Patent Publication Number: US-2015075252-A1

Title: Method Of Determining Wear Abrasion Resistance Of Polycrystalline Diamond Compact (PDC) Cutters

Description:
TECHNICAL FIELD 
     The present invention relates generally to methods for testing PDC cutters or other superhard components; and more particularly, to methods for testing and evaluating the abrasive wear resistance of PDC cutters or other superhard components. 
     BACKGROUND 
     Down-hole tools used in drilling operations typically include a superhard component, such as a cutter inserted with the down-hole tool. The superhard component cuts or grinds away rock bits to create path in a rock formation for the remainder of the tool or tool string. The superhard component typically includes a cutting table fabricated from a superhard material such as polycrystalline diamond (“PCD”) or polycrystalline cubic boron nitride (“PCBN”). Common problems associated with these superhard components include chipping, spalling, partial fracturing, cracking, flaking, or dulling of the cutting table. These problems can result in the early failure of the cutting table. Typically, high magnitude stresses generated on the cutting table at the region where the cutting table makes contact with earthen formations during drilling can cause these problems. Such problems increase the cost of drilling due to costs associated with repair, production downtime, and labor costs. For these reasons, testing methods have been developed to ascertain the abrasion resistance and/or impact resistance of superhard components so that improved cutter longevity is achieved and the problems mentioned above are substantially reduced. 
     Superhard components, which include PDC cutters, have been tested for abrasive wear resistance through the use of two conventional testing methods. Early in the development of PDC materials, the abrasive wear resistance was tested using a conventional granite log test. However, as the PDC cutters became more wear resistant, and too much time and conventional target cylinders were required to complete the conventional granite log test, the conventional vertical turret lathe test (“VTL”) test replaced the conventional granite log test for testing abrasive wear resistance. Both the conventional granite log test and the vertical turret lathe test involved relative motion between the cutter and a target material, in which the cutter cuts away at the target material as it moves across a surface of the target material. In both the conventional vertical turret lathe test and the conventional granite log test, wear resistance of a cutter is determined as a ratio between the amount of target material removed and the amount of the cutting table of the cutter removed. This is known as a G-ratio and is commonly used to measure and compare cutter performance. However, the G-ratio is purely a geometric parameter and does not take into account the energetic efficiency of the cutting process. Specifically, two cutters with the same G-ratio may require very different cutting forces depending on the sharpness of the cutting table. Thus, these two cutters may require difference amounts of energy and thus have different effective lifetimes down-hole. However, the G-ratio is not indicative of this. 
     SUMMARY 
     According to an example embodiment of the present disclosure, a method of testing a superhard component includes obtaining a superhard material, obtaining a target material having a volume and a surface, and contacting the superhard material to the surface of the target material. The method further includes removing a portion of the target material with the superhard material by moving the superhard material along the surface of the target material with reference to the target material. The method measures a normal force applied to the superhard material by the surface of the target material, and determines a ratio between the normal force and the value of a first variable. 
     According to another aspect of the present disclosure, a method of determining relative wear resistance of superhard components includes obtaining a first data set from a first vertical turret lathe test of a first superhard material, in which the first data set comprises a first normal force and a first variable. The method also includes obtaining a second data set from a second vertical turret lathe test of a second superhard material, in which the second data set comprises a second normal force and a second variable. The method then determines a first ratio of the value of the first variable to the first normal force and also determines a second ratio of the value of the second variable to the second normal force. 
     According to yet another example embodiment of the present disclosure, a method of determining relative wear resistance of superhard components includes obtaining a first efficiency ratio of a first superhard material. The first efficiency ratio includes a ratio of a first amount of a first target material removed to a first normal force applied to the first superhard material by the first target material under a first set of test conditions. The method further obtains a second efficiency ratio of a second superhard material. The second efficiency ratio comprises a ratio of a second amount of a second target material removed to a second normal force applied to the second superhard material by the second target material under a second set of test conditions. The first wear resistance value is then compared to the second wear resistance value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and aspects of the invention are best understood with reference to the following description of certain exemplary embodiments, when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a superhard component that is insertable within a downhole tool in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 2  is a side view of a vertical turret lathe test for testing abrasive wear resistance of a superhard component, in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 3  is a flowchart of a method for testing the abrasive wear resistance of a superhard component, in accordance with exemplary embodiments of the present disclosure; 
         FIG. 4  is a flowchart of a method for ranking the abrasive wear resistance of multiple superhard components, in accordance with exemplary embodiments of the present disclosure; and 
         FIG. 5  is a graph of efficiency ratios for a plurality of superhard components, in accordance to exemplary embodiments of the present disclosure. 
     
    
    
     The drawings illustrate only exemplary embodiments of the invention and are therefore not to be considered limiting of its scope, as the invention may admit to other equally effective embodiments. 
     BRIEF DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The present invention is directed to a method and apparatus for testing the abrasive wear resistance of superhard components. Although the description of exemplary embodiments is provided below in conjunction with a PDC cutter, alternate embodiments of the invention may be applicable to other types of superhard components including, but not limited to, PCBN cutters or other superhard components known or not yet known to persons having ordinary skill in the art. Additionally, though the following description of example embodiments makes reference to vertical turret lathe testing techniques, alternative embodiments of the invention are used with other cutter testing techniques, include granite log testing techniques. 
     The invention is better understood by reading the following description of non-limiting, exemplary embodiments with reference to the attached drawings, wherein like parts of each of the figures are identified by like reference characters, and which are briefly described as follows.  FIG. 1  is a perspective view of a superhard component  100  that is insertable within a downhole tool (not shown) in accordance with an exemplary embodiment of the invention. One example of a superhard component  100  is a cutting element  100 , or cutter, for rock bits. The cutting element  100  typically includes a substrate  110  having a contact face  115  and a cutting table  120 . The cutting table  120  is fabricated using an ultra hard layer which is bonded to the contact face  115  by a sintering process. The substrate  110  is generally made from tungsten carbide-cobalt, or tungsten carbide, while the cutting table  120  is formed using a polycrystalline ultra hard material layer, such as polycrystalline diamond (“PCD”), polycrystalline cubic boron nitride (“PCBN”), or tungsten carbide mixed with diamond crystals (impregnated segments). These cutting elements  100  are fabricated according to processes and materials known to persons having ordinary skill in the art. The cutting element  100  is referred to as a polycrystalline diamond compact (“PDC”) cutter when PCD is used to form the cutting table  120 . PDC cutters are known for their toughness and durability, which allow them to be an effective cutting insert in demanding applications. Although one type of superhard component  100  has been described, other types of superhard components  100  can be utilized. 
       FIG. 2  is a side view of a vertical turret lathe test  200  for testing abrasive wear resistance of a superhard component  100 , in accordance with embodiments of the present disclosure. Although one exemplary apparatus configuration for the vertical turret lathe  200  is provided, other apparatus configurations can be used without departing from the scope and spirit of the exemplary embodiment. The vertical turret lathe test  200  includes a rotating table  214  and a tool holder  202  positioned above the rotating table  214 . The vertical turret lathe is used with a target cylinder  210  which is disposed atop the rotating table  214 . The target cylinder  210  has a first end  212 , a second end  204 , and a sidewall  208  extending from the first end  212  to the second end  204 . According to certain example embodiments, the second end  204  includes an exposed surface  206  which makes contact with a superhard component&#39;s cutting table  120  during the test. In an example embodiment, the target cylinder  210  is typically about thirty inches to about sixty inches in diameter, but can be smaller or larger depending upon the testing requirements. 
     The first end  212  of the target cylinder  210  is mounted on the lower rotating table  214  of the vertical turret lathe  200 , and the exposed surface  206  faces the tool holder  202 . The PDC cutter  100  is mounted in the tool holder  202  above the target cylinder&#39;s exposed surface  206  and makes contact with the exposed surface  206 . The target cylinder  210  is rotated via the rotating table  214  as the tool holder  202  cycles the PDC cutter  100  from the center of the conventional target cylinder&#39;s exposed surface  206  out to its edge and back again to the center of the conventional target cylinder&#39;s exposed surface  206 , or along its radius. In certain alternate embodiments, the tool holder  202  and PDC cutter  100  are stationary and the target cylinder moves laterally back and forth, with or without rotation. Thus, motion of the PDC cutter  100  on the target cylinder  210  refers to a relative motion between the PDC cutter  100  and the target cylinder  210 . As the PDC cutter  100  contacts and moves across or along the exposed surface  206  of the target cylinder  210 , the PDC cutter  100  removes, or cuts away, a portion of the target cylinder  210 . In certain example embodiments, the tool holder  202  has a predetermined depth of cut. Thus, the volume of target cylinder  210  that is removed has a constant relationship to the distance of travel between the PDC cutter  100  and the target cylinder  210 . 
     The vertical turret lathe further includes a load cell  216  disposed within the tool holder  202  between the tool holder  202  and the PDC cutter  100 . The load cell  216  senses one or more components of force applied to the PDC cutter  100  from the target cylinder  210 . In an example embodiment, the load cell  216  senses a normal force applied to the PDC cutter  100  by the target cylinder  210 , the normal force being perpendicular to the exposed surface  206  of the target cylinder  210 . In another example embodiment, the load cell  216  senses the normal force as well as two other components of force applied to the PDC cutter  100  by the target cylinder  210 , in which the two other components of force are perpendicular to each other as well as to the normal force. Specifically, in certain example embodiments, the two other components of force include a tangential force, which is a force coming into the PDC cutter  100  from the spinning motion of the target cylinder  210 , and a radial force, which is a force generated by the resistance against the PDC cutter  100  as the PDC cutter  100  traverses the radius of the target cylinder  210 . The load cell  216  feeds the collected force data to a computer or other data processor where it can be observed or analyzed. In an example embodiment, the load cell  216  handles data acquisition at 7 kHz, delivering 7000 data points per second for each component of force. However, such high data resolution may be noisy and very data heavy, making the data more difficult to handle and process. Thus, various data averaging or sampling techniques may be utilized to provide a more usable data set. The data can be averaged or sampled to provide a lower data resolution. For example, in an exemplary embodiment, three data points are collected per pass of the PDC cutter  100  across the radius of the target cylinder  210 , in which the three data points can be averages of multiple data points or samples. 
     In certain example embodiments, the target cylinder  210  is fabricated entirely from granite; however, the target cylinder  210  can be fabricated entirely from another single uniform natural or manmade material that includes, but is not limited to, Jackfork sandstone, Indiana limestone, Berea sandstone, Carthage marble, Champlain black marble, Berkley granite, Sierra white granite, Texas pink granite, Georgia gray granite, concrete, and the like. Additionally, the target cylinder  210  can be fabricated from two or more different materials. The target cylinder  210  has a compressive strength of about 25,000 psi or less and an abrasiveness of about 6 CAI or less when natural rock types are used. The conventional cylinder  210  has a compressive strength of about 12,000 psi or less and an abrasiveness of about 2 CAI or less when concrete is used. These example compressive strength values and CAI values are provided herein as a guidance, and the values may differ in other example embodiments. The abrasive wear resistance for the PDC cutter  100  is determined as an efficiency ratio, which is defined as the volume of target cylinder  210  that is removed by the PDC cutter  100  before or when the normal force on the PDC cutter  100 , as measured by the load cell  216 , reaches a certain normal force threshold to the value of the normal force threshold. Alternatively, instead of using volume of rock removed, the total distance that the PDC cutter  100  travels across the conventional target cylinder  210  or the duration of test before the normal force threshold is reached can also be measured and used to quantify the abrasive wear resistance or efficiency ratio for the PDC cutter  100 . Such alternate data parameters are useful because they can be linearly manipulated to obtain the volume of rock removed, and thus, have a direct correlation to the volume of rock removed. 
     In performing a vertical turret lathe test, a number of testing conditions are defined, such parameters including depth of cut, feed rate, rake angles, rotation speed of the target cylinder, type and shape of the target cylinder, and other milling conditions such as moisture levels, temperature, and the like. The vertical turret lathe test can be used to compare or rank several distinct cutters  100  to each other. The vertical turret lathe test can also be used to compare or rank the performance or efficiency of the same cutter  100  under a range of testing conditions, such as those listed above. 
     In comparing several distinct cutters  100 , all of the testing conditions are held constant, such that resulting differences in efficiency ratios between the cutters  100  is attributable to the distinct cutters  100 . Inversely, in comparing the performance of the same cutter  100  under different testing conditions, the physical properties of the cutters  100  tested are held constant and one (or more) testing parameter is varied. Thus, the difference in the efficiency ratio between tests is attributable to the testing parameter that is varied. For example, the same type of cutter  100  may be tested at varying back rake angles. Thus, the resulting efficiency ratios of each test can be ranked to show which back rake angle is most advantageous under the other given test conditions for the specific type of cutter  100  tested. 
     In certain exemplary embodiments, the efficiency ratios of the tested cutters  100  (distinct or identical), are defined at the same normal force, or the normal force threshold. The normal force threshold is chosen to be appropriate for the type of target cylinder  210  used as well as the known performance capabilities of the tested cutters  100 . With regard to the type of target cylinder  210  used, typically the harder the material of the target cylinder, the higher the normal force threshold is, because higher normal force is required for the overall test. For example, vertical turret lathe tests using concrete may have a normal force threshold of 500 lbs., while vertical turret lathe tests using granite, which is much harder than concrete, may have a normal force threshold of 6000 lbs. In certain cases, when testing a new cutter  100  on a new target cylinder  210 , preliminary test runs are performed to determine an appropriate normal force threshold for the cutter/target cylinder combination. 
     Choosing the appropriate normal force threshold or a series of VTL tests of distinct cutters  100  may also include known performance capabilities of the tested cutters  100 . Specifically, in certain example embodiments, the normal force threshold is chosen to be high enough such that all the tested cutters  100  in a comparative group are capable of reaching the normal force threshold. 
     In certain example embodiments, the vertical turret lathe test  200  is stopped when the normal force threshold is reached, and the volume of target cylinder  210  removed during the test is determined. This indicates how much energy it took for the specific cutter  100  to remove the volume of target cylinder  210 . In actual drilling applications, more and more force is applied to the cutters  100  to keep drilling at a constant speed. When it is not appropriate to apply any more force or when the load of drilling is too high, drilling is stopped. Thus, the vertical turret lathe test  200  and the resultant efficiency ratio is indicative of which type of cutter or which settings will allow for longer and more efficient drilling, as a higher efficiency ratio may be directly correlated to the cutter staying sharper for a longer time, thus requiring less force. 
       FIG. 3  illustrates a method  300  for testing a superhard component, such as a PDC cutter  100  ( FIGS. 1 and 2 ), in accordance with embodiments of the present disclosure. Referring to  FIG. 3 , the method  300  includes obtaining a superhard material at step  302 . In certain example embodiments, the superhard material is a PDC cutter  100  ( FIG. 1 ) or other type of cutter  100  ( FIG. 1 ). The method  300  further includes obtaining a target material at step  304 . In certain example embodiments, the target material is a target cylinder  210  ( FIG. 2 ) as described above and can be fabricated from any of the aforementioned materials and compositions. The method  300  includes contacting the superhard material to the target material at step  306  and removing a portion of the target material with the superhard material at step  308 . In certain example embodiments, in removing a portion of the target material, the superhard material travels across a surface, such as the exposed surface  206  ( FIG. 2 ), of the target material  210  ( FIG. 2 ) with a specific depth of cut. In an exemplary embodiment, traveling across the surface of the target material includes moving back and forth between the center or inner radius of the target material to the outer radius of the target material if the target material is cylindrically shaped. In alternative embodiments, the superhard material moves in alternate paths about the surface of the target material. In an example embodiment, the superhard material  100  ( FIG. 1 ) removes the portion of the target material at a constant depth of cut. In establishing a depth of cut of the superhard material onto the target material, a normal force is created and applied onto the superhard material from the target material, the normal force being perpendicular to the surface of the target material. Thus, the method further includes measuring the normal force applied onto the superhard material from the target material at step  310 . In an exemplary embodiment, the normal force is collected by the load cell  216  ( FIG. 2 ). In certain example embodiments, the load cell  216  also measures other components of force applied onto the superhard material by the target material. Finally, in certain example embodiments, the method  300  includes determining a ratio between the value of a variable related to the test and the normal force, in which the normal force and the value are correlated by time at step  312 . For example, the ratio is between the value of the variable at the time the normal force reaches a predetermined threshold and the value of the normal force threshold. In an exemplary embodiment, the variable is the volume of the target material removed by the superhard material in the time it took for the normal force to reach the threshold. However, in other example embodiments, the variable can be another variable indicative of the volume of the target material removed, such as total distance traveled by the superhard material in relation to the target material, number of passes made by the superhard material, time, or the like. In certain example embodiments, given that certain parameters, such as depth of cut, feed rate, distance per pass, rotation speed of the target material, and the like, are held constant during the test, the total volume of target material removed can be calculated from one or more of these parameters. For example, given a known and constant depth of cut and rotation speed, the first variable can be the total distance travelled by the superhard component. The value of the total distance travelled, in conjunction with the values of the depth of cut and rotation speed, can be used to derive the volume of the target material removed. 
       FIG. 4  illustrates a method  400  for determining relative wear resistance between one or more superhard materials, such as PDC cutters  100  ( FIGS. 1 and 2 ), in accordance with example embodiments of the present disclosure. The method  400  includes using a first set of vertical turret lathe test data of a first superhard component at step  402   a,  and obtaining a first normal force from the first set of vertical turret lathe test data  402   a  at step  404   a.  The method  400  further includes obtaining the value of a first variable from the first set of vertical turret lathe test data  402   a  at step  406   a.  The value of the first variable is correlated with the value of the first normal force by time. In an exemplary embodiment, the obtained value of the first variable is the value of the first variable when the first normal force reaches a predetermined threshold, the threshold being the value of the first normal force obtained in step  404   a.  The first variable is a volume of a target material removed by the first superhard material during the first vertical turret lathe test according to some exemplary embodiments. In alternative embodiments, the first variable is another parameter through which the volume of target material removed can be calculated. The method  400  further includes determining a ratio between the value of the first variable and the value of the first normal force at step  408   a,  thereby providing the first efficiency ratio at step  410   a.    
     Additionally, the method  400  further includes using a second set of vertical turret lathe test data of a second superhard component at step  402   b,  and obtaining a second normal force from the second set of vertical turret lathe test data  402   b  at step  404   b.  The method  400  further includes obtaining the value of a second variable from the second set of vertical turret lathe test data  402   b  at step  406   b.  The value of the second variable is correlated with the value of the second normal force by time. In an exemplary embodiment, the obtained value of the second variable is the value of the second variable when the second normal force reaches a predetermined threshold, the threshold being the value of the second normal force obtained in step  404   b.  The second variable is a volume of a target material removed by the second superhard material during the second vertical turret lathe test. In alternative embodiments, the second variable is another parameter through which the volume of target material removed can be calculated. The method  400  further includes determining a second ratio between the value of the second variable and the value of the second normal force at step  408   b,  thereby providing the second efficiency ratio at step  410   b.    
     In certain example embodiments, the method  400  further includes comparing the first efficiency ratio from step  410   a  and the second efficiency ratio from step  410   b  and determining if the first efficiency ratio from step  410   a  is greater than the second efficiency ratio from step  410   b  at step  412 . If the first efficiency from step  410   a  is indeed greater than the second efficiency ratio from step  410   b,  then the method  400  determines that the first superhard material is advantageous over the second superhard material at step  414 . Specifically, this indicates that the first superhard material is advantageous over the second superhard material under the respective testing conditions of the first and second vertical turret lathe tests. Likewise, if the first efficiency ratio is not greater than the second efficiency ratio, then the method  400  decides if the second efficiency ratio from step  410   b  is greater than the first ratio from step  410   a  at step  416 . If the second efficiency ratio is greater than the first efficiency ratio, then the method  400  determines that the second superhard material is advantageous over the first superhard material at step  418 . If the second efficiency ratio is not greater than the first efficiency ratio, meaning the first and second efficiency ratios are the same, then the method  400  determines that the first and second superhard materials are equally advantageous at step  420 . In certain exemplary embodiments, such conclusions are based on the first and second vertical turret lathe tests being performed under the same testing conditions, meaning the comparative advantage of the first and second superhard materials is applicable under the specific set of testing condition values. However, the results may or may not be true under another set of testing condition values. 
     In some example embodiments, the first and second superhard materials are distinct components, possibly having distinct physical or chemical compositions, distinct shapes, or another variant. In such embodiments, the first and second vertical turret lathe tests are performed under the same testing conditions (e.g., depth of cut, composition and size of target material, feed rate, rake angle, rotation speed, and the like) such that the only difference between the first and second vertical turret lathe tests is the superhard material used. Thus, difference in results, or efficiency ratio, can be attributed to the superhard materials used. Thus, the same vertical turret lathe test can be performed on several superhard materials to establish an efficiency ranking of the superhard materials. 
     In another example embodiment, the first and second superhard materials are substantially identical components, having substantially identical physical and chemical compositions and shapes. In such embodiments, at least one testing condition is varied between the first and second vertical turret lathe tests. Thus, difference in results, or efficiency ratios, between the first and second superhard materials can be attributed to the at least one testing condition that was varied. Thus, the same superhard material can be tested in vertical turret lathe tests having a varying parameter to rank performance of the superhard material under different values of the varying parameter. This allows the different values of said parameter to be ranked for effectiveness. 
       FIG. 5  illustrates a graph  500  of the efficiency ratios for eight superhard materials  506 , similar to superhard material  100  ( FIG. 1 ), in accordance with an example embodiment of the present disclosure. Referring to  FIG. 5 , the graph  500  is defined by volume of target material removed  502  as one axis, and the value of normal force  504  as another axis. Thus, any point on the graph  500  corresponds to a certain ratio of volume removed  502  to normal force  504 , also known as an efficiency ratio. Accordingly, the higher the volume removed  502  and/or lower the normal force  504 , the higher the efficiency. Thus, given the same normal force  504 , the superhard material  506  with the highest volume removed  502  is the most efficient under the specific testing conditions and at the define normal force, as described above. For example, according to the graph  500 , given a normal force  504  of 500 lbs., the 4 th  superhard material  510  removed the highest volume  502  of the target material, while the 5 th  superhard material  512  and 7 th  superhard material  514  removed the lowest volume  502  of the target material, with the remaining superhard materials falling somewhere in between. These example results indicate that the 4 th  superhard material  510  is the most efficient superhard material of the eight superhard materials  506  tested under the testing conditions and at 500 lbs  508  of normal force  504 . 
     The efficiency ratio, which is indicative of the relationship between amount of rock removed and the downward normal force required by the cutter, allows cutters to be tested and evaluated with regard to energy efficiency. Thus, the methods and techniques disclosed herein provide a more realistic indication of cutter performance and usability under real field conditions. 
     Although each exemplary embodiment has been described in detail, it is to be construed that any features and modifications that are applicable to one embodiment are also applicable to the other embodiments. Furthermore, although the invention has been described with reference to specific embodiments, these descriptions are not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention will become apparent to persons of ordinary skill in the art upon reference to the description of the exemplary embodiments. It should be appreciated by those of ordinary skill in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures or methods for carrying out the same purposes of the invention. It should also be realized by those of ordinary skill in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. It is therefore, contemplated that the claims will cover any such modifications or embodiments that fall within the scope of the invention.