DRILL BITS

Abstract: Drag-type drilling bits (20) are disclosed which have at least one blade (36) and a plurality of fluid flow channels (44) incorporated in the blade for conducting drilling fluid or drilling mud from the hollow interior (32) of the bit to discharge or ejection ports (46) located in the front cutting edge (40) of the blade. Rods (48) of diamonds or of like "hard" cutter insert materials are incorporated in the blade in such a configuration that as the blade wears away or erodes and small pieces of diamonds are lost during drilling, more diamonds are exposed to the formation for drilling. During erosion or wear of the blades, the fluid discharge ports (46) continue to operate to eject drilling fluid adjacent to substantially each diamond rod (48), whereby the flushing away of cuttings and cooling of the diamonds is greatly improved. In some embodiments of the invention rods of alternating hard and soft materials (52 and 58) are also disposed substantially parallel with the diamond or like "hard" cutter insert rods. When the soft material of the rods is exposed for drilling the formation, kerfs (64) are formed which are thereafter "chipped away" by the subsequently exposed hard material of the rods.

Description: The present invention relates to drill bits. More particularly, but not exclusively, the present invention is directed to blade-type drag bits incorporating diamond cutter inserts wherein, even though the blades erode during drilling in a formation, the diamond inserts nevertheless remain effective for attacking the formation. Drilling bits or rock bits are well known in the art. Such drilling bits are used for drilling in subterranean formations when prospecting for oil or minerals. The term "drag bit", generally speaking, designates a drilling bit which has no rotating cones and which is rotated either from the surface through a string of drill pipes and drill collars (drill string) or by a suitable "downhole" motor. In contrast, rotary cone or "roller" bits have several journals each of which carries a freely rotatable drill bit cone. Regardless whether rotary cone or drag bits are used for drilling in a formation, drilling fluid or "drilling mud" is continuously circulated from the surface through the drill string down to the drilling bit, and up to the surface again. As is well known, the circulating drilling mud serves several important functions; these include continuous cooling of the drill bit and removal of the cuttings which are generated by the drilling action. Several types of drag bits are known in the art; these include fishtail bits, auger bits, as well as more "conventional" drag bits which lack relatively large extending blades but nevertheless may be provided with "hard" diamond, tungsten-carbide, or the like cutter inserts. Blade-type rotary drag bits are also known in the art which have diamond or other "hard" cutter inserts imbedded or affixed to the blades. Such blade-type bits are described, for example, in United States Patent Nos. 4,440,247 and 4,499,958. US Patent Specification No. 3,140,748 discloses a drag bit for drilling in subterranean formations. The drag bit has a pin end adapted for being removably attached to a drill string for receiving drilling fluid. The bit has two drilling blades attached to the drill bit body at the opposite end from the pin. Each of the drilling blades has a leading edge for contacting the formation when the drill bit is used for drilling and a plurality of elongate rods comprising hard drilling material, the rods being affixed to the blade in cavities in the blade and being exposed for drilling the formation at the leading edge of the blade. The respective longitudinal axes of the rods are substantially perpendicular to the direction of rotation of the blade, whereby as the blade and rods of hard drilling material erode during drilling, the rods will continue to be exposed in the eroding leading edge to the blade. Generally speaking, one serious problem encountered in the prior art in connection with diamond or like "hard" insert studded drag bits is overheating of the diamond inserts due to inadequate flushing and cooling action of the drilling fluid. As is known, heat, unless dissipated through adequate cooling with drilling fluid, may convert the diamond of the inserts into graphite with a resulting loss of hardness and drilling power. Another serious problem encountered in connection with diamond studded drag bits involves loss of the diamond cutters from the bit. Yet another problem, which is especially serious in the field of blade-type bits is the relatively rapid wear or erosion of the blades of the bit. The erosion, of course can also rapidly lead to loss of diamonds or like hard inserts from the blades. Generally speaking, the prior art has attempted to solve the foregoing problems by providing drilling fluid outlet passages or holes adjacent to the diamond or like inserts in the drag bits, and by appropriate choosing the configuration of the drag bit body so as to optimise the flushing and cooling action of the drilling fluid on the cutter inserts. In summary, the foregoing patent disclosures provide evidence of intense efforts in the prior art to develop rock bits in general, and diamond or like "hard" cutter insert studded drag bits in particular, which have prolonged working lives and improved wear characteristics. In spite of the foregoing efforts, there is definitely still need and room for improvement in this field. Specifically, there is need in the art for blade-type drag bits having diamond or like "hard" inserts, which are retained for operation in the blade even as a major portion of the blade is eroded or worn away during drilling. It is an object of the present invention to provide an improved drag bit. According to the present invention there is provided a drill bit for drilling in subterranean formations and the like, comprising: a drill bit body having a pin end adapted for being removably attached to a drill string, an interior cavity which is in fluid communication with the drill string for receiving drilling fluid and at least two drilling blades attached to the drill bit body at the opposite end from the pin, each of the drilling blades having a leading edge for contacting the formation when the drill bit is used for drilling, and a plurality of elongate rods comprising hard drilling material, the rods being affixed to the blade in cavities in the blade and being exposed for drilling the formation at the leading edge of the blade with the respective longitudinal axes of the rods being substantially perpendicular to the direction of rotation of the blade, whereby, as the blade and the rods of hard drilling material erode during drilling, the rods continue to be exposed in the eroding leading edge of the blade characterised in that each blade comprises a plurality of channels equal in number to the number of rods and means for conducting drilling fluid from the interior cavity of the drill bit body to each of the channels to form a fluid discharge port, whereby as the blade erodes during drilling, the drilling fluid continues to be ejected from the several discharge ports in the eroding leading edge of the blade and at least one fluid discharge port being located adjacent to the exposed end of each rod. Drill bits embodying the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a perspective view of a first preferred embodiment of the blade-type drilling bit of the present invention; Figure 2 is a plan view of a blade of the first preferred embodiment shown in Figure 1; Figure 3 is a partial cross-sectional view taken on lines 3,3 of Figure 1; Figure 4 is an enlarged partial view of the area designated in Figure 3; Figure 5 is a cross-sectional view taken on lines 5,5 of Figure 4; Figure 6 is a partial top view of a blade of a second preferred embodiment of the blade-type drilling bit of the present invention; Figure 7 is a partial cross-sectional view taken on lines 7,7 of Figure 6; Figure 8 is a cross-sectional view of the first preferred embodiment assembled to a drill string; Figure 9 is a schematic side view showing the first preferred embodiment of the blade-type drilling bit of the present invention in operation in a borehole; Figure 10 is a schematic side view showing the second preferred embodiment of the blade-type drilling bit of the present invention in operation in a borehole; Figure 11 is a schematic side view of a third preferred embodiment of the blade-type drilling bit of the present invention; and Figure 12 is a bottom view of the third preferred embodiment. It should be noted at the outset of the present description that the novel blade-type drilling bits of the present invention incorporate, in addition to the hereinafter-emphasized novel features, certain conventional features as well. Such conventional features, which are well known to those skilled in the art, are described here only to the extent necessary to explain and illuminate the novel features of the drilling bits of the invention. Referring now to Figures 1 through 5 and 8 of the appended drawings, a fishtail bit comprising the first preferred embodiment 20 of the blade-type drilling bit of the present invention is disclosed. The blade-type drilling bit 20 includes a pin portion 22 which has a threaded end 24 wherethrough the drilling bit 20 is attached to a drill string. A lower portion 26 of the drill string is shown in Figure 8. The pin portion 22 has a second threaded end 28, the male threads of which are attached to a generally conically-shaped bit body 30. The bit body 30 is hollow so that its interior cavity 32 is in fluid communication, through the hollow pin portion 22, with the drill string 26. Consequently, the interior cavity 32 receives a pressurized supply of drilling fluid or drilling mud from the surface (not shown) from where, in accordance with standard practice in the art, the drilling mud is continuously pumped down to the drilling bit 20. The drilling fluid or drilling mud is not shown in the appended drawings, although its direction of flow through the first preferred embodiment 20 of the drilling bit of the present invention is indicated by arrows 34 on Figure 3. A principal novel feature of the present invention is in the construction of the blades 36 which are affixed by welding (or other suitable means) to the bit body 30. In the fishtail bit of the herein-described first preferred embodiment 20 there are three blades 36 placed at a 120° angle relative to one another. Each blade 36 is welded into a suitable slot (not specifically shown) provided on the conical surface 38 of the bit body 30. It should be understood, of course, that in alternative embodiments, less or more than three blades 36, constructed in accordance with the present invention, may be affixed to the bit body 30. Each blade 36 includes a leading edge 40 which is configured to come into contact with the formation 42 during drilling. The formation 42 is schematically shown in Figures 9 and 10. A plurality of substantially evenly spaced channels or apertures 44 penetrate through the body of the blade 36, with the longitudinal axes of the channels 44 being substantially at right angles to the front cutting or leading edge 40 of the blade 36. The apertures or channels 44 are in fluid communication with the interior cavity 32 of the bit body 30. This is best shown on the cross-sectional view of Figure 3. At the leading edge 40 of the blade 36 the channels 44 terminate in discharge or ejection ports 46. It should be apparent from the foregoing that during the drilling process, drilling fluid or drilling mud is ejected from each of the discharge ports 46. Referring still principally to Figure 3, a second set of substantially evenly spaced apertures or holes 48 in the body of the blades 36 is shown, disposed substantially parallel with the apertures or channels 44 for the drilling fluid. The second set of holes 48 are, however, "blind" in that they terminate somewhat above the line where the blade 36 is attached to the conical surface 38 of the bit body 30. On the plan view of Figure 2 the apertures or holes 48 of the second set are shown as the smaller diameter holes, relative to the larger diameter discharge ports 46 for the drilling fluid. In the herein-described preferred embodiment the diameter of the discharge ports 46 is approximately 3/4" (20 mm), whereas the diameter of the blind holes 48 is approximately 0.5" (13 mm). It should, of course, be understood that the diameter of the discharge ports 46 and of the holes 48 are design features which may be varied without departing from the spirit of the invention. In accordance with the present invention a rod of "hard" cutter insert material is affixed in each of the apertures or holes 48, as is best shown on Figures 3, 4 and 5. The best suited "hard" material for this purpose is diamond, although other materials, such as cubic boron nitride, and even tungsten-carbide in a suitable metal matrix, may also be used. Because the preferred embodiments of the present invention utilize diamond inserts, and because primarily diamonds are contemplated to be used as the hard cutter inserts in connection with the present invention, the ensuing description principally refers to the cutter inserts as "diamonds". Nevertheless, it should be kept in mind that other "hard" cutter insert materials, which, per se , are known in the art, may also be used in connection with the present invention. Still more particularly, the diamond insert rods 50, which are incorporated in the drilling bits of the present invention, may comprise natural, synthetic or composite diamonds. Composite diamonds are synthetic diamonds in a suitable metal matrix formed into practically any desired shape. In the herein-described preferred embodiments synthetic polycrystalline diamonds are used, which are commercially available in the United States from several sources including the General Electric Company, and from Megadiamond, a division of Smith International, Inc. As is known by those skilled in the art, synthetic polycrystalline diamonds can also be formed into practically any desired shape, such as rods, cubes, cylinders and the like. For example, cubes of synthetic polycrystalline diamonds are available from the General Electric Company under the GEOSET trademark. Referring still primarily to Figures 3, 4 and 5, the diamond rods 50 of the herein-described first preferred embodiment 20 are shown to be built from a plurality of similarly shaped synthetic polycrystalline diamond cubes 52. These may be simply placed, in a stacked fashion as shown, into the blind holes 48. Thereafter the remaining space in the holes 48 is filled with a suitable tungsten-carbide powder, and the diamond cubes 52 are affixed together with the powder in the holes 48 with a suitable copper-nickel or like brazing alloy. Alternative modes of affixing diamonds of various configuration in the holes 48 include placing diamonds into a tungsten-carbide matrix and thereafter brazing the assembly into the holes 48. Inasmuch as affixing diamonds into holes or cavities of drilling tools and the like is known technology, still other methods of affixing the diamonds, or forming diamond rods, in the holes 48 of the drilling bit 20 of the present invention may become readily apparent to those skilled in the art. To complete the description of the drilling bit 20 it is noted that the blades 36 comprise grade 4130 or like steel, which is commonly used in the art for the construction of fishtail bits. Moreover, the sides of the blades 36 may be carburized or otherwise hardened so as to prevent such erosion on the sides which may result in "breakthrough" to the drilling fluid flow channels 44. Figure 8 shows the first preferred embodiment 20 of the drilling bit in operation. As is well known, the conventional steel blades of fishtail bits wear away or erode relatively rapidly, and the rate of erosion relative to the centre of the blades 36 increases with the square of the distance from the centre. Stated in other words, the blade erodes significantly faster radially outwardly from the centre of the blade than in the centre. As the fishtail drilling bit is operated for many hours, it is not uncommon for several inches to be lost from the blade, particularly on the radially remote portions, whereby the blade attains the configuration schematically shown on Figure 9. The actual rate of erosion, of course, depends greatly on the nature of the formation being drilled. In conventional diamond studded fishtail bits significant erosion or wear normally results in loss of the diamonds from the leading cutting edge of the blades, and seriously impairs the ability of the bit to function. In the drilling bit 20 of the present invention, however, as the blades 36 wear away and as small pieces of the diamond rods 50 break off or wear off, successive portions of the embedded diamond rods 50 become exposed for drilling the formation 42. Thus, the fishtail bit 20 of the present invention has very significantly increased useful life compared to prior art diamond studded fishtail bits. Moreover, in the fishtail bit 20 of the present invention each exposed diamond rod 50 is immediately adjacent to at least one discharge or ejection port 46 for the drilling fluid, whereby optimal flushing away of cuttings and cooling of the diamonds is attained. As the blades 36 and the diamond rods 50 erode, the relative configuration of the discharge ports 46 to the exposed diamond rods 50 does not change in the foregoing respect, so that the optimal flushing and cooling pattern is retained during the prolonged useful life of the drilling bit 20. Referring now to Figures 6, 7 and 10, a fishtail-type drilling bit comprising the second preferred embodiment 54 of the present invention is disclosed. The construction of the second preferred embodiment 54 is similar in many respects to the construction of the first preferred embodiment 20, except that alternating hard and soft materials are placed into the blind holes, which, in the first preferred embodiment, hold the diamond rods 50 only. This particular feature of the second preferred embodiment 54 is best shown on the cross-sectional view of Figure 7. More particularly, with reference to Figure 7, a first blind hole 56 of the second preferred embodiment 54 contains alternately, relative to the longitudinal axis of the hole 48, pieces of hard material, preferably diamond cubes 52 of the type described in connection with the first embodiment 20, and steel cubes 58. As it is described in more detail below, the steel behaves during drilling as "soft" material. The alternating pieces of diamonds 52 and steel 58 may be affixed in the blind hole 56 in several ways known in the art. For example, and advantageously, the alternating pieces of diamond and steel may be embedded in a tungsten-carbide matrix and thereafter brazed into the hole 56. A second and adjacent blind hole 60 contains a diamond rod 50 which may be affixed into the blind hole 48 in the same manner as in the above-described first preferred embodiment 20. A third blind hole 62 again contains alternating pieces of hard diamond and soft steel material. This alternating structural arrangement is repeated preferably in the entire blade 36, or at least in a portion thereof. Each blade 36 of the second preferred embodiment 54 also includes the channels 44 and discharge ports 46 for the drilling fluid adjacent to each blind hole containing, in this embodiment, either diamond rods 50 or alternating diamond 52 and steel 58 pieces. The operation and advantages of the fishtail drilling bit comprising the second preferred embodiment 54 of the present invention is best explained with reference to Figure 10. As the blades 36 of the bit 54 erode during drilling, the diamonds 52 and the "soft" steel pieces 58 become alternately exposed to contact the formation 42. Figure 10 schematically illustrates operation of the drill bit 54 when the "soft" steel pieces 58 are exposed. In this condition, substantially concentric kerfs 64 are formed in the formation 42 in the areas where the soft pieces 58 are exposed. This is, of course, due to the fact that the soft steel 58 is much less efficient in drilling than the harder steel of the blades 36 and the still harder diamond rods 50. When the exposed soft piece 58 erodes or wears away in the drilling process, then a "hard" diamond piece 52 is exposed in its place. The hard diamond readily chips or grinds away the laterally unsupported kerf 64. Consequently the entire process of drilling is facilitated. Referring now to Figures 11 and 12, an auger-type drilling bit comprising the third preferred embodiment 66 of the present invention is disclosed. The generic principles disclosed in detail in connection with the first preferred embodiment 20 of the drilling bit of the present invention are also applied in the third preferred embodiment 66. Thus, in the third preferred embodiment 66, a plurality of channels 44 are provided in the blade 68 to communicate with the hollow interior (not shown) of the bit body 30. The channels 44 terminate in discharge ports 46 in the front leading or cutting edge 70 of the blade 68. As in the other previously described embodiments, drilling fluid or drilling mud is ejected from the discharge ports 46 during the drilling operation. Adjacent to each discharge port 46 a diamond rod 50 (or like "hard" material) is mounted in a hole 48 located in the blade 68. Consequently, as the blade 68 wears or erodes during drilling in the formation 42, and as small pieces of diamonds are broken off, additional diamonds become exposed to drill the formation. Moreover, as in the other previously described preferred embodiments, the drilling fluid is ejected from a discharge port 46 adjacent to each diamond rod 50, so that the flushing away of cuttings and cooling of the exposed diamond rods 50 is optimized. In light of the foregoing, the auger-type drilling bit 66 of the present invention also has a greatly prolonged useful life relative to prior art auger-type drilling bits.

Claims: A drill bit for drilling in subterranean formations and the like, comprising: a drill bit body (30) having a pin end (22) adapted for being removably attached to a drill string, an interior cavity (32) which is in fluid communication with the drill string for receiving drilling fluid and at least two drilling blades (36) attached to the drill bit body (30) at the opposite end from the pin (22), each of the drilling blades (36) having a leading edge for contacting the formation when the drill bit is used for drilling, and a plurality of elongate rods (50) comprising hard drilling material, the rods (50) being affixed to the blade (36) in cavities (48) in the blade (36) and being exposed for drilling the formation at the leading edge of the blade (36) with the respective longitudinal axes of the rods (50) being substantially perpendicular to the direction of rotation of the blade (36), whereby, as the blade (36) and the rods (50) of hard drilling material erode during drilling, the rods (50) continue to be exposed in the eroding leading edge of the blade characterised in that each blade comprises a plurality of channels (44) equal in number to the number of rods (50) and means for conducting drilling fluid from the interior cavity (32) of the drill bit body (30) to each of the channels (44) to form a fluid discharge port (46), whereby as the blade (36) erodes during drilling, the drilling fluid continues to be ejected from the several discharge ports in the eroding leading edge of the blade (36) and at least one fluid discharge port (46) being located adjacent to the exposed end of each rod (50). The drill bit of Claim 1 wherein the elongate rods (50) comprise diamonds. The drill bit of Claim 2 wherein the elongate rods (50) comprise a plurality of similarly shaped bodies of polycrystalline diamonds. The drill bit of Claim 2 or of Claim 3 wherein the diamonds are disposed in a matrix which is brazed into apertures in the blade with a brazing alloy. The drill bit of any one of Claims 1 to 4 wherein the channels (44) penetrate through the body of the blade (36) parallel to the elongate rods (50) and each fluid discharge port (46) is beside a rod (50). The drill bit of any one of Claims 1 to 4 comprising three blades (36) in the form of a fishtail-type bit. The drill bit of Claim 1 wherein at least a portion of the elongate rods (50) comprise, relative to their respective longitudinal axes, alternately spaced hard and soft materials, whereby during drilling, when the soft material is exposed to the formation, kerfs are formed in the formation, and whereby the kerfs are eroded when the hard material of the rods are exposed to the formation. The drill bit of Claim 7 wherein the hard material of the rods (50) comprises diamonds. The drill bit of Claim 7 or Claim 8 wherein the soft material of the rods (50) comprises steel. The drill bit of any one of Claims 1 to 4 further comprising a plurality of elongate rods of a second kind mounted into cavities (44) in the blades (36) substantially parallel with the first-mentioned elongate rods and having, relative to their respective longitudinal axes, alternating hard and soft materials, the rods (50) of the second kind being disposed to be exposed at the respective leading edges of the blades (36) to come into contact with the formation during drilling, whereby when the soft material of the rods of the second kind is exposed to the formation, kerfs (64) are formed in the formation and when the hard material of the rods (50) of the second kind is exposed to the formation, the kerfs (64) are eroded. The drill bit of Claim 10 wherein the rods (50) of the second kind are substantially regularly and alternately spaced with the rods of hard material.

Inventors: JONES, KENNETH WILLIAM
Applicants: SMITH INTERNATIONAL, INC.
Application year: 1987
Main classification: E21B10
IPC codes: E21B10