Note: Descriptions are shown in the official language in which they were submitted.
<br/> CA 02584928 2007-04-10<br/>DRILL BIT HAVING DIAMOND IMPREGNATED INSERTS PRIMARY<br/>CUTTING STRUCTURE<br/> This application is a division of Canadian Patent Application No.<br/>2,311,020 filed June 8, 2000 for Drill Bit Having Diamond Impregnated Inserts<br/>Primary Cutting Structure.<br/> CROSS-REFERENCE TO RELATED APPLICATIONS<br/>Not applicable.<br/> STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR<br/>DEVELOPMENT<br/> Not applicable.<br/> TECHNICAL FIELD OF THE INVENTION<br/> The present invention relates generally to drill bits used in the oil and gas<br/>industry and more particularly, to drill bits having diamond-impregnated <br/>cutting<br/>surfaces. Still more particularly, the present invention relates to drag bits <br/>in<br/>which the diamond particles imbedded in the cutting surface have not suffered<br/>the deleterious thermal exposure that is normally associated with the<br/>manufacture of such bits.<br/> BACKGROUND OF THE INVENTION<br/> An earth-boring drill bit is typically mounted on the lower end of a drill<br/>string and is rotated by rotating the drill string at the surface or by <br/>actuation of<br/>downhole motors or turbines, or by both methods. When weight is applied to<br/>the drill string, the rotating drill bit engages the earthen formation and<br/>proceeds to form a borehole along a predetermined path toward a target zone.<br/>Different types of bits work more efficiently against different formation<br/>hardnesses. For example, bits containing inserts that are designed to shear <br/>the<br/>formation frequently drill formations that range from soft to medium hard.<br/> These inserts often have polycrystalline diamond compacts (PDC's) as their<br/>cutting faces.<br/> Roller cone bits are efficient and effective for drilling<br/>through formation materials that are of medium to hard hardness.<br/>The mechanism for drilling with a roller cone bit is primarily a<br/> 1<br/><br/> CA 02584928 2007-04-10<br/>crushing and gouging action, in that the inserts of the rotating cones are <br/>impacted against the<br/>formation material. This action compresses the material beyond its compressive <br/>strength and<br/>allows the bit to cut through the formation.<br/>For still harder materials, the mechanism for drilling changes from shearing <br/>to abrasion.<br/>For abrasive drilling, bits having fixed, abrasive elements are preferred. <br/>While bits having abrasive<br/>polycrystalline diamond cutting elements are known to be effective in some <br/>formations, they have<br/>been found to be less effective for hard, very abrasive formations such as <br/>sandstone. For these,<br/>hard formations, cutting structures that comprise particulate diamond, or <br/>diamond grit,<br/>impregnated in a supporting matrix are effective. In the discussion that <br/>follows, components of<br/>this type are referred to as "diamond impregnated."<br/>During abrasive drilling with a diamond-impregnated cutting structure, the <br/>diamond<br/>particles scour or abrade away concentric grooves while the rock formation <br/>adjacent the grooves is<br/>fractured and removed. As the matrix material around the diamond granules is <br/>worn away, the<br/>diamonds at the surface eventually fall out and other diamond particles are <br/>exposed.<br/>To form a diamond-impregnated bit, the diamond, which is available in a wide <br/>variety of<br/>shapes and grades, is placed in predefined locations in a bit mold. <br/>Alternatively, composite<br/>components, or segments comprising diamond particles in a matrix material such <br/>as tungsten<br/>carbide/cobalt (WC-Co) can be placed in predefined locations in the mold. Once <br/>the diamond-<br/>containing components have been positioned in the mold, other components of <br/>the bit are<br/>positioned in the mold. Specifically, the steel shank of the bit is supported <br/>in its proper position in<br/>the mold cavity along with any other necessary fonners, e.g. those used to <br/>form holes to receive<br/>fluid nozzles. The remainder of the cavity is filled with a charge of tungsten <br/>carbide powder.<br/>Finally, a binder, and more specifically an infiltrant, typically a nickel <br/>brass alloy, is placed on top<br/>2<br/><br/> CA 02584928 2007-04-10<br/>of the charge of powder. The mold is then heated sufficiently to melt the <br/>infiltrant and held at an<br/>elevated temperature for a sufficient period to allow it to flow into and bind <br/>the powder matrix or<br/>matrix and segments. For example, the bit body may be held at an elevated <br/>temperature (>1800 F)<br/>for on the order of 0.75 to 2.5 hours, depending on the size of the bit body, <br/>during the infiltration<br/>process. By this process, a monolithic bit body that incorporates the desired <br/>components is<br/>formed. It has been found, however, that the life of both natural and <br/>synthetic diamond is<br/>shortened by the lifetime thermal exposure experienced in the furnace during <br/>the infiltration<br/>process. Hence it is desired to provide a technique for manufacturing bits <br/>that include imbedded<br/>diamonds than have not suffered the thermal exposure that is normally <br/>associated with the<br/>manufacture of such bits.<br/>Another type of bit is disclosed in U. S. Patents 4,823,892, 4,889,017, <br/>4,991,670 and<br/>4,718,505, in which diamond-impregnated abrasion elements are positioned <br/>behind the cutting<br/>elements in a conventional tungsten carbide (WC) matrix bit body. The abrasion <br/>elements are not<br/>the primary cutting structures during normal bit use. Hence, it is further <br/>desired to provide a bit<br/>that includes diamond particles in its primary or leading cutting structures <br/>without subjecting the<br/>diamond particles to undue thermal stress or thermal exposure.<br/> BRIEF SUMMARY OF THE INVENTION<br/>The present invention provides a bit with cutting structures that include <br/>diamond particles,<br/>in which a portion of the diamond particles have not been subjected to undue <br/>amounts of thermal<br/>stress or thermal exposure. Specifically, the present invention comprises a <br/>bit that includes<br/>diamond-impregnated inserts as the cutting structures on at least one blade of <br/>the bit. The<br/>diamond-impregnated inserts are manufactured separately from the bit body. <br/>Once formed, the<br/>diamond-impregnated inserts are affixed to the:bit body by brazing or other <br/>means of attachment.<br/>3<br/><br/> CA 02584928 2007-04-10<br/>The total thermal exposure of the diamond particles during manufacture in <br/>accordance with the<br/>present invention is significantly lower than the total manufacturing-related <br/>thermal exposure in<br/>previously known diamond-impregnated cutting structures. Thus, the operating <br/>life of the cutting<br/>structures, and therefore the life of the bit itself, is increased.<br/> BRIEF DESCRIPTION OF THE DRAWINGS<br/>For an introduction to the detailed description of the preferred embodiments <br/>of the<br/>invention, reference will now be made to the accompanying drawings, wherein:<br/>Figure 1 shows a variety of possible configurations for a diamond-impregnated <br/>insert in<br/>accordance with the present invention;<br/>Figure 2 is a perspective view of an earth-boring bit made in accordance with <br/>the principles<br/>of the present invention;<br/>Figure 3 is a perspective view of a altemative embodiment of an earth-boring <br/>bit made in<br/>accordance with the principles of the present invention; and<br/>Figure 4 is a plot showing a comparison of the wear ratios for inserts <br/>constructed according<br/>to the present invention to prior art diamond-impregnated bits.<br/> DETAILED DESCRIPTION OF THE INVENTION<br/>According to a preferred embodiment, diamond-impregnated inserts that will <br/>comprise the<br/>cutting structure of a bit are formed separately from the bit. Because the <br/>inserts are smaller than a<br/>bit body, they can be hot pressed or sintered for a much shorter time than is <br/>required to infiltrate a<br/>bit body.<br/>In the preferred - embodiment of the invention, the diamond-impregnated <br/>inserts 10 are<br/>manufactured as individual components, as indicated in Figure 1. According to <br/>one preferred<br/>embodiment, diamond particles 12 and powdered matrix material are placed in a <br/>mold. The<br/>4<br/><br/> CA 02584928 2007-04-10<br/>contents are then hot-pressed or sintered at an . appropriate temperature, <br/>preferably between about<br/>1000 and 2200 F, more preferably below 1800 F, to form a composite insert 20. <br/>Heating of the<br/>material can be by furnace or by electric induction heating, such that the <br/>heating and cooling rates<br/>are rapid and controlled in order to prevent damage to the diamonds.<br/>If desired, a very long cylinder having the outside diameter of the ultimate <br/>insert shape can<br/>be forrned by this process and then cut into lengths to produce diamond-<br/>impregnated inserts 10<br/>having the desired length. The dimensions and shape of the diamond-impregnated <br/>inserts 10 and<br/>of their positioning on the bit can be varied, depending on the nature of the <br/>formation to be d.--illed.<br/>The diamond particles can be either natural or synthetic diamond, or a <br/>combination of both.<br/>The matrix in which the diamonds are embedded to form the diamond impregnated <br/>inserts 10 must<br/>satisfy several requirements. The matrix must have sufficient hardness so that <br/>the diamonds<br/>exposed at the cutting face are not pushed into the matrix material under the <br/>very high pressures<br/>used in drilling. In addition, the matrix must have sufficient abrasion <br/>resistance so that the<br/>diamond particles are not prematurely released. Lastly, the heating and <br/>cooling time during<br/>sintering or hot-pressing, as well as the maximum temperature of the thermal <br/>cycle, must be<br/>sufficiently low that the diamonds imbedded therein are not thermally damaged <br/>during sintering or<br/>hot-pressing.<br/>To satisfy these requirements, the following materials may be used for the <br/>matrix in which<br/>the diamonds are embedded: tungsten carbide (WC), tungsten alloys such as <br/>tungsten/cobalt alloys<br/>(WC-Co), and tungsten carbide or tungsten/cobalt alloys in combination with <br/>elemental tungsten<br/>(all with an appropriate binder phase to facilitate bonding of particles and <br/>diamonds) and the like.<br/>Referring now to Figure 2, a drill bit 20 according to the present invention <br/>comprises a<br/>shank 24 and a crown 26. Shank 24 is typically formed of steel and includes a <br/>threaded pin 28 for<br/>5<br/><br/> CA 02584928 2007-04-10<br/>attachment to a drill string. Crown 26 has a cutting face 22 and outer side <br/>surface 30. According<br/>to one preferred embodiment, crown 26 is formed by infiltrating a mass of <br/>tungsten-carbide<br/>powder impregnated with synthetic or natural diamond, as described above. <br/>Crown 26 may<br/>include various surface features, such as raised ridges 27. Preferably, <br/>formers are included during<br/>the manufacturing process, so that the infiltrated, diamond-impregnated crown <br/>includes a plurality<br/>of holes or sockets (not shown) that are sized and shaped to receive a <br/>corresponding plurality of<br/>diamond-impregnated inserts 10. Once crown 26 is formed, inserts 10 are <br/>mounted in the sockets<br/>and affixed by any suitable method, such as brazing, adhesive, mechanical <br/>means such as<br/>interference fit, or the like. As shown in Figure 2, the sockets can each be <br/>substantially<br/>perpendicular to the surface of the crown. Alternatively, and as shown in <br/>Figure 3, holes 29 can be<br/>inclined with respect to the surface of the crown. In this embodiment, the <br/>sockets are inclined such<br/>that inserts 10 are oriented substantially in the direction of rotation of the <br/>bit, so as to enhance<br/>cutting.<br/>As a result of the present manufacturing technique, each diamond-impregnated <br/>insert is<br/>subjected to a total thennal exposure that is significantly reduced as <br/>compared to previously known<br/>techniques for manufacturing infiltrated diamond-impregnated bits. For <br/>example, diamonds<br/>imbedded according to the present invention have a total thermal exposure of <br/>less than 40 minutes,<br/>and more typically less than 20 minutes, above 1500 F. This limited thermal <br/>exposure is due to<br/>the hot pressing period and the brazing process. This compares very favorably <br/>with the total<br/>thermal exposure of at least about 45 minutes, and more typically about 60-120 <br/>minutes, at<br/>temperatures above 1500 F, that occur in conventional manufacturing of furnace-<br/>infiltrated,<br/>diamond-impregnated bits. If the present diamond-impregnated inserts are <br/>affixed to the bit body<br/>6<br/><br/> CA 02584928 2007-04-10<br/>by adhesive or by mechanical means such as interference fit, the total thermal <br/>exposure of the<br/>diamonds is even less.<br/>Referring now to Figure 4, a plot of the wear resistance as measured for each <br/>of several<br/>insert types shows the superiority of inserts according to the present <br/>invention. The wear ratio is<br/>defined as the ratio of the volume of rock removed to the volume of the insert <br/>wom during a given<br/>cutting period. Thus, a higher wear ratio is more desirable than a lower wear <br/>ratio. Column 1<br/>indicates the wear ratio for natural diamond impregnated into a matrix in a <br/>conventional manner,<br/>i.e. placed in the mold before furnace infiltration of the bit and subjected <br/>to a conventional thermal<br/>history. Column 2 indicates the wear ratio for synthetic diamond, also <br/>impregnated into a matrix in<br/>a conventional manner. Columns 3 and 4 indicate the wear ratios for natural <br/>diamond and<br/>synthetic diamond, respectively, impregnated into inserts and brazed into a <br/>bit body and thereby<br/>subjected to a thermal history in accordance with the present invention. It <br/>can be clearly seen that<br/>cutting structures constn.3eted according to the present invention have wear <br/>ratios that are at least<br/>two, and often three or more tiines greater, than conventional diamond-<br/>impregnated cutting<br/>structures.<br/>In the present invention, at least about 15%, more preferably about 30%, and <br/>still more<br/>preferably about 40% of the diamond volume in the entire cutting structure is <br/>present in the inserts,<br/>with the balance of the diamond being present in the bit body. However, <br/>because the diamonds in<br/>the inserts, have 2-3 times the rock cutting life of the diamonds in the bit <br/>body, in a preferred<br/>embodiment the inserts provide about 57% to about 67% of the available wear <br/>life of the cutting<br/>structure. It will further be understood that the coticentration of diamond in <br/>the inserts can vary<br/>from the concentration of diamond in the bit body. According to a preferred <br/>embodiment, the<br/>7<br/><br/> CA 02584928 2007-04-10<br/>concentrations of diamond in the inserts and in the bit body are in the range <br/>of 50 to 100 (100 = 4.4<br/>carat/cc3).<br/>It will be understood that the materials commonly used for construction of bit <br/>bodies can<br/>be used in the present invention. Hence, in the preferred embodiment, the bit <br/>body may itself is<br/>diamond-impregnated. In an alternative embodiment, the bit body comprises <br/>infiltrated tungsten<br/>carbide matrix that does not include diamond.<br/>In another alternative embodiment, the bit body can be made of steel, <br/>according to<br/>techniques that are known in the art. Again, the final bit body includes a <br/>plurality of holes having a<br/>desired orientation, which are sized to receive and support diamond-<br/>impregnated inserts 10.<br/>Inserts 10 are affixed to the steel body by brazing, mechanical means, <br/>adhesive or the like. The bit<br/>according to this embodiment can optionally be provided with a layer of <br/>hardfacing.<br/>In still another embodiment, one or more of the diamond-impregnated inserts <br/>include<br/>imbedded thermally stable polycrystalline diamond (also known as TSP), so as <br/>to enhance shearing<br/>of the formation. The TSP can take any desired form, and is preferably formed <br/>into the insert<br/>during the insert manufacturing process. Similarly, additional primary andlor <br/>secondary cutting<br/>structures that are not diamond-impregnated can be included on the bit, as may <br/>be desired.<br/>The present invention allows bits to be easily constructed having inserts in <br/>which the size,<br/>shape, and/or concentration of diamond in the cutting structure is controlled <br/>in a desired manner.<br/>Likewise, the inserts can be created to have; different lengths, or mounted in <br/>the bit body at<br/>different heights or angles, so as to produce a bit having a multiple height <br/>cutting structure. This<br/>may provide advantages in drilling efficiency. For example, a bit having <br/>extended diamond-<br/>impregnated inserts as a cutting structure will be able to cut through <br/>downhole float equipment that<br/>could not be cut by a standard diamond-impregnated bit, thereby eliminating <br/>the need to trip out of<br/>8<br/><br/> CA 02584928 2007-04-10<br/>the hole to change bits. Additionally, a bit having such extended diamond-<br/>impregnated inserts will<br/>be able to drill sections of softer formations that would not be readily <br/>drillable with conventional<br/>diamond-impregnated bits. This is made possible by the shearing action of the <br/>inserts that extend<br/>beyond the surface of the bit body.<br/>While various preferred embodiments of the invention have been shown and <br/>described,<br/>modifications thereof can be made by one skilled in the art without departing <br/>from the spirit and<br/>teachings of the invention. The embodiments described herein are exemplary <br/>only, and are not<br/>limiting. Many variations and modifications of the invention and apparatus <br/>disclosed herein are<br/>possible and are within the scope of the invention. Accordingly, the scope of <br/>protection is not<br/>limited by the description set out above, but is only limited by the claims <br/>which follow, that scope<br/>including all equivalents of the subject matter of the claims. In any method <br/>claim, the recitation of<br/>steps in a particular order is not intended to limit the scope of the claim to <br/>the performance of the<br/>steps in that order unless so stated.<br/>9<br/>
