阅读说明：本技术 具有切削脊和倾斜切削面的复合片及pdc钻头 (Composite sheet with cutting ridges and inclined cutting faces and PDC drill bit ) 是由 于家庆 程晓敏 杨雄文 王旭 刘宇 彭齐 于 2021-05-24 设计创作，主要内容包括：本发明提供了一种具有切削脊和倾斜切削面的复合片及PDC钻头。PDC钻头包括钻头本体、本发明的多个具有切削脊和倾斜切削面的复合片、以及多个分别容纳具有切削脊和倾斜切削面的复合片的带凹槽的刀翼。具有切削脊和倾斜切削面的复合片(后称切削齿)包括基底；超硬层；超硬层顶部的倾斜面,倾斜面从超硬层切削刃向超硬层后缘向下倾斜。具有切削脊和倾斜切削面的复合片还包括在超硬层的侧壁处从倾斜面的外围延伸到切削刃的倒角。(The invention provides a composite sheet with cutting ridges and inclined cutting faces and a PDC drill bit. PDC bits include a bit body, a plurality of composite sheets of the present invention having cutting ridges and angled cutting faces, and a plurality of fluted blades that receive the composite sheets having cutting ridges and angled cutting faces, respectively. A composite sheet (hereinafter referred to as a cutting tooth) having a cutting ridge and an inclined cutting face includes a substrate; an ultra-hard layer; the inclined plane at the top of the superhard layer inclines downwards from the cutting edge of the superhard layer to the rear edge of the superhard layer. The composite sheet having a cutting ridge and an inclined cutting face further includes a chamfer extending from the periphery of the inclined face to the cutting edge at the side wall of the ultrahard layer.)

1. A composite sheet having a cutting ridge and a sloping cutting face, comprising:

a substrate;

an ultra-hard layer;

the inclined surface at the top of the super-hard layer;

wherein the inclined surface is inclined downward from the superhard layer cutting edge to the superhard layer rear edge.

2. The composite sheet having cutting ridges and an inclined cutting face as claimed in claim 1, further comprising chamfers extending from the periphery of the inclined face to the cutting edges at the side walls of the ultrahard layer.

3. The composite sheet having a cutting ridge and an inclined cutting face as claimed in claim 1, wherein the inclined face comprises a cutting ridge extending diametrically from the cutting edge to the trailing edge at the top of the inclined face.

4. A composite sheet having a cutting ridge and an inclined cutting face as claimed in claim 3, wherein said inclined face comprises two side faces each inclined downwardly from said cutting ridge to the periphery of said inclined face.

5. The composite sheet having a cutting ridge and an inclined cutting face as claimed in claim 4, wherein the profile angle at the trailing edge is greater than the profile angle at the cutting edge.

6. A composite sheet having a cutting ridge and a sloping cutting face as claimed in claim 1, wherein the height of the cutting tooth at the cutting edge is higher than the height of the cutting tooth at the trailing edge.

7. The composite sheet having cutting ridges and inclined cutting faces of claim 3, wherein said cutting ridges are rounded cutting ridges.

8. A composite sheet having a cutting ridge and an inclined cutting face as claimed in claim 1, wherein said inclined face comprises two cutting ridges intersecting a cutting point on which said cutting edge intersects and extending from said cutting point to said trailing edge.

9. The composite sheet having cutting ridges and an inclined cutting face as claimed in claim 8, wherein two of said cutting ridges divide said inclined face into two lateral planes and a central plane.

10. A composite sheet having a cutting ridge and an inclined cutting face as claimed in claim 9, wherein said central plane slopes downwardly from said cutting edge to said trailing edge.

11. The composite sheet having a cutting ridge and an inclined cutting face as claimed in claim 9, wherein said two lateral planes are inclined downwardly from said two cutting ridges to the periphery of said inclined face, respectively.

12. The composite sheet having cutting ridges and an inclined cutting face as claimed in claim 11, wherein the two angles of inclination of the two lateral planes are equal or different.

13. The composite sheet having cutting ridges and an inclined cutting face of claim 1, wherein said inclined face comprises two converging ridges and a central cutting ridge that intersect at a point distal from said cutting edge, said two converging ridges and said central cutting ridge dividing said inclined face into two lateral planes and a central plane.

14. The composite sheet having a cutting ridge and an inclined cutting face of claim 13, wherein said two lateral planes intersect at said central cutting ridge and said two lateral planes and said central plane intersect at said two converging ridges, respectively.

15. A composite sheet having cutting ridges and angled cutting faces as set forth in claim 14, wherein the outer end of said central cutting ridge intersects said cutting edge at a cutting point.

16. The composite sheet of claim 15, wherein the central cutting ridge is parallel to the bottom surface of the substrate.

17. The composite sheet having cutting ridges and angled cutting faces of claim 15, wherein said central plane has an inclination.

18. A compact having cutting ridges and angled cutting faces as in claim 1, wherein said superhard layer is formed of PCD.

19. The composite sheet having cutting ridges and inclined cutting faces as claimed in claim 1, wherein said inclined faces are formed by Electrical Discharge Machining (EDM), laser ablation, grinding or other material reduction methods, or may be formed directly by sintering.

20. A PDC bit comprising the composite sheet of any one of claims 1 to 19 having cutting ridges and inclined cutting faces, the composite sheet being one or more in number.

Technical Field

The invention mainly relates to a drill bit used in petroleum exploration and drilling operation in the oil and gas industry. The invention relates in particular to cutting elements in the field of drill bits for oil exploration and drilling operations, a compact with cutting ridges and inclined cutting faces and a PDC drill bit.

Background

For example, in surface drilling for oil and gas development or for other applications, it is conventional practice to attach a drill bit at the lower end of a drill string. The drill bit is rotated by rotating the drill string at the surface or by activating a downhole screw or turbine to turn the drill string. The drill bit is rotated to drill into the subterranean formation. As the drill bit rotates, the cutter or abrasive structure cuts, crushes, shears, and abrades the formation to form the wellbore. Drill bits typically include a bit body made of steel or a matrix. The bit body has blades or similar structures to which a plurality of cutting elements are arranged in a predetermined manner. The manner in which the blades are configured and the manner in which the cutting elements are disposed on the blades depends, among other factors, on the type of formation being drilled and the drilling assembly to which the drill bit is linked.

FIG. 1 illustrates a conventional drill bit suitable for drilling through a rock formation to form a wellbore. The drill bit comprises a bit body 3 and a plurality of blades 4 and a connection sub or sub 32 for connecting the drill bit to a drill string (not shown), the connection sub or sub 32 being for rotating the drill bit about a longitudinal bit axis 6 for drilling a borehole. Blades 4 are separated by channels or gaps that allow drilling fluid to flow through and clean and cool blades 4 and cutting teeth 5. The cutting teeth 5 are placed in the blades 4 at a predetermined angular orientation and radial position so that the working face 503 forms a desired back rake angle with respect to the formation to be drilled. A fluid passage 31 is formed in the bit body 3, and a plurality of ports 33 communicate with the fluid passage 31. Drilling fluid may be pumped in selected directions and at selected flow rates into the spaces between blades 4 to lubricate and cool the drill bit, blades 4 and cutting teeth 5. The drilling fluid may also clean the bottom of the well and remove cuttings as the drill bit rotates and passes through the formation.

The bit body 3 is cylindrical. A plurality of cutting teeth 5 are provided on the outer edge of the wing bit 4, and further, the outer edge of the wing bit 4 includes an inner cone portion 431, a nose portion 432, a shoulder portion 433, and a gage portion 434. The inner cone portion 431 is close to the central axis of the bit body 3, the gauge portion 434 is located on the side wall of the bit body 3, and the cutting teeth 5 are distributed on the inner cone portion 431, the nose portion 432, the shoulder portion 433 and the gauge portion 434 of the blade 4.

As shown in fig. 2A-2C, a typical cutting element 5 (also referred to as a cutting tooth 5) is shown, which is a cylinder, has a cutting tooth axis 505, and includes a bottom end portion of the cylinder and a top end portion of the cylinder. The cylindrical bottom end portion, i.e., substrate 504, is typically made of a hard composite material such as tungsten carbide, while the top end portion, also referred to as the superhard layer 502, is typically made of a hard, wear resistant material such as polycrystalline diamond (PCD). The interface 513 between the substrate 504 and the superhard layer 502 can be planar or non-planar, according to many variations of interfaces known in the art. The substrate 504 and the superhard layer 502 are sintered together by a high pressure, high temperature process. At the top of the ultrahard layer 502, a chamfer 507 is machined to increase the durability of the cutting edge when entering the wellbore and at least initially contacting the formation to begin drilling. Those skilled in the art will recognize that at least a portion of chamfer 507 may also serve as a working surface for contacting subterranean formations during drilling operations. The top surface 503 of the superhard layer 502 and the surface of the chamfer 507 meet at a top cutting edge 515 and the cylindrical side 512 of the superhard layer 502 and the surface of the chamfer 507 also meet at a lower edge 514 forming a primary cutting edge having the same curvature as the outer cylindrical surface of the substrate 504.

For a typical cutter, the top surface 503 of the ultrahard layer (also referred to as the cutting face) is flat and parallel to the bottom surface of the substrate, i.e., perpendicular to the cutter axis 505. The height of any point on the cutting face relative to the base of the substrate is equal to the cutting tooth height 506. It should also be noted that if interface 513 is planar, the thickness of the superhard layer is uniform. Some non-planar interfaces 513 may be employed to reduce residual stresses at the interface and within the superhard layer due to the mismatch in thermal expansion coefficients between the superhard layer material and the substrate material. In this case, the thickness of the ultrahard layer is not uniform, but the cutting face is still parallel to the bottom surface of the base and perpendicular to the cutter axis, i.e., the cutting face angle 560 between the cutting face and the cutter axis is 90 degrees.

As shown in fig. 3A and 3B, a conventional cutter 5 planar cutting face 503 is shown cutting a formation 410. During drilling, a drill bit (see FIG. 1) will be placed at the bottom of the wellbore and rotated to cut the inner surface of the wellbore. The cutting teeth on the blades are mounted on the blades in a predetermined angular orientation relative to the formation to be drilled by brazing or by mechanical locking. Drilling fluid is pumped into the interior of the bit body and out of the nozzles. As the drill bit rotates, the PDC cutters scrape and shear the rock while simultaneously withstanding the large impacts from the formation.

One feature of the arrangement of the cutting teeth is referred to as a relief angle, which is the angle between the cutting tooth axis and the top surface of the formation 410. Maintaining a certain relief angle is necessary to prevent the cutting teeth from rubbing against the formation and to avoid frictional heat and additional reactive torque during drilling.

Another feature of the arrangement of cutting teeth is referred to as the back rake angle. The caster angle is used to describe the working angle of the working surface 503. As shown in FIG. 3A, the back rake angle 610 is defined as the angle between the working surface 503 and a plane perpendicular to the surface of the formation 410 at the cutting edge 514. For a cylindrical planar cutting tooth, back rake angle 610 is equal to back rake angle 620. The back rake angle 610 in fig. 3A is greater than the back rake angle 612 in fig. 3B because the back angle 620 in fig. 3A is greater than the back angle 630 in fig. 3B. The back rake angle required for the most efficient drilling depends on the type of formation to be drilled. Typically, drill bits are designed such that the cutting teeth have a relatively small back rake angle. The small back rake angle provides high drilling efficiency and fast rate of penetration by reducing the Weight On Bit (WOB) required to damage a particular formation.

However, in hard formations such as carbonate rock, igneous rock, sandstone rock, etc., a large back rake angle is required to increase the strength of the cutting edge and prevent the cutting teeth from being broken or chipped due to excessive cutting force. In this case, the cutting efficiency is reduced, and the cutting teeth are difficult to bite into the formation, which may cause unstable drilling.

For soft formations, such as shale, claystone and mudstone, shearing formations requires lower cutting forces and cutting tooth damage is not significant. A relatively small back rake angle may be used to maximize cutting efficiency without causing damage to the cutting teeth. However, for conventional cutting teeth having planar cutting faces, the desired backrake angle may not be achievable. If the back rake angle (which is the same as the relief angle of a planar cutting tooth) is too small, the lower circumferential surface of the cutting tooth adjacent the cutting edge will rub against the formation or the compressed chips, increasing frictional heat and additional reactive torque. The increased frictional heat may reduce the wear and impact resistance of the cutting teeth and shorten the life of the drill bit. Another disadvantage of drilling soft formations, particularly shale and claystone formations, under high ambient pressure, high bottom hole temperatures conditions is the continuous production of string cuttings during the cutting process. A continuous strip of rock debris may accumulate and compact ahead of the cutting face. The accumulation of debris between the cutter and the rock has a significant effect on the cutter/rock interaction. Energy is lost in plastic deformation of the rock fragments rather than breaking the intact rock. Debris accumulation can also lead to other inefficient drilling conditions, such as inefficient cooling and even the formation of pockets of debris on the cutter.

Accordingly, cutting teeth having a small back rake angle are required to improve cutting efficiency and lifespan while maintaining a desired back angle.

Disclosure of Invention

The invention mainly aims to provide a composite sheet with cutting ridges and an inclined cutting surface and a PDC drill bit, so as to solve the problem of low cutting efficiency of the composite sheet in the prior art.

In one aspect, the present invention relates to a composite sheet (cutter) having cutting ridges and an inclined cutting face for cutting earth formations for use on a drill bit. The cutting tooth includes a base; an ultra-hard layer; the inclined plane at the top of the superhard layer inclines downwards from the cutting edge of the superhard layer to the rear edge of the superhard layer. The composite sheet having a cutting ridge and an inclined cutting face further includes a chamfer extending from the periphery of the inclined face to the cutting edge at the side wall of the ultrahard layer.

In some embodiments related to the inclined surface, the inclined surface includes a cutting ridge extending diametrically from the cutting edge to the trailing edge at the top of the inclined surface. The inclined surface includes two side surfaces respectively inclined downward from the cutting ridge to an outer periphery of the inclined surface. The profile angle at the trailing edge is greater than the profile angle at the cutting edge. The height of the cutting teeth at the cutting edge is higher than the height of the cutting teeth at the trailing edge. In some embodiments, the cutting ridge is a rounded cutting ridge.

In some embodiments relating to an inclined plane, the inclined plane comprises two cutting ridges in comparison to the cutting point on the cutting edge and extending from the cutting point to the trailing edge. The two cutting ridges divide the inclined surface into two lateral planes and a central plane. The central plane is inclined downwardly from the cutting edge to the trailing edge. The two lateral planes are respectively inclined downward from the two cutting ridges to the periphery of the inclined surface. The two angles of inclination of the two lateral planes are equal or different.

In some embodiments relating to the rake face, the rake face comprises two converging ridges and a central cutting ridge that intersect at a point distal from the cutting edge, the two converging ridges and the central cutting ridge dividing the rake face into two lateral planes and a central plane. The two lateral planes intersect at the central cutting ridge and the two lateral planes and the central plane intersect at two converging ridges, respectively. The outer end of the central cutting ridge intersects the cutting edge at a cutting point. The central cutting ridge is parallel to the bottom surface of the base of the cutting tooth. The central plane has a slope.

In some embodiments, the ultrahard layer is formed of PCD and the angled surface is formed by Electrical Discharge Machining (EDM), laser ablation, grinding, or other material reduction methods. It can also be directly shaped by sintering.

In another aspect, the present invention relates to a PDC bit for cutting a subterranean formation. The drill bit includes a bit body, a plurality of composite sheets of the present invention having cutting ridges and angled cutting faces, and a plurality of fluted blades that receive the composite sheets having cutting ridges and angled cutting faces, respectively.

The foregoing has outlined rather broadly the features of the present invention in order that the detailed description that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims.

Drawings

In order that the objects of the invention will be attained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described with additional specificity and detail through the use of the accompanying drawings.

FIG. 1 is a cross-sectional view of a prior art drill bit;

FIG. 2A is a perspective view of a prior art cutting tooth having a planar working surface;

FIG. 2B is a cross-sectional view of the cutting tooth of FIG. 2A;

FIG. 2C is a top view of the cutting tooth of FIG. 2A;

FIG. 3A is a schematic view of a planar cutter cutting a subterranean formation with a greater back rake angle;

FIG. 3B is a schematic view of a planar cutter cutting a formation with a small back rake angle;

FIG. 4A is a perspective view of a cutting tooth having a non-planar cutting face including two angled sides and an angled cutting ridge in accordance with an embodiment of the present invention;

FIG. 4B is a front view of the cutting tooth of FIG. 4A with a non-planar cutting face;

FIG. 4C is a cross-sectional view of the cutting tooth of FIG. 4A with a non-planar cutting face;

FIG. 5 is a schematic view of the cutter of FIG. 4A cutting a formation at a reduced back rake angle;

FIG. 6A is a perspective view of the non-planar cutting tooth of FIG. 4A having a rounded cutting ridge;

FIG. 6B is a front view of the non-planar cutting tooth of FIG. 6A;

FIG. 6C is a side view of the non-planar cutting tooth of FIG. 6A;

FIG. 7A is a perspective view of a cutting tooth having a non-planar cutting face including three inclined planes converging at the cutting edge in accordance with an embodiment of the present invention;

FIG. 7B is a front view of the cutting tooth of FIG. 7A with a non-planar cutting face;

FIG. 7C is a side view of the cutting tooth of FIG. 7A with a non-planar cutting face;

FIG. 8A is a perspective view of a cutting tooth having three flat surfaces and three cutting ridges in accordance with an embodiment of the present invention;

FIG. 8B is a front view of the cutting tooth of FIG. 8A with a non-planar cutting face;

FIG. 8C is a side view of the cutting tooth of FIG. 8A with a non-planar cutting face;

fig. 9 is a schematic diagram of the cutting tooth of fig. 8A cutting a highly heterogeneous formation having hard and soft interlayers.

Detailed Description

The particulars shown herein are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only. The particulars shown herein are by way of example and for purposes of illustrative discussion of the principles and conceptual aspects of various embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of such principles and conceptual aspects of various embodiments of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention. It will be apparent to those skilled in the art from this disclosure that the several forms of the invention can be embodied in practice by way of illustration.

The composite sheet having the cutting ridge and the inclined cutting face in the present invention will be simply referred to as a cutting tooth hereinafter.

Fig. 4A-4C illustrate an embodiment of a cutting tooth 51 of the present invention. In accordance with the present invention, cutter 51 has a base 504 and an ultrahard layer 502 disposed thereon. The superhard layer 502 is comprised of polycrystalline diamond, cubic boron nitride, silicon carbide, and the substrate 504 is comprised of tungsten carbide. The cutter 51 is substantially cylindrical and symmetrical about the longitudinal axis 505, although such symmetry is not required and asymmetric cutters are known in the art. Chamfer 507 extends from the periphery of top surface 503 to sidewall 512 of superhard layer 502. Chamfer 507 may extend to the entire periphery of superhard layer 502 as shown, or may simply extend along a portion of the periphery near the point of cutting. Chamfer 507 may increase the durability of the cutting edge, but it should be noted that cutting teeth that do not exhibit a distinct chamfer may be used in certain selected outer regions of the drill bit for certain specific applications.

The top surface 503 (inclined surface) of the cutting tooth in the present invention comprises two side surfaces 531, 533 which intersect at the center of the cutting tooth and form a cutting ridge 541. The top surface 503 may be constructed from typical flat cutting teeth, formed using a method known as loft cutting. The cutting ridge 541 extends diametrically down from the cutting edge 521 at the top of the inclined surface 503 to a trailing edge 523 at the top of the inclined surface 503. The two side surfaces 531, 533 are respectively inclined downward from the cutting ridge 541 to the periphery of the inclined surface 503 in the vertical direction with respect to the cutting ridge. The intersection of the cutting ridge 541 and the cutting edge 521, the lowest point on the side 531 and the lowest point on the side 533 define the three vertices of the cutting triangle. The projection of the cutting triangle on a plane perpendicular to the cutting ridge 541 forms a cutting triangle profile with three vertices 542, 524, 525. Similarly, the intersection of the cutting ridge 541 and the trailing edge 523, the lowest point on the side 531, and the lowest point on the side 533 define the three vertices of the trailing edge triangle. The projection of the trailing edge triangle on a plane perpendicular to the cutting ridges 541 forms a trailing edge triangle profile with three vertices 543, 524, 525.

The apex 542 of the cutting triangular profile is higher than the apex 543 of the trailing triangular profile. An angle between a straight line connecting the vertexes 542 and 524 and the cutting tooth axis 505 is defined as a first cutting edge profile angle 551, and an angle between a straight line connecting the vertexes 542 and 525 and the cutting tooth axis 505 is defined as a second cutting edge profile angle 552. The angle between the line connecting the vertices 543, 524 and the cutting tooth axis 505 is defined as a first trailing edge profile angle 555, and the angle between the line connecting the vertices 543, 525 and the cutting axis 505 is defined as a second trailing edge profile angle 556. The convex curved surface can be formed by taking a connecting line between the vertexes of the triangular outline as a guide curve. The slope of the side is determined by the profile angle. The profile angle at the trailing edge is greater than the profile angle at the cutting edge in order to maintain a reasonable diamond layer thickness at the trailing edge 523. In particular, the first trailing edge profile angle 555 is greater than the first cutting edge profile angle 551 and the second trailing edge profile angle 556 is greater than the second cutting edge profile angle 552. The cutting ridge 541 is generally located at the center of the inclined surface. The profile angles of each profile may be equal or different. Loft cutting is the manufacture of shapes by Electrical Discharge Machining (EDM), laser ablation, grinding, or material reduction methods. It may also be shaped by sintering.

By constructing the cutter using the foregoing method, the cutter height 506 at the cutting edge is higher than the cutter height 508 at the trailing edge. The cutting ridges 541 slope from the cutting edge to the trailing edge with a rake angle 509 greater than 90 degrees. The cutting ridge inclination angle is measured between the cutting ridge 541 and the cutting pinion 505. The cutting ridge inclination angle is defined as an angle between the cutting ridge 541 and the cutting tooth axis 505.

The advantages of the non-planar cutting tooth depicted in fig. 4A-4C may be illustrated in fig. 5 and 3A. Fig. 3A shows a planar cutting tooth cutting rock with a back rake angle 610 and a back angle 620. Fig. 5 shows the cutting tooth 51 of fig. 4A with a beveled cutting face cutting rock at the same relief angle. When cutting the formation 410, the planar cutter 5 and the non-planar cutter 51 have the same relief angle in fig. 3A and 5. Due to the rake of the cutting face, the backrake angle 613 of the cutting tooth 51 (equal to the backrake angle 610 minus the cutting ridge rake angle 509 plus 90 degrees in fig. 4C) is less than the backrake angle 610 of the planar cutting tooth 5. The non-planar cutting teeth of fig. 4A-4C have a reduced back rake angle and a sharp cutting ridge, requiring less cutting force to fracture the formation while maintaining a reasonable back angle.

The cutting teeth of fig. 4A-4C have several other advantages. When the back rake angle is reduced, the time for the rock debris to contact the cutting surface is shortened, and the frictional heat is reduced. The frictional heat may reduce the wear and impact resistance of the superhard layer. The non-planar cutting face provides a good drilling fluid flow path that facilitates more efficient cooling of the cutting teeth. The cutting ridges 541 and the angled cutting surfaces 531, 533 will intercept the debris and reduce the tendency of the debris to compact ahead of the cutting edge. The compaction of the cuttings in front of the cutting edge may result in inefficient cooling even in other inefficient drilling situations where the cutting teeth become balling.

In an embodiment of the present application, the inclined cutting face may have a rounded cutting ridge in the middle. Fig. 6A-6C illustrate a cutting tooth 52 having a beveled surface and a rounded cutting ridge. Specifically, the cutter 52 has a base 504 and an ultrahard layer 502 disposed thereon. Chamfer 507 extends from the periphery of top surface 503 to sidewall 512 of ultrahard layer 502. The top surface 503 of the superhard layer 502 is sloped. The cutting ridge 541 extends diametrically down from the cutting edge 521 to the trailing edge 523 at the top of the cutting face 503. Meanwhile, the two side surfaces 531, 533 are respectively inclined downward from the cutting ridge 541 to the periphery of the top surface 503 in the vertical direction with respect to the cutting ridge.

As will be appreciated by those skilled in the art, there are other cutting tooth designs that are in accordance with features of the present invention. In a preferred embodiment, referring to FIGS. 7A-7C, a cutting tooth 53 having a beveled surface is illustrated. Cutting tooth 53 has a base 504 and an ultrahard layer 502 disposed thereon. Chamfer 507 extends from the periphery of top surface 503 to sidewall 512 of ultrahard layer 502. The top surface 503 of the superhard layer 502 is sloped.

The cutting top surface 503 includes three inclined planes 531, 532, and 533. The central plane 532 has an inclination A between the central plane 532 and the bottom surface of the cutting tooth. The inclination a determines the amount of reduction of the back rake angle compared to a planar cutting tooth. The inclination A ranges from 1 to 45 degrees. The preferred range is 3-15 degrees. The side surfaces 531, 533 have inclinations B and C, the lower sides of which intersect the cylindrical surfaces of the cutting teeth. The inclinations B and C are measured between the flanks 531, 533 and the cutting tooth axis 505, respectively. The three surfaces meet at two cutting ridges 541, 542, thereby forming a sharp cutting point 522. Specifically, plane 531 intersects central plane 532 at cutting ridge 541 and plane 533 intersects central plane 532 at cutting ridge 542. The cutting ridges 541, 542 intersect at the cutting point 522 and extend from the cutting point 522 to the trailing edge such that the two cutting edges form a substantially "V" shaped pattern. The three surfaces 531, 532 and 533 are each inclined downwardly from the cutting edge 521 to the trailing edge 523, while the side surfaces 531, 533 are each inclined downwardly from the two cutting ridges 541, 542 to the periphery of the cutting tooth. It is worth mentioning that the flanks are symmetrical with respect to a plane passing through the cutting point and perpendicular to the base of the cutting tooth in fig. 7A-7B, in which case the angles of inclination B and C are equal, but in other embodiments they may be asymmetrical.

Fig. 8A-8C illustrate an alternative embodiment of a cutting tooth 54 of the present invention. Similar to the cutting tooth of fig. 7A-7C, the cutting face has three inclined planes, but they intersect at a point remote from the cutting edge. The cutting tooth 54 has a base 504 and an ultrahard layer 502 disposed thereon. Chamfer 507 extends from the periphery of top surface 503 to sidewall 512 of ultrahard layer 502. The central cutting ridge is parallel to the bottom surface of the cutting tooth and the two diverging cutting ridges extend down to the peripheral trailing edge of the cutting tooth.

The top surface 503 of the superhard layer 502 is sloped and has three cutting ridges 541, 542, and 543. The inner ends of the three cutting ridges converge at 545 on the top surface 503, while the ends of the three cutting ridges extend to the outer edge of the top surface 503. The three cutting ridges form a substantially "Y" shaped pattern when viewed from the top of the cutting tooth, and the three cutting ridges divide the top surface into two lateral planes 531, 533 and a central plane 532. The two lateral planes 531, 533 intersect at the central cutting ridge 541. The outer end of the central cutting ridge 541 intersects the cutting edge 521 at a cutting point. The two lateral planes 531, 533 intersect the central plane 532 at two diverging cutting ridges 542 and 543, respectively. In one embodiment, the central cutting ridge 541 is parallel to the cutting tooth base surface, and the two diverging cutting ridges 542, 543 extend down to the cutting tooth peripheral trailing edge 523. The angle of inclination is measured between the central plane and a plane parallel to the bottom surface of the cutting tooth. In fig. 8B, the central plane 532 has an inclination angle D. It is worth mentioning that in fig. 8A-8C the central cutting ridge 541 is parallel to the cutting tooth base surface, but it may be inclined downwards from the cutting edge to the central plane at an inclination angle smaller than the inclination angle D of the central plane.

The central ridge is used for cutting the stratum, and the length of the central ridge can be optimized according to the cutting depth of the stratum with high cutting heterogeneity and staggered hardness and softness. The embodiment of fig. 8A-8C may accommodate formation changes in a stepped back-rake manner. Referring to fig. 9, the formation 410 has a hard formation and a soft formation, and is highly heterogeneous. When the drill bit is cutting relatively hard intervals at the highly heterogeneous layer 410, a large back rake angle is preferred to maintain cutter edge strength against breakage or chipping due to high cutting forces acting on the cutter. However, when the drill bit cuts relatively soft intervals in highly heterogeneous formations, a smaller back rake angle is preferred to improve cutting efficiency. In particular, the cutting teeth 54 produce a hard formation strip 414 with a low cut depth 415 when cutting into a hard formation segment of the formation 410. At low cut depths, the cutting ridges 541 are in contact with the hard formation strip, and the back rake angle a is the angle between the cutting ridges 541 and a line 411 normal to the surface of the formation 410. When cutting a soft interval segment of the formation 410, the cutting teeth create a soft formation strip 418 at a high cut depth 419. At high cut depths, the back rake angle B is the angle between the central surface 532 and the line 411. Since the central plane 532 has an inclination angle D, the back rake angle B is smaller than the back rake angle A, allowing a higher rate of penetration. Therefore, when the cutting tooth of the invention is used for cutting heterogeneous strata, the same relief angle can be kept, and the back inclination angle can be automatically adjusted, thereby improving the cutting efficiency and prolonging the service life of the drill bit.

For the cutting teeth of fig. 7A-7C and 8A-8C, the cutting face is made up of three flat surfaces. Other surface shapes, such as curved surfaces, domed surfaces, convex or concave surfaces, are also contemplated by the present invention.

In some embodiments, the present invention also provides a PDC bit that includes at least one cutter disclosed herein in any position.

All of the compositions and methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and methods in terms of steps or in terms of the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain agents which are in a chemical relationship may be substituted for the agents of the present invention while the same or similar results would be achieved. It will be apparent to those skilled in the art that all such similar substitutes and modifications are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.