Method for drilling with a fixed bladed bit

Abstract

A downhole fixed bladed bit comprises a working surface comprising a plurality of blades converging at a center of the working surface and diverging towards a gauge of the bit, at least one blade comprising a cutting element comprising a superhard material bonded to a cemented metal carbide substrate at a non-planer interface, the cutting element being positioned at a positive rake angle, and the superhard material comprising a substantially conical geometry with an apex comprising a curvature.

Description

BACKGROUND OF THE INVENTION

This invention relates to drill bits, specifically drill bit assemblies for use in oil, gas and geothermal drilling. More particularly, the invention relates to cutting elements in fix bladed bits comprised of a carbide substrate with a non-planar interface and an abrasion resistant layer of super hard material affixed thereto using a high-pressure/high-temperature press apparatus.

Cutting elements typically comprise a cylindrical super hard material layer or layers formed under high temperature and pressure conditions, usually in a press apparatus designed to create such conditions, cemented to a carbide substrate containing a metal binder or catalyst, such as cobalt. A cutting element or insert is normally fabricated by placing a cemented carbide substrate into a container or cartridge with a layer of diamond crystals or grains loaded into the cartridge adjacent one face of the substrate. A number of such cartridges are typically loaded into a reaction cell and placed in the high-pressure/high-temperature (HPHT) press apparatus. The substrates and adjacent diamond crystal layers are then compressed under HPHT conditions which promotes a sintering of the diamond grains to form the polycrystalline diamond structure. As a result, the diamond grains become mutually bonded to form a diamond layer over the substrate interface. The diamond layer is also bonded to the substrate interface.

Such cutting elements are often subjected to intense forces, torques, vibration, high temperatures and temperature differentials during operation. As a result, stresses within the structure may begin to form. Drag bits for example may exhibit stresses aggravated by drilling anomalies, such as bit whirl or bounce, during well boring operations, often resulting in spalling, delamination or fracture of the super hard abrasive layer or the substrate, thereby reducing or eliminating the cutting elements' efficacy and decreasing overall drill bit wear-life. The super hard material layer of a cutting element sometimes delaminates from the carbide substrate after the sintering process as well as during percussive and abrasive use. Damage typically found in drag bits may be a result of shear failures, although non-shear modes of failure are not uncommon. The interface between the super hard material layer and substrate is particularly susceptible to non-shear failure modes due to inherent residual stresses.

U.S. Pat. No. 6,332,503 by Pessier et al., which is herein incorporated by reference for all that it contains, discloses an array of chisel-shaped cutting elements mounted to the face of a fixed cutter bit. Each cutting element has a crest and an axis which is inclined relative to the borehole bottom. The chisel-shaped cutting elements may be arranged on a selected portion of the bit, such as the center of the bit, or across the entire cutting surface. In addition, the crest on the cutting elements may be oriented generally parallel or perpendicular to the borehole bottom.

U.S. Pat. No. 6,408,959 by Bertagnolli et al., which is herein incorporated by reference for all that it contains, discloses a cutting element, insert or compact that is provided for use with drills used in the drilling and boring of subterranean formations.

U.S. Pat. No. 6,484,826 by Anderson et al., which is herein incorporated by reference for all that it contains, discloses enhanced inserts formed having a cylindrical grip and a protrusion extending from the grip.

U.S. Pat. No. 5,848,657 by Flood et al., which is herein incorporated by reference for all that it contains, discloses a domed polycrystalline diamond cutting element, wherein a hemispherical diamond layer is bonded to a tungsten carbide substrate, commonly referred to as a tungsten carbide stud. Broadly, the inventive cutting element includes a metal carbide stud having a proximal end adapted to be placed into a drill bit and a distal end portion. A layer of cutting polycrystalline abrasive material is disposed over said distal end portion such that an annulus of metal carbide adjacent and above said drill bit is not covered by said abrasive material layer.

U.S. Pat. No. 4,109,737 by Bovenkerk which is herein incorporated by reference for all that it contains, discloses a rotary bit for rock drilling comprising a plurality of cutting elements mounted by interference-fit in recesses in the crown of the drill bit. Each cutting element comprises an elongated pin with a thin layer of polycrystalline diamond bonded to the free end of the pin.

US Patent Application Publication No. 2001/0004946 by Jensen, now abandoned, is herein incorporated by reference for all that it discloses. Jensen teaches that a cutting element or insert has improved wear characteristics while maximizing the manufacturability and cost effectiveness of the insert. This insert employs a superabrasive diamond layer of increased depth and makes use of a diamond layer surface that is generally convex.

BRIEF SUMMARY OF THE INVENTION

In one aspect of the present invention, a downhole fixed bladed bit comprises a working surface comprising a plurality of blades converging at a center of the working surface and diverging towards a gauge of the bit, at least one blade comprising a cutting element comprising a superhard material bonded to a cemented metal carbide substrate at a non-planer interface, the cutting element being positioned at a positive rake angle, and the superhard material comprising a substantially conical geometry with an apex comprising a curvature.

In some embodiments, the positive rake angle may be between 15 and 20 degrees, and may be substantially 17 degrees. The cutting element may comprise the characteristic of inducing fractures ahead of itself in a formation when the drill bit is drilling through the formation. The cutting element may comprise the characteristic of inducing fractures peripherally ahead of itself in a formation when the drill bit is drilling through the formation.

The substantially conical geometry may comprise a side wall that tangentially joins the curvature, wherein the cutting element is positioned to indent at a positive rake angle, while a leading portion of the side wall is positioned at a negative rake angle.

The cutting element may be positioned on a flank of the at least one blade, and may be positioned on a gauge of the at least one blade. The included angle of the substantially conical geometry may be 75 to 90 degrees. The superhard material may comprise sintered polycrystalline diamond. The sintered polycrystalline diamond may comprise a volume with less than 5 percent catalyst metal concentration, while 95 percent of the interstices in the sintered polycrystalline diamond comprise a catalyst.

The non-planar interface may comprise an elevated flatted region that connects to a cylindrical portion of the substrate by a tapered section. The apex may join the substantially conical geometry at a transition that comprises a diameter less than one-third of a diameter of the carbide substrate. In some embodiments, the diameter of the transition may be less than one-quarter of the diameter of the substrate.

The curvature may be comprise a constant radius, and may be less than 0.120 inches. The curvature may be defined by a portion of an ellipse or by a portion of a parabola. The curvature may be defined by a portion of a hyperbola or a catenary, or by combinations of any conic section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an embodiment of a drilling operation.

FIG. 2 a is a perspective view of an embodiment of a drill bit.

FIG. 2 b is a cross-sectional view of the drill bit in FIG. 2a.

FIG. 2 c is an orthogonal view a cutting element profile of the drill bit in FIG. 2a.

FIG. 3 is a cross-sectional view of an embodiment of a cutting element.

FIG. 4 is a cross-sectional view of an embodiment of a cutting element impinging a formation.

FIG. 5 is a cross-sectional view of another embodiment of a cutting element impinging a formation.

FIG. 6 is a cross-sectional view of another embodiment of a cutting element impinging a formation.

FIG. 7 is a time vs. parameter chart of an embodiment of a drill bit.

FIG. 8 is a penetration vs. parameter chart of an embodiment of a drill bit.

FIG. 9 is a perspective view of a bottom of a borehole drilled by an embodiment of a drill bit.

FIG. 10 is a cross-sectional view of a cutting path of several embodiments of a cutting element.

FIG. 11 is a perspective view of another embodiment of a drill bit.

FIG. 12 is a perspective view of another embodiment of a drill bit.

FIG. 13 is an orthogonal view of a cutting element profile of another embodiment of a drill bit.

FIG. 14 is a cross-sectional view of another embodiment of a cutting element.

FIG. 15 is a cross-sectional view of another embodiment of a cutting element.

FIG. 16 is a cross-sectional view of another embodiment of a cutting element.

FIG. 17 is a cross-sectional view of another embodiment of a cutting element.

FIG. 18 is a cross-sectional view of another embodiment of a cutting element.

FIG. 19 is a cross-sectional view of another embodiment of a cutting element.

FIG. 20 is a cross-sectional view of another embodiment of a cutting element.

FIG. 21 is a cross-sectional view of another embodiment of a cutting element.

FIG. 22 is a cross-sectional view of another embodiment of a cutting element.

FIG. 23 is a cross-sectional view of another embodiment of a cutting element.

FIG. 24 is a cross-sectional view of another embodiment of a cutting element.

FIG. 25 is a cross-sectional view of another embodiment of a cutting element.

FIG. 26 is a diagram of an embodiment of a method of drilling a well bore.

FIG. 27 is a diagram of another embodiment of a method of drilling a well bore.

DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENT

Referring now to the figures, FIG. 1 is a cross-sectional diagram of an embodiment of a drill string 100 suspended by a derrick 101. A bottom-hole assembly 102 is located at the bottom of a bore hole 103 and comprises a fixed bladed drill bit 104a. As the drill bit 104a rotates down hole the drill string 100 advances farther into the earth. The drill string 100 may penetrate soft or hard subterranean formations 105.

FIG. 2 a discloses an embodiment of a drill bit 104b. Drill bit 104b comprises a working surface 201a comprising a plurality of radial blades 202a. Blades 202a converge towards a center 203a of the working surface 201a and diverge towards a gauge portion 204a. Blades 202a may comprise one or more cutting elements 200a that comprise a superhard material bonded to a cemented metal carbide substrate at a non-planer interface. Cutting elements 200a may comprise substantially pointed geometry, and may comprise a superhard material such as polycrystalline diamond processed in a high-temperature/high-pressure press. The gauge portion 204a may comprise wear-resistant inserts 205 that may comprise a superhard material. Drill Bit 104b may comprise a shank portion 206 that may be attached to a portion of a drill string or a bottom-hole assembly (BHA). In some embodiments, one or more cutting elements 200a may be positioned on a flank portion or a gauge portion 204a of the drill bit 104b.

In some embodiments, the drill bit 104b may comprise an indenting member 207 comprising a cutting element 208. Cutting element 208 may comprise the same geometry and material as cutting elements 200a, or may comprise a different geometry, dimensions, materials, or combinations thereof. The indenting member 207 may be rigidly fixed to the drill bit 104 through a press fit, braze, threaded connection, or other method. The indenting member 207 may comprise an asymmetrical geometry. In some embodiments, the indenting member 207 is substantially coaxial with an axis of rotation of the drill bit 104b. In other embodiments, the indenting member 207 may be off-center.

FIG. 2 b discloses a cross section of the embodiment of the drill bit 104b. The indenting member 207 is retained in the body of the drill bit 104b. A nozzle 209 carries drilling fluid to the working surface 201a to cool and lubricate the working surface 201a and carry the drilling chips and debris to the surface.

FIG. 2 c shows a blade profile 210 with cutter profiles 211 from a plurality of blades 202a superimposed on the blade profile 210. Cutter profiles 211 substantially define a cutting path when the drill bit 104b is in use. Cutter profiles 211 substantially cover the blade profile 210 between a central portion 212 of the blade profile 210 and a gauge portion 213 of the blade profile 210.

FIG. 3 discloses an embodiment of a cutting element 200b. In this embodiment, the cutting element 200b comprises a superhard material portion 301 comprising sintered polycrystalline diamond bonded to a cemented metal carbide substrate 302 at a non-planar interface 303. The cutting element 200b comprises substantially pointed geometry 304a and an apex 305a.

The apex 305a may comprise a curvature 306. In this embodiment, curvature 306 comprises a radius of curvature 307. In this embodiment, the radius of curvature 307 may be less than 0.120 inches.

In some embodiments, the curvature may comprise a variable radius of curvature, a portion of a parabola, a portion of a hyperbola, a portion of a catenary, or a parametric spline.

The curvature 306 of the apex 305a may join the pointed geometry 304a at a substantially tangential transition 308. The transition 308 forms a diameter 309 that may be substantially smaller than a diameter 310, or twice the radius of curvature 307. The diameter 309 may be less than one-third of a diameter 318 of the carbide substrate 302. In some embodiments, the diameter 309 may be less than one-fourth of the diameter 318 of the carbide substrate 302.

An included angle 311 is formed by walls 320a and 320b of the pointed geometry 304a. In some embodiments, the included angle 311 may be between 75 degrees and 90 degrees. Non-planar interface 303 comprises an elevated flatted region 313 that connects to a cylindrical portion 314 of the substrate 302 by a tapered section 315. The elevated flatted region 313 may comprise a diameter 322 larger than the diameter 309.

A volume of the superhard material portion 301 may be greater than a volume of the cemented metal carbide substrate 302.

A thickness 324 of the superhard material portion 301 along a central axis 316 may be greater than a thickness 326 of the cemented metal carbide substrate 302 along the central axis 316. The thickness 326 of the cemented metal carbide substrate 302 may be less than 10 mm along the central axis 316.

In some embodiments, the sintered polycrystalline diamond comprises a volume with less than 5 percent catalyst metal concentration, while 95 percent of the interstices in the sintered polycrystalline diamond comprise a catalyst.

The cemented metal carbide substrate 302 may be brazed to a support or bolster 312. The bolster 312 may comprise cemented metal carbide, a steel matrix material, or other material and may be press fit or brazed to a drill bit body.

FIG. 4 discloses a cutting element 200c interacting with a formation 400a. Surprisingly, the pointed cutting element 200c has a different cutting mechanism than that of traditional shear cutters (generally cylindrical shaped cutting elements), resulting in the pointed cutting element 200c having a prolonged life. The short cutting life of the traditional shear cutter is a long-standing problem in the art, which the curvature of the present cutting element 200c overcomes.

Cutting element 200c comprises a pointed geometry 304b and an apex 305b. The apex 305b comprises a curvature that is sharp enough to easily penetrate the formation 400a, but is still blunt enough to fail the formation 400a in compression ahead of the cutting element 200c.

As the cutting element 200c advances in the formation 400a, apex 305b fails the formation 400a ahead of the cutting element 200c and peripherally to the sides of the cutting element 200c, creating fractures 401.

Fractures 401 may continue to propagate as the cutting element 200c advances into the formation 400a, eventually reaching the surface 402 of the formation 400a and allowing large chips 403 to break from the formation 400a.

Traditional shear cutters drag against the formation and shear off thin layers of formation. The large chips 403 comprise a greater volume size than the debris removed by the traditional shear cutters. Thus, the specific energy required to remove formation 400a with the pointed cutting element 200c is lower than that required with the traditional shear cutters. The cutting mechanism of the pointed cutting element 200c is more efficient since less energy is required to remove a given volume of rock.

In addition to the different cutting mechanism, the curvature of the apex 305b produces unexpected results. Applicants tested the abrasion of the pointed cutting element 200c against several commercially available shear cutters with diamond material of better predicted abrasion resistant qualities than the diamond material of the pointed cutting element 200c. Surprisingly, the pointed cutting element 200c outperformed the shear cutters. Applicant found that a radius of curvature between 0.050 to 0.120 inches produced the best wear results.

The majority of the time the cutting element 200c engages the formation 400a, the cutting element 200c is believed to be insulated, if not isolated, from virgin formation. Fractures 401 in the formation 400a weaken the formation 400a below the compressive strength of the virgin formation 400a. The fragments of the formation 400a are surprisingly pushed ahead by the curvature of the apex 305b, which induces fractures 401 further ahead of the cutting element 200c. In this repeated manner, the apex 305b may hardly, if at all, engage virgin formation 400a and thereby reduce the exposure of the apex 305b to the most abrasive portions of the formation 400a.

FIG. 5 discloses a cutting element 200d comprising a positive rake angle 500. Rake angle 500 is formed between an imaginary vertical line 501 and a central axis 502 of the cutting element 200d. In this embodiment, positive rake angle 500 is less than one-half of an included angle (e.g., included angle 311 in FIG. 3) formed between conical side walls (e.g., side walls 320a and 320b in FIG. 3) of the cutting element 200d, causing a leading portion 503 of a side wall 520 to form a negative rake angle with respect to the vertical line 501. The positive rake angle 500 may be 15-20 degrees, and in some embodiments may be substantially 17 degrees.

As the cutting element 200d advances in a formation 400b, it induces fractures ahead of the cutting element 200d and peripherally ahead of the cutting element 200d. Fractures may propagate to the surface 504 of the formation 400b allowing a chip 505 to break free.

FIG. 6 discloses another embodiment of a cutting element 200e engaging a formation 400c. In this embodiment, a positive rake angle 600 between a vertical line 601 and a central axis 602 of the cutting element 200e is greater than one-half of the included angle (e.g., included angle 311 in FIG. 3) formed between conical side walls (e.g., side walls 320a and 320b in FIG. 3) of the cutting element 200e, causing a leading portion 603 of a side wall 620 to form a positive rake angle with the imaginary vertical line 601. This orientation of the cutting element 200e may encourage propagation of fractures 604, lessening the reaction forces and abrasive wear on the cutting element 200e.

FIG. 7 is a chart 700 showing relationships between weight-on-bit (WOB) 701, mechanical specific energy (MSE) 702, rate of penetration (ROP) 703, and revolutions per minute (RPM) 704 of a drill bit from actual test data generated at TerraTek, located in Salt Lake City, Utah. As shown in the chart 700, ROP 703 increases with increasing WOB 701. MSE 702 represents the efficiency of the drilling operation in terms of an energy input to the operation and energy needed to degrade a formation. Increasing WOB 701 can increase MSE 702 to a point of diminishing returns shown at approximately 16 minutes on the abscissa. These results show that the specific mechanical energy for removing the formation is better than a traditional test.

FIG. 8 is a chart 800 showing the drilling data of a drill bit with an indenting member also tested at TerraTek. As shown in the chart, WOB 801 and torque 802 oscillate. Torque 802 applied to the drill string undergoes corresponding oscillations opposite in phase to the WOB 801.

It is believed that these oscillations are a result of the WOB 801 reaction force at the drill bit working face alternating between the indenting member (e.g., indenting member 207 in FIG. 2a) and the blades (e.g., blades 202s in FIG. 2a). When the WOB 801 is substantially supported by the indenting member, the torque 802 required to tum the drill bit is lower. When the WOB 801 at the indenting member gets large enough, the indenting member fails the formation ahead of it, transferring the WOB 801 to the blades. When the drill bit blades come into greater engagement with the formation and support the WOB 801, the torque 802 increases. As the blades remove additional formation, the WOB 801 is loaded to the indenting member and the torque 802 decreases until the formation ahead of the indenting member again fails in compression. The compressive failure at the center of the working face by the indenting member shifts the WOB 801 so as to hammer the blades into the formation thereby reducing the work for the blades. The geometry of the indenting member and working face may be chosen advantageously to encourage such oscillations.

In some embodiments, such oscillations may be induced by moving the indenting member along an axis of rotation of the drill bit. Movements may be induced by a hydraulic, electrical, or mechanical actuator. In one embodiment, drilling fluid flow is used to actuate the indenting member.

FIG. 9 shows a bottom of a borehole 900 of a sample formation drilled by a drill bit comprising an indenting member and radial blades comprising substantially pointed cutting elements. A central area 901 comprises fractures 902 created by the indenting member. Craters 903 form where blade elements on the blades strike the formation upon failure of the rock under the indenting member. The cracks ahead of the cutting elements propagate and create large chips that are removed by the pointed cutting elements and the flow of drilling fluid.

FIG. 10 is an orthogonal view of a cutting path 1000. A cutting element 200f comprises a central axis 1001a and rotates about a center of rotation 1002. Central axis 1001a may form a side rake angle 1003a with respect to a tangent line to the cutting path 1000 of substantially zero. In some embodiments, a cutting element 200g comprises a central axis 1001b that forms a side rake angle 1003b that is positive. In other embodiments a side rake angle may be substantially zero, positive, or negative.

FIG. 11 discloses another embodiment of a drill bit 104c. This embodiment comprises a plurality of substantially pointed cutting elements 200h affixed by brazing, press fit or another method to a plurality of radial blades 202b. Blades 202b converge toward a center 203b of a working surface 201b and diverge towards a gauge portion 204b. Cylindrical cutting elements 1101 are affixed to the blades 202b intermediate the working surface 201b and the gauge portion 204b.

FIG. 12 discloses another embodiment of a drill bit 104c. In this embodiment, cylindrical cutters 1201 are affixed to radial blades 202c intermediate a working surface 201c and a gauge portion 204c. Drill bit 104c also comprises an indenting member 1202.

FIG. 13 discloses another embodiment of a blade profile 1300. Blade profile 1300 comprises the superimposed profiles 1301 of cutting elements from a plurality of blades. In this embodiment, an indenting member 1302 is disposed at a central axis of rotation 1303 of the drill bit. Indenting member 1302 comprises a cutting element 1304 capable of bearing the weight-on-bit. An apex 1305 of the indenter cutting element 1304 protrudes a protruding distance 1309 beyond an apex 1306 of a most central cutting element 1307. Distance 1309 may be advantageously chosen to encourage oscillations in torque and WOB. Distance 1309 may be variable by moving the indenting member 1302 axially along rotational axis 1303, or the indenting member 1302 may be rigidly fixed to the drill bit. The distance 1309 in some embodiments may not extend to the apex 1306 of the most central cutting element 1307. Cylindrical shear cutters 1308 may be disposed on a gauge portion of the blade profile 1300.

FIG. 14 discloses an embodiment of a substantially pointed cutting element 1400. Cutting element 1400 comprises a superhard material portion 1403 with a substantially concave pointed portion 1401 and an apex 1402. Superhard material portion 1403 is bonded to a cemented metal carbide portion 1404 at a non-planer interface 1405.

FIG. 15 discloses another embodiment of a substantially pointed cutting element 1500. A superhard material portion 1501 comprises a linear tapered pointed portion 1502 and an apex 1503.

FIG. 16 discloses another embodiment of a substantially pointed cutting element 1600. Cutting element 1600 comprises a linear tapered pointed portion 1601 and an apex 1602. A non-planer interface 1605 between a superhard material portion 1604 and a cemented metal carbide portion 1606 comprises notches 1603.

FIG. 17 discloses another embodiment of a substantially pointed cutting element 1700. Cutting element 1700 comprises a substantially concave pointed portion 1701 and an apex 1702.

FIG. 18 discloses another embodiment of substantially pointed cutting element 1800. Cutting element 1800 comprises a substantially convex pointed portion 1801.

FIG. 19 discloses another embodiment of a substantially pointed cutting element 1900. A superhard material portion 1901 comprises a height 1902 greater than a height 1903 of a cemented metal carbide portion 1904.

FIG. 20 discloses another embodiment of a substantially pointed cutting element 2000. In this embodiment, a non-planer interface 2001 intermediate a superhard material portion 2002 and a cemented metal carbide portion 2003 comprises a spline curve profile 2004.

FIG. 21 comprises another embodiment of a substantially pointed cutting element 2100 comprising a pointed portion 2101 with a plurality of linear tapered portions 2102.

FIG. 22 discloses another embodiment of a substantially pointed cutting element 2200. In this embodiment, an apex 2201 comprises substantially elliptical geometry 2202. The ellipse may comprise major and minor axes that may be aligned with a central axis 2203 of the cutting element 2200. In this embodiment, the major axis 2204 is aligned with the central axis 2203.

FIG. 23 discloses another embodiment of a substantially pointed cutting element 2300. In this embodiment, an apex 2301 comprises substantially hyperbolic geometry.

FIG. 24 discloses another embodiment of a substantially pointed cutting element 2400. An apex 2401 comprises substantially parabolic geometry.

FIG. 25 discloses another embodiment of a substantially pointed cutting element 2500. An apex 2501 comprises a curve defined by a catenary. A catenary curve is believed to be the strongest curve in direct compression, and may improve the ability of the cutting element to withstand compressive forces.

FIG. 26 is a method 2600 of drilling a wellbore, comprising the steps of providing 2601a fixed bladed drill bit at the end of a tool string in a wellbore, the drill bit comprising at least one indenter protruding from a face of the drill bit and at least one cutting element with a pointed geometry affixed to the working face, rotating 2602 the drill bit against a formation exposed by the wellbore under a weight from the tool string, and alternately 2603 shifting the weight from the indenter to the pointed geometry of the cutting element while drilling.

FIG. 27 is a method 2700 for drilling a wellbore, comprising the steps of providing 2701 a drill bit in a wellbore at an end of a tool string, the drill bit comprising a working face with at least one cutting element attached to a blade fixed to the working face, the cutting element comprising a substantially pointed polycrystalline diamond body with a rounded apex comprising a curvature, and applying 2702 a weight to the drill bit while drilling sufficiently to cause a geometry of the cutting element to crush a virgin formation ahead of the apex into enough fragments to insulate the apex from the virgin formation.

The step of applying weight 2702 to the drill bit may include applying a weight that is over 20,000 pounds. The step of applying weight 2702 may include applying a torque to the drill bit. The step of applying weight 2702 may force the substantially pointed polycrystalline diamond body to indent the formation by at least 0.050 inches.

Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.

Claims

1. A method for drilling a well bore, comprising the steps of: positioning a drill bit at an end of a tool string in the well bore, the drill bit comprising: a shank;a bit body attached to the shank, the bit body having a working surface that comprises at least one blade for engaging a formation, the at least one blade extending away from the working surface;at least one cutting element attached to the at least one blade, the cutting element comprising: a superhard material that comprises: a central axis;a first side wall;a second side wall;an apex at which the first side wall and the second side wall intersect to form an included angle;the first side wall, the second side wall, and the apex forming a substantially pointed geometry that in cross-section comprises a diameter between a transition where a curvature of the apex tangentially meets the first side wall and the second side wall, the curvature being bounded within the first side wall and the second side wall;a cemented metal carbide substrate bonded to the superhard material at a non-planar interface;applying at least one of a weight and a torque to the drill bit while drilling; andusing the curvature of the apex of the at least one cutting element to penetrate and fail the formation in compression ahead of the at least one cutting element while drilling.

2. The method of claim 1, wherein the weight is over 20,000 pounds and the torque is 2,500 foot-pounds to 15,000 foot-pounds.

3. The method of claim 1, wherein the cutting element is positioned at a positive rake angle.

4. The method of claim 3, wherein the positive rake angle is between 15 degrees and 20 degrees.

5. The method of claim 4, wherein a leading portion of one of the first side wall and the second side wall is positioned at a negative rake angle.

6. The method of claim 5, wherein the positive rake angle is less than one-half the included angle.

7. The method of claim 1, wherein the included angle is between 75 degrees and 90 degrees.

8. The method of claim 1, wherein the superhard material is sintered polycrystalline diamond.

9. The method of claim 8, wherein the sintered polycrystalline diamond comprises a volume with less than 5 percent catalyst metal concentration and 95 percent of a plurality of interstices in the sintered polycrystalline diamond comprise a catalyst.

10. The method of claim 1, wherein the non-planar interface comprises an elevated flatted region that connects to a cylindrical portion of the cemented metal carbide substrate by a tapered section.

11. The method of claim 1, wherein the diameter is less than one-third of a diameter of the cemented metal carbide substrate.

12. The method of claim 1, wherein the diameter is less than one-quarter of the diameter of the cemented metal carbide substrate.

13. The method of claim 1, wherein the curvature is a radius of curvature.

14. The method of claim 13, wherein the radius of curvature is less than 0.120 inches.

15. The method of claim 14, wherein the radius of curvature is between 0.050 inches and 0.120 inches.

16. The method of claim 1, wherein the curvature is defined by a portion of at least one of an ellipse, a parabola, a hyperbola, a catenary, and a parametric spline.

17. The method of claim 1, wherein the non-planar interface comprises at least one of notches and a spline curve profile.

18. The method of claim 1, wherein at least one of the first side wall and the second side wall comprise at least one of a linear tapered portion, a concave portion, and a convex portion.

19. The method of claim 1, wherein the superhard material comprises a height greater than a height of the cemented metal carbide substrate.

20. The method of claim 1, further comprising an indenting member that extends a distance from the working surface.