Patent Application
20080041627
As seen more readily in
Single cone cutter body 22 includes a plurality of cutter elements 46 on the distal end of the cutter body 22. As shown in
To assemble the lubricating nutating single cone drill bit 10, the thrust bearing 28 and the first 30 and second 32 radial bearings are disposed between the cutter body 22 and the bit shank 12. In the illustrated embodiment, a thrust bearing 28 is disposed concentrically within a cage 29 and adjacent a hardened seat 31 before assembly, such a subassembly (e.g., thrust bearing 28, cage 29, and hardened seat 31) can be referred to in its entirety as a thrust bearing. With the above components installed in the interior of the cutter body 22 and/or on the axially skewed journal 18, the cutter body 22 can be inserted onto the axially skewed journal 18 of the bit shank 12.
To allow rotation, the cutter body 22 and the axially skewed bore 18 are preferably sized relative to each other to provide a gap therebetween, said gap can include bearings. After the cutter body 22 is inserted onto the axially skewed journal 18, at least one ball bearing 26 can then be added therebetween to limit axial movement of the cutter body 22 relative to the axially skewed journal 18, and thus impede separation of the bit shank 12 and cutter body 22.
The bearing race to house the ball bearings 26 can include a first channel 56 circumferentially formed in the axially skewed journal 18 portion of the bit shank 12 and a second channel 58 circumferentially formed in the interior of the cutter body 22. To allow the insertion of ball bearings 26 into the bearing race (56, 58) of the bit 10, a ball bearing passage 60 is formed in the bit shank 12. Ball bearing passage 60 can be selected to allow ball bearings 26 to be disposed through the lubricant chamber 76 into the bearing race (56, 58). Ball bearings 26 can be retained within bearing race (56, 58) by a ball bearing retention sleeve 64. Ball bearing retention sleeve 64 can be retained in the distal end of lubricant chamber 76, for example, by threads (not shown), a friction fit, or a snap ring (not shown). Ball bearing retention sleeve 64 is sized to retain a ball bearing 26 from ejecting itself from the bearing race (56, 58) through ball bearing passage 60. As the outer surface of ball bearing retention sleeve 64 forms a section of the first channel 56 in the axially skewed journal 18, it is preferably retained in a position so as to not interfere with the rolling of the ball bearings 26. So configured, a plurality of ball bearings 26 can be added to the bearing race (56, 58) through the lubricant chamber 76 and ball bearing passage 60, and the ball bearing retention sleeve 64 installed to retain the ball bearings 26. The number of ball bearings 26 utilized is design dependent, but is preferably a full-complement.
Lubricant can be added to the bearings (26, 28, 30, 32) at any time before, during, or after assembly. For example, bearings and/or surfaces between the axially skewed journal 18 and the cutter body 22 interior can be coated with lubricant during assembly. To retain the lubricant and to restrict the ingress of any contaminants, the invention includes a set of seals (66, 68) between the cutter body 22 and the axially skewed journal 18. In a preferred embodiment, the seals (66, 68) are radial dynamic seals. A radial seal is typically designed for an interference fit on the diameters between two concentric, or somewhat eccentric, cylinders. As used herein, the term dynamic seal shall refer to a seal wherein at least one face of a seal substantially retains a sealing engagement when in contact with a dynamic or other motile surface, for example, a rotating shaft. A radial dynamic seal (66, 68) can be any appropriate seal, including, but not limited to, an O-ring, 30 square-ring, U-cup seal, shaft seal, etc.
Radial dynamic seals (66, 68) are typically installed in a groove in a housing (e.g., a groove in the interior bore of the cutter body 22) and compress against a shaft (e.g., the axially skewed journal 18). A first radial dynamic seal 66 is disposed adjacent a proximal end of the cutter body 22 and circumferential the proximal portion of the axially skewed journal 18. A second radial dynamic seal 68 is disposed adjacent the distal end of the cutter body 22 and circumferential the distal portion 36 of the axially skewed journal 18. The first 66 and second 68 radial dynamic seals are preferably axially spaced to define a gap therebetween containing a bearing (e.g., 26, 28, 30, and/or 32). Optionally, a portion of the axially skewed journal 18 and/or a portion of the interior or exterior of the cutter body 22 can be formed from, or coated with, a hardened material. In a preferred embodiment, the hardening adds corrosion resistance suitable for use in a downhole environment. Non limiting examples of hardening are nitriding, alloying, cyaniding, and quenching-polishing-quenching (QPQ).
Alternatively, a radial dynamic seal (66, 68) can be disposed in a groove (not shown) formed in the axially skewed journal 18, a groove in the cutter body 22 (as shown), or a combination thereof. In the embodiment of
To provide lubrication, which is preferably continuous, the invention includes a lubricant chamber 76 formed in bit shank 12. The proximal end of the lubricant chamber 76 forms a fluid inlet port 78 on an exterior of the bit shank 12, illustrated as adjacent a drill string connection 14 shoulder. The distal end of the lubricant chamber 76 is in communication with the gap formed between the cutter body 22 and the axially skewed journal 18 of the bit shank 12. The gap is conventionally bounded by first 66 and second 68 radial dynamic seals and is sized to provide clearance to allow rotation of the cutter body 22.
The lubricant chamber 76 is in communication with the bearing surfaces. In the illustrated embodiment, the distal end of the lubricant chamber 76 is in communication with ball bearing passage 60, said ball bearing passage 60 in further communication with ball bearing race (56, 58).
Communication between ball bearing passage 60, which is optionally cylindrical, and lubricant chamber 76 can be achieved by an intersection therebetween for ease of manufacture. So configured, the lubricant chamber 76 is in communication with the gap formed between cutter body 22 and the axially skewed bore 18 bounded by first 66 and second 68 radial dynamic seals through the ball bearing passage 60.
After insertion of ball bearings 26 into bearing race (56, 58), a ball bearing retention sleeve 64 can be inserted into lubricant passage 76 to inhibit the egress of the ball bearing 26 from the port of the ball bearing passage 60 in first channel 56 of ball bearing race (56, 58). In one embodiment, the axis of the ball bearing passage 60 is not perpendicular to the axis of the lubricant chamber 76, as shown. Such a skew of the ball bearing passage 60 allows a lubricant to flow through the bore of the ball bearing retention sleeve 64, into the ball bearing passage 60, and thus to the bearings (26, 28, 30, 32). Similarly, the ball bearing retention sleeve 64 can have radially extending passages in a wall thereof to allow the passage of lubricant therethrough into the ball bearing passage 60. In the illustrated embodiment, the port of the ball bearing passage 60 in the first channel 56 of the ball bearing race (56, 58) functions as both a lubricant flow passage and bearing insertion aperture. Any space between the ball bearings 26 and the race (56, 58) allows a lubricant to flow past the ball bearings 26 and into the gap formed between the cutter body 22 and the axially skewed journal 18 as bounded by the first 66 and second 68 radial dynamic seals. Lubricant chamber 76 can be in communication with the gap between the axially skewed journal 18 and the cutter body 22 at any location and is not limited to being in communication with the ball bearing race (56, 58) as shown. An axially skewed journal 18 can provide a larger unitary volume of lubricant chamber 76 due to the offset nature of the journal 18 providing a larger continuous volume in the shank 12 as compared with a lubricant chamber that has a parallel axis to the shank (i.e., journal 18, if substantially coaxial to bit shank 12, would decrease the volume of bit shank 12 usable to form the lubricant chamber 76).
A lubricant can then be added to the lubricating nutating single cone drill bit 10, by any means known in the art. A lubricant can be any type in the art, including those conventionally known as grease. A lubricant can be a liquid without departing from the spirit of the invention. The lubricant chamber 76 can optionally be used during assembly to inject a lubricant into the gap between the cutter body 22 and axially skewed journal 18 (e.g., to the bearings 26, 28, 30, 32). In one embodiment, lubricant can be added to the bearings (26, 28, 30, 32) and/or the lubricant chamber 76 by any means known in the art. A plunger 80 can be disposed within the lubricant chamber 76, for example, to prevent the ingress of annulus fluid and/or the egress of lubricant. Plunger 80 can include a longitudinal bore therethrough. A plug 81 can be inserted into the longitudinal bore of the plunger 80 to form a seal, as shown. In one embodiment, the plug 81 threadably engages the longitudinal bore of the plunger 80. A removable plug can allow the disposition of lubricant through the plug 81 when desired. Plug 81 can include any type of drive, for example, a hexagonal socket drive as shown. Plunger 80 can include a built-in sealing mechanism (not shown), or have a radial seal 82 and respective seal grove formed in the plunger 80 or vice-versa. Plunger 80 can be a compensating piston, as is known in the art, to aid in the dispensing of the lubricant. To retain a plunger 80 within a lubricant chamber 76, a snap ring 84 (or equivalent) can be disposed in a groove in the proximal end of the lubricant chamber 76. The inner diameter of the snap ring 84 is preferably sized to restrict the passage of the plunger 80.
Lubricating nutating single cone drill bit 10 also includes a fluid passage 90 formed therethrough to allow the passage of a drilling fluid, for example. Fluid passage 90 extends from a second fluid inlet port 88. Second fluid inlet port 88 is in the proximal end 16 of the bit shank 12 and is preferably in communication with a bore of a drill string attached to the drill string connection 14. Fluid passage 90 includes a first section 96 of fluid passage 90 through the bit shank 12. First section 96 of fluid passage 90 is in communication with a fluid outlet port 98 located on the distal end 36 of bit shank 12, or more specifically, of the axially skewed journal 18. Second section 92 of fluid passage 90 is in communication with a second fluid outlet port 94 on the exterior of the bit shank 12. In the illustrated embodiment, second fluid outlet port 94 is formed in a shoulder defined by a recess in the shank 12. Although not shown in the view of
To use, the lubricating nutating single cone drill bit 10 is attached to a drill string (not shown) by a drill string connection 14, for example, including box threads. Bit shank 12 can include an optional bit breaker slot 99, shown as a dotted line, formed in the outer surface to permit the engagement and disengagement of bit 10 and drill string. Nutating single cone drill bit 10 can then be engaged into a formation to form a well bore (WB), as is known the art. The orientation of the cutter or crushing elements 46 and the axially offset geometry of the cutter body 22 with respect to the axis 20 of the bit shank 12 enables a portion of cutter or crushing elements 46 to contact the well bore (WB) while the adjacent section of cutter or crushing elements does not contact the floor of the well bore (WB). Such a configuration can minimize or eliminate the dragging of the cutter or crushing elements 46 across the opposing face of the well bore (WB) and thereby reduce the wear experienced by the bit 10 overall. The rolling nutating action of the present bit 10 offers low resistance to the rotational movement of the drill string, and thus provides a much lower operating torque that allows for operation at a higher rotational speed as compared to a typical scraping drill bit.
The lubricating nutating single cone drill bit 10 can then be rotated and loaded to drill the formation as is known to one of ordinary skill in the art. The drilling fluid is pumped down the drill string and into contact with the proximal end 16 of the bit shank 12. Any fluid pumped through an attached drill string will thus flow into the fluid inlet port 88, through fluid passage 90 and into first 96 and second 92 fluid passage sections. Fluid can then flow through first fluid passage section 96 and discharge from the fluid outlet port 98 formed in the distal end 36 of the axially skewed journal 18 into the face of the well bore (WB). Fluid can concurrently flow through second fluid passage section 92 and discharge from the fluid outlet port 92 in a shoulder in the lateral wall of the bit shank 12 into well bore wall. The first 66 and second 68 radial dynamic seals form a fluid barrier between the axially skewed journal 18 and the interior of the cutter body 22.
A well bore (WB) typically contains a fluid referred to as an annulus fluid which can include, for example, drilling fluid discharged from the bit 10 and/or a formation fluid. The annulus fluid can act on the proximal end of plunger 80. The proximal face of first radial dynamic seal 66 can be acted on by the annulus fluid (e.g., at the annulus fluid pressure) and the distal face of the first radial dynamic seal 66 can be acted on by a lubricant pressurized by plunger 80 at the annulus fluid pressure. Similarly, the distal face of second radial dynamic seal 68 can be acted on by the annulus fluid (e.g., at the annulus fluid pressure) and the proximal face of the second radial dynamic seal 68 can be acted on by a lubricant pressurized by plunger 80 at the annulus fluid pressure. In such an embodiment, the faces of each radial dynamic seal (66, 68) are contacted by fluid(s) at substantially equivalent pressures, more specifically an annulus fluid and a lubricant both at the annulus fluid pressure, and no pressure differential is experienced. Such a balanced configuration aids in the prevention of the undesirable ingress of drilling fluid into the rotational bearing surfaces due to unbalanced pressures on a radial seal. The lubricant chamber 76 allows for longer periods of use of a lubricating nutating single cone drill bit 10 without repacking lubricant and/or replacing any bearings (26, 28, 30, 32). The consumption of lubricant can allow additional lubricant to replenish the bearings (26, 28, 30, 32) and a corresponding displacement of the plunger 80 can occur.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of the invention.
