Patent Application
20090084606
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.
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.
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.
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.
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.
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
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
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 100. 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
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.
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 324a, 324b, 324c illustrated. Furthermore, the drill bit 310 may have bosses associated with fewer than all of the blades 324a, 324b, 324c 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
Each boss 330, 331, 332 respectively rotationally leads its associated blade 324a, 324b, 324c, 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 324a, 324b and 324c 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
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.
