Patent Publication Number: US-10787862-B2

Title: Displacement elements in the manufacture of a drilling tool

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a U.S. National Stage Application of International Application No. PCT/US2015/044495 filed Aug. 10, 2015, which is incorporated herein by reference in its entirety for all purposes. 
     TECHNICAL FIELD 
     The present disclosure relates generally to drilling tools, such as earth-boring drill bits. 
     BACKGROUND 
     Various types of drilling tools including, but not limited to, rotary drill bits, reamers, core bits, under reamers, hole openers, stabilizers, and other downhole tools are used to form wellbores in downhole formations. Examples of rotary drill bits include, but are not limited to, fixed-cutter drill bits, drag bits, polycrystalline diamond compact (PDC) drill bits, matrix drill bits, and hybrid bits associated with forming oil and gas wells extending through one or more downhole formations. 
     Matrix drill bits are typically formed by placing loose reinforcement material such as tungsten carbide, typically in powder form, into a mold and infiltrating the reinforcement material with a binder material such as a copper alloy. The reinforcement material infiltrated with a molten metal alloy or binder material may form a matrix bit body after solidification of the binder material with the reinforcement material. Hybrid bits containing matrix drill bit features may be formed in a similar manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and its features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagram of an elevation view of a drilling system according to certain embodiments of the present disclosure; 
         FIG. 2  is a diagram of an isometric view of a rotary drill bit oriented upwardly according to certain embodiments of the present disclosure; 
         FIG. 3  is a flow chart of an example method of forming an MMC drill bit according to certain embodiments of the present disclosure; 
         FIG. 4  is a schematic drawing in section with portions broken away showing an example of a mold assembly used to manufacture an MMC drill bit according to certain embodiments of the present disclosure; 
         FIGS. 5-7  are diagrams showing bottom views of various drill bits similar to that shown in  FIG. 2  manufactured using interior displacement elements according to certain embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     When drilling a well in a subterranean formation, various downhole tools, including drill bits, coring bits, reamers, and/or hole enlargers, may be lowered in a wellbore. Some of these tools may have tool bodies comprising a metal-matrix composite (MMC). According to various systems and methods disclosed herein, such MMC structures may be formed by placing loose reinforcement material, e.g., in powder form, into a mold and infiltrating the reinforcement material with a binder material. The reinforcement material infiltrated with a molten metal alloy or binder material may form an MMC bit body after solidification of the binder material with the reinforcement material. 
     Metal-matrix composites manufactured using these techniques typically exhibit high strength, but may be relatively brittle or susceptible to propagation of cracks therein. According to various systems and methods disclosed herein, one or more interior displacement elements may be placed within a mold for the drill bit during manufacturing, which may be configured to displace the reinforcement material from interior portions of the drill bit and/or reduce the total amount of reinforcement material and/or binder material needed (and its associated cost) in the manufacture of the drill bit. As used herein, the interior displacement elements of the present disclosure are solid displacement materials that are located within a drill bit or a mold for a drill bit in a region corresponding to an interior region of the drill bit such that they will be surrounded by the metal-matrix composite material. As used herein, a material may be deemed to “surround” an interior displacement element despite a limited number of standoff materials or spacers are placed at certain contact points between the interior displacement element and other components in the mold, as described further below. In some embodiments, the interior displacement element may facilitate the formation of regions within the bit that are relatively binder-rich in that they comprise lesser amounts of reinforcement material and thus may exhibit different properties from the remainder of the bit. In other embodiments, the interior displacement element may facilitate the formation of hollow regions within the bit that do not comprise a significant amount of reinforcement material or binder material. In some embodiments, the interior displacement elements may be placed in a region of the bit where typical properties of an MMC material (e.g., high strength) may be less critical, or where enhanced toughness or reduced brittleness may be desired. 
       FIG. 1  is an elevation view of a drilling system. Drilling system  100  may include a well surface or well site  106 . Various types of drilling equipment such as a rotary table, drilling fluid pumps and drilling fluid tanks (not expressly shown) may be located at well surface or well site  106 . For example, well site  106  may include drilling rig  102  that may have various characteristics and features associated with a land drilling rig. However, downhole drilling tools incorporating teachings of the present disclosure may be satisfactorily used with drilling equipment located on offshore platforms, drill ships, semi-submersibles, and/or drilling barges (not expressly shown). 
     Drilling system  100  may include drill string  103  associated with drill bit  101  that may be used to drill and/or form a wide variety of wellbores or bore holes such as generally vertical wellbore  114   a  or generally horizontal wellbore  114   b  or any combination thereof. Various directional drilling techniques and associated components of bottom hole assembly (BHA)  120  of drill string  103  may be used to form horizontal wellbore  114   b . For example, lateral forces may be applied to BHA  120  proximate kickoff location  113  to form generally horizontal wellbore  114   b  extending from generally vertical wellbore  114   a . The term directional drilling may be used to describe drilling a wellbore or portions of a wellbore that extend at a desired angle or angles relative to vertical. Such angles may be greater-than-normal variations associated with vertical wellbores. Direction drilling may include horizontal drilling. 
     Drilling system  100  may also include rotary drill bit (drill bit)  101 . Drill bit  101 , discussed in further detail in  FIG. 2 , may be an MMC drill bit which may be formed by placing loose reinforcement material including tungsten carbide powder, into a mold and infiltrating the reinforcement material with a binder material including a copper alloy and/or an aluminum alloy. The mold may be formed by milling a block of material, such as graphite, to define a mold cavity having features that correspond generally with the exterior features of drill bit  101 . 
       FIG. 2  is an isometric view of an example configuration of the rotary drill bit  101  of  FIG. 1 . The present view is oriented upwardly in a manner often used to model or design fixed-cutter drill bits. To the extent that at least a portion of the drill bit is formed of an MMC, the drill bit may be any of various types of fixed-cutter drill bits, including PDC bits, drag bits, matrix-body drill bits, steel-body drill bits, and the like operable to form wellbore  114  (as illustrated in  FIG. 1 ) extending through one or more downhole formations. Drill bit  101  may be designed and formed in accordance with teachings of the present disclosure and may have many different designs, configurations, and/or dimensions according to the particular application of drill bit  101 . 
     Drill bit  101  may include one or more blades  126  that may be disposed outwardly from exterior portions of rotary bit body  124  of drill bit  101 . Rotary bit body  124  may be generally cylindrical and blades  126  may be any suitable type of projections extending outwardly from rotary bit body  124 . Drill bit  101  may rotate with respect to bit rotational axis  104  in a direction defined by directional arrow  105 . Blades  126  may include one or more cutting elements  128  disposed outwardly from exterior portions of each blade  126 . Blades  126  may further include one or more gage pads (not expressly shown) disposed on blades  126 . Drill bit  101  may be designed and formed in accordance with teachings of the present disclosure and may have many different designs, configurations, and/or dimensions according to the particular application of drill bit  101 . 
     During a subterranean operation, different regions of drill bit  101  may be exposed to different forces and/or stresses. During manufacturing of drill bit  101 , the properties of drill bit  101  may be customized such that some regions of drill bit  101  may have different properties from other regions of drill bit  101 , including but not limited to enhanced toughness, resistance to crack propagation, and reduced brittleness. The localized properties may be achieved by placing a selected type of displacement element in selected locations and in selected configurations in a mold for drill bit  101 . The type, location, and/or configuration of the interior displacement element may be selected to provide localized properties for drill bit  101  based on the downhole conditions experienced by the region of drill bit  101  and/or the function of the region of drill bit  101 . 
     Drill bit  101  may be an MMC drill bit which may be formed by placing loose reinforcement material, including tungsten carbide powder, into a mold and infiltrating the reinforcement material with a binder material, which may be a copper alloy. During the mold loading process, one or more displacement elements may be placed in selected locations of the mold corresponding to the interior of drill bit  101 . The reinforcement material (and, in some cases, the interior displacement element) may be infiltrated with the molten binder material to form bit body  124  after solidification of the binder material. 
     The mold may be formed by milling a block of material, such as graphite, to define a mold cavity having features that correspond generally with the exterior features of drill bit  101 . Various features of drill bit  101  including blades  126 , cutter pockets  166 , and/or fluid flow passageways may be provided by shaping the mold cavity and/or by positioning temporary displacement elements within interior portions of the mold cavity. A preformed steel shank or bit mandrel (sometimes referred to as a blank) may be placed within the mold cavity to provide reinforcement for bit body  124  and to allow attachment of drill bit  101  with a drill string and/or BHA. A quantity of reinforcement material may be placed within the mold cavity and infiltrated with a molten binder material to form bit body  124  after solidification of the binder material with the reinforcement material. 
     Prior to or during the mold loading process, one or more interior displacement elements may be placed in selected locations of the mold to displace the reinforcement material from certain interior regions within drill bit  101 . The interior displacement elements may be placed in a variety of configurations based on the selected localized properties for the regions of drill bit  101  in which the interior displacement element is placed, as described in more detail with reference to  FIGS. 4-7  below. For example, in certain embodiments, the interior displacement element may be placed in certain regions closer to the central axis of the body of drill bit  101  since these regions may not experience high levels of stress. 
     Drill bit  101  may include shank  152  with drill pipe threads  155  formed thereon. Threads  155  may be used to releasably engage drill bit  101  with a bottom hole assembly (such as BHA  120  shown in  FIG. 1 ) whereby drill bit  101  may be rotated relative to bit rotational axis  104 . Plurality of blades  126   a - 126   g  may have respective junk slots or fluid flow paths  140  disposed therebetween. 
     Drilling fluids may be communicated to one or more nozzles  156 . The regions of drill bit  101  near nozzle  156  may be subject to stresses during the subterranean operation that may cause cracks in drill bit  101 . Thus, in some embodiments, an interior displacement element may be placed near nozzles  156  to increase the toughness and/or crack-arresting properties of the region of the drill bit near nozzles  156 . 
     Drill bit  101  may include one or more blades  126   a - 126   g , collectively referred to as blades  126 , that may be disposed outwardly from exterior portions of rotary bit body  124 . Rotary bit body  124  may have a generally cylindrical body and blades  126  may be any suitable type of projections extending outwardly from rotary bit body  124 . For example, a portion of blade  126  may be directly or indirectly coupled to an exterior portion of bit body  124 , while another portion of blade  126  may be projected away from the exterior portion of bit body  124 . Blades  126  formed in accordance with the teachings of the present disclosure may have a wide variety of configurations including, but not limited to, substantially arched, helical, spiraling, tapered, converging, diverging, symmetrical, and/or asymmetrical. 
     Each of blades  126  may include a first end  141  disposed proximate or toward bit rotational axis  104  and a second end  143  disposed proximate or toward exterior portions of drill bit  101  (i.e., disposed generally away from bit rotational axis  104  and toward uphole portions of drill bit  101 ). Blades  126  may have apex  142  that may correspond to the portion of blade  126  furthest from bit body  124  and blades  126  may join bit body  124  at landing  145 . 
     In some cases, blades  126  may have substantially arched configurations, generally helical configurations, spiral shaped configurations, or any other configuration satisfactory for use with each drilling tool. One or more blades  126  may have a substantially arched configuration extending from proximate rotational axis  104  of drill bit  101 . The arched configuration may be defined in part by a generally concave, recessed shaped portion extending from proximate bit rotational axis  104 . The arched configuration may also be defined in part by a generally convex, outwardly curved portion disposed between the concave, recessed portion and exterior portions of each blade which correspond generally with the outside diameter of the rotary drill bit. 
     Blades  126  may have a general arcuate configuration extending radially from rotational axis  104 . The arcuate configurations of blades  126  may cooperate with each other to define, in part, a generally cone shaped or recessed portion disposed adjacent to and extending radially outward from the bit rotational axis. Exterior portions of blades  126 , cutting elements  128  and other suitable elements may be described as forming portions of the bit face. 
     Blades  126   a - 126   g  may include primary blades disposed about bit rotational axis  104 . For example, in  FIG. 2 , blades  126   a ,  126   c , and  126   e  may be primary blades or major blades because respective first ends  141  of each of blades  126   a ,  126   c , and  126   e  may be disposed closely adjacent to associated bit rotational axis  104 . In some configurations, blades  126   a - 126   g  may also include at least one secondary blade disposed between the primary blades. Blades  126   b ,  126   d ,  126   f , and  126   g  shown in  FIG. 2  on drill bit  101  may be secondary blades or minor blades because respective first ends  141  may be disposed on downhole end  151  a distance from associated bit rotational axis  104 . The number and location of primary blades and secondary blades may vary such that drill bit  101  includes more or less primary and secondary blades. Blades  126  may be disposed symmetrically or asymmetrically with regard to each other and bit rotational axis  104  where the disposition may be based on the downhole drilling conditions of the drilling environment. In some cases, blades  126  and drill bit  101  may rotate about rotational axis  104  in a direction defined by directional arrow  105 . 
     Each blade may have a leading (or front) surface  130  disposed on one side of the blade in the direction of rotation of drill bit  101  and a trailing (or back) surface  132  disposed on an opposite side of the blade away from the direction of rotation of drill bit  101 . Blades  126  may be positioned along bit body  124  such that they have a spiral configuration relative to rotational axis  104 . In other configurations, blades  126  may be positioned along bit body  124  in a generally parallel configuration with respect to each other and bit rotational axis  104 . The leading side of the root or base portion of blades  126  may be subjected to relatively high stresses when the drill bit  101  is used in subterranean operations. Thus, in certain embodiments, it may be less desirable to place displacement elements in those regions of the drill bit  101 . 
     Blades  126  may include one or more cutting elements  128  disposed outwardly from exterior portions of each blade  126 . For example, a portion of cutting element  128  may be directly or indirectly coupled to an exterior portion of blade  126  while another portion of cutting element  128  may be projected away from the exterior portion of blade  126 . Cutting elements  128  may be any suitable device configured to cut into a formation, including but not limited to, primary cutting elements, back-up cutting elements, secondary cutting elements, or any combination thereof. By way of example and not limitation, cutting elements  128  may be various types of cutters, compacts, buttons, inserts, and gage cutters satisfactory for use with a wide variety of drill bits  101 . Cutting elements  128  may be set on the surfaces of the blades  126 , brazed to the surfaces of blades  126 , or otherwise attached to blades  126  by any other suitable means. 
     Cutting elements  128  may include respective substrates with a layer of hard cutting material, including cutting table  162 , disposed on one end of each respective substrate, including substrate  164 . Blades  126  may include recesses or cutter pockets  166  that may be configured to receive cutting elements  128 . For example, cutter pockets  166  may be concave cutouts on blades  126 . Cutter pockets  166  may be subject to impact forces during the subterranean operation. 
     Blades  126  may further include one or more gage pads (not expressly shown) disposed on blades  126 . A gage pad may be a gage, gage segment, or gage portion disposed on exterior portion of blade  126 . Gage pads may often contact adjacent portions of wellbore  114  formed by drill bit  101 . Exterior portions of blades  126  and/or associated gage pads may be disposed at various angles, positive, negative, and/or parallel, relative to adjacent portions of generally vertical portions of wellbore  114 . A gage pad may include one or more layers of hardfacing material. 
     Drill bits, such as drill bit  101 , may be formed using a mold assembly.  FIG. 3  is a flow chart of an example method of forming a metal-matrix composite drill bit having localized properties. The steps of method  300  may be performed by a person or manufacturing device (referred to as a manufacturer) that is configured to fill molds used to form MMC drill bits. 
     Method  300  may begin at step  302  in which the manufacturer may place one or more displacement elements in a matrix bit body mold in a location corresponding to an interior region within the bit body (e.g., not in contact or communication with an outer surface of the bit body). The matrix bit body mold may be similar to the mold described with respect to  FIG. 4 . The interior displacement elements used in the methods and drill bits of the present disclosure may comprise any solid material that is sufficiently rigid to support the weight of the reinforcement material and the binder material that will be placed on top of and/or around it without being crushed or undesirably compressed or deformed (although some deformation or compression may be acceptable). Examples of materials that the interior displacement elements may comprise include, but are not limited to metals, alloys, ceramics, cements, polymers, fibers, wool, and any combination thereof. In certain embodiments, an interior displacement element may comprise a combination of materials, for example, with a structure or matrix made of one material whose outer surface is coated with another material. Alternatively, in certain embodiments, an interior displacement element may be encapsulated in a structure or material that is refractory to the process and retains the interior displacement element in place during the infiltration process. In the embodiments of the present disclosure, the interior displacement elements of the present disclosure may be foam displacement elements that comprises one or more porous foam materials (e.g., open-cell or closed-cell foam). In certain embodiments, an interior foam displacement element of the present disclosure may be encapsulated in a structure or material that is refractory to the process and retains the foam in place during the infiltration process. 
     The interior displacement elements according to the present disclosure may be completely pre-formed (e.g., molded, machined, etc.) prior to the manufacturing of the drill bit (e.g., by a vendor other than the manufacturer of the drill bit), or they may be formed at least in part during the manufacture of the drill bit. The interior displacement elements may be provided in the form of hollow structures, porous structures (e.g., open-cell or closed-cell structures), fibrous structures, and the like, and may be of any suitable size and/or shape. In some embodiments, the interior displacement element may comprise a hollow structure with one or more holes or openings in the surface, allowing the hollow region to be filled with binder material (as discussed below) or another material in the course of the manufacturing process. For example, the displacement material may comprise a hollow ceramic shell, which may be filled with ceramic or metallic powder. The hollow shell may be filled with powder before it is placed in the mold, or it may be fabricated with holes or openings therein which allow the powder to enter the interior of the shell as it is loaded into the mold. In certain embodiments, one or more standoff materials or spacers may be placed at certain contact points between the interior displacement element and other components in the mold, among other reasons, to retain the interior displacement element in place during the mold loading process. 
     In some embodiments, the size, shape, composition, configuration, and/or placement of the interior displacement element may depend on the forces and/or stresses experienced by particular portions of the drill bit and the desired localized properties in those portions of the bit. For example, the strength, brittleness, and/or other properties of the drill bit may be affected by the size, shape, composition, configuration, and/or location of the interior displacement elements within the mold used to manufacture the bit. Examples of different configurations for the interior displacement elements are shown in  FIGS. 4-7 , which are discussed in greater detail below. 
     At step  304 , the manufacturer may place a reinforcement material in the matrix bit body mold. In certain embodiments of the present disclosure, the interior displacement elements may be layered with or otherwise placed within the mold in a manner that allows the reinforcement material to at least partially surround the interior displacement elements. For example, in some embodiments, a first portion of the reinforcement material may have been placed in the matrix bit body mold prior to placing the interior displacement elements into the mold, followed by a second portion of the reinforcement material, among other reasons, to more easily place the interior displacement elements in the desired location in the mold. Depending upon the structure of the interior displacement elements, the reinforcement material may enter certain regions within the interior displacement elements, e.g., openings in the surface or porous or hollow regions of the interior displacement element connected to the outer surface thereof. However, these regions may comprise significantly less of the reinforcement material than the regions within the mold where displacement elements are not placed. 
     The reinforcement material may be selected to provide designed characteristics for the resulting drill bit, such as strength, fracture resistance, toughness, and/or erosion, abrasion, and wear resistance. The reinforcement material may be any suitable material, such as, but are not limited to, particles of metals, metal alloys, superalloys, intermetallics, borides, carbides, nitrides, oxides, silicides, ceramics, diamonds, and the like, or any combination thereof. More particularly, examples of reinforcing particles suitable for use in conjunction with the embodiments described herein may include particles that include, but are not limited to, tungsten, molybdenum, niobium, tantalum, rhenium, iridium, ruthenium, beryllium, titanium, chromium, rhodium, iron, cobalt, nickel, nitrides, silicon nitrides, boron nitrides, cubic boron nitrides, natural diamonds, synthetic diamonds, cemented carbide, spherical carbides, low-alloy sintered materials, cast carbides, silicon carbides, boron carbides, cubic boron carbides, molybdenum carbides, titanium carbides, tantalum carbides, niobium carbides, chromium carbides, vanadium carbides, iron carbides, tungsten carbides, macrocrystalline tungsten carbides, cast tungsten carbides, crushed sintered tungsten carbides, carburized tungsten carbides, steels, stainless steels, austenitic steels, ferritic steels, martensitic steels, precipitation-hardening steels, duplex stainless steels, ceramics, iron alloys, nickel alloys, cobalt alloys, chromium alloys, HASTELLOY® alloys (e.g., nickel-chromium containing alloys, available from Haynes International), INCONEL® alloys (e.g., austenitic nickel-chromium containing superalloys available from Special Metals Corporation), WASPALOYS® (e.g., austenitic nickel-based superalloys), RENE® alloys (e.g., nickel-chromium containing alloys available from Altemp Alloys, Inc.), HAYNES® alloys (e.g., nickel-chromium containing superalloys available from Haynes International), INCOLOY® alloys (e.g., iron-nickel containing superalloys available from Mega Mex), MP98T (e.g., a nickel-copper-chromium superalloy available from SPS Technologies), TMS alloys, CMSX® alloys (e.g., nickel-based superalloys available from C-M Group), cobalt alloy 6B (e.g., cobalt-based superalloy available from HPA), N-155 alloys, any mixture thereof, and any combination thereof. In some embodiments, the reinforcing particles may be coated. In some cases, multiple different types of reinforcement material may be used to form a single resulting drill bit. 
     At step  308 , the manufacturer may place a binder material in the matrix bit body mold. The binder material may be placed in the mold after the reinforcement material has been packed into the mold. The binder material may include any suitable binder material such as copper, nickel, cobalt, iron, aluminum, molybdenum, chromium, manganese, tin, zinc, lead, silicon, tungsten, boron, phosphorous, gold, silver, palladium, indium, and/or alloys thereof. The binder material may be selected such that the downhole temperatures during the subterranean operation are less than the melting point of the binder material. 
     At step  310 , the manufacturer may heat the matrix bit body mold and the materials disposed therein via any suitable heating mechanism, including a furnace. When the temperature of the binder material exceeds the melting point of the binder material, the liquid binder material may flow into the reinforcement material (and, in some cases, the interior displacement elements). 
     At step  312 , as the binder material infiltrates the reinforcement material, the binder material may additionally infiltrate the interior displacement elements. For example, if an interior displacement element comprises a porous material or a hollow structure with one or more holes or openings in the outer surface thereof, the binder material may penetrate those pores, holes, openings, or passages therein and infiltrate the interior of the interior displacement element and/or interlock with it. If the reinforcement material did not substantially enter these regions of the interior displacement element, this may result in the formation of relatively “binder-rich” regions of the drill bit that comprise a relatively larger proportion of the binder. In other embodiments, if the interior displacement element comprises a solid, hollow, or closed-cell structure that does not permit the binder material to penetrate its surface, that region of the drill bit may not comprise a significant amount of binder material or reinforcement material, and may simply comprise the interior displacement element as formed. Depending on the type of material of which the interior displacement element is comprised, the interior displacement element may remain intact through the manufacturing process and remain in place in the resulting drill bit. In other embodiments, the interior displacement element may comprise a material that melts, dissolves, burns, or otherwise degrades at some point after the binder material is introduced into the mold. If this occurs prior to or during the infiltration of the binder material, the binder material may fill in the regions previously occupied by the interior displacement element, resulting in the formation of relatively “binder-rich” regions of the bit. If the interior displacement element remains intact as the binder material infiltrates the reinforcement material but is subsequently melted, dissolved, burned, or otherwise degraded, this may result in the formation of one or more voids or empty spaces in the regions previously occupied by the interior displacement element. 
     At step  314 , the manufacturer may cool the matrix bit body mold, the reinforcement material, the binder material, and the interior displacement element. The cooling may occur at a controlled rate. After the cooling process is complete, the mold may be broken away to expose the body of the resulting drill bit. The resulting drill bit body may be subjected to further manufacturing processes (e.g., machining) to complete the drill bit. 
       FIG. 4  is a schematic drawing in section with portions broken away showing an example of a mold assembly in accordance with certain embodiments of the present disclosure. Mold assembly  400  may include mold  470 , gauge ring  472 , and funnel  474  which may be formed of any suitable material, such as graphite. Gauge ring  472  may be threaded to couple with the top of mold  470  and funnel  474  may be threaded to couple with the top of gauge ring  472 . Funnel  474  may be used to extend mold assembly  400  to a height based on the size of the drill bit to be manufactured using mold assembly  400 . The components of mold assembly  400  may be created using any suitable manufacturing process, such as casting and/or machining. The shape of mold assembly  400  may have a reverse profile from the exterior features of the drill bit to be formed using mold assembly  400  (the resulting drill bit). 
     Interior displacement elements  492  are shown positioned in an interior region  491  of an MMC drill bit. In the embodiment shown, displacement elements  492  are in the shapes of rings, rods, pellets, and/or spheres. However, interior displacement elements  492  may have various sizes and shapes as mentioned above. For example, interior displacement elements  492  may have a geometric shape, including a cube, sphere, star, ring, rectangular prism, and/or parallelepiped shape, or may be in foils or plates. In certain embodiments, the interior displacement elements may have regular shapes, irregular shapes, or a combination thereof, and multiple displacement elements used in the manufacture of a single drill bit may have the same shape or different shapes. 
     In some cases, various types of additional displacements and/or mold inserts such as junk slot displacement  496  may be installed within mold assembly  400 , depending on the configuration of the resulting drill bit. The additional displacements and/or mold inserts may be formed from any suitable material, such as consolidated sand and/or graphite. The additional displacements and/or mold inserts may be used to form voids in the surface of the resulting drill bit. For example, consolidated sand may be used to form core  476  and/or fluid flow passage  480 , which may communicate with a nozzle, e.g., one of nozzles  156  in  FIG. 2 , or one of nozzles  556 ,  656 , or  756  in  FIGS. 5-7 . Additionally, mold inserts (not expressly shown) may be placed within mold assembly  400  to form pockets  466  in blade  426 . Cutting elements, including cutting elements  128  shown in  FIG. 2 , may be attached to pockets  466 , as described with respect to cutter pockets  166  in  FIG. 2 . 
     A generally hollow, cylindrical metal mandrel  478  may be placed within mold assembly  400 . The inner diameter of metal mandrel  478  may be larger than the outer diameter of core  476  and the outer diameter of metal mandrel  478  may be smaller than the outer diameter of the resulting drill bit. Metal mandrel  478  may be used to form a portion of the interior of the drill bit. 
     After interior displacement elements  492  and any additional displacements or inserts are placed within mold assembly  400 , mold assembly may be filled with reinforcement material  490 . Reinforcement material  490  may be selected to provide designed characteristics for the resulting drill bit, such as fracture resistance, toughness, and/or erosion, abrasion, and wear resistance. Reinforcement material  490  may be any suitable material, such as particles of metals, metal alloys, superalloys, intermetallics, borides, carbides, nitrides, oxides, silicides, ceramics, diamonds, and the like, or any combination thereof. While a single type of reinforcement material  490  is shown in  FIG. 4 , multiple types of reinforcement material  490  may be used. 
     Once reinforcement material  490  and interior displacement element  492  are loaded in mold assembly  400 , reinforcement material  490  may be packed into mold assembly  400  using any suitable mechanism, such as a series of vibration cycles. The packing process may help to ensure consistent density of reinforcement material  490  and provide consistent properties throughout the portions of the resulting drill bit formed of reinforcement material  490 . 
     After the packing of reinforcement material  490 , binder material  494  may be placed on top of reinforcement material  490 , core  476 , and/or metal mandrel  478 . Binder material  494  may include any suitable binder material such as copper, nickel, cobalt, iron, aluminum, molybdenum, chromium, manganese, tin, zinc, lead, silicon, tungsten, boron, phosphorous, gold, silver, palladium, indium, and/or alloys thereof. Binder material  494  may be selected such that the downhole temperatures during the subterranean operation are less than the critical temperature or melting point of binder material  494 . 
     Mold assembly  400  and the materials disposed therein may be heated via any suitable heating mechanism, including a furnace. When the temperature of binder material  494  exceeds the melting point of binder material  494 , binder material  494  may flow into reinforcement material  490  towards mold  470 . As binder material  494  infiltrates reinforcement material  490 , binder material  494  may additionally infiltrate interior displacement elements  492  as described above. For example, if interior displacement elements  492  comprise open-cell porous structures or hollow shells with one or more holes or openings in the shell, the binder material  494  may flow into the interior of at least a portion of interior displacement elements  492 . 
     Once binder material  494  has infiltrated reinforcement material  490 , mold assembly  400  may be removed from the furnace and cooled at a controlled rate. After the cooling process is complete, mold assembly  400  may be broken away to expose the body of the resulting drill bit. The resulting drill bit body may be subjected to further manufacturing processes to complete the drill bit. For example, cutting elements (for example, cutting elements  128  shown in  FIG. 2 ) may be brazed to the drill bit to couple the cutting elements to pockets  466 . During the brazing process, binder material  494  and/or interior displacement elements  492  may be heated above their melting points and some additional reaction, deformation, and/or degradation of those materials may occur. For example, interior displacement elements  492  may be melted, dissolved, or burned away to leave voids within the drill bit where interior displacement elements  492  were previously located. 
       FIG. 5  is a diagram of bottom view of an example of a drill bit similar to that shown in  FIG. 2  (viewed from above the top portion of the bit, as oriented in  FIG. 2 ) manufactured according to the processes described with respect to  FIGS. 3 and 4  above. Similar to the elements shown in  FIG. 2 , drill bit  501  includes a bit body  524  having a central axis  504 , a plurality of blades  526  disposed outwardly from exterior portions of bit body  524 , nozzles  556  formed in the bit body  524  between the blades  526 , and a plurality of cutting elements  528  disposed outwardly from exterior portions of each blade  526 . In the embodiment shown, bit body  524  further comprises a plurality of interior displacement elements  592  that were placed within the mold during the manufacture of the bit body. As shown, interior displacement elements  592  are located in an interior region  591  of the bit body  524  (e.g., they are surrounded by the MMC material  595 ), and are distributed relatively uniformly across the bit body. As shown, interior displacement elements  592  have round cross-sectional shape, and may comprise spheres or cylindrically shaped rods or pellets that were oriented vertically within the bit mold, in a manner similar to that shown for interior displacement elements  492  in  FIG. 4 . 
       FIG. 6  is a diagram of a bottom view of another example of a drill bit similar to that shown in  FIG. 2  and manufactured according to the processes described with respect to  FIGS. 3 and 4  above. Similar to the elements shown in  FIGS. 2 and 5 , drill bit  601  includes a bit body  624  having a central axis  604 , a plurality of blades  626 , nozzles  656 , and a plurality of cutting elements  628 . In the embodiment shown, bit body  624  further comprises a plurality of interior displacement elements  692  of irregular cross-sectional shapes that were placed within the mold during the manufacture of the bit body in locations corresponding to an interior region  691  of the bit body  624  (e.g., they are surrounded by the MMC material  695 ). As shown, interior displacement elements  692  comprise a greater volume of the bit body  624  as compared to the interior displacement elements shown in  FIG. 5 , although they are generally located in the vicinity of nozzles  656 . 
       FIG. 7  is a diagram of a bottom view of another example of a drill bit similar to that shown in  FIG. 2  and manufactured according to the processes described with respect to  FIGS. 3 and 4  above. Similar to the elements shown in  FIGS. 2, 5, and 6 , drill bit  701  includes a bit body  724  having a central axis  704 , a plurality of blades  726 , nozzles  756 , and a plurality of cutting elements  728 . In the embodiment shown, bit body  724  further comprises a single interior displacement element  792  of irregular cross-sectional shape that was placed within the mold during the manufacture of the bit body in a location corresponding to an interior region  791  of the bit body  724  (e.g., surrounded by the MMC material  795 ). As a person of skill in the art with the benefit of this disclosure will recognize, this cross-sectional view instead could represent an embodiment in which a plurality of interior displacement elements  792  having the same cross-sectional shape shown are disposed within bit body  724  at various locations along the height of the bit body. As shown, interior displacement element  792  comprises a greater volume of the bit body  724  as compared to the interior displacement elements shown in  FIGS. 5 and 6 . As shown interior displacement element  792  is primarily located in the vicinity of the center (e.g., the central rotational axis  704 ) of the bit body  724 , and extends away from the leading edges of the root portions of the blades  726  as it extends away from the center of the bit body. Due to the relatively large volume occupied by the interior displacement element  792  in  FIG. 7 , in certain embodiment, the durability or useful life of drill bit  701  and other drill bits having similar structures may be limited as compared to other embodiments of drill bits according to the present disclosure. 
     As would be understood by a person of ordinary skill in the art with the benefit of this disclosure, if the interior displacement elements shown in  FIGS. 5-7  were melted, dissolved, burned, or otherwise degraded at some point during or after the manufacture of the bit, regions  592 ,  692 , and/or  792  (or some subset thereof) in drill bits resulting from those processes may not actually represent the interior displacement elements themselves, but instead may represent “binder-rich” regions of the bit body and/or voids left where the interior displacement elements were placed during manufacture. 
     The regions of drill bits  101 ,  501 ,  601 , and  701  corresponding to the regions near flow passage  480  in  FIG. 4  and/or nozzles  156  in  FIG. 2 or 556, 656 , or  756  in  FIGS. 5-7  may be subject to stresses during the subterranean operation that may cause cracks in drill bit  101 . Thus, in some embodiments, an interior displacement element may be located in the vicinity of one or more of nozzles  156 ,  556 ,  656 , or  756  among other reasons, to increase the toughness and/or crack-arresting properties of the drill bit in those regions. 
     The interior displacement element configurations shown in  FIGS. 4-7  are provided as examples only. Any number of interior displacement element configurations are anticipated by the present disclosure. The type, shape, and size of the interior displacement element may be based on the properties selected for the region of the drill bit in which the interior displacement element is placed. Additionally the spacing between individual pieces of displacement element may vary based on the type, shape, and/or size of displacement element used and the properties selected for the region of the drill bit in which the interior displacement element is placed. 
     Modeling of an MMC drill bit and/or simulation of a subterranean operation may be used to obtain an analysis of the stresses to which the MMC drill bit may be subjected during the subterranean operation. The stress analysis may be used to select the type of displacement element used in the MMC drill bit, the size, shape, and/or spacing of the interior displacement element, and/or the placement of the interior displacement element. 
     An embodiment of the present disclosure is a drill bit comprising: a body; a plurality of blades on the body; a plurality of cutting elements on at least one of the plurality of blades; a reinforcement material forming portions of the body and the plurality of blades; a binder material infiltrated through the reinforcement material to form a composite material and forming portions of the body and the plurality of blades; and at least one interior displacement element located in an interior region of the body that is surrounded by the composite material. 
     Another embodiment of the present disclosure is a drill bit comprising: a body; a plurality of blades on the body; a plurality of cutting elements on at least one of the plurality of blades; a reinforcement material forming portions of the body and the plurality of blades; a binder material infiltrated through the reinforcement material to form a composite material and forming portions of the body and the plurality of blades; and at least one area located in an interior region of the body surrounded by the composite material wherein an interior displacement element at least partially displaced the reinforcement material therefrom. 
     Another embodiment of the present disclosure is a method of making a matrix drill bit comprising: placing at least one interior displacement element in a region of a matrix bit body mold corresponding to an interior region of a bit body formed using the matrix bit body mold; placing a reinforcement material in the matrix bit body mold; placing a binder material in the matrix bit body mold on top of the reinforcement material and surrounding the interior displacement element; heating the matrix bit body mold, the reinforcement material, the interior displacement element, and the binder material to a temperature above the melting point of the binder material; infiltrating the reinforcement material with the binder material; and cooling at least the matrix bit body mold, the reinforcement material, and the binder material to form a matrix composite drill bit body. 
     Another embodiment of the present disclosure is a drilling system comprising: a drill string; and a drilling tool coupled to the drill string, the drilling tool comprising: a body; a plurality of blades on the body; a plurality of cutting elements on at least one of the plurality of blades; a reinforcement material forming portions of the body and the plurality of blades; a binder material infiltrated through the reinforcement material to form a composite material and forming portions of the body and the plurality of blades; and at least one interior displacement element located in an interior region of the body that is surrounded by the composite material. 
     Another embodiment of the present disclosure is a method of drilling a well bore comprising: providing a drill string and a drilling tool coupled to the drill string, the drilling tool comprising a body, a plurality of blades on the body, a plurality of cutting elements on at least one of the plurality of blades, a reinforcement material forming portions of the body and the plurality of blades, a binder material infiltrated through the reinforcement material to form a composite material and forming portions of the body and the plurality of blades, and at least one interior displacement element located in an interior region of the body that is surrounded by the composite material; and using the drill string and drilling tool to drill at least a portion of a well bore penetrating at least a portion of a subterranean formation. 
     Another embodiment of the present disclosure is a method of drilling a well bore comprising: providing a drill string and a drilling tool coupled to the drill string, the drilling tool comprising a body, a plurality of blades on the body, a plurality of cutting elements on at least one of the plurality of blades, a reinforcement material forming portions of the body and the plurality of blades, a binder material infiltrated through the reinforcement material to form a composite material and forming portions of the body and the plurality of blades, and at least one area located in an interior region of the body surrounded by the composite material wherein an interior displacement element at least partially displaced the reinforcement material therefrom; and using the drill string and drilling tool to drill at least a portion of a well bore penetrating at least a portion of a subterranean formation. 
     Each of the embodiments described above may have one or more of the following additional elements in any combination:
         Element 1: wherein the interior displacement element has a shape of at least one of: a pellet, a sphere, and a cylinder;   Element 2: wherein the interior displacement element comprises at least one material selected from the group consisting of: an open-cell foam, a closed-cell foam, wool, a ceramic material, a metallic material, a cement, a polymeric material, and any combination thereof;   Element 3: wherein the interior displacement element comprises a foam;   Element 4: wherein at least one of the interior displacement elements is located in the vicinity of a central axis of the body of the drill bit or one or more nozzles formed in the body of the drill bit.   Element 5: wherein the area located within the interior region of the body comprises a binder-rich area.   Element 6: wherein the area located within the interior region of the body comprises an empty space or void.   Element 7: wherein the interior displacement material melts, dissolves, or otherwise degrades prior to the step of cooling the matrix bit body mold, the reinforcement material, and the binder material.       

     Therefore, the present disclosure is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present disclosure may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. While numerous changes may be made by those skilled in the art, such changes are encompassed within the spirit of the subject matter defined by the appended claims. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present disclosure. The terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.