US20090084606A1

US20090084606A1 - Drill bits and tools for subterranean drilling

Info

Publication number: US20090084606A1
Application number: US11/865,296
Authority: US
Inventors: Michael L. Doster
Original assignee: Individual
Current assignee: Baker Hughes Holdings LLC
Priority date: 2007-10-01
Filing date: 2007-10-01
Publication date: 2009-04-02
Also published as: WO2009046069A3; WO2009046069A2; WO2009046069A4

Abstract

A drill bit that includes a boss extending rotationally forward of at least one blade thereof in a gage region of a bit body for increasing stability and reducing impact shock caused by a lateral imbalance force acting on the bit while drilling a subterranean formation is disclosed. The boss includes a circumferential bearing surface that rotationally precedes a circumferential bearing surface of the at least one blade. A drill bit that includes a boss having a nozzle port extending therein is also disclosed.

Description

FIELD OF INVENTION

The invention, in various embodiments, relates to drill bits and tools for subterranean drilling and, more particularly, to a drill bit or tool incorporating structure for enhancing stabilization and improving hydraulic configuration.

BACKGROUND

Fixed cutter rotary drill bits for subterranean earth boring have been employed for decades. It is well known that increasing the rotational speed of such drill bit, for a given weight on bit and subject to the ability of the bit's hydraulic structure to adequately clear formation cuttings from the bit, increases the rate of penetration of the drill string. However, increased rotational speed also tends to decrease the life of a drill bit due to premature damage to and destruction of cutting elements, commonly polycrystalline diamond compacts (PDC's).
It has been recognized that cutting element destruction, particularly at higher rotational speeds, is at least in part attributable to a phenomenon known as “whirl” or “bit whirl.” Radially directed centrifugal imbalance forces exist to some extent in every rotating drill bit and drill string. Such forces are in part attributable to mass imbalance within the drill bit and in part to dynamic forces generated by contact of the drill bit with the formation. In the latter instance, aggressive cutter placement and orientation creates a high tangential cutting force relative to the normal force applied to the bit and aggravates the imbalance. In any event, these imbalance forces tend to cause the drill bit to rotate or roll about the bore hole in a direction counter to the normal direction of rotation imparted to the bit during drilling. This counter-rotation is termed “whirl,” and is a self-propagating phenomenon, as the side forces on the bit cause its center of rotation to shift to one side, after which there is an immediate tendency to shift again. Since cutting elements are designed to cut and to resist impact received in the normal direction of bit rotation (clockwise, looking down a drill string), contact of the cutting elements with the bore hole wall in a counter-clockwise direction due to whirl places stresses on the cutting elements beyond their designed limits.
One solution to the problems caused by bit whirl has been to focus or direct the imbalance forces as a resultant side force vector to a particular side of the bit via changes in cutting element placement and orientation and bit mass location, and to cause the bit to ride on a low-friction bearing zone or pad on the gage of that side of the bit, thus substantially reducing the drill bit/bore hole wall tangential forces which induce whirl. This solution is disclosed in U.S. Pat. Nos. 4,982,802; 4,932,484; 5,010,789 and 5,042,596, all assigned on their faces to Amoco Corporation of Chicago, Ill.
The above-referenced patents conventionally require that the low friction bearing zone or pad on the gage and adjacent bit profile or flank be devoid of cutting elements and, indeed, many alternative bearing zone configurations are disclosed, including wear coatings, diamond stud inserts, diamond pads, rollers, caged ball bearings, etc. It has also been suggested by others that the bearing zone on the bit gage may include cutting elements of different sizes, configurations, depths of cut and/or rake angles than the cutting elements located in the cutting zone of the bit, which extends over the bit face from the cutting elements thereof outwardly to the gage, except in the flank area of the face adjacent the bearing zone. However, it is represented in the prior art that such bearing zone cutting elements should undesirably generate lesser cutting forces than the cutting elements in the cutting zone of the bit so that the bearing zone will have a relatively lower coefficient of friction. See U.S. Pat. No. 4,982,802, Col. 5, lines 29-36; U.S. Pat. No. 5,042,596, Col. 4, lines 18-25. Furthermore, while the prior art provides for focusing or directing the imbalance forces as a resultant side force vector toward a particular side of the bit, it does so by compromising aggressiveness of the bit, particularly affecting the placement and aggressiveness of cutting elements. Moreover, while the above-referenced patents reduce hole wall tangential forces which are generally noted to induce whirl, they do not protect the cutting elements from chipping as a result of the impact loads caused by vibrational instabilities commensurate with bit whirl, particularly when drilling in harder subterranean formations.
In order to mitigate the damage upon the cutting elements caused by side impact forces, conventional wisdom has been to direct the imbalance force, i.e., the resultant side force vector, of the bit toward the center and trailing bearing surface of a bit blade or toward the gage region of a particular blade, which undesirably limits design placement of the imbalance force upon the bit. Damage to the cutting elements may also be mitigated by increasing the circumferential width of the of the bearing surface, which undesirably reduces the hydraulic cross-section available for the junks slot, thus reducing hydraulic flow of drilling fluid and potentially decreasing the volume of cuttings which may be carried therethrough by the drilling fluid. In order to improve the stability of the bit while militating against damage, conventional wisdom also includes extending the bearing surface across the width of one or more channels between blades. Such bits are known as so called “steering wheel” bits and generally include fins or cylindrical portions that extend the bearing surface circumferentially about the gage region of the bit as shown and described in U.S. Pat. 5,671,818, 5904213 and 5,967,246. While these so called “steering wheel” bits may increase stability by militating against vibrational instabilities and enhance the ability of such bits to hold bore hole gage diameter, such bits undesirably increase the outer perimeter surface of the bit bearing on the bore hole side wall, making directional drilling more difficult. Furthermore, the configuration of such so called “steering wheel” bits also undesirably reduces the available hydraulic cross-section of the junk slots and may restrict formation cuttings removal from the bit face by substantially circumscribing the flow channels provided by the junk slots. In additional the configuration of the steering wheel bits impedes tripping the bit in and out of the bore hole, and may cause swabbing (removal of formation material from the bore hole side wall) during tripping.
Accordingly, it is desirable to provide improvements for a drill bit to enhance stability while maintaining or even improving hydraulic performance.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, a drill bit includes at least one boss for increasing stability and reducing impact shock caused by a lateral imbalance force acting on the drill bit while drilling a subterranean formation. The drill bit includes a bit body having a face extending to a gage region, at least one blade extending longitudinally and radially outward over the face of the bit body from a longitudinal axis thereof, the at least one blade including a boss coupled to the blade in the gage region of the bit body. The boss includes a circumferential bearing surface that rotationally precedes the blade when rotated about the longitudinal axis. The blade may also include a circumferential bearing surface.
In other embodiments, a drill bit comprises at least one boss extending into an open fluid course circumferentially between two blades, the fluid course communicating with a junk slot of the drill bit. The boss provides enhanced stability to the drill bit.
Further embodiments comprise a drill that including a boss having a nozzle port extending therein. The nozzle port further enhances the ability of the drill bit to hydraulically remove formation cuttings.
Other embodiments comprise a drill bit having at least one blade and a boss extending therefrom rotationally preceding cutting elements carried on a rotationally leading edge of the at least one blade.
Still other embodiments comprise a drill bit having at least one blade with a circumferential bearing surface rotationally forwardly shifted for enhanced alignment with a lateral force vector acting upon the drill bit during operation.
Other advantages and features of the invention will become apparent when viewed in light of the detailed description of the various embodiments of the invention when taken in conjunction with the attached drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective, inverted view of a drill bit configured with bosses according to an embodiment of the invention;

FIG. 2 shows a partial face view of one of the bosses of the drill bit shown in FIG. 1;

FIG. 3 shows a partial face view of a conventional drill bit schematically representing an imbalance force and reaction forces acting between a blade of the drill bit and a side wall of a borehole when drilling a subterranean formation;

FIG. 4 shows a partial face view of a drill bit schematically representing an imbalance force and reaction forces acting between a blade and a boss of a drill bit in accordance with embodiments of the invention and a side wall of a borehole when drilling a subterranean formation;

FIG. 5 shows a face view of a drill bit configured with bosses in accordance with another embodiment of the invention; and

FIGS. 6A-6C show partial perspective views of variations of bearing surface configurations for the bosses shown in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

In the description which follows, like elements and features among the various drawing figures are identified for convenience with the same or similar reference numerals.
FIG. 1 shows a perspective, inverted view of a drill bit 10 configured with bosses 30 according to an embodiment of the invention. The drill bit 10 is configured as a fixed cutter rotary full bore drill bit, also known in the art as a “drag” bit. The drill bit 10 includes a bit crown or body 11 comprising, for example, tungsten carbide infiltrated with a metal alloy binder, a machined steel casting or forging, or a sintered tungsten or other suitable carbide, nitride or boride as discussed in further detail below, and coupled to a support 19. The support 19 includes a shank 13 and a crossover component (not shown) coupled to the shank 13 in this embodiment of the invention. It is recognized that the support 19 may be made from a unitary material piece or multiple pieces of material in a configuration differing from the shank 13 being coupled to the crossover by weld joints as described with respect to this particular embodiment. The shank 13 of the drill bit 10 includes conventional male threads 12 configured to API standards and adapted for connection to a component of a drill string, not shown. Blades 24 that radially and longitudinally extend from the face 14 of the bit body 11 each have mounted thereon a plurality of cutting elements, generally designated by reference numeral 16. Each cutting element 16 comprises a polycrystalline diamond compact (PDC) table 18 formed on a cemented tungsten carbide substrate 20. The cutting elements 16, conventionally secured in respective cutter pockets 21 by brazing, for example, are positioned to cut a subterranean formation being drilled when the drill bit 10 is rotated in a clock-wise direction looking down the drill string under weight on bit (WOB) in a bore hole. In order to enhance stability of the bit 10 while protecting the cutting elements 16 from the undesirable impact stresses caused particularly by bit whirl, a boss 30 rotationally precedes the blade 24 substantially in the gage region 23 of body 11 the bit 10. Stated another way, each boss 30 may be said, in some embodiments, to rotationally precede cutting elements 16 carried on its associated blade 24 proximate a rotationally leading edge thereof. Each boss 30 may be configured according to an embodiment of the invention, as hereinafter described. In some embodiments, the bit 10 may have bosses rotationally preceding less than all of the blades. In other embodiments, the bit 10 may have only one boss 30 rotationally preceding a single blade 24 of the bit 10. Bosses in accordance with several embodiments of the invention are described in further detail below.
The bit body 11 may also carry gage trimmers (not shown) including the aforementioned PDC tables 18 which may be configured with a flat cutting edge aligned parallel to the longitudinal axis 27 of the drill bit 10 to trim the side wall of the bore hole (not shown) and hold the gage diameter thereof, and gage pads comprising bearing surfaces 22 in the gage region 23 for contacting or riding upon the walls of the bore hole to maintain the hole diameter and help stabilize the drill bit 10 while drilling through a subterranean formation. Optionally, the gage pads 22 may include a bearing zone or pad (not shown) configured with wear-resistant coatings, tungsten carbide inserts in the form of bricks or discs, diamond stud inserts, diamond-faced pads, rollers, caged ball bearings, for example.
During drilling, drilling fluid is discharged through nozzles 26 located in ports 28 in fluid communication with the face 14 of bit body 11 for cooling the PDC tables 18 of cutting elements 16 and removing formation cuttings from the face 14 of drill bit 10 as the fluid moves into passages 15 and through junk slots 17. The nozzles 26 may be sized for different fluid flow rates depending upon the desired flushing required in association with each group of cutting elements 16 to which a particular nozzle assembly directs drilling fluid.
The bosses 30 may be formed from the material of the bit body 11 and manufactured together with the blades 24 that extend from the face 14 of the bit body 11. The material of the bit body 11, blades 24 and bosses 30 of the drill bit 10 may be formed, for example, from a cemented carbide that is coupled to the body blank by welding, for example, after a forming and sintering process and is termed a “cemented” bit. The cemented carbide in this embodiment of the invention comprises tungsten carbide particles in a cobalt-based alloy matrix made by pressing a powdered tungsten carbide material, a powdered cobalt alloy material and admixtures that may comprise a lubricant and adhesive, into what is conventionally known as a green body. A green body is relatively fragile, having enough strength to be handled for subsequent furnacing or sintering, but not strong enough to handle impact or other stresses required to prepare the green body into a finished product. In order to make the green body strong enough for particular processes, the green body is then sintered into the brown state, as known in the art of particulate or powder metallurgy, to obtain a brown body suitable for machining, for example. In the brown state, the brown body is not yet fully hardened or densified, but exhibits compressive strength suitable for more rigorous manufacturing processes, such as machining, while exhibiting a relatively soft material state to advantageously obtain features in the body that are not practicably obtained during forming or are more difficult and costly to obtain after the body is fully densified. While in the brown state for example, the cutter pockets 21 or nozzle ports 28 may also be formed in the brown body by machining or other forming methods. Thereafter, the brown body is sintered to obtain a fully dense cemented bit.
As an alternative to tungsten carbide, one or more of diamond, boron carbide, boron nitride, aluminum nitride, tungsten boride and carbides or borides of Ti, Mo, Nb, V, Hf, Zr, TA, Si and Cr may be employed. As an alternative to a cobalt-based alloy matrix material, or one or more of iron-based alloys, nickel-based alloys, cobalt- and nickel-based alloys, aluminum-based alloys, copper-based alloys, magnesium-based alloys, and titanium-based alloys may be employed.
In order to maintain particular sizing of machined features, such as cutter pockets 21 or nozzle ports 28, displacements as know to those of ordinary skill in the art may be utilized to maintain nominal dimensional tolerance of the machined features, e.g., maintaining the shape and dimensions of a cutter pocket 21 or nozzle port 28 as described below. The displacements help to control the shrinkage, warpage or distortion that may be caused during final sintering process required to bring the brown body to full density and strength. While the displacements help to prevent unwanted nominal change in associated dimensions of the brown body during final sintering, invariably, critical component features, such as threads, may require reworking prior to their intended use, as the displacement may not adequately prevent against shrinkage, warpage or distortion. While the material of the body 11 as described may be made from a tungsten carbide/cobalt alloy matrix, other materials suitable for use as a bit body may also be utilized.
While bosses 30 are formed in the cemented carbide material of the drill bit 10 of this embodiment of the invention, a drill bit may be manufactured in accordance with embodiments of the invention using a matrix bit body or a steel bit body as are well known to those of ordinary skill in the art, for example, without limitation. Drill bits, termed “matrix” bits are conventionally fabricated using particulate tungsten carbide infiltrated with a molten metal alloy, commonly copper based. Steel body bits comprise steel bodies generally machined from castings or forgings. While steel body bits are not subjected to the same manufacturing sensitivities as noted above, steel body bits may enjoy the advantages of the invention as described herein, particularly with respect to having bosses 30 for improving the stability and impact protection of the cutting elements 16, particularly cutting elements 16 oriented proximate to the forward face or leading edges 25 of the blades 24, as opposed to so-called “backup” cutters which significantly rotationally trail the rotationally leading edges 25 of the blades 24.
The blades 24 together with any associated bosses 30 may be distributed upon or about the bit body 11 in order to substantially provide rotational balance of the drill bit 10 when rotating about its axis 27, and may be distributed upon or about the face 14 of the bit body 11 to symmetrically or asymmetrically provide for a desired balance or relative imbalance of the drill bit 10, respectively.
FIG. 2 shows a partial face view of one of the bosses 30 of the drill bit 10 as shown in FIG. 1. Reference may also be made back to FIG. 1. The bosses 30 advantageously enhance stability of the bit body 11, particularly in the gage region 23 thereof, by enhancing lateral surface area of contact of the drill bit 10 against the side wall of the borehole being drilled by desirably decreasing the cross-sectional “footprint” of the bit body in the bore hole and decreasing the hydraulic restriction through the junk slot 17 in comparison to that conventionally experienced with so called “steering wheel” bits. Adjacently located next to the bearing surface 22 of the blade 24 and substantially in the gage region 23 of the bit body 11 is a boss 30 that also includes a bearing surface 32. In order to maintain clarity, bearing surface 22 associated with the blade 24 will hereinafter be referred to as “first bearing surface” with reference to numeral 22, and bearing surface 32 associated with the boss 30 will hereinafter be referred to as “second bearing surface” with reference to numeral 32.
The second bearing surface 32 of the boss 30 rotationally precedes the first bearing surface 22 about the longitudinal axis 27 with reference to the rotational direction of the drill bit 10. Generally, the first bearing surface 22 and the second bearing surface 32 will be circumferentially adjacent or even contiguous in the gage region 23 extending across a boss 30 and its associated blade 24, as illustrated in FIG. 1, in order to provide a smooth, uninterrupted and substantially transitionless engagement when riding, or impinging, upon or making contact against the side wall of the borehole through the formation being drilled. However, in some embodiments there may be an abrupt or discontinuous circumferential transition between the first bearing surface 22 and the second bearing surface 32. Moreover, the first bearing surface 22 and the second bearing surface 32 may include additional features thereupon to further improve contact conditions between the drill bit 10 and the formation, for example, by providing low friction bearing surfaces and abrasion-resistant surfaces, such as inserts or wear knots, thereupon.
Each boss 30 rotationally leads its associated blade 24, and protrudes or extends into the fluid course 15 of the junk slot 17 from the face surface 25 of the blade 24. The boss 30 includes the second bearing surface 32 and a leading edge, or surface, 34 that advantageously reduces impact stress to the cutting elements 16 caused by non-normal forces, i.e., forces not acting in the normal direction of bit rotation (clockwise, looking down a drill string), by providing leading contact with the formation when the drill bit 10 is subjected to bit whirl or other deleterious instabilities or perturbations. Specifically, the second bearing surface 32 and/or leading surface 34 of the boss 30 may be configured to directly engage the formation during bit whirl to provide protection for the cutting elements 16 by absorbing energy and reducing impact and engagement stresses principally caused by bit whirl as the drill bit 10 rotates in the borehole. In this aspect, the first bearing surface 22 and the second bearing surface 32 provide contact surface area particularly suited for directing imbalance forces there toward, which is particularly advantageous for forcing the bearing surfaces 22 and 32 toward and against the side wall of the borehole allowing the drill bit 10 to ride thereupon, increasing what is known as so-called “secondary” stability by reducing the effects of bit whirl, which ultimately improves the so-called “primary” stability by reducing impact stresses causing fracture or chipping of the cutting elements 16. The imbalance forces may also include side force vectors, i.e., radial force vectors, resulting from strategic placement and orientations of the cutting elements 16 in the bit body 10. Generally, the imbalance force referred to herein includes the net combined forces of all non-Normal forces of the cutting elements 16 (not acting in the Normal direction perpendicular to bit rotation), such Normal forces including inline axial forces (up and down the longitudinal axis of the drill string) acting upon the bit body 10. A designed lateral imbalance force is further discussed with respect to a conventional drill bit shown in FIG. 3 and then with respect to a drill bit in accordance with embodiments of the invention as shown in FIG. 4.
FIG. 3 shows a partial face view of a conventional drill bit 110 schematically representing an imbalance force Fi and reaction forces Fr between a blade 124 of the drill bit 110 and a side wall 102 of a borehole 100 when drilling in a subterranean formation. It is to be noted that the weight-on-bit, or axial force, and the normal force of the cutting elements are not shown or described in further detail. The vector of imbalance force Fi, particularly is located substantially perpendicular to the longitudinal bit axis 27 and is achieved by selectively positioning and orienting the cutting elements 16 upon the bit body 111 to achieve a net radial imbalance force vector Fi as is well understood by a person having ordinary skill in the art. The magnitude and direction of the net radial imbalance force vector Fi will depend on the positioning and orientation of the cutting elements 16, and the shape of the drill bit as the shape influences cutter position. Orientation of a cutting element includes backrake and siderake. The magnitude and direction of force vector Fi is also influenced by a number of factors such as the specific configuration and size of the individual cutting elements, the weight-on-bit load applied to the drill bit, the speed of rotation, and the physical properties of the materials of the subterranean formation. While the imbalance force or net radial imbalance force vector Fi is shown being directed radially outward from the axis 27, it may be directed radially outward from another location of the drill bit 110 while being oriented substantially perpendicular with the axis 27.
The reaction forces Fr are the result of the imbalance force Fi of the drill bit as it makes contact with the side wall 102 of the borehole 1 00. The reaction forces Fr are representatively illustrated herein, i. e., not determinative of actual force magnitudes, and substantially act upon the bearing surface 122 of the drill bit 110 as it is rotated in the borehole 100. The reaction forces Fr are also representative of the impact stresses caused upon the cutting elements 16 by bit whirl. Specifically, the cutting elements 16, particularly those cutting elements 16 located proximate leading face 125 of the blade 124 of the drill bit 110 and on the shoulder of the bit face below the gage and down to the nose (as the bit is oriented during drilling), are more prone to being directly impacted against the material of the formation thus sustaining impact stresses having force magnitude of reaction force Fr thereupon, which tend to cause damage to cutting elements 16. The potential damage to the cutting elements 16 caused by reaction forces Fr is further increased as the imbalance force Fi is directed toward the forward or leading portions of bearing surface 122 (as illustrated) or even rotationally leading the leading face 125 of the blade 124. In still other conventional bits having little to no designed imbalance force vector Fi, the cutting elements 16 are also subject to reaction forces Fr caused by bit whirl or other perturbations during drilling. A description of how the damage caused by reaction forces Fr may be mitigated with a drill bit having one or more bosses in accordance with embodiments of the invention will be described with respect to FIG. 4.
FIG. 4 shows a partial face view of a drill bit 210 schematically representing an imbalance force Fi and reaction forces Fr acting between a blade 224 and a boss 230 of a drill bit 210 in accordance with embodiments of the invention and a side wall 202 of a borehole 200 when drilling a subterranean formation. As illustrated, a bearing surface 232of the boss 230, is aligned with the imbalance force Fi and related reaction force Fr that is particularly directed toward the leading face 225 of the blade 224 absent the presence of boss 230. The additional presence of leading surface 234 of boss 230 essentially alleviates any tendency, as exhibited in conventional drill bits, for the blade 224 to “bite” into the formation as drill bit 210 rotates and initiate whirl and other perturbations. The boss 230 also increases the primary and second stability of the drill bit 210 by providing an increase in the total bearing surface, i.e., the first bearing surface 222 of blade 224 and the second bearing surface 232 of boss 230, which resultantly decreases instabilities, such as bit whirl, while primarily preventing against unintended direct impact of cutting elements 16 with the formation. It is recognized that the cutting elements 16 are designed to directly engage and shear material from a formation while moving primarily in the normal direction of bit rotation. Impact stress from reaction forces Fr in a direction other than the intended direction of cutter movement may potentially cause one of the cutting elements 16 to become chipped, cracked, or even dislodged from its attachment with the bit body 211.
The boss 230 allows the cutting elements 16 to be more efficiently positioned and oriented for cutting upon rotational movement of the bit body about the axis 27 when drilling a formation, while reducing potential damage to the cutting elements 16 by bit whirl or other perturbations. The boss 230 enables the imbalance force Fi to be radially directed substantially towards the first bearing surface 222 and the second bearing surface 232, as illustrated, thus providing improved protection for the cutting elements 16 as described herein. It should be noted that the circumferentially extended bearing surface area enables greater accommodation of variations in the direction of imbalance force Fi under various drilling conditions and as cutting elements 16 wear. Thus, the imbalance force Fi may be nominally centered on the combined circumferential extent of bearing surfaces 222 and 232. It should also be noted that the use of bosses according to embodiments of the present invention enables the circumferential width of the blades (not including the boss) to be reduced at the rotationally trailing side thereof, with the additional circumferential width being moved rotationally forward into the boss. Thus, junk slot area may be easily preserved even with the presence of a boss rotationally forwardly protruding into a junk slot.
In order to further increase the durability of the drill bit 210, abrasion and impact resistant features (not shown) may be place upon the second bearing surface 232 of the boss 230 and/or the first bearing surface 222 of the blade 224. The abrasion and impact resistant features may include low friction attributes known by a person having ordinary skill in the art.
FIG. 5 shows a face view of a drill bit 310 configured with bosses 330, 331, 332 in accordance with another embodiment of the invention. Reference may also be made to FIGS. 6A-6C showing partial perspective views of the bosses 330, 331, 332 shown in FIG. 5. The drill bit 310 comprises a bit body 311, three blades 324 a, 324 b, 324 c, three open fluid courses 340, 341, 342 and three bosses 330, 331, 332. The bit body 311 includes a face 314, a longitudinal axis (not shown) and a gage region 323. Each of the three blades 324 a, 324 b, 324 c extends longitudinally and radially outward over the face 314 of the bit body 311. Each of the three blades 324 a, 324 b, 324 c either rotationally leads or trails another of the three blades 324 a, 324 b, 324 c. Each of the open fluid courses 340, 341, 342 extends between one of the three blades 324 a, 324 b, 324 c and another of the three blades 324 a, 324 b, 324 c in the gage region 323 of the bit body 311. Each of the three bosses 330, 331, 332 is coupled to one of the three blades 324 a, 324 b, 324 c and extends into one of the three open fluid courses 340, 341, 342, respectively. Each of the three bosses 330, 331, 332, as previously noted with respect to other embodiments, helps to reduce the tendency of drill bit 310 to whirl in operation and to minimize the impact stresses caused by bit whirl upon the cutting elements 16 when engaging the material of the formation being drilled.
It is to be recognized that the drill bit 310 may have fewer or greater number of open fluid courses than the three open fluid courses 340, 341, 342 illustrated. Also, the drill bit 310 may have fewer or greater number of blades than the three blades 324 a, 324 b, 324 c illustrated. Furthermore, the drill bit 310 may have bosses associated with fewer than all of the blades 324 a, 324 b, 324 c as illustrated. For example, in the case of an intentionally significantly laterally imbalanced bit, it may be desirable to include only a single boss on the bit body in the gage area to which the lateral imbalance is directed.
Each boss 330, 331, 332 is located next to one of a first bearing surface 322 (see FIGS. 6A-6C) of each blade 324 a, 324 b, 324 c substantially in the gage region 323 of the bit body 311. Each boss 330,331, 332 also includes a second bearing surface 332 (see FIGS. 6A-6C) located in the gage region 323 of the bit body 311. The second bearing surface 332 of each boss 330, 331, 332 rotationally precedes the first bearing surface 322 of each blade 324 a, 324 b, 324 c, respectively, about the axis with reference to the rotational direction of the drill bit 10. Generally, the first bearing surfaces 322 and the second bearing surfaces 332 of a select boss 330, 331, 332 and blade 324 a, 324 b, 324 c, respectively, will be adjacently, or continuously, coupled together between the boss 330, 331, 332 and the respectively associated gage region 323 of the blade 324 a, 324 b, 324 c, as illustrated, in order to provide a smooth, uninterrupted or transitionless engagement when impinging, or riding, upon or making contact against the formation being drilled. However, there may be a perceptible transition or even a gap between the first bearing surface 322 and the second bearing surface 332. Moreover, the first bearing surface 322 and the second bearing surface 332 may include additional features thereupon to further improve the contact condition between the drill bit 310 and the formation being drilled, for example, by providing low friction bearing surfaces and abrasion-resistant surfaces, such as inserts, thereupon.
Each boss 330, 331, 332 respectively rotationally leads its associated blade 324 a, 324 b, 324 c, and protrudes or extends from the face surface 325 thereof into its corresponding fluid course 315 proximate its juncture with an associated the junk slot 317. The bosses 330, 331, 332 advantageously reduce any potential for impact stress to the cutting elements 16 caused by contact with the formation by providing the second bearing surface 332 and a leading surface 334. Specifically, the second bearing surface 332 and/or leading surface 334 of each boss 330, 331, 332 may be configured to directly engage the formation during drilling to provide protection for the cutting elements 16 by reducing if not eliminating any tendency toward bit whirl as the drill bit 310 rotates while drilling a borehole. In this aspect, the first bearing surface 322 and the second bearing surface 332 provide surface area particularly suited for directing a designed imbalance force toward and against the side wall of the borehole allowing the drill bit 310 to ride thereupon, increasing the so-called “secondary” stability by reducing the tendency toward bit whirl, which ultimately improves and maintains the so-called “primary” stability by reducing impact stresses causing fracture or chipping of the cutting elements 16.
In order to reduce any tendency of the leading edges 325 of any of blades 324 a, 324 b and 324 c to “bite” of the drill bit 310 as it rotates in the borehole under the affects of bit whirl, the leading surface 334 of the bosses 330, 331, 332 may be configured as a blunt leading edge 334 as shown in FIG. 6A, an oblique leading edge 334 as shown in FIG. 6B, or a rounded leading edge 334 as shown if FIG. 6C, respectively. The leading edge 334 is substantially aligned with the longitudinal axis of drill bit 310 in the gage region 323 of the bit body 311. Further, the leading edge 334 provides a smooth transition between the second bearing surface 332 and the fluid course 315. The leading edge 334 of anyone of the bosses 330, 331, 332 may have the shape of a blunt, oblique or rounded leading edge, and may have any other suitable shape that is consistent with the disclosure herein presented. The leading edges 334 take the brunt of load on the blade during initiation of bit whirl or other lateral perturbation. Any one, or all, of the bosses 330, 331, 332 enhance stability of the drill bit. Optionally, any one of the bosses 330, 331, 332 may also be used to improve the hydraulic configuration of drill bit 310 by advantageously utilizing its stability improvements to circumferentially outwardly locate at least one nozzle port in one of the bosses 330, 331, 332 of the bit for improved removal of formation cuttings as describe below.
Each of the bosses 330, 331, 332 further includes a plateau or land 350 and a nozzle port 328 extending into the land 350, the land 350 being substantially orthogonal to the axis of the bit body 310. A nozzle 326 may be removably secured by threaded or other engagement into the nozzle port 328 allowing drilling fluid to be selectively directed towards the front blade surface 325 of the blade 324 substantially from the gage region 323 of the bit body 311. The land 350 also allows the nozzle 326 to be selectively placed such that drilling fluid exiting the nozzle 326 from substantially the gage region 323 of the bit body 311 may be directed generally toward specific cutting elements 16 and having a selected radially outward, axial or inward orientation as desired, thus allowing for improved hydraulic configuration for cleaning and lubricating the cutting elements 16.
While each of the bosses 330, 331, 332 includes a land 350 and a nozzle port 328 extending into the land 350, it is recognized that any or all of the bosses 330, 331, 332 may include fewer or more nozzle ports extending into the land 350 than illustrated.
The drill bit 310 also includes cutting elements 16 coupled to each of the blades. As in the case of the previously described embodiments, cutting elements 16 may be configured, positioned and oriented to provide a selected, directed imbalance force upon rotational movement of the bit body 311 about its axis under weight on bit when drilling a borehole in a formation. The imbalance force may be directed radially toward one of the novel bearing surfaces 332 as described above.
It is to be understood that each of the “bearing surfaces,” as presented in the embodiments of the invention herein above, are defined as being substantially parallel with respect to a longitudinal, rotational axis of a bit body extending in the gage region at a substantially constant radius from the axis.
While particular embodiments of the invention have been shown and described, numerous variations and other embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be only limited in terms of the appended claims.

Claims

1. A drill bit comprising:

a bit body having a longitudinal axis, and a face extending to a gage region;

at least one blade extending longitudinally and radially outward over the face and having a plurality of cutting elements disposed thereon; and

a boss coupled to and extending forward of the at least one blade in a direction of intended bit rotation about the longitudinal axis, the boss including a circumferential bearing surface in the gage region.

2. The drill bit of claim 1, wherein the at least one blade includes a circumferential bearing surface in the gage region.

3. The drill bit of claim 1, wherein the at least one blade comprises a plurality of blades circumferentially separated by junk slots.

4. The drill bit of claim 3, further including additional blades, at least one of the additional blades being without a boss associated therewith.

5. The drill bit of claim 1, further including additional blades each having a plurality of cutting elements disposed thereon, wherein at least some of the cutting elements disposed on the blades are configured, positioned and oriented to provide a lateral imbalance force upon rotation of the bit body about the longitudinal axis when drilling a formation under weight on bit, the lateral imbalance force being circumferentially directed substantially toward the circumferential bearing surface.

6. The drill bit of claim 5, wherein the at least one blade includes a circumferential bearing surface in the gage region and the lateral imbalance force is substantially centered over a combined extent of the boss bearing surface and the at least one blade bearing surface.

7. The drill bit of claim 1, wherein the boss further includes a land and a nozzle port therein, the land being substantially orthogonal to the longitudinal axis of the bit body.

8. The drill bit of claim 7, further comprising a nozzle coupled to the nozzle port.

9. The drill bit of claim 8, wherein the nozzle is aimed toward a rotationally leading blade surface of the at least one blade.

10. The drill bit of claim 8, wherein the nozzle is aimed directionally inward from longitudinal axis extending from substantially the gage region of the blade.

11. A drill bit comprising:

a bit body having a longitudinal axis and a face extending to a gage region;

a plurality of blades extending longitudinally and radially outward over the face, the plurality of blades including at least a first blade and a second blade, the second blade rotationally trailing the first blade about the longitudinal axis;

an open fluid course between the first blade and the second blade extending to a junk slot in the gage region of the bit body; and

a boss coupled to the second blade in the gage region of the bit body, the boss extending into the open fluid course.

12. The drill bit of claim 11, wherein each of the plurality of blades includes a boss coupled thereto.

13. The drill bit of claim 11, wherein at least one blade of the plurality of blades is without a boss coupled thereto.

14. The drill bit of claim 11, wherein the boss includes a circumferential bearing surface preceding the second blade.

15. The drill bit of claim 14, further comprising a plurality of cutting elements coupled to each of the plurality of blades, at least some of the plurality of cutting elements, in combination configured, positioned and oriented to provide lateral imbalance force upon rotational movement of the bit body about the longitudinal axis under weight on bit when drilling a formation, the lateral imbalance force being generally directed toward the circumferential bearing surface.

16. The drill bit of claim 15, wherein the second blade including a circumferential bearing surface in the gage region and the lateral imbalance force is generally directed to the boss bearing surface and the second blade bearing surface.

17. The drill bit of claim 11, wherein the boss further includes a plateau and a nozzle port extending therein, the plateau being generally orthogonal to the axis of the bit body, and further comprising a nozzle coupled to the nozzle port.

18. The drill bit of claim 17, wherein the nozzle is aimed toward a rotationally leading blade surface of the second blade.

19. A drill bit comprising:

a bit body having a longitudinal axis and a face extending to a gage region;

a plurality of blades extending longitudinally and radially outward over the face of the bit body to the gage region; and

a boss extending forward from a rotationally leading blade surface of at least one blade of the plurality of blades substantially in the gage region, the boss including a land and a nozzle port extending therein, the land being substantially orthogonal to the axis of the bit body; and

a nozzle coupled to the nozzle port.

20. The drill bit of claim 19, wherein each of the plurality of blades includes a boss.