Abstract:
A cutting element for an earth-boring tool. The cutting element comprises a substrate base, and a volume of polycrystalline diamond material on an end of the substrate base. The volume of polycrystalline diamond material comprises a generally conical surface, an apex centered about a longitudinal axis extending through a center of the substrate base, a flat cutting surface extending from a first point at least substantially proximate the apex to a second point on the cutting element more proximate a lateral side surface of the substrate base. Another cutting element is disclosed, as are a method of manufacturing and a method of using such cutting elements.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/204,459, filed Aug. 5, 2011, now U.S. Pat. No. 9,022,149, issued May 5, 2015, which application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/371,554, filed Aug. 6, 2010. The subject matter of this application is also related to the subject matter of U.S. Provisional Patent Application Ser. No. 61/330,757, which was filed May 3, 2010. The disclosures of the above-identified applications are hereby incorporated herein in their entirety by this reference. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention relate generally to cutting elements that include a table of superabrasive material (e.g., polycrystalline diamond or cubic boron nitride) formed on a substrate, to earth-boring tools including such cutting elements, and to methods of forming and using such cutting elements and earth-boring tools. 
     BACKGROUND 
     Earth-boring tools are commonly used for forming (e.g., drilling and reaming) bore holes or wells (hereinafter “wellbores”) in earth formations. Earth-boring tools include, for example, rotary drill bits, core bits, eccentric bits, bicenter bits, reamers, underreamers, and mills. 
     Different types of earth-boring rotary drill bits are known in the art including, for example, fixed-cutter bits (which are often referred to in the art as “drag” bits), rolling-cutter bits (which are often referred to in the art as “rock” bits), diamond-impregnated bits, and hybrid bits (which may include, for example, both fixed cutters and rolling cutters). The drill bit is rotated and advanced into the subterranean formation. As the drill bit rotates, the cutters or abrasive structures thereof cut, crush, shear, and/or abrade away the formation material to form the wellbore. 
     The 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 the formation. Often 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 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 also coupled to the drill string and disposed proximate the bottom of the wellbore. The downhole motor may comprise, for example, a hydraulic Moineau-type motor having a shaft, to which the drill bit is attached, 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. 
     Rolling-cutter drill bits typically include three roller cones attached on supporting bit legs that extend from a bit body, which may be formed from, for example, three bit head sections that are welded together to form the bit body. Each bit leg may depend from one bit head section. Each roller cone is configured to spin or rotate on a bearing shaft that extends from a bit leg in a radially inward and downward direction from the bit leg. The cones are typically formed from steel, but they also may be formed from a particle-matrix composite material (e.g., a cermet composite such as cemented tungsten carbide). Cutting teeth for cutting rock and other earth formations may be machined or otherwise formed in or on the outer surfaces of each cone. Alternatively, receptacles are formed in outer surfaces of each cone, and inserts formed of hard, wear resistant material are secured within the receptacles to form the cutting elements of the cones. As the rolling-cutter drill bit is rotated within a wellbore, the roller cones roll and slide across the surface of the formation, which causes the cutting elements to crush and scrape away the underlying formation. 
     Fixed-cutter drill bits typically include a plurality of cutting elements that are attached to a face of bit body. The bit body may include a plurality of wings or blades, which define fluid courses between the blades. The cutting elements may be secured to the bit body within pockets formed in outer surfaces of the blades. The cutting elements are attached to the bit body in a fixed manner, such that the cutting elements do not move relative to the bit body during drilling. The bit body may be formed from steel or a particle-matrix composite material (e.g., cobalt-cemented tungsten carbide). In embodiments in which the bit body comprises a particle-matrix composite material, the bit body may be attached to a metal alloy (e.g., steel) shank having a threaded end that may be used to attach the bit body and the shank to a drill string. As the fixed-cutter drill bit is rotated within a wellbore, the cutting elements scrape across the surface of the formation and shear away the underlying formation. 
     Impregnated diamond rotary drill bits may be used for drilling hard or abrasive rock formations such as sandstones. Typically, an impregnated diamond drill bit has a solid head or crown that is cast in a mold. The crown is attached to a steel shank that has a threaded end that may be used to attach the crown and steel shank to a drill string. The crown may have a variety of configurations and generally includes a cutting face comprising a plurality of cutting structures, which may comprise at least one of cutting segments, posts, and blades. The posts and blades may be integrally formed with the crown in the mold, or they may be separately formed and attached to the crown. Channels separate the posts and blades to allow drilling fluid to flow over the face of the bit. 
     Impregnated diamond bits may be formed such that the cutting face of the drill bit (including the posts and blades) comprises a particle-matrix composite material that includes diamond particles dispersed throughout a matrix material. The matrix material itself may comprise a particle-matrix composite material, such as particles of tungsten carbide, dispersed throughout a metal matrix material, such as a copper-based alloy. 
     It is known in the art to apply wear-resistant materials, such as “hardfacing” materials, to the formation-engaging surfaces of rotary drill bits to minimize wear of those surfaces of the drill bits cause by abrasion. For example, abrasion occurs at the formation-engaging surfaces of an earth-boring tool when those surfaces are engaged with and sliding relative to the surfaces of a subterranean formation in the presence of the solid particulate material (e.g., formation cuttings and detritus) carried by conventional drilling fluid. For example, hardfacing may be applied to cutting teeth on the cones of roller cone bits, as well as to the gage surfaces of the cones. Hardfacing also may be applied to the exterior surfaces of the curved lower end or “shirttail” of each bit leg, and other exterior surfaces of the drill bit that are likely to engage a formation surface during drilling. 
     The cutting elements used in such earth-boring tools often include polycrystalline diamond cutters (often referred to as “PCDs”), which are cutting elements that include a polycrystalline diamond (PCD) material. Such polycrystalline diamond cutting elements are formed by sintering and bonding together relatively small diamond grains or crystals under conditions of high temperature and high pressure in the presence of a catalyst (such as, for example, cobalt, iron, nickel, or alloys and mixtures thereof) to form a layer of polycrystalline diamond material on a cutting element substrate. These processes are often referred to as high temperature/high pressure (or “HTHP”) processes. The cutting element substrate 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 cutting element substrate may be drawn into the diamond grains or crystals during sintering and serve as a catalyst material for forming a diamond table from the diamond grains or crystals. In other methods, powdered catalyst material may be mixed with the diamond grains or crystals prior to sintering the grains or crystals together in an HTHP process. 
     Upon formation of a diamond table using an HTHP process, catalyst material may remain in interstitial spaces between the grains or crystals of diamond in the resulting polycrystalline diamond table. The presence of the catalyst material in the diamond table may contribute to thermal damage in the diamond table when the cutting element is heated during use due to friction at the contact point between the cutting element and the formation. Polycrystalline diamond cutting elements in which the catalyst material remains in the diamond table are generally thermally stable up to a temperature of about 750° Celsius, although internal stress within the polycrystalline diamond table may begin to develop at temperatures exceeding about 350° Celsius. This internal stress is at least partially due to differences in the rates of thermal expansion between the diamond table and the cutting element substrate to which it is bonded. This differential in thermal expansion rates may result in relatively large compressive and tensile stresses at the interface between the diamond table and the substrate, and may cause the diamond table to delaminate from the substrate. At temperatures of about 750° Celsius and above, stresses within the diamond table may increase significantly due to differences in the coefficients of thermal expansion of the diamond material and the catalyst material within the diamond table itself. For example, cobalt thermally expands significantly faster than diamond, which may cause cracks to form and propagate within the diamond table, eventually leading to deterioration of the diamond table and ineffectiveness of the cutting element. 
     In order to reduce the problems associated with different rates of thermal expansion in polycrystalline diamond cutting elements, so-called “thermally stable” polycrystalline diamond (TSD) cutting elements have been developed. Such a thermally stable polycrystalline diamond cutting element may be formed by leaching the catalyst material (e.g., cobalt) out from interstitial spaces between the diamond grains in the diamond table using, for example, an acid. All of the catalyst material may be removed from the diamond table, or only a portion may be removed. Thermally stable polycrystalline diamond cutting elements in which substantially all catalyst material has been leached from the diamond table have been reported to be thermally stable up to a temperatures of about 1200° Celsius. It has also been reported, however, that such fully leached diamond tables are relatively more brittle and vulnerable to shear, compressive, and tensile stresses than are non-leached diamond tables. In an effort to provide cutting elements having diamond tables that are more thermally stable relative to non-leached diamond tables, but that are also relatively less brittle and vulnerable to shear, compressive, and tensile stresses relative to fully leached diamond tables, cutting elements have been provided that include a diamond table in which only a portion of the catalyst material has been leached from the diamond table. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming what are regarded as embodiments of the present invention, various features and advantages of this invention may be more readily ascertained from the following description of example embodiments of the invention provided with reference to the accompanying drawings, in which: 
         FIG. 1  is a side perspective view of an embodiment of a cutting element of the invention; 
         FIG. 2  is a perspective view of the cutting element shown in  FIG. 1 , taken from a viewpoint approximately forty-five degrees (45°) clockwise of that of  FIG. 1 ; 
         FIG. 3  is a front perspective view of the cutting element shown in  FIG. 1 , taken from a viewpoint approximately ninety degrees (90°) clockwise of that of  FIG. 1 ; 
         FIG. 4  is a side perspective view of another embodiment of a cutting element of the invention; 
         FIG. 5  is a perspective view of the cutting element shown in  FIG. 4 , taken from a viewpoint approximately forty-five degrees (45°) clockwise of that of  FIG. 4 ; 
         FIG. 6  is a front perspective view of the cutting element shown in  FIG. 4 , taken from a viewpoint approximately ninety degrees (90°) clockwise of that of  FIG. 4 ; 
         FIG. 7  is a perspective view of an embodiment of a fixed-cutter earth-boring rotary drill bit of the invention that includes cutting elements as described herein; 
         FIG. 8  is a front view of an embodiment of a roller cone earth-boring rotary drill bit of the invention that includes cutting elements as described herein; 
         FIGS. 9 and 10  are side perspective views of different embodiments of cutting elements of the invention wherein the cutting elements are mounted on a drilling tool and provided with a negative physical back rake angle (e.g., physical forward rake) and a negative effective back rake angle (e.g., effective forward rake) relative to a formation surface; 
         FIGS. 11 and 12  are side perspective views of different embodiments of cutting elements of the invention wherein the cutting elements are mounted on a drilling tool and provided with a positive physical back rake angle (e.g., physical back rake) and a positive effective back rake angle (e.g., effective back rake) relative to a formation surface; 
         FIGS. 13 and 14  are side perspective views of different embodiments of cutting elements of the invention wherein the cutting elements are mounted on a drilling tool and provided with a neutral physical back rake angle (e.g., physical neutral rake) and a positive effective back rake angle (e.g., effective back rake) relative to a formation surface; 
         FIGS. 15 and 16  are side perspective views of different embodiments of cutting elements of the invention wherein the cutting elements are mounted on a drilling tool and provided with a negative physical back rake angle (e.g., physical forward rake) and a positive effective back rake angle (e.g., effective back rake) relative to a formation surface; and 
         FIGS. 17 and 18  are side perspective views of different embodiments of cutting elements of the invention wherein the cutting elements are mounted on a drilling tool and provided with a negative physical back rake angle (e.g., physical forward rake) and a neutral effective back rake angle (e.g., effective neutral rake) relative to a formation surface. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The illustrations presented herein are not meant to be actual views of any particular cutting element, earth-boring tool, or portion of a cutting element or tool, but are merely idealized representations which are employed to describe embodiments of the present invention. Additionally, elements common between figures may retain the same numerical designation. 
     As used herein, the term “earth-boring tool” means and includes any tool used to remove formation material and form a bore (e.g., a wellbore) through the formation by way of the removal of the formation material. Earth-boring tools include, for example, rotary drill bits (e.g., fixed-cutter or “drag” bits and roller cone or “rock” bits), hybrid bits including both fixed cutters and roller elements, coring bits, percussion bits, bi-center bits, reamers (including expandable reamers and fixed-wing reamers), and other so-called “hole-opening” tools. 
     As used herein, the term “apex,” when used in relation to a shaped cutting element, means and includes the most distant point on a cutting tip of a shaped cutting element relative to a center of a basal surface on an opposing side of the cutting element. 
     Referring to  FIGS. 1-3 , an embodiment of the present disclosure includes a cutting element  10  having a longitudinal axis  11 , a substrate base  12 , and a cutting tip  13 . The substrate base  12  may have a generally cylindrical shape. The longitudinal axis  11  may extend through a center of the substrate base  12  in an orientation that may be at least substantially parallel to a lateral side surface  14  of the substrate base  12  (e.g., in an orientation that may be perpendicular to a generally circular cross-section of the substrate base  12 ). The lateral side surface  14  of the substrate base may be coextensive and continuous with a generally cylindrical lateral side surface  15  of the cutting tip  13 . The cutting tip  13  also includes a generally conical surface  16 , an apex  17 , and a flat cutting surface  18 . A portion of the generally conical surface  16  may extend between the edge of the flat cutting surface  18  and the generally cylindrical lateral side surface  15 . The generally conical surface  16  may be defined by an angle φ 1  existing between the generally conical surface  16  and a phantom line extending from the generally cylindrical lateral side surface  15  of the cutting tip  13 . The angle φ 1  may be within a range of from about thirty degrees (30°) to about sixty degrees (60°). The generally conical surface  16  may extend from the generally cylindrical lateral side surface  15  to the apex  17 , and may extend to the edges of the flat cutting surface  18 . The location of the apex  17  may be centered about the longitudinal axis  11 . The flat cutting surface  18  may extend from a location at least substantially proximate the apex  17  to a location on the cutting element  10  at a selected or predetermined distance from the apex  17 , such that an angle α 1  between the longitudinal axis  11  and the flat cutting surface  18  may be within a range of from about fifteen degrees (15°) to about ninety degrees (90°). Portions of the cutting tip  13 , such as the flat cutting surface  18 , may be polished. 
     In  FIGS. 1-3 , the angle φ 1  is about thirty degrees (30°), the apex  17  of the cutting tip  13  is centered about the longitudinal axis  11 , and the flat cutting surface  18  extends from the apex  17  to the lateral side surface  14  of the substrate base  12 . In turn, the angle α 1  is less than thirty degrees (30°).  FIG. 1  illustrates a side perspective view of the cutting element  10  showing the non-symmetrical configuration of the cutting tip  13  about the longitudinal axis  11 .  FIG. 2 , which is a perspective view of the cutting element  10  taken from a viewpoint approximately 45 degrees clockwise of that of  FIG. 1 , shows the flat cutting surface  18  of the cutting tip  13 .  FIG. 3  illustrates a front perspective view of the cutting element  10 , taken from a viewpoint approximately ninety degrees (90°) clockwise of that of  FIG. 1 , in which the cutting tip  13  is symmetrical about the longitudinal axis  11 . 
     Referring to  FIGS. 4-6 , another embodiment of the present disclosure includes a cutting element  20  having a longitudinal axis  21 , a substrate base  22 , and a cutting tip  23 . The substrate base  22  may have a generally cylindrical shape. The longitudinal axis  21  may extend through a center of the substrate base  22  in an orientation that may be at least substantially parallel to a lateral side surface  24  of the substrate base  22  (e.g., in an orientation that may be perpendicular to a generally circular cross-section of the substrate base  22 ). The lateral side surface  24  of the substrate base  22  may be coextensive and continuous with a generally cylindrical lateral side surface  25  of the cutting tip  23 . The cutting tip  23  also includes a generally conical surface  26 , an apex  27 , and a flat cutting surface  28 . A portion of the generally conical surface  26  may extend between the edge of the flat cutting surface  28  and the generally cylindrical lateral side surface  25  of the cutting tip  23 . The generally conical surface  26  may be defined by an angle ( 1 ) 2  existing between the generally conical surface  26  and a phantom line extending from the generally cylindrical lateral side surface  25  of the cutting tip  23 . The angle φ 2  may be within a range of from about thirty degrees (30°) to about sixty degrees (60°). The generally conical surface  26  may extend from the generally cylindrical lateral side surface  25  to the apex  27 , and may extend to the edges of the flat cutting surface  28 . The location of the apex  27  may be offset from the longitudinal axis  21 . The flat cutting surface  28  may extend from a location at least substantially proximate the apex  27  to a location on the cutting element  20  at a selected or predetermined distance from the apex  27 , such that an angle α 2  between the longitudinal axis  21  and the flat cutting surface  28  may be within a range of from about fifteen degrees (15°) to about ninety degrees (90°). Portions of the cutting tip  23 , such as the flat cutting surface  28 , may be polished. 
     In  FIGS. 4-6  the angle φ 2  is about thirty degrees (30°), the apex  27  is offset from the longitudinal axis  21 , and the flat cutting surface  28  extends from the apex  27  to a location on the generally conical surface  26  of the cutting tip  23 . The angle α 2  is about sixty degrees (60°). The viewing angles represented by  FIGS. 4-6  correspond, respectively, to those of  FIGS. 1-3 . 
     Each of the cutting tips  13  and  23  may comprise a polycrystalline diamond (PCD) material. Certain regions of the cutting tips  13  and  23 , or the entire cutting tips  13  and  23 , optionally may be processed (e.g., etched) to remove metal binder from between the interbonded diamond grains of the PCD material of each of the cutting tips  13  and  23 , such that each of the cutting tips  13  and  23  are relatively more thermally stable. Each of the cutting tips  13  and  23  may be formed on their respective substrate bases  12  and  22 , or each of the cutting tips  13  and  23  and their respective substrate bases  12  and  22  may be separately formed and subsequently attached together. Each of the substrate bases  12  and  22  may be formed from a material that is relatively hard and resistant to wear. As one non-limiting example, the substrate bases  12  and  22  may be at least substantially comprised of a cemented carbide material, such as cobalt-cemented tungsten carbide. Optionally, the cutting tips  13  and  23  may be formed for use without the respective substrate bases  12  and  22  (e.g., the substrate bases  12  and  22  may be omitted from the respective cutting elements  10  and  20 ). Optionally, an entirety of the cutting elements  10  and  20  (e.g., the cutting tips  13  and  23 , and the substrate bases  12  and  22 ) may comprise a PCD material. 
     Each of the cutting elements  10  and  20  may be attached to an earth-boring tool such that the respective cutting tips  13  and  23  will contact a surface of a subterranean formation within a wellbore during a drilling or reaming process.  FIG. 7  is a simplified perspective view of a fix-cutter rotary drill bit  100 , which includes a plurality of the cutting elements  10  and  20  attached to blades  101  on the body of the drill bit  100 . In additional embodiments, the drill bit  100  may include only cutting elements  10 . In yet further embodiments, the drill bit  100  may include only cutting elements  20 .  FIG. 8  is a simplified front view of a roller cone rotary drill bit  200 , which includes a plurality of the cutting elements  10  and  20  attached to roller cones  201  thereof. In additional embodiments, the drill bit  200  may include only cutting elements  10 . In yet further embodiments, the drill bit  200  may include only cutting elements  20 . 
     Referring to  FIGS. 9-18 , the cutting elements  10  and  20  may each be attached to a portion  400  of the earth-boring tool such that at least a portion of the respective flat cutting surfaces  18  and  28  contact a surface  300  of the subterranean formation within the wellbore. The portion  400  of the earth-boring tool may be a portion of a fixed cutter earth-boring rotary drill bit, such as the drill bit  100  depicted in  FIG. 7 , or a portion of a roller cone earth-boring rotary drill bit, such as the drill bit  200  depicted in  FIG. 8 . A shape and configuration of each of the cutting elements  10  and  20  may enable versatility in orienting each of the cutting elements  10  and  20  relative to the surface  300  of the subterranean formation. 
     Referring to  FIGS. 9-18 , effective back rake angles θ 1  and θ 2  between the respective flat cutting surfaces  18  and  28  and a reference plane  500  at least substantially perpendicular to the surface  300  of the subterranean formation may be negative (i.e., effective forward rake), positive (i.e., effective back rake), or neutral (i.e., effective neutral rake). The effective back rake angles θ 1  and θ 2  may be considered negative where the corresponding flat cutting surfaces  18  and  28  are behind the reference plane  500  in the direction of cutter movement (i.e., the flat cutting surfaces  18  and  28  form an obtuse angle with the surface  300  of the subterranean formation), as depicted in  FIGS. 9 and 10 . The effective back rake angles θ 1  and θ 2  may be considered positive where the respective flat cutting surfaces  18  and  28  are ahead of the reference plane  500  in the direction of cutter movement (i.e., the flat cutting surfaces  18  and  28  form an acute angle with the surface of the subterranean formation  300 ), as depicted in  FIGS. 11-16 . The effective back rake angles θ 1  and θ 2  may be considered neutral where the respective flat cutting surfaces  18  and  28  are parallel with the reference plane  500  (i.e., the flat cutting surfaces  18  and  28  substantially form a right angle with the surface of subterranean formation  300 ), as depicted in  FIGS. 17 and 18 . In at least some embodiments, the effective back rake angles θ 1  and θ 2  of the corresponding cutting elements  10  and  20  may be within a range of from about thirty degrees (30°) negative back rake to about forty-five degrees (45°) positive back rake relative to the reference plane  500 . Subterranean formation cuttings may be deflected over and across the flat cutting surfaces  18  and  28  in directions that may be up and away from the surface  300  of the subterranean formation. 
     A magnitude of each of the effective rake angles θ 1  and θ 2  may be at least partially determined by an orientation in which each of the respective cutting elements  10  and  20  is attached to the earth-boring tool. With continued reference to  FIGS. 9-18 , each of the cutting elements  10  and  20  may be attached to the earth-boring tool as to include respective physical back rake angles π 1  and π 2  that may be negative (i.e., physical forward rake), positive (i.e., physical back rake), or neutral (i.e., physical neutral rake). The physical back rake angles π 1  and π 2  may be considered negative where at least a portion of the respective longitudinal axes  11  and  21  extending through the respective cutting elements  10  and  20  are behind the reference plane  500  (i.e., the longitudinal axes  11  and  21  form an obtuse angle with the surface of the subterranean formation  300 ), as in depicted in  FIGS. 9, 10, and 15-18  (the vertically opposite physical back rake angles π 1  and π 2  being marked therein). The physical back rake angles π 1  and π 2  may be considered positive where at least a portion of the corresponding longitudinal axes  11  and  21  extending through the cutting elements  10  and  20  are ahead the reference plane  500  (i.e., the longitudinal axes form an acute angle with the surface of the subterranean formation  300 ), as depicted in  FIGS. 11 and 12  (the vertically opposite physical back rake angles η 1  and π 2  being marked therein). The physical back rake angles π 1  and π 2  may be considered neutral where the corresponding longitudinal axes  11  and  21  are parallel with the reference plane  500 , as depicted in  FIGS. 13 and 14 . 
     The magnitude of each of the effective back rake angles θ 1  and θ 2  may also be affected by the magnitudes of the angles α 1  and α 2  between the longitudinal axes  11  and  21  and the flat cutting surfaces  18  and  28 , respectively. The magnitudes of the angles α 1  and α 2  may be influenced at least by the respective locations of the apex  17  and the apex  27  on the corresponding cutting tips  13  and  23 , the length of the respective flat cutting surfaces  18  and  28 , and the respective angles φ 1  and φ 2  between the corresponding generally conical surfaces  16  and  26  and the corresponding phantom lines extending from the generally cylindrical lateral side surfaces  15  and  25  of the cutting elements  10  and  20 . 
     The physical back rake angles π 1  and π 2 , the size and shape of the flat cutting surfaces  18  and  28 , and the effective back rake angles θ 1  and θ 2  of the cutting tips  13  and  23 , respectively, may each be tailored to optimize the performance of the cutting elements  10  and  20  for the earth-boring tool being used and characteristics of the surface  300  of the subterranean formation  300 . The non-limiting embodiments illustrated in  FIGS. 9-18  include different combinations of these variables that may result in effective back rake angles θ 1  and θ 2  of between about thirty degrees (30°) negative back rake and about forty-five degrees (45°) positive back rake of the reference plane  500 . 
       FIGS. 9 and 10  illustrate that the cutting elements  10  and  20  may be formed and oriented on an earth-boring tool such that the corresponding physical back rake angles π 1  and π 2  are negative (i.e., physical forward rake) and the effective back rake angles θ 1  and θ 2  are negative (i.e., effective forward rake).  FIG. 9  shows the side perspective view of the embodiment of the cutting element  10  illustrated in  FIG. 1 , as oriented on the earth-boring tool to include a physical back rake angle π 1  that is negative.  FIG. 10  shows the side perspective view of the embodiment of the cutting element  20  illustrated in  FIG. 4 , as oriented on the earth-boring tool to include a physical back rake angle π 2  that is negative. In embodiments including relatively larger angles α 1  and α 2 , the corresponding effective back rake angles θ 1  and θ 2  may be closer to neutral. In embodiments including relatively larger angles α 1  and α 2 , the corresponding physical rake angles π 1  and π 2  may be more negative to facilitate effective back rake angles θ 1  and θ 2  that are negative. Conversely, in embodiments including relatively smaller angles α 1  and α 2 , the corresponding physical back rake angles π 1  and π 2  may be less negative (i.e., closer to zero degrees), while still including effective back rake angles θ 1  and θ 2  that are negative. 
       FIGS. 11 and 12  illustrate that the cutting elements  10  and  20  may be formed and oriented on an earth-boring tool such that the corresponding physical back rake angles π 1  and π 2  are positive (i.e., physical back rake) and the respective effective back rake angles θ 1  and θ 2  are positive (i.e., effective back rake).  FIG. 11  shows the side perspective view of the embodiment of the cutting element  10  illustrated in  FIG. 1 , as oriented on the earth-boring tool to include a physical back rake angle π 1  that is positive.  FIG. 12  shows the side perspective view of the embodiment of the cutting element  20  illustrated in  FIG. 4 , as oriented on the earth-boring tool to include a physical back rake angle π 2  that is positive. In embodiments including relatively larger angles α 1  and α 2 , the corresponding effective back rake angles θ 1  and θ 2  may be more positive. In embodiments including relatively larger angles α 1  and α 2 , the corresponding physical rake angles π 1  and π 2  may be more negative to facilitate effective back rake angles θ 1  and θ 2  that are within forty-five degrees (45°) of positive back rake angle relative to the reference plane  500 . Conversely, in embodiments including relatively smaller angles α 1  and α 2 , the corresponding physical rake angles π 1  and π 2  may be more positive while still including respective back rake angles θ 1  and θ 2  within forty-five degrees (45°) of positive back rake angle relative to the reference plane  500 . 
       FIGS. 13 and 14  illustrate that cutting elements  10  and  20  may be formed and oriented on an earth-boring tool such that the corresponding effective back rake angles θ 1  and θ 2  are positive (i.e., effective back rake), and respective physical back rake angles π 1  and π 2  are neutral (i.e., physical neutral rake).  FIG. 13  shows the side perspective view of the embodiment of the cutting element  10  illustrated in  FIG. 1 , as oriented on the earth-boring tool to include a physical back rake angle π 1  that is neutral.  FIG. 14  shows the side perspective view of the embodiment of the cutting element  20  illustrated in  FIG. 4 , as oriented on the earth-boring tool to include a physical back rake angle π 2  that is neutral. The magnitudes of the angles α 1  and α 2  may affect the sign and magnitude of the effective back rake angles θ 1  and θ 2 . In embodiments including relatively larger angles α 1  and α 2 , the corresponding effective back rake angles θ 1  and θ 2  may be closer to forty-five degrees (45°) of positive back rake angle relative to the reference plane  500 . In embodiments including relatively smaller angles α 1  and α 2 , the corresponding effective back rake angles θ 1  and θ 2  may be closer to neutral. 
       FIGS. 15 and 16  illustrate that cutting elements  10  and  20  may be formed and oriented on an earth-boring tool such that the corresponding the effective back rake angles θ 1  and θ 2  are positive (i.e., effective back rake), and the respective physical back rake angles π 1  and π 2  are negative (i.e., physical forward rake).  FIG. 15  shows the side perspective view of the embodiment of the cutting element  10  illustrated in  FIG. 1 , as oriented on the earth-boring tool to include a physical back rake angle π 1  that is negative.  FIG. 16  shows the side perspective view of the embodiment of the cutting element  20  illustrated in  FIG. 4 , as oriented on the earth-boring tool to include a physical back rake angle π 2  that is negative. In embodiments including relatively larger angles α 1  and α 2 , the corresponding effective back rake angles θ 1  and θ 2  may be more positive. In embodiments including relatively larger angles α 1  and α 2 , the corresponding physical rake angles π 1  and π 2  may be more negative to facilitate effective back rake angles θ 1  and θ 2  that are about forty-five degrees (45°) of positive back rake to the reference plane  500  or less. Conversely, in embodiments including relatively smaller angles α 1  and α 2 , the effective back rake angles θ 1  and θ 2  may be closer to neutral. In at least some embodiments including relatively smaller angles α 1  and α 2 , the corresponding physical back rake angles π 1  and π 2  may be more positive to facilitate effective back rake angles θ 1  and θ 2  that are negative. 
       FIGS. 17 and 18  illustrate that cutting elements  10  and  20  may be formed and oriented on an earth-boring tool such that the corresponding the effective back rake angles θ 1  and θ 2  are neutral (i.e., effective back rake), and the physical back rake angles π 1  and π 2  are negative (i.e., physical forward rake).  FIG. 17  shows the side perspective view of the embodiment of the cutting element  10  illustrated in  FIG. 1 , as oriented on the earth-boring tool to include a physical back rake angle π 1  that is negative.  FIG. 18  shows the side perspective view of the embodiment of the cutting element  20  illustrated in  FIG. 4 , as oriented on the earth-boring tool to include a physical back rake angle π 2  that is negative. In embodiments including relatively larger angles α 1  and α 2 , the corresponding physical back rake angles π 1  and π 2  may be more negative to facilitate corresponding effective back rake angles θ 1  and θ 2  that are neutral. Conversely, in embodiments including relatively smaller angles α 1  and α 2 , the corresponding physical back rake angles π 1  and π 2  may be more positive to facilitate corresponding effective back rake angles θ 1  and θ 2  that are neutral. 
     The enhanced shape of the cutting elements described herein may be used to improve the behavior and durability of the cutting elements when drilling in subterranean earth formations. The shape of the cutting elements may allow the cutting element to fracture and damage the formation, while also providing increased efficiency in the removal of the fractured formation material from the subterranean surface of the wellbore. The shape of the cutting elements may be used to provide a positive, negative, or neutral effective back rake angle, regardless of whether the cutting element has a positive, negative, or neutral physical back rake angle. 
     While the present invention has been described herein with respect to certain embodiments, those of ordinary skill in the art will recognize and appreciate that it is not so limited. Rather, many additions, deletions and modifications to the embodiments described herein may be made without departing from the scope of the invention as hereinafter claimed, including legal equivalents. In addition, features from one embodiment may be combined with features of another embodiment while still being encompassed within the scope of the invention as contemplated by the inventor.