Drill bit and cutter element having multiple extensions
A cutting element is disclosed having multiple cutting extensions extending from the base portion and separated by valleys. The cutting extensions of the cutting element include both crested and rounded shapes. The cutting extensions may differ in extension height, shape, extension angle, cant angle, and crest angle in other characteristics such as in material properties such as wear resistance, hardness and fracture toughness. The cutting elements have particular, but not exclusive, application in the nose portion of the cone cutters of a rolling cone bit.
This application is a continuation-in-part of U.S. patent application Ser. No. 11/113,747 filed Apr. 25, 2005, entitled “Multi-Lobed Cutter Element for Drill Bit;” which is a continuation application of U.S. patent application Ser. No. 10/355,493, filed Jan. 31, 2003, entitled “Multi-Lobed Cutter Element For Drill Bit;” this application is also a continuation-in-part application of U.S. patent application Ser. No. 10/371,388, filed Feb. 21, 2003, entitled “Drill Bit Cutter Element Having Multiple Cusps.”
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTNot applicable.
FIELD OF THE INVENTIONThe invention relates generally to earth-boring bits used to drill a borehole for the ultimate recovery of oil, gas or minerals. More particularly, the invention relates to rolling cone rock bits and to an improved cutting structure for such bits. Still more particularly, the invention relates to enhancements in cutting element design.
BACKGROUND OF THE INVENTIONAn earth-boring drill bit is typically mounted on the lower end of a drill string and is rotated by revolving the drill string at the surface or by actuation of downhole motors or turbines, or by both methods. With weight applied to the drill string, the rotating drill bit engages the earthen formation and proceeds to form a borehole toward a target zone. The borehole formed in the drilling process will have a diameter generally equal to the diameter or “gage” of the drill bit.
A typical earth-boring bit includes one or more rotatable cone cutters that perform their cutting function due to the rolling movement of the cone cutters acting against the formation material. The cone cutters roll and slide upon the bottom of the borehole as the bit is rotated, the cone cutters thereby engaging and disintegrating the formation material in the bit's path. The rotatable cone cutters may be described as generally conical in shape and are therefore referred to variously as rolling or rotary cones, cone cutters, or rolling cone cutters.
Rolling cone bits typically include a bit body with a plurality of journal segment legs. The rolling cones are mounted on bearing pin shafts that extend downwardly and inwardly from the journal segment legs. The borehole is formed as the gouging and scraping or crushing and chipping action of the rotary cones remove chips of formation material which are carried upward and out of the borehole by drilling fluid which is pumped downwardly through the drill pipe and out of the bit.
The earth disintegrating action of the rolling cone cutters is enhanced by providing the cone cutters with a plurality of cutting elements. Cutting elements are generally of two types: inserts formed of a very hard material, such as tungsten carbide, that are secured in apertures in the cone surface; or teeth that are milled, cast or otherwise integrally formed from the material of the rolling cone. Bits having tungsten carbide inserts are typically referred to as “TCI” bits, while those having teeth formed from the cone material are commonly known as “steel tooth bits.” In each instance, the cutting elements on the rotating cone cutters break up the formation to form new borehole by a combination of gouging and scraping or chipping and crushing.
In oil and gas drilling, the cost of drilling a borehole is proportional to the length of time it takes to drill to the desired depth and location. The time required to drill the well, in turn, is greatly affected by the number of times the drill bit must be changed before reaching the targeted formation. This is the case because each time the bit is changed, the entire string of drill pipes, which may be miles long, must be retrieved from the borehole, section by section. Once the drill string as been retrieved and the new bit installed, the bit must be lowered to the bottom of the borehole on the drill string, which must be reconstructed, section by section. As is thus obvious, this process, known as a “trip” of the drill string, requires considerable time, effort and expense. Accordingly, it is always desirable to employ drill bits which will drill faster and longer and which are usable over a wider range of formation hardness.
The length of time that a drill bit may be employed before it must be changed depends upon its ability to “hold gage” (meaning its ability to maintain a full gage borehole diameter), its rate of penetration (“ROP”), as well as its durability or ability to maintain an acceptable ROP. The form and positioning of the cutting elements (both steel teeth and tungsten carbide inserts) upon the cone cutters greatly impact bit durability and ROP and thus, are important to the success of a particular bit design.
The inserts in TCI bits are typically arranged in circumferential rows on the rolling cone cutters. Most such bits include a row of inserts in the heel surface of the rolling cone cutters. The heel surface is a generally frustoconical surface and is configured and positioned so as to align generally with and ream the sidewall of the borehole as the bit rotates. The heel inserts function primarily to maintain a constant gage and secondarily to prevent the erosion and abrasion of the heel surface of the rolling cone.
In addition to the heel row inserts, conventional bits typically include a circumferential gage row of cutting elements mounted adjacent to the heel surface but oriented and sized in such a manner so as to cut the corner of the borehole. Conventional bits also include a number of additional rows of cutting elements that are located on the cones in circumferential rows disposed radially inward or in board from the gage row. These cutting elements are sized and configured for cutting the bottom of the borehole, and are typically described as inner row cutting elements.
Typically positioned on or near the apex of one or more of the rolling cone cutters, are cutting elements commonly referred to as a nose cutter or nose row cutters. Such cutters are generally responsible for cutting the central portion (or core) of the hole bottom. They may be positioned as a single cutter at or very near the apex of the cone cutter, or may be in a circumferential row of several cutting elements disposed near to the cone apex.
Earthen formations generally undergo two types of fractures when penetrated by a cutting element. A first type of fracture is generally referred to as a plastic fracture, and is a fracture where the cutting element penetrates into the rock and volumetrically displaces the rock by compressing it. In this circumstance, shearing or tearing fracture, rather than tensile fracture, is the major mode of crack propagation. A plastic fracture generally creates a crater in the rock that is the size and shape of that portion of the cutting element that has penetrated into the rock.
A second principal type of fracture is what is referred to as a brittle fracture. A brittle fracture typically occurs after a plastic fracture has first taken place. That is, when the rock first undergoes plastic fracture, a region around the crater made by the cutting element will experience increased tensile stress and will weaken and may crack in that region, even though the rock in that region surrounding the crater has not been displaced. This region of increased stress is generally recognized as the “Hertzian” contact zone. However, in certain formations, when the cutting element displaces enough of the rock and creates enough stress in the Hertzian contact zone adjacent to the plastic fracture, that rock in the region of increased stress may itself break and chip away from the crater. Where this occurs, the cutting element effectively removes a volume of rock that is larger than the volume of rock displaced in the plastic fracture.
The characteristics of these fractures depend largely on the geometry of the cutting element and the properties of the rock that is being penetrated. In general, for a given formation, a sharper insert will generally create more of a plastic fracture whereas a more blunt cutting element will produce more of a brittle fracture. The more blunt insert will typically require a higher force, however, to penetrate to the same depth into the rock as compared to a sharper cutting element. Because a brittle fracture generally removes more rock material than a plastic fracture, it is advantageous to provide a cutting element suitable for inducing brittle fractures and that performs that function without requiring increased force or weight on bit. Thus, to increase a bit's rate of penetration (ROP), it is desirable to increase the bit's ability to initiate brittle fractures at the locations where the cutting element engages the formation material so that the volume of rock removed by each hit or impact of the cutting element is greater than the volume of rock actually penetrated by the cutting element.
A variety of different shapes of cutting elements have been devised. In most instances, each cutting element is designed to optimize the amount of formation material that is removed with each “hit” of the formation by the cutting element. At the same time, however, the shape and design of a particular cutting element is also dependent upon the location in the drill bit in which it is to be placed, and thus the cutting duty to be performed by that cutting element. For example, in general, heel row cutting elements are generally made of a harder and more wear resistant material, and have a less aggressive cutting shape for reaming the borehole side wall, as compared to the inner row cutting elements where the cutting duty is more of a gouging, digging and crushing action. Thus, in general, bottom hole cutting elements generally tend to have more aggressive cutting shapes than heel row cutters.
In many conventional TCI bits, conventional nose row cutters are typically of the chisel-shaped or conical designs. A chisel-shaped insert possesses a crest forming an elongated cutting edge that impacts the core portion of the hole bottom. It is particularly suited for softer formations. By contrast, as compared to a standard chisel-shaped cutter, a conical insert is considered less aggressive as it has a relatively blunt cutting surface, and does not include the relatively sharper cutting edge formed by the chisel's crest. As such, the conical design tends to be more durable than the chisel-shaped cutting element, particularly in harder formations. Regardless of its shape, conventional nose row cutters will only contact the core approximately 1.25 times per bit revolution. At the same time, due to their greater numbers, a row of cutting elements in other locations on each cone contact the hole bottom with much greater frequency, thereby removing formation material faster than at the borehole center. In certain formations, this may result in a core of material that remains uncut and builds up in the center of the borehole, causing the drilling of the borehole to be slower and more costly.
Accordingly, there remains a need in the art for a cutting element with a cutting structure that will allow it to remove more material from the hole bottom, and in particular—the hole core, with fewer revolutions of the bit. Such an enhanced design would hopefully provide a higher ROP and an increase in the footage drilled. It would be desirable to provide cutting elements designed and oriented so as to enhance brittle fracture of the rock formation being drilled, and to present to the formation multiple cutting edges as the cutting surface of the cutting element rotates through its cutting trajectory so as to take advantage of multiple cutting modes. At the same time, however, the cutting element should be able to withstand drilling in multiple formations as typically encountered when drilling with TCI bits. Thus, the desire for a more aggressive cutting element must be tempered by the need for providing a durable and relatively long-lasting cutter, one that will resist breakage.
BRIEF SUMMARY OF THE PREFERRED EMBODIMENTS OF THE INVENTIONPreferred embodiments of the invention are disclosed which provide an earth boring bit and cutting element design intended to provide the potential for increased ROP, as compared with bits employing cutting elements of conventional shape. The embodiments disclosed include cutting elements having aggressive cutting surfaces that have particular, but not exclusive, application in the nose region of a rolling cone cutter.
In one preferred embodiment, a cutting element for a drill bit includes a base portion and a cutting portion having two or more cutting extensions extending away from the base portion, and having valleys between the cutting extensions. The cutting surfaces of the various cutting extensions of the cutting element may be different in shape, or uniform in shape, and may have different extension heights. The cutting extensions may be crested extensions, such as extensions having a chiseled-shaped cutting surface. Further, with respect to crested cutting extensions, such cutting extensions include crests that may differ in crest length, and may form angles relative to the cutting element axis. The angles, referred to as twist angles or crest angles, may be the same or different for different cutting extensions on the cutting element. Further, the cutting extensions define extension angles relative to the longitudinal axis of the cutting element. The extension angles among the plurality of cutting extensions, of a cutting element, may differ, or may be the same. One embodiment includes a cutting element wherein the cutting portion includes a plurality of cutting extensions configured and arranged such that the cutting element includes an asymmetrical cutting surface. In certain embodiments, the cutting extensions are canted and may differ in cant angles.
In certain embodiments, the cutting portion of the cutting element includes a foundation surface adjacent to the base portion, and the cutting extensions extend from the foundation surface. In certain such cutting elements, the foundation surface is generally frustoconical, generally or partially dome-shaped, or other non-planar shape. Furthermore, as previously mentioned, the cutting extensions may include at least two cutting extensions that have cutting surfaces that differ in shape, height, extension angle, crest angle, or cant angle.
The cutting surfaces of the various cutting extensions (as well as the entire cutting extension itself) may be made of differing materials, in particular those having differing degrees of wear resistance, hardness and durability. The materials employed as the cutting surface, like the extension angles, extension height, cutting shapes, twist angle and cant angle may be varied to optimize the cutting element for the particular duty that is expected. For example, relatively long and relatively sharp crested cutting extensions may be included in a cutting element for particular use in soft formations. The same cutting element may include shorter and more rounded cutting extensions as being advantageous when the bit encounters harder formations. As stated, various combinations of the cutting extensions' geometric characteristics or material properties allow the bit designer abundant latitude in optimizing a particular cutting element, where the term “optimizing” includes appropriate compromises in design.
Other embodiments of the invention include a drill bit for drilling through earthen formations including a bit body, at least one rolling cone cutter rotatably mounted on the bit body, and a plurality of cutting elements mounted in the cone cutter, wherein at least one of the cutting elements includes a base portion secured in the cone cutter and a cutting portion having a plurality of cutting extensions extending from the base and being separated by valleys. The drill bit may include such a cutting element located in the nose portion of the bit where the longitudinal axis of the cutting element may be aligned with the cone axis. Alternatively, the bit may have a plurality of cutting elements with multiple cutting extensions where the elements are mounted in the nose region of the cone cutter and disposed in a circumferential row about the cone axis. The cutting extensions may vary in size, shape, extension height, extension angle, crest length, as examples.
The cutting elements and drill bit described herein provide an aggressive cutting structure and cutting element with multiple cutting extensions. At least when employed in the nose region of a bit, these embodiments, offer potential in ROP enhancement given, in particular, that the cutter's multiple cutting extensions will engage and cut the borehole bottom more times per bit revolution than, for example, a conventional chisel-shaped element having only a single cutting surface or the conventional conical cutter having only a relatively blunt cutting surface.
Thus, the embodiments described herein comprise a combination of features intended to enhance the state of the art relating to bit and cutting element design. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGSFor an introduction to the detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings, wherein:
Presently-preferred embodiments of the invention are shown and described below. These embodiments are exemplary only, and are not limiting. That is, the scope of the invention is not limited by the description of the specific embodiments described below, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims
As used herein to compare or claim particular features or characteristics (such as, for example, heights, lengths, angles) of different cutting extensions or cutting elements, the term “differs” or “different” means that the value or magnitude of the characteristic being compared varies by an amount that is greater than that resulting from accepted variances or tolerances normally associated with the manufacturing processes that are used to formulate the raw materials and to process and form those materials into a cutting element. Thus, particular characteristics selected so as to have the nominal value will not “differ,” as that term has thus been defined, even though the characteristics, if measured, would vary about the nominal value by a small amount.
In the description that follows, like parts or features are referred to throughout the specification and drawings with the same reference numerals. The drawing figures are not necessarily to scale. In the figures, certain features of the invention may be shown exaggerated in scale or in somewhat schematic form, and some details of certain elements may be omitted in the interest of clarity and conciseness.
Referring first to
Referring now to
Referring still to
Referring back to
Referring again to
In the embodiment shown in
Referring now to
A cutting element in the form of an insert 70 is shown in
Insert 70 generally includes a base portion 71 and a cutting portion 75 connected to and extending form base 71. Base 71 includes bottom surface 72 and a generally cylindrical side surface 73 that is formed about a central, longitudinal insert axis 74. Cutting portion 75 intersects or joins base portion 71 at a generally circular junction 76. Axis 74 extends generally perpendicular to bottom 72 and a plane containing junction 76. In this embodiment, cutting portion 75 and base portion 71 are integrally-formed of tungsten carbide, although other materials and other manufacturing processes may be employed to form insert 70. Base 71, which may also be referred to as the insert's “grip,” is embedded and retained in cone 34. Cutting portion 75 is that portion of insert 70 that extends beyond the steel of the cone cutter.
Cutting portion 75 generally includes foundation surface 78. Foundation surface 78 intersects cylindrical side surface 73 of base 71 at junction 76, and extends inwardly from junction 76 toward insert axis 74 and upwardly in the direction away from bottom surface 72. In this manner, foundation surface 78 may be said to taper upwardly and away from base 71.
Cutting portion 75 further includes cutting extensions that extend from the foundation surface in a direction upward and away from base 71. In this embodiment, cutting portion 75 includes three cutting extensions 81, 82, 83 separated from one another by valleys 84, 85, 86, best shown in
As best shown in
Cutting extension 81 includes a generally dome-shaped cutting surface 90 which may be hemispherical or a greater or lower portion of a dome. Cutting surface 90 intersects with foundation surface 78 in a curved junction or fillet 91. Cutting extension 83 includes a generally chisel-shaped cutting surface 92, including sloping sides 93 and crest 94, which forms a crest axis 95. The chisel-shaped cutting surface 92 intersects foundation surface 98 in a rounded intersection or fillet 96. Cutting extension 82 also includes a chisel-shaped cutting surface 98 having a crest 101 that generally extends along crest axis 104. Cutting surface 98 includes sloping sides 100 that slope from crest 101 to intersect with foundation surface 78 in a rounded or radiused fillet 99. Preferably, the radius of junctions 91, 96 and 99 is selected to be not less than 0.080. As best shown in
Cutting extensions 81-83 are spaced apart from one another and separated by valleys 84-87, meaning that a planar cross-section of cutting portion 75 taken perpendicular to insert axis 74 will intersect the extensions in a plurality of spaced-apart closed figures when the cross-section is taken at at least one axial position along insert axis 74. Thus, it is understood with reference to
In the embodiment shown in
In the embodiment shown in
In the embodiment shown in
The cutting elements described herein as having a generally chisel-shape and crest may take many forms. For example, cutting extensions having the chisel-shape depicted and described with reference to
Although the cutting surfaces of extensions 81-83 are shown and have been described as being continuously contoured, in order to illustrate certain aspects of insert 70, it is useful to refer to certain portions of the cutting extensions as having distinct boundaries that do not actually exist. Thus, for ease of explanation only,
Referring to
Referring now to
The embodiments thus described include features believed to enable a nose row cutting element to cut the core portion of the borehole effectively, and to do so in a variety of formation hardnesses. For example, and referring to
Additional wear-resistance may be provided to cutting extensions 81-83. In particular, some or all of the cutting surfaces of these cutting extensions may be coated with diamond or other super-abrasive material in order to optimize (which may include compromising) cutting effectiveness and/or wear-resistance. In the embodiment shown in
Super abrasives are significantly harder than cemented tungsten carbide. As used herein, the term “super abrasive” means polycrystalline diamond (PCD), carbon boron nitron (CBN)thermal stable diamond (TSP), cubic boron nitride (PCBN), and any other material having a hardness of at least 2,700 Knoop (kg/mm2). As examples, PCD grades have a hardness range of about 5,000-8,000 Knoop (kg/mm2) while PCBN grades have hardnesses which fall within the range of about 2,700-3,500 Knoop (kg/mm2). By way of comparison, conventional cemented tungsten carbide grades typically have a hardness of less than 1,500 Knoop (kg/mm2).
Certain methods of manufacturing cutting elements with PDC or PCBN coatings are well known. Examples of these methods are described, for example, in U.S. Pat. Nos. 5,766,394, 4,604,106, 4,629,373, 4,694,918 and 4,811,801, the disclosures of which are all incorporated herein by this reference.
There are today a number of commercially available cemented tungsten carbide grades that have differing, but in some cases overlapping, degrees of hardness, wear resistance, compressive strength and fracture toughness. Some of such grades are identified in U.S. Pat. No. 5,967,245, the entire disclosure of which is hereby incorporated by reference. With this understanding, and referring to
In another embodiment shown in
The cutting extensions 83 may be oriented differently than shown in
Further still, and referring to
Referring to
Another embodiment is shown in
While the embodiments described above are shown having three cutting extensions, it should be understood that the number of cutting extensions may vary depending upon the application. Thus, for example, the cutting elements shown herein may instead be formed having two or even four or more cutting extensions.
The cutting elements described herein may be advantageously employed in the nose region of a cone cutter, or in other locations. When employed in the nose region or portion, as shown in
The following co-pending patent applications are hereby incorporated by reference in their entireties: U.S. patent application Ser. No. 10/355,493, filed Jan. 31, 2003, entitled “Multi-Lobed Cutting element For Drill Bit” and of U.S. patent application Ser. No. 10/371,388, filed Feb. 21, 2003, entitled “Drill Bit Cutting element Having Multiple Cusps.”
Claims
1. A cutting element for a drill bit comprising:
- a base portion having a longitudinal axis and a cutting portion extending from said base portion;
- said cutting portion comprising a non-planar foundation surface extending from said base toward said axis, a plurality of cutting extensions extending from said foundation surface, and a valley between said cutting extensions.
2. The cutting element of claim 1 wherein said plurality of cutting extensions include at least two cutting extensions having cutting surfaces that differ in at least one characteristic selected from shape, extension height, extension angle, twist angle and cant angle.
3. The cutting element of claim 1 wherein said foundation surface has a shape selected from generally frustoconical and generally dome-shaped.
4. The cutting element of claim 1 wherein said plurality of cutting extensions includes at least a first cutting extension having a first crest.
5. The cutting element of claim 4 wherein said base includes a longitudinal axis, and wherein said first crest defines a crest axis, said first cutting extension being formed such that said first crest axis does not intersect said longitudinal axis.
6. The cutting element of claim 4 wherein said base includes a cutting element axis, and wherein said cutting portion includes a first cutting extension having a first crest and first crest axis and a second cutting extension having a second crest and second crest axis, wherein said first crest axis forms a first angle of intersection with said element axis, and said second crest axis forms a second angle of intersection with said element axis that is different than said first angle of intersection.
7. The cutting element of claim 1 wherein said cutting extensions include at least three cutting extensions having cutting surfaces, and wherein at least a first of said cutting surface differs in shape from a second of said cutting surfaces.
8. The cutting element of claim 1 wherein said cutting extensions include at least a first cutting extension having a generally dome-shaped cutting surface, and a second cutting extension having a cutting surface comprising a crest.
9. The cutting element of claim 1 wherein said plurality of cutting extensions includes at least one cutting extension having a crest with first and second ends, and wherein said first end is more narrow than said second end.
10. The cutting element of claim 9 wherein said base includes a longitudinal axis, and wherein said second end of said crest is closer to said longitudinal axis than said first end.
11. The cutting element of claim 1 wherein said cutting extensions comprise materials having differing mechanical properties.
12. A cutting element for a drill bit comprising:
- a base portion and a cutting portion extending from said base portion;
- said cutting portion comprising a plurality of cutting extensions extending away from said base and valleys between said cutting extensions, at least one of said cutting extensions having a crest.
13. The cutting element of claim 12 wherein said cutting portion comprises at least two cutting extensions having cutting surfaces that differ in at least one characteristic selected from shape, extension height, extension angle, cant angle and twist angle.
14. The cutting element of claim 12 wherein said plurality of cutting extensions includes at least one cutting extension having a crest that is more narrow at a first end than a second end.
15. The cutting element of claim 12 wherein said cutting portion further comprises a foundation surface adjacent said base having a shape selected from one of generally conical, and generally dome-shaped, said cutting extensions extending from said foundation surface.
16. The cutting element of claim 12 wherein a first of said cutting extensions includes a dome-shaped cutting surface and wherein a second of said cutting extensions includes a cutting surface comprising a crest.
17. The cutting element of claim 16 wherein said second cutting extension has a greater extension height than said first cutting extension.
18. The cutting element of claim 12 wherein said cutting element includes a longitudinal axis, and wherein said crest includes a crest axis, and wherein said crest axis does not intersect said longitudinal axis.
19. A drill bit for drilling through earthen formations, the drill bit comprising:
- a bit body;
- at least one rolling cone cutter rotatably mounted on said bit body for rotation about a cone axis, said cone cutter including a backface, a nose portion generally opposite said backface, and a generally conical surface between said nose portion and said backface;
- a plurality of cutting elements mounted in said cone cutter, at least one of said cutting elements comprising a base portion secured within said cone cutter and a cutting portion extending from said base portion, said cutting portion comprising a plurality of cutting extensions, said cutting extensions being separated by valleys.
20. The drill bit of claim 19 wherein said at least one cutting element is mounted in said cone cutter in a position selected from one of said nose portion and said generally conical surface.
21. The drill bit of claim 19 wherein said at least one cutting element further comprises a foundation surface extending from said base portion and, wherein, said plurality of cutting extensions extend from said foundation surface, said foundation surface being one of generally flat, generally frustoconical and generally dome-shaped.
22. The drill bit of claim 19 wherein at least two of said cutting extensions include cutting surfaces that differ in at least one characteristic selected from shape, extension height, extension angle, twist angle and cant angle.
23. The drill bit of claim 19 wherein at least one of said cutting extensions includes a cutting surface comprising a crest.
24. The cutting element of claim 19 wherein said at least one cutting element includes a first cutting extension having a cutting surface that is generally dome shaped and a second cutting extension having a cutting surface that includes a crest.
25. The cutting element of claim 24 wherein said second cutting extension includes an extension height that is greater than the extension height of said first cutting extension.
26. The drill bit of claim 19 wherein said at least one cutting element includes a longitudinal axis, and wherein said cutting extensions form extension angles with said longitudinal axis, and wherein said extension angles of at least two of said cutting extensions differ.
27. The drill bit of claim 19 wherein said at least one cutting element includes cutting extensions that include cutting surfaces that differ in at least one mechanical property selected from hardness, wear-resistance, and fracture toughness.
28. The drill bit of claim 22 wherein said at least one cutting element includes a longitudinal axis, and wherein said cutting element is mounted in said cone cutter such that said element axis is substantially aligned with said cone axis.
29. The drill bit of claim 28 wherein said plurality of cutting extensions includes at least a first cutting extension having a crested cutting surface and at least a second cutting element including a generally dome-shaped cutting surface.
30. A drill bit for drilling through earthen formations, the drill bit comprising:
- a bit body;
- at least one rolling cone cutter rotatably mounted on said bit body for rotation about a cone axis, said cone cutter including a backface, a nose portion generally opposite said backface, and a generally conical surface between said nose portion and said backface;
- at least one nose cutting element mounted in said nose portion, said nose cutting element comprising a base portion having an outer surface secured within said cone cutter, an element axis, and a cutting portion extending from said base portion, said cutting portion comprising a plurality of cutting extensions separated by valleys.
31. The drill bit of claim 30 wherein said nose cutting element is mounted in said cone with said element axis generally aligned with said cone axis.
32. The drill bit of claim 30 further comprising a plurality of said nose cutting elements retained in said cone cutter in a circumferential row that is disposed about said cone axis.
Type: Application
Filed: Jun 13, 2005
Publication Date: Jan 19, 2006
Inventors: Mohammed Boudrare (Houston, TX), Prabhakaran Centala (The Woodlands, TX), Scott McDonough (Houston, TX), Zhou Yong (Spring, TX), Vincent Shotton (Cordova, TN)
Application Number: 11/151,495
International Classification: E21B 10/36 (20060101);