FIXED CUTTER DRILL BITS INCLUDING CUTTER ELEMENTS WITH VARIABLE EXPOSURES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application claims benefit of U.S. provisional patent application Ser. No. 63/677,435 filed Jul. 31, 2024, and entitled “Fixed Cutter Drill Bits Including Cutter Elements with Variable Exposures,” 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 high aspect-ratio cutter elements and fixed cutter drill bits including high aspect-ratio cutter elements.

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 fixed cutter drill bits for drilling earthen formations are disclosed herein. In one embodiment, a fixed cutter drill bit for drilling an earthen formation comprises a bit body having a central axis and a bit face. The bit body is configured to rotate about the central axis in a cutting direction of rotation. The bit face includes a concave cone region extending radially from the central axis, a convex shoulder region extending radially from the cone region, a nose at the intersection of the cone region and the shoulder region, and a gage region extending radially from the shoulder region to a full gage diameter of the drill bit. The drill bit also comprises a cutting structure disposed on the bit face. The cutting structure includes a primary blade extending radially from proximal the bit axis through the cone region and the shoulder region to the gage region. 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. In addition, the drill bit comprises a plurality of cutter elements mounted to the cutter-supporting surface of the primary blade in the cone region, the shoulder region, and the gage region. The cutter elements are arranged in a row proximal the leading side of the primary blade and extending radially from the cone region proximal the bit axis to a gage pad extending from the primary blade. The plurality of cutter elements comprises a plurality of high-aspect ratio cutter elements in the cone region. Each cutter element has an exposure H measured perpendicularly from the cutter-supporting surface of the primary blade to a cutting tip of the cutter element distal the primary blade. The exposure H of one or more of the high-aspect ratio cutter elements in the cone region is greater than the exposure H of one or more cutter elements in the shoulder region and the gage region.

[0009]In another embodiment, a fixed cutter drill bit for drilling an earthen formation comprises a bit body having a central axis and a bit face. The bit body is configured to rotate about the central axis in a cutting direction of rotation. The bit face includes a concave cone region extending radially from the central axis, a convex shoulder region extending radially from the cone region, a nose at the intersection of the cone region and the shoulder region, and a gage region extending radially from the shoulder region to a full gage diameter of the drill bit. The drill bit also comprises a cutting structure disposed on the bit face. The cutting structure includes a plurality of circumferentially-spaced primary blades, wherein each primary blade extends radially from proximal the bit axis through the cone region and the shoulder region to the gage region, wherein each primary 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. Further, the drill bit comprises a plurality of gage pads. Each gage pad extends from an end of each primary blade distal the bit axis in the gage region. In addition, the drill bit comprises a plurality of high-aspect ratio cutter elements mounted to the cutter-supporting surface of each primary blade and arranged in a row proximal the leading side of the primary blade that extends radially from proximal the bit axis through the cone region to the shoulder region, into the shoulder region, or to the gage region. Moreover, the drill bit comprises a plurality of low-aspect ratio cutter elements mounted to the cutter-supporting surface of each primary blade and arranged in a row proximal the leading side of the primary blade that extends radially from the row of high-aspect ratio cutter elements through the shoulder region or the gage region to the gage pad.

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

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

[0014]FIG. 3 is an end view of the drill bit of FIG. 2;

[0015]FIG. 4 is a partial cross-sectional schematic view of the bit shown in FIG. 2 with the blades and the cutting faces of the cutter elements rotated into a single composite profile;

[0016]FIG. 5 is an enlarged, partial front view of one of the blades of the drill bit of FIG. 2;

[0017]FIG. 6 is a perspective view of one of the cutter elements of the drill bit of FIG. 2;

[0018]FIG. 7 is a front view of the cutter element of FIG. 6;

[0019]FIG. 8 is a side view of the cutter element of FIG. 6;

[0020]FIG. 9 is an enlarged, partial front view of an exemplary primary blade of an embodiment of a fixed cutter drill bit illustrating a plurality of the high-aspect ratio cutter elements of FIG. 7 oriented at different tilt angles;

[0021]FIG. 10 is an enlarged view of one primary blade and associated cutter elements the drill bit of FIG. 2;

[0022]FIG. 11 is a perspective view of an embodiment of a cutter element in accordance with the principles described herein for use with a fixed cutter drill bit;

[0023]FIG. 12 is a front view of the cutter element of FIG. 11;

[0024]FIG. 13 is a side view of the cutter element of FIG. 11;

[0025]FIG. 14 is a perspective view of an embodiment of a cutter element in accordance with the principles described herein for use with a fixed cutter drill bit;

[0026]FIG. 15 is a front view of the cutter element of FIG. 14;

[0027]FIG. 16 is a perspective view of an embodiment of a cutter element in accordance with the principles described herein for use with a fixed cutter drill bit;

[0028]FIG. 17 is a front view of the cutter element of FIG. 16;

[0029]FIG. 18 is a side view of an embodiment of a drill bit in accordance with the principles described herein;

[0030]FIG. 19 is an end view of the drill bit of FIG. 18;

[0031]FIG. 20 is a side view of an embodiment of a drill bit in accordance with the principles described herein; and

[0032]FIG. 21 is an end view of the drill bit of FIG. 20.

DETAILED DESCRIPTION

[0033]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.

[0034]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 or features 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.

[0035]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.

[0036]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.

[0037]Without regard to the type of bit, the cost of drilling a borehole for recovery of hydrocarbons may be very high, and is proportional to the length of time it takes to drill to the desired depth and location. The time required to drill the well, in turn, is greatly affected by the number of times the drill bit must be changed before reaching the targeted formation. This is the case because each time the bit is changed, the entire string of drill pipe, which may be miles long, must be retrieved from the borehole, section by section. Once the drill string has been retrieved and the new bit installed, the bit must be lowered to the bottom of the borehole on the drill string, which again must be constructed section by section. This process, known as a “trip” of the drill string, requires considerable time, effort and expense. Accordingly, it is desirable to employ drill bits which will drill faster and longer.

[0038]The length of time that a drill bit may be employed before it must be changed depends upon a variety of factors. These factors include the bit's rate of penetration (“ROP”), as well as its durability or ability to maintain a high or acceptable ROP. One factor that significantly affects bit ROP and durability is the arrangement of the cutter elements along the face of the drill bit. For example, the exposure of cutter elements from the blades and corresponding depth-of-cut (“DOC”) of the cutter elements, as well as the radial spacing of cutter elements along the blades of the drill bit can impact the aggressiveness and ROP of the drill bit. More specifically, the greater the exposure of cutter elements, the greater the aggressiveness and ROP of the drill bit, and the greater the radial spacing of cutter elements, the greater the aggressiveness and ROP of the drill bit. However, the cutter elements in the radially outer portions of the drill bit usually experience more wear and damage than the cutter elements in the radially inner portions of the drill bit. Thus, overly aggressive cutter element arrangements in the radially outer portions of the bit can compromise the durability of the drill bit. Accordingly, in contrast to most conventional fixed cutter drill bits that employ uniform radial spacing and exposure of cutter elements along the radially inner and radially outer portions of the drill bit, embodiments described herein include more aggressive cutter elements having relatively larger radial spacing and exposure in the radially inner portions of the drill bit and less aggressive cutter elements with relatively smaller radial spacing and exposure in the radially outer portions of the drill bit.

[0039]Referring now to FIG. 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 11. 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).

[0040]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.

[0041]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.

[0042]Referring now to FIGS. 2 and 3, 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.

[0043]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 FIG. 3, in this embodiment, cutting structure 140 includes three angularly spaced-apart primary blades 141 and two 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 and the two secondary blades 142 (a total of five blades 141, 142) are uniformly angularly spaced about 72° apart. In other embodiments, one or more of the blades may be spaced non-uniformly about bit face 111. Still further, in this embodiment, each secondary blade 142 is disposed between a pair of circumferentially-adjacent primary blades 141. Although bit 100 is shown as having three primary blades 141 and two 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, or three primary blades and three secondary blades.

[0044]Referring still to FIGS. 2 and 3, 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 141a, 142a, respectively, and a trailing edge or side 141b, 142b, respectively, relative to the cutting direction of rotation 106 of bit 100.

[0045]Each blade 141, 142 includes a cutter-supporting surface 144 that generally faces the formation during drilling and extends circumferentially from the leading side 141a to the trailing side 142 of the corresponding blade 141, 142. In this embodiment, a plurality of cutter elements 200, 300 are fixably attached to each blade 141, 142 and extend from cutter-supporting surface 144 of each blade 141, 142. Cutter elements 200, 300 are generally arranged adjacent one another in a radially extending row proximal the leading side 141a of each primary blade 141 and each secondary blade 142. However, in other embodiments, the cutter elements (for example, cutter elements 200, 300) may be arranged differently. In this embodiment of drill bit 100, cutter elements 200, 300 have different geometries. Namely, in this embodiment, each cutter element 200 has a generally oval prismatic shape, whereas each cutter element 300 has a generally cylindrical shape.

[0046]Referring now to FIGS. 2, 3, and 5, as will be described in more detail below, cutter elements 200 include a generally oval prismatic support base or substrate 201 and an oval prismatic disk or tablet-shaped hard cutting layer 220 bonded to the exposed end of substrate 201. Substrate 201 is made of a carbide material such as tungsten carbide, whereas cutting layer 220 is made of polycrystalline diamond or other superabrasive material. Substrate 201 has a central axis 205 that defines the central axis of cutter element 200. Each cutter element 200 is received and secured in a pocket formed along the cutter-supporting surface 144 of the corresponding blade 141, 142 to which it is mounted. Hard cutting layer 220 defines a cutting face 221 of the corresponding cutter element 200. In this embodiment, each cutting face 221 is the same and is planar. However, in other embodiments, one or more cutting faces (e.g., cutting faces 221) 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.

[0047]In this embodiment, each cutter element 300 includes an elongated and generally cylindrical support base or substrate 301 and a cylindrical disk or tablet-shaped, hard cutting layer 320 bonded to the exposed end of substrate 301. Substrate 301 is made of a carbide material such as tungsten carbide, whereas cutting layer 320 is made of polycrystalline diamond or other superabrasive material. Substrate 301 has a central axis 305 that defines the central axis of cutter element 300. Each cutter element 300 is received and secured in a pocket formed along the cutter-supporting surface 144 of the corresponding blade 141, 142 to which it is mounted. The cylindrical disc, hard cutting layer 320 defines a cutting face 321 of the corresponding cutter element 300. In this embodiment, each cutting face 321 is the same and is planar. However, in other embodiments, one or more cutting faces (e.g., cutting faces 321) 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.

[0048]In the embodiments described herein, each cutter element 200, 300 is mounted such that central axis 205, 305, respectively, 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 221, 321 being generally forward-facing relative to cutting direction 106 of bit 100. The portion of cutting face 221, 321 of each cutter element 200, 300, respectively, 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 228, 328 of cutting face 221, 321, respectively. As best shown in FIG. 5, each cutter element 200, 300 has an exposure or extension height H₂₀₀, H₃₀₀, respectively, measured perpendicularly from cutter-supporting surface 144 of the corresponding blade 141, 142 to cutting tip 228, 328, respectively.

[0049]Referring again to FIGS. 2 and 3, 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 elements 200 wear slightly under gage. Gage pads 147 also help stabilize bit 100 against vibration.

[0050]Referring now to FIG. 4, an exemplary profile of blades 141, 142 (right side of FIG. 4) and an exemplary profile of cutting faces 221, 321 (left side of FIG. 4) are shown as each would appear with blades 141, 142 and cutting faces 221, 321 rotated into a single rotated profile. In rotated profile view, blades 141, 142 form a combined or composite blade profile 148a generally defined by cutter-supporting surfaces 144 of blades 141, 142, and cutting tips 228, 328 of cutting faces 221, 321 form a combined or composite cutting tip profile 148b generally defined by a line passing through cutting tips 228, 328 of cutting faces 221, 321 mounted to 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 148a; and cutting tips 228, 328 on different blades 141, 142 are generally disposed along the generally smooth and continuous cutting profile 148b. As shown in FIG. 4, profiles 148a, 148b have a similar shape and are generally parallel to each other when rotated into a single profile.

[0051]Profiles 148a, 148b 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 148a 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 to herein as the nose 149d, occurs at the axially outermost portion of composite blade profile 148a (relative to bit axis 105) where a tangent line to the blade profile 148a 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 148a. As shown in composite blade profile 148a, gage pads 147 generally define the gage region 149c and the outer radius R₁₁₀ of bit body 110. Outer radius R₁₁₀ extends to and therefore defines the full gage diameter of bit 100.

[0052]Referring briefly to FIG. 3, 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 111 from cone region 149a 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. Further, in this embodiment, secondary blades 142 extend radially inward just inside cone region 149a proximal nose 149d, and thus, secondary blades 142 occupy very little 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 elements 200, 300) are possible.

[0053]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 FIGS. 2 and 3, 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 elements 200, 300 during drilling.

[0054]Referring again to FIGS. 2 and 3, on each blade 141, 142, cutter elements 200 are arranged side-by-side in a row along the corresponding cutter-supporting surface 144 proximal leading side 141a, 142a. Thus, in this embodiment, cutter elements 200 are positioned radially adjacent one another (relative to bit axis 105) on a given blade 141, 142. However, in other embodiments, the cutter elements (for example, cutter elements 200) may be arranged in rows with one or more cutter element having different geometries on the same blade (for example, blade 141, 142).

[0055]In general, a cutter element (e.g., cutter element 200, 300) may be described as having a “radial position” defined by the radial distance measured from the bit axis (e.g., bit axis 105) to the cutting tip (e.g., cutting tip 228, 328) along the cutting face (e.g., cutting face 221, 321) of the cutter element. It is to be understood that cutter elements arranged in a radially extending row on a given blade are disposed at different radial positions. In general, during rotation of the bit, cutter elements disposed at different radial positions on the same blade (e.g., blade 141, 142) or on different blades follow different paths that may partially overlap, whereas cutter elements disposed at the same radial positions on the same blade or on different blades follow in essentially the same path. Accordingly, each cutter element 200 has a radial position defined by the radial distance measured from bit axis 105 to the cutting tip 228 of the cutting face 221 of the cutter element 200, and each cutter element 300 has a radial position defined by the radial distance measured from bit axis 105 to the cutting tip 328 of the cutting face 321 of the cutter element 300. In addition, cutter elements 200, 300 arranged in a radially extending row on a given blade 141, 142 are disposed at different radial positions. Thus, each cutter element 200 on any given blade 141, 142 has a different radial position. In this embodiment, cutter elements 200, 300 on each and every blade 141, 142 are disposed at a different radial position. In other words, in this embodiment, each cutter element 200, 300 of bit 100 is disposed at a unique radial position. However, in other embodiments, two or more cutter elements (e.g., cutter elements 200, 300) may be disposed at the same radial position.

[0056]Referring now to FIGS. 6-8, one cutter element 200 will be described, it being understood the other cutter elements 200 are the same. As previously described, cutter element 200 includes substrate 201 and cutting layer 220 bonded to substrate 201. In particular, cutting layer 220 and substrate 201 meet at a reference plane of intersection 219 that defines the location at which substrate 201 and cutting layer 220 are fixably attached. Substrate 201 is made of tungsten carbide and cutting layer 220 is made of an ultrahard material such as polycrystalline diamond (PCD) or other superabrasive material. Part or all of the diamond in cutting layer 220 may be leached, finished, polished, or otherwise treated to enhance durability, efficiency or effectiveness. While cutting layer 220 is shown as a single layer of material mounted to substrate 201, in general, the cutting layer (for example, layer 220) may be formed of one or more layers of one or more materials. In addition, although substrate 201 is shown as a single, homogenous material, in general, the substrate (for example, substrate 201) may be formed of one or more layers of one or more materials.

[0057]Substrate 201 has central axis 205 as previously described, which defines the central axis of cutter element 200. In addition, substrate 201 has a first end 201a bonded to cutting layer 220 at plane of intersection 219, a second end 201b opposite end 201a and distal cutting layer 220, and a radially outer surface 202 extending axially between ends 201a, 201b. In this embodiment, ends 201a, 201b of substrate 201 are defined by planar surfaces oriented perpendicular to axis 205. As shown in FIGS. 2 and 3, each cutter element 200 is mounted to a corresponding blade 141, 142 with first end 201a leading second end 201b relative to cutting direction 106. Accordingly, first end 201a may also be referred to as “leading” end 201a, and second end 201b may also be described as “trailing” end 201b.

[0058]Referring again to FIGS. 6-8, as previously described, in this embodiment, cutter element 200 has a generally oval prismatic shape. More specifically, substrate 201 has a longitudinal axis 215 that defines the longitudinal axis of cutter element 200. In this embodiment, longitudinal axis 215 of substrate 201 is intersected by and oriented perpendicular to central axis 205, and further, longitudinal axis 215 is oriented parallel to the planar surfaces defining ends 201a, 201b. In addition, in this embodiment, axes 205, 215 lie in a common plane that divides cutter element 200 lengthwise into equal, mirror image halves.

[0059]Outer surface 202 includes a pair of parallel, planar lateral sides 213, a first or upper convex (bowed outwardly) surface 214 extending between lateral sides 213, and a second or lower convex (bowed outwardly) surface 216 extending between lateral sides 213. Lateral sides 213 are oriented parallel to axes 205, 215, convex surfaces 214, 216 are oriented parallel to central axis 205 but are intersected by longitudinal axis 215. In this embodiment, convex surfaces 214, 216 are semi-cylindrical surfaces that are intersected by longitudinal axis 215 at their respective centers that are furthest from central axis 205.

[0060]Referring still to FIGS. 6-8, cutting layer 220 has a central axis coincident with central axis 205 of substrate 201. In addition, cutting layer 220 has a first end 220a distal substrate 201, a second end 220b opposite end 220a and bonded to substrate 201 at plane of intersection 219, and a radially outer surface 222 extending axially between ends 220a, 220b. In this embodiment, ends 220a, 220b of cutting layer 220 are defined by planar surfaces oriented perpendicular to axis 205. In particular, end 220a of cutting layer 220 defines planar cutting face 221 as previously described. In this embodiment, a chamfer or bevel 227 extends about the entire outer perimeter of cutting layer 220 at the intersection of outer surface 222 and cutting face 221. As shown in FIGS. 2 and 3, each cutter element 200 is mounted to a corresponding blade 141, 142 with first end 220a leading second end 220b relative to cutting direction 106. Accordingly, first end 220a may also be referred to as “leading” end 220a, and second end 220b may also be described as “trailing” end 220b.

[0061]Referring again to FIGS. 6-8, cutting layer 220 has a geometry that is the generally the same as substrate 201 with the exception that, in this embodiment, cutting layer 220 has a thickness measured axially relative to axis 205 from leading end 220a to trailing end 220b that is less than a thickness of substrate 201 measured axially relative to axis 205 from leading end 201a to trailing end 201b. More specifically, cutting layer 220 has a longitudinal axis 225 that is intersected by and oriented perpendicular to central axis 205, and oriented parallel to the planar surfaces defining ends 220a, 220b. In this embodiment, axes 205, 215, 225 lie in a common plane that divides cutter element 200 lengthwise into equal, mirror image halves. Outer surface 222 of cutting layer 220 is contiguous with outer surface 202 of substrate 201. In particular, outer surface 222 includes a pair of parallel, planar lateral sides 223 that are contiguous and coplanar with sides 213 of substrate 201, a first or upper convex (bowed outwardly) surface 224 extending between lateral sides 223 and contiguous with surface 214 of substrate 201, and a second or lower convex (bowed outwardly) surface 226 extending between lateral sides 223 and contiguous with surface 216 of substrate 201. Thus, lateral sides 223 are oriented parallel to axes 205, 215, 225, convex surfaces 224, 226 are oriented parallel to central axis 205 but are intersected by longitudinal axis 225. Convex surfaces 224, 226 are contiguous with convex surfaces 214, 216, and thus, convex surfaces 224, 226 are semi-cylindrical surfaces that are intersected by longitudinal axis 225 at their respective centers that are furthest from central axis 205.

[0062]As best shown in FIG. 7, cutter element 200, substrate 201, and cutting layer 220 have a common length L₂₀₀ measured axially relative to axes 215, 225 from convex surface 214, 216 to convex surface 224, 226, respectively; and a width W₂₀₀ measured perpendicularly to longitudinal axes 215, 225 and sides 213, 223, respectively, in front view from one side 213, 223 to the opposite side 213, 223, respectively. Due to the oval prismatic shape of cutter element 200 (and substrate 201 and cutting layer 220), the length L₂₀₀ is greater than the width W₂₀₀. In embodiments described herein, for most drilling applications, the length L₂₀₀ of cutter element 200 is preferably greater than or equal to 10.0 mm and less than or equal to 30.0 mm, and the width W₂₀₀ of cutter element 200 is preferably greater than or equal to 5.0 mm and less than 30.0 mm. Cutter element 200 may also be characterized by an aspect ratio equal to the ratio of the length L₂₀₀ of cutter element 200 to the width W₂₀₀ of cutter element 200. As the length L₂₀₀ is greater than the width W₂₀₀, the aspect ratio of cutter element 200 is greater than 1.0. More specifically, in embodiments described herein, the aspect ratio of cutter element 200 is greater than 1.0 and preferably less than or equal to 2.0. It should be appreciated that a conventional cylindrical cutter element such as cutter element 300 has an aspect ratio of 1.0 as the length and the width of such a cutter element in front view (as viewed perpendicular to the cutting face) are the same, and in particular, the length and the width is each equal to the outer diameter of the cutter element. For purposes of clarity and further explanation, a cutter element having an aspect ratio greater than 1.0 (e.g., cutter element 200) may also be referred to herein as a “high-aspect ratio” cutter element, and a cutter element having an aspect ratio equal to 1.0 (e.g., conventional cylindrical cutter elements such as cutter element 300) may also be referred to herein as a “low-aspect ratio” cutter element. Thus, oval cutter element 200 is a high-aspect ratio cutter element, whereas cylindrical cutter element 300 is a low-aspect ratio cutter element. In the embodiment shown in FIGS. 6-8, the length L₂₀₀ of cutter element 200 is 25.0 mm and the width W₂₀₀ of cutter element 200 is 16.0 mm, and thus, the aspect ratio of cutter element 200 is 1.5625.

[0063]Referring now to FIGS. 2-5, as previously described, cutter elements 200, 300 are generally arranged adjacent one another in a radially extending row proximal the leading side 141a of each primary blade 141 and each secondary blade 142. More specifically, in this embodiment, on each primary blade 141, high-aspect ratio cutter elements 200 are positioned adjacent each other in a row extending along cone region 149a and nose 149d into shoulder region 149b; on each secondary blade 142, a high-aspect ratio cutter element 200 is positioned in shoulder region 149b adjacent nose 149d; and on each blade 141, 142, low-aspect ratio cutter elements 300 are positioned adjacent each other in a row extending along shoulder region 149b and gage region 149c of bit face 111. Thus, in this embodiment, with the exception of up to one high-aspect ratio cutter element 200 on one or more blades 141, 142 that may extend into shoulder region 149c radially adjacent nose 149d, high-aspect ratio cutter elements 200 are generally not positioned in shoulder region 149b or gage region 149c of bit face 111; and low-aspect ratio cutter elements 300 are generally not positioned in cone region 149a of bit face 111. Collectively, cutter elements 200, 300 on each blade 141, 142 form a single row along the blade 141, 142 with high-aspect ratio cutter elements 200 forming a portion of the row extending from proximal bit axis 105 to shoulder 149b, and low-aspect ratio cutter elements 300 forming a portion of the row extending from shoulder region 149b radially adjacent nose 149d to outer radius R₁₁₀ and the full gage diameter of bit 100. As will be described in more detail below, in other embodiments, on one or more primary blades (e.g., primary blades 141) and/or one or more secondary blades (e.g., secondary blades 142), the row of cutter elements along the leading side of the blade (e.g., leading side 141a) may include (i) radially adjacent high-aspect ratio cutter elements (e.g., cutter elements 200) extending along the row through the cone region (e.g., cone region 149a) and into the shoulder region (e.g., more than one high-aspect ratio cutter element 200 in shoulder region 149b), with the remaining cutter elements in the row on the same blade being low-aspect ratio cutter elements (e.g., low aspect-ratio cutter elements 300) disposed along the remainder of the shoulder region and the gage region (e.g., gage region 149c) (e.g., only high-aspect ratio cutter elements 200 in the cone region 149a, only high-aspect ratio cutter elements 200 in a radially inner portion of the shoulder region 149b, only low-aspect ratio cutter elements in a radially outer portion of the shoulder region 149b, and only low-aspect ratio cutter elements in the gage region 149c); or (ii) radially adjacent high-aspect ratio cutter elements (e.g., cutter elements 200) extending along the row through the cone region (e.g., cone region 149a) and the shoulder region to the gage region, with the remaining cutter elements in the row on the same blade being low-aspect ratio cutter elements (e.g., low aspect-ratio cutter elements 300) disposed along the gage region (e.g., only high-aspect ratio cutter elements 200 in the cone region 149a and the shoulder region 149b, and only low-aspect ratio cutter elements in the gage region 149c).

[0064]Referring still to FIGS. 2-5, in this embodiment, the radial spacing between each pair of radially adjacent high-aspect ratio cutter elements 200 on each blade 141, 142 (FIGS. 2, 3, and 5) and in composite blade profile 148b (FIG. 4) is greater than the radial spacing between each pair of radially adjacent low-aspect ratio cutter elements 300 on each blade 141, 142 (FIGS. 2, 3, and 5) and in composite blade profile 148b (FIG. 4); and further, with the exception of the radially outermost high-aspect ratio cutter element 200 on each blade 141, 142, the exposure H₂₀₀ of each high-aspect ratio cutter element 200 on each blade 141, 142 (FIGS. 2, 3, and 5) and in composite blade profile 148b (FIG. 4) is greater than the exposure H₃₀₀ of each low-aspect ratio cutter element 300 on each blade 141, 142 (FIGS. 2, 3, and 5) and in composite blade profile 148b (FIG. 4). Without being limited by this or any particular theory, the greater the spacing of radially adjacent cutter elements, the greater the aggressiveness of the cutter elements, and the greater the exposure of cutter elements, the greater the aggressiveness of the cutter elements. Thus, in embodiments described herein, high-aspect ratio cutter elements 200 are generally more aggressive than low-aspect ratio cutter elements 200. It should also be appreciated that cutter elements positioned in the cone region of the bit face (e.g., cone region 149a) and proximal the nose region (e.g., nose region 149d) offer the potential to enhance ROP to a greater extent as compared to cutter elements positioned in the shoulder and gage region (e.g., shoulder region 149b and gage region 149c) of the bit face; whereas cutter elements positioned in the shoulder and gage region of the bit face are more susceptible to wear as compared to cutter elements in the cone region of the bit face and proximal the nose region. Thus, the more aggressive high-aspect ratio cutter elements 200 are positioned along bit face 111 in locations that offer the greatest potential to increase ROP and are least susceptible to wear.

[0065]Referring now to FIG. 5, the spacing of radially adjacent cutter elements 200, 300 will be described it being understood cutter elements 200, 300 on each blade 141, 142 are similarly arranged in this embodiment. In front view of each blade 141, 142 (i.e., when viewing leading side 141a, 142a of blade 141, 142 parallel to cutting direction 106 and perpendicular to leading side 141a, 142a), each pair of radially adjacent high-aspect ratio cutter elements 200 are spaced apart a minimum distance D₂₀₀ measured parallel to cutter-supporting surface 144 of the blade 141, 142 between the radially adjacent cutter elements 200, and each pair of radially adjacent low-aspect ratio cutter elements 300 are spaced apart a minimum distance D₃₀₀ measured parallel to cutter-supporting surface 144 of the blade 141, 142 between the radially adjacent cutter elements 300. In this embodiment, the minimum distance D₂₀₀ between each pair of radially adjacent high-aspect ratio cutter elements 200 mounted to blade 141 is greater than the minimum distance D₃₀₀ between each pair of radially adjacent low-aspect ratio cutter elements 300 mounted to blade 141. It should be appreciated that although each minimum distance D₂₀₀ is greater than each minimum distance D₃₀₀, one or more distances D₂₀₀ may be different from one or more other distances D₂₀₀ and one or more distances D₃₀₀ may be different from one or more other distances D₃₀₀. In other words, each minimum distance D₂₀₀ does not need to be the same and each minimum distance D₃₀₀ does not need to be the same. In embodiments described herein, each minimum distance D₂₀₀ ranges from about 4.0 mm to about 20.0 mm, alternatively ranges from about 6.0 mm to about 18.0 mm, alternatively ranges from about 8.0 mm to about 16.0 mm, and alternatively ranges from about 10.0 mm to about 12.0 mm; and each minimum distance D₃₀₀ ranges from 1.0 mm to 3.0 mm. Still further, in embodiments described herein, the minimum distance D₂₀₀ between each pair of radially adjacent high-aspect ratio cutter elements 200 on each blade 141, 142 is at least 1.5 times the minimum distance D₃₀₀ between each pair of radially adjacent low-aspect ratio cutter elements 300 on each blade 141, 142 (i.e., at least 50% greater), alternatively the minimum distance D₂₀₀ between each pair of radially adjacent high-aspect ratio cutter elements 200 on each blade 141, 142 is at least 2.0 times the minimum distance D₃₀₀ between each pair of radially adjacent cutter elements 300 on each blade 141, 142 (i.e., at least 100% greater), alternatively the minimum distance D₂₀₀ between each pair of radially adjacent high-aspect ratio cutter elements 200 on each blade 141, 142 is at least 3 times the minimum distance D₃₀₀ between each pair of radially adjacent cutter elements 300 on each blade 141, 142 (i.e., at least 200% greater), alternatively the minimum distance D₂₀₀ between each pair of radially adjacent high-aspect ratio cutter elements 200 on each blade 141, 142 is at least 4 times the minimum distance D₃₀₀ between each pair of radially adjacent cutter elements 300 on each blade 141, 142 (i.e., at least 300% greater), alternatively the minimum distance D₂₀₀ between each pair of radially adjacent high-aspect ratio cutter elements 200 on each blade 141, 142 is at least 5 times the minimum distance D₃₀₀ between each pair of radially adjacent cutter elements 300 on each blade 141, 142 (i.e., at least 400% greater), and alternatively the minimum distance D₂₀₀ between each pair of radially adjacent high-aspect ratio cutter elements 200 on each blade 141, 142 is at least 6 times the minimum distance D₃₀₀ between each pair of radially adjacent cutter elements 300 on each blade 141, 142 (i.e., at least 500% greater). Although the minimum distance D₂₀₀ between each pair of radially adjacent high-aspect ratio cutter elements 200 mounted to a given blade 141, 142 is greater than the minimum distance D₃₀₀ between each pair of radially adjacent low-aspect ratio cutter elements 300 mounted to the same blade 141, 142 in the embodiment of drill bit 100 shown and described above, in other embodiments, the minimum distance D₂₀₀ between each pair of radially adjacent high-aspect ratio cutter elements 200 mounted to a given blade 141, 142 may be equal to or greater than the minimum distance D₃₀₀ between each pair of radially adjacent low-aspect ratio cutter elements 300 mounted to the same blade 141, 142.

[0066]Referring still to FIG. 5, the exposures H₂₀₀, H₃₀₀ of cutter elements 200, 300 mounted to one exemplary primary blade 141 will be described it being understood the exposures H₂₀₀, H₃₀₀ of cutter elements 200, 300 on each blade 141, 142 are similarly arranged. The radially outermost high-aspect ratio cutter element 200 on blade 141 is radially adjacent the low-aspect ratio cutter elements 300 on blade 141 at or proximal nose 149d, and hence, the radially outermost high-aspect ratio cutter element 200 on blade 141 generally marks the transition between high-aspect ratio cutter elements 200 on blade 141 and low-aspect ratio cutter elements 300 on blade 141. Accordingly, the radially outermost high-aspect ratio cutter element 200 on blade 141 may also be referred to herein as the “transition” high-aspect ratio cutter element 200, and the remaining high-aspect ratio cutter elements 200 on blade 141 may also be referred to herein as the “non-transition” high-aspect ratio cutter elements 200. As previously described, in this embodiment, each cutter element 200, 300 is disposed at a unique radial position, and thus, each transition high-aspect ratio cutter element 200 is disposed at a different and unique radial position. Consequently, the transition from high-aspect ratio cutter elements 200 to low-aspect ratio cutter elements 300 on each blade 141, 142 occurs at a different and unique radial position.

[0067]In this embodiment, the exposure H₂₀₀ of the transition high-aspect ratio cutter element 200 on blade 141 is the same or substantially the same as the exposure H₃₀₀ of each low-aspect cutter element 300 on blade 141 to ensure a generally continuous and smooth transition along cutting profile 148b between high-aspect ratio cutter elements 200 and low-aspect ratio cutter elements 300. However, the exposure H₂₀₀ of each non-transition high-aspect ratio cutter element 200 mounted to blade 141 (i.e., each high-aspect ratio cutter element 200 mounted to blade 141 other than the transition high-aspect ratio cutter element 200) is greater than the exposure H₃₀₀ of each low-aspect ratio cutter element 200 mounted to blade 141. Thus, the exposure H₂₀₀ of each non-transition high-aspect ratio cutter element 200 mounted to blade 141 is greater than the exposure H₂₀₀ of the transition high-aspect ratio cutter element 200 mounted to blade 141. It should be appreciated that although exposure H₂₀₀ of each non-transition high-aspect ratio cutter element 200 is greater than each exposure H₃₀₀, one or more exposure(s) H₂₀₀ of non-transition high-aspect ratio cutter elements 200 may be different from one or more other exposure(s) H₂₀₀, and one or more exposure(s) H₃₀₀ may be different from one or more other exposure(s) H₃₀₀. In other words, exposure H₂₀₀ of each non-transition high-aspect ratio cutter element 200 does not need to be the same and each exposure H₃₀₀ does not need to be the same. In embodiments described herein, the exposure H₂₀₀ of each non-transition high-aspect ratio cutter element 200 preferably ranges from about 6.0 mm to about 15.0 mm, alternatively ranges from 10.0 mm to 15.0 mm; and the exposure H₂₀₀ of the transition high-aspect ratio cutter element 200 and the exposure H₃₀₀ of each low-aspect ratio cutter element 300 ranges from 5.0 mm to 13.0 mm. In addition, in embodiments described herein, the exposure H₂₀₀ of each non-transition high-aspect ratio cutter element 200 on each blade 141, 142 ranges from 40% to 60% of the length L₂₀₀ of the high-aspect ratio cutter element 200. Still further, in embodiments described herein, the exposure H₂₀₀ of each non-transition high-aspect ratio cutter element 200 of bit 100 is greater than 1.0 times the exposure H₃₀₀ of each low-aspect ratio cutter element 300 on bit 100, alternatively at least 1.25 times the exposure H₃₀₀ of each low-aspect ratio cutter element 300 on bit 100, alternatively at least 1.5 times the exposure H₃₀₀ of each low-aspect ratio cutter element 300 on bit 100, and alternatively at least 1.75 times the exposure H₃₀₀ of each low-aspect ratio cutter element 300 on bit 100.

[0068]Referring again to FIGS. 2-5, the high-aspect ratio cutter elements 200 may be tilted to ensure and/or maintain a desired clearance with each radially adjacent cutter element 200, 300. More specifically as best shown in FIG. 5, the tilting of high-aspect ratio cutter elements 200 mounted to one exemplary primary blade 141 will be described it being understood the high-aspect ratio cutter elements 200 on each blade 141, 142 are similarly arranged. In front view of each blade 141, 142 (i.e., when viewing leading side 141a, 142a of blade 141, 142 parallel to cutting direction 106 and perpendicular to leading side 141a, 142a), one or more high-aspect ratio cutter elements 200 can be tilted or rotated relative to cutting profile 148b. More specifically, one or more high-aspect ratio cutter elements 200 can be oriented at a non-zero tilt angle α measured from the longitudinal axis 215, 225 of the cutter element 200 to a reference axis A oriented perpendicular to cutting profile 148b at the cutting tip 228 and passing through the cutting tip 228 of the cutter element 200. For purposes of clarity, for a high-aspect ratio cutter element 200 with a tilt angle α greater than zero (i.e., a positive tilt angle α), the longitudinal axis 215, 225 of the cutter element 200 is rotated counter-clockwise relative to the corresponding reference axis A in front view; for a high-aspect ratio cutter element 200 with a tilt angle α less than zero (i.e., a negative tilt angle α), the longitudinal axes 215, 225 of cutter element 200 are rotated clockwise relative to the corresponding reference axis A in front view; and for a high-aspect ratio cutter element 200 with a tilt angle α equal to zero (i.e., a cutter element that is not tilted), the longitudinal axes 215, 225 of cutter element 200 are coincident with the corresponding reference axis A in front view. In embodiments described herein, the tilt angle α of each high-aspect ratio cutter element 200 ranges from 0° to +/−45°, and preferably ranges from 0° to +/−15°. In the embodiment of bit 100 shown in FIGS. 2-5, each high-aspect cutter element 200 on each blade 141, 142 is oriented at a positive tilt angle α, and more particularly, oriented at a tilt angle α of +10°. However, in other embodiments, one or more high-aspect ratio cutter elements 200 on a given blade 141, 142 and/or different blades 141, 142 may be oriented at a positive tilt angle α, one or more high-aspect ratio cutter elements 200 on a given blade 141, 142 and/or different blades 141, 142 may be oriented at a negative tilt angle α, one or more high-aspect ratio cutter elements 200 on a given blade 141, 142 and/or different blades 141, 142 may be oriented at a tilt angle α of 0°, or combinations thereof. In addition, the tilt angles α of any two or more high-aspect ratio cutter elements 200 on a given blade 141, 142 and/or different blades 141, 142 may be the same or different. For example, referring briefly to FIG. 9, one exemplary primary blade 141 and associated cutter elements 200, 300 as previously described is shown. Blade 141 is the same as blade 141 shown in FIG. 5 and previously described with the exception that high-aspect ratio cutter elements 200 are oriented at different tilt angles α. More specifically, the radially innermost high-aspect ratio cutter element 200 (also labeled 200′ in FIG. 9) is oriented at a tilt angle α of 0°, the second radially innermost high-aspect ratio cutter element 200 (also labeled 200″ in FIG. 9) is oriented at a negative tilt angle α, and the third radially innermost high-aspect ratio cutter element 200 (also labeled 200″ in FIG. 9) is oriented at a positive tilt angle α.

[0069]Referring again to FIGS. 2 and 3, cutter elements 200, 300 are disposed in mating sockets in blades 141, 142 and extend from cutter-supporting surfaces 144 of blades 141, 142 to an extension height H₂₀₀, H₃₀₀, respectively, as previously described. In addition, the rear or trailing end of the portion of each high-aspect ratio cutter element 200 extending from cutter-supporting surface 144 of the corresponding blade 141, 142 is engaged by a back support 150 that extends or projects perpendicularly from the cutter supporting surface 144; and the rear or trailing end of the portion of each low-aspect ratio cutter element 300 extending from cutter-supporting surface 144 of the corresponding blade 141, 142 is engaged by a back support 160 that extends or projects perpendicularly from the cutter supporting surface 144. Back supports 150, 160 are integral with and monolithically formed with the corresponding blade 141, 142, and generally function to support cutter elements 200, 300 during drilling operations.

[0070]Referring now to FIG. 10, one exemplary back support 150 and one exemplary back support 160 of one exemplary primary blade 141 will be described it being understood that back supports 150, 160 on each blade 141, 142 is generally the same. Back support 150, 160 has a central axis 155, 165, respectively, a front or leading end 150a, 160a, respectively, relative to cutting direction 106, a rear or trailing end 150b, 160b, respectively, relative to cutting direction 106, and an outer surface 151, 161, respectively, extending axially (relative to the corresponding axis 155, 165) from the leading end 150a, 160a, respectively, to trailing end 150b, 160b, respectively.

[0071]As extension heights H₂₀₀ of the non-transition high-aspect ratio cutter elements 200 are greater than the extension heights H₃₀₀ of the low-aspect ratio cutter elements 300, and the minimum distance D₂₀₀ between radially adjacent high-aspect ratio cutter elements 200 is greater than the minimum distance D₃₀₀ between the radially adjacent low-aspect ratio cutter elements 300, high-aspect ratio cutter elements 200 generally experience greater impact loads (forces oriented perpendicular to cutting faces 221) during drilling operations as compared to the impact loads experienced by low-aspect ratio cutter elements 300 (forces oriented perpendicular to cutting faces 321) during drilling operations. Accordingly, in embodiments described herein, back supports 150 supporting high-aspect ratio cutter elements 200 are larger and more robust than back supports 160 supporting low-aspect ratio cutter elements 300 to enable back supports 150 to support the greater loads experienced by high-aspect ratio cutter elements 200 as compared to low-aspect ratio cutter elements 300. In particular, leading ends 150a, 160a of back supports 150, 160 are generally contiguous and have the same cross-sectional profile (in a plane oriented perpendicular to central axis 155, 165, respectively) as the trailing end of the portion of the corresponding cutter element 200, 300, respectively, that extends from the corresponding cutter supporting surface 144. Thus, at leading end 150a, 160a, outer surface 151, 161, respectively, is generally contiguous with outer surface of the trailing end of the portion of the corresponding cutter element 200, 300, respectively, that extends from the corresponding cutter supporting surface 144. Moving axially relative to central axis 155, 165 from leading end 160a, 150a, respectively, to trailing end 150b, 160b, respectively, the portion of the outer surface 151, 161, respectively, of each back support 150, 160, respectively, distal the corresponding cutter-supporting surface 144 continuously curves or slopes toward the corresponding cutter-supporting surface 144, and the lateral sides of the outer surface 151, 161, respectively, of each back support 150, 160, respectively, that extend from the corresponding cutter-supporting surface 144 on opposite sides of central axis 155, 165, respectively, continuously slope or taper radially inwardly toward central axis 155, 165, respectively. However, each back support 150 has a length L₁₅₀ measured axially relative to central axis 155 from leading end 150a to trailing end 150b that is greater than a length L₁₆₀ of each back support 160 measured axially relative to central axis 165 from leading end 160a to trailing end 160b. In addition, as the exposure H₂₀₀ of each high-aspect ratio cutter element 200 is greater than the exposure H₃₀₀ of each low-aspect ratio cutter element 300, back supports 150 extend perpendicularly from the corresponding cutter-support surface 144 further than back supports 160 of low-aspect ratio cutter elements 300. In other words, back supports 150 are taller and longer than back supports 160. Thus, back supports 150 associated with high-aspect ratio cutter elements 200 are generally longer, larger, and more robust than back supports 160 associated with low-aspect ratio cutter elements 300.

[0072]Referring still to FIG. 3, due to the rotation of drill bit 100 about central axis 105 and the axial advancement of drill bit 100 along central axis 105 during drilling operations, each cutter element 200, 300 generally moves in a helical path during drilling operations. Due to the extended length L₁₅₀ and height (relative to the corresponding cutter-supporting surface 144) of each back support 150 associated with a corresponding high-aspect ratio cutter element 200 as compared to the shorter length L₁₆₀ and height (relative to the corresponding cutter-supporting surface 144) of each back support 160 associated with a corresponding low-aspect ratio cutter element 160, outer surfaces 151 of the relatively large back supports 150 are more susceptible to undesirable engagement and rubbing against the formation within the kerf cut by the associated cutter element 200. Accordingly, in embodiments described herein, central axis 155 and outer surface 151 of each back support 150 follows a curved helical path (i) generally disposed and centered at the radial position of the corresponding high-aspect ratio cutter element 200, and (ii) with the portion of outer surface 151 distal the corresponding cutter-supporting surface 144 continuously sloping toward the cutter-supporting surface 144 moving axially (relative to central axis 155) from leading end 150a to trailing end 150b to prevent and/or reduce the likelihood of outer surface 151 undesirable rubbing against the formation within the kerf cut by the associated cutter element 200.

[0073]As previously described and shown in FIG. 5, high-aspect ratio cutter elements 200 may be tilted to ensure and/or maintain a desired clearance with each radially adjacent cutter element 200, 300. In the embodiment of high-aspect ratio cutter element 200 shown in FIGS. 2-9, planar lateral sides 213 are oriented parallel to each other. However, in other embodiments, the orientation of the planar lateral sides of the high-aspect ratio cutter element (e.g., lateral sides 213 of high-aspect ratio cutter element 200) can taper toward each other to offer the potential for enhanced clearance with radially adjacent cutter elements without or with reduced tilting. For example, referring now to FIGS. 11-13, an embodiment of a tear-drop shaped high-aspect ratio cutter element 400 that can be used in place of one or more high-aspect ratio cutter elements 200 of bit 100 is shown. High-aspect ratio cutter element 400 is substantially the same as high-aspect ratio cutter element 200 previously described with the exception that the lateral sides of high-aspect ratio cutter element 400 are not oriented parallel to teach other, but rather, taper inwardly toward each other. More specifically, cutter element 400 includes a substrate 401 and a cutting layer 420 bonded to substrate 401 at a reference plane of intersection 419 that defines the location at which substrate 401 and cutting layer 420 are fixably attached. Substrate 401 is made of tungsten carbide and cutting layer 420 is made of an ultrahard material such as polycrystalline diamond (PCD) or other superabrasive material. Part or all of the diamond in cutting layer 420 may be leached, finished, polished, or otherwise treated to enhance durability, efficiency or effectiveness. While cutting layer 420 is shown as a single layer of material mounted to substrate 401, in general, the cutting layer (for example, layer 420) may be formed of one or more layers of one or more materials. In addition, although substrate 401 is shown as a single, homogenous material, in general, the substrate (for example, substrate 401) may be formed of one or more layers of one or more materials.

[0074]Substrate 401 has central axis 405, which defines the central axis of cutter element 400. In addition, substrate 401 has a first end 401a bonded to cutting layer 420 at plane of intersection 419, a second end 401b opposite end 401a and distal cutting layer 420, and a radially outer surface 402 extending axially between ends 401a, 401b. In this embodiment, ends 401a, 401b of substrate 401 are defined by planar surfaces oriented perpendicular to axis 405. Cutter element 400 is mounted to a corresponding blade of a fixed cutter drill bit (e.g., a blade 141, 142) with first end 401a leading second end 401b relative to cutting direction of rotation of the drill bit (e.g., cutting direction 106). Accordingly, first end 401a may also be referred to as “leading” end 401a, and second end 401b may also be described as “trailing” end 401b.

[0075]Referring still to FIGS. 11-13, in this embodiment, cutter element 400 has a tear drop prismatic shape. More specifically, substrate 401 has a longitudinal axis 415 that defines the longitudinal axis of cutter element 400. In this embodiment, longitudinal axis 415 of substrate 401 is intersected by and oriented perpendicular to central axis 405, and further, longitudinal axis 415 is oriented parallel to the planar surfaces defining ends 401a, 401b. In addition, in this embodiment, axes 405, 415 lie in a common plane that divides cutter element 400 lengthwise into equal, mirror image halves.

[0076]Outer surface 402 includes a pair of planar lateral sides 413, a first or upper convex (bowed outwardly) surface 414 extending between lateral sides 413, and a second or lower convex (bowed outwardly) surface 416 extending between lateral sides 413. Unlike lateral sides 213 of cutter element 200 previously described, which are oriented parallel to axes 205, 215, in this embodiment, planar lateral sides 413 are oriented parallel to central axis 405, but slope or taper radially inwardly relative to axis 415 toward each other moving from upper convex surface 414 to lower convex surface 416. Convex surfaces 414, 416 are oriented parallel to central axis 405 and are intersected by longitudinal axis 415. In this embodiment, convex surfaces 414, 416 are semi-cylindrical surfaces that are intersected by longitudinal axis 415 at their respective centers that are furthest from central axis 405.

[0077]Referring still to FIGS. 11-13, cutting layer 420 has a central axis coincident with central axis 405 of substrate 401. In addition, cutting layer 420 has a first end 420a distal substrate 401, a second end 420b opposite end 420a and bonded to substrate 401 at plane of intersection 419, and a radially outer surface 422 extending axially between ends 420a, 420b. In this embodiment, ends 420a, 420b of cutting layer 420 are defined by planar surfaces oriented perpendicular to axis 405. In particular, end 420a of cutting layer 420 defines a planar cutting face 421. In this embodiment, a chamfer or bevel 427 extends about the entire outer perimeter of cutting layer 420 at the intersection of outer surface 422 and cutting face 421. Cutter element 400 is mounted to a corresponding blade with first end 420a leading second end 420b relative to cutting direction of the drill bit. Accordingly, first end 420a may also be referred to as “leading” end 420a, and second end 420b may also be described as “trailing” end 420b.

[0078]Cutting layer 420 has a geometry that is the generally the same as substrate 401 with the exception that, in this embodiment, cutting layer 420 has a thickness measured axially relative to axis 405 from leading end 420a to trailing end 420b that is less than a thickness of substrate 401 measured axially relative to axis 405 from leading end 401a to trailing end 401b. More specifically, cutting layer 420 has a longitudinal axis 425 that is intersected by and oriented perpendicular to central axis 405, and oriented parallel to the planar surfaces defining ends 420a, 420b. In this embodiment, axes 405, 415, 425 lie in a common plane that divides cutter element 400 lengthwise into equal, mirror image halves. Outer surface 422 of cutting layer 420 is contiguous with outer surface 402 of substrate 401. In particular, outer surface 422 includes a pair of planar lateral sides 423 that are contiguous and coplanar with sides 413 of substrate 401, a first or upper convex (bowed outwardly) surface 424 extending between lateral sides 423 and contiguous with surface 414 of substrate 401, and a second or lower convex (bowed outwardly) surface 426 extending between lateral sides 423 and contiguous with surface 416 of substrate 401. Thus, lateral sides 423 are oriented parallel to axis 405 but slope or taper radially inwardly relative to axis 425 toward each other moving from upper convex surface 424 to lower convex surface 426. Convex surfaces 424, 426 are oriented parallel to central axis 405 but are intersected by longitudinal axis 425. Convex surfaces 424, 426 are contiguous with convex surfaces 414, 416, and thus, convex surfaces 424, 426 are semi-cylindrical surfaces that are intersected by longitudinal axis 425 at their respective centers that are furthest from central axis 205.

[0079]As co-planar lateral sides 413, 423 taper toward each other moving from convex surfaces 414, 424 to convex surfaces 416, 426, semi-cylindrical convex surfaces 414, 426 have a radius of curvature that is greater than a radius of curvature of semi-cylindrical convex surfaces 424, 426.

[0080]As best shown in FIG. 12, cutter element 400, substrate 401, and cutting layer 420 have a common length L₄₀₀ measured axially relative to axes 415, 425 from convex surface 414, 416 to convex surface 424, 426, respectively; and a width W₄₀₀ measured perpendicularly to longitudinal axes 415, 425 in front view from one side 413, 423 to the opposite side 413, 423, respectively. Due to the tear drop prismatic shape of cutter element 400 (and substrate 401 and cutting layer 420) and sloped lateral sides 413, 423, the width W₄₀₀ decreases moving axially relative to axes 215, 225 from convex surfaces 412, 424 to convex surfaces 416, 426. Similar to cutter element 200, the length L₄₀₀ is greater than the width W₄₀₀. In embodiments described herein, for most drilling applications, the length L₄₀₀ of cutter element 400 is preferably greater than or equal to 10.0 mm and less than or equal to 30.0 mm, and the maximum width W₄₀₀ of cutter element 200 is preferably greater than or equal to 5.0 mm and less than 30.0 mm. Cutter element 400 has an aspect ratio equal to the ratio of the length L₄₀₀ of cutter element 400 to the maximum width W₄₀₀ of cutter element 400. As the length L₄₀₀ is greater than the maximum width W₄₀₀, the aspect ratio of cutter element 400 is greater than 1.0. More specifically, in embodiments described herein, the aspect ratio of cutter element 400 is greater than 1.0 and preferably less than or equal to 2.0. Accordingly, tear drip cutter element 400 is a high-aspect ratio cutter element.

[0081]As previously described, cutter element 400 can replace one or more cutter elements 200 on bit 200. Each cutter element 400 is generally mounted to a corresponding blade (e.g., blade 141, 142) in the same manner as cutter element 200, however, cutter element 500 is preferably mounted such that convex surfaces 414, 424 are positioned distal the cutter-supporting surface 144 and a portion of cutting face 421 at or proximal the intersection of bevel 427 and convex surface 424 defines a cutting tip 428 of cutter element 400.

[0082]Referring now to FIGS. 14 and 15, another embodiment of a high-aspect ratio cutter element 500 that can be used in place of one or more cutter elements 200 on bit 100 is shown. Cutter element 500 is substantially the same as cutter element 200 previously described with the exception that cutter element 500 includes a pair of flats extending across semi-cylindrical convex surfaces 214, 224 and a pair of flats extending across semi-cylindrical convex surfaces 216, 226. More specifically, cutter element 500 includes a substrate 201 and cutting layer 220 bonded to substrate 201. Substrate 201 and cutting layer 220 are each as previously described. However, in this embodiment, a pair of planar flats or surfaces 230 extend from leading end 220a and cutting face 221 across convex surface 224 of cutting layer 220 and across a portion of convex surface 214 of substrate 201; and a pair of planar flats or surfaces 240 extend from leading end 220a and cutting face 221 across convex surface 226 of cutting layer 220 and across a portion of convex surface 216 of substrate 201. Bevel 227 extends along the intersection between each planar flat 230, 240 and cutting face 221. Thus, each planar flat 230 has a first or leading end 230a along outer surface 222 of cutting layer 220 adjacent bevel 227 and cutting face 221, and a second or trailing end 230b along outer surface 202 of substrate 201 distal cutting face 221; and similarly, each planar flat 240 has a first or leading end 240a along outer surface 222 of cutting layer 220 adjacent bevel 227 and cutting face 221, and a second or trailing end 240b along outer surface 202 of substrate 201 distal cutting face 221. Each planar flat 230, 240 slopes radially outwardly relative to central axis 215 as it extends generally axially relative to central axis 205 from leading end 230a, 240a, respectively, to trailing end 230b, 240b, respectively.

[0083]In this embodiment, planar flats 230 are positioned on opposite sides of the common plane that contains axes 215, 225, 205 and bisects cutter element 500 lengthwise into halves, and planar flats 240 are positioned on opposite sides of the common plane that contains axes 215, 225, 205 and bisects cutter element 500 lengthwise into halves. In particular, planar flats 230 are symmetric across the common plane, and planar flats 240 are symmetric across the common plane. In addition, each planar flat 230 has a surface vector V₂₃₀ oriented at an acute angle β₂₃₀ relative to the common reference plane in front view (as viewed along central axis 205), and each planar flat 240 has a surface vector V₂₄₀ oriented at an acute angle β₂₄₀ relative to the common reference plane in front view (as viewed along central axis 205). In general, each angle β₂₃₀, β₂₄₀ can be any acute angle (i.e., greater than 0° and less than) 90°, and any two or more acute angles β₂₃₀, β₂₄₀ can be the same or different. In this embodiment, each acute angle β₂₃₀ is the same, and in particular, each angle β₂₃₀ is 45°; and further, each angle β₂₄₀ is the same, and in particular, each angle β₂₄₀ is 45°. As previously described, cutter element 500 can replace one or more cutter elements 200 on bit 200. Each cutter element 500 is generally mounted to a corresponding blade (e.g., blade 141, 142) in the same manner as cutter element 200, however, cutter element 500 is preferably mounted such that (i) a portion of cutting face 221 at or proximal the intersection of bevel 227 and convex surface 214 laterally between planar flats 230 defines a cutting tip and exposure of cutter element 500; or (ii) a portion of cutting face 221 at or proximal the intersection of bevel 227 and convex surface 214 laterally between planar flats 240 defines a cutting tip and exposure of cutter element 500. For purposes of clarity and further explanation, in FIGS. 14 and 15, the portion of cutting face 221 laterally between planar flats 230 that can be positioned to define the cutting tip and exposure of cutter element 500 is labeled with reference numeral 528; and the portion of cutting face 221 laterally between planar flats 240 that can define the cutting tip and exposure of cutter element 500 is labeled with reference numeral 528′. It should be appreciated that cutter element 500 is preferably mounted such that one portion 528, 528′ defines the cutting tip, however, as portions 528, 528′ are angularly spaced 180° apart about central axis 205, when one such portion 528, 528′ defining the cutting tip of cutter element 500 is sufficiently worn or damaged, cutter element 500 can be removed from the corresponding blade of the bit, rotated 180°, and the reattached to the same or different blade of the bit such that the other portion 528, 528′ defines a new and fresh cutting tip of cutter element 500. In other words, by angularly spacing portions 528, 528′ 180° apart about central axis 205, portions 528, 528′ define two potential cutting tips for cutter element 500 such that cutter element 500 can be rotated and reused, thereby prolonging the effective operating life of cutter element 500.

[0084]As previously described and shown in FIGS. 14 and 15, planar flats 230 are positioned on opposite sides of the common plane that contains axes 215, 225, 205, planar flats 240 are positioned on opposite sides of the common plane that contains axes 215, 225, 205, planar flats 230 are symmetric across the common plane, and planar flats 240 are symmetric across the common plane. In addition, each planar flat 230 is oriented at the same acute angle β₂₃₀ of 45°, and each planar flat 240 is oriented at the same acute angle β₂₄₀ of 45°. However, in other embodiments, planar flats 230 may not be positioned on opposite sides of the common plane that contains axes 215, 225, 205, planar flats 240 may not be positioned on opposite sides of the common plane that contains axes 215, 225, 205, planar flats 230 may not be symmetric across the common plane, planar flats 240 may not be symmetric across the common plane, or combinations thereof. In addition, in other embodiments, one or more planar flats 230 may be oriented at an acute angle β₂₃₀ other than 45° and/or one or more planar flats 240 may be oriented at an acute angle β₂₄₀ other than 45°. For example, referring now to FIGS. 16 and 17, another embodiment of a high-aspect ratio cutter element 600 that can be used in place of one or more cutter elements 200 on bit 100 is shown. Cutter element 600 is substantially the same as cutter element 500 previously described with the exception that planar flats 230 are not disposed on opposite sides of the common reference plane containing axes 205, 215, 225, planar flats 240 are not disposed on opposite sides of the common reference plane containing axes 205, 215, 225, planar flats 230 are not symmetric across the common reference plane containing axes 205, 215, 225, flats 240 are not symmetric across the common reference plane containing axes 205, 215, 225, 240, planar flats 230 are oriented at different acute angle β₂₃₀ other than 45°, and planar flats 240 are oriented at different acute angle β₂₄₀ other than 45°. In this embodiment, one planar flat 230 (on the right in FIG. 17) is intersected by the common reference plane containing axes 205, 215, 225 and is oriented at an acute angle β₂₃₀ of 30° and the other planar flat 230 (on the left in FIG. 17) is laterally spaced from the common reference plane and is oriented at an acute angle β₂₃₀ of 60°; and one planar flat 240 (on the left in FIG. 17) is intersected by the common reference plane containing axes 205, 215, 225 and is oriented at an acute angle β₂₄₀ of 30° and the other planar flat 240 (on the right in FIG. 17) is laterally spaced from the common reference plane and is oriented at an acute angle β₂₄₀ of 60°. As previously described, cutter element 600 can replace one or more cutter elements 200 on bit 200. Each cutter element 600 is generally mounted to a corresponding blade (e.g., blade 141, 142) in the same manner as cutter element 200, however, cutter element 600 is preferably mounted such that (i) a portion of cutting face 221 at or proximal the intersection of bevel 227 and convex surface 214 laterally between planar flats 230 defines a cutting tip and exposure of cutter element 600; or (ii) a portion of cutting face 221 at or proximal the intersection of bevel 227 and convex surface 214 laterally between planar flats 240 defines a cutting tip and exposure of cutter element 600. For purposes of clarity and further explanation, in FIGS. 16 and 17, the portion of cutting face 221 laterally between planar flats 230 that can be positioned to define the cutting tip and exposure of cutter element 600 is labeled with reference numeral 628; and the portion of cutting face 221 laterally between planar flats 240 that can define the cutting tip and exposure of cutter element 600 is labeled with reference numeral 628′. It should be appreciated that cutter element 600 is preferably mounted such that one portion 628, 628′ defines the cutting tip, however, as portions 628, 628′ are angularly spaced 180° apart about central axis 205, when one such portion 528, 528′ defining the cutting tip of cutter element 600 is sufficiently worn or damaged, cutter element 600 can be removed from the corresponding blade of the bit, rotated 180°, and the reattached to the same or different blade of the bit such that the other portion 628, 628′ defines a new and fresh cutting tip of cutter element 600. In other words, by angularly spacing portions 628, 628′ 180° apart about central axis 205, portions 628, 628′ define two potential cutting tips for cutter element 600 such that cutter element 600 can be rotated and reused, thereby prolonging the

[0085]In the embodiment of drill bit 100 previously described and shown in FIGS. 2, 3, and 5, the minimum distance D₂₀₀ between each pair of radially adjacent high-aspect ratio cutter elements 200 on each blade 141, 142 is greater than the minimum distance D₃₀₀ between each pair of radially adjacent low-aspect ratio cutter elements 300 on each blade 141, 142. In addition, in the embodiment of drill bit 100 previously described and shown in FIGS. 2, 3, and 5, cutter elements 200, 300 are arranged in a row along the leading side 141a, 142a of each blade 141, 142, respectively, with the radially adjacent high-aspect ratio cutter elements 200 in each row extending radially from proximal the bit axis 105, through cone region 149a, and into shoulder region 149b proximal nose 149d; and the radially adjacent low-aspect ratio cutter elements 300 in each row extending radially from the shoulder region 149b proximal nose 149d, through the remainder of shoulder region 149b and the gage region 149c to the corresponding gage pad 147 of bit 100. However, in other embodiments, the minimum distance D₂₀₀ between each pair of radially adjacent high-aspect ratio cutter elements 200 in a row on any one or more blades 141, 142 may be the same or substantially the same as the minimum distance D₃₀₀ between each pair of radially adjacent low-aspect ratio cutter elements 300 in the row on the same blade 141, 142 or in a row any other one or more blades 141, 142; and/or the radially adjacent high-aspect ratio cutter elements 200 on one or more blades 141, 142 may extend radially into the shoulder region 149b beyond nose 149d or to gage region 149c. For example, referring now to FIGS. 18 and 19, an embodiment of a drill bit 700 is shown. Drill bit 700 is substantially the same as drill bit 100 previously described with the exception that (i) the minimum distance D₂₀₀ between each pair of radially adjacent high-aspect ratio cutter elements 200 in the row on each blade 141, 142 is the same or substantially the same as the minimum distance D₃₀₀ between each pair of radially adjacent low-aspect ratio cutter elements 300 in the row on each blade 141, 142; and (ii) the radially adjacent high-aspect ratio cutter elements 200 in the row on each blade 141, 142 extend radially into the shoulder region 149b beyond nose 149d but not to gage region 149c or the corresponding gage pad 147, while the radially adjacent low-aspect ratio cutter elements 300 in the row on each blade 141, 142 extend radially from the high-aspect ratio cutter elements 200 on the same blade 141, 142 through a portion of shoulder region 149b and through gage region 149c to the corresponding gage pad 147. As another example, referring now to FIGS. 20 and 21, an embodiment of a drill bit 800 is shown. Drill bit 800 is substantially the same as drill bit 100 previously described with the exception that (i) the minimum distance D₂₀₀ between each pair of radially adjacent high-aspect ratio cutter elements 200 in the row on each blade 141, 142 is the same or substantially the same as the minimum distance D₃₀₀ between each pair of radially adjacent low-aspect ratio cutter elements 300 in the row on each blade 141, 142; and (ii) the radially adjacent high-aspect ratio cutter elements 200 in the row on each blade 141, 142 extend radially into and through shoulder region 149b to gage region 149c but not into gage region 149c, while the radially adjacent low-aspect ratio cutter elements 300 in the row on each blade 141, 142 extend through gage region 149c to the corresponding gage pad 147, but are not disposed in shoulder region 149b.

[0086]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.