Patent Application
20140202774
There are several types of tools used to bore through, and to otherwise form bore holes in, subterranean rock formations when drilling oil and natural gas wells: drag bits and roller cone bits. Examples include rotary drag bits, roller cone bits, and reamers.
Drag bits have no moving parts. As a drag bit is rotated, typically by rotating a drill string to which it is attached, discrete cutting elements (“cutters”) affixed to the face of the bit drag across the bottom of the well, scraping or shearing the formation. Each cutter of a rotary drag bit is positioned and oriented on a face of the drag bit so that a portion of it, which will be referred to as its wear surface, engages the earth formation as the bit is being rotated. The cutters are spaced apart on an exterior cutting surface or face of the body of a drill bit in a fixed, predetermined pattern. The cutters are typically arrayed along each of several blades, which are raised ridges extending generally radially from the central axis of the bit, toward the periphery of the face. When the tool is rotated, its cutters to fracture the formation through a shearing action, resulting in formation of small chips that are then evacuated hydraulically by drilling fluid pumped through carefully placed nozzles in the body of the tool.
Roller cone bits are comprised of one or more cone-shaped cutters that rotate on an axis at approximately thirty-five degree angle to the axis of rotation of the drill bit. As the bit is rotated, the cones roll across the bottom of the hole. Cutting elements—also called cutters—on the surfaces of the cones crush the rock as they pass between the cones and the formation.
In order to improve performance cutters and the earth boring tools on which they are mounted, one or more wear or working surfaces of the cutting elements are made from a layer of sintered polycrystalline diamond (“PCD”), polycrystalline cubic boron nitride, wurtzite boron nitride, aggregated diamond nanotubes (ADN) or other hard, crystalline materials. The layer, usually made in the form of compact, is attached to a substrate typically made, at least in part, from cemented metal carbide, with tungsten carbide being the most common. Cemented metal carbide substrates are formed by sintering powdered metal carbide with a metal alloy binder.
The composite of a polycrystalline diamond compact (“PDC”) and the substrate can be fabricated in a number of different ways. It may also, for example, include transitional layers in which the metal carbide and diamond are mixed with other elements for improving bonding and reducing stress between the PCD and substrate. Each cutter is fabricated as a discrete piece, separate from the drill bit. Fixed cutters are mounted on an exterior of the body of an earth boring tool in a predetermined pattern or layout.
For a so-called “PDC bit”, which is rotary drag bit with PDC cutters, the cutters are typically arrayed along each of several blades, which are comprised of raised ridges formed on the body of the earth boring tool. In a PDC bit, for example, blades are generally arrayed in a radial fashion around the center axis (axis of rotation) of the bit. The length or height of the substrate is typically long enough to act as a mounting stud, with a portion of it fitting into a pocket or recess formed in the body of the drag bit or, in the case of a roller cone bit, the pocket formed in a cutter.
A polycrystalline diamond compact is made with polycrystalline diamond grains, in powder form, which is referred to as “diamond grit,” with the possible addition of one or more powdered metal catalysts and other materials, forming the mixture into a compact, and then sintering it using high heat and pressure or microwave heating. Although cobalt or an alloy of cobalt is the most common catalyst, other Group VIII metal, such as nickel, iron and alloys thereof can be used as catalyst. For a cutter, a PDC is typically formed by packing diamond grit without the metal catalyst adjacent a substrate of cemented tungsten carbide, and then sintering the two together. Sintering typically takes place at pressure of less than 1,000,000 pounds per square inch and at temperatures between 1300 degrees Celsius and 1500 degrees Celsius. During sintering, metal binder in the substrate—cobalt in the case of cobalt cemented tungsten carbide—sweeps into and infiltrates the compact, acting as a catalyst to cause formation of diamond-to-diamond bonds between adjacent diamond grains. The result is a mass of bonded diamond crystals, which has been described as continuous or integral matrix of diamond and even a “lattice,” having interstitial voids between the diamond. The interstitial voids are at least partly filled with the metal catalyst. Polycrystalline cubic boron nitride, wurtzite boron nitride, aggregated diamond nanotubes (ADN) or other hard, crystalline materials can be substituted for polycrystalline diamond. It may also, for example, include transitional layers in which the metal carbide and diamond are mixed with other elements for improving bonding and reducing stress between the PDC and substrate. Such layers, if they are present, will be treated as being part of the substrate for purposes of the following description.
Because of the presence of metal catalyst, PDC exhibits thermal instability. Any metal catalyst will have a different coefficient of expansion to diamond. It expands at a greater rate, thus tending to weaken the diamond structure at higher temperatures. Furthermore, the melting point of the metal catalyst is lower than diamond, which can lead to the metal catalyst causing diamond crystals within the PDC to begin to graphitize when temperatures reach or exceed the melting point, also weakening the PDC. To make the PDC at least more thermally stable, a substantial percentage—usually more than 50%; often 70% to 85%; and possibly more—of the catalyst is removed from at least a region next to one or more working surfaces that experience the highest temperatures due to friction. The working surfaces are often defined as the surfaces of the cutter designed or intended for engaging the formation. In the case of a PDC cutter, for example, they are typically the top surface of the diamond crown or table, at least part of its side surface, and, if present, a beveled edge, radiused or shaped transition between the top and side surfaces.
Removal of the catalyst is, however, thought to reduce toughness of the PCD, thus decreasing the cutter's impact resistance. Furthermore, leaching the PCD can result in removal of some of the catalyst metal that cements or binds the substrate, thus affecting the strength or integrity of the substrate and/or the interface of the substrate and diamond interface.
The invention pertains generally to a wear element for a downhole, earth cutting tool for forming bore holes, comprising a wear layer made of superhard carbon allotropes. Superhard carbon allotropes are sometimes referred to as cold-pressed graphite, and include M-carbon, W-carbon, Z-carbon, cbt-C4 and oC16-II depending on the arrangement of carbon and the bonds between the carbon atoms. The superhard carbon allotropes feature SP2 and/or SP3 bonds, and are formed, as the name suggests, at relative low (“cold”) temperatures but at very high pressures, typically in excess of 10 Gigapascals (GPa).
In one embodiment of an exemplary wear element for an earth cutting tool, one or more layers of superhard carbon allotrope, or cold pressed graphite, is attached to a substrate comprised of, for example, a cemented metal carbide. The substrate of the wear element is brazed, mechanically fastened, or otherwise attached to a body of a downhole tool.
In another illustrative embodiment of a wear element for a downhole tool, cold pressed graphite is formed by pressing, with a previously formed cemented carbide substrate, particles of one or more carbon allotropes at pressures in excess of 1,000,000 pounds per square inch, or 6.89 GPa, at relatively “cold” temperatures, to form one or more wear layers on the substrate. Cold temperatures are those substantially below 600 degrees Celsius. In one example, one or more carbon allotropes are selected from a class of SP2 bonded carbon allotropes, including, for example, Fullerenes, carbon nanotubes and graphite. In another example, the particles of carbon allotropes are pressed at a pressure in the range of 10 GPa (or 1.4 million pounds per square inch) to 20 GPa to form a superhard carbon allotrope, or, in the alternative, at a pressure of over 20 GPa (or 2.9 million pound per square inch) to form a superhard carbon allotrope, in each case at cold temperatures. In each of the foregoing examples, the particles can be pressed without a catalyst to form a superhard carbon allotrope.
In another illustrative embodiment, one or more wear layers of superhard carbon allotrope are bonded to the substrate by pressing one or more previously formed wear layers of superhard carbon allotrope on a substrate containing a metal binder, at a lower pressure and at a higher temperature than is required to form the cold-pressed graphite, the temperature being sufficient to cause the metal binder in the substrate to wet adjacent surfaces of a layer of cold-pressed graphite, without damaging the cold-pressed graphite or the substrate.
A cutter comprising a wear layer of cold pressed graphite will possess one or more of the following: enhanced mechanical properties; higher abrasion resistance through higher thermal conductivity in a more homogenous structure that is largely devoid of metal catalyst, at least along the working surfaces and edges of the edges of the cutter; and higher impact resistance due to an amorphic lattice structure and reduced cleavage plains.
In the following description, like numbers refer to like elements.
Disposed on the bit face are a plurality of raised “blades,” each designated 110, that rise from the face of the bit. Each blade extends generally in a radial direction, outwardly to the periphery of the cutting face. In this example, there are six blades substantially equally spaced around the central axis and each blade, in this embodiment, sweeps or curves backwardly in relation to the direction of rotation indicated by arrow 115.
On each blade is mounted a plurality of discrete cutting elements, or “cutters,” 112. Each discrete cutting element is disposed within a recess or pocket. In a drag bit the cutters are placed along the forward (in the direction of intended rotation) side of the blades, with their working surfaces facing generally in the forward direction for shearing the earth formation when the bit is rotated about its central axis. In this example, the cutters are arrayed along blades to form a structure cutting or gouging the formation and then pushing the resulting debris into the drilling fluid which exits the drill bit through the nozzles 117. The drilling fluid in turn transports the debris or cuttings up the bore hole, to the surface.
In this example of a drag bit, all of the cutters 112 are comprised of substrate bonded or otherwise attached to a wear layer comprising cold-pressed graphite. This example of a drill bit includes gauge pads 114.
In this example, an edge between top surface 206 and side surface 208 of the wear layer 204 is beveled to form a beveled edge 210. The top surface and the beveled surface are, in this example, each a working surface for contacting and cutting through the formation. A portion of the side surface, particularly nearer the top, may also come into contact with the formation or debris. Not all of the cutters on a bit or downhole tool must be of the same size, configuration, or shape. In addition to being sintered with different sizes and shapes, such cutters can be cut, ground, or milled to change their shapes. Furthermore, the cutter could have multiple discrete wear layers. Other examples of possible cutter shapes might be pre-flattened gauge cutters, pointed or scribe cutters, chisel-shaped cutters, and dome inserts.
Cold pressed graphite can take many forms that are neither hexagonal nor cubic diamond. Although it is not yet fully understood, one of the most likely structures to result from cold-pressing graphite currently is a low-enthalpy monoclinic structure called M-carbon (space group C2/m, Z516). It has also been referred to as “superhard graphite.” All carbon atoms in the M-carbon structure are four-coordinate and form 5-membered and 7-membered rings. However, other possible structures for cold pressed graphite have been proposed. All of the candidate structures have distinct topologies featuring different patterns, combining odd (5 and 7) and even (4, 6, and 8) rings. In addition to M-carbon other possible structures for cold pressed graphite include a body-centered tetragonal structure called bct-C4 (space group I/4 mmm, Z58), with four-coordinate carbon atoms forming 4-membered and 8-membered rings on the (001) projection, and W-carbon (space group Pnma, Z516). The structure of W-carbon is very similar to that of M-carbon, featuring 5-membered and 7-membered rings. Still other possible structures are an orthorhombic structure, called oC16-II (Cmmm, Z516) and structures that combine even-membered rings (4, 6, and 8), such as oC16-I, mC12, and mC32. All of these structures possess, in theory, similar physical properties, such as bulk moduli and hardness, and, unless specifically indicated otherwise, should all be considered as cold pressed graphite for purposes of this description.
One method of forming cold pressed graphite comprises pressing particles of one or more carbon allotropes, and subjecting the particles during the pressing to pressures greater than 6.89 GigaPascals (GPa) at the temperatures substantially less than 600 degrees Celsius. Examples of carbon allotropes suitable for pressing to form cold-pressed graphite include SP2 bonded carbon allotropes. SP2 bonded carbon allotropes include graphite, fullerenes, and carbon nanotubes, as well as mixtures of two or more of these, or other suitable, allotropes. More specifically, example embodiments of methods of forming cold pressed graphite comprises pressing particles of an SP2 bonded carbon allotrope, and specifically, for example, graphite, under a pressure not less than 6.89 GPa, and, depending on the allotrope, at pressures of greater than 10 GPa (for example at pressures between 15 and 19 GPa), and at pressures greater than 20 GPa, and at ambient temperatures or at temperatures between 0 and 200 degrees Celsius. Unless otherwise specified, cold pressing will refer to a process of applying to particles of one or more carbon allotropes, using a press, pressures greater 1,000,000 pounds per square inch, which is approximately 6.89 GPa, at temperatures of substantially less than 600 degrees Celsius to form cold pressed graphite. At temperatures of 600 degrees Celsius or higher, Lonsdalite will tend to form.
Once the particles are transformed into a cold pressed carbon allotrope, the process 300 may stop, skip step 308, or continue to the optional step 308. Step 308 can also be performed at a later time, separately from process 300. During step 308, the part is subjected to another or second pressing. The second pressing can be comprised of a second phase, or an extension, of the press cycle started at step 306, where the part is not removed between the pressings. Step 308 may also comprise a second or additional press cycle, which can take place at a later time. During the second pressing, the part is subjected to higher temperatures and lower pressures as compared to the first pressing.
During cold pressing at step 304, since the temperature is well below the melting point of the metal binder, the metal from the substrate does not leave or migrate from the substrate. In the second pressing of step 308, the temperature is raised high enough to cause metal binder in the substrate to melt and wet the cold press carbon along the interface between the two, without damaging either the cold pressed carbon or the substrate. Wetting the surface or surfaces of the cold pressed graphite that contact the substrate improves adhesion, once the part cools, between the wear layer of cold pressed carbon and the substrate. In one example the second pressing occurs, depending on the particular metal binder in the substrate, at a temperature at or above 1300 degrees Celsius, and in another example at or above 495 degrees Celsius. In each example, pressing occurs at substantially lower pressures than cold pressing step, for example, at less than 5 GPa. Once the second pressing finishes, the part is removed from the press at step 310 and finished at step 312. As a final step, the wear part is attached, joined, or fastened to a body of a down hole earth cutting tool, by, for example, brazing, welding or press-fitting it to the body or a part of the body, or to a pocket formed in the body or the part of the body.
Alternatively, the wear layer of cold-pressed graphite may be formed separately from the substrate in the form of, for example, a wafer, cylinder, or other disk shaped element, and then joined, attached or affixed to a cemented carbide substrate. In one embodiment, the cold-pressed graphite wear layer is, if desired, milled, ground or otherwise formed into the desired shape prior to being joined, attached or affixed to the substrate. In another embodiment, it is formed into the desired shape (if not already in the desired shape after being pressed) after it is joined, attached or affixed to the substrate. In one example, the wear layer is joined to the substrate by brazing it, using a brazing alloy, or by welding it to the substrate. In another example, an adhesive joins the wear layer and substrate. In yet another example, it is mechanically joined by means of, for example, a fastener, interfering or interlocking members on the wear layer and substrate, or other mechanical means.
The foregoing description is of exemplary and preferred embodiments. The invention, as defined by the appended claims, is not limited to the described embodiments. Alterations and modifications to the disclosed embodiments may be made without departing from the invention. The meaning of the terms used in this specification are, unless expressly stated otherwise, intended to have ordinary and customary meaning and are not intended to be limited to the details of the illustrated or described structures or embodiments.
This application claims the benefit of U.S. provisional application No. 61/754,963, filed Jan. 21, 2013, entitled, “Wear Element for Downhole Tool with a Cold-Pressed Graphite Wear Layer,” which is incorporated herein in its entirety by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61754963 | Jan 2013 | US |
