EP2430279A2

EP2430279A2 - Cutting element for use in a drill bit for drilling subterranean formations

Info

Publication number: EP2430279A2
Application number: EP10775271A
Authority: EP
Inventors: Jorge Dovalina
Original assignee: Baker Hughes Inc
Current assignee: Baker Hughes Holdings LLC
Priority date: 2009-05-13
Filing date: 2010-05-04
Publication date: 2012-03-21
Also published as: WO2010132235A2; WO2010132235A3; US20100288564A1

Abstract

A cutting element for use in a drill bit for drilling subterranean formations including a substrate having a body including an upper surface extending transversely to a longitudinal axis of the body, a superabrasive layer overlying the upper surface of the substrate, wherein the superabrasive layer includes an annular shape having a central opening defined by an inner surface. The cutting element further includes an abrasive insert overlying the upper surface of the substrate and disposed within the central opening of the superabrasive layer, wherein the abrasive insert has an upper surface having a surface roughness (Ra) of greater than about 1 micron.

Description

CUTTING ELEMENT FOR USE IN A DRILL BIT FOR DRILLING SUBTERRANEAN FORMATIONS

TECHNICAL FIELD

The following is directed to cutting elements for use in drill bits for drilling subterranean formations and more particularly, cutting elements utilizing a cutting table comprising a superabrasive layer and an abrasive insert.

BACKGROUND ART

In the past, rotary drill bits have incorporated cutting elements employing superabrasive materials, including synthetic diamond cutters using polycrystalline diamond compacts, otherwise termed "PDC" cutters. Such PDC cutters have had various shapes and designs, including self-supported cutters, otherwise a monolithic object solely of the made of the desired cutting material, or alternatively, cutters employing a polycrystalline diamond layer or "table" on a substrate made of a hard metal material suitable for supporting the diamond layer.

Despite improvements in PDC cutter designs, certain obstacles remain, including for example, performance degradation and failure of cutters due to mechanical strain, thermal-induced strain, and a combination of such forces. Delamination and fracture of a cutter can occur given the extreme loading and temperatures generated during drilling operations. Furthermore, repetitive heating and cooling of the cutter can amplify damage to the cutter due to differences in thermal expansion coefficient and thermal conductivity of the cutter components. Wear characteristics of cutters have also been studied to mitigate catastrophic damage to the cutter surfaces.

Various different configurations of cutters have been used to overcome some of the above noted obstacles, however, significant shortcomings are still exhibited by conventional cutters, and there remains a need in the art for improvements.

- I - SUMMARY

According to one aspect, a cutting element for use in a drill bit for drilling subterranean formations includes a substrate having a body having an upper surface extending transversely to a longitudinal axis of the body, a superabrasive layer overlying the upper surface of the substrate, wherein the superabrasive layer comprises an annular shape having a central opening defined by an inner surface, and an abrasive insert overlying the upper surface of the substrate. The abrasive insert can be disposed within the central opening of the superabrasive layer, wherein the abrasive insert comprises an upper surface having a surface roughness (R₃) of greater than about 1 micron.

In another aspect, a cutting element for use in a drill bit for drilling subterranean formations includes a cutting table made of a superabrasive layer comprising an annular shape having a central opening defined by an inner surface, and an abrasive insert overlying the upper surface of the substrate and disposed within the central opening of the superabrasive layer. The abrasive insert includes abrasive grit contained within a matrix material, wherein an upper region of the abrasive insert comprising an upper surface has a different amount of abrasive grit than a lower region of the abrasive insert.

In accordance with still another aspect, a cutting element for use in a drill bit for drilling subterranean formations includes a cutting table made of a superabrasive layer having an annular shape having a central opening defined by an inner surface, and an abrasive insert disposed within the central opening of the superabrasive layer, wherein the abrasive insert comprises an upper surface having a texture comprising protrusions and recesses.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

FIG. 1 includes an illustration of a subterranean drilling operation.

¹^" _*.• "* FIG. 2 includes an illustration of a drill bit in accordance with an embodiment.

FIGs. 3A-3C include cross-sectional illustrations and a perspective view of cutter elements in accordance with embodiments.

FIG. 4 includes a cross-sectional illustration of a portion of a cutter element in accordance with an embodiment.

FIG. 5 includes a cross-sectional illustration of a portion of a cutter element in accordance with an embodiment.

FIG. 6 includes a cross-sectional illustration of a portion of a cutter element in accordance with an embodiment.

FIGs. 7A-7C include top view illustrations of cutter elements in accordance with embodiments.

The use of the same reference symbols in different drawings indicates similar or identical items.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The following is directed to earth boring drill bits, and more particularly, towards cutting elements used in such drill bits. The terms "bit", "drill bit", and "matrix drill bit" may be used in this application to refer to "rotary drag bits", "drag bits", "fixed cutter drill bits" or any other earth boring drill bit incorporating the teachings of the present disclosure. Such drill bits may be used to form well bores or boreholes in subterranean formations.

An example of a drilling system for drilling such well bores in earth formations is illustrated in FIG. 1. In particular, FIG. 1 illustrates a drilling system including a drilling rig 101 at the surface, serving as a station for a crew of workers to operate a drill string 103. The drill string 103 defines a well bore 105 extending into the earth and can include a series of drill pipes 100 and 103 that are coupled together via joints 104 facilitating extension of the drill string 103 for great depths into the well bore 105. The drill string 103 may include additional components, such as tool joints, a kelly, kelly cocks, a kelly saver sub, blowout preventers, safety valves, and other components known in the art.

Moreover, the drill string can be coupled to a bottom hole assembly 107 (BHA) including a drill bit 109 used to penetrate earth formations and extend the depth of the well bore 105. The BHA 107 may further include one or more drill collars, stabilizers, a downhole motor, MWD tools, LWD tools, jars, accelerators, push and pull directional drilling tools, point stab tools, shock absorbers, bent subs, pup joints, reamers, valves, and other components. A fluid reservoir 111 is also present at the surface that holds an amount of liquid that can be delivered to the drill string 103, and particularly the drill bit 109, via pipes 113, to facilitate the drilling procedure.

FIG. 2 includes a perspective view of a fixed cutter drill bit according to an embodiment. As shown in FIG. 2, the fixed cutter drill bit 200 can include a bit body

213 which may be connected to a shank portion 214 via a weld. The shank portion

214 can include a threaded portion 215 for connection of the drill bit 200 to other components of the BHA. The drill bit body 213 can further include a breaker slot 221 extending laterally along the circumference of the drill bit body 213 to aid coupling and decoupling of the drill bit 200 to other components.

The drill bit 200 can include a crown portion 222 coupled to the drill bit body 213. As will be appreciated, the crown portion 222 can be integrally formed with the drill bit body 213 such that they are a single, monolithic piece. The crown portion 222 can include gage pads 224 situated along the sides of protrusions or blades 217 that extend radially from the crown portion 222. Each of the blades 217 extend from the crown portion 222 and include a plurality of cutting members 219 bonded to the blades 217 for cutting, scraping, and shearing through earth formations when the drill bit 200 is rotated during drilling. The cutting members 219 may be tungsten carbide inserts, polycrystalline diamond compacts (PDC), milled steel teeth, and particularly those cutting elements described herein. Coatings or hard facings may be applied to the cutting members 219 and other portions of the bit body 213 or crown portion 222 to reduce wear and increase the life of the drill bit 200.

The crown portion 222 can further include junk slots 227 or channels formed between the blades 217 that facilitate fluid flow and removal of cuttings and debris from the well bore. Notably, the junk slots 227 can further include openings 223 for passages extending through the interior of the crown portion 222 and bit body 213 for communication of drilling fluid through the drill bit 200. The openings 223 can be positioned at exterior surfaces of the crown portion 222 at various angles for dynamic fluid flow conditions and effective removal of debris from the cutting region during drilling.

FIGs. 3A-3C include cross-sectional illustrations and a perspective view illustration of cutting elements in accordance with an embodiment. Referring to FIG. 3 A, a cross-sectional illustration of a cutting element is provided. The cutting element 300 includes a substrate 301 which can have a shape suitable for maintaining a cutting table 306 thereon. The substrate 301 can have various shapes, for example, a cylindrical shape having a height as defined by a longitudinal axis 310 extending through the body of the substrate 301. Substrates herein can have an upper surface 305 that extends transversely to the longitudinal axis 310, and a rear surface opposite and parallel to the upper surface 305. It will be appreciated that other geometries may be suitable for the substrate 301.

The substrate 301 can have a hardness suitable for withstanding drilling operations. That is, certain substrates 301 can be made of a material having a Mohs hardness of at least about 8, or at least about 8.5, at least about 9.0, or even at least about 9.5. Particular metals or metal alloy materials may be used to form the substrate 301. For example, the substrate 301 can be formed of carbides, nitrides, oxides, borides, carbon-based materials, and a combination thereof. Reference herein to carbon-based materials is reference to synthetically-produced molecules made entirely of carbon and the various carbon allotropes, such as carbon nanotubes and the like. In some instances, the substrate 301 may be made of a cemented material such as a cemented carbide. Some suitable cemented carbides may include metal carbides, and more particularly cemented tungsten carbide such that the substrate 301 consists essentially of cemented tungsten carbide.

As illustrated, the cutting element 300 can be formed such that a cutting table 306 overlies the upper surface 305 of the substrate 301. The cutting table 306 can be formed of two components, notably including a superabrasive layer 302 having an annular shape and comprising a central opening 329 as defined by an inner surface 315 of the superabrasive layer 302. Furthermore, the cutting table 306 includes an abrasive insert 303 overlying the upper surface 305 of the substrate 301 and disposed within the central opening 329 of the superabrasive layer 302 as defined by the inner surface 315.

Referring briefly to FIG. 3B, a perspective view illustration provides an alternative view demonstrating the orientation between the superabrasive layer 302 and the abrasive insert 303. The superabrasive layer 302 is formed such that it has an annular shape, including a central opening 329 extending radially and axially around a central point at the center of the cutting table 306. As further illustrated in FIG. 3B, the cutting table 306 is formed such that the abrasive insert 303 is configured to fit within the central opening 329 of the superabrasive layer 302.

Referring again to FIG. 3A, the superabrasive layer 302 can be formed such that the central opening 329, and therein the abrasive insert 303, extend through the entire height 333 of the cutting table 306. However, in other embodiments, the central opening may extend for a fraction of the height 333, and therein the abrasive insert 303 extends for only a fraction of the height 333 of the abrasive table 306. In such designs, the superabrasive layer 302 would be formed with a central recess (as opposed to a central opening 329) that would contain the abrasive insert 303.

Moreover, the cutting table 306 can be formed such that the superabrasive layer 302 comprises a bottom surface 312 that can directly contact the upper surface 305 of the substrate 301, and more particularly can be bonded to the upper surface 305 of the substrate 301. The abrasive insert 303 of the cutting table 306 can be formed such that it comprises a rear surface 313 that is directly contacting the upper surface 305 of the substrate 301, and more particularly is bonded to the upper surface 305 of the substrate 301. Additionally, the cutting table 306 can be formed such that the superabrasive layer 302 is bonded to the abrasive insert 303 at the inner surface 315 defining the interface between the components.

The superabrasive layer 302 can include superabrasive materials such as diamond, boron nitride (e.g., cubic boron nitride), carbon-based materials, and a combination thereof. Some superabrasive layers may be in the form of polycrystalline materials. For instance, the superabrasive layer 302 can consist essentially of polycrystalline diamond. With reference to those embodiments using polycrystalline diamond, the superabrasive layer 302 can be made of various types of diamond including thermally-stable polycrystalline diamond, which can contain a lesser amount of catalyst materials (e.g., cobalt) than other diamond materials, making the material stable at higher temperatures.

The cutting table 306 can be formed such that the superabrasive layer 302 comprises a side surface 309 that extends parallel to the longitudinal axis 310, an upper surface 307 that extends transversely to the longitudinal axis 310, and a chamfered surface 308 extending between the side surface 309 and upper surface 307 at an angle to the longitudinal axis 310. The length and angle of the chamfered surface 308 may be controlled depending on the intended application of the cutting element 300. It will further be appreciated that embodiments herein may utilize cutting elements having a radiused edge, wherein the edge between the upper surface and the side surface of the cutting element comprises a curved or arcuate surface defined by a radius.

The abrasive insert 303 can be formed such that it includes abrasive grit 331 contained within a matrix material 332, which may facilitate improved wear characteristics, mechanical integrity, and cutting ability of the cutting table 306. As used herein, reference to a matrix material is reference to a solid material for containing abrasive grit therein, such as a polycrystalline material, formed from a metal or cermet material as will be described in more detail. For some cutter designs, the abrasive insert 303 can be formed such that the abrasive grit 331 is dispersed uniformly throughout the entire volume of matrix material 332. In accordance with one embodiment, the abrasive insert 303 is formed such that it includes at least 10 vol% abrasive grit 331 contained within the matrix material 332 for the entire volume of the abrasive insert 303. In other designs, the amount of abrasive grit can be greater, such as on the order of at least 15 vol%, at least 25 vol%, at least 40 vol%, or even at least about 50 vol% of abrasive grit 331 contained within the matrix material 332 for the entire volume of the abrasive insert 303. In particular instances, the cutting table 306 is designed such that the abrasive insert 303 contains an amount of abrasive grit within a range between about 10 vol% and 70 vol%, such as between about 15 vol% and 60 vol%, and more particularly between about 20 vol% and 50 vol%. The abrasive grit 331 can be contained within a matrix material 332 that comprises a metal or metal alloy material. For example, the matrix material 332 can be made of a carbide material, such as a metal carbide. One suitable metal carbide material is tungsten carbide, and in fact, some cutter designs utilize a matrix material 332 that consists essentially of tungsten carbide. Some other suitable metals or metal alloys may include transition metal elements.

Additionally, the abrasive grit 331 can be formed of abrasive material having suitable abrading and cutting capabilities. For example, suitable abrasive materials can include oxides, borides, nitrides, carbides, carbon-containing materials, and a combination thereof. Reference herein to carbon-based materials is reference to synthetically produced molecules made entirely of carbon and various carbon allotropes, such as carbon nanotubes and the like. Certain abrasive materials for use as the abrasive grit can include alumina, silica, silicon carbide, combinations thereof and the like. In certain instances, the abrasive grit 331 is formed of a superabrasive material, such as diamond, cubic boron nitride, and a combination thereof. Particular cutting elements are formed such that the abrasive insert 303 uses only abrasive grit 331 consisting of diamond.

With particular reference to embodiments employing diamond abrasive grit, the grit material can have particular multi-faceted shapes providing a plurality of sharp edges suitable for cutting and abrading hard formations. For example, the diamond abrasive grit can be cubo-octahedral, cubic faced, and the like.

Additionally, the abrasive grit 331 can employ encapsulated grit, such that each of the particles of abrasive grit 331 are substantially surrounded by an encapsulating material. The encapsulating material may improve the mechanical properties of the abrasive grit (e.g., wear resistance), provide added protection for the abrasive grit during processing, particularly with regard to thermal cycling used in various manufacturing processes, and further improve the bonding characteristics between the abrasive grit and the matrix material 332. Additionally, provision of encapsulated grit can facilitate proper spacing and distribution of the abrasive grit 331 within the matrix material 332. Suitable compositions for use as the encapsulant material can include ceramics, such as oxides, carbides, borides, nitrides, and carbon-based materials. Other encapsulant materials can include refractory metal or refractory metal alloy compositions.

Certain sizes of abrasive grit 331 can be used to aid proper functioning of the abrasive insert 303. For example, the abrasive grit 331 can have an average grit size of at least about 25 microns, such as at least about 50 microns, at least about 100 microns, or even at least about 200 microns. In certain instances, the abrasive grit has an average grit size within a range between about 25 microns and about 2 millimeters and more particularly between about 100 microns and about 1 millimeters, and even more particularly between about 100 microns and about 0.5 millimeter.

FIG. 3C includes a cross-sectional illustration of a cutting element in accordance with an embodiment. The cutting element 350 includes a cutting table 306 overlying the upper surface 305 of the substrate 301 as previously described in accordance with FIG. 3 A. Notably, the cutting table 306 of FIG. 3C demonstrates an abrasive insert 303 having a different shape than the abrasive insert of embodiment in FIG. 3A. The abrasive insert 303 and particularly, the superabrasive layer 302 is formed such that the interface between the abrasive insert 303 and superabrasive layer 303 comprises a tapered surface 325. The tapered surface 325 extends at an angle to the longitudinal axis 310 such that the diameter of the central opening 329 at the upper surface 307 of the superabrasive layer 302 is smaller than the diameter of the central opening 329 at the bottom surface 312.

FIG. 4 includes a cross-sectional illustration of a portion of a cutting element in accordance with an embodiment. The cutting element 400 includes a cutting table 406 comprising the superabrasive layer 302 and abrasive insert 303 disposed within a central opening of the superabrasive layer 302. As illustrated, the abrasive insert 303 is formed such that it has an upper surface 317 having particular features. That is, in accordance with one embodiment, the abrasive insert 303 can be formed such that the upper surface 317 has a particular surface roughness, which may be suitable for conducting certain types of cutting operations and improving the wear characteristics of the cutting table 406. In accordance with one embodiment, the abrasive insert 303 can have a surface roughness (R_a) of greater than about 1 micron. It will be noted that the reference to surface roughness is an arithmetic average of the roughness profile as measured through physical (e.g., a stylus) or optical measuring techniques. In other embodiments, the abrasive insert 303 is formed such that the upper surface 317 has a greater surface roughness, such as on the order of greater than about 3 microns, greater than about 5 microns, greater than about 10 microns, or even greater than about 15 microns. In particular instances, the abrasive insert 303 can be formed such that the upper surface 317 has a surface roughness (R_a) within a range between about 1 micron and about 50 microns, such as between about 1 micron and about 30 microns, and more particularly between 1 micron and 20 microns or even more particularly between 1 micron and about 10 microns.

In addition to the characteristics of surface roughness described herein, the abrasive insert 303 can be formed with an upper surface 317 that has a texture defined by projections 403 and recesses 404 extending across the upper surface 317. Notably, the projections 403 can be formed by abrasive grit 332 protruding through the matrix material 332, while the recesses 404 can be regions along the upper surface 317 that may be absent the abrasive grit 332. In particular, the recesses 404 can be regions comprising primarily the matrix material 332 between the projections 403 formed by the abrasive grit 332.

In certain embodiments, the arrangement of projections 403 along the upper surface 317 of the abrasive insert 303 can be a random orientation. That is, there is no long range or short range order between the orientation of the projections 403 with respect to each other. Moreover, the recesses 404 can have a random arrangement with no short range order or long range order with respect to the projections 403 or each other. However, in other embodiments, the abrasive insert 303 can be formed such that the upper surface 317 has a pattern of projections 403 and recesses 404 such that they are ordered relative to each other in an array. In such embodiments, the abrasive insert 303 may be cast or molded initially to form the pattern of projections 403 and recesses 404.

Embodiments herein may utilize a particular arrangement between the amount of superabrasive layer and the amount of abrasive insert forming the cutting table. For example, in certain designs the abrasive insert is formed such that it comprises at least 10 vol% of the total volume of the cutting table. In fact, certain embodiments may utilize a larger abrasive insert, such that it comprises at least 20 vol%, at least about 30 vo 1%, or even at least about 40 vol% of the total volume of the cutting table. Still, the size of the abrasive insert 303 may be limited such that the abrasive insert comprises between about 10 vol% and 60 vol%, and more particularly between about 10 vol% and 50 vol% of the total volume of the cutting table.

Additionally, cutting tables of the cutting elements herein may utilize a particular arrangement between the superabrasive layer 302 and abrasive insert 303 such that a certain amount of the upper surfaces of these components 307 and 317 is exposed. For example, certain designs utilize a cutting table wherein the upper surface of the abrasive insert 303 comprises at least about 10% of the total surface area of the upper surface of the cutting table, which includes the upper surface 307 of the superabrasive layer 302 and the upper surface 317 of the abrasive insert 303. In other embodiments, the percentage of the surface area occupied by the upper surface 317 of the abrasive insert 303 is greater, such as on the order of at least 20%, at least about 25%, or even at least 30% of the total surface area of the upper surface of the cutting table. However, the total surface area occupied by the upper surface 317 of the abrasive insert 303 may be limited such that it may be between about 10% and 75%, such as between about 20% and 60%, and more particularly between about 20% and 50% of the total surface area of the upper surface of the cutting table.

FIG. 5 includes a cross-sectional illustration of a portion of a cutting element in accordance with an embodiment. The cutting element 500 illustrates a cutting table 506 comprising a superabrasive layer 302 and an abrasive insert 303 disposed within the central opening of the superabrasive layer 302. In particular, the abrasive insert 303 comprises a lower region 501 that includes the rear surface 313, which is bonded to the upper surface 305 of the substrate 301. Additionally, the abrasive insert 303 comprises an upper region 503 comprising the upper surface 317 that is axially spaced apart from the rear surface 313 along the longitudinal axis 310. Notably, the abrasive insert 303 comprises at least two distinct regions; the lower region 501 and upper region 503, which can represent at least two distinct layers within the abrasive insert 303.

In particular cutting elements, the abrasive insert 303 can be formed such that the upper region 503 includes a different amount of abrasive grit 505 within the matrix material 504 than the amount of abrasive grit 509 contained within the matrix material 508 of the lower region 501. For example, in particular embodiments, the bonding interface at the rear surface 313 of the lower region 501 and the upper surface 305 of the substrate 301 can be substantially free of abrasive grit 509 to facilitate bonding between the lower region 501 of the abrasive insert 303 and the upper surface 305 of the substrate 301. Such a design may facilitate bonding of the lower region 501 to the upper surface 305 of the substrate 301

In certain designs, the upper region 503 comprises at least about 10% greater amount (per unit volume) of abrasive grit than the lower region 501 of the abrasive insert 303. In other embodiments, the amount of abrasive grit in the upper region 503 as compared to the lower region 501 may be greater, such as on the order of at least about 15% greater, at least about 20% greater, or even at least about 50% greater amount of abrasive grit within the upper region 503 than the lower region 501. Such a design may facilitate a greater amount of abrasive grit in the upper region for improved cutting and wear resistance and a lower amount of abrasive grit in the lower region 501 for improved bonding of the abrasive insert 303 to the substrate 301. In particular embodiments, the upper region 503 comprises between about 10% and about 100%, and more particularly between about 15% and about 80% greater amount of abrasive grit than the lower region 501 of the abrasive insert 503.

In alternative embodiments, the upper region 503 can be formed such that it contains a lesser amount of abrasive grit than the lower region 501. For instance, particular cutting designs utilize an upper region 503 having at least about 10% lesser amount (per unit volume) of abrasive grit than the lower region 501 of the abrasive insert 303. In other embodiments, the amount of abrasive grit in the upper region 503 as compared to the lower region 501 may be lesser, such as on the order of at least about 15% less, at least about 20% less, or even at least about 30% less than the lower region 501. Such a design can facilitate a greater stiffness of material within the lower region 501 for supporting the upper region 503.

While the cutting table 506 is illustrated as having distinct or discrete layers defining the lower region 501 and upper region 503, it will be appreciated that such a change in the amount of abrasive grit may not necessarily include a layered structure, but a gradual change in the amount of abrasive grit present within the matrix material over the height of the abrasive insert 303. FIG. 6 includes a cross-sectional illustration of a portion of a cutting element in accordance with an embodiment. The cutting element 600 includes a cutting table 606 having a superabrasive layer 302 of an annular shape and defining a central opening, and further includes an abrasive insert 303 disposed within the central opening of the superabrasive layer 302. In accordance with one particular embodiment, the abrasive insert 303 can comprise a graded concentration of abrasive grit 625 through the height of the abrasive insert 303 such that the amount of abrasive grit 625 within the matrix material 626 is different at different positions along the longitudinal axis 310 from the rear surface 313 of the abrasive insert 303 to the upper surface 317 of the abrasive insert.

In particular designs the amount of abrasive grit at the upper surface 317 is greater than the amount of abrasive grit at the rear surface 313 such that the amount of abrasive grains increases along the height of the abrasive insert 303 as defined by the longitudinal axis 310. In particular instances, the upper surface . It will be appreciated, that in certain embodiments, the abrasive insert 303 can be formed such that the upper surface 317 is formed to have a greater amount of abrasive grit 625 than matrix material 626.

Still, in some alternative embodiments, the direction of abrasive grit concentration grading through the volume of the abrasive insert 303 can be alternated in an axial direction, radial direction, or a combination thereof. For example, the graded direction of abrasive grit may be reversed, such that the amount of abrasive grit 625 contained within the matrix material 626 decreases at distances along the longitudinal axis 310 away from the rear surface 313. In still other alternative embodiments, a cutting element can be formed that includes an abrasive insert having a graded amount of abrasive grit 625 contained within the matrix material 626, wherein the concentration of abrasive grit increases with proximity to the inner surface 605 of the superabrasive layer 302. That is, the abrasive insert can be formed such that regions in the center of the abrasive insert along the longitudinal axis 310 comprise a lesser amount of abrasive grit 625 than regions within the abrasive insert spaced apart from the longitudinal axis 310 at a radial distance which are closer in proximity to the inner surface 605 of the superabrasive layer 302. Such designs may facilitate the formation of a cutting element capable of maintaining suitable cutting rates when the cutting table 606 wears into the abrasive insert.

FIG. 7A-7C provides top view illustrations of cutting elements in accordance with an embodiment. In particular, FIGs. 7A-7C demonstrate various shapes of the abrasive insert that can be formed. In particular, FIG. 7A illustrates an abrasive insert 701 contained within a central opening of a superabrasive layer 302, wherein the abrasive insert 701 comprises an elliptical shape. FIG. 7B includes an abrasive insert 703 having an irregular shaped abrasive insert 703 containing long arm sections 704 and 705 that are joined by short arm sections 706 and 707. FIG. 7B illustrates that various irregular shapes are suitable for use in the abrasive insert. FIG. 7C includes a polygonal shaped abrasive insert 709, in particular, an octahedral-shaped abrasive insert 703 contained within a central opening of a superabrasive layer 302 for use in a cutting element.

The cutting elements described herein can be formed using one or more particular methods. For example, the superabrasive layer of the cutting table and the substrate can be formed using a high pressure/high temperature (HP/HT) process, wherein the substrate material is loaded into a HP/HT cell with the appropriate orientation and amount of diamond crystal material, typically of a size of 100 microns or less. Furthermore, a metal catalyst powder can be added to the HP/HT cell, which can be provided in the substrate or intermixed with the diamond crystal material. The loaded HP/HT cell is then placed in a process chamber, and subject to high temperatures (approximately between 1450-1600⁰C) and high pressures (approximately between 50-70 kilobar), wherein the diamond crystals, stimulated by the catalytic effect of the metal catalyst powder, bond to each other and to the substrate material to form a PDC product.

For certain cutting elements, the PDC product can be further processed to form a thermally stable polycrystalline diamond material (commonly referred to as "TSP") by leaching out the remaining metal catalyst material in the diamond layer. Alternatively, silicon, which possesses a coefficient of thermal expansion similar to that of diamond, may be used to bond diamond particles to produce a Si-bonded TSP. Such TSP materials are capable of enduring higher temperatures (on the order of 1200⁰C). With regard the to the abrasive insert, in certain processes, the abrasive insert can be formed separately from the superabrasive layer and the substrate. Certain suitable forming methods can include molding, casting, heating, pressing, and a combination thereof to give the abrasive insert the proper shape such that it fits into the cutting table with the superabrasive layer as described in embodiments herein. Notably, for more complex designs of the abrasive insert, such as those having layers or graded compositions of abrasive grit within the matrix material, individual layers or films of the appropriate material may be formed in a molding or casting cell before the final forming process. For example, a series of layers may be formed in a molding cell that includes a first layer having a predetermined amount of abrasive grit, a second layer may be formed on the first layer having a greater content of abrasive grit than the first layer, and a third layer may be formed on the second layer having a greater content of abrasive grit than the second layer, and so on. The layered structure may then be formed in a single process utilizing heat and/or pressure, such as a hot isostatic pressing process to form the abrasive insert.

After forming the abrasive insert, the insert may be fit into the cutting table, and may be particularly bonded to the superabrasive layer and the substrate. Some machining may take place such that the abrasive insert has the proper dimensions for fitting into the cutting table. Suitable processes for bonding of the abrasive insert may include hot pressing, brazing, and the like.

In other alternative processes, the abrasive insert can be formed using a high pressure/high temperature (HP/HT) process, such as the one used to form the superabrasive layer and the substrate. In fact, some forming methods may simultaneously form the superabrasive layer, abrasive insert, and the substrate in the same chamber at the same time. Such a process may require a special HP/HT cell capable of accommodating all of the components and effectively forming said components. Notably, such a process may be suitable for designs utilizing complex geometries between the superabrasive layer and the abrasive insert.

As will be appreciated, after the formation of the cutting element, finishing processes can be undertaken to prepare the surfaces for drilling applications. For example, surfaces of the superabrasive layer may be formed to have chamfers in accordance with the embodiments herein. Moreover, the surfaces of the cutting body may be polished.

The embodiments herein represent a departure from conventional cutting elements. While changes to cutting elements for use in drill bits have been disclosed, such changes generally are directed to the use of different or new materials, combinations of different materials within the cutting table, and different arrangements of the cutting table with the substrate to improve bonding between the components and reduce the likelihood of certain failure mechanisms. The embodiments herein include a combination of features not previously recognized including the provision of a cutting table including a superabrasive layer with an abrasive insert having unique surface features and employing abrasive grit in a matrix material. Such features facilitate the formation of cutting elements using less precious materials, while maintaining cutting ability and having suitable resistance to thermally-induced and mechanically induced failure mechanisms. The cutting elements herein may be particularly suitable for use in impreg drill bits and PDC drill bits. The cutting elements may be suitable for impreg drill bits designed to drill through soft formations transitioning to harder formations. For instance, in transitioning from soft formations to harder formations, the superabrasive portion of the cutting table may be worn in an initial drilling operation and as the surface wears to expose the abrasive insert, the drill bit may be capable of functioning more like an impregnated drill bit capable of moving through the harder formations. PDC drill bits may utilize such cutting elements as backup cutters, or peripheral cutters proximate to the gauge pads. Notably, such cutting elements may be utilized as rubbing or depth of cut limiting devices, strategically positioned on the drill bit at the cone, nose, or shoulder regions.

The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true scope of the present invention. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description. The Abstract of the Disclosure is provided to comply with Patent Law and is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description of the Drawings, various features may be grouped together or described in a single embodiment for the purpose of streamlining the disclosure. This disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may be directed to less than all features of any of the disclosed embodiments. Thus, the following claims are incorporated into the Detailed Description of the Drawings, with each claim standing on its own as defining separately claimed subject matter.

Claims

CLAIMS:

1. A cutting element for use in a drill bit for drilling subterranean formations comprising: a substrate comprising a body having an upper surface extending transversely to a longitudinal axis of the body; a superabrasive layer overlying the upper surface of the substrate, wherein the superabrasive layer comprises an annular shape having a central opening defined by an inner surface; and an abrasive insert overlying the upper surface of the substrate and disposed within the central opening of the superabrasive layer, wherein the abrasive insert comprises an upper surface having a surface roughness (R_a) of greater than about 1 micron.

2. The cutting element of claim 1, wherein the surface roughness (R_a) of the upper surface is greater than about 3 microns.

3. The cutting element of claim 1, wherein the upper surface of the abrasive insert comprises a texture formed by projections and recesses across the upper surface, wherein the projections comprise abrasive grit.

4. The cutting element of claim 1, wherein the abrasive insert comprises abrasive grit contained within a matrix material.

5. The cutting element of claim 4, wherein the matrix material comprises a metal.

6. The cutting element of claim 4, wherein the matrix material comprises a carbide material.

7. The cutting element of claim 4, wherein the abrasive grit comprises a superabrasive material.

8. The cutting element of claim 7, wherein the abrasive grit comprises diamond grit.

9. The cutting element of claim 4, wherein the abrasive grit comprises an average grit size of at least about 25 microns.

10. The cutting element of claim 9, wherein the abrasive grit comprises an average grit size within a range between about 25 microns and about 2 mm.

11. The cutting element of claim 4, wherein the abrasive grit is dispersed uniformly throughout the entire volume of the matrix material.

12. The cutting element of claim 1, wherein the superabrasive layer is directly bonded to the abrasive insert.

13. The cutting element of claim 1, wherein the central opening has a circular cross-sectional contour as viewed perpendicular to the longitudinal axis.

14. The cutting element of claim 1, wherein the central opening comprises a side surface that is tapered at an angle relative to the longitudinal axis of the body.

15. A cutting element for use in a drill bit for drilling subterranean formations comprising: a cutting table comprising: a superabrasive layer comprising an annular shape having a central opening defined by an inner surface; and an abrasive insert overlying the upper surface of the substrate and disposed within the central opening of the superabrasive layer, wherein the abrasive insert comprises abrasive grit contained within a matrix material, wherein an upper region of the abrasive insert comprising an upper surface has a different amount of abrasive grit than a lower region of the abrasive insert.

16. The cutting element of claim 15, wherein the upper region comprises at least about 10% less amount of abrasive grit than the lower region of the abrasive insert.

17. The cutting element of claim 15, wherein the upper region comprises at least about a 10% greater amount of abrasive grit than the lower region of the abrasive insert.

18. The cutting element of claim 15, wherein the abrasive insert comprises a graded amount of abrasive grit throughout the height of the abrasive insert.

19. The cutting element of claim 15, wherein the upper surface comprises a greater amount of abrasive grit than matrix material.

20. A cutting element for use in a drill bit for drilling subterranean formations comprising: a cutting table comprising: a superabrasive layer comprising an annular shape having a central opening defined by an inner surface; and an abrasive insert disposed within the central opening of the superabrasive layer, wherein the abrasive insert comprises an upper surface having a texture comprising protrusions and recesses.

21. The cutting element of claim 20, wherein the abrasive insert comprises abrasive grit contained within a matrix material and the protrusions of the upper surface comprise abrasive grit extending from the upper surface of the matrix material.