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 as are disclosed for example in <CIT> or <CIT>.

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 material 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 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 cutting table <NUM> and the substrate <NUM>. The cutting edge <NUM> of the PDC cutting element <NUM> is where the planar front cutting face <NUM> meets the longitudinal side surface of the of the diamond table <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>. Eventually, the cutting edge <NUM> in contact with the formation becomes linear as the wear scar forms and develops. A wear scar <NUM> for a conventional PDC cutting element <NUM> is illustrated in <FIG>.

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 that a cutting element <NUM> is exposed to. 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. Thus there is a need for cutting elements with improved rates of penetration and improved durability while the heat build-up at the cutting element is reduced.

One method to enhance the durability of a PDC cutting element is modify the cutting edge of the PDC cutting element to reduce stress points. One way to do this is to form tapered surfaces into the cylindrical side surface of the cutting element as illustrated in <FIG> illustrate perspective, face and side views of a prior art PDC cutting element <NUM>. The PDC cutting element <NUM> comprises a polycrystalline diamond table <NUM> and a substrate <NUM> bonded together at an interface <NUM>. It is known in the industry to form planar tapered surfaces <NUM> into the side surface of the PDC cutting element <NUM> adjacent to the cutting face <NUM> and cutting edge <NUM> of the cutting element <NUM>.

Another method to improve the efficiency and durability of cutting element <NUM> is to form chamfered edges <NUM> on the cutting edge <NUM> of the diamond table <NUM>. It is known in the industry to chamfer edges of a PDC cutting element <NUM> to enhance the durability of the PDC cutting element <NUM>. Diamond tables <NUM> with chamfered edges <NUM> on the cutting edge <NUM> have been found to have a reduced the tendency 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 polycrystalline diamond material 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.

<CIT> to Stockey 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 non-planar cutting elements. One variation, illustrated in <FIG> of Jensen, comprises a foursided pyramidal shape with a planar square surface at the top.

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

<CIT> is directed to cutting elements having geometries for high Rate of Penetration (ROP). One cutting element variation, illustrated in <FIG> and <FIG> of Durairajan et al. , comprises a cutting element having a shaped cutting surface comprising a raised triangular shape. Another cutting element variation, illustrated in <FIG> and <FIG>, of Durairajan 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 Durairajan et al.

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

Cutting elements with raised surfaces and chamfered edges are known in the industry. However, these innovations have not addressed thermal issues related to cutting elements and a need still exists for further improvements in reliability and durability of cutting elements.

In one aspect of the invention a cutting element for an earth-boring tool for forming a borehole through a subterranean formation is provided according to claim <NUM>.

In another aspect of the invention an earth-boring downhole tool is provided according to claim <NUM>.

In another aspect of the invention a method of manufacturing an earth-boring tool for forming a borehole through a subterranean formation is provided according to claim <NUM>.

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

<FIG> illustrate perspective, face and side views of an embodiment of a PDC cutting element <NUM> in accordance with the present disclosure. The PDC cutting element <NUM> comprises a raised cutting surface <NUM> having cutting edges <NUM>, a recess <NUM>, and transition surfaces <NUM>. As illustrated in <FIG>, the raised cutting surface <NUM> is in the shape of a rectangle and has two cutting edges <NUM> proximate a side surface <NUM> of the cutting element <NUM>. The optimal orientation for PDC cutting element <NUM> is to have the cutting edge <NUM> at the end of the rectangle of the raised cutting surface <NUM> oriented towards the formation material. When significant wear has worn down one side 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 the other cutting edge <NUM> towards the formation material to be drilled.

<FIG> also illustrate a chamfered edge <NUM> along the raised cutting surface <NUM> and between the side surface <NUM> and the transition surfaces <NUM> of the PDC cutting element <NUM>. In some embodiments, the transition surfaces <NUM> extend from the raised cutting surface <NUM> to a side surface <NUM> of the PDC cutting element <NUM>. In some embodiments, the transition surface <NUM> may be planar and may be parallel to a top face <NUM> of the raised cutting surface <NUM> of the PDC cutting element <NUM>. In some embodiments, the transition surface <NUM> may be concave or convex. In some embodiments, the transition surface <NUM> may define a more complex shape. Similarly, in some embodiments, the recess <NUM> may be square, round, concave, convex, or still may define a more complex shape. In some embodiments, at least a portion of the recess <NUM> may be planar and may be in the same plane as the transition surface <NUM>. The recess <NUM> may be formed such that it is deeper, the same depth, or less deep than transition surface <NUM>. The raised cutting surface <NUM> may comprise between about <NUM>% and <NUM>% of the overall surface area of the PDC cutting element <NUM>. The polycrystalline diamond material <NUM> is bonded to the substrate <NUM> at an interface <NUM>.

<FIG> illustrate perspective, face and side views of an embodiment of a PDC cutting element <NUM> in accordance with the present disclosure. In this embodiment, the PDC cutting element <NUM> has been configured to form a raised cutting surface <NUM> having three cutting edges <NUM>, a recess <NUM> in the center of the raised cutting surface <NUM>, and planar transition surfaces <NUM>. The planar transition surfaces <NUM> extend from the raised cutting surface <NUM> to a longitudinal side surface <NUM> of the PDC cutting element. The polycrystalline diamond material <NUM> is bonded to the substrate <NUM> at an interface <NUM>. In some embodiments, the raised cutting surface <NUM> may be perpendicular to a longitudinal axis <NUM> of the cutting element <NUM> and may be generally parallel to the interface <NUM> between the polycrystalline diamond material <NUM> and the substrate <NUM>. Formation material will be cut by the cutting edges <NUM> of the raised cutting surface <NUM>. Formation material may also be cut by the planar transition surfaces <NUM>, and the edges where the planar transition surfaces <NUM> meet the longitudinal side surface <NUM> of the cutting element.

Tests have shown that the optimal orientation for PDC cutting element <NUM> is to have the apex (or point) of the triangular shape oriented (or pointed) towards the formation. The planar transition surfaces <NUM> may be configured to improve the flow of the formation cuttings and drilling fluid around the face of the cutting element <NUM>. When significant wear has worn down one side 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) apex towards the formation material to be drilled.

The raised cutting surface <NUM> may extend to the longitudinal side surface <NUM> of the PDC cutting element <NUM> as illustrated in <FIG> or it may not extend all the way to the longitudinal side surface <NUM> of the PDC cutting element <NUM>. In some embodiments the total thickness of the polycrystalline diamond material <NUM> may be between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, more preferably about <NUM> to <NUM>.

The planar transition surfaces <NUM> and the recess <NUM> may be formed by grinding, milling, or laser machining the polycrystalline diamond material, or by any other suitable method known in the art. The top surface <NUM> of the raised cutting surface <NUM> may be planar and may be parallel to the interface <NUM> between the substrate <NUM> and the polycrystalline diamond material <NUM>.

The planar transition surfaces <NUM> adjacent to the planar top surface <NUM> of the raised cutting surface <NUM> may form an angle between <NUM> and <NUM> degrees with respect to the planar top surface <NUM> of the raised cutting surface <NUM>. In this embodiment, the cutting edges <NUM> of the raised cutting surface <NUM> are not chamfered, but as illustrated in <FIG>, <FIG>, <FIG>, and <FIG>, the edges of the raised cutting surface <NUM> and the edges between the longitudinal side surface <NUM> of PDC cutting element <NUM> and the planar transition surfaces <NUM> may be chamfered. In this embodiment, the transition surfaces <NUM> between the cutting edge <NUM> of the raised cutting surface <NUM> and the longitudinal side surface <NUM> of the PDC cutting element <NUM> are planar. However, the transition surfaces <NUM> may be concave (as illustrated in <FIG> and <FIG>), convex, or the transition surfaces <NUM> may define a different and/or more complex shape.

The top surface <NUM> of the raised cutting surface <NUM> may comprise between about <NUM>% and <NUM>% of the overall surface area of the PDC cutting element <NUM>. The cutting edges <NUM> of the raised cutting surface <NUM> may be linear (straight) as illustrated in <FIG>, or they may form a portion of an arc. In some embodiments, the edges of the raised cutting surface <NUM> may define a more complex non-linear shape. The grinding, machining, milling or other processes used to remove material from the polycrystalline diamond material <NUM> may extend into as much as <NUM>% of the thickness of the polycrystalline diamond material <NUM> to form the recess <NUM> and the planar transition surfaces <NUM>, (and thus also forming (or exposing) the raised cutting surface <NUM>).

The recess <NUM> inside the raised cutting surface <NUM> may conform to the shape of the exterior edges of the raised cutting surface <NUM>. However, the recess <NUM> inside the raised cutting surface <NUM> may define a different shape and may be in the form of a circle, square, rectangle, or other shape. The depth of the recess <NUM> as compared to the depth of the machining outside the recess <NUM> may be deeper, the same depth, or not as deep. The edges of the recess <NUM> may form a <NUM> degree angle with respect to the top surface <NUM> of the PDC cutting element <NUM>, or they may be at any angle between <NUM> and <NUM> degrees. At least a portion of the recess <NUM>, (e.g. the bottom), may be planar and may also be parallel to the top surface <NUM> of the raised cutting surface <NUM> and/or to the interface <NUM> between the substrate <NUM> and the polycrystalline diamond material <NUM>. In some embodiments, the bottom of the recess <NUM> may define a non-planar surface.

The recess <NUM> of the PDC cutting element <NUM> may improve cutting performance in at least two ways: First, the recess <NUM> may aid in breaking up the formation material after it has been cut away. As described above, the PDC cutting element <NUM> shears the formation material with a cutting action like that of a lathe. Thus, a cutting from the formation material may be in the form of a long ribbon that can make disposal of the cutting more difficult and can lead to bit balling and flow problems. Testing has shown that the recess <NUM> aids in breaking up the formation material into smaller chunks rather than a long ribbon, thus improving the cutting efficiency of the PDC cutting element <NUM>. Improved cutting action with better flow around the PDC cutting element <NUM> will improve the efficiency of the drill bit and may allow operation of the drill bit using less force (axial and tangential) to maintain a specified Rate Of Penetration (ROP). This would result in less torque to rotate the drill bit and less weight on the bit.

Second, tests indicate that the recess <NUM> aids in keeping the polycrystalline diamond material <NUM> of the PDC cutting element <NUM> cooler during operation. This may be because the recess <NUM> adds surface area which improves heat transfer from the top surface <NUM> of the PDC cutting element <NUM> to the drilling fluid. Tests have demonstrated <NUM>% better cooling of the PDC cutting element <NUM> which allows for increased cutting with better performance properties and less diamond-to-diamond bond degradation or thermal damage to the polycrystalline diamond material <NUM>.

<FIG> illustrate perspective, face and side views of an embodiment of a PDC cutting element <NUM> in accordance with the present disclosure. In this embodiment, the PDC cutting element <NUM> has been configured to form a raised cutting surface <NUM> having three cutting edges <NUM>, a recess <NUM> in the center of the raised cutting surface <NUM>, and planar transition surfaces <NUM>. The planar transition surfaces <NUM> extend from the cutting edges <NUM> of the raised cutting surface <NUM> to a side surface <NUM> of the PDC cutting element <NUM>. The polycrystalline diamond material <NUM> is bonded to the substrate <NUM> at an interface <NUM>. <FIG> also illustrate a chamfered edge <NUM> along the raised cutting surface <NUM> and between the side surface <NUM> and the planar transition surfaces <NUM> of the PDC cutting element <NUM>. As described above, a chamfered edge <NUM> has been found to reduce the tendency of the polycrystalline diamond material <NUM> to spall and fracture.

<FIG> illustrate perspective, face and side views of an embodiment of a PDC cutting element <NUM> in accordance with the present disclosure. In this embodiment, the PDC cutting element <NUM> has been configured to form a raised cutting surface <NUM> having three cutting edges <NUM>, a recess <NUM>, and concave transition surfaces <NUM>. The concave transition surfaces <NUM> extend from the cutting edges <NUM> to a side surface <NUM> of the PDC cutting element <NUM>. The polycrystalline diamond material <NUM> is bonded to the substrate <NUM> at an interface <NUM>. The concave transition surfaces <NUM>, similar to the planar transition surfaces <NUM> and <NUM>, illustrated in <FIG> and <FIG> respectively, improve the flow of fluid around the PDC cutting element <NUM> and increase the efficiency and durability of the PDC cutting element <NUM>.

<FIG> illustrate perspective, face and side views of an embodiment of a PDC cutting element <NUM> in accordance with the present disclosure. In this embodiment, the PDC cutting element <NUM> has been configured to form a raised cutting surface <NUM> having three cutting edges <NUM>, a recess <NUM>, and concave transition surfaces <NUM>. The concave transition surfaces <NUM> extend from the cutting edges <NUM> to a side surface <NUM> of the PDC cutting element <NUM>. The polycrystalline diamond material <NUM> is bonded to the substrate <NUM> at an interface <NUM>. <FIG> also illustrate a chamfered edge <NUM> along the edge of the raised cutting surface <NUM> and between the concave transition surfaces <NUM> and the side surface <NUM> of the PDC cutting element <NUM>. As described above, a chamfered edge <NUM> has been found to reduce the tendency of the polycrystalline diamond material <NUM> to spall and fracture.

<FIG> illustrates an embodiment of a PDC cutting element <NUM> in accordance with the present disclosure. In this embodiment, the PDC cutting element has been configured to form a raised cutting surface <NUM> having four cutting edges <NUM>, a recess <NUM>, and planar transition surfaces <NUM>. In this embodiment, the raised cutting surface <NUM> forms the shape of a square. Similar to the triangular shaped raised cutting surfaces described above, it is expected that the highest cutting rates will be achieved when the cutting edge <NUM> at the corner of the square of the raised cutting surface <NUM> is oriented towards the formation material.

<FIG> also illustrates a chamfered edge <NUM> along the cutting edges <NUM> of the raised cutting surface <NUM> and between the side surface <NUM> and the planar transition surfaces <NUM> of the PDC cutting element <NUM>. The polycrystalline diamond material <NUM> is bonded to the substrate <NUM> at an interface <NUM>. The planar transition surfaces <NUM> extend from the raised cutting surface <NUM> to a side surface <NUM> of the PDC cutting element <NUM>.

<FIG> is a graph of axial load on a cutting element over time. Axial load is the force applied to a cutting element that is required for the cutting element to cut into the formation material. This could also be referred to as Weight On Bit (WOB), because in operation, a cutting element will be attached to a spinning drill bit and axial load is a measure of the amount of axial force (weight on bit) needed to allow the drill bit to engage the formation material.

The plot lines in <FIG> each represent one individual cutting element as it is being tested interacting with formation material. Axial load is plotted on the Y axis in units of kilograms while the X axis represents time and each dot represents a measurement (or series of measurements) at a specific time. A prior art conventional cylindrical cutting element is represented by the lighter gray dots. An embodiment of the invention, namely, an improved geometry three edge cutting element is represented with the darker black dots.

The increase over time of the two lines of <FIG> indicates that greater axial load (or force) is required for each cutting element to maintain a given penetration rate over time. Greater force on the cutting elements is required as the cutting elements abrade and get worn (dull) over time. As can be seen in <FIG>, the prior art conventional cylindrical cutting element consistently requires about <NUM>-<NUM> more kg of axial load than does the improved geometry three edge cutting element. More force required to move the cutting element means more WOB. It also means more abrasion on the cutting element and a shorter lifetime for the cutting element. Moreover, more force also means more heat generated at the cutting element which (as described above) may cause thermal damage to the cutting element and to the polycrystalline diamond material.

<FIG> is a graph of tangential load on a cutting element over time. Tangential load is the sideways force imposed on a cutting element as it engages the formation material. Tangential load represents the torque necessary to spin the drill bit to maintain a given ROP in the formation material.

Similar to the graph of <FIG>, <FIG> illustrates that the prior art conventional cylindrical cutting element requires about <NUM> to <NUM> more kg of force (torque) than does the improved geometry three edge cutting element. As described above, higher torque (force) requirements mean, hotter operating temperatures, more abrasion, and shorter lifetimes for the cutting elements and the drill bit.

<FIG> illustrates a wear scar <NUM> for a prior art conventional cylindrical cutting element <NUM> having a cutting edge <NUM>. <FIG> illustrates a wear scar <NUM> for a prior art cutting element <NUM> having planar tapered surfaces <NUM> and a cutting edge <NUM>. <FIG> illustrates a wear scar <NUM> for a cutting element <NUM> having a raised cutting surface <NUM>, a recess <NUM>, and planar transition surfaces <NUM>. In this embodiment, the raised cutting surface <NUM> has three cutting edges <NUM>. <FIG> illustrates a wear scar <NUM> for a cutting element <NUM> having a raised cutting surface <NUM>, a recess <NUM>, and arcuate transition surfaces <NUM>. In this embodiment, the raised cutting surface <NUM> has three cutting edges <NUM>. As demonstrated in the chart below, close inspection reveals that the wear scar area is smaller for <FIG> than it is for <FIG>.

The chart above compares the wear states of the four cutting elements described above. Wear state <NUM> means that one-sixteenth of the cutting element edge is worn down. Wear state <NUM> means one-eighth of the cutting element edge is worn down and <NUM> means that three-sixteenths of the cutting element edge is worn down. <FIG> illustrate the cutting elements in the "<NUM>" (or one-eighth) state. As illustrated in <FIG>, and demonstrated in the chart, the prior art conventional cylindrical element had a larger "wear scar" area than any of the modified cutting elements. The three edge concave cutting element, illustrated in <FIG>, had the smallest wear scar area for two of the three measurement states.

The graphs in <FIG> and the chart above demonstrate that an embodiment, the modified raised cutting surface, requires less torque, less weight on the bit (WOB), and forms a smaller wear scar area than the prior art conventional cylindrical bit. Therefore, the graphs and chart demonstrate that the modified raised cutting surface may last longer and be more durable than the prior art conventional cylindrical bit.

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 without departing from the spirit of the present invention. Further, the invention may be practiced on non-rotary drill bits, the invention having applicability to any drilling-related structure including percussion, impact or "hammer" bits. It will also be appreciated by one of ordinary skill in the art that one or more features of any of the illustrated embodiments may be combined with one or more features from another embodiment to form yet another combination within the scope of the invention as described and claimed herein. Thus, while certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes in the invention disclosed herein may be made without departing from the scope of the invention, which is defined in the appended claims.

Claim 1:
A cutting element (<NUM>) comprising:
a substrate (<NUM>); and
a polycrystalline diamond material (<NUM>) affixed to the substrate at an interface (<NUM>), the polycrystalline diamond material comprising:
a raised cutting surface (<NUM>) comprising at least four cutting edges (<NUM>);
a recess (<NUM>) in a center of the raised cutting surface; and
at least one transition surface (<NUM>) between at least one of the at least four cutting edges (<NUM>) of the raised cutting surface (<NUM>) and a longitudinal side surface (<NUM>) of the cutting element.