WO2024044707A1

WO2024044707A1 - Modular drill bits with mechanically attached cutter element assemblies

Info

Publication number: WO2024044707A1
Application number: PCT/US2023/072850
Authority: WO
Inventors: David P. Miess
Original assignee: National Oilwell Varco, L.P.
Priority date: 2022-08-24
Filing date: 2023-08-24
Publication date: 2024-02-29

Abstract

A modular fixed cutter drill bit for drilling an earthen formation has a central axis and a cutting direction of rotation about the central axis. The drill bit includes a bit body configured to rotate about the central axis in the cutting direction of rotation. The bit body includes a bit face. In addition, the drill bit includes a blade extending radially along the bit face. The blade has a leading side relative to the cutting direction of rotation, a trailing side relative to the cutting direction of rotation, and a cutter-supporting surface extending from the leading side to the traling side. The blade includes a socket extending from the cutter-supporting surface of the blade. Further, the drill bit includes a cutter element assembly mounted to the blade and extending from a cutter-supporting surface of the blade. The cutter element assembly includes a pod seated in the socket and fixably attached to the blade and a cutter element fixably attached to the pod.

Description

MODULAR DRILL BITS WITH MECHANICALLY ATTACHED CUTTER ELEMENT ASSEMBLIES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. provisional patent application Serial No. 63/400,595 filed August 24, 2022, and entitled "Modular Drill Bits With Mechanically Attached Cutters," which is hereby incorporated herein by reference in its entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

FIELD

[0003] The present disclosure relates generally to earth-boring bits used to drill a borehole for the ultimate recovery of oil, gas or minerals. More particularly, the present disclosure relates to modular fixed cutter drill bits with mechanical attached cutter elements, as well as to methods of making the same and to methods of using the same.

BACKGROUND

[0004] An earth-boring drill bit is typically mounted on the lower end of a drill string and is rotated by rotating the drill string at the surface or by actuation of downhole motors or turbines, or by both methods. With weight applied to the drill string, the rotating drill bit engages the earthen formation and proceeds to form a borehole along a predetermined path toward a target zone. The borehole thus created has a diameter generally equal to the diameter or "gage" of the drill bit.

[0005] Fixed cutter bits, also known as rotary drag bits, are one type of drill bit commonly used to drill boreholes. Fixed cutter bit designs include a plurality of blades angularly spaced about a bit face. The blades generally project radially outward along the bit face and form flow channels therebetween. Cutter elements are typically grouped and mounted on the blades. The configuration or layout of the cutter elements on the blades may vary widely, depending on a number of factors. One of these factors is the formation itself, as different cutter element layouts engage and cut the various strata with differing results and effectiveness.

[0006] The cutter elements disposed on the several blades of a fixed cutter bit are typically formed of extremely hard materials and include a layer of polycrystalline diamond ("PCD") material. In the typical fixed cutter bit, each cutter element includes an elongate and generally cylindrical support member that is received and secured in a pocket formed in the surface of one of the several blades. In addition, each cutter element typically has a hard cutting layer of polycrystalline diamond or other superabrasive material such as cubic boron nitride, thermally stable diamond, polycrystalline cubic boron nitride, or ultrahard tungsten carbide (meaning a tungsten carbide material having a wear-resistance that is greater than the wear-resistance of the material forming the substrate), as well as mixtures or combinations of these materials. The cutting layer is mounted to one end of the corresponding support member, which is typically formed of tungsten carbide.

[0007] While the bit is rotated, drilling fluid is pumped through the drill string and directed out of the face of the drill bit. The fixed cutter bit typically includes nozzles or fixed ports spaced about the bit face that serve to inject drilling fluid into the passageways between the several blades. The drilling fluid exiting the face of the bit through nozzles or ports performs several functions. In particular, the fluid removes formation cuttings (for example, rock chips) from the cutting structure of the drill bit. Otherwise, accumulation of formation cuttings on the cutting structure may reduce or prevent the penetration of the drill bit into the formation. In addition, the fluid removes formation cuttings from the bottom of the hole. Failure to remove formation materials from the bottom of the hole may result in subsequent passes by cutting structure to essentially re-cut the same materials, thereby reducing the effective cutting rate and potentially increasing wear on the cutting surfaces of the cutter elements. The drilling fluid flushes the cuttings removed from the bit face and from the bottom of the hole radially outward and then up the annulus between the drill string and the borehole sidewall to the surface. Still further, the drilling fluid removes heat, caused by contact with the formation, from the cutter elements to prolong cutter element life.

BRIEF SUMMARY

[0008] Embodiments of modular fixed cutter drill bits are disclosed herein. In one embodiment, a modular fixed cutter drill bit for drilling an earthen formation has a central axis and a cutting direction of rotation about the central axis. In addition, the drill bit comprises a bit body configured to rotate about the central axis in the cutting direction of rotation. The bit body includes a bit face. Further, the drill bit comprises a blade extending radially along the bit face. The blade has a leading side relative to the cutting direction of rotation, a trailing side relative to the cutting direction of rotation, and a cutter-supporting surface extending from the leading side to the traling side. The blade includes a socket extending from the cutter-supporting surface of the blade. Still further the drill bit comprises a cutter element assembly mounted to the blade and extending from a cutter-supporting surface of the blade. The cutter element assembly comprises a pod seated in the socket and fixably attached to the blade and a cutter element fixably attached to the pod.

[0009] In another embodiment, a modular fixed cutter drill bit for drilling an earthen formation has a central axis and a cutting direction of rotation about the central axis. The drill bit comprises a bit body configured to rotate about the central axis in the cutting direction of rotation. The bit body includes a bit face. In addition, the drill bit comprises a blade extending radially along the bit face. The blade has a leading side relative to the cutting direction of rotation, a trailing side relative to the cutting direction of rotation, and a cutter-supporting surface extending from the leading side to the trailing side. The blade includes a socket extending from the cutter-supporting surface of the blade. Further, the drill bit comprises a cutter element assembly fixably attached to the blade. The cutter element assembly comprises a cutter element carrier comprising a head and a post extending from the head. The cutter element carrier is seated in the socket with the head extending from the cutter-supporting surface. The cutter element assembly also comprises a cutter element disposed in a cylindrical recess in the head and fixably attached to the head. The cutter element has a forwardfacing cutting face.

[0010] Embodiments described herein comprise a combination of features and characteristics intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical characteristics of the disclosed embodiments in order that the detailed description that follows may be better understood. The various characteristics and features described above, as well as others, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes as the disclosed embodiments. It should also be realized that such equivalent constructions do not depart from the spirit and scope of the principles disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a detailed description of various exemplary embodiments, reference will now be made to the accompanying drawings in which:

[0012] Figure 1 is a schematic view of a drilling system including an embodiment of a drill bit in accordance with the principles described herein;

[0013] Figure 2 is a perspective view of the drill bit of Figure 1 ;

[0014] Figure 3 is a side view of the drill bit of Figure 2;

[0015] Figure 4 is an end view of the drill bit of Figure 2;

[0016] Figure 5 is a partial cross-sectional schematic view of the bit shown in Figure 2 with the blades and the cutting faces of the cutter elements rotated into a single composite profile;

[0017] Figure 6 is a front perspective view of one of the blades, corresponding cutter element assemblies, and corresponding cutter elements of the bit of Figure 2;

[0018] Figure 7 is a rear perspective view of one of the blades, corresponding cutter element assemblies, and corresponding cutter elements of the bit of Figure 2;

[0019] Figure 8 is a perspective end view of the blade of Figure 7 with the cutter element assemblies removed;

[0020] Figure 9 is a perspective front view of one of the cutter element assemblies of the bit of Figure 2;

[0021] Figure 10 is a perspective rear view of the cutter element assembly of Figure 9;

[0022] Figure 11 is a side view of the cutter element assembly of Figure 9;

[0023] Figure 12 is a cross-sectional view of the cutter element assembly of Figure 9 in section 12-12 of Figure 11 ;

[0024] Figure 13 is an end view of the cutter element assembly of Figure 9;

[0025] Figure 14 is a cross-sectional view of the cutter element assembly of Figure 9 in section 14-14 of Figure 13;

[0026] Figure 15 is a perspective front view of the pod of the cutter element assembly of Figure 9; [0027] Figures 16-18 are schematic end views of embodiments of cutter element assemblies in accordance with principles described herein and illustrating windows in the head of the pod having different widths;

[0028] Figure 19 is a cross-sectional side view of the blade of Figure 6 and one of the cutter element assemblies mounted thereto;

[0029] Figure 20 is a cross-sectional view of a blade and an embodiment of a corresponding cutter element in accordance with the principles described herein;

[0030] Figure 21 is a front perspective view of an embodiment of a blade of a drill bit and corresponding cutter element assembly in accordance with the principles described herein;

[0031] Figure 22 is a cross-sectional side view of the blade of Figure 21 and one of the cutter element assemblies mounted thereto;

[0032] Figure 23 is a front perspective view of one of the cutter element assemblies of Figure 21 ;

[0033] Figure 24 is a side view of the cutter element assembly of Figure 23;

[0034] Figure 25 is a front perspective view of an embodiment of a cutter element assembly in accordance with the principles described herein;

[0035] Figure 26 is a side view of the cutter element assembly of Figure 25;

[0036] Figure 27 is a front perspective view of an embodiment of a cutter element assembly in accordance with the principles described herein;

[0037] Figure 28 is a side view of the cutter element assembly of Figure 27;

[0038] Figure 29 is a front perspective view of an embodiment of a cutter element assembly in accordance with the principles described herein;

[0039] Figure 30 is a side view of the cutter element assembly of Figure 29; and

[0040] Figure 31 is a cross-sectional side view of an embodiment of a blade of a drill bit and corresponding cutter element assembly in accordance with the principles described herein.

DETAILED DESCRIPTION

[0041] The following discussion is directed to various exemplary embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment. [0042] Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components orfeatures that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

[0043] Unless the context dictates the contrary, all ranges set forth herein should be interpreted as being inclusive of their endpoints, and open-ended ranges should be interpreted to include only commercially practical values. Similarly, all lists of values should be considered as inclusive of intermediate values unless the context indicates the contrary.

[0044] In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to... .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct engagement between the two devices, or through an indirect connection that is established via other devices, components, nodes, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a particular axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to a particular axis. For instance, an axial distance refers to a distance measured along or parallel to the axis, and a radial distance means a distance measured perpendicular to the axis. Any reference to up or down in the description and the claims is made for purposes of clarity, with “up”, “upper”, “upwardly”, “uphole”, or “upstream” meaning toward the surface of the borehole and with “down”, “lower”, “downwardly”, “downhole”, or “downstream” meaning toward the terminal end of the borehole, regardless of the borehole orientation. As used herein, the terms “approximately,” “about,” “substantially,” and the like mean within 10% (i.e., plus or minus 10%) of the recited value. Thus, for example, a recited angle of “about 80 degrees” refers to an angle ranging from 72 degrees to 88 degrees.

[0045] Drill bits are typically made in a manufacturing plant or factory. From the plant or factory, the drill bits are transported to the field for use. When worn, bits are transported to a repair center or back to the originating factory for maintenance, repair, and/or replacement. During maintenance, the bits are heated, and the cutter elements are rotated and/or replaced. After maintenance, the drill bits are then transported back to field for further use. This “lifecycle” of drill bits includes wasteful, non-value-added activities, such as transport time from and back to the field, and the associated costs. During such non-value-added activities, bits are not being used in a way that generates revenue, but instead, are idle (e.g., while being transported).

[0046] During maintenance, matrix bits are susceptible to cracking when heated due to the thermal mismatch of the interior steel core (for attaching the threaded pin) and the matrix bit body. Additionally, when bits are heated, the cutter elements may sustain thermal damage, which often results in loss of wear resistance, and in extreme cases, cracking. Furthermore, when the drill bits are heated and cutter elements are brazed, there is a risk of human error that the drill bit will be overheated or a cutter element will be placed directly into an acetylene flame, thereby potentially causing thermal damage. It should also be appreciated that a considerable amount of time is required to heat and braze cutter elements into a drill bit, and still further time is necessary after heating the drill bit to clean the bit (e.g., remove flux in a bath). Subsequent to such heating and cleaning, the drill bits are blasted (e.g., to remove excess braze) and then dye checked for potential cracks in the bit body and/or cutter elements.

[0047] It should also be appreciated that with typical drill bit designs, attaching a secondary or backup row of cutter elements that trail a primary row of cutter elements on the same blade relative to the direction of rotation of the drill bit presents challenges due to spaced limitations on the blade for securing the cutter elements in the backup row. This can be particularly problematic on smaller drill bits. With existing bit designs that are already optimized, there is a reluctance to make radical redesigns for retrofitting the drill bits to accommodate the mechanical attachment of cutter elements. In particular, drillers would generally prefer not to expose bolts, threads, and clamps that can fall off by fluid erosion or abrasion. Moreover, matrix bits bring additional challenges and potentially less flexibility as the matrix material tends to be more brittle and prone to cracking during machining.

[0048] For at least the foregoing reasons, there exists a need for drill bits than can be maintained and repaired more efficiently, and for cutter elements that can be replaced or rotated during maintenance and repairs more efficiently. Such drill bits and associated cutter elements would be particularly well received if they offered the potential for such maintenance, repair, replacement, and rotation without enhanced risk of damage to the drill bit or cutter elements.

[0049] Accordingly, embodiments described herein are directed to drill bits including cutter elements that are mechanically coupled to the blades extending from the bit bodies. In particular, the blades are configured for relatively quick removal and attachment of cutter elements, and thus, the bit body and blades can act as a disposable and/or recyclable “chassis” for the cutter elements. As a result, rather than require transport to a factory or repair center, a field office can be positioned in the field for rapid drill bit build customization, repair, and maintenance. In other words, the drill bits and cutter elements thereon can be repaired, maintained, and replaced (as desired) on site, without transport over long distances (after initial delivery to the field). In addition, the fundamental drill bit designs can be minimally changed to accommodate such customizations. The cutter elements can be replaced, maintained, and rotated with relative ease. In some embodiments disclosed herein, the cutter elements can be replaced at the field location without requiring heating of the bit, which requires time for both heating and cooling of the bit, as well as presents the risk of thermal damage to the cutter elements. Further, the cutter elements can be brazed in a controlled, lab environment separate from the bit, thereby avoiding the time required need to heat and cool the entire drill bit, increasing the speed of the brazing process, reducing the propensity for thermal damage to the cutter elements, and reducing the amount of time the cutter elements are exposed to a deleterious oxygen containing atmosphere at elevated temperatures. Moreover, some embodiments allow for use of active brazing techniques to braze superhard polycrystalline diamond. The bit components can be delivered (e.g., daily) to the field (e.g., via FedEx or another such package service), providing for a lean pull system. Thus, the present disclosure includes methods and systems that reduce the number of bits that are idle.

[0050] Referring now to Figure 1 , a schematic view of an embodiment of a drilling system 10 in accordance with the principles described herein is shown. Drilling system 10 includes a derrick 11 having a floor 12 supporting a rotary table 14 and a drilling assembly 90 for drilling a borehole 26 from derrick 1 1 . Rotary table 14 is rotated by a prime mover such as an electric motor (not shown) at a desired rotational speed and controlled by a motor controller (not shown). In other embodiments, the rotary table (for example, rotary table 14) may be augmented or replaced by a top drive suspended in the derrick (for example, derrick 11) and connected to the drillstring (for example, drillstring 20).

[0051] Drilling assembly 90 includes a drillstring 20 and a drill bit 100 coupled to the lower end of drillstring 20. Drillstring 20 is made of a plurality of pipe joints 22 connected end-to-end, and extends downward from the rotary table 14 through a pressure control device 15, such as a blowout preventer (BOP), into the borehole 26. The pressure control device 15 is commonly hydraulically powered and may contain sensors for detecting certain operating parameters and controlling the actuation of the pressure control device 15. Drill bit 100 is rotated with weight-on-bit (WOB) applied to drill the borehole 26 through the earthen formation. Drillstring 20 is coupled to a drawworks 30 via a kelly joint 21 , swivel 28, and line 29 through a pulley. During drilling operations, drawworks 30 is operated to control the WOB, which impacts the rate-of-penetration of drill bit 100 through the formation. In this embodiment, drill bit 100 can be rotated from the surface by drillstring 20 via rotary table 14 or a top drive, rotated by downhole mud motor 55 disposed along drillstring 20 proximal bit 100, or combinations thereof (for example, rotated by both rotary table 14 via drillstring 20 and mud motor 55, rotated by a top drive and the mud motor 55, etc.). For example, rotation via downhole motor 55 may be employed to supplement the rotational power of rotary table 14, if required, or to effect changes in the drilling process. In either case, the rate-of-penetration (ROP) of the drill bit 100 into the borehole 26 for a given formation and a drilling assembly largely depends upon the WOB and the rotational speed of bit 100.

[0052] During drilling operations, a suitable drilling fluid 31 is pumped under pressure from a mud tank 32 through the drillstring 20 by a mud pump 34. Drilling fluid 31 passes from the mud pump 34 into the drillstring 20 via a desurger 36, fluid line 38, and the kelly joint 21. The drilling fluid 31 pumped down drillstring 20 flows through mud motor 55 and is discharged at the borehole bottom through nozzles in face of drill bit 100, circulates to the surface through an annular space 27 radially positioned between drillstring 20 and the sidewall of borehole 26, and then returns to mud tank 32 via a solids control system 36 and a return line 35. Solids control system 36 may include any suitable solids control equipment known in the art including, without limitation, shale shakers, centrifuges, and automated chemical additive systems. Control system 36 may include sensors and automated controls for monitoring and controlling, respectively, various operating parameters such as centrifuge rpm. It should be appreciated that much of the surface equipment for handling the drilling fluid is application specific and may vary on a case-by-case basis.

[0053] Referring now to Figures 2-4, drill bit 100 is a fixed cutter bit, sometimes referred to as a drag bit, and is designed for drilling through formations of rock to form a borehole. Bit 100 has a central or longitudinal axis 105, a first or uphole end 100a, and a second or downhole end 100b. Bit 100 rotates about axis 105 in the cutting direction represented by arrow 106. In addition, bit 100 includes a bit body 110 extending axially from downhole end 100b, a threaded connection or pin 120 extending axially from uphole end 100a, and a shank 130 extending axially between pin 120 and body 110. Pin 120 couples bit 100 to a drill string (not shown), which is employed to rotate the bit 100 in order to drill the borehole. Bit body 110, shank 130, and pin 120 are coaxially aligned with axis 105, and thus, each has a central axis coincident with axis 105.

[0054] The portion of bit body 110 that faces the formation at downhole end 100b includes a bit face 111 provided with a cutting structure 140. Cutting structure 140 includes a plurality of blades that extend from bit face 111. As best shown in Figure 4, in this embodiment, cutting structure 140 includes three angularly spaced-apart primary blades 141 and three angularly spaced apart secondary blades 142. Further, in this embodiment, the plurality of blades (for example, primary blades 141 , and secondary blades 142) are uniformly angularly spaced on bit face 111 about bit axis 105. In particular, the three primary blades 141 are uniformly angularly spaced about 120° apart, the three secondary blades 142 are uniformly angularly spaced about 120° apart, and each primary blade 141 is angularly spaced about 60° from each circumferentially adjacent secondary blade 142. In other embodiments, one or more of the blades may be spaced non-uniformly about bit face 1 11. Still further, in this embodiment, the primary blades 141 and secondary blades 142 are circumferentially arranged in an alternating fashion. In other words, one secondary blade 142 is disposed between each pair of circumferentially-adjacent primary blades 141. Although bit 100 is shown as having three primary blades 141 and three secondary blades 142, in general, bit 100 may comprise any suitable number of primary and secondary blades. As one example only, bit 100 may comprise two primary blades and four secondary blades. [0055] Referring again to Figures 2-4, in this embodiment, primary blades 141 and secondary blades 142 are integrally formed as part of, and extend from, bit body 110 and bit face 111. Primary blades 141 and secondary blades 142 extend generally radially along bit face 111 and then axially along a portion of the periphery of bit 100. In particular, primary blades 141 extend radially from proximal central axis 105 toward the periphery of bit body 110. Primary blades 141 and secondary blades 142 are separated by drilling fluid flow courses 143. Each blade 141 , 142 has a leading edge or side 141 a, 142a, respectively, and a trailing edge or side 141 b, 142b, respectively, relative to the direction of rotation 106 of bit 100.

[0056] Referring still to Figures 2-4, each blade 141 , 142 includes a cutter-supporting surface 144 that generally faces the formation during drilling and extends circumferentially from the leading side 141 a to the trailing side 142 of the corresponding blade 141 , 142. In this embodiment, a plurality of cutter element assemblies 200 are fixably attached to cutter supporting surface 144 of each blade 141 , 142. Cutter element assemblies 200 are generally arranged adjacent one another in a radially extending row proximal the leading edge 141 a of each primary blade 141 and each secondary blade 142. However, in other embodiments, the cutter element assemblies (for example, cutter element assemblies 200) may be arranged differently.

[0057] As will be described in more detail below, each cutter element assembly 200 includes a cutter element carrier or pod 210 fixably mounted to the corresponding blade 141 , 142 and a cutter element 230 fixably secured to and carried by the pod 210. Although cutter element assemblies 200 are fixably mounted to blades 141 , 142, and thus, do not move rotationally or translationally during drilling operations, cutter element assemblies 200 are mechanically attached to blades 141 , 142 such that any one or more cutter element assemblies 200 can be independently removed for repair, maintenance, or replacement. Accordingly, drill bit 100, as well as other embodiments of drill bits described herein, may be referred to as “modular.”

[0058] Each cutter element 230 includes an elongated and generally cylindrical support base or substrate 231 and a cylindrical disk or tablet-shaped, hard cutting layer 232 bonded to the exposed end of substrate 231. Substrate 231 is typically made of a carbide material such as tungsten carbide, whereas cutting layer 232 is typically made of polycrystalline diamond or other superabrasive material. Substrate 231 has a central axis 235, and as will be described in more detail below, is received and secured in a pocket formed in the corresponding pod 210, which in turn is fixably received by and secured to the corresponding blade 141 , 142 to which it is mounted. The cylindrical disc, hard cutting layer 232 defines a cutting face 233 of the corresponding cutter element 230. As will be described in more detail below, in this embodiment, each cutting face 233 is the same and is planar. However, in other embodiments, one or more cutting faces (e.g., cutting faces 233) may not be completely planar, but rather, be non-planar. As used herein, the phrase “non-planar” may be used to refer to a cutting face that includes one or more curved surfaces (for example, concave surface(s), convex surface(s), or combinations thereof), a plurality of distinct planar surfaces that intersect at distinct edges along the cutting face, or both. As best shown in Figure 4, some cutter elements 230, which are also labeled with reference numeral 230’, may be directly attached to the cutter-supporting surface 144 of the corresponding blade 141 , 142 without a pod 210.

[0059] In the embodiments described herein, each cutter element assembly 200 is mounted such that the central axis 235 of the corresponding cutter element 230 is oriented substantially parallel to or at an acute angle relative to the cutting direction of the bit (for example, cutting direction 106 of bit 100). Such orientation results in the corresponding cutting face 233 being generally forward-facing relative to the cutting direction of the bit (for example, cutting direction 106 of bit 100). The portion of cutting face 233 of each cutter element 230 positioned furthest from the cutter supporting surface 144 of the corresponding blade 141 , 142 as measured perpendicular to the corresponding cutter supporting surface 144 defines a cutting tip 234 of cutting face 233.

[0060] Referring still to Figures 2-4, bit body 110 further includes gage pads 147 of substantially equal axial length measured generally parallel to bit axis 105. Gage pads 147 are circumferentially-spaced about the radially outer surface of bit body 110. Specifically, one gage pad 147 intersects and extends from each blade 141 , 142. In this embodiment, gage pads 147 are integrally formed as part of the bit body 110. In general, gage pads 147 can help maintain the size of the borehole by a rubbing action when cutter element assemblies 200 wear slightly under gage. Gage pads 147 also help stabilize bit 100 against vibration.

[0061] Referring now to Figure 5, an exemplary profile of blades 141 , 142 is shown as it would appear with blades 141 , 142 and cutting faces 233 rotated into a single rotated profile. In rotated profile view, blades 141 , 142 form a combined or composite blade profile 148 generally defined by cutter-supporting surfaces 144 of blades 141 , 142. In this embodiment, the profiles of surfaces 144 of blades 141 , 142 are generally coincident with each other, thereby forming a single composite blade profile 148.

[0062] Composite blade profile 148 and bit face 111 may generally be divided into three regions conventionally labeled cone region 149a, shoulder region 149b, and gage region 149c. Cone region 149a is the radially innermost region of bit body 110 and composite blade profile 148 that extends from bit axis 105 to shoulder region 149b. In this embodiment, cone region 149a is generally concave. Adjacent cone region 149a is generally convex shoulder region 149b. The transition between cone region 149a and shoulder region 149b, referred herein to as the nose 149d, occurs at the axially outermost portion of composite blade profile 148 (relative to bit axis 105) where a tangent line to the blade profile 148 has a slope of zero. Moving radially outward, adjacent shoulder region 149b is the gage region 149c, which extends substantially parallel to bit axis 105 at the outer radial periphery of composite blade profile 148. As shown in composite blade profile 148, gage pads 147 define the gage region 149c and the outer radius Rno of bit body 110. Outer radius R110 extends to and therefore defines the full gage diameter of bit 100.

[0063] Referring briefly to Figure 4, moving radially outward from bit axis 105, bit 100 and bit face 111 include cone region 149a, shoulder region 149b, and gage region 149c as previously described. Primary blades 141 extend radially along bit face 111 from within cone region 149a proximal bit axis 105 toward gage region 149c and outer radius R110. Secondary blades 142 extend radially along bit face 11 1 from proximal nose 149d toward gage region 149c and outer radius R110. Thus, in this embodiment, each primary blade 141 and each secondary blade 142 extends substantially to gage region 149c and outer radius R110. In this embodiment, secondary blades 142 do not extend into cone region 149a, and thus, secondary blades 142 occupy no space on bit face 111 within cone region 149a. Although a specific embodiment of bit body 110 has been shown in described, one skilled in the art will appreciate that numerous variations in the size, orientation, and locations of the blades (for example, primary blades 141 , secondary blades, 142, etc.), and cutter elements (for example, cutter element assemblies 200) are possible.

[0064] Bit 100 includes an internal plenum extending axially from uphole end 100a through pin 120 and shank 130 into bit body 110. The plenum allows drilling fluid to flow from the drill string into bit 100. Body 110 is also provided with a plurality of flow passages extending from the plenum to downhole end 100b. As best shown in Figures 2-4, a nozzle 108 is seated in the lower end of each flow passage. Together, the plenum, passages, and nozzles 108 serve to distribute drilling fluid around cutting structure 140 to flush away formation cuttings and to remove heat from cutting structure 140, and more particularly cutter element assemblies 200, during drilling.

[0065] Referring again to Figures 2-4, on each blade 141 , 142, cutter element assemblies 200 are arranged side-by-side in a row along the corresponding cutter supporting surface 144. Thus, in this embodiment, cutter element assemblies 200 are positioned radially adjacent one another on a given blade 141 , 142. However, in other embodiments, the cutter element assemblies (for example, cutter element assemblies 200) may be arranged in rows with one or more cutter element having a different geometries on the same blade (for example, blade 141 , 142).

[0066] Referring now to Figures 6-8, enlarged views of exemplary blades 141 , 142 are shown. Each blade 141 , 142 includes a plurality of radially adjacent sockets 150 for receiving cutter element assemblies 200, and in particular, receiving mating pods 210. In particular, each socket 150 extends into the corresponding blade 141 , 142 generally perpendicularly from cutter-supporting surface 144 at leading side 141 a, 142a. As best shown in Figure 8, each socket 150 intersects the corresponding cuttersupporting surface 144 and a portion of the convex edge between the corresponding cutter-supporting surface 144 and leading side 141 a, 142a.

[0067] Referring now to Figure 8, each socket 150 has a central or longitudinal axis 155, a first or open end 150a at the corresponding cutter-supporting surface 144 and leading side 141 a, 142a, and a second or closed end 150b opposite end 150a. In addition, each socket 150 includes a first cylindrical section or bore 151a extending axially (relative to central axis 155) from open end 150a, a second cylindrical section or bore 151 b extending axially (relative to central axis 155) from closed end 150b, and an annular shoulder or seat 151 c extending between cylindrical sections 151a, 151 b. The diameter of first cylindrical bore 151 a is greater than the diameter of second cylindrical bore 151 b, and thus, annular seat 151c extends radially inward (relative to axis 155) from first cylindrical bore 151a to second cylindrical bore 151 b. A cylindrical bore 152 extends from first cylindrical bore 151 a of socket 150 to the convex edge between the corresponding cutter-supporting surface 144 and leading side 141 a, 142a. Bore 152 defines an annular, cylindrical edge or seat 153 along leading side 141 a, 142a of the corresponding blade 141 , 142 that receives and supports cutter element 230. Although seat 153 is shown as directly engaging and supporting cutting layer 232, in other embodiments, the blade seat (e.g., seat 153) may directly engage and support the substrate of the cutter element (e.g., substrate 231 ) or the pod (e.g., pod 210). The portion of blade 141 , 142 surrounding cutter element 230 along cylindrical seat 153 cradles cutter element 230 to prevent and/or reduce the propensity for rotation of cutter element assembly 200 and also functions as a sheath that provides for increased protection of cutter element 230. Hardfacing can be applied to blade 141 , 142 around pod 210 and cutter element 230 to provide additional protection. As best shown in Figures 7 and 8, an internally threaded bore 156 extends from each second cylindrical section 151 b to trailing side 141 b, 142b of the corresponding blade 141 , 142, respectively.

[0068] Referring now to Figures 9-14, one cutter element assembly 200 will be described with the understanding that each cutter element assembly 200 is the same. As previously described, in this embodiment, cutter element assembly 200 includes cutter element pod 210 and cutter element 230 seated therein. Pod 210 has a central or longitudinal axis 215, a first or upper end 210a, and a second or lower end 210b. As previously described, each cutter element assembly 200 is mounted and oriented such that the corresponding cutting face 233 is generally forward-facing relative to cutting direction 106 of bit 100. Accordingly, cutter element pod 210 may be described as having a front or leading side 211 and a rear or trailing side 212 (relative to the cutting direction 106). In addition, pod 210 includes a base or blade attachment member 220 and a head 225 fixably attached to blade attachment member 220. Head 225 receives cutter element 230. In this embodiment, blade attachment member 220 is an elongate post, and thus, may also be referred to herein as post 220. Head 225 extends axially (relative to axis 215) from first end 210a to post 220, and post 220 extends axially (relative to axis 215) from second end 210b to head 225. In this embodiment, pod 210 is a single, monolithic component, and thus, head 225 is integral with and monolithically formed with post 220.

[0069] Pod 210 (or portions thereof such as post 220 and head 225) can be made of a material suitable for a particular application and/or to enhance durability of cutter element assembly 200. For example, pod 210 (or portion thereof) can be made of a high strength material, a high abrasion resistant material, a corrosion resistant material, or combinations thereof. Examples of suitable materials for pod 210 include, without limitation, steel, super alloy, cemented carbide, matrix or similar high- performance or hard material, Stellite, Inconel, Monel, metal alloys with niobium or nickel, or combinations thereof (e.g., steel, carbide, steel, hardfacing, superalloy, and carbide). In addition, pods 210 can be laser marked, etch, and/or machined to include indices that identify backrake, grade, bit design, brand of cutter, number of rotations, build date, leached or unleached, and other relevant information about the corresponding cutter element 230.

[0070] It should also be appreciated that head 225 generally surrounds cutter element 230, and thus, the use of a high strength material, a high abrasion resistant material, a corrosion resistant material, or combination thereof for head 225 provides some added protection to cutter element 225 disposed therein. For example, during drilling, bit 100 may be exposed to harsh pH conditions that may otherwise cause the carbide substrate 231 of cutter element 230 to corrode or wear prematurely. However, by wrapping head 225 around substrate 231 , pod 210 provides additional protection to substrate 231 of cutter element 230.

[0071] Referring still to Figures 9-14, post 220 has a central axis defining central axis 215 of pod 210 and is generally cylindrical. Accordingly, post 220 has a radially outer cylindrical surface 221 extending axially from second end 210b to head 225. In this embodiment, a plurality of uniformly circumferentially-spaced ribs 222 extend radially from cylindrical outer surface 221 . Ribs 222 are linear and axially oriented (parallel to axis 215). As best shown in Figures 10, 11 , and 14, in this embodiment, a recess 223 is provided in outer surface 221 on trailing side 212 of pod 210. In this embodiment, recess 223 is generally rectangular and is defined by a first or upper planar shoulder 224a, a second or lower planar shoulder 224b, and a planarflat 224c extending axially (relative to axis 215) between shoulders 224a, 224b. Shoulders 224a, 224b face inwardly each other, are oriented parallel to each other, and are disposed in planes oriented perpendicular to axis 215. Planar flat 224c is oriented perpendicular to shoulders 224a, 224b and is disposed in a plane oriented parallel to axis 215.

[0072] As will be described in more detail below, post 220 is sized to be disposed in mating cylindrical bore 151 b with outer cylindrical surface 221 slidingly engaging the corresponding blade 141 , 142. Ribs 222 extending radially from outer cylindrical surface 221 may be provided to form a tight, interference fit between post 220 and the corresponding blade 141 , 142 to enhance retention of post 220 therein. Although post 220 and mating bore 151 b in blade 141 , 142 are cylindrical in this embodiment, in other embodiments, the post (e.g., post 220) and the mating bore (e.g., bore 151 b) may be frustoconical to aid in distribute axial loads (i.e. , loads oriented parallel to the bit axis).

[0073] Head 225 includes a planar flat 226 at first end 210a, a cylindrical recess 227 extending from leading side 211 , and a through slot or window 228 extending axially from planarflat 226 to cylindrical recess 227. In addition, head 225 has a radially outer cylindrical surface 225a axially positioned between flat 226 and post 220 and an annular shoulder 225b axially positioned between outer cylindrical surface 225a of head 225 and outer cylindrical surface 221 of post 220. Outer cylindrical surface 225a of head 225 that defines the maximum width of head 225. The diameter of outer cylindrical surface 225a of head 225 is greater than the diameter of outer cylindrical surface 221 of post 220, and thus, annular shoulder 225b extends radially inward from outer cylindrical surface 225a of head 225 to outer cylindrical surface 221 of post 220. [0074] Cylindrical recess 227 has a central axis 227a and intersects outer cylindrical surface 225a at leading side 211. Accordingly, recess 227 extends along central axis 227a from an open end at leading side 211 to a closed end proximal trailing side 212. Recess 227 is sized and shaped to receive mating cutter element 230 with axes 235, 227a coaxially aligned. In particular, recess 227 has a diameter that is the same or substantially the same as the outer diameter of cutter element 230, and thus, cutter element 230 slidingly engages head 225 when disposed in recess 227. However, the axial length or depth of recess 227 (measured parallel to axis 227a) is less than the axial length of cutter element 230 (measured parallel to axis 235), and thus, in this embodiment, at least a portion of cutting layer 232 extends axially (relative to axes 227a, 235) from recess 227, head 225, and pod 210. However, in other embodiments, the cutting layer (e.g., cutting layer 232) may not extend axially from the recess n the pod (e.g., recess 227), the head of the pod (e.g., head 225), and the pod (e.g., pod 210). In side view of Figure 11 , central axis 227a is oriented at an acute angle a relative to central axis 215 of pod 210.

[0075] In this embodiment, window 228 is generally rectangular and extends linearly (parallel to central axis 227a) along planar flat 226 from leading side 211 toward trailing side 212. More specifically, window 228 extends from an end at the opening of recess 227 at leading side 211 to an end proximal trailing side 212. As best shown in Figure 13, window 228 has a circumferential width W measured circumferentially about central axis 227a between the parallel sides of window 228. [0076] To secure cutter element 230 to pod 210 within mating recess 227, cutter element 230 is slidingly disposed within recess 227 with substrate 231 seated against the closed end of recess 227, and then cutter element 230 is rotated within recess 227 while simultaneously being brazed to head 225. In particular, the melted or “wet” brazing filler material is applied between the outer surface of cutter element 230 and head 225 within recess 227, and flows therebetween via capillary action. Cutter element 230 is rotated during the process to allow dispersion of the wet brazing filler material across the entire outer surface of cutter element 230 disposed in recess 227 to maximize the surface area coverage and strength of the bond between cutter element 230 and head 225. Surface area coverage of the wet brazing material can be visually confirmed as cutter element 230 is rotated by viewing the outer surface of cutter element 230 through window 228. It should be appreciated that cutter element 230 can be removed from recess 227 of head 225 for maintenance, repair, or replacement by heating pod 210 and/or cutter element 230 to melt the brazing therebetween, and then rotating and pulling cutter element 230 from recess 227. Similarly, cutter element 230 can be rotated relative to head 225 to position a fresh or unworn portion of cutting edge of cutting layer 232 for engaging the formation during subsequent drilling operations by heating pod 210 and/or cutter element 230 to melt the brazing therebetween and then rotating cutter element 230 relative to head 225, and then re-brazing cutter element 230 to head 225 as previously described. These processes for attaching cutter element 230 to pod 210, removing cutter element 230 from pod 210, and rotating cutter element 230 relative to pod 210 are preferably performed without pod 210 attached to bit 100, which offers the potential to speed the process by eliminating the need to heat and cool the entire bit 100, as well as enable the brazing to be done in a controlled lab environment separate from the bit 100. To minimize exposure of cutter element 230 to excess heat, pod 210 can be heated and/or a heat sink applied to cutter element 230.

[0077] Although cutter element 230 is brazed to pod 210 in this embodiment, in other embodiments, alternative techniques can be employed to fixably secure the cutter element (e.g., cutter element 230) to the corresponding pod (e.g., pod 210). For example, a cutter element can be fixably secured to the corresponding pod via fusing, press fitting, e-beam welding, or Morris taper lock.

[0078] Referring briefly to Figures 16-18, the circumferential width W of window 228 can be varied. The greater the circumferential width W of window 228, the easier to visually confirm the surface area coverage of the wet brazing material while brazing cutter element 230 to head 225 within recess 227. However, the greater the circumferential width W of window, the lesser the angular distance (about axes 227a, 235) over which head 225 extends about cutter element 230; and the lesser the angular distance (about axes 227a, 235) over which head 225 extends about cutter element 230, the lesser the contact surface area between head 225 and cutter element 230), and the weaker the bond and retention strength between head 225 and cutter element. In embodiments described herein, head 225 preferably extends at least 180° (measured about axes 227a, 235) about cutter element 230.

[0079] Referring briefly to Figure 20, in some embodiments, hardfacing 201 can be applied to head 225 at or proximal upper end 210a (e.g., along planar flat 226 on opposite lateral sides of window 228 to enhance the abrasion resistance of pod 210 and head 225. The hardfacing 201 can also function as a depth-of-cut limiter if shaped as a protuberance as shown in Figure 20. In yet other embodiments, a tungsten carbide insert is positioned along the head (e.g., head 225) at or proximal the upper end of the pod (e.g., at or proximal upper end 210a) to enhance the abrasion resistance of the pod and the head.

[0080] Referring now to Figures 6, 7, and 19, each cutter element assembly 200 is mounted to the corresponding blade 141 , 142 with pod 210 fixably and mechanically secured within a corresponding, mating socket 150. More specifically, axes 155, 215 are coaxially aligned, post 220 is disposed in mating cylindrical bore 151 b of socket 150 with cylindrical outer surface 221 of post 220 slidingly engaging blade 141 , 142, annular shoulder 225b of pod 220 is seated against mating annular seat 151 c, head 225 is at least partially disposed in mating cylindrical bore 151a with cylindrical outer surface 225a of head 225 slidingly engaging blade 141 , 142, and the portion of cutter element 230 extending from head 225 seated in mating seat 153. As best shown in Figure 19, a set screw 157 is threaded into bore 156 until its tip is securely seated in recess 223 against flat 224c between shoulders 224a, 224b. With such arrangement, the interference fit between post 220 and the corresponding blade 141 , 142 restricts and/or prevents cutter element assembly 200 from moving rotationally and translationally relative to the corresponding blade 141 , 142 during drilling operations; seating of set screw 157 within recess 223 restricts and/or prevents cutter element assembly 200 from moving rotationally and translationally relative to the corresponding blade 141 , 142 during drilling operations; and engagement of cutter element 230 and mating seat 153 of the corresponding blade 141 , 142 restricts and/or prevents cutter element assembly 200 from moving rotationally relative to the corresponding blade 141 , 142 during drilling operations. In general, cutter element 230 can be disposed within recess 227 of head 225 and secured thereto as previously described before or after securing pod 210 to the corresponding blade 141 , 142.

[0081] In the manner described, cutter element assembly 200 is fixably and mechanically secured to the corresponding blade 141 , 142. However, in other embodiments, alternative techniques can be employed to fixably and mechanically secure cutter element assembly 200 to the corresponding blade 141 , 142. For example, a splined connection between the post of the pod (e.g., post 220) and the corresponding blade (e.g., blade 141 , 142) can be included to prevent rotation of the cutter element assembly about its central axis. As another example, a compression lock ring can be provided between the post and the corresponding blade to prevent axial movement of the cutter element assembly relative to the corresponding blade.

[0082] Referring now to Figure 19, cutter element assembly 200 is mounted with central axis 235 of cutter element 230 oriented at an acute angle p measured between axis 235 and cutter-supporting surface 144 of the corresponding blade 141 , 142. It should be appreciated that during drilling operations, cutter-supporting surface 144 is parallel to the surface of the formation being cut by cutter element 230, and thus, central axis 235 is also oriented at acute angle relative to the surface of the formation being cut by cutter element 230. Angle p may also be commonly known as a “rake angle,” or more specifically, a “backrake angle” as cutter element 230 is tilted backward such that cutting face 233 generally slopes rearwardly relative to the cutting direction 106 moving radially outward along cutting face 233 toward cutting tip 234. In embodiments described herein, each cutter element (for example, each cutter element 200) is oriented at an acute backrake angle p ranging from 0° to 45°, and alternatively ranging from 10° to 30°. In general, the backrake angle p of any two or more cutter elements can be the same or different. In general, the desired backrake angle p for any given cutter element 230 can be achieved by adjusting (i) the acute angle a (Figure 11 ) by changing the orientation of recess 227, and/or (ii) the orientation of central axes 155, 215 of socket 150 and pod 210, respectively, in a plane containing axes 155, 215 and oriented generally perpendicular to sides 141 a, 141 b (as shown in Figure 19).

[0083] Referring still to Figure 19, during drilling operations, the formation being sheared exerts a torque F-rorque acting on cutter element 230 at cutting tip 234 in a direction opposite to the cutting direction 106 and a force FWOB acting on cutter element 230 at cutting tip 234 in a direction opposite to the weight-on-bit applied to the drillstring 20 (i.e., generally uphole). For balancing of forces acting on cutter element 230 while ensuring a fixed, secure connection between cutter element assembly 200 and the corresponding blade 141 , 142 in embodiments described herein, as the ratio of torque Fiorque to force FWOB increases, axes 155, 215 are rotated in the plane containing axes 155, 215 and oriented generally perpendicular to sides 141a, 141 b (as shown in Figure 19) to move post 220 further “behind” cutter element 230 and more toward alignment with torque F-rorque (axes 155, 215 are rotated clockwise in Figure 19); and as the ratio of torque F-rorque to force FWOB decreases, axes 155, 215 are rotated in the plane containing axes 155, 215 and oriented generally perpendicular to sides 141 a, 141 b (as shown in Figure 19) to move post 220 closer to a position more aligned with WOB (axes 155, 215 are rotated counter-clockwise in Figure 19).

[0084] Referring now to Figure 21 , an embodiment of a blade 341 of a drill bit and a plurality of cutter element assemblies 400 fixably secured thereto is shown. In general, blade 341 and associated cutter element assemblies 400 can be used in place of any one or more blades 141 , 142 and cutter element assemblies 200 on bit 100 shown in Figures 2-4.

[0085] Blade 341 has a leading edge or side 341 a and a trailing edge or side 341 b relative to the direction of rotation 306 of the corresponding drill bit. In addition, blade 341 includes a cutter-supporting surface 344 that generally faces the formation during drilling and extends circumferentially (relative to the central axis of the corresponding bit) from the leading side 341 a to the trailing side 341 b. In this embodiment, a plurality of cutter element assemblies 400 are fixably secured to cutter supporting surface 344 of blade 341. Cutter element assemblies 400 are generally arranged adjacent one another in a radially extending row along the leading side 341 a of blade 341 .

[0086] As will be described in more detail below, each cutter element assembly 400 includes a cutter element carrier or pod 410 fixably and removably mounted to blade 341 and a cutter element 230 as previously described fixably secured to and carried by the pod 410. Cutter element 230 is received and secured in a pocket formed in the corresponding pod 410, which in turn is fixably received by and secured to blade 341 . [0087] In the embodiments described herein, each cutter element assembly 400 is mounted such that the central axis 235 of the corresponding cutter element 230 is oriented substantially parallel to or at an acute angle relative to the cutting direction of the bit (for example, cutting direction 106 of bit 100). Such orientation results in the corresponding cutting face 233 being generally forward-facing relative to the cutting direction of the bit (for example, cutting direction 106 of bit 100).

[0088] Referring now to Figures 21 and 22, blade 341 includes a plurality of radially adjacent sockets 350 for receiving cutter element assemblies 400, and in particular, receiving mating pods 410. In particular, each socket 350 extends into blade 341 generally perpendicularly from cutter-supporting surface 344 and perpendicularly from leading side 341 a. As best shown in Figure 22, each socket 350 extends through the convex edge between the corresponding cutter-supporting surface 344 and leading side 341a.

[0089] Referring still to Figures 21 and 22, one socket 350 will be described with the understanding each socket 350 is the same. Socket 350 has a central or longitudinal axis 355, a first end 350a at cutter-supporting surface 344, and a second end 350b along leading side 341 a opposite end 350a (spaced from cutter-supporting surface 344). As best shown in Figure 22, socket 350 includes a generally cylindrical base section or bore 351 a extending generally perpendicularly from leading side 341 a of blade 341 along cutter supporting surface 344 at first end 350a and an elongate leg section or recess 351 b extending axially (relative to the bit axis) from base section 351 a to end 350b along leading side 341 a of blade 341. Base bore 351a and leg recess 351 b are oriented generally perpendicular to each other, and thus, socket 350 generally has L-shape geometry. Accordingly, a convex edge or seat 354 is formed in socket 350 at the intersection of base bore 351 a and leg recess 351 b.

[0090] Referring still to Figure 22, a semi-spherical recess 352 extends from base bore 351 a into blade 341. Semi-spherical recess 352 is coaxially aligned with base bore 351 a (i.e., semi-spherical recess 352 is centered along the central axis of base bore 351 a). The diameter of base bore 351a is greater than the diameter of semi-spherical recess 352. An internally threaded bore 357 extends from leg recess 351 b into blade 341.

[0091] Referring now to Figures 22-24, one cutter element assembly 400 will be described with the understanding that each cutter element assembly 400 is the same. As previously described, in this embodiment, cutter element assembly 400 includes cutter element pod 410 and cutter element 230 seated therein. Cutter element 230 is as previously described. Pod 410 has a central or longitudinal axis 415, a first or upper end 410a, and a second or lower end 410b. As previously described, each cutter element assembly 400 is mounted and oriented such that the corresponding cutting face 233 is generally forward-facing relative to cutting direction of the bit to which it is mounted (e.g., cutting direction 106 of bit 100). Accordingly, cutter element pod 410 may be described as having a front or leading side 411 and a rear or trailing side 412 (relative to the cutting direction). In addition, pod 410 includes a base or blade attachment member 420 and a head 425 for receiving cutter element 230 fixably attached to blade attachment member 420. In this embodiment, blade attachment member 420 is an elongate tab, and thus, may also be referred to herein as tab 420. Head 425 is disposed at first end 410a and extends generally perpendicularly from tab 420, and tab 420 extends axially (relative to axis 415) from second end 410b to head 425. Accordingly, pod 410 generally has an L-shaped geometry that mates with the L-shaped geometry of socket 350. In this embodiment, pod 410 is a single, monolithic component, and thus, head 425 is integral with and monolithically formed with tab 420. In general, pod 410 (or portions thereof such as tab 420 and head 425) can be made of the same materials as pod 210 previously described.

[0092] Referring now to Figures 22-24, tab 420 has a central axis defining central axis 415 of pod 410 and, in this embodiment, is a generally U-shaped flat plate. In particular, tab 420 has a planar front surface 421 extending axially from second end 410b to head 425 along front side 411 of pod 410 and a planar rear surface 422 extending axially from second end 410b to head 425 along rear side 412. Front side 421 and rear side 422 lie in planes oriented parallel to each other. In this embodiment, a through hole 423 extends perpendicularly from front side 421 to rear side 422.

[0093] As will be described in more detail below, tab 420 is sized to be disposed in mating leg recess 351 b of socket 350 in blade 341 with front surface 421 generally flush with leading side 341 a of blade 341. Although tab 420 and mating leg recess 351 b are generally U-shaped in this embodiment, in other embodiments, the post (e.g., tab 420) and the mating recess (e.g., recess 351 b) may have other mating geometries. [0094] Head 425 includes a generally cylindrical pocket 427 and a semi-spherical projection 429 along rear side 422. Pocket 427 has a central axis 427a and extends along central axis 427a from an open end at leading side 411 to a closed end proximal trailing side 412. Central axis 427a is oriented at an acute angle a relative to axis 415 of pod 410. In this embodiment, pocket 427 is open at first end 410a, and thus, defines a semi-cylindrical seat 428 in head 425. Pocket 427 is sized and shaped to receive mating cutter element 230 with axes 235, 427a coaxially aligned. In particular, pocket 427 has a diameter that is the same or substantially the same as the outer diameter of cutter element 230, and thus, cutter element 230 slidingly engages head 425, and more specifically seat 428 when disposed in recess 427. Seat 428 extends circumferentially about the outer cylindrical surface of cutter element 230. In this embodiment, seat 428 extends circumferentially about 120° about cutter element 230. In general, the greater the seat (e.g., seat 428) extends circumferentially about the corresponding cutter element (e.g., cutter element 230), the greater the strength of the attachment or bond therebetween and the less likely the cutter element will detach from the pod (e.g., pod 410). Accordingly, in some embodiments, the seat (e.g., seat 428) extends circumferentially more than 120° about the corresponding cutter element (e.g., cutter element 230) such as for example greater than 180° about the corresponding cutter element.

[0095] The axial length or depth of pocket 427 (measured parallel to axis 427a) is less than the axial length of cutter element 230 (measured parallel to axis 235), and thus, in this embodiment, at least a portion of cutting layer 232 extends axially (relative to axes 427a, 235) from pocket 427, head 425, and pod 420. In side view of Figure 24, central axis 427a is oriented at an acute angle a relative to central axis 415 of pod 410. Semi-spherical projection 429 is coaxially aligned with central axis 427a and is shaped to be received by mating semi-spherical recess 352 of socket 350. In some embodiments, a rubber gasket or epoxy seal can be sandwiched between trailing side 41 1 along the outer perimeter of pod 410 and blade 341 to reduce the potential for fluid erosion.

[0096] To secure cutter element 230 within mating pocket 427, cutter element 230 is slidingly disposed within pocket 427 with substrate 231 seated against the closed end of pocket 427 and the cylindrical outer surface of cutter element 230 seated against seat 428. Then cutter element 230 is rotated within pocket 427 while simultaneously being brazed to head 425. In particular, the melted or “wet” brazing filler material is applied between the outer surface of cutter element 230 and head 425 within mating seat 428, and flows therebetween via capillary action. Cutter element 230 is rotated during the process to allow dispersion of the wet brazing filler material across the outer surface of cutter element 230 engaging head 425 to maximize the surface area coverage and strength of the bond between cutter element 230 and head 425. Surface area coverage of the wet brazing material can be visually confirmed as cutter element 230 is rotated by viewing the outer surface of cutter element 230 through the open portion of pocket 427 at first end 410a. It should be appreciated that cutter element 230 can be removed from pocket 427 of head 425 for maintenance, repair, or replacement by heating pod 410 and/or cutter element 230 to melt the brazing therebetween, and then rotating and pulling cutter element 230 from pocket 427. Similarly, cutter element 230 can be rotated relative to head 425 to position a fresh or unworn portion of cutting edge of cutting layer 232 for engaging the formation during subsequent drilling operations by heating pod 410 and/or cutter element 230 to melt the brazing therebetween and then rotating cutter element 230 relative to head 425, and then re-brazing cutter element 230 to head 425 as previously described. These processes for attaching cutter element 230 to pod 410, removing cutter element 230 from pod 410, and rotating cutter element 230 relative to pod 410 are preferably performed without pod 410 attached to the bit (e.g., bit 100) for the reasons previously described. To minimize exposure of cutter element 230 to excess heat, pod 410 can be heated and/or a heat sink applied to cutter element 230.

[0097] Referring now to Figure 22, cutter element assembly 400 is mounted to the corresponding blade 341 with pod 410 fixably secured within a corresponding, mating socket 350. More specifically, axis 427a of pocket 427 is coaxially aligned with the central axis of base section 351 a of socket 351 , head 425 is seated in mating base section 351a of socket 351 , semi-spherical projection 429 seated in mating semi- spherical recess 352 of socket 350 to form a ball-and-socket joint or connection, and tab 420 is seated in mating leg recess 351 b with leading side 411 generally flush with leading side 341 a of blade 341 . Hole 423 in tab 420 is coaxially aligned with internally threaded bore 357, and a bolt 424 is passed through hole 423 and threaded into bore 357, thereby removably and fixably securing pod 410 to blade 341. With such arrangement, pod 410, and hence cutter element assembly 400, is restricted and/or prevented from moving rotationally and translationally relative to blade 341 during drilling operations. In general, cutter element 230 can be disposed within recess 427 of head 425 and secured thereto as previously described before or after securing pod 410 to blade 341.

[0098] Referring still to Figure 22, cutter element assembly 400 is mounted with central axis 235 of cutter element 230 oriented at an acute backrake angle measured between axis 235 and cutter-supporting surface 344 of blade 341 . As previously described, during drilling operations, cutter-supporting surface 344 is parallel to the surface of the formation being cut by cutter element 230, and thus, central axis 235 is also oriented at acute angle p relative to the surface of the formation being cut by cutter element 230. The backrake angle can be varied by adjusting the angle a between axis 427a (and the central axis of base section 351 a of socket 351 ) and axis 415 of pod 410. As previously described, for balancing of forces acting on cutter element 230 while ensuring a fixed, secure connection between cutter element assembly 400 and blade 341 in embodiments described herein, as the ratio of torque F-rorque to force FWOB increases, axes 355, 415 are rotated in the plane containing axes 355, 415 and oriented generally perpendicular to sides 341a, 341 b (as shown in Figure 22) to move post 420 further “behind” cutter element 230 and more toward alignment with torque F-rorque (axes 355, 415 are rotated clockwise in Figure 22); and as the ratio of torque F-rorque to force FWOB decreases, axes 355, 415 are rotated in the plane containing axes 355, 415 and oriented generally perpendicular to sides 341 a, 341 b (as shown in Figure 22) to move post 420 closer to a position more aligned with WOB (axes 355, 415 are rotated counter-clockwise in Figure 22).

[0099] In the embodiment of cutter element assembly 400 previously described, cutter element 230 incudes a carbide substrate 231 and a polycrystalline diamond cutting layer 232. However, in some embodiments, it may be desirable to make the entire cutter element from polycrystalline diamond (i.e. , eliminate the carbide substrate). For example, referring now to Figures 25 and 26, an embodiment of a cutter element assembly 500 including a pod 510 and a cutter element 530 consisting entirely of a fully leached disc of polycrystalline diamond (i.e., a free standing diamond table) is shown. Pod 510 is the same as pod 410 previously described with the exception that seat 428 extends circumferentially more than 180° about the cylindrical outer surface of cutter element 530. Cutter element 530 is substantially the same as cutting layer 232 previously described, and thus, cutter element 530 has a central axis 235 and a cutting face 233 as previously described. Cutter element assembly 500 is attached to a blade (e.g., blade 341 ) in the same manner as previously desired with respect to cutter element assembly 400 and blade 341 . Cutter element 530 can be attached to pod 510 within pocket 427 against seat 428 via active brazing techniques (containing Titanium, silicon, chromium or like material to create a chemical reaction with the diamond). Cutter element assembly 500 is mounted in a socket in a blade of a drill bit (e.g., socket 350 of blade 341) in the same manner as previously described.

[00100] In some embodiments, a plurality of cutter elements 530 are stacked within the pocket of the pod (e.g., within pocket 427 of pod 510) such that as the leading cutter elements 530 wears, a new trailing cutter element 530 is exposed to take over cutting duties. In still other embodiments, alternating cutter elements 530 can be sandwiched between discs of tungsten carbide or other hard materials. Different grades of diamond can be used in different cutter elements 530 stacked within the pocket of the pod to provide tailored cutting characteristics.

[00101] In some embodiments, the pod may extend across a portion of the cutting face of the cutter element to aid in securing the cutter element within the pocket of the pod. For example, referring now to Figures 27 and 28, an embodiment of a cutter element assembly 600 including a pod 610 and a cutter element 530 as previously described is shown. Pod 610 is the same as pod 510 previously described with the exception that leading side 411 of pod 510 extends across a portion of cutting face 233 of cutter element 530. In particular, a wall 611 extends axially (relative to longitudinal axis 415) from tab 420 along leading side 41 1 across a portion of the open end of pocket 427. Wall 611 provides a barrier to restrict and/or prevent cutter element 530 from moving axially (relative to axis 427a) and detaching from pod 610. Cutter element 530 can be attached to pod 610 within pocket 427 against seat 428 via active brazing techniques. Cutter element assembly 600 is mounted in a socket in a blade of a drill bit (e.g., socket 350 of blade 341 ) in the same manner as previously described.

[00102] In the embodiments of cutter element assemblies 400, 500, 600 previously described, projection 429 is seated in mating recess 352 of socket 350 to form a ball- and-socket joint. Such a connection results in positive engagement of pod 410, 510, 610 and blade 341 , thereby restricting and/or preventing movement of cutter element assembly 400, 500, 600 relative to blade 341. However, in other embodiments, different types of interlocking and positively engaging structures can be employed between the pod of the cutter element assembly and the blade to restrict and/or prevent movement of the cutter element assembly relative to the blade. For example, referring now to Figures 29-31 , an embodiment of a cutter element assembly 700 including a pod 710 and a cutter element 530 as previously described is shown. Pod 710 is the same as pod 510 previously described with the exception that semi- spherical projection 429 of head 425 is replaced with an elongate planar shoulder 729 that extends laterally across trailing side 412. Shoulder 729 generally slopes toward first end 410a (away from end 410b) moving axially (relative to central axes 235, 427a) rearwardly away from leading side 411 . Consequently, shoulder 729 is oriented at a negative draft angle less than 90° relative to the adjacent portion of trailing side 412 extending toward end 410a.

[00103] As best shown in Figure 31 , an embodiment of a blade 741 having a socket 750 for receiving mating pod 710 is shown. Blade 741 and socket 750 are the same as blade 341 and socket 350 previously described with the exception that semispherical recess 352 is replaced by an elongate planar shoulder 752 sized and oriented to mate with and positively engage shoulder 729 of pod 710. It should be appreciated that due to the negative draft angle less than 90°, when pod 710 is seated in socket 750 and bolt 424 is threaded into bore 357, pod 710 and cutter element assembly 700 are restricted and/or prevented from moving translationally and rotationally relative to blade 741 .

[00104] In the manner described, embodiments of cutter element assemblies (e.g., cutter element assemblies 200, 400, 500, 600, 700) and associated cutter element carrying pods (e.g., pods 210, 410, 510, 610, 710) can be fixably and removably secured to blades of a drill bit (e.g., blades 141 , 142, 341 , 741 ). In general, the cutter element assemblies and associated pods are mounted in mating sockets (e.g., sockets 150, 350, 750) in the blade and then secured thereto (within the socket) via a removably attachment mechanism such as set screw, bolt, lock ring, or the like. The cutter element assemblies and associated pods can generally be removed by performing the mounting steps in reverse. If a particular pod is excessively worn, it can be removed and discarded (recycled) and a new pod can be mounted to the blade. [00105] The cutter element (e.g., cutter element 230, 530) is disposed in a mating pocket of the pod (e.g., pocket 227, 427) and brazed to the pod. In some embodiments, the entire bit is heated, and then individual cutters are inserted into mating pockets of the pods and rotated to promote optimal braze layer wetting and distribution. Alternatively, in other embodiments, individual cutter elements can be induction brazed to corresponding pods (not attached to the bit) relatively quickly using an automated system to quick heat the cutter element to a precise temperature and then drop the temperature back down quickly. In some embodiments, a window in the pod (e.g., window 228) facilitates visual inspection of the distribution of the molten braze during attachment of the cutter element to the pod. A cutter element can have a heat sink placed against the diamond hard cutting layer to minimize and/or avoid damage thereto while brazing the cutter into the pod socket. This avoids the pitfalls associated with heating the entire bit for extended periods of time. Once the cutter element is brazed to a pod, the pod can be individually cleaned, and grit blasted.

[00106] The cutter element can be rotated relative to the pod and/or removed from the pod during repair, maintenance, or replacement operations by heating the cutter element and/or the pod to melt the brazing. Such may be done while the pod is mounted to the blade or when the pod is not mounted to the blade. Upon repair of the bit, the pod can be removed, and the assembly can be induction heated upon which the cutter is rotated for a new use.

[00107] Hardfacing can be applied to the portions of the cutter elements that face the formation and/or applied to the portion of the pods that face the formation to enhance the abrasion resistance of the cutter elements and pods. For example, hardfacing can be applied by CNC application to precisely apply rows of hard material in a controlled manner on the outer surface of the pods. To minimize distortion of the pod and/or damage to a cutter element, a “dummy” plug of inert material such as graphite, compacted sand or pressed ceramic can be inserted into the pocket of the pod (instead of a cutter element) during application of the hardfacing.

[00108] In some embodiments, the pod substantially surrounds and encapsulates the corresponding cutter element (e.g., pod 210). Such encapsulation provides protection from harsh drilling environments, and protection from corrosion damage.

[00109] Pre-existing bit designs can be modified to accommodate embodiments of cutter element assemblies and pods described herein. In addition, the modular design of the embodiments of cutter element assemblies disclosed herein can accommodate installation into matrix material or steel bits. Traditional bit designs, in some embodiments, can be retained. In some embodiments, modification of traditional bit designs to receive the pods includes adding a socket extending vertically into the blade or forming a recess in the leading side of the blade. Matrix bits can be created using a graphite mold with displacements to create such sockets or recesses.

[00110] While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1 ), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.

Claims

CLAIMS What is claimed is:

1 . A modular fixed cutter drill bit for drilling an earthen formation, the drill bit having a central axis and a cutting direction of rotation about the central axis, the drill bit comprising: a bit body configured to rotate about the central axis in the cutting direction of rotation, wherein the bit body includes a bit face; a blade extending radially along the bit face, wherein the blade has a leading side relative to the cutting direction of rotation, a trailing side relative to the cutting direction of rotation, and a cutter-supporting surface extending from the leading side to the trailing side, and wherein the blade includes a socket extending from the cutter-supporting surface of the blade; a cutter element assembly mounted to the blade and extending from a cuttersupporting surface of the blade, wherein the cutter element assembly comprises: a pod seated in the socket and fixably attached to the blade; a cutter element fixably attached to the pod.

2. The modular fixed cutter drill bit of claim 1 , wherein the socket has an open end at the cutter-supporting surface and closed end distal the cutter-supporting surface.

3. The modular fixed cutter drill bit of claim 2, wherein the pod has a longitudinal axis, a first end, and a second end opposite the first end; wherein the pod includes a head at the first end and a post extending from the head to the second end; wherein the post and a portion of the head are slidingly disposed in the socket, and wherein the head extends from the open end of the socket; wherein the cutter element is fixably mounted to the head.

4. The modular fixed cutter drill bit of claim 3, wherein a cylindrical bore extends from the leading side of the blade to the socket, wherein the cylindrical bore defines a seat that engages and cradles the cutter element.

5. The modular fixed cutter drill bit of claim 3, wherein the pod has a front side relative to the cutting direction of rotation and a rear side relative to the cutting direction of rotation; wherein the head includes a recess extending from the front side of the pod; wherein the cutter element is seated in the recess of the head.

6. The modular fixed cutter drill bit of claim 5, wherein the recess of the head has a central axis oriented at an acute angle relative to the longitudinal axis of the pod.

7. The modular fixed cutter drill bit of claim 5, wherein the head includes a window extending from the first end of the pod to the recess of the head, wherein the window is configured to provide visual access to the portion of the cutter element disposed in the recess of the head.

8. The modular fixed cutter drill bit of claim 7, wherein the cutter element is brazed to the pod.

9. The modular fixed cutter drill bit of claim 1 , wherein the socket is disposed along the leading side of the blade.

10. The modular fixed cutter drill bit of claim 9, wherein the pod has a longitudinal axis, a first end, and a second end opposite the first end; wherein the pod includes a head at the first end of the pod and an elongate tab extending from the head to the second end of the pod; wherein the cutter element is fixably mounted to the head.

11 . The modular fixed cutter drill bit of claim 10, wherein the elongate tab is bolted to the blade.

12. The modular fixed cutter drill bit of clam 1 , wherein the cutter element consists entirely of leached polycrystalline diamond.

13. A modularfixed cutter drill bit for drilling an earthen formation, the drill bit having a central axis and a cutting direction of rotation about the central axis, the drill bit comprising: a bit body configured to rotate about the central axis in the cutting direction of rotation, wherein the bit body includes a bit face; a blade extending radially along the bit face, wherein the blade has a leading side relative to the cutting direction of rotation, a trailing side relative to the cutting direction of rotation, and a cutter-supporting surface extending from the leading side to the trailing side, and wherein the blade includes a socket extending from the cutter-supporting surface of the blade; a cutter element assembly fixably attached to the blade, wherein the cutter element assembly comprises: a cutter element carrier comprising a head and a post extending from the head, wherein the cutter element carrier is seated in the socket with the head extending from the cuttersupporting surface; a cutter element disposed in a cylindrical recess in the head and fixably attached to the head, wherein the cutter element has a forward-facing cutting face.

14. The modular fixed cutter drill bit of claim 13, wherein the socket has an open end at the cutter-supporting surface and closed end distal the cutter-supporting surface; wherein an internally threaded bore extends from the leading side of the blade to the socket; wherein a set screw is threadably disposed in the internally threaded bore and has a tip seated in a recess of the post.

15. The modular fixed cutter drill bit of claim 13, wherein the socket includes an annular seat; wherein the cutter element carrier has a radially outer surface comprising an annular shoulder that matingly engages the annular seat of the socket.

16. The modular fixed cutter drill bit of claim 13, wherein the cylindrical recess of in the head has a central axis oriented at an acute angle relative to a central axis of the post.

17. The modular fixed cutter drill bit of claim 13, wherein the head extends at least 180° about the cutter element.

18. The modular fixed cutter drill bit of claim 13, wherein the head extends at least 180° about the cutter element.

19. The modular fixed cutter drill bit of claim 13, wherein the cutter element is brazed to the pod.

20. The modular fixed cutter drill bit of claim 13, wherein a cylindrical bore extends from the leading side of the blade to the socket, wherein the cylindrical bore defines a seat that engages and cradles the cutter element.