Patent Publication Number: US-9840876-B2

Title: Polycrystalline diamond compact cutter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. Section 119(e) from U.S. Provisional Patent Application Ser. No. 62/060,265, filed on 6 Oct. 2014, entitled “POLYCRYSTALLINE DIAMOND COMPACT CUTTER”. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     THE NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not applicable. 
     INCORPORATION-BY-REFERENCE OM MATERIAL SUBMITTED ON A COMPACT DISC OR AS A TEXT FILE VIA THE OFFICE ELECTRONIC FILING SYSTEM (EFS-WEB) 
     Not applicable. 
     STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINT INVENTOR 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to cutting elements on a drill bit. More particularly, the present invention relates to polycrystalline diamond compact cutters on a drill bit. Even more particularly, the present invention relates to polycrystalline diamond compact cutters having different zones of thermal stability and hardness. 
     2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98 
     Polycrystalline diamond compact (PDC) cutters are used in drilling operations for oil and gas. Prior art drill bits were roller cone bits with multiple parts and rotating surfaces to grind through the rock formation. Newer drill bits were fixed-head bits, which were composed of a single part without any moving components. The fixed-head bits could be rotated by the drill string, so additional moving parts on the bit were not needed. Cutters attached to a fixed-head surface grind through a rock formation. The fixed cutters were more reliable under extreme heat and pressure conditions of the wellbore because there were no moving components. However, the wear on these cutters was substantial. The material composition of the cutters has evolved to extend the working life and to increase productivity of the cutters. 
     Diamond is the hardest material known, so cutters of diamond composition have been pursued. Bonding diamond to metal is a challenge, so the drill bits evolved from steel to composite materials, in particular, tungsten carbide. Tungsten carbide composite readily bonds to diamond. The basic prior art cutter is comprised of a diamond table made from diamond grit with a formation agent and a substrate of tungsten carbide. The formation agent is a metallic binder, usually cobalt. The diamond grit is sintered under high temperature and high pressure conditions, forming a layer bonded to the tungsten carbide or other substrate with the formation agent as a catalyst. The High Temperature-High Pressure (HT-HP) press can form the layer with a Cobalt or other Group VIII element as the catalyst, and the properties of the layer have been modified for various thicknesses, profiles, and patterns to affect the working life of the cutters. Alternatively, the diamond table can be sintered and removed from the substrate. The diamond table as a disk can undergo leaching for the removal of metal content, without the substrate. Then, the leached disk can be replaced on a substrate to form a cutter. The formation agent, such as a cobalt compound, is the binder in this formation of a cutter. 
     PDC cutters face additional problems, during drilling operations in the oil and gas industry. Down the wellbore, the drilling conditions are extreme. There can be excessive heat, over 750 degrees Celsius, which causes thermal expansion of the diamond-binder bond in the diamond table. The PDC cutter weakens when the binder expands and the diamond table is less stably mounted on the substrate. The diamond surface is more likely to become damaged or dislodged from the substrate. The PDC cutter is tough, but limited by thermal expansion problems. 
     The prior art has further modified PDC cutters, according to the limitations of the diamond-binder bond. For example, once sintered to the tungsten carbide substrate, the Cobalt binder can be removed from the diamond table in a process called “leaching”. The PDC cutter lasts longer without as much thermal expansion, but the PDC cutter fractures more easily. Adjusting for the thermal stability, the PDC cutter loses toughness. 
     Various patents and patent applications disclose selective leaching to form layers of different thermal stability and toughness. Various shapes of the layers at various depths are also disclosed. 
     United States Publication No. 20140166371, published for Whittaker on Jun. 19, 2014, and United States Publication No. 20110056141, published for Miess, et al. on Mar. 10, 2011, both disclose methods for selective leaching. There can be a deep leach or a shallow leach. Masking can be used to set the layers so that the Cobalt or other binder can be removed at different rates and depths in the diamond table. Various shapes and patterns are disclosed as possible with this method. Besides masking, other additives can be added to form the desired pattern of leached diamond composite. United States Publication No. 20140069726, published for Mumma, et al. on Mar. 13, 2014, discloses a hydrophile additive. 
     Other patents disclose a particular arrangement of layers. U.S. Pat. No. 8,197,936, issued to Keshavan on Jun. 12, 2012, discloses a first thermally stable polycrystalline diamond layer, a second carbide substrate layer, and a third polycrystalline cubic boron nitride layer. The layers are in a particular configuration with the third layer surrounded by the first and second layer. U.S. Pat. No. 8,567,531, issued to Belnap et al on Oct. 29, 2013, covers an even more specific arrangement of layers and range of physical properties. U.S. Pat. No. 7,972,395, issued to Dadson on Mar. 13, 2014, discloses a system and method for processing a polycrystalline material with the specific recipe of the complexing agent. 
     It is an object of the present invention to provide a cutting element with thermal stability and toughness. 
     It is an object of the present invention to provide a cutting element with a balance of thermal stability and toughness in designated critical regions for extending the working life of the cutter. 
     It is another object of the present invention to provide a cutting element with a balance of thermal stability and toughness at a working edge of the cutting element to a worn edge of the cutting element. 
     It is an object of the present invention to provide a cutting element with a plurality of zones of different thermal stability and toughness. 
     It is another object of the present invention to provide a cutting element having zones of different metal content percentages. 
     It is still another object of the present invention to provide a cutting element having an arrangement of different metal content percentages in the diamond table. 
     It is an object of the present invention to provide a cutting element having an interrelationship of zones of different metal content percentages in the diamond table to affect working life. 
     It is an object of the present invention to provide a cutting element having an interrelationship of zones of different metal content percentages in the diamond table to account for cutting angle across the cutter. 
     It is an object of the present invention to provide a cutting element with a working life determined by wear resistance and impact resistance. 
     It is another object of the present invention to provide a cutting element with an interrelationship of zones of different metal content percentages in the diamond table setting wear resistance and impact resistance of the cutter. 
     These and other objectives and advantages of the present invention will become apparent from a reading of the attached specification. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the polycrystalline diamond compact cutter of the present invention include a diamond table comprised of polycrystalline diamond particles and a formation agent, and a carbide substrate. The diamond table has a cylindrical profile with a top surface, a bottom surface, and a working edge around the top surface, and the carbide substrate bonds to the bottom surface of the diamond table. The formation agent is a metal compound, usually cobalt. The thermal stability and toughness of the cutter are balanced by selective leaching of different zones in the diamond table to set weight percentage metal content of each zone. The interrelationship of the zones extends working life of the cutter and effectiveness of the cutter. 
     There is a thermally stable zone comprising a first portion of the diamond table and forms at least a part of the top surface. There is a base zone comprising a second portion of the diamond table. The base zone bonds to the carbide substrate on the bottom surface. There is an anchor zone comprising a third portion of the diamond table. The anchor zone sets between the thermally stable zone and the base zone. There is also an absorbing zone comprising a fourth portion of the diamond table. The absorbing zone is circumscribed by thermally stable zone and anchor zone and extends from the top surface to the base zone. At least another part of the top surface is formed by the absorbing zone. 
     In embodiments of the invention, thermally stable zone extends over the anchor zone and down from the top surface so as to be adjacent to the base zone. The base zone attaches the anchor zone, the absorbing zone, and the thermally stable zone to the substrate. The thermally stable zone has a weight percentage metal content less than the anchor zone, the absorbing zone, and the base zone. The anchor zone has a weight percentage metal content less than the base zone, and the base zone has a weight percentage metal content less than the absorbing zone. The absorbing has a weight percentage metal content greater than the anchor zone, the absorbing zone, and the thermally stable zone. In some embodiments, the amount of difference in weight percentage metal content between zones is also balanced for thermal stability and toughness. 
     The arrangement and relative weight percentage metal content of the zones of the present invention balance thermal stability and toughness. The interrelationship between the zones also accounts for the position of the cutter against the formation to be cut and the relative wear on the cutter because of the angle of the cut and position relative to the formation. The working edge remains thermally stable and stronger to cut, even as the thermally stable zone is worn. The anchor zone adds toughness, while still remaining thermally stable enough to be effective as a working edge, when the cutter is worn. The absorbing zone has greater toughness to prevent breakage and release from the substrate, while the working edge progresses through the thermally stable zone and the anchor zone. 
     Embodiments of the present invention include the thermally stable zone extending downward from the top surface more than 500 micrometers. The thermally stable zone can also extend downward from the top surface less than or equal to 60% of a distance between the top surface and the bottom surface of the diamond table. In some embodiments, the thermally stable zone circumscribes the absorbing zone along the working edge, as a ring shape. As a ring shape, the ring is thick. The thermally stable zone can extend inward from the working edge at least 25% of a diameter of the diamond table. 
     The base zone forms the bottom surface of the diamond table, and the anchor zone circumscribes the absorbing zone. Similarly, the anchor zone can have a ring shape placed between the thermally stable zone and the base zone and around the absorbing zone. The anchor zone is a transition from the thermally stable efficient cutting of the thermally stable zone to the tougher base zone and absorbing zone. 
     Embodiments of the invention include the absorbing zone being centered over the base zone and surrounded by the thermally stable zone at the top surface. The absorbing zone is surrounded by the anchor zone beneath the top surface. The absorbing zone can abut the thermally stable zone at an inclined face, slanted downward from the top surface. The absorbing zone is a thick core of the cutter, ending before at least 25% of a diameter of the diamond table. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a schematic view of a cutter engaging a formation in a drilling operation. 
         FIG. 2  is a schematic view of an embodiment of the cutter of the present invention. 
         FIG. 3  is a partial sectional view of an embodiment of the cutter according to the present invention. 
         FIG. 4  is a photo representation of a scanning electron microscope in analysis of weight percentage metal content. 
         FIG. 5  shows other photo representations of a scanning electron microscope view of a thermally stable zone of the diamond table of the present invention. 
         FIG. 6  is a schematic view of embodiment of a cutter being set for selective leaching to form zones of the present invention. 
         FIG. 7  is a graph illustration of the weight percentage metal content of zones of the cutter according to the present invention. 
         FIG. 8  is a graph illustration of fracture toughness as related to grain size of the cutter according to the present invention. 
         FIG. 9  is a graph illustration of the toughness as wear resistance and impact resistance of the cutter according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In a drilling operation illustrated in  FIG. 1 , the cutter  1  slices through the formation  2 . Various obstacles  3 , such as minerals, ore, and impurities are interspersed throughout the formation  2 . The cutter must power through to remove both formation  2  and obstacles  3 . The cutter  1  experiences a lateral force  4  along the surface of the formation  2  and an upward force  5  perpendicular to the surface of the formation  2 . The forces are not directly flush against a surface of the cutter  1 , especially with obstacles  3  in the formation  2 . The wear on the cutter  1  can also uneven across the surfaces of the cutter  1 . The present invention is a cutting element to account for these variations by balancing thermal stability and toughness. The cutting element of the present invention is tough enough to cut through the formation and withstand the disruptive torsional forces trying to dislodge the cutting element from the bit. The relationship between the placement and relative weight percentage metal content of different zones in the present invention control thermal stability and toughness of the cutter or cutting elements so that zones are have resiliency and durability in different portions of the diamond table for an extended working life through actual drilling conditions. 
     Referring to  FIGS. 2-3 , an embodiment of the polycrystalline diamond compact cutter  10  of the present invention is shown. The cutter  10  includes a diamond table  20  comprised of polycrystalline diamond particles and a formation agent, and a carbide substrate  40 . The diamond table  20  has a cylindrical profile with a top surface  12 , a bottom surface  14 , and a working edge  16  around the top surface  12 . The carbide substrate  40  bonds to the bottom surface  14 . In some embodiments, the diamond table  20  is comprised of polycrystalline diamond particles and a formation agent, usually cobalt. The diamond particles bond to other diamond particles and the formation agent as a catalyst, during sintering to form the diamond table. The distribution of grain size of the diamond particles and the formation agent set the initial amounts of metal content. Alternatively, the formation agent can be a binder. A pre-formed diamond table disk, previously formed by sintering and previous leached for different layers of metal content, can be re-attached to a carbide substrate with the formation agent being a binder. A formation agent is a metal compound. When heat expands the formation agent, the bonds with the diamond particles can break, and the expanding formation agent can also break the bonds between diamond particles. The conventional formation agent as a binder or catalyst is comprised of metal, such as cobalt. The weight percentage metal content is an indicator of the amount of metal present. 
     The diamond table  20  is comprised of a first portion, second portion, third portion, and a fourth portion. Each portion corresponds to a zone. Thermal stability and toughness of the cutter  10  are balanced by selective leaching of different zones in the diamond table  20  to account for extending working life of the cutter  10  and effectiveness of the cutter  10  as positioned relative to the formation in an actual drilling operation. The selective leaching removes formation agent, in particular, the metal compound. The initial formation by distribution of grain size and the formation agent during sintering or initial formation with an alternate metal content can undergo selective leaching for physical properties and relative positions of the different zones enable the particular effectiveness and working life of the cutter  10  of the present invention. 
       FIGS. 2-3  show an embodiment of the diamond table  20  with a thermally stable zone  22  being comprised of a first portion of the diamond table  20  and forming at least a part of the top surface  12 . There is a base zone  24 , being comprised of a second portion of the diamond table  20  and bonding to the carbide substrate  40  on the bottom surface  14 . There is an anchor zone  26 , being comprised of a third portion of the diamond table  20  and being set between the thermally stable zone  22  and the base zone  24 . There is also an absorbing zone  28 , being comprised of a fourth portion of the diamond table  20 . The absorbing zone  28  is surrounded by thermally stable zone  22  and anchor zone  26  and extends from the top surface  12  to the base zone  24 . At least another part of the top surface  12  is formed by the absorbing zone  28 . The thermally stable zone  22  extends over the anchor zone  26  and adjacent to the base zone  24  from the top surface  12 . The base zone  24  attaches the anchor zone  26 , the absorbing zone  28 , and the thermally stable zone  22  to the carbide substrate  40 . 
     According to embodiments of the invention, the thermally stable zone  22  has a weight percentage metal content less than the anchor zone  26 , the absorbing zone  28 , and the base zone  24 . The thermally stable zone  22  has the least metal content for the most stable zone. There is less metal content so that the thermally stable zone  22  expands the least. With less metal, there is less expansion and breakage of links between diamond particles. The thermally stable zone  22  initial forms a working edge  16  of the diamond table  20  to cut the rock formation. The anchor zone  26  has a weight percentage metal content less than the base zone  24 , and the base zone  24  has a weight percentage metal content less than the absorbing zone  28 . The absorbing zone  28  has a weight percentage metal content greater than the anchor zone  26 , the base zone  24 , and the thermally stable zone  22 . 
     Metal content is inversely related to thermal stability and directly related to toughness. With more metal content in the anchor zone  26  than the thermally stable zone  22 , the diamond table  20  has an extended working life. The diamond table  20  retains the superior cutting of the thermally stable zone  22  for cutting efficiency, and the additional tough backing by the anchor zone  26  supports thermally stable zone  22  for this cutting efficiency. The absorbing zone  28  also supports the thermally stable zone  22  in an actual drilling orientation. The top surface  12  of the diamond table includes the thermally stable zone  22  and the absorbing zone  28 , the least and most metal content. The cut angle of the diamond table  20  in the rock formation forms the working edge  16  only in the thermally stable zone  22 , so that the least metal content is not needed across the entire top surface  12 . The present invention balances the need for the cutting efficiency with the absorbing zone  28  having more metal content and more toughness to resist impacts. The top surface  12  is not uniform so as to account for fracture toughness and cutting efficiency. 
       FIG. 4-6  show embodiments of the cutter  10  of the present invention.  FIGS. 4 and 5  show measurement of the metal content percentage by Scanning Electron Microscope (SEM) to do EDAX analysis within diamond. The thermally stable zone  22  can be identified from  FIG. 4  and mapped to the presentation in  FIG. 5 . The top dark layer in  FIG. 5  represents the thermally stable zone  22 .  FIG. 6  shows the cutter  10  with the diamond table  20  and the carbide substrate  40  after sintering. Using grain size distribution, the metal content of the diamond table  20  is initially set. In some embodiments, the fourth portion to become the absorbing zone  28  has the most coarse and largest grains to hold the most metal content. The first and third portions to become the thermally stable zone  22  and the anchor zone  26  have the finest grains for the most effective cutting surface.  FIG. 6  shows selective leaching to remove metal content from the first and third portions. The leaching process exposes the cutter  10  to a mixture of chemicals, most notably acid. The leaching activity the first and third portion and drips down to the second portion, which becomes the base zone  24 . In some embodiments, the second portion also has finer grains, so that the weight percentage of metal content is initially set by sintering. Other techniques, such as laser removal or the formation agent as binder, can be used to set the zones  22 ,  24 ,  26 ,  28  of the diamond table  20 . The cutter  10  of the present invention can be assembled with known techniques in the field of polycrystalline diamond compact cutters. Sintering with grain size distribution of the diamond particles and a metal formation agent as catalyst is one example. 
     For a sample cutter  10  of the present invention with Cobalt as the metal, EDAX analysis from a scanning electron microscope, according to  FIGS. 4-5 , shows one example of metal content percentage as: 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Zone 
                 Metal Content Percentage 
                 Error 
               
               
                   
                   
               
             
            
               
                   
                 Anchor zone 
                  Co 8.5% + W 2.5% 
                 +/−1% 
               
               
                   
                 Base zone 
                 Co 10.1% + W 3.3% 
                 +/−1% 
               
               
                   
                 Absorbing zone 
                 Co 10.5% + W 4.0% 
                 +/−1% 
               
               
                   
                   
               
            
           
         
       
     
     In the present invention, the amount of difference in weight percentage metal content can also be disclosed. The zones  22 ,  24 ,  26 ,  28  can be different, but not too different so that the zones  22 ,  24 ,  26 ,  28  remain interactive to achieve the extended working life. The entire diamond table  20  should remain attached to the carbide substrate  40 , without individual zones  22 ,  24 ,  26 ,  28  breaking loose. In some embodiments, the base zone  24  has a weight percentage metal content less than or equal to 0.135e 1.187x , wherein x is weight percentage metal content of the anchor zone  26 . Also, the absorbing zone  28  has a weight percentage metal content less than or equal to 0.135e 1.187y , wherein y is weight percentage metal content of the base zone  24 .  FIG. 7  shows weight percentage metal content according to grain size between two zones in a graph illustration. A zone can be identified by grain size from the sintering or other initial formation process. There is a linear approximation for a smooth gradient transition of the diamond grain size changes. In  FIG. 7 , the grain size of the absorbing zone  28  can be identified between 0.12 and 0.13, which relates to a weight percentage metal content. According to the invention, the weight percentage metal content of the base zone  24  must be selected within the range identified by the dotted line between 0.12 and 0.13. The grain size of the base zone  24  can be different, so the base zone  24  may need leaching to fit the desired relationship to the absorbing zone  28 . Similarly, the grain size of the base zone  24  can be identified between 0.09 and 0.10, which relates to a weight percentage metal content. According to the invention, the weight percentage metal content of the anchor zone  26  must be selected within the range identified by the dotted line between 0.09 and 0.10. 
     In the embodiment of  FIG. 7 , the difference between the anchor zone  26  and the base zone  24  can be larger, while the difference between base zone  24  and the absorbing zone  28  can be smaller. The relationship prevents a thermal mismatch, which affects cutter performance. One zone expanding relative to another zone may affect the integrity of the diamond table  20  too much or dislodge the diamond table  20  from the carbide substrate  40 . The toughness must stay within a range so that zones remain bonded to each other and the brittleness of the lower metal content is balanced by toughness. 
     The relative weight percentage metal content balances the base zone  24  to be tougher and less thermally stable than the absorbing zone  28  by a certain amount. The weight percentage metal content of the thermally stable zone  22  is less than any other zone. The thermally stable zone  22  is the least tough portion with little metal content, as needed for the working edge  16  of the cutter  10 . The thermally stable zone  22  is the best cutting portion with high diamond content, but has less toughness. The thermally stable zone  22  may still wear and be less bonded to the substrate  40  without any binder catalyst. The other zones  24 ,  26  and  28  balance this “sharpest” portion of the cutter  10  with additional toughness to stay attached to the substrate  40 . 
     The arrangement and relative weight percentage metal content of the zones of the present invention balance thermal stability and toughness. The arrangement and relationship between zones accounts for the position of the cutter against the formation to be cut and the relative wear on the cutter because of this angle and position relative to the formation. For wear, the working edge  16  moves across the thermally stable zone  22  on the top surface  12  and down toward the base zone  24  on the side. As the diamond table  20  wears, the anchor zone  26  can also start to form the working edge  16 . The metal content of the anchor zone  26  remains sufficient for cutting efficiency and tougher to withstand impacts deeper into the cutter  10 . 
     Embodiments of the present invention in  FIGS. 2-3  include the thermally stable zone  22  extending downward from the top surface  12  more than 500 micrometers. The thermally stable zone can also extend downward from the top surface  12  less than or equal to 60% of a distance between the top surface  12  and the bottom surface  14  of the diamond table  20 , as shown in  FIG. 3 . In some embodiments, the thermally stable zone  22  circumscribes the absorbing zone  28  along the working edge  16 , as a ring shape. As a ring shape, the ring is thick. The thermally stable zone  22  can extend inward from the working edge  16  at least 25% of a diameter of the diamond table  20 . The depth of the thermally stable zone  22  relative to the thickness of the diamond table  20  limits the cutting torque and prevents the diamond table  20  from dislodging from the substrate  40 . A portion is a stable cutting surface, which may wear and be less stably attached. The other zones support and balance the toughness. 
     The base zone  24  forms the bottom surface  14  of the diamond table  20 . The base zone  24  is bonded to the carbide substrate at seal  32  shown in  FIGS. 2 and 6 . The base zone  24  centers the diamond table  20  and can extend the full diameter of the carbide substrate. Impact energy to the top surface  12  of the diamond table is absorbed by the base zone  24  by axial vibration, when the impact energy is normal to the top surface  12 . The base zone  24  remains adjacent or touching the three other zones. There can be a thickened area, which is also thermally stable. The base zone  24  prevents the diamond table  20  from dislodging from the substrate. In some cutting angles, a corner of the base zone  24  may cut the formation before engaging the anchor zone  26 . 
     The anchor zone  26  circumscribes the absorbing zone  28 . In some embodiments, the anchor zone  26  can have a compatible ring shape placed between the thermally stable zone  22  and the base zone  24 , within the thermally stable zone  22  and around the absorbing zone  28 . The anchor zone  26  is a transition from the thermally stable efficient cutting of the thermally stable zone  22  to the tougher base zone  24  and absorbing zone  28 . If the thermally stable zone  22  is worn, cutting capability is maintained by the anchor zone  26 . In the arrangement of the present invention, the position of the anchor zone  26  and thermally stable zone  22  relative to the base zone  24  and absorbing zone  28  allows effective cutting of the formation without loss of resilience and toughness of the base zone  24 . 
       FIG. 3  shows the embodiment of the absorbing zone  28  being centered over the base zone  24  and surrounded by the thermally stable zone  22  at the top surface  12 . The absorbing zone  28  can be surrounded by the anchor zone  26  beneath the top surface  12  too. The absorbing zone  28  abuts the thermally stable zone at an inclined face  34 , slanted downward from the top surface  12 . The absorbing zone  28  is a thick core of the cutter  10 , ending before at least 25% of a diameter of the diamond table  20  and extending from the top surface to the base zone  24 . The absorbing zone  28  is less thermally stable, but has greater toughness to withstand and absorb forces from drilling the formation. The torsional forces of the rotating bit against the formation are absorbed so that the diamond table  20  remains stably affixed to the substrate  40 . The lateral force along the surface of the formation are also resisted and absorbed by the absorbing zone  28  at the top surface  12 . The absorbing zone  28  balances the superior cutting ability of the thermally stable zone  22  at that top surface  12  for an effective arrangement accounting for actual position of the cutter  10  in a drilling operation. 
       FIG. 8  shows fracture toughness related to grain size. From a sintered cutter, grain size can determine fracture toughness, as in the follow table: 
                                             Grain Size   Fracture Toughness                                                    5   10.8           25   12           45   13.8           70   15                        
Without selective leaching, the cutter has portions set by the grain size of the diamond particles. The distribution of grain size relates to fracture toughness by the amount of metal content. As coarser particles hold more metal, these portions are tougher. In the present invention, the cutter forms portions with an interrelationship of thermal stability and toughness. Zones without the same grain size are adjusted for the actual cutting angle application and improved cutting efficiency and toughness. The present invention balances metal content of the zones of different grain sizes in a formation for extending working life of the cutter.
 
       FIG. 9  shows a graph illustration of the working life of the cutter related to wear resistance and impact resistance. The data of the graph matches the table as follows: 
                                     Grain Size   Wear Resistance   Impact Resistance                                            5   100%    67%       25   70%   73%       45   52%   87%       70   35%   100%                     
The working life of the cutter  10  relates to wear resistance, which corresponds to less metal content, and impact resistance, which corresponds to fracture toughness. The thermally stable zone has the best cutting efficiency because there is the least metal content of all zones. The thermally stable zone as the cutting surface is not subject to much heat expansion due to the lack of metals. The remaining zones adjust according to the invention for a longer lasting cutter. Even with the same grains in the thermally stable zone and the anchor zone, the wear resistance and impact resistance are balanced to account for the cutting efficiency at an actual cutting angle and for extending the working life of the cutter. In the present invention, embodiments include a base zone of grain size between the thermally stable zone and the anchoring zone with a metal content to affect the relationship between the thermally stable zone, the anchor zone, and the absorbing zone. The differences on wear resistance and impact resistance of the present invention increase the working life of the cutter in the claimed relationship. The present invention moves beyond simply removing metal content to be more thermally stable and wear resistant. Each zone, relative placement of each zone, and the cutting angle contributes to the relationship between zones as claimed to extending working life of the cutter or cutting element.
 
     Embodiments of the present invention provide a polycrystalline diamond compact cutter as a cutting element against a formation. The four zones of the diamond table of the cutting element interact with each other to balance of thermal stability and toughness in designated critical regions for extending the working life of the cutter. The pattern and relative thermal stabilities and toughness set a particular cutting efficiency and working life. The diamond table is balanced through the designated critical portions of the diamond table. The cutter of the present invention accounts for the actual position of the cutter relative to the formation and forces encountered from the formation. The working edge wears from the thermally stable zone to the anchor zone with different toughness. The working edge remains effective and attached was the amount of wear increases. The superior cutting ability of thermally stable diamond is balanced with toughness to remain intact and attached to the substrate. The best cutting surface is isolated at the working edge of the cutter and can move deeper into the cutter with adjusted toughness. The toughest portion is isolated at the center of the cutter. Forces to dislodge the diamond table from the substrate are countered by the arrangement of different zones with different relative weight percentage metal content. 
     Embodiments of the present invention include zones of different thermal stability and toughness. The zones can have different metal content percentages and an arrangement of different metal content percentages in the diamond table. The position and relative toughness of different metal content percentages in the diamond table to affect working life in actual drilling conditions with cutting across the cutter. The working life determined by wear resistance and impact resistance is set by the relationship of the zones with different orientations relative to each other and different metal content percentages in the diamond table 
     The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated structures, construction and method can be made without departing from the true spirit of the invention.