Patent Description:
Wellbores are formed in subterranean formations for various purposes including, for example, extraction of oil and gas from the subterranean formation and extraction of geothermal heat from the subterranean formation. Wellbores may be formed in a subterranean formation using earth-boring tools, such as an earth-boring rotary drill bit. The earth-boring rotary drill bit is rotated and advanced into the subterranean formation. As the earth-boring rotary drill bit rotates, the cutters or abrasive structures thereof cut, crush, shear, and/or abrade away the formation material to form the wellbore.

The earth-boring rotary drill bit is coupled, either directly or indirectly, to an end of what is referred to in the art as a "drill string," which comprises a series of elongated tubular segments connected end-to-end that extends into the wellbore from the surface of earth above the subterranean formations being drilled. Various tools and components, including the drill bit, may be coupled together at the distal end of the drill string at the bottom of the wellbore being drilled. This assembly of tools and components is referred to in the art as a "bottom-hole assembly" (BHA).

The earth-boring rotary drill bit may be rotated within the wellbore by rotating the drill string from the surface of the formation, or the drill bit may be rotated by coupling the drill bit to a downhole motor, which is coupled to the drill string and disposed proximate the bottom of the wellbore. The downhole motor may include, for example, a hydraulic Moineau-type motor having a shaft, to which the earth-boring rotary drill bit is mounted, that may be caused to rotate by pumping fluid (e.g., drilling mud or fluid) from the surface of the formation down through the center of the drill string, through the hydraulic motor, out from nozzles in the drill bit, and back up to the surface of the formation through the annular space between the outer surface of the drill string and the exposed surface of the formation within the wellbore. The downhole motor may be operated with or without drill string rotation.

Different types of earth-boring rotary drill bits are known in the art, including fixed-cutter bits, rolling-cutter bits, and hybrid bits (which may include, for example, both fixed cutters and rolling cutters). Fixed-cutter bits, as opposed to roller cone bits, have no moving parts and are designed to be rotated about the longitudinal axis of the drill string. Most fixed-cutter bits employ Polycrystalline Diamond Compact (PDC) cutting elements. The cutting edge of a PDC cutting element drills rock formations by shearing, like the cutting action of a lathe, as opposed to roller cone bits that drill by indenting and crushing the rock. The cutting action of the cutting edge plays a major role in the amount of energy needed to drill a rock formation.

A PDC cutting element is usually composed of a thin layer, (about <NUM>), of polycrystalline diamond bonded to a cutting element substrate at an interface. The polycrystalline diamond table is often referred to as the "diamond table". A PDC cutting element is generally cylindrical with a diameter from about <NUM> up to about <NUM>. However, PDC cutting elements may be available in other forms such as oval or triangle-shapes and may be larger or smaller than the sizes stated above.

A PDC cutting element may be fabricated separately from the bit body and secured within cutting element pockets formed in the outer surface of a blade of the bit body. A bonding material such as an adhesive or, more typically, a braze alloy may be used to secure the PDC cutting element within the pocket. The diamond table of a PDC cutting element is formed by sintering and bonding together relatively small diamond grains under conditions of high temperature and high pressure (HTHP) in the presence of a catalyst (such as, for example, cobalt, iron, nickel, or alloys and mixtures thereof) to form a layer or "table" of polycrystalline diamond material on the cutting element substrate.

<FIG> illustrate perspective, face, and side views respectively of a prior art conventional Polycrystalline Diamond Compact (PDC) cutting element <NUM>. The polycrystalline diamond table (diamond table) <NUM> is bonded to the substrate <NUM> at an interface <NUM>. Before being used, a PDC cutting element <NUM> typically has a planar front cutting face <NUM> and a conventional cylindrical cutting edge <NUM>. The planar front cutting face <NUM> is perpendicular to a longitudinal axis <NUM> of the cutting element <NUM> and generally parallel to the interface <NUM> between the diamond table <NUM> and the substrate <NUM>. The cutting edge <NUM> of the PDC cutting element <NUM> is at the interface between the planar front cutting face <NUM> and the longitudinal side surface <NUM> of the of the PDC cutting element <NUM>. The cutting edge <NUM> of a PDC cutting element <NUM> drills rock formations by shearing the formation material (like the cutting action of a lathe). The cutting action of the cutting edge <NUM> plays a major role in the amount of energy needed to drill a rock formation. During use, as the cutting edge <NUM> of the PDC cutting element <NUM> abrades, a wear scar develops at the cutting edge <NUM>.

The cutting element substrate <NUM> may comprise a cermet material (i.e., a ceramic metal composite material) such as, for example, cobalt cemented tungsten carbide. In such instances, the cobalt (or other catalyst material) in the substrate <NUM> may be swept into the diamond grains during sintering and serve as the catalyst material for forming the inter-granular diamond-to-diamond bonds between the diamond grains in the diamond table <NUM>.

Upon formation of a diamond table using the HTHP process, catalyst material may remain in interstitial spaces between the grains of the diamond table. The presence of the catalyst material in the diamond table may contribute to degradation in the diamond-to-diamond bonds between the diamond grains in diamond table when the cutting element <NUM> gets hot during use.

Degradation of the diamond-to-diamond bonds due to heat is referred to as "thermal damage" to the diamond table <NUM>. Therefore, it is advantageous to minimize the amount heat to which a cutting element <NUM> is exposed. This may be accomplished by reducing the rate of penetration of the earth-boring rotary drill bit. However, reduced rate of penetration, means longer drilling time and more costs associated with drilling while cutting element <NUM> failure means stopping the drilling process to remove the drill string in order to replace the drill bit. Therefore, there is a need for cutting elements that cut more efficiently, thus improving the rate of penetration and while minimizing heat build-up in the cutting element <NUM>. Furthermore, cutting elements need to be more durable to reduce costs associated with removing and replacing the down-hole drill bit.

One method to enhance the durability of a PDC cutting element <NUM> is modify the cutting edge of the PDC cutting element to reduce stress points by forming a chamfer on the cutting edge of the diamond table. Forming a chamfer on the cutting edge <NUM> of the PDC cutting element <NUM> has been found to reduce the tendency of the diamond table to spall and fracture.

Multi-chamfered Polycrystalline Diamond Compact (PDC) cutting elements are also known in the art. For example a multi-chamfered cutting element is taught by <CIT>, assigned to the assignee of the present invention. In particular the Cooley et al. patent discloses a PDC cutting element having a diamond table having two concentric chamfers.

It is also known in the industry to modify the shape of the diamond table to improve cutting element efficiency and durability. <CIT> is directed to a cutting element having a spherical first end opposite the cutting end. Cutting element variations, illustrated in FIGS. <NUM>-<NUM> of Thigpin et al. , comprise channels or holes formed in the cutting face. <CIT>is directed to cutting elements with grooves on the cutting face as illustrated in FIGS. <NUM>-<NUM> of Patel.

<CIT>is directed toward cutting elements having a thin layer of polycrystalline diamond bonded to a free end of an elongated pin. One particular cutting element variation illustrated in FIG. <NUM> of Bovenkerk, comprises a generally hemispherical diamond layer having a plurality of flats formed on the outer surface thereof. Cutting elements with concave faces are typically not used in the industry, because at higher depths of cut, the sides of the cutting element push the cuttings back towards the center of the cutter causing the cuttings to merge. This is inefficient and may cause bit-balling and other flow problems.

<CIT>and U. Patent Publication <CIT> are directed towards a cutting face of a cutting element having multiple chamfers forming concentric rings on the cutting face. One particular cutting element variation, illustrated in <FIG> of Stockey, comprises a ring surface with a chamfer at the cutting edge surrounding an annular recess which in turn surrounds planar circle at the center of the cutting face. Another cutting element variation illustrated in <FIG> of Patel et al. , comprises multiple raised ring surfaces and multiple annular recesses surrounding a planar circle at the center of the cutting face.

<CIT>is directed to raised surface geometries on nonplanar cutting elements. One variation, illustrated in FIG. 4a of Jensen, comprises a four-sided pyramidal shape with a planar square surface at the top.

<CIT>is directed toward a cutting element with a raised hexagonal shape. One cutting element variation, illustrated in FIG. 5A of Chen, comprises a raised hexagonal shape having chamfered edges. Another cutting element variation, illustrated in FIG. 5C of Chen, comprises a raised cutting surface having six round "teeth".

<CIT> is directed to an ultra-hard material cutter with a shaped cutting surface. Middlemiss discloses a cutting element having a radially extending depression formed on the exposed cutting element's cutting layer.

<CIT> is directed to a cutting element having a shaped working surface with varying edge chamfer. One cutting element variation, illustrated in FIG. <NUM> of Shen, comprises a shaped working surface having three depressions and a varied geometry chamfer circumferentially around a cutting edge at the intersection of the shaped working surface and a side surface. <NUM>-<NUM> illustrated alternate embodiments of cutting elements having shaped working surfaces.

<CIT> is directed to cutting elements having geometries for high Rate of Penetration (ROP). One cutting element variation, illustrated in FIGS. <NUM> and5 of Durairajan et al. , comprises a cutting element having a shaped cutting surface comprising a raised triangular shape. Another cutting element variation, illustrated in FIGS. <NUM> and6, of Durairaj an et al. , comprises a cutting element with a raised triangle having a beveled or chamfered edge.

<CIT> is directed to superabrasive bits with multiple raised cutting surfaces. One cutting element variation, illustrated in <FIG>, of Cuillier De Maindreville et al. , comprises raised triangular shapes similar to Durairaj an et al.

<CIT>is directed to PDC cutting elements. Cutting element variations, illustrated in FIGS. <NUM>-<NUM> of Dennis, comprise cutting elements with various raised shapes including triangular and hexagonal shapes.

<CIT> discloses another arrangement of the prior art.

Cutting elements with shaped surfaces and chamfered edges are known in the industry. However, a need still exists for further improvements in reliability and durability of cutting elements.

One aspect of the invention includes a cutting element for an earth-boring tool for forming a borehole through a subterranean formation. The cutting element comprises a substrate and a diamond table wherein the diamond table has a first end and a second end. The first end of the diamond table is affixed to the substrate at an interface. The second end of the diamond table comprises a concave surface, at least two concave indentations, and at least two cutting edges at an interface between the concave surface and an outer diameter of the diamond table. Each of the at least two concave indentations intersects the concave surface and extends radially outward from the concave surface to the outer diameter of the diamond table. The concave surface and the concave indentations each respectively define a portion of a sphere.

In some embodiments, the present disclosure includes a method of manufacturing an earth-boring downhole tool comprising: providing a tool body and securing to the tool body the cutting element, as recited in any one of the claims.

The illustrations presented herein are not actual views of any particular cutting assembly, tool, or drill string, but are merely idealized representations employed to describe example embodiments of the present disclosure. The drawings accompanying the application are for illustrative purposes only, and are not drawn to scale. Additionally, elements common between figures may have corresponding numerical designations.

As used herein, the term "may" with respect to a material, structure, feature, or method act indicates that such is contemplated for use in implementation of an embodiment of the disclosure, and such term is used in preference to the more restrictive term "is" so as to avoid any implication that other compatible materials, structures, features and methods usable in combination therewith should or must be excluded.

As used herein, relational terms, such as "first," "second," "top," "bottom," etc., are generally used for clarity and convenience in understanding the disclosure and accompanying drawings and do not connote or depend on any specific preference, orientation, or order, except where the context clearly indicates otherwise.

As used herein, the term "earth-boring tool" means and includes any type of bit or tool used for drilling during the formation or enlargement of a wellbore and includes, for example, rotary drill bits, percussion bits, core bits, eccentric bits, bi-center bits, reamers, mills, drag bits, roller-cone bits, hybrid bits, and other drilling bits and tools known in the art.

Improvements in the flow characteristics of cutting elements along with improvements in the cutting element efficiency and durability of cutting elements may be achieved in accordance with embodiments of the present disclosure. Downhole earth-boring tools, comprising cutting elements having novel geometries for improved flow characteristics and mechanical efficiency are described in further detail hereinbelow.

<FIG> illustrate a face view and two side views respectively of an embodiment of a PDC cutting element <NUM> in accordance with the present disclosure. In this embodiment, the PDC cutting element <NUM> comprises a diamond table <NUM> bonded to a substrate <NUM> at an interface <NUM>. <FIG> further illustrate three concave subtractions or cutouts that have been taken from diamond table <NUM> thus defining a concave surface <NUM> and two concave indentations <NUM>.

The concave surface <NUM> forms more aggressive cutting edges <NUM> than the prior art planar front cutting face <NUM> illustrated in <FIG> and much more aggressive cutting edges <NUM> than the prior art domed surfaces described in the background section. As described in the background section, a cutting face having a concave surface is typically not used in the industry because the concave surface directs drilling fluid and cuttings back towards the center of the cutting element creating issues with bit balling and fluid flow. However, in the embodiment illustrated in <FIG>, the concave surface <NUM> is used in conjunction with the concave indentations <NUM> that cause drilling fluid and cuttings to flow away from the center of the cutting element <NUM>. Thus, the concave surface <NUM> creates more aggressive cutting edges <NUM> and the concave indentations <NUM> improve flow characteristics around the cutting edges <NUM>. These improvements in the geometry of cutting element <NUM> may improve the Rate of Penetration (ROP) while reducing heat, abrasion, and bit balling at the drilling face of the drill bit.

<FIG> illustrates a concave surface <NUM> that is symmetric about line <NUM> and extends across the diamond table <NUM> from one side of the PDC cutting element <NUM> to the opposite side of the PDC cutting element <NUM>, forming a dish-like top surface <NUM> into the diamond table <NUM>. In some embodiments, the radius of curvature of the concave surface may be between about <NUM> millimeters and <NUM> millimeters. The concave surface defines a portion of a sphere. In some embodiments, the concave surface <NUM> may comprise between about <NUM>% and <NUM>% of the overall surface area of the diamond table <NUM> and may extend down into as much as <NUM>% of the thickness of the diamond table <NUM>. In some embodiments, the concave subtraction (or cutout) process may use grinding, milling, laser machining, or any other suitable method known in the art to remove diamond material from the diamond table <NUM> to form the concave surface <NUM> and the concave indentations <NUM> in the diamond table <NUM>. Two cutting edges <NUM> are disposed at an interface between the concave surface <NUM> and the outer diameter or longitudinal side surface <NUM> of the cutting element <NUM>.

In drilling a borehole, the optimal orientation for PDC cutting element <NUM> is to have one of the cutting edges <NUM> of the concave surface <NUM> oriented towards the formation material to be drilled. When significant wear has worn down the first of the cutting edges <NUM> of the PDC cutting element <NUM>, the cutting element <NUM> may be reoriented by removing the drill bit, and by removing, rotating, and reattaching the PDC cutting element <NUM> on the drill bit to orient the second of the cutting edges <NUM> towards the formation material.

<FIG> also illustrates two concave indentations <NUM> that form two edges of the concave surface <NUM> and extend from the concave surface <NUM> radially outward to an outer diameter or longitudinal side surface <NUM> of the diamond table <NUM>. As illustrated in <FIG>, the two concave indentations <NUM> may be formed into the diamond table <NUM> on opposite sides of the concave surface <NUM>, intersecting the diamond table <NUM> and extending radially to an outside diameter of the cutting element <NUM>. The concave indentations <NUM> may also symmetric with respect to line <NUM>, which is illustrated in <FIG> running vertically across a center of the concave surface <NUM>. The concave indentations each define a portion of a sphere. In some embodiments, the two concave indentations <NUM> may be formed into the diamond table <NUM> at other locations, may be adjacent to each other, and may overlap and/or merge into each other. In some embodiments, the concave indentations <NUM> may extend into as much as <NUM>% of the thickness of the diamond table <NUM>. In some embodiments, the radius of curvature between of the concave surface may be between about <NUM> millimeters and <NUM> millimeters.

<FIG> also illustrate a chamfered edge <NUM> along at least a portion of the cutting edges <NUM>, and between the concave indentations <NUM> and the outer diameter of the diamond table (or longitudinal side surface <NUM> of the PDC cutting element <NUM>). The chamfered edge <NUM> illustrated in the figures has a constant width around the circumference of cutting element <NUM>. As described above, a chamfered edge <NUM> has been found to reduce the tendency of the diamond table <NUM> to spall and fracture.

The order in which the concave subtractions are formed does not matter. The concave indentations <NUM> could be formed before or after the concave surface <NUM>, or all of the concave subtractions could be formed in a substantially simultaneous fashion.

<FIG> illustrate perspective, face, and side views respectively of an embodiment of a PDC cutting element <NUM>, in accordance with the present disclosure, in which four concave subtractions or cutouts have been taken from diamond table <NUM>, thus defining three concave indentations <NUM> and a concave surface <NUM>. The concave indentations <NUM> form three edges of the concave surface <NUM> and extend from the concave surface <NUM> radially outward to an outer diameter of the diamond table <NUM> (or longitudinal side surface <NUM> of the PDC cutting element <NUM>).

In some embodiments, the PDC cutting element <NUM> comprises a diamond table <NUM> bonded to a substrate <NUM> at an interface <NUM>. In some embodiments, the total thickness of the diamond table <NUM> may be between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, more preferably about <NUM> to <NUM>.

As illustrated in <FIG>, the top surface of the diamond table <NUM> comprises a concave surface <NUM>, three concave indentations <NUM>, and three cutting edges <NUM>. The three concave indentations <NUM> extend from a concave surface <NUM> that is roughly triangular with curved edges. The concave surface defines a portion of a sphere. <FIG>, also illustrate three concave indentations <NUM> that are spaced equidistantly from each other around an outer edge of the diamond table and do not meet or merge into each other. In some embodiments, the concave indentations <NUM> may not be spaced equidistantly from each other around an outer edge of the diamond table and may meet or merge into each other. In some embodiments, there may be four or more concave indentations. In some embodiments, the concave indentations <NUM> may extend into as much as <NUM>% of the thickness of the diamond table <NUM>. The concave indentations each define a portion of a sphere.

As illustrated in <FIG>, the concave surface <NUM> is symmetric about line <NUM> and extends from one side of the diamond table <NUM> to the opposite side of the diamond table. In the embodiment illustrated in <FIG>, the concave surface <NUM> is concave or dish-like. In some embodiments, concave surface <NUM> may extend to the outer diameter or longitudinal side surface <NUM> of the PDC cutting element <NUM>. The concave surface <NUM> may comprise between about <NUM>% and <NUM>% of the overall surface area of the diamond table <NUM> and may extend down into as much as <NUM>% of the thickness of the diamond table <NUM>.

As described above, the concave indentations <NUM> and the concave surface <NUM> may be formed in the diamond table <NUM> by grinding, machining, milling, or any other suitable method known in the art to remove polycrystalline diamond material. Furthermore, the order in which the concave subtractions are formed does not matter. The grinding, milling, or machining etc. to form the concave subtraction surfaces may be done in any order, or the surfaces may be formed substantially simultaneously.

<FIG>, also illustrate three cutting edges <NUM> disposed at an interface between the concave surface <NUM> and the outer diameter of the diamond table <NUM> (or longitudinal side surface <NUM> of the cutting element <NUM>). When forming a borehole, the optimal orientation for PDC cutting element <NUM> is to have one of the cutting edges <NUM> oriented (or pointed) towards the formation material to be drilled. When significant abrasion has worn down a first of the cutting edges <NUM> of the PDC cutting element <NUM>, the PDC cutting element <NUM> may be rotated by removing the drill bit, and by removing, rotating, and reattaching the PDC cutting element <NUM> on the drill bit in order to orient a second (and then a third etc.) of the cutting edges <NUM> towards the formation material to be drilled. The concave indentations <NUM> may be configured and oriented to improve the flow of the drilling fluid and formation cuttings around the face of the cutting element <NUM>.

<FIG> also illustrates a chamfered edge <NUM> along at least a portion of the cutting edges <NUM>, and between the concave indentations <NUM> and the outer diameter of the diamond table <NUM> (or longitudinal side surface <NUM> of the PDC cutting element <NUM>). The chamfered edge <NUM> illustrated in the figures has a uniform width around the circumference of the PDC cutting element <NUM>. As described above, a chamfered edge <NUM> has been found to reduce the tendency of the diamond table <NUM> to spall and fracture.

Computer modeling indicates that the concave surface <NUM> with concave indentations <NUM>, will cut more efficiently and improve flow characteristics around the cutting element and the drill bit. It is expected that, drill bits having cutting elements with this improved geometry may require less torque and less weight on the bit than other prior art bits to achieve a similar Rate of Penetration (ROP). Therefore, it is expected that the concave cutting surface will last longer and be more durable than prior art bits.

The embodiments of the disclosure described above and illustrated in the accompanying drawing figures do not limit the scope of the invention, since these embodiments are merely examples of embodiments of the invention, which is defined by the appended claims.

In exemplary embodiments, a typical rotary-type "drag" bit made from steel and using PDC cutting elements is described. Those skilled in the art, however, will appreciate that the size, shape, and/or configuration of the bit may vary according to operational design parameters.

Claim 1:
A cutting element (<NUM>; <NUM>) comprising:
a substrate (<NUM>; <NUM>); and
a diamond table (<NUM>; <NUM>) having a first end and a second end, the first end of the
diamond table (<NUM>; <NUM>) affixed to the substrate (<NUM>; <NUM>) at a first interface (<NUM>; <NUM>), the second end of the diamond table (<NUM>; <NUM>) comprising;
a concave surface (<NUM>; <NUM>);
at least two concave indentations (<NUM>; <NUM>), each of the at least two concave indentations (<NUM>; <NUM>) intersecting the concave surface (<NUM>; <NUM>) and extending radially outward from the concave surface (<NUM>; <NUM>) to an outer diameter of the diamond table (<NUM>; <NUM>); and
at least two cutting edges (<NUM>; <NUM>) at an interface (<NUM>; <NUM>) between the concave surface (<NUM>; <NUM>) and the outer diameter of the diamond table (<NUM>; <NUM>); characterised in that
the concave surface (<NUM>; <NUM>) and the concave indentations (<NUM>; <NUM>) each respectively define a portion of a sphere.