Downhole tools with improved arrangements of cutters

Abstract

Earth boring tools having offset blades with a plurality of fixed cutters having side rake or lateral rakes configured for improving chip removal and evacuation, drilling efficiency, and/or depth of cut management as compared with conventional arrangements.

Claims

1. A drill bit to advance a borehole comprising: a bit body having a central axis about which the bit is intended to rotate, the body having a gauge and a cutting face on which is formed a plurality of radially extending blades that are separated from each other by channels, each of the plurality of blades supporting a plurality of discrete, fixed cutters for shearing rock along a leading edge of each of the blades next to one of the channels to evacuate rock shavings; each of the cutters having a fixed location on one of the plurality of blades, a fixed cutter position in a cutting profile that is defined at least in part by the plurality of cutters, and a fixed side rake angle, the side rake angle having a polarity that can be negative, positive, or zero; wherein: at least one of the blades is an offset blade that extends radially outwardly from near the central axis toward the gauge and has a leading front edge adjacent to one of the channels, the blade having a first section and at least one second section that is radially and angularly displaced from the first section; at least two of the plurality of cutters are mounted along the leading edge in the first section and at least two of the plurality of cutters are mounted along the leading edge of the second section; the at least two cutters in the first section and the at least two cutters in the second section each form a group of cutters the at least two cutters in each group of cutters have side rake angles that differ from one another by at least 4 degrees; and the polarity of the side rake angle of a particular cutter of the at least two cutters within each group of cutters differs from the polarity of the side rake angle of a different cutter of the at least two cutters within each group of cutters.

2. The drill bit of claim 1, wherein at least one cutter within the group of cutters is adjacent on the offset blade to another cutter in the group of cutters.

3. The drill bit of claim 2, wherein all of the cutters within each group of cutters are adjacent to each other on the offset blade.

4. The drill bit of claim 2, wherein the at least one cutter within the group of cutters is adjacent in the cutting profile to another cutter in the group of cutters.

5. The drill bit of claim 4, wherein all of the cutters within the group of cutters are adjacent in the cutting profile to another cutter in the group of cutters.

6. The drill bit of claim 1, wherein the bit body has a cone, a nose, a shoulder, and the gauge and all of the cutters within the group of cutters are located within one of the cone, the nose, the shoulder, or the gauge.

7. The drill bit of claim 1, wherein the side rake angle of each cutter in the group of cutters is defined by the angular orientation of a cutting face of the cutter about an axis that is normal to a tangent to the cutting profile at the radial position of that cutter.

8. The drill bit of claim 1, wherein the side rake angle of each cutter in the group of cutters is defined by the angular orientation of a cutting face of the cutter about an axis that is normal to the tangent to the cutting profile at the radial position of that cutter projected onto the plane of the cutting face.

9. The drill bit of claim 1, wherein the particular cutter and the different cutter are adjacent one another.

10. A drill bit to advance a borehole comprising: a bit body having a central axis about which the bit is intended to rotate, the body having a plurality of radially extending blades that are separated from each other by channels, each of the plurality of blades supporting a plurality of cutters; each of the cutters having a fixed location on one of the plurality of blades, a fixed cutter position in a cutting profile that is defined at least in part by the plurality of cutters, and a fixed side rake angle, the side rake angle having a polarity that can be negative, positive, or zero; wherein, at least one of the blades is an offset blade that has a leading edge adjacent to one of the plurality of channels, the blade having a first section and a second section where the second section is radially and angularly displaced from the first section; wherein, the plurality of cutters comprises at least one group of two or more primary cutters mounted in a row along the leading edge of the offset blade, wherein at least two primary cutters in the group of cutters have side rake angles that differ from one another by at least 4 degrees; and wherein the polarity of the side rake angle of a particular cutter of the at least two cutters within the group of cutters differs from the polarity of the side rake angle of a different cutter of the at least two cutters within the group of cutters.

11. The drill bit of claim 10, wherein at least one cutter within the group of cutters is adjacent on the offset blade to another cutter in the group of cutters.

12. The drill bit of claim 11, wherein all of the cutters within the group of cutters are adjacent to each other on the offset blade to another cutter in the group of cutters.

13. The drill bit of claim 10, wherein the at least one cutter within the group of cutters is adjacent in the cutting profile to another cutter in the group of cutters.

14. The drill bit of claim 13, wherein all of the cutters within the group of cutters are adjacent in the cutting profile to another cutter in the group of cutters.

15. The drill bit of claim 10, wherein the bit body has a cone, a nose, a shoulder, and a gauge and all of the cutters within the group of cutters are located within one of the cone, the nose, the shoulder, or the gauge.

16. The drill bit of claim 10, wherein the side rake angle of each cutter on the bit is defined by the angular orientation of a cutting face of the cutter about an axis that is normal to a tangent to the cutting profile at the radial position of that cutter.

17. The drill bit of claim 10, wherein the first section and the second section of the offset blade are connected.

18. The drill bit of claim 10, wherein the first section and the second section of the offset blade are not connected.

19. The drill bit of claim 10, wherein the particular cutter and the different cutter are adjacent one another.

20. A downhole tool for removing rock to form a well bore, the tool comprising: a bit body having a central axis about which the bit is intended to rotate, the body having a gauge and a cutting face; a plurality of blades disposed on the cutting face and extending radially outwardly from the central axis that are separated from each other by a plurality of channels, each of the plurality of blades having a leading edge extending along one of the plurality of channels; each of the plurality of blades having mounted along a leading edge of the blade a row of primary cutters for failing rock with a shearing action, each of the cutters having in fixed radial location within a cutting profile; wherein, one of the plurality of blades is an offset blade comprising at least two portions, the two portions comprising an inner blade portion and an outer blade portion that is angular displaced with respect to the inner blade portion at an offset; and wherein the row of primary cutters on the offset blade comprises a first primary cutter and a second primary cutter that are adjacent to each other on the offset blade; wherein the first and second primary cutters each has a non-zero side rake angle that differs from the other by at least 3 degrees; and wherein a polarity of the side rake angle of the first primary cutter differs from the polarity of the side rake angle of the second primary cutter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A represents a schematic illustration of a face view of a rotary drag bit.

(2) FIG. 1B represents a schematic illustration of a cutting profile for a PDC bit.

(3) FIG. 1C represents a schematic illustration of one of the cutters from FIG. 1B.

(4) FIG. 2A represents a cutting profile of cutters on a blade for typical PDC bit.

(5) FIG. 2B represents a two-dimensional rendering of the three dimensional geometry of the cutters shown in the cutting profile of FIG. 2A.

(6) FIG. 3 is a face view of an example of a PDC bit that is representative of a rotary drag bit with fixed cutters and, more generally, a downhole tool for cutting rock with fixed cutters arranged on blades.

(7) FIG. 4 is a face view of a second, representative example of a PDC bit.

(8) FIG. 5A is a cutting profile for a first example of cutters mounted on an offset blade.

(9) FIG. 5B illustrates a three dimensional cutter geometry corresponding to the cutting profile of FIG. 5A.

(10) FIG. 6A represents a cutting profile of a second example of a cutter geometry for an offset blade.

(11) FIG. 6B illustrates the cutter geometry corresponding to the cutting profile of FIG. 6A.

(12) FIG. 7 illustrates a cutter geometry of a third example of an offset blade.

(13) FIG. 8A-8J are graphs plotting cutter position to a side inclination, such as a side rake or lateral angle, and represent examples of schemes or patterns of such angles across a blade or cutting profile of an earth boring tool with fixed cutters.

(14) FIG. 9A is a graph plotting primary cutter radial positions to side rake angle in degrees for cutters on an example of a PDC bit with offset blades.

(15) FIG. 9B is a graph plotting cutter number to side rake angle for the example of FIG. 9B.

(16) FIG. 10A is a graph plotting cutter radial position to side rake angle in degrees for cutters on second example of a PDC bit with offset blades.

(17) FIG. 10B is a graph plotting cutter number to side rake angle for the example side rake scheme of FIG. 10B

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(18) In the following description, like numbers refer to like elements.

(19) Referring now to FIGS. 2A and 2B, primary cutters on a particular blade of a bit will be mounted on the bit's primary cutting profile. FIGS. 2A and 2B depict a representative example of a cutter geometry for a conventional of a PDC bit and the cutter profile of the cutters on the blade relative to the bit's primary cutting profile. A plurality (eight in this example) of fixed primary cutters 212-224 (plus one additional that cannot be seen in FIG. 2B) are rendered in the positions and orientations in which they would be mounted on a blade (not shown) of a PDC bit (also not shown.) The positions of the cutters in a three-dimensional coordinate frame and their orientation comprise a cutter geometry. This figure thus represents the cutter geometry for a blade. In this representative example, cutters 212 and 214 are in the nose region; cutters 216 and 218 are in the nose region or area of the bit; and cutters 236, 238, 240, and 242 are in the shoulder area or region.

(20) The bit's primary cutting profile is indicated by line 210. The primary cutting profile for a bit and for a blade is defined by the primary cutters when they are rotated around the bit's axis of rotation through an imaginary plane coincident with the axis of rotation. The individual cutter's profiles 228-242 are circular or oval in shape and indicate the radial positions of the cutters and the periphery (shape and size) of the cutting face each cutter as it passes through the plane.

(21) In the figures, the individual cutting profile of each cutter is a projection and will not indicate contours of the surface or surfaces that comprise the cutting face. A cutting face may comprise multiple surfaces. Furthermore, the entire cutting face will not, typically, be used to fail the formation, though much or most of it may contact cuttings as they curl away from the formation. The size and shape of the working surfaces will be determined by a number of factors, including the type of formation, the amount of weight on the bit, the exposure of the cutters (height of the cutter extending above the blade), and features on the blade or elsewhere on the bit that limit depth of cut.

(22) Line 210, which is tangent to circles 228-242 that represent the cutting profile of the individual cutters, represents the cutting profile of the blade and aligns with and corresponds to the cutting profile for the bit. All primary cutters on a bit are mounted so that they are on the same profile, the primary cutting profile. The individual cutting profiles of each of the other cutters on other blades of the bit that are in the same cutting profile will be tangent to this line as they rotate through the imaginary plane.

(23) Only seven of the eight cutters can be seen in FIG. 2B, as cutter 224 is occluded from this perspective, the eighth cutter that corresponds with cutter profile 242. FIG. 2B includes a rendering of the profile of FIG. 2A as it would appear from the perspective from which that rendering is created. The cutters oriented with non-zero side rake angles will tend to have the cutting profile that is narrower (more elliptical) in a blade or bit cutting profile and the cutting profiles for the cutters that is shown in the three-dimensional cutter geometry view of FIG. 2B will appear to be rotated with respect to the plane of the cutting profile. Any backup cutters on the blade (not shown) would or may be on a different cutting profile.

(24) FIG. 3 represents a view of the face a PDC bit 310, which is a non-limiting, representative example of a rotary drag bit. PDC bit 310 has a plurality of cutters (PDC or other types) mounted on a plurality of blades. This particular embodiment has six blades, three of which are primary blades. The other three are secondary blades. The primary blades extend from near the center of the axis of rotation 301, through the cone, nose and shoulder regions, to the gauge of the bit. In this example, each are an offset blade 326. The secondary blades 336 extend from the nose region of the bit, through the shoulder region, and then to the gauge of the bit. They are not offset. In alternative embodiments, one or more of the blades are offset blades. The various features or aspects of the improvements disclosed herein are not limited to a bit with a particular size or number of cutters or blades unless otherwise specifically stated.

(25) The leading edge of a traditional blade, where front wall of the blade transitions to the top surface of the blade and along which the primary cutters are mounted, is curvilinear. However, each offset blade has a leading edge with a pronounced step or set back where it transitions from a first blade portion to a second blade portion. The distal end of the first leading edge portion is rotationally or angularly offset from the proximal end of the second leading edge portions, forming a step or offset such that the difference between the angular position of last cutter (most radially distant) on the first blade portion and the angular position of the first cutter on the second blade portion is much greater than the differences in angular positions of the last two cutters on the first blade section and the difference in the angular positions of the first two cutters on the second blade portion. In the illustrated embodiment, an offset blade is continuous, without a gap in the wall of the blade where the offset occurs. However, in alternative embodiments, a small gap between the blade portions may be formed.

(26) Each offset blade has seven cutters 312-324, which are primary cutters. They are mounted along a leading edge of the offset blade, adjacent to one of the channels or “junk slots” 334 that extends along the length of the offset blade. The offset blades 326 may also have cutters in the gauge area of bit 310, which are not visible in this view of this embodiment. Each offset blade 326 in this example is one continuous blade that has an offset in the blade geometry along the face or front wall of the blade. The offset is, in this embodiment, between cutter 316 and cutter 318. The offset creates two blade portions, a first (or inner) blade portion closer to the centerline or axis of rotation 401 of the bit that extends through the cone region of the bit to the offset, and a second (or outer) blade portion that extends from the offset, through the nose and shoulder regions, to the gauge of the bit. A proximal end of the second blade portion is displaced radially (outwardly from the axis of rotation) and angularly from a distal end of the first blade portion. In this example, the offset in offset blade 326 occurs approximately where the cone region of the bit transitions to the nose region of the bit. However, in other embodiments, for example, the offset may occur in or near other regions of the bit, such in the nose or shoulder, or at the transition of the nose to the shoulder. Furthermore, alternative embodiments of bits may have one or more, or all, of its offset blades with more than one offset and different numbers of offsets. For example, an offset blade could have three portions: a first, a second and third, with a first offset between the first two portions and a second offset between the second and third portions. Furthermore, one or more of the offset blades on a bit could have one offset; and one or more of the other offset blades could have two offsets. One or more additional offset blades on the bit could have three or more offsets.

(27) The secondary blades 336 are used to increase the cutter density of the bit in the nose and shoulder of a bit. Cutters in these regions typically perform much of the work forming a wellbore. As the bit progresses downhole, more material must be removed from the borehole in these regions relative to the cone region because the wider radius of these regions, relative to the cone region, results in a greater surface area of rock that must be removed. The secondary blades allow for balancing the amount of exposed cutter in a region to the area of rock that must be removed from that region. Each of the secondary blades has four primary cutters 338-344 that are visible in this view and may have cutters in the gauge region of the bit 310 that are occluded from view. Cutters 338-344 each have a fixed position on bit 310. The fixed position of a particular cutter being defined by the blade on which the cutter is mounted, the axial distance from the center of rotation of the bit, and the relative radial position of the cutter on the face of the bit. Each cutter also has a set orientation: a back rake and a side rake.

(28) Bit 310 also has a plurality of nozzles 328-332 which are located in a plurality of channels or junk slots 334. The junk slots 334 are located in front of each of the blades and are defined by the front wall of the blade and a back wall of the blade it follows. Nozzles 328-332 direct drilling fluid being pumped through the drill string, which is not shown, toward the cutters to flush cuttings from the face of the bit. Junk slots 334 create room for collecting and evacuating cuttings, with the junk slots direction the flow of drilling fluid and cuttings radially outwardly and then up through the gauge region and into an annulus between the wellbore side wall and the drilling string (not shown.)

(29) Nozzles 330 are in front of the first blade portion (inner portion) of offset blade 326. The drilling fluid flowing from each of the nozzles 330 is primarily intended to clear cuttings coming off of primary cutters mounted along a leading of the first blade portion of each offset blade 326, which in this example are cutters 312, 314, and 316. The drilling fluid flowing from each of the nozzles 330 is secondarily intended to provide cooling and manage the operating temperature of primary cutters mounted along a leading of the first blade portion of each offset blade 326, which in this example are cutters 312, 314, and 316. Nozzle 330 are therefore directed so that drilling fluid flows across the face of these cutters 312-315 and down the junk slot 334 that is between the front of the offset blade and the back side of the secondary blade 326 in front of it.

(30) Nozzles 328 are each tucked into the corner formed in the front wall of the blade formed by the offset in the offset blade 326. Each directs drilling fluid along the second blade, portion of each of the offset blades, toward faces of cutters 318, 320, 322, and 324, which are primary cutters mounted along a leading edge of the second blade portion of the offset blade.

(31) Nozzles 328 are rotationally offset rearwardly with respect to nozzle 330 and radially outwardly. Because each nozzle 328 is rotationally displaced with respect to nozzle 330, fluid flowing from nozzle 328 tends not to interfere with fluid flow from the nozzle 330 or interferes much less than it would if it were not rotationally displaced. The nozzle 330 is aimed so that the drilling fluid from the nozzle, after flowing across the face of cutters 312, 314, and 318 in the first section of offset blade 326, tends for flow with the cuttings produced by those cutters primarily through the area between the back of secondary blade 336 and nozzle 328. Fluid flowing from nozzle 328 primarily flows across the face of cutters 318, 320, 322, and 324 and then continues along the front wall or leading edge of the second blade portion of the offset blade 326 into the annular space of the borehole.

(32) The offset blades 326 and the secondary blades 336 of bit 310 in FIG. 3 also features sloped surfaces 346 and 348, respectively, on the back of the blades, behind the cutters that are arranged along the leading edge of the blades. The cutting face of the body of the bit, in particular the top surfaces of the blade, act to limit the penetration of the cutters into the formation. The primary cutters extend above the top of the blades or other feature or aspect of the bit that limits how far the cutters can penetrate into rock, which is referred to as cutter exposure. Generally, higher exposures will allow the primary cutters to penetrate deeper into the formation, which can increase the rate that the bit penetrates the formation (the rate of penetration or ROP) to advance the bore hole. On the other hand, if the primary cutter exposure is too high, other problems may arise that might retard rate of penetration or lead to premature failure of cutters and eventual damage or destruction of the drill bit. Therefore, exposure is chosen to optimize ROP while maintaining an acceptable degree of reliability. At high ROP the back part of the top surface of the blades might contact the formation before the front part of the top surface contacts the formation, resulting in added friction and possibly also a shallower penetration than the bit is otherwise capable of. Sloped surfaces 346 and 348 remove some of the blade without substantially weakening it where the back of each blade might otherwise contact the formation during high ROP. Instead of a sloped surface, a step or series of steps could be substituted, but possibly at the cost of added fabrication difficulties and/or a weaker blade.

(33) FIG. 4 depicts another example of a PDC bit 410 similar to the example depicted in FIG. 3. It is intended to be representative of embodiments in the form of rotary drag bits generally, and more specifically PDC bits. It shares many similar features. The basic physical structure of bit 410 and bit 310 (FIG. 3) are similar. It has primary blades that are offset blades: an offset blade 426 with primary cutters 412-424; and offset blades 450, each with primary cutters 452, 454, 456, 458, 460, 462, and 464. Offset blades 450 each have a geometry with features similar to the features of the geometry of offset blades 326 shown in the embodiment of FIG. 3. (Note, however, that the cutter layouts and the orientations of the cutters are not the exactly the same.) Bit 410 has three secondary blades 436, each with cutters, cutters 452-464. These blades are not offset and have blade geometries and cutter layouts that are similar to the non-offset, secondary blades 336 in FIG. 3. Nozzles 428-432 are positioned within junk slots 434 in a manner that is similar to the positioning of nozzles 328, 330 and 332, respectively in the junk slots 334 in the embodiment of FIG. 3. They function in a similar manner. Nozzle 428, which is placed within the corner in the front wall of offset blade 426, is oriented so that drilling fluid reaches primary cutter 418. Sloping regions 446 and 448 are similar in terms of function and geometry to slope surfaces 346 and 348 of the bit in FIG. 3.

(34) Though it shares many of the same features, offset blade 426 of bit 410 has a different offset blade geometry and cutter layout than the other offset blades 450. Briefly, the differences involve the last primary cutter of the first blade portion (the inner blade portion) of offset blade 426, which is primary cutter 416, partially overlaps the cutting profile of the first primary cutter of offset blade 426, which is primary cutter 418.

(35) Referring now to FIGS. 3 and 4, the side rakes of the primary cutters along the leading edges of the offset and non-offset blades in each of these examples can be set to have relatively high side rake. Rotating a cutter angles its cutting face to the formation. When angled to the formation the cutter will tend to generate a reactive lateral force on the bit as the cutter when the cutter engages the formation. Selectively orienting two or more cutters on the bit to generate counteracting lateral forces on the bit can dampen vibrations, increase rate of penetration, and/or improve steerability of the bit. The side rake angles of two or more adjacent primary cutters along each of the offset blades in the illustrated examples are may be set to cause the generation opposing or counteracting lateral forces along the blade while engaging a formation. Furthermore, one or more primary cutters along one blade may coordinate or cooperate with one or more cutters on other blades with different side rake angles in a way that reactive lateral forces are created on the bit that counteract each other in ways that dampen bit vibration. For example, these could be radially adjacent or overlapping primary cutters on different blades. Or, for example, the side rakes of the primary cutters within each of two or more groups of primary cutters on the bit can be chosen to generate lateral forces that counteract each other to dampen lateral vibrations or to improve direction control and steerability. The cutters are grouped by, for example, radial positions within the cutting profiles, the region of the bit in which they are located (e.g. cone, nose, shoulder), angular position, location along a blade, by adjacency along a blade or in the bit's cutting profile, or a combination of two or more of these parameters.

(36) A primary cutter that is rotated to give it side rake (either inwardly toward the axis of rotation or outwardly toward the gauge) requires more room than a cutter that has no side rake due to the cutters having both a length, as measured along the central axis, and diameter (substrate and cutting face. There is also a minimum separation that is required to form a pocket or recess formed within the blade for mounting the cutter that has sufficient strength. Furthermore, the areas of the formation between areas removed adjacent by cutters on the same blade must be removed by primary cutters on other blades. Too great a separation of adjacent primary cutters on a blade is not desirable, especially in the cone region of a PDC bit, where there is a lower concentration of cutters. Therefore, there is a limit on the amount of side rake that a cutter can be set at without having to reduce the number of cutters on a blade, to limit the side rake angles of at least adjacent cutters on the same blade, and/or to necessitate trade-offs that might adversely affect bit performance.

(37) Referring now to FIG. 3, the first primary cutter 318 on the outer blade portion of each offset blade 326 is set back far enough with respect to last primary cutter 316 on the inner blade portion to allow more spacing to rotate cutters on the inner blade portion to increase side rake angles without being limited by cutter 318. Thus, as compared to a non-offset blade of these length and same number of cutters of the same size, the offset allows not only for the primary cutters 314-316 on the inner blade portion more space to allow for larger side rake for any one or more of the primary cutters on the inner blade portion, but also for larger differences in side rake angles between any two adjacent pairs, or between any two or more of them, without having to shift the radial position of primary cutter 318.

(38) In the illustrated example, the primary cutters 314 appear to be rotated more inwardly than cutters 312 and 316, and thus has a more inward side rake, with the cutter 314 being rotated inwardly with respect to cutter 312, and cutter 316 being rotated outwardly relative to the side rake of cutter 314. All three primary cutters are in the cone region of the blade.

(39) As compared to a non-offset blade with the same cutters and the size bit diameter, the offset also allows the last primary cutter 316 to be rotated to relatively higher side rake without (1) being limited by first primary cutter 318 on the outer blade portion or (2) having to change the radial locations or side rakes of the primary cutters 312 and 314 on the inner blade portion and/or primary cutter 318. Furthermore, the offset in the blade moves primary cutter 318 rotationally backward and exposes the side of cutter 316 to the formation to provide an additional lateral point of contact with the formation that can be used to improve bit stability. The offset also allows for first primary cutter 318 on the outer blade portion to be given a much higher (non-zero) side rake angle than would otherwise be possible and/or for its radial position moved slightly inwardly as compared to a non-offset blade. For similar reasons, the offset allows for more spacing and greater side rake angles for a primary cutter, and/or larger differences in side rake angles between two or more adjacent primary cutters or any two primary cutters, on the outer blade portions of the offset blades. Finally, the offset also allows for the difference in side rake between last primary cutter 316 on the inner blade portion and the first primary cutter 318 on the outer blade portion to be much greater. Because of the offset in blade 326, cutters 316 and 318 are rotationally offset to a degree that they can be rotated without affecting the other's orientation.

(40) Referring now to FIG. 4, the offset blades 426 and 450 are similar to blades 326 of bit 310 (FIG. 3) and have the same advantages. However, offset blade 426 also demonstrates an additional advantage of accommodating at least a partial overlapping of primary cutters on an offset blade. The degree of angular offset or step between the distal end of the inner blade portion and proximal end of the outer blade portion is larger relative to the degree of angular or rotational offset between the blade portions of offset blade 326 of FIG. 3 and offset blades 450 of FIG. 4. Furthermore, the distal end of the inner blade portion overlaps with the proximally end of the outer blade portion. This structure allows the cutting profile of primary cutter 416, the last cutter on the inner blade portion of the offset of blade 426, to overlap at least partially the cutting profile of the first primary cutter 418 on the outer blade portion of offset of blade 426. The side rakes of primary cutters 416 and 418 can thus each be set without concern for spacing between them.

(41) Offset blade 426 therefore allows overlapping of primary cutters on the same blade. Primary cutter 418 has the same exposure to the formation as other primary cutters on the blade and is on the primary cutting profile for the bit. It also has access to junk slot 434 and to the drilling fluid flowing within junk slot 434 for evacuating cuttings it produces. Furthermore, the blade's geometry allows the primary cutter 416 and primary cutter 418 to each be rotated to even larger side rake angles than might be have been possible on one of the other offset blades. These cutters do not interfere with each other and thus will not limit each other in terms of the degree of rotation even though they are on the same blade. Furthermore, the overlapping allows for additional spacing one or both of the inner and outer blade portions. More room on each blade portion of the offset blade allows greater side rake angles of one or more of the primary cutters each blade portion and allows for larger side rake differences between adjacent cutters.

(42) Referring now also FIG. 3 in addition to FIG. 4, PDC bits 310 of FIG. 3 and 410 of FIG. 4 are examples of rotary drag bits with cutter side rake schemes for generating counter acting lateral forces that tend to dampen vibration, improve cutting efficiency, improve ROP, and/or otherwise improve bit performance. Such cutter rake schemes may embody one or more of the following:

(43) (1) A pair or a set of three or more primary cutters mounted on one or more leading edges of one or more offset blades with side rakes that generate counteracting lateral forces on the bit. The pair or set of cutters are mounted, in one embodiment, on the same offset blade or, in another embodiment, on different offset blades. If they are on different offset blades, the cutters in the pair or the set of three or more may be in radially adjacent positions on the bit's primary cutting profile. The pair or set of cutters are, in one embodiment, primary cutters that are adjacent to each other on the same offset blade and, optionally be in radially adjacent locations on the bit's primary cutting profile, and/or partially or completing overlapping in the primary cutting profile. An offset blade like offset blade 426 allows primary cutters to be both adjacent on the offset blade and in radially adjacent locations and/or partially or completely overlapping in the cutting profile.

(44) (2) A group of two or more primary cutters on one offset blade with side rake angles set to generate counteracting lateral forces on the bit during drilling. All of the cutters in the group may be in one the following locations: in the cone section of the bit; on opposite sides of the offset in the offset blade; on the first or inner blade portion on the offset blade; or on the second or outer blade portion of the offset blade. The cutters in the group are, in one embodiment, adjacent to each other on the offset blade, and in another embodiment are not adjacent. Primary cutters on an offset blade may have non-zero side rake angles. Primary cutters on non-offset blades, including secondary blades, may also have such a group of one or more cutters. Furthermore, one or more primary cutters on an offset and one or more non-offset blades may form a group of cutters with side rake angles.

(45) (3) Three cutters in a group of three or more cutters that have side rake angles that vary in polarity (positive and negative, positive and zero, and negative and zero) or a change in the side rake of the cutters by rotation inwardly or outwardly relative to another (high positive and low positive, high negative and low negative). For example, if there are three cutters, the second cutter and rotated laterally outwardly relative to the first cutter, and cutter three then rotated inwardly relative to cutter the second cutter. The cutters may be adjacent to each other along a blade, radially adjacent to each other in a cutting profile, or possibly both.

(46) (4) A pair of adjacent cutters have side rakes that are negative and positive, high positive and low positive, high negative and low negative, negative and zero, or positive and zero and face each other or turn away from each other.

(47) (5) Multiple groups of three or more cutters with side rakes are set to generate counteracting lateral forces on the bit. Side rakes of cutters in a group, particularly those that are adjacent on a blade or in a cutting profile may change polarity or exhibit relatively large changes between them.

(48) (6) All of the primary cutters on the bit in particular region or on a blade or on multiple blades of a bit have a distribution of side rake angles (the number of cutters at each side rake angle or a range of side rake angles) that is bimodal or that has multiple maxima. Examples of regions or particular blades include all primary cutters in the cone, cone and nose, nose and shoulder, or cone, nose and shoulder regions; all such primary cutters in the region on offset blades; all primary cutters on any two blades; all primary cutters on one or more offset blades; all primary cutters on one or more offset and one or more non-offset blades; all primary cutters on two or more offset blades; and all primary cutters on the bit.

(49) (7) The magnitude of the differences in side rake angles between at least three, and up to all, of the cutters that are radially adjacent along a blade or that are radially adjacent in at least a portion or region of a bit's cutting profile are mostly, if not always, non-zero and relatively constant in magnitude and/or not less than a certain value. In different embodiments, the differences are 3 or more degrees; 5 or more degrees plus or minus two degrees; and at least 7 degrees. In different embodiments, averages of these differences are at least 3 degrees; at least 5 degrees; and at least 7 degrees. With primary cutters on offset blades, the values of these differences, the minimum value of the differences, and/or the average value of these difference can be made greater than with a conventional blade. Examples of regions include all primary cutters on at least offset blades in the cone, cone and nose, nose and shoulder; and cone, nose and shoulder regions.

(50) Each of the foregoing embodiments of rotary drag bit may have two cutters in a group of two or more fixed cutters, which can be radially adjacent in the cutting profile or on a blade, with large differences in side rake angles. In one example, a large difference between the side rake angles of two cutters is at least 4 degrees or more; in another example at least 7 degrees or more; and in another example at 10 degrees or more; and in another example at least 13 degrees or more.

(51) Unless otherwise noted, differences between side rake angles between a first cutter and a second cutter that are negative indicate that second cutter is turned more inwardly than first cutter. If it is positive, it means that the second cutter turn is turned more outwardly than the first cutter. Thus, a change from −2 degrees to +2 degrees, or from −11 to −7, is a +4 degree difference. A change from +2 to −2 degrees or a change from 11 to 7, is a −4 degree difference. However, if no polarity is indicated, the change or delta should be interpreted as a scaler quantity, without regard to the direction of change. Furthermore, “small side rake angle” and a “large side rake angle” each refer to the scalar value of the angle, meaning the amount of side rotation from the zero angle. Thus, to say that the cutter has high or large side rake angle means that it has a negative or a positive side rake angle with a large value.

(52) FIGS. 5A and 5B depict the cutter geometry (FIG. 5B) of cutters 512, 514, 515, 518, 520, 522, 524 and 526 on an offset blade (not shown) of a rotary drag bit (not shown) with an offset blade geometry like the offset blades 326 and 450 in FIGS. 3 and 4. Cutters 512-525 are depicted as they would be when mounted along a leading edge on an offset blade, with the offset located between cutters 516 and 518. A profile 528-542 corresponding to cutting face of each cutter 512-526, respectively, is indicated in relation to a primary cutting profile 510 for the bit, which shows that each of the primary cutter are on the primary cutting profile.

(53) From FIG. 5B the side rake of each of the cutters can be appreciated. For example, cutter 512 has a positive side rake angle that orients the face of cutter 512 laterally outwardly. Cutter 514 is rotated inwardly and has a negative side rake. Cutter 516 is rotated outwardly as compared to cutter 514. The cutter geometry illustrates that each blade portion of the offset blade (the inner and outer) allows more room for turning or rotating the cutters to achieve the desired side rake scheme. As can be seen in FIG. 5a, the profiles of the cutters are relatively evenly spaced along the blade. However, without the offset between them, the outward rotation of cutter 516 and the further outward rotation of cutter 518 would not have been possible. If cutters 516 and 518 were next to each other on a conventional blade, cutter 516 and the minimum spacing requirement would interfere with the rotation of cutter 516 to a high side rake angle.

(54) FIGS. 6A and 6B illustrate an example of cutter geometry and cutter profile of primary cutters 612-626 mounted along a leading edge of an offset blade (not shown) like offset blade 426 of FIG. 4. Cutters 612-616 are mounted on a first or inner blade portion of the offset blade; cutters 618-626 are mounted on the second or outer portion of the offset blade. As indicated by the profiles 628-642 that correspond, respectively, to cutters 612-626, the cutters are on a primary cutting profile 610. As indicated by the overlapping of cutter profiles 632 and 634, primary cutters 616 and 618 are partially overlapping, like cutters 416 and 418 on the offset blade 426 in FIG. 4. Furthermore, the difference in side rake angles of primary cutters 616 and 618 is relatively large—much larger than would be possible on a conventional blade or an offset blade like those in FIG. 3. Although not indicated in this example, the overlapping cutters may allow for additional cutters to be placed on the outer blade portion of the offset blade.

(55) The additional space afforded by the offset blade allows for side rake scheme in which blade-adjacent cutters 612-616 on the inner blade portion of the offset bit, which is in the cone region of the bit, are turned or oriented to give any two (adjacent or non-adjacent) of them larger differences in side rake angles than what would be possible with a non-offset or conventional blade, and to employ side rake schemes with that would otherwise not be possible. Larger differences in side rake angles will tend to result in larger counteracting lateral forces on the bit in a region of the cone where counteracting lateral forces tend to have greater effect on dampening vibration and improving cutting performance of the bit. Specifically, in this example cutter 612 is turned outwardly, cutter 614 is turned inwardly to face cutter 612, and cutter 616 is turned outwardly, each by a significant amount. Such a side rake scheme, with the large changes in side rake, likely would have not be possible on cutters on the same blade, particularly within the cone region, without spacing apart the cutters more and possibly having to reduce the number of cutters on the blade, or without applying the scheme instead to a group of radially adjacent primary cutters spread across multiple blades.

(56) FIG. 7 is another example of a cutter geometry an offset blade (not shown) of a rotary drag bit, in particular a PDC bit. Primary cutters 712, 714, 716, 718, 720, 724, and 726 are mounted along a leading edge of an offset blade similar offset blade 426, with an offset between the third and fourth primary cutters on the blade, which are cutters 716 and 718. Cutter profiles 744, 746, 748, 750, 752, 754, 756 and 758 that correspond to the cutters show that they are on the bit's primary cutting profile 710. As indicated by the cutter profiles 748 and 750, the primary cutters 716 and 718 are adjacent. Because they overlap, a bit designer is able to set the side rake angles of the cutters to opposite polarities give one or both a high side rake angle. In this example, primary cutter 716, which is the third cutter on the blade, has a side rake angle of negative 7 degrees. Cutter 718 has a side rake angle of 10 degrees, a difference of 17 degrees. In these cutters where on a non-offset blade and set close to the minimum separation needed for mounting them on the blade, it would not possible to achieve such a large difference in side rakes close to minimum separation. The largest negative side rake for the third cutter (cutter 716) would be negative one degree and the maximum positive side rake of the fourth cutter (cutter 718) would be five degrees, only a 6 degree difference.

(57) The graphs of FIGS. 8A to 8G illustrate various examples of side rake schemes for fixed cutters on a rotary earth boring tool, such as a PDC bit or reamer, that illustrate or embody patterns relative side rake angles or changes in side rake changes between cutter that can be used on bits with offset blades for generating counteracting lateral forces on the tool. The x-axis represents successive positions of cutters along a blade or, in an alternative embodiment, successive radial locations of cutters or cutter positions in a bit's cutting profile. An offset blade can be used to increase the side rake angles and differences in side rake angles.

(58) The origin represents, in some embodiments, the axis of rotation of the tool, with successive positions along the x axis representing positions closer to the gauge of the body of the tool and more distant from the axis of rotation. However, the patterns could start at some outer location within the cutting profile or blade. The number of cutters on a bit depends, at least in part, on the size of the bit. The number of data points indicated along the x axis is therefore not intended to be limiting, but representative of a side rake scheme embodying examples of patterns can be used on bits with offset blades for generating counteracting lateral forces on a rotary earth boring with fixed cutters. The y axis indicates the side rake angle of the cutters. The graphs are not intended to imply any particular range of positions on a blade or within a cutting profile. Furthermore, although primary cutters are assumed for the exemplary side rake schema, the patterns in side rake that they embody could be used in side rake schema for a row of backup cutters or cutters on a secondary cutting profile, or a combination of both.

(59) The example of FIG. 8A represents a side rake scheme in which the differences or changes in side rake angles of at least three cutters in adjacent positions alternate directions. For example, the angle of the cutter in the first position and the angle of the cutter in the second position have opposite polarities. The direction of change or the difference is negative. The change between the cutters in the second and the third positions is a direction opposite the direction of the change from the first to the second cutter. The side rake angle increases, and the difference is positive.

(60) The example of FIG. 8B is similar to FIG. 8a, except that it is comprised of two related patterns 850 and 852, which are the inverse of each other. In each of these two patterns the change of the side rake from an individual cutter to a group of two or more cutters with a similar side take is in one direction, and then the change in angle from the group to a single cutter is in the opposite direction.

(61) In the example configuration of FIG. 8C, the differences in side rake angles within group 854 of at least two successive cutters, four in this example, is in a first direction. The angle in this group progressively increase, in this example from negative to positive. In a next adjacent group 856 of two or more cutters, the side rake angles change in the opposite direction between adjacent members of cutters within that group. In this example, the angles decrease, and furthermore they decrease from being positive angles to negative angles. A third group of at least cutters 858, having increasing angles, and thus the direction of change in angle within this group is positive. The pattern thus illustrates an alternating of the direction of change within adjacent groups of cutters.

(62) FIG. 8D is similar to FIG. 8C, except that the changes in side rake angles follow a sinusoidal pattern rather than a linear pattern.

(63) FIG. 8E shows an example of a pattern in which the side rake angles within groups 860 and 862 of two or more successive cutters are similar, for example, all the same magnitude or all negative or positive, but that every third or more cutter 864 has a different angle, for example, positive when the angles in the group 860 are negative. The angles change in a first direction from group 860 to cutter 864, and then in the opposite direction between cutter 864 and group 862. Inverting the pattern is an alternative embodiment. The cutter having one polarity of side take might be positioned on one side of the bit and the cutters with the opposing polarity would be positioned on the other side of the bit. For instance, one side rake would be used on blades 1 to 3 and the second side rake would be used for cutters on blades 4 to 6 of a six bladed bit.

(64) FIG. 8F is an example of a pattern for a bit in which side rakes of two or more adjacent cutters within group 866, for example within a cone of a bit, are positive, and then a group of two or more adjacent cutters are negative in an adjacent group 868. The second group could be, for example, along the nose and shoulder of the bit. The side rake angle then becomes positive again. The pattern also illustrates stepwise decreases or increases of side rake within a group.

(65) FIG. 8G is an example of a step wise pattern or configuration in which the side rake angle is generally increasing. In this example, the side rake angle is increasing generally in a non-linear fashion, but the change in angle swings between an increasing direction and a neutral direction. In this example the increasing positive side rake pushes cuttings increasingly to the outer diameter of the but, increasing drilling efficiency.

(66) Alternative embodiments to the patterns or configurations of FIGS. 8A to 8D comprise inverting the patterns. Furthermore, although the polarity of the angles (positive or negative) form part of the exemplary patters, the values of the angles in alternative embodiments can be shifted positive or negative directions without changing the polarity of the sides of the cutters in the grouping. In the configuration of FIG. 8A, for example, the cutters could have either all positive or all negative side rake while employing alternating changes in direction of the differences between the cutters. Furthermore, the alternating a pattern of positive and negative direction changes could occur first between cutters with positive angles, and then between cutters with positive and negative side rake angles, and then between cutters with only negative side rake polarities, all without interrupting the alternating pattern. Another embodiment is a bit with, for instance, blades 1 to 3 having one side rake and blades 4 to 6 having an opposing or substantially different side rake, similar to the arrangement shown in FIGS. 8E and 8F. This design could recede walk tendency, and might be configured to be more laterally stable than a more conventional design.

(67) FIGS. 8H and 8J are additional examples of alternative patterns. In FIG. 8H, the side rake angles are positive and generally increase. But, at some frequency, the angle decreases. In this example, the frequency is every third cutter in the sequence. However, a different frequency could be chosen, or the point at which the decrease occurs can be based on a transition between section of the bit or blade, such as between cone and nose, nose and shoulder, and shoulder and gauge, or at a blade offset

(68) FIG. 8I is an alternative embodiment to FIG. 8A, in which the side rake angles remaining positive, but increase and decrease in alternating fashion.

(69) FIG. 8I is an alternative embodiment to FIG. 8A in which the side rake angles remaining positive but increase and decrease in an alternating fashion.

(70) FIG. 8J illustrates that patterns of side rake angles changes may also involve varying the magnitude of change in the side rake angle between cutters in addition to direction.

(71) FIGS. 9A and 9B depict the side rake schema of an example of a PDC bit with offset blades as primary blades with a side rake schema for its primary cutters embodying patterns that generate counteracting lateral forces on the bit that tend to reduce or dampen vibration that reduces bit cutting performance. The PDC bit is be a representative, non-limiting example of a rotary drag bit with fixed cutters and offset blades.

(72) FIG. 9A plots side rake angle against radial location of the primary cutters; FIG. 9B plots side rake angle against cutter number for the same primary cutters. Table 1 below gives the values of side rake, cutter number, blade number and bit profile region (which can be used to determine in what region the cutter is located on the blade) for each of the bit's primary cutters. The bit has three primary blades, each of which is an offset blade, and the offsets for the blades occur within the cone region between the second and third cutters on each primary blade.

(73) TABLE-US-00001 TABLE 1 Cutter Side Rake Blade No Region (deg.) Number 1 Cone 8 1 2 Cone 3 5 3 Cone 5 3 4 Cone 1 1 5 Cone 5 5 6 Cone 1 3 7 Cone 5 1 8 Cone 3 5 9 Cone 5 3 10 Cone −4 2 11 Cone 5 1 12 Nose −4 5 13 Nose 5 4 14 Nose −4 3 15 Nose 5 2 16 Nose −4 1 17 Nose 5 6 18 Nose −5 5 19 Shoulder 5 4 20 Shoulder −4 3 21 Shoulder 5 2 22 Shoulder −4 1 23 Shoulder 5 6 24 Shoulder −5 5 25 Shoulder 5 4 26 52.49 −5 3 27 Shoulder 5 2 28 Shoulder −5 1 29 Shoulder 5 6 30 Shoulder −5 5 31 Shoulder 5 4 32 Shoulder −5 3 33 Shoulder 5 2 34 Gauge 0.01 1 35 Gauge 0.01 6 36 Gauge 0.01 5 37 Gauge 0.01 4 38 Gauge 0.01 3 39 Gauge 0.01 2

(74) In this example, the side rakes of the primary cutters alternate in magnitude or alternate in both magnitude and polarity along the cutting profile of the bit. Thus, radially adjacent cutters on the primary cutting profile have alternating side rakes that provide an alternating series of positive and negative changes in side rake angle. Similarly, the cutters on the inner blade portion and the first cutter on the lower blade portion of at least two of the primary blades have large difference in side rake angles that alternate from positive to negative, with the largest change being negative seven degrees. Alternating negative and positive differences occur between cutters with positive side rake angles in the cone region, and that the alternating pattern of side rakes in the nose and shoulder regions occurs between primary cutters with positive and negative side rakes.

(75) FIGS. 10A and 10B are graphs that plot, respectively, side rakes of primary cutters against cutter number and cutter position in a primary cutting profile of a PDC bit that is intended to be another representative, non-limiting example of a rotary drag bit with fixed cutters and offset blades. This example has 6 blades, with blades 1,3 and 5 being primary blades with offset geometries. The offsets occur between the third and fourth cutters on blades in the nose region. Table 2 below gives the values of size rake, radial location, and cutter number, as well as angular position, blade number and profile angle (which can be used to determine in what region the cutter is located on the blade) for each of the bit's primary cutters.

(76) TABLE-US-00002 TABLE 2 Cutter Profile Angle Side Rake Blade No (deg.) (deg.) Number 1 Cone 1 1 2 Cone 1 5 3 Cone 1 3 4 Cone −5 1 5 Cone −5 5 6 Cone −5 3 7 Nose −1 1 8 Nose −1 5 9 Nose −1 3 10 Nose 4 2 11 Shoulder 4 1 12 Shoulder 4 6 13 Shoulder 4 5 14 Shoulder 4 4 15 Shoulder 4 3 16 Shoulder −2 2 17 Shoulder −2 1 18 Shoulder −2 6 19 Shoulder −2 5 20 Shoulder −2 4 21 Shoulder −2 3 22 Shoulder 3 2 23 Shoulder 3 1 24 Shoulder 3 6 25 Shoulder 3 5 26 Shoulder 3 4 27 Shoulder 3 3 28 Shoulder −3 2 29 Shoulder −3 1 30 Gauge −3 6 31 Gauge 0.01 5 32 Gauge 0.01 4 33 Gauge 0.01 3 34 Gauge 0.01 2 35 Gauge 0.01 1

(77) The three cutters along the inner blade portions and the first cutter on the outer blade portion change in alternating directions, with side rake differences of least 4 degrees. Cutters in the bit profile form groups of cutters (with at least three cutters in each group) 1002, 1004, 1006, 1008, 1010, 1012, 1014, and 1016 that have the same side rake angles (in alternative embodiments, the angle may different slightly), with relatively large side rake angle differences between groups, with the direction of change alternating between positive and negative between successive groups along the bit's cutting profile, except the two changes between group 1004 and 1006 and 1006 and 1008, both of which of are positive. These patterns of side rake angles help to generate counteracting lateral forces on the bit that dampen bit vibration.

(78) The foregoing are representative, non-limiting examples of downhole tools. Each example may embody several improvements, each of which might be separately claimed or claimed in different combinations. Furthermore, an example is not intended to limit of the scope of a claim to an improvement to the details of the example, as modifications can be made to the examples by those of ordinary skill in the art while still embodying a claimed improvement. The appended claims are not intended to be construed to be limited only to a specific example where their literal language permits a broader construction consistent with the specification set forth above.