held in the blades 14 at predetermined angular orientations and radial locations to present working surfaces 20 with a desired backrake angle against a formation to be drilled. Typically, the working surfaces 20 are generally perpendicular to the axis 19 and side surface 21 of a cylindrical cutter 18. Thus, the working surface 20 and the side surface 21 meet or intersect to form a circumferential cutting edge 22.

Nozzles 23 are typically formed in the drill bit body 12 and positioned in the gaps 16 so that fluid can be pumped to discharge drilling fluid in selected directions and at selected rates of flow between the cutting blades 14 for lubricating and cooling the drill bit 10, the blades 14, and the cutters 18. The drilling fluid also cleans and removes the cuttings as the drill bit rotates and penetrates the geological formation. The gaps 16, which may be referred to as “fluid courses,” are positioned to provide additional flow channels for drilling fluid and to provide a passage for formation cuttings to travel past the drill bit 10 toward the surface of a wellbore (not shown).

The drill bit 10 includes a shank 24 and a crown 26. Shank 24 is typically formed of steel or a matrix material and includes a threaded pin 28 for attachment to a drill string. Crown 26 has a cutting face 30 and outer side surface 32. The particular materials used to form drill bit bodies are selected to provide adequate toughness, while providing good resistance to abrasive and erosive wear. For example, in the case where an ultra hard cutter is to be used, the bit body 12 may be made from powdered tungsten carbide (WC) infiltrated with a binder alloy within a suitable mold form. In one manufacturing process the crown 26 includes a plurality of holes or pockets 34 that are sized and shaped to receive a corresponding plurality of cutters 18.

The combined plurality of surfaces 20 of the cutters 18 effectively forms the cutting face of the drill bit 10. Once the crown 26 is formed, the cutters 18 are positioned in the pockets 34 and affixed by any suitable method, such as brazing, adhesive, mechanical means such as interference fit, or the like. The design depicted provides the pockets 34 inclined with respect to the surface of the crown 26. The pockets 34 are inclined such that cutters 18 are oriented with the working face 20 at a desired rake angle in the direction of rotation of the bit 10, so as to enhance cutting. It should be understood that in an alternative construction (not shown), the cutters may each be substantially perpendicular to the surface of the crown, while an ultra hard surface is affixed to a substrate at an angle on a cutter body or a stud so that a desired rake angle is achieved at the working surface.

A typical cutter 18 is shown in FIG. 1B. The typical cutter 18 has a cylindrical cemented carbide substrate body 38 having an end face or upper surface 54 referred to herein as the “interface surface” 54. An ultra hard material layer (cutting layer) 44, such as polycrystalline diamond or polycrystalline cubic boron nitride layer, forms the working surface 20 and the cutting edge 22. A bottom surface 52 of the ultra hard material layer 44 is bonded on to the upper surface 54 of the substrate 38. The bottom surface 52 and the upper surface 54 are herein collectively referred to as the interface 46. The top exposed surface or working surface 20 of the cutting layer 44 is opposite the bottom surface 52. The cutting layer 44 typically has a flat or planar working surface 20, but may also have a curved exposed surface, that meets the side surface 21 at a cutting edge 22.

Generally speaking, the process for making a cutter 18 employs a body of tungsten carbide as the substrate 38. The carbide body is placed adjacent to a layer of ultra hard material particles such as diamond or cubic boron nitride particles and the combination is subjected to high temperature at a pressure where the ultra hard material particles are thermodynamically stable. This results in recrystallization and formation of a polycrystalline ultra hard material layer, such as a polycrystalline diamond or polycrystalline cubic boron nitride layer, directly onto the upper surface 54 of the cemented tungsten carbide substrate 38.

One type of ultra hard working surface 20 for fixed cutter drill bits is formed as described above with polycrystalline diamond on the substrate of tungsten carbide, typically known as a polycrystalline diamond compact (PDC), PDC cutters, PDC cutting elements, or PDC inserts. Drill bits made using such PDC cutters 18 are known generally as PDC bits. While the cutter or cutter insert 18 is typically formed using a cylindrical tungsten carbide “blank” or substrate 38 which is sufficiently long to act as a mounting stud 40, the substrate 38 may also be an intermediate layer bonded at another interface to another metallic mounting stud 40.

The ultra hard working surface 20 is formed of the polycrystalline diamond material, in the form of a cutting layer 44 (sometimes referred to as a “table”) bonded to the substrate 38 at an interface 46. The top of the ultra hard layer 44 provides a working surface 20 and the bottom of the ultra hard layer cutting layer 44 is affixed to the tungsten carbide substrate 38 at the interface 46. The substrate 38 or stud 40 is brazed or otherwise bonded in a selected position on the crown of the drill bit body 12 (Figure la). As discussed above with reference to FIG. 1a, the PDC cutters 18 are typically held and brazed into pockets 34 formed in the drill bit body at predetermined positions for the purpose of receiving the cutters 18 and presenting them to the geological formation at a rake angle.

Bits 10 using conventional PDC cutters 18 are sometimes unable to sustain a sufficiently low wear rate at the cutter temperatures generally encountered while drilling in abrasive and hard rock. These temperatures may affect the life of the bit 10, especially when the temperatures reach 700-750° C., resulting in structural failure of the ultra hard layer 44 or PDC cutting layer. A PDC cutting layer includes individual diamond “crystals” that are interconnected. The individual diamond crystals thus form a lattice structure. A metal catalyst, such as cobalt may be used to promote recrystallization of the diamond particles and formation of the lattice structure. Thus, cobalt particles are typically found within the interstitial spaces in the diamond lattice structure. Cobalt has a significantly different coefficient of thermal expansion as compared to diamond. Therefore, upon heating of a diamond table, the cobalt and the diamond lattice will expand at different rates, causing cracks to form in the lattice structure and resulting in deterioration of the diamond table.

It has been found by applicants that many cutters 18 develop cracking, spalling, chipping and partial fracturing of the ultra hard material cutting layer 44 at a region of cutting layer subjected to the highest loading during drilling. This region is referred to herein as the “critical region” 56. The critical region 56 encompasses the portion of the ultra hard material layer 44 that makes contact with the earth formations during drilling. The critical region 56 is subjected to high magnitude stresses from dynamic normal loading, and shear loadings imposed on the ultra hard material layer 44 during drilling. Because the cutters are typically inserted into a drag bit at a rake angle, the critical region includes a portion of the ultra hard material layer near and including a portion of the layer's circumferential edge 22 that makes contact with the earth formations during drilling.

The high magnitude stresses at the critical region 56 alone or in combination with other factors, such as residual thermal stresses, can result in the initiation and growth of cracks 58 across the ultra hard layer 44 of the cutter 18. Cracks of sufficient length may cause the separation of a sufficiently large piece of ultra hard material, rendering the cutter 18 ineffective or resulting in the failure of the cutter 18. When this happens, drilling operations may have to be ceased to allow for recovery of the drag bit and replacement of the ineffective or failed cutter. The high stresses, particularly shear stresses, may also result in delamination of the ultra hard layer 44 at the interface 46.

In some drag bits, PDC cutters 18 are fixed onto the surface of the bit 10 such that a common cutting surface contacts the formation during drilling. Over time and/or when drilling certain hard but not necessarily highly abrasive rock formations, the edge 22 of the working surface 20 that constantly contacts the formation begins to wear down, forming a local wear flat, or an area worn disproportionately to the remainder of the cutting element. Local wear flats may result in longer drilling times due to a reduced ability of the drill bit to effectively penetrate the work material and a loss of rate of penetration caused by dulling of edge of the cutting element. That is, the worn PDC cutter acts as a friction bearing surface that generates heat, which accelerates the wear of the PDC cutter and slows the penetration rate of the drill. Such flat surfaces effectively stop or severely reduce the rate of formation cutting because the conventional PDC cutters are not able to adequately engage and efficiently remove the formation material from the area of contact. Additionally, the cutters are typically under constant thermal and mechanical load. As a result, heat builds up along the cutting surface, and results in cutting element fracture. When a cutting element breaks, the drilling operation may sustain a loss of rate of penetration, and additional damage to other cutting elements, should the broken cutting element contact a second cutting element.

Additionally, another factor in determining the longevity of PDC cutters is the generation of heat at the cutter contact point, specifically at the exposed part of the PDC layer caused by friction between the PCD and the work material. This heat causes thermal damage to the PCD in the form of cracks which lead to spalling of the polycrystalline diamond layer, delamination between the polycrystalline diamond and substrate, and back conversion of the diamond to graphite causing rapid abrasive wear. The thermal operating range of conventional PDC cutters is typically 750° C. or less.

In U.S. Pat. No. 4,553,615, a rotatable cutting element for a drag bit was disclosed with an objective of increasing the lifespan of the cutting elements and allowing for increased wear and cuttings removal. The rotatable cutting elements disclosed in the '615 patent include a thin layer of an agglomerate of diamond particles on a carbide backing layer having a carbide spindle, which may be journalled in a bore in a bit, optionally through an annular bush. With significant increases in loads and rates of penetration, the cutting element of the '615 patent is likely to fail by one of several failure modes. Firstly, thin layer of diamond is prone to chipping and fast wearing. Secondly, geometry of the cutting element would likely be unable to withstand heavy loads, resulting in fracture of the element along the carbide spindle. Thirdly, the retention of the rotatable portion is weak and may cause the rotatable portion to fall out during drilling. Fourthly, the prior art does not disclose optimization of the location of rotatable cutting elements on a bit body.

Accordingly, there exists a continuing need for cutting elements that may stay cool and avoid the generation of local wear flats, and the incorporation of those cutting elements on a drill bit or other cutting tool.

SUMMARY

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

In one aspect, embodiments disclosed herein relate to a cutting tool that includes a tool body having a plurality of blades extending radially therefrom, a plurality of rotatable cutting elements having a first chamfer mounted on at least one of the plurality of blades, and a plurality of non-rotatable cutting elements having a second, distinct chamfer mounted on at least one of the plurality of blades.

In another aspect, embodiments disclosed herein relate to a cutting tool that includes a tool body having a plurality of blades extending radially therefrom; a plurality of rotatable cutting elements, wherein the plurality of rotatable cutting elements have at least two differing chamfer sizes based on their positioning along the plurality of blades

Other aspects and advantages of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A shows a perspective view of a conventional fixed cutter bit.

FIG. 1B shows a perspective view of a conventional PDC cutter.

FIG. 2 shows the progression of a wear flat in a conventional cutting element.

FIGS. 3A-B show profile views of a drill bit according to embodiments disclosed herein.

FIG. 4 shows a rotated profile view of a drill bit according to embodiments disclosed herein.

FIGS. 5A-B show an example small chamfer for use in an embodiment disclosed herein.

FIGS. 6-8 show an example large chamfer for use in an embodiment disclosed herein.

FIG. 9 shows the cutting force acting on two bevel sizes.

FIG. 10 shows the side force acting on two bevel sizes.

FIG. 11 shows a bit profile according to one embodiment disclosed herein.

FIG. 12 shows an exploded view of a cutting element assembly according to embodiments of the present disclosure.

FIG. 13 shows a cross-sectional view of a cutting element assembly according to embodiments of the present disclosure.

DETAILED DESCRIPTION

In one or more aspects, embodiments disclosed herein relate to downhole tools (including fixed cutter drill bits) using rotatable cutting structures. In one or more aspect, embodiments disclosed herein relate to downhole tools (including fixed cutter drill bits) using rotatable cutting structures in conjunction with conventional fixed cutters. Specifically, embodiments disclosed herein relate to improving the life of a drill bit (or other downhole tool) by positioning rotatable cutting elements in particular arrangements on the drill bit.

Generally, rotatable cutting elements (also referred to as rolling cutters) described herein allow at least one surface or portion of the cutting element to rotate as the cutting elements contact a formation. As the cutting element contacts the formation, the cutting action may allow portion of the cutting element to rotate around a cutting element axis extending through the cutting element. Rotation of a portion of the cutting structure may allow for a cutting surface to cut the formation using the entire outer edge of the cutting surface, rather than the same section of the outer edge, as observed in a conventional cutting element. The following discussion describes various embodiments for a rotatable cutting element; however, the present disclosure is not so limited. One skilled in the art would appreciate that any cutting element capable of rotating may be used with the drill bit or other cutting tool of the present disclosure.

The rotation of the inner rotatable cutting element may be controlled by the side cutting force and the frictional force between the bearing surfaces. If the side cutting force generates a torque which can overcome the torque from the frictional force, the rotatable portion will have rotating motion. The side cutting force may be affected by cutter side rake, back rake and geometry, including the working surface patterns disclosed herein. Additionally, the side cutting force may be affected by the surface finishing of the surfaces of the cutting element components, the frictional properties of the formation, as well as drilling parameters, such as depth of cut. The frictional force at the bearing surfaces may affected, for example, by surface finishing, mud intrusion, etc. The design of the rotatable cutters disclosed herein may be selected to ensure that the side cutting force overcomes the frictional force to allow for rotation of the rotatable portion. Various design considerations of the present disclosure are described below, as well as exemplary embodiments of rolling cutters.

Placement of Rolling Cutters

According to embodiments of the present disclosure, a bit design consideration may include placement of rolling cutters on a drill bit. Placement design of rolling cutters on a drill bit may involve, first, predicting where conventional cutter (fixed cutter) wear occurs most frequently or quickly on a drill bit. For example, fixed cutter wear may be predicted using engineering and design software, such as I-DEAS, “Integrated Design and Engineering Analysis Software”, or CAD software. Such engineering and design software may also be used to optimize bit stabilization dynamics using various placements of rolling cutters. Fixed cutter wear may also be predicted by observing and/or measuring wear flat sizes on dull drill bits. In particular, as a drill bit having conventional, fixed cutters contacts and cuts an earthen formation, the cutting surface and cutting edge of a fixed cutter may wear and form a wear flat. An example of a wear flat 2305 progression in a fixed cutter 2300 is shown in FIG. 2.

Once fixed cutter wear is predicted, criteria for the placement of rolling cutters may be set according to where the fixed cutter wear occurs. For example, according to embodiments of the present disclosure, rolling cutter placement design may include replacing fixed cutters having the most amount of wear with rolling cutters. In one embodiment, rolling cutter placement design may include replacing half of the total number of fixed cutters experiencing the largest amount of wear with rolling cutters. Further, in other embodiments, rolling cutter placement design may include replacing fixed cutters with rolling cutters on only certain blades of a drill bit.

According to embodiments of the present disclosure, rolling cutter placement design criteria may be set so that rolling cutters and fixed cutters on a drill bit have a plural set configuration. Drill bits having a plural set configuration have more than one cutting element at at least one radial position with respect to the bit axis. Expressed alternatively, at least one cutting element includes a “back up” cutting element disposed at about the same radial position with respect to the bit axis. For example, referring to FIGS. 3A and 3B, a face side profile view of a drill bit 2400 having a plurality of cutting blades 2410 are shown, wherein the bits rotate in direction R. Primary blades 2410a extend radially from substantially proximal the longitudinal axis A of the bit toward the periphery of the bit. Secondary blades 2410b do not extend from substantially proximal the bit axis A, but instead extend radially from a location that is a distance away from the bit axis A. Cutting elements 2420, 2430 are positioned at the leading side of blades 2410, wherein the leading sides of blades 2410 face in the direction of bit rotation R and trailing sides of blades face the opposite direction. Further, as shown, cutting element 2420 trails cutting element 2430 in plural set configuration, i.e., cutting element 2420 “backs up” cutting element 2430 at about the same radial position with respect to the bit axis A. Either cutting element 2420 or cutting element 2430, or both cutting elements 2420 and 2430, may be rolling cutters. In a particular embodiment, a bit having a plural set cutter configuration may have at least one trailing or backup cutting element that is rotatable (a rolling cutter) and at least one leading or primary cutting element that is a fixed cutter. In another embodiment, a bit having a plural set configuration may have at least one fixed cutter trailing cutting element and at least one rolling cutter leading cutting element. Advantageously, by using a plural set configuration having at least one rolling cutter, the cutting structure may be more robust.

Further, a bit may have a single set configuration of cutting elements, wherein each cutting element in a single set configuration is at a unique radial position of the bit. In embodiments having a single set configuration, a plurality of rolling cutters may be placed at various unique radial positions with respect to the bit axis. For example, a plurality of rolling cutters may have a forward spiral or a reverse spiral single set configuration, wherein the rolling cutters are placed in areas experiencing wear. As used herein, a forward spiral layout refers to a cutter placement where cutters having incrementally increasing radial distances from the bit centerline are placed in a clockwise distribution whereas a reverse spiral layout refers to a cutter placement where cutters having incrementally increasing radial distances from a bit centerline are placed in a counterclockwise distribution. In some embodiments, the cutters may be placed in a forward spiral, where rotatable cutters are at least placed in the nose and/or shoulder region, are placed in the nose, shoulder, and gage regions in particular embodiments, and are placed in the cone, nose, shoulder, and gage regions in more particular embodiments. In some embodiments, the cutters may be placed in a reverse spiral, where rotatable cutters are at least placed in the nose and/or shoulder region, are placed in the nose, shoulder, and gage regions in particular embodiments, and are placed in the cone, nose, shoulder, and gage regions in more particular embodiments.

Additionally, leading and trailing cutting elements may be placed on a single blade.

However, as used herein, the term “backup cutting element” is used to describe a cutting element that trails any other cutting element on the same blade when the bit is rotated in the cutting direction. Further, as used herein, the term “primary cutting element” is used to describe a cutting element provided on the leading edge of a blade. In other words, when a bit is rotated about its central longitudinal axis in the cutting direction, a “primary cutting element” does not trail any other cutting elements on the same blade. Suitably, each primary cutting elements and optional backup cutting element may have any suitable size and geometry. Primary cutting elements and backup cutting elements may have any suitable location and orientation and may be rolling cutters or fixed cutters. In an example embodiment, backup cutting elements may be located at the same radial position as the primary cutting element it trails, or backup cutting elements may be offset from the primary cutting element it trails, or combinations thereof may be used.

In particular, each blade on a bit face (e.g., primary blades and secondary blades) provides a cutter-supporting surface to which cutting elements are mounted. Primary cutting elements may be disposed on the cutter-supporting surface of the blades and one or more of the primary blades may also have backup cutting elements disposed on the cutter-supporting surface of the bit. In an exemplary embodiment, backup cutting elements may be provided on the cutter-supporting surface of one or more of the bit primary blades in the cone region. In a different example embodiment, backup cutting elements may be provided on the cutter-supporting surface of any one or more secondary blades in the shoulder and/or gage region. In another example embodiment, backup cutting elements may be provided on the cutter-supporting surface of any one or more primary blades in the gage region. In yet another example embodiment, the primary and/or secondary blades may have at least two rows of backup cutting elements disposed on the cutter-supporting surfaces.

Primary cutting elements may be placed adjacent one another generally in a first row extending radially along each primary blade of a bit and along each secondary blade of a bit. Further, backup cutting elements may be placed adjacent one another generally in a second row extending radially along each primary blade in the shoulder region. Suitably, the backup cutting elements form a second row that may extend along each primary blade in the shoulder region, cone region and/or gage region. Backup cutting elements may be placed behind the primary cutting elements on the same primary blade, wherein backup cutting elements trail the primary cutting elements on the same primary blades.

In general, primary cutting elements as well as backup cutting elements need not be positioned in rows, but may be mounted in other suitable arrangements provided each cutting element is either in a leading position (e.g., primary cutting element) or a trailing position (e.g., backup cutting element). Examples of suitable arrangements may include without limitation, rows, arrays or organized patterns, randomly, sinusoidal pattern, or combinations thereof. Further, in other embodiments, additional rows of cutting elements may be provided on a primary blade, secondary blade, or combinations thereof.

In some embodiments of the present disclosure, rolling cutter placement design criteria may be set so that rolling cutters are positioned in the areas of the bit experiencing the greatest wear. For example, rolling cutters may be placed in the shoulder region of a drill bit. Referring to FIG. 4, a profile 39 of a bit 10 is shown as it would appear with all blades and all cutting elements (including primary cutting elements and back up cutting elements) rotated into a single rotated profile. A blade profile 39 (most clearly shown in the right half of bit 10 in FIG. 4) may generally be divided into three regions conventionally labeled cone region 24, shoulder region 25, and gage region 26. Cone region 24 comprises the radially innermost region of bit 10 (e.g., cone region 24 is the central most region of bit 10) and composite blade profile 39 extending generally from bit axis 11 to shoulder region 25. As shown in FIG. 4, in most fixed cutter bits, cone region 24 is generally concave. Adjacent cone region 24 is shoulder (or the upturned curve) region 25. Thus, composite blade profile 39 of bit 10 includes one concave region-cone region 24, and one convex region-shoulder region 25. In most fixed cutter bits, shoulder region 25 is generally convex. Moving radially outward, adjacent shoulder region 25 is the gage region 26 which extends parallel to bit axis 11 at the outer radial periphery 23 of composite blade profile 39. Outer radius 23 extends to and therefore defines the full gage diameter of bit 10. Cone region 24 is defined by a radial distance along the x-axis measured from central axis 11. It is understood that the x-axis is perpendicular to central axis 11 and extends radially outward from central axis 11. Cone region 24 may be defined by a percentage of outer radius 23 of bit 10. The actual radius of cone region 24, measured from central axis 11, may vary from bit to bit depending on a variety of factors including without limitation, bit geometry, bit type, location of one or more secondary blades, location of back up cutting elements 50, or combinations thereof. The axially lowermost point of convex shoulder region 25 and composite blade profile 39 defines a blade profile nose 27. At blade profile nose 27, the slope of a tangent line 27a to convex shoulder region 25 and composite blade profile 39 is zero. Thus, as used herein, the term “blade profile nose” refers to the point along a convex region of a composite blade profile of a bit in rotated profile view at which the slope of a tangent to the composite blade profile is zero. For most fixed cutter bits (e.g., bit 10), the composite blade profile includes only one convex shoulder region (e.g., convex shoulder region 25), and only one blade profile nose (e.g., nose 27). Advantageously, by placing rolling cutters in areas of the bit experiencing the greatest wear, for example at the shoulder region 26 of a bit, the wear rate of the bit may be improved.

Further, in a particular embodiment, a bit may have cutting elements placed in a single set configuration with rolling cutters placed in areas of the bit experiencing the greatest wear. In another embodiment, a bit may have cutting elements placed in a plural set configuration, wherein at least one rolling cutter is placed in areas of the bit experiencing the greatest wear.

In addition to varying the placement of rolling cutters, other strategies may be employed to enhance the life of a drill bit. Specifically, in one or more embodiments, the use of different chamfer sizes depending on the radial location and/or type of cutting element (fixed or rotatable) may be utilized. For example, one design strategy is to use a set of rolling cutters that employ a first chamfer, and a second set of non-rolling cutters that employ a second chamfer. In one embodiment, the rolling cutters have a “small chamfer” while the non-rolling cutters employ a “large chamfer,” but variations are within the scope of the present invention. In another embodiment, the rolling cutters have a “large chamfer” while the non-rolling cutters employ a “small” chamfer. In another embodiment, cutters (rolling or fixed) in a radially interior region of cutting profile may have a “large” chamfer while the outer radial positions may be rolling cutters having a “small” chamfer. As used herein, the terms “small” and “large” are used as relative terms, i.e., the “small chamfer” is simply smaller than the “large chamfer.”

FIGS. 5A and 5B depict an example “smaller chamfer” cutting element 1000 comprised of a superabrasive, diamond table 1012 supported by a carbide substrate 1014. The interface 1016 between the PDC diamond table 1012 and the substrate 1014 may be planar or non-planar, according to many varying designs for same as known in the art. Cutting element 1000 is substantially cylindrical and symmetrical about longitudinal axis 1018, although such symmetry is not required and non-symmetrical cutters are known in the art.

Cutting face 1020 of cutting element 1000, to be oriented on a bit facing generally in the direction of bit rotation, extends substantially transversely to such direction, and to axis 1018. The surface 1022 of the central portion of cutting face 1020 is planar as shown, although concave, convex, ridged or other substantially, but not exactly, planar surfaces may be employed. A chamfer 1024 extends from the periphery of surface 1022 to cutting edge 1026 at the sidewall 1028 of diamond table 1012. Chamfer 1024 and cutting edge 1026 may extend about the entire periphery of table 1012, or only along a periphery portion to be located adjacent the formation to be cut.

Chamfer 1024 may comprise a 0.012 inch at 45° conventional chamfer, or may lie at some other angle, as referenced with respect to the chamfer 1124 of cutter 1110 described below. For conventional PDC cutters, a conventional chamfer size (radial width) and angle would be 0.012 inch (looking at and perpendicular to the cutting face of the diamond table) oriented at a 45° angle with respect to the longitudinal cutter axis, thus providing a larger radial width as measured on the chamfer surface itself. While 0.012 inch chamfer size is referenced as an example (within conventional tolerances), the present disclosure relates to the use of multiple chamfer sizes.

FIGS. 6 through 8 depict an exemplary “larger chamfer” cutting element 1110 comprised of a superabrasive, diamond table 1112 supported by a carbide substrate 1114.

The interface 1116 between the diamond table 1112 and the substrate 1114 may be planar or non-planar, according to many varying designs for same as known in the art (see especially FIGS. 7 and 8). Cutting element 1110 is substantially cylindrical and symmetrical about longitudinal axis 1118, although such symmetry is not required and non-symmetrical cutters are known in the art.

Cutting face 1120 of cutting element 1110, to be oriented on a bit facing generally in the direction of bit rotation, extends substantially transversely to such direction, and to axis 1118. The surface 1122 of the central portion of cutting face 1120 is planar as shown, although concave, convex, ridged or other substantially, but not exactly, planar surfaces may be employed. A chamfer 1124 extends from the periphery of surface 1122 to cutting edge 1126 at the sidewall 1128 of diamond table 1112. Chamfer 1124 and cutting edge 1126 may extend about the entire periphery of table 1112, or only along a periphery portion to be located adjacent the formation to be cut. Chamfer 1124 may comprise a surface oriented at 45° to axis 1118, of a width, measured looking at and perpendicular to the cutting face 1120, of 0.018 inches.

However, as mentioned above, the “small chamfer” and “large chamfer” may be relative to one another, and chamfer sizes other than 0.012 and 0.018 inches may certainly be used. In one or more embodiments, a first chamfer size may fall within the range of 0.001 to about 0.010 inch (measured as previously described), with 0.006 to 0.008 inches being an example sub-range. In one or more embodiments, a second chamfer size may fall within the range of 0.008 to 0.020 inches, with 0.010 to about 0.014 inches and 0.014 to 0.020 as being example sub-ranges. In one or more embodiments, a third chamfer size may fall within a range of 0.020 to 0.035 inches, and a fourth chamfer size may fall within a range of 0.035 inch to 0.060 (or larger). Thus, the “small chamfer” and “large chamfer” may be selected from the above ranges (or sub-ranges), and the “small chamfer” may be, but does not have to be, selected from the first size range or second size range, for example. It is also within the scope of the present disclosure that the different chamfer sizes may be selected within the same size range (such as in FIGS. 5-8 above), so long as the sizes selected are themselves varied. Further, in one embodiment, the smaller chamfer may have an upper limit of any of 0.018, 0.016, 0.014, 0.012, or 0.010 inches, and the larger chamfer may have a lower limit of any of 0.012, 0.014, 0.016, 0.018, 0.020, or 0.024. Further, it is also within the scope of the present disclosure that a third or intermediate chamfer size (or more) may also be used.

For either of the cutting element types, chamfer angles of about 10° to about 80° to axis 1118 may be useful, with angles in the range of about 30° to about 60° being used in particular embodiments. The effective rake angle of a chamfer with respect to the formation may be altered by changing the back rake of the cutter. Further, it is also within the scope of the present disclosure that one or more cutting elements may incorporate a variable bevel, as described in U.S. Pat. No. 7,726,420, which is assigned to the present assignee and herein incorporated by reference in its entirety.

Specifically, embodiments disclosed herein include rolling cutters, or non-rolling cutters, disposed in a nose and/or shoulder of the bit, having small bevel (or chamfer) size. In one or more other embodiments, the rolling or non-rolling cutters disposed in a nose and/or shoulder of the bit can have a large bevel (or chamfer). However, using a small bevel on the rolling cutters in a shoulder area may provide a number of advantages. First, by employing a small bevel, there is a lower force required to rotate the rolling cutter, which may enhance the rolling cutter life by allowing more even wear. In addition, much of the cutting action in directional drilling applications and other applications occurs at the shoulder, and simply by the larger path drilled, cutting elements in the shoulder tend to experience more wear than cutting elements in radially interior locations (such as the cone). By having a smaller bevel in the shoulder, the rolling cutters have a higher diamond volume, which allows the cutters to cut more effectively. Additionally, the rolling cutters wear in a different manner than conventional, fixed cutters. Specifically, the wear pattern observed effectively enlarges the chamfer size by creating an even wear around the entire circumference.

Conversely, by providing large bevel cutting elements (rolling or non-rolling) adjacent the center, (such as in the cone and/or nose of the bit), better impact resistance and durability is provided to those cutting elements, which is important around the center of the bit, particularly as these cutting elements tend to experience the highest depth of cut. Moreover, it is believed that such an arrangement may help to avoid bit slip, and torque spikes associated with bit slip.

Further, it is also within the scope of the present disclosure that the cutting elements within nose may have a distinct chamfer size as compared to the cone and shoulder. For example, in one or more embodiments, the nose may have an intermediate chamfer size. Further, it is also within the scope of the present disclosure that multiple chamfer sizes may be used within a single zone (i.e., cone, nose, shoulder).

Additionally, as mentioned above, there is also a region of the cutting profile referred to as the gage. In one or more embodiments, the gage region may incorporate any of rolling cutters having a “small” chamfer, rolling cutters having a “large chamfer”, non-rolling cutters having a “small” chamfer, or non-rolling cutters having a “large chamfer” (relative to radially interior cutting elements). In particular embodiments, the gage cutting element may have a large chamfer, or may even be a pre-flat, as that term is understood by those skilled in the art.

In one particular embodiment the effect of varying the bevel size on a rolling cutter for a given formation and weight on bit combination was analyzed. In this embodiment, carthage marble, having a compressive strength of 3,000 psi was used as an exemplary rock formation. The weight on bit was set at 20,000 lbs. The cutting and side forces seen by two rolling cutters having different bevels was then determined using analysis software such as disclosed in U.S. Pat. No. 7,844,426, which is expressly incorporated by reference in its entirety.

In this embodiment a “standard” bevel of 0.012 in. at 45 degrees was analyzed, as well as a “medium” bevel of 0.016 in. at 45 degrees. The results from the software are shown in FIGS. 9 and 10. As shown in FIG. 9, the standard bevel (marked as 1802) has a higher cutting force than the medium bevel (shown at 1804). Similarly, in FIG. 10, the standard bevel (1902) has a higher side force than the medium bevel (1904). As a result, the standard bevel is predicted to both penetrate deeper into the formation (based on the higher cutting force) than the medium bevel. As a result, it is believed that having a smaller bevel size on the rolling cutters than on the non-rolling cutters is advantageous in this embodiment.

In selected embodiments, because cutters in the cone/nose area see higher overall forces than the cutters in the shoulder/flank area, larger bevels are preferred in the cone/nose area, to provide increased cutter durability in this area. Typical bevel size mix for cone/nose to shoulder/flank area should be 0.012″-0.030″ to 0.010″-0.025″. The Table below provides representative groups of bevel size mixes (where the rolling cutters are placed in the shoulder/flank, and non-rolling or rolling cutters are placed in the cone/nose). All bevels in the table are at 45 degrees.

		Cone/nose bevel	Shoulder/Flank
	Example	size	bevel size
	Ex 1	0.010″	0.006-0.010″
	Ex 2	0.012″	0.008-0.012″
	Ex 3	0.016″	0.010-0.016″
	Ex 4	0.020″	0.012-0.020″
	Ex 5	0.025″	0.016-0.025″

The table above is exemplary only, and other embodiments are within the scope of the present invention. Within the table, however, when selecting a cone/nose bevel size, the shoulder/flank bevel size will be set smaller than the cone/nose.

Bits having a plurality of rolling cutters of the present disclosure may include at least two rolling cutters, for example at least three, at least 4, at least 6, at least 9, or at least 12 rolling cutters, with any remaining cutting elements being conventional fixed cutting elements. In one or more embodiments, two or more primary blades may contain one or more rolling cutters, for example each primary blade may contain one or more rolling cutters. In one or more additional embodiments, one or more secondary blades may also contain one or more rolling cutters, for example each secondary blade may contain one or more rolling cutters. In one or more embodiments, all cutting elements may be rotatable.

Other Design Options

According to some embodiments, the extension height of cutting element cutting faces (i.e., the upper surface of the cutting table of the cutting element) may vary. In an example embodiment, cutting faces of primary cutting elements may have a greater extension height than the cutting faces of backup cutting elements (i.e., “on-profile” primary cutting elements engage a greater depth of the formation than the backup cutting elements; and the backup cutting elements are “off-profile”). As used herein, the term “off-profile” may be used to refer to a structure extending from the cutter-supporting surface (e.g., the cutting element, depth-of-cut limiter, etc.) that has an extension height less than the extension height of one or more other cutting elements that define the outermost cutting profile of a given blade. As used herein, the term “extension height” is used to describe the distance a cutting face extends from the cutter-supporting surface of the blade to which it is attached. In some example embodiments, one or more backup cutting faces may have the same or a greater extension height than one or more primary cutting faces. Such variables may impact the properties of the bottom hole assembly, in particular the drill bit, which can affect the arrangement or positioning of the different types of cutting elements. For example, “on-profile” cutting elements may experience a greater amount of wear and load than “off-profile” cutting elements. Also, primary cutting elements may experience a greater amount of wear and load than backup cutting elements.

Referring to FIG. 11, a cutting structure profile of a bit according to one embodiment is shown. As shown in this embodiment, cutters 2600 positioned on a blade 2602 may have side rake or back rake. Side rake is defined as the angle between the cutting face 2605 and the radial plane of the bit (x-z plane). When viewed along the z-axis, a negative side rake results from counterclockwise rotation of the cutter 2600, and a positive side rake, from clockwise rotation. Back rake is defined as the angle subtended between the cutting face 2605 of the cutter 2600 and a line parallel to the longitudinal axis 2607 of the bit. In one embodiment, a cutter may have a side rake ranging from 0 to ±45 degrees, for example ±5 to ±35 degrees, ±10 to ±35 degrees or ±15 to ±30 degrees. In a particular embodiment, the direction (positive or negative) of the side rake may be selected based on the cutter distribution, i.e., whether the cutters are arranged in a forward or reverse spiral configuration. For example, in embodiments, if cutters are arranged in a reverse spiral, positive side rake angles may be particularly desirable. Conversely, if cutters are arranged in a forward spiral, negative side rake angles may be particularly desirable.

In some embodiments, each rolling cutter placed in the nose and/or shoulder region of the bit may have a side rake ranging from 10 to 30 degrees or −10 to −30 degrees. In other embodiments, each rolling cutter placed in the nose and/or shoulder region of the bit may have a side rake ranging from 20 to 30 degrees or −20 to −30 degrees. In some embodiments, rolling cutters radially outside the shoulder, i.e., in the gage region, may range from 5 to 35 degrees or −5 to −35 degrees. In more particular embodiments, rolling cutters in the gage region may be >5 degrees, >10 degrees, >15 degrees, >20 degrees, >25 degrees, >30 degrees, and/or <10 degrees, <15 degrees, <20 degrees, <25, <30 degrees, <35 degrees, with any of such angles being positive or negative, and any upper limit being used with any lower limit. Further, in some embodiments, cutters may be placed in the cone region of the bit may have a side rake of less than 20 degrees or ranging from 10 to 15 degrees in more particular embodiments. In various embodiments, cutters in the cone region may be either fixedly attached or may be rolling, but may have such side rake range if fixed or rolling. It is specifically understood that any of the side rake angles for any region may be used in singly or in combination with any of the other ranges for other regions. Further, in one or more embodiments, the fixed cutters may be oriented at a side rake that is less than the side rake of the rotatable cutting elements, such as at side rake angles of less than 10 degrees.

In another embodiment, a cutter may have a back rake ranging from about 5 to 35 degrees. In a particular embodiment, the back rake angle of a rolling cutter may be >5 degrees, >10 degrees, >15 degrees, >20 degrees, >25 degrees, >30 degrees, and/or <10 degrees, <15 degrees, <20 degrees, <25, <30 degrees, <35 degrees, with any upper limit being used with any lower limit. Such back rake angles may be used for rolling cutters in any of the cone, nose, shoulder or gage region of the bit, but in particular embodiments, a back rake of between 10 and 35 degrees (or 15 to 35 degrees or 20 to 30 degrees in more particular embodiments) may be particularly suitable for cutters in the nose and/or shoulder region of the bit. A cutter may be positioned on a blade with a selected back rake to assist in removing drill cuttings and increasing rate of penetration. A cutter disposed on a drill bit with side rake may be forced forward in a radial and tangential direction when the bit rotates. In some embodiments, because the radial direction may assist the movement of a rotatable cutting element, such rotation may allow greater drill cuttings removal and provide an improved rate of penetration. One of ordinary skill in the art may realize that any back rake and side rake combination may be used with the cutting elements of the present disclosure to enhance rotatability and/or improve drilling efficiency.

In one or more other embodiments, cutting elements may be disposed in cutting tools that do not incorporate back rake and/or side rake. When the cutting element is disposed on a drill bit with substantially zero degrees of side rake and/or back rake, the cutting force may be random instead of pointing in one general direction. The random forces may cause the cutting element to have a discontinuous rotating motion. Generally, such a discontinuous motion may not provide the most efficient drilling condition, however, in certain embodiments, it may be beneficial to allow substantially the entire cutting surface of the insert to contact the formation in a relatively even manner. In such an embodiment, alternative inner rotatable cutting element and/or cutting surface designs may be used to further exploit the benefits of rotatable cutting elements. Further, in one or more other embodiments, a bevel or chamfer size, angle, or design may be selected to accommodate for a zero back or side rake.

Exemplary Embodiments of Rolling Cutters

Rolling cutters of the present disclosure may include various types and sizes of rolling cutters. For example, rolling cutters may be formed in sizes including, but not limited to, 9 mm, 13 mm, 16 mm, and 19 mm. Further, the type of rolling cutter is of no limitation to the present disclosure. Rather, it may be of any type and/or include any feature such as those described in U.S. Pat. No. 7,703,559, U.S. patent application Ser. Nos. 13/152,626, 61/479,183, 61/479,151, or 61/556,454, all of which are assigned to the present assignee and herein incorporated by reference in their entirety. Exemplary embodiments of rolling cutters are also described below; however, the types of rotatable cutting elements that may be used with the present disclosure are not necessarily limited to those described below.

Referring now to FIGS. 12 and 13, a rotatable cutting element assembly according to embodiments of the present disclosure is shown. Particularly, an exploded view of the cutting element is shown in FIG. 12, including a rolling cutter 300, a retaining ring 320, and a sleeve 330. The rolling cutter 300 has an axis of rotation A extending longitudinally therethrough, a cutting face 302, and a body 304 extending axially downward from the cutting face 302. The body 304 has an outer surface 306 and a circumferential groove 310 formed therein. Particularly, the circumferential groove 310 is formed on a shaft 308 portion of the body 304 and extends a height axially along the shaft 308 and around the circumference of the shaft 308. Further, a cutting edge 303 is formed at the intersection of the cutting face 302 and the outer surface 306 of the rolling cutter 300. As shown, the cutting face 302 and cutting edge 303 may be formed from a diamond or other ultra-hard material table 305.

A cross-sectional view of the assembled cutting element is shown in FIG. 13, wherein the rolling cutter 300 is partially disposed within the sleeve 330, and wherein the retaining ring 320 is disposed between the rolling cutter 300 and the sleeve 330, within the circumferential groove 310. Particularly, the shaft 308 portion of the rolling cutter 300 is disposed within the sleeve 330. As shown, the portion of the rolling cutter 300 outside of the sleeve 330 has a first diameter X₁, and the shaft 308 has a second diameter X₂, wherein the first diameter X₁ is larger than the second diameter X₂. The sleeve 330 has a first inner diameter Y ₁ and a second inner diameter Y ₂, wherein the second inner diameter Y ₂ is larger than the first inner diameter Y ₁ and located at a lower axial position than the first inner diameter Y₁. The second diameter X₂ of the shaft 308 may be substantially equal to the first inner diameter Y₁ of the sleeve, so that the shaft may fit within the sleeve 330. As used herein, a substantially equal diameter includes a sufficient gap to allow the rolling cutter 300 to rotate within the sleeve 330. For example, the gap formed by difference between the shaft second diameter X₂ and the sleeve first inner diameter Y₁ may range from about 0.001 to 0.030 inches. Further, the sleeve 330 may have an outer diameter Y₃. As shown, the portion of the rolling cutter 300 remaining outside the sleeve 330 may have a first diameter X₁ that is substantially equal to the sleeve outer diameter Y₃, such that the assembled cutting element has a cylindrical shape. However, according to other embodiments, the rolling cutter first diameter X₁ be greater than or less than the sleeve outer diameter Y₃.

The sleeve 330 may have varying inner diameter sizes in addition to the first inner diameter Y₁ and the second inner diameter Y₂. For example, as shown in FIG. 5, a top end 331 of the sleeve 330 may have a gradually increasing inner diameter from the first inner diameter Y₁. According to some embodiments, a sleeve may also have an inner diameter smaller than the second inner diameter located axially downward from the second inner diameter and from the circumferential groove of an assembled cutting element. In such embodiments, a retaining ring may protrude from the circumferential groove into the space provided by the second inner diameter.

The circumferential groove 310 formed around the outer surface of the rolling cutter body may be axially positioned along the shaft 308 so that the circumferential groove 320 abuts the transition 332 between the sleeve first inner diameter Y₁ and second inner diameter Y₂. In other words, the circumferential groove 320 and the sleeve second inner diameter Y₂ both extend a distance in the same axial direction from the same axial position along the assembled cutting element. For example, as shown in FIG. 5, the circumferential groove has a first sidewall 311, a second side wall 312, and a base surface 313. The circumferential groove 310 extends a height axially along the shaft 308 from the first sidewall 311 to the second sidewall 312. The first sidewall 311 is located axially at the same position along the assembled cutting element as the transition 332 to the second inner diameter Y₂, thereby aligning the circumferential groove 310 with the transition 332 to the second inner diameter Y2 to create an interface surface 314 adjacent to the retaining ring 320. The retaining ring 320 may rotate around the interface surface 314, and the rolling cutter 300 may rotate within the sleeve 330, such that the transition surface 332 and first sidewall 311 maintain the interface surface 314 with the retaining ring 320.

As assembled, the cutting element has a retaining ring 320 disposed in the circumferential groove 310, wherein the retaining ring 320 extends at least around the entire circumference of the shaft 308. For example, in the embodiment shown in FIGS. 12 and 13, the retaining ring 320 may extend greater than 1.5 times around the circumference of the shaft 308. As shown in FIG. 13, the retaining ring 320 protrudes from the circumferential groove 310 to contact the second inner diameter Y₂ of the sleeve 330, thereby retaining the rolling cutter 300 within the sleeve 330. However, according to other embodiments, the retaining ring may protrude from the circumferential groove without contacting the second inner diameter to retain the rolling cutter within the sleeve.

However, the present disclosure is not limited to the rolling cutter type illustrated in FIGS. 12 and 13, but instead, as mentioned above, any type of rolling cutter may be used on the bits and tools of the present disclosure.

In various embodiments, the cutting face of the inner rotatable cutting element may include an ultra hard layer that may be comprised of a polycrystalline diamond table, a thermally stable diamond layer (i.e., having a thermal stability greater than that of conventional polycrystalline diamond, 750° C.), or other ultra hard layer such as a cubic boron nitride layer.

As known in the art, thermally stable diamond may be formed in various manners. A typical polycrystalline diamond layer includes individual diamond “crystals” that are interconnected. The individual diamond crystals thus form a lattice structure. A metal catalyst, such as cobalt, may be used to promote recrystallization of the diamond particles and formation of the lattice structure. Thus, cobalt particles are typically found within the interstitial spaces in the diamond lattice structure. Cobalt has a significantly different coefficient of thermal expansion as compared to diamond. Therefore, upon heating of a diamond table, the cobalt and the diamond lattice will expand at different rates, causing cracks to form in the lattice structure and resulting in deterioration of the diamond table.

To obviate this problem, strong acids may be used to “leach” the cobalt from a polycrystalline diamond lattice structure (either a thin volume or entire tablet) to at least reduce the damage experienced from heating diamond-cobalt composite at different rates upon heating. Examples of “leaching” processes can be found, for example, in U.S. Pat. Nos. 4,288,248 and 4,104,344. Briefly, a strong acid, typically hydrofluoric acid or combinations of several strong acids may be used to treat the diamond table, removing at least a portion of the co-catalyst from the PDC composite. Suitable acids include nitric acid, hydrofluoric acid, hydrochloric acid, sulfuric acid, phosphoric acid, or perchloric acid, or combinations of these acids. In addition, caustics, such as sodium hydroxide and potassium hydroxide, have been used to the carbide industry to digest metallic elements from carbide composites. In addition, other acidic and basic leaching agents may be used as desired. Those having ordinary skill in the art will appreciate that the molarity of the leaching agent may be adjusted depending on the time desired to leach, concerns about hazards, etc.

By leaching out the cobalt, thermally stable polycrystalline (TSP) diamond may be formed. In certain embodiments, only a select portion of a diamond composite is leached, in order to gain thermal stability without losing impact resistance. As used herein, the term TSP includes both of the above (i.e., partially and completely leached) compounds. Interstitial volumes remaining after leaching may be reduced by either furthering consolidation or by filling the volume with a secondary material, such by processes known in the art and described in U.S. Pat. No. 5,127,923, which is herein incorporated by reference in its entirety.

Alternatively, TSP may be formed by forming the diamond layer in a press using a binder other than cobalt, one such as silicon, which has a coefficient of thermal expansion more similar to that of diamond than cobalt has. During the manufacturing process, a large portion, 80 to 100 volume percent, of the silicon reacts with the diamond lattice to form silicon carbide which also has a thermal expansion similar to diamond. Upon heating, any remaining silicon, silicon carbide, and the diamond lattice will expand at more similar rates as compared to rates of expansion for cobalt and diamond, resulting in a more thermally stable layer. PDC cutters having a TSP cutting layer have relatively low wear rates, even as cutter temperatures reach 1200° C. However, one of ordinary skill in the art would recognize that a thermally stable diamond layer may be formed by other methods known in the art, including, for example, by altering processing conditions in the formation of the diamond layer.

The substrate on which the cutting face is disposed may be formed of a variety of hard or ultra hard particles. In one embodiment, the substrate may be formed from a suitable material such as tungsten carbide, tantalum carbide, or titanium carbide. Additionally, various binding metals may be included in the substrate, such as cobalt, nickel, iron, metal alloys, or mixtures thereof. In the substrate, the metal carbide grains are supported within the metallic binder, such as cobalt. Additionally, the substrate may be formed of a sintered tungsten carbide composite structure. It is well known that various metal carbide compositions and binders may be used, in addition to tungsten carbide and cobalt. Thus, references to the use of tungsten carbide and cobalt are for illustrative purposes only, and no limitation on the type substrate or binder used is intended. In another embodiment, the substrate may also be formed from a diamond ultra hard material such as polycrystalline diamond and thermally stable diamond. While the illustrated embodiments show the cutting face and substrate as two distinct pieces, one of skill in the art should appreciate that it is within the scope of the present disclosure the cutting face and substrate are integral, identical compositions. In such an embodiment, it may be preferable to have a single diamond composite forming the cutting face and substrate or distinct layers.

The cutting elements of the present disclosure may be incorporated in various types of downhole cutting tools, including for example, as cutters in fixed cutter bits or as inserts in roller cone bits, reamers, hole benders, or any other tool that may be used to drill earthen formations. Cutting tools having the cutting elements of the present disclosure may include a single rotatable cutting element with the remaining cutting elements being conventional cutting elements, all cutting elements being rotatable, or any combination therebetween of rotatable and conventional cutting elements.

The cutting elements of the present disclosure may be attached to or mounted on a drill bit by a variety of mechanisms, including but not limited to conventional attachment or brazing techniques in a cutter pocket, as well as by mechanical means. It is also within the scope of the present disclosure that in some embodiments, an inner rotatable cutting element may be mounted on the bit directly such that the bit body acts as the outer support element, i.e., by inserting the inner rotatable cutting element into a hole that may be subsequently blocked to retain the inner rotatable cutting element within.

Advantageously, embodiments disclosed herein may provide for at least one of the following. Cutting elements that include a rotatable cutting portion may avoid the high temperatures generated by typical fixed cutters. Because the cutting surface of prior art cutting elements is constantly contacting formation, heat may build-up that may cause failure of the cutting element due to fracture. Embodiments in accordance with the present disclosure may avoid this heat build-up as the edge contacting the formation changes. The lower temperatures at the edge of the cutting elements may decrease fracture potential, thereby extending the functional life of the cutting element. By decreasing the thermal and mechanical load experienced by the cutting surface of the cutting element, cutting element life may be increased, thereby allowing more efficient drilling.

Further, rotation of a rotatable portion of the cutting element may allow a cutting surface to cut formation using the entire outer edge of the cutting surface, rather than the same section of the outer edge, as provided by the prior art. The entire edge of the cutting element may contact the formation, generating more uniform cutting element edge wear, thereby preventing formation of a local wear flat area. Because the edge wear is more uniform, the cutting element may not wear as quickly, thereby having a longer downhole life, and thus increasing the overall efficiency of the drilling operation.

Additionally, because the edge of the cutting element contacting the formation changes as the rotatable cutting portion of the cutting element rotates, the cutting edge may remain sharp. The sharp cutting edge may increase the rate of penetration while drilling formation, thereby increasing the efficiency of the drilling operation. Further, as the rotatable portion of the cutting element rotates, a hydraulic force may be applied to the cutting surface to cool and clean the surface of the cutting element.

Some embodiments may protect the cutting surface of a cutting element from side impact forces, thereby preventing premature cutting element fracture and subsequent failure. Still other embodiments may use a diamond table cutting surface as a bearing surface to reduce friction and provide extended wear life. As wear life of the cutting element embodiments increase, the potential of cutting element failure decreases. As such, a longer effective cutting element life may provide a higher rate of penetration, and ultimately result in a more efficient drilling operation.

Advantageously, therefore, embodiments disclosed herein may provide for improved drilling performance, in directional and non-directional applications, and/or may increase cutter life. Also advantageously, by providing larger sized bevels in the cone region, when the bit is subject to directional drilling (under sliding conditions), there can be a reduction in cutter breakage. This is due to the weight transfer from the drilling string to the bit which can be intermittent and hard to control, thus, could accidently damage the cone/nose cutters having a smaller bevel size due to sudden depth of cut increase.

Also, by using a larger bevel in the cone/nose area, the DOC (depth of cut) could be limited by the larger bevel in the cone/nose area to prevent accidental deeper bite into the rock which creates high torque and vibration during transitional drilling. This is especially important when the bit is used in directional drilling where tool face control is more important than the rate of penetration.

Also advantageously, by providing the smaller bevel on the shoulder/flank area there may be less contact area as compared to a larger bevel if the ROP is the same, thus further reducing the torsional spikes. Also advantageously, with rolling cutters installed in the shoulder/flank area, the smaller bevel (comparing to the cutters in the cone/nose area) could also have less side/cutting force as compared to a larger bevel, enabling better rotation due to less friction within the rolling cutter assembly, leading to enhanced durability.

While the above describes a situation where the rolling cutters have a first chamfer and the non-rolling cutters have a second chamfer, it is also contemplated that mixed chamfers may be used on the same type of cutter. In other words, it is expressly within the scope of the present invention that the rolling cutters may be mixed smaller and larger chamfers. One other option is to provide a depth limiter on the non-rolling cutters, instead of a large bevel.

Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.

Claims

1. A cutting tool comprising:

a tool body having a plurality of blades extending radially therefrom;

a plurality of rotatable cutting elements, having a first chamfer mounted on at least one of the plurality of blades; and

a plurality of non-rotatable cutting elements, having a second, distinct chamfer mounted on at least one of the plurality of blades.

2. The cutting tool of claim 1, wherein the first chamfer is smaller than the second chamfer.

3. The cutting tool of claim 2, wherein the first chamfer is no more than 0.014 inches.

4. The cutting tool of claim 3, wherein the first chamfer is no more than 0.012 inches.

5. The cutting tool of claim 1, wherein the first chamfer is larger than the second chamfer.

6. The cutting tool of claim 1, wherein the plurality of rotatable cutting elements are located in a shoulder region of the blade.

7. The cutting tool of claim 1, where at least one rotatable cutting element is disposed in a nose region of the blade.

8. The cutting tool of claim 7, wherein the at least one rotatable cutting element in the nose region has a third chamfer.

9. The cutting tool of claim 1, wherein the plurality of non-rotatable cutting elements are located in a cone region of the blade.

10. The cutting tool of claim 1, where at least one non-rotatable cutting element is disposed in a nose region of the blade.

11. The cutting tool of claim 10, wherein the at least one non-rotatable cutting element in the nose region has a third chamfer.

12. The cutting tool of claim 1, wherein the second chamfer is at least 0.014 inches.

13. The cutting tool of claim 12, wherein the second chamfer is at least 0.016 inches.

14. A cutting tool comprising:

a tool body having a plurality of blades extending radially therefrom;

a plurality of rotatable cutting elements, wherein the plurality of rotatable cutting elements have at least two differing chamfer sizes based on their positioning along the plurality of blades.

15. The cutting tool of claim 14, further comprising a plurality of non-rotatable cutting elements

16. The cutting tool of claim 15, wherein the plurality of non-rotatable cutting element have a chamfer distinct from at least one rotatable cutting element.

17. The cutting tool of claim 14, wherein at least one rotatable cutting element located in the cone has a larger chamfer than at least one rotatable cutting element located in the shoulder.

18. The cutting tool of claim 14, wherein at least one rotatable cutting elements located in the cone has a smaller chamfer than at least one rotatable cutting element located in the shoulder.

19. The cutting tool of claim 17, wherein the at least one rotatable cutting element in the nose region has a chamfer in between the chamfer size of the at least one rotatable cutting element located and in the cone and the at least one rotatable cutting element located in the nose.