MODIFIED CUTTERS AND A METHOD OF DRILLING WITH MODIFIED CUTTERS
A cutter for a drag bit may include a substrate and an ultrahard layer on an end surface of the substrate. The ultrahard layer may include an exposed surface having at least three depressions extending from an interior of the exposed surface radially outward to a peripheral edge formed between the working surface and a side surface of the ultrahard layer, the at least three depressions separated from each other by at least three raised regions forming an apex of the exposed surface, the at least three raised regions connected to each other proximate the central axis and extending from proximate the central axis to the peripheral edge. Other working surfaces are also included.
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This application is a continuation of U.S. application Ser. No. 14/180,121, filed on Feb. 13, 2014, which is a broadening reissue of U.S. application Ser. No. 12/796,560, filed on Jun. 8, 2010, issued as U.S. Pat. No. 8,113,303 on Feb. 14, 2012, which is a continuation of U.S. application Ser. No. 11/855,770, filed Sep. 14, 2007 issued as U.S. Pat. No. 7,757,785 on Jul. 20, 2010, which is a continuation of U.S. patent application Ser. No. 11/117,647, filed Apr. 28, 2005, now abandoned, which claims priority, pursuant to 35 U.S.C. §119(e), to U.S. Provisional Patent Application No. 60/648,863, filed Feb. 1, 2005, U.S. Provisional Patent Application No. 60/584,307 filed Jun. 30, 2004, and U.S. Provisional Patent Application No. 60/566,751 filed Apr. 30, 2004. These applications are incorporated herein by reference in their entireties.
BACKGROUND1. Technical Field
The disclosure relates generally to modified cutters.
2. Background Art
Rotary drill bits with no moving elements on them are typically referred to as “drag” bits. Drag bits are often used to drill a variety of rock formations. Drag bits include those having cutters (sometimes referred to as cutter elements, cutting elements or inserts) attached to the bit body. For example, the cutters may be formed having a substrate or support stud made of cemented carbide, for example tungsten carbide, and an ultra hard cutting surface layer or “table” made of a polycrystalline diamond material or a polycrystalline boron nitride material deposited onto or otherwise bonded to the substrate at an interface surface.
An example of a prior art drag bit having a plurality of cutters with ultra hard working surfaces is shown in
Nozzles 23 are typically formed in the drill bit body 12 and positioned in the gaps 16 so that fluid can be pumped to discharge drilling fluid in selected directions and at selected rates of flow between the cutting blades 14 for lubricating and cooling the drill bit 10, the blades 14 and the cutters 18. The drilling fluid also cleans and removes the cuttings as the drill bit rotates and penetrates the geological formation. The gaps 16, which may be referred to as “fluid courses,” are positioned to provide additional flow channels for drilling fluid and to provide a passage for formation cuttings to travel past the drill bit 10 toward the surface of a wellbore (not shown).
The drill bit 10 includes a shank 24 and a crown 26. Shank 24 is typically formed of steel or a matrix material and includes a threaded pin 28 for attachment to a drill string. Crown 26 has a cutting face 30 and outer side surface 32. The particular materials used to form drill bit bodies are selected to provide adequate toughness, while providing good resistance to abrasive and erosive wear. For example, in the case where an ultra hard cutter is to be used, the bit body 12 may be made from powdered tungsten carbide (WC) infiltrated with a binder alloy within a suitable mold form. In one manufacturing process the crown 26 includes a plurality of holes or pockets 34 that are sized and shaped to receive a corresponding plurality of cutters 18.
The combined plurality of surfaces 20 of the cutters 18 effectively forms the cutting face of the drill bit 10. Once the crown 26 is formed, the cutters 18 are positioned in the pockets 34 and affixed by any suitable method, such as brazing, adhesive, mechanical means such as interference fit, or the like. The design depicted provides the pockets 34 inclined with respect to the surface of the crown 26. The pockets 34 are inclined such that cutters 18 are oriented with the working face 20 at a desired rake angle in the direction of rotation of the bit 10, so as to enhance cutting. It will be understood that in an alternative construction (not shown), the cutters can each be substantially perpendicular to the surface of the crown, while an ultra hard surface is affixed to a substrate at an angle on a cutter body or a stud so that a desired rake angle is achieved at the working surface.
A typical cutter 18 is shown in
Cutters may be made, for example, according to the teachings of U.S. Pat. No. 3,745,623, whereby a relatively small volume of ultra hard particles such as diamond or cubic boron nitride is sintered as a thin layer onto a cemented tungsten carbide substrate. Flat top surface cutters as shown in
Generally speaking, the process for making a cutter 18 employs a body of cemented tungsten carbide as the substrate 38, wherein the tungsten carbide particles are cemented together with cobalt. The carbide body is placed adjacent to a layer of ultra hard material particles such as diamond or cubic boron nitride particles and the combination is subjected to high temperature at a pressure where the ultra hard material particles are thermodynamically stable. This results in recrystallization and formation of a polycrystalline ultra hard material layer, such as a polycrystalline diamond or polycrystalline cubic boron nitride layer, directly onto the upper surface 54 of the cemented tungsten carbide substrate 38.
It has been found by applicants that many cutters develop cracking, spalling, chipping and partial fracturing of the ultra hard material cutting layer at a region of cutting layer subjected to the highest loading during drilling. This region is referred to herein as the “critical region” 56. The critical region 56 encompasses the portion of the cutting layer 44 that makes contact with the earth formations during drilling. The critical region 56 is subjected to the generation of high magnitude stresses from dynamic normal loading, and shear loadings imposed on the ultra hard material layer 44 during drilling. Because the cutters are typically inserted into a drag bit at a rake angle, the critical region includes a portion of the ultra hard material layer near and including a portion of the layer's circumferential edge 22 that makes contact with the earth formations during drilling.
The high magnitude stresses at the critical region 56 alone or in combination with other factors, such as residual thermal stresses, can result in the initiation and growth of cracks 58 across the ultra hard layer 44 of the cutter 18. Cracks of sufficient length may cause the separation of a sufficiently large piece of ultra hard material, rendering the cutter 18 ineffective or resulting in the failure of the cutter 18. When this happens, drilling operations may have to be ceased to allow for recovery of the drag bit and replacement of the ineffective or failed cutter. The high stresses, particularly shear stresses, can also result in delamination of the ultra hard layer 44 at the interface 46.
One type of ultra hard working surface 20 for fixed cutter drill bits is formed as described above with polycrystalline diamond on the substrate of tungsten carbide, typically known as a polycrystalline diamond compact (PDC), PDC cutters, PDC cutting elements, or PDC inserts. Drill bits made using such PDC cutters 18 are known generally as PDC bits. While the cutter or cutter insert 18 is typically formed using a cylindrical tungsten carbide “blank” or substrate 38 which is sufficiently long to act as a mounting stud 40, the substrate 38 may also be an intermediate layer bonded at another interface to another metallic mounting stud 40.
The ultra hard working surface 20 is formed of the polycrystalline diamond material, in the form of a cutting layer 44 (sometimes referred to as a “table”) bonded to the substrate 38 at an interface 46. The top of the ultra hard layer 44 provides a working surface 20 and the bottom of the ultra hard layer cutting layer 44 is affixed to the tungsten carbide substrate 38 at the interface 46. The substrate 38 or stud 40 is brazed or otherwise bonded in a selected position on the crown of the drill bit body 12 (
In order for the body of a drill bit to be resistant to wear, hard and wear-resistant materials such as tungsten carbide are typically used to form the drill bit body for holding the PDC cutters. Such a drill bit body is very hard and difficult to machine. Therefore, the selected positions at which the PDC cutters 18 are to be affixed to the bit body 12 are typically formed during the bit body molding process to closely approximate the desired final shape. A common practice in molding the drill bit body is to include in the mold, at each of the to-be-formed PDC cutter mounting positions, a shaping element called a “displacement.”
A displacement is generally a small cylinder, made from graphite or other heat resistant materials, which is affixed to the inside of the mold at each of the places where a PDC cutter is to be located on the finished drill bit. The displacement forms the shape of the cutter mounting positions during the bit body molding process. See, for example, U.S. Pat. No. 5,662,183 issued to Fang for a description of the infiltration molding process using displacements.
It has been found by applicants that cutters with sharp cutting edges or small back rake angles provide a good drilling ROP, but are often subject to instability and are susceptible to chipping, cracking or partial fracturing when subjected to high forces normal to the working surface. For example, large forces can be generated when the cutter “digs” or “gouges” deep into the geological formation or when sudden changes in formation hardness produce sudden impact loads. Small back rake angles also have less delamination resistance when subjected to shear load. Cutters with large back rake angles are often subjected to heavy wear, abrasion and shear forces resulting in chipping, spalling, and delamination due to excessive downward force or weight on bit (WOB) required to obtain reasonable ROP. Thick ultra hard layers that might be good for abrasion wear are often susceptible to cracking, spalling, and delamination as a result of residual thermal stresses associated with forming thick ultra hard layers on the substrate. The susceptibility to such deterioration and failure mechanisms is accelerated when combined with excessive load stresses.
Different types of bits are generally selected based on the nature of the geological formation to be drilled. Drag bits are typically selected for relatively soft formations such as sands, clays and some soft rock formations that are not excessively hard or excessively abrasive. However, selecting the best bit is not always straightforward because many formations have mixed characteristics (i.e., the geological formation may include both hard and soft zones), depending on the location and depth of the well bore. Changes in the geological formation can affect the desired type of a bit, the desired ROP of a bit, the desired rotation speed, and the desired downward force or WOB. Where a drill bit is operated outside the desired ranges of operation, the bit can be damaged or the life of the bit can be severely reduced.
For example, a drill bit normally operated in one general type of formation may penetrate into a different formation too rapidly or too slowly subjecting it to too little load or too much load. For another example, a drill bit rotating and penetrating at a desired speed may encounter an unexpectedly hard formation material, possibly subjecting the bit to a “surprise” or sudden impact force. A formation material that is softer than expected may result in a high rate of rotation, a high ROP, or both, that can cause the cutters to shear too deeply or to gouge into the geological formation.
This can place greater loading, excessive shear forces and added heat on the working surface of the cutters. Rotation speeds that are too high without sufficient WOB, for a particular drill bit design in a given formation, can also result in detrimental instability (bit whirling) and chattering because the drill bit cuts too deeply or intermittently bites into the geological formation. Cutter chipping, spalling, and delamination, in these and other situations, are common failure modes for ultra hard flat top surface cutters.
Dome cutters have provided certain benefits against gouging and the resultant excessive impact loading and instability. This approach for reducing adverse effects of flat surface cutters is described in U.S. Pat. No. 5,332,051. An example of such a dome cutter in operation is depicted in
Scoop cutters, as shown at 80 in
What is still needed, however, are improved cutters for use in a variety of applications.
SUMMARYIn one aspect, the present disclosure relates to a modified cutting element that includes a base portion, an ultrahard layer disposed on said base portion, and at least one modified region disposed adjacent to a cutting face of the cutter.
In one aspect, the present disclosure relates to a drill bit that includes a bit body; and at least one cutter, the at least one cutter comprising a base portion, an ultrahard layer disposed on said base portion, and at least one modified region disposed adjacent to a cutting face of the cutter.
Other aspects and advantages of the disclosure will be apparent from the following description and the appended claims.
The present disclosure relates to shaped cutters that provide advantages when compared to prior art cutters. In particular, embodiments of the present disclosure relate to cutters that have structural modifications to the cutting surface in order to improve cutter performance. As a result of the modifications, embodiments of the present disclosure may provide improved cooling, higher cutting efficiency, and longer lasting cutters when compared with prior art cutters.
Embodiments of the present disclosure relate to cutters having a substrate or support stud, which in some embodiments may be made of cemented carbide, for example tungsten carbide, and an ultra hard cutting surface layer or “table” made of a polycrystalline diamond material or a polycrystalline boron nitride material deposited onto or otherwise bonded to the substrate at an interface surface. Also, in selected embodiments, the ultra-hard layer may comprise a “thermally stable” layer. One type of thermally stable layer that may be used in embodiments of the present disclosure is leached polycrystalline diamond.
A typical polycrystalline diamond layer includes individual diamond “crystals” that are interconnected. The individual diamond crystals thus form a lattice structure. A metal catalyst, such as cobalt may be used to promote recrystallization of the diamond particles and formation of the lattice structure. Thus, cobalt particles are typically found within the interstitial spaces in the diamond lattice structure. Cobalt has a significantly different coefficient of thermal expansion as compared to diamond. Therefore, upon heating of a diamond table, the cobalt and the diamond lattice will expand at different rates, causing cracks to form in the lattice structure and resulting in deterioration of the diamond table.
In order to obviate this problem, strong acids may be used to “leach” the cobalt from the diamond lattice structure. Examples of “leaching” processes can be found, for example in U.S. Pat. Nos. 4,288,248 and 4,104,344. Briefly, a hot strong acid, e.g., nitric acid, hydrofluoric acid, hydrochloric acid, or perchloric acid, or combinations of several strong acids may be used to treat the diamond table, removing at least a portion of the catalyst from the PDC layer.
Removing the cobalt causes the diamond table to become more heat resistant, but also causes the diamond table to be more brittle. Accordingly, in certain cases, only a select portion (measured either in depth or width) of a diamond table is leached, in order to gain thermal stability without losing impact resistance. As used herein, thermally stable polycrystalline diamond compacts include both of the above (i.e., partially and completely leached) compounds. In one embodiment, only a portion of the polycrystalline diamond compact layer is leached. For example, a polycrystalline diamond compact layer having a thickness of 0.010 inches may be leached to a depth of 0.006 inches. In other embodiments, the entire polycrystalline diamond compact layer may be leached. A number of leaching depths may be used, depending on the particular application, for example, in one embodiment the leaching depth may be 0.05 mm.
The original height of the diamond table layer is shown as unmodified portion 608, as the modified regions 604 are designed such that the unmodified portion 608 has a discrete width in this embodiment. In some instances the modified region or regions 604 may be formed when the cutter is actually being bonded together (i.e., a modified region is originally built into the ultrahard layer), but in other instances, the modified region may be formed after the formation of the ultrahard layer, by using electrical discharge machining, for example. In addition, in select embodiments, only portions of the modified surface may be leached. Those having ordinary skill in the art will recognize that masking agents may be used to prevent leaching in certain areas, to provide regions that are leached and legions that are unleached.
Wire electrical discharge machining (EDM) is an electrical discharge machining process with a continuously moving conductive wire as tool electrode. The mechanism of metal removal in wire EDM involves the complex erosion effect of electric sparks generated by a pulsating direct current power supply between two closely spaced electrodes in dielectric liquid. The high energy density erodes material from both the wire and workpiece by local melting and vaporizing. Because the new wire keeps feeding to the machining area, the material is removed from the workpiece with the moving of wire electrode. Eventually, a cutting shape is formed on the workpiece by the programmed moving trajectory of wire electrode.
As the term is used herein, a modified region constitutes at least one area, adjacent to the cutting face, that has a lower overall height than the cutting face itself. Cutters containing the modified region 604 have a number of advantages when compared to prior art planar cutters. For example, because the modified region is a depressed area adjacent to the cutting face, improved cooling (due to better fluid flow and/or air flow) around the cutting edge may be seen, which may help prevent failure due to thermal degradation.
In the embodiment shown in
In
After formation of the saddle-shaped cutter, mill tests were performed to determine the performance of the cutters. Test results showed that approximately a 20% increase in performance when compared to prior art cutters was seen when a polycrystalline diamond surface was used. In addition, when thermally stable polycrystalline diamond was used as the ultrahard layer, a performance jump of nearly 70% was seen as compared to unmodified thermally stable polycrystalline diamond cutters. As stated above, without being limited to any particular theory, that the improved performance may be due to a number of factors such as, improved cooling around the cutting face, higher cutting efficiency (due to the non-planar interaction at the cutting face), and the fact that a non-planar interface leads to less flaking of the thermally stable polycrystalline diamond.
Cutters formed in accordance with embodiments of the present invention may be used either alone or in conjunction with standard cutters depending on the desired application. In addition, while reference has been made to specific manufacturing techniques, those of ordinary skill will recognize that any number of techniques may be used.
Depending upon the embodiment, the face 154 may be a planar shaped surface, a dome shaped surface or a surface having another shape. The depressions 150a-c in this embodiment comprise planar surfaces or facets each at an obtuse angle relative to a central axis 152 of the cylindrical ultra hard top layer. The obtuse angle is different from the angle of other portions of the working surface, such that a relative depressed area defining the depressions 150a-c is formed the face 154. Where the surrounding portions of the face 154 are planar and at a 90-degree angle with respect to the axis of the cutter, the obtuse angle is generally greater than 90 degrees with respect to the axis 152 of the cutter. However, according to alternative embodiments of the invention, the obtuse angle may be less than 90 degrees. It will also be understood that in other alternative embodiments, each of the depressions 150a-c can be multi-faceted or comprised of multiple planar surfaces. Alternatively, the depressions 150a-c can also be formed with simple curved surfaces that may be concave or convex or can be formed with a plurality of curved surfaces or with a smooth complex curve.
The depressions 150a-c may be formed and shaped during the initial compaction of the ultra hard layer 140 or can be shaped after the ultra hard layer is formed, for example by Electro Discharge Machining (EDM) or by Electro Discharge Grinding (EDG). The ultra hard layer 140 may, for example, be formed as a polycrystalline diamond compact or a polycrystalline cubic boron nitride compact. Also, in selected embodiments, the ultra-hard layer may comprise a “thermally stable” layer. One type of thermally stable layer that may be used in embodiments may be a TSP element or partially or fully leached polycrystalline diamond. The depressions 150a-c extend generally at an angle relative to the face 154 outward to the edge of the cutter. It has been found that a varied chamfer 144 can be conveniently made with a fixed angle and fixed depth EDM or EDG device. For example, an EDM device will typically cut deepest into the edge 146 where the raise areas of face 154 extend to the edge 146 and will cut less deep where the depressions 150a-c extend to the edge 146. The chamfer 144 is cut the least at the lowest edge point in each depression 150a-c and progressively deeper on either side of the lowest edge point. A varied width or size chamfer is conveniently formed circumferentially around the edge 146 of the ultra hard cutter layer 140. Alternatively, variable or programmable angle and depth EDM or EGM can be used to form the variable geometry chamfer.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.
Claims
1. A cutter, comprising:
- a substrate; and
- an ultrahard layer on an end surface of the substrate, the ultrahard layer including a central axis and an exposed surface having at least three depressions extending from an interior of the exposed surface radially outward to a peripheral edge formed between the working surface and a side surface of the ultrahard layer, the at least three depressions separated from each other by at least three raised regions forming an apex of the exposed surface, the at least three raised regions connected to each other proximate the central axis and extending from proximate the central axis to the peripheral edge.
2. The cutter of claim 1, wherein at least one raised region has a width that varies on a length of the raised region.
3. The cutter of claim 1, wherein the peripheral edge undulates between the at least three raised regions and the at least three depressions.
4. The cutter of claim 1, wherein the peripheral edge extends to an outer diameter of the cutter.
5. The cutter of claim 1, wherein the at least three raised ridges comprise a flat region extending from a first portion of the peripheral edge to the central axis.
6. The cutter of claim 1, wherein the at least three depressions have a concave curvature.
7. The cutter of claim 1, wherein the apex comprises a convex curvature.
8. The cutter of claim 1, wherein the peripheral edge has a varied geometry around at least a portion of the periphery of the exposed top surface.
9. A fixed cutter drill bit comprising a body having the cutter as recited in claim 1 mounted thereon.
10. A cutter for a drag bit, the cutter comprising:
- a substrate;
- an ultrahard layer on an end surface of the substrate, the ultrahard layer including an exposed top surface surrounded by a peripheral edge, the exposed top surface comprising: an apex extending from the first cutting edge to another portion of the peripheral edge, wherein the exposed top surface decreases in height away from the apex to other portions of the peripheral edge which have a lower overall height than the height of the apex, wherein the apex has a width that varies along its length.
11. The cutter of claim 10, wherein the apex comprises a convex curvature.
12. The cutter of claim 10, wherein the exposed top surface has a concave curvature as it decreases in height away from the apex.
13. The cutter of claim 10, wherein the peripheral edge has a varied geometry around at least a portion of the periphery of the exposed top surface.
14. The cutter of claim 10, wherein the apex comprises a flat region extending from the first cutting edge to the other portion of the peripheral edge.
15. A fixed cutter drill bit comprising a body having the cutter as recited in claim 10 mounted thereon.
16. A cutter, comprising:
- a substrate;
- an ultrahard layer on an end surface of the substrate, the ultrahard layer including an exposed dome shaped top surface surrounded by a peripheral edge, the dome shaped exposed top surface comprising: an apex extending from the first cutting edge to another portion of the peripheral edge, wherein the exposed top surface decreases in height away from the apex to other portions of the peripheral edge which have a lower overall height than the height of the apex.
17. The cutter of claim 16, wherein the apex comprises a convex curvature.
18. The cutter of claim 16, wherein the exposed top surface has a concave curvature as it decreases in height away from the apex.
19. The cutter of claim 16, wherein the peripheral edge has a varied geometry around at least a portion of the periphery of the exposed top surface.
20. A fixed cutter drill bit comprising a body having the cutter as recited in claim 16 mounted thereon.
Type: Application
Filed: Oct 12, 2015
Publication Date: Feb 4, 2016
Applicant: Smith International, Inc. (Houston, TX)
Inventors: Youhe Zhang (Spring, TX), Yuelin Shen (Spring, TX)
Application Number: 14/880,740