Patent Application
20050045387
Not Applicable.
1. Field of the Invention
The invention relates generally to earth-boring bits. More particularly, the invention relates to maintaining lubrication of rolling cone cutters that are mounted on journal pins. Still more particularly, the invention relates to a combination lubrication pump and cone movement dampening system that retards or dampens axial cone movement to lessen the likelihood of seal damage and thereby extend seal and bit life.
2. Description of the Related Art
An earth-boring drill bit is typically mounted on the lower end of a drill string and is rotated by revolving the drill string at the surface or by actuation of downhole motors or turbines, or by both methods. With weight applied to the drill string, the rotating drill bit engages the earthen formation and proceeds to form a borehole along a predetermined path toward a target zone. A typical earth-boring bit includes one or more rotatable cone cutters that perform their cutting function due to the rolling movement of the cone cutters acting against the formation material. The cone cutters roll and slide upon the bottom of the borehole as the drillstring and bit are rotated, the cone cutters thereby engaging and disintegrating the formation material in their path. The rotatable cone cutters may be described as generally conical in shape and are therefore referred to as rolling cones.
Rolling cone bits typically include a bit body with a plurality ofjournal segment legs. The cones are mounted on bearing pin shafts (also called journal shafts or journal pins) that extend downwardly and inwardly from the journal segment legs. As the bit is rotated in the borehole, each cone cutter is caused to rotate on its respective journal shaft as the cone contacts the bottom of the borehole. The borehole is formed as the action of the cone cutters removes chips of formation material (“cuttings” or “drilled solids”) which are carried upward and out of the borehole by the flow of drilling fluid which is pumped downwardly through the drill pipe and out of the bit.
In oil and gas drilling, the cost of drilling a borehole is proportional to the length of time it takes to drill to the desired depth and location. The time required to drill the well, in turn, is greatly affected by the number of times the drill bit must be changed in order to reach the targeted formation. This is the case because each time the bit is changed, the entire string of drill pipe—which may be miles long—must be retrieved from the borehole, section by section.
Once the drill string has been retrieved and the new bit installed, the bit must be lowered to the bottom of the borehole on the drill string, which again must be constructed section by section. As is thus obvious, this process, known as a “trip” of the drill string, requires considerable time, effort and expense. The amount of time required to make a round trip for replacing a bit is “downtime,” and is essentially lost time and lost productivity from drilling operations. It is therefore advantageous to maximize the service life of a drill bit. Accordingly, it is always desirable to employ drill bits that will be durable enough to drill for a substantial period of time with acceptable rate of penetration (ROP).
One cause of bit failure arises from the severe wear or damage that may occur to the bearings on which the cone cutters are mounted. These bearings can be friction bearings (also referred to as journal bearings) or roller type bearings, and are typically subjected to high drilling loads, high hydrostatic pressures in the hole being drilled, and high temperatures. Lubricant is supplied to the narrow space—or journal gap—which exists between the journal pin and cone cutter. The journal gap is defined by the first surface formed by the exterior of the journal pin and by the second surface formed by the adjacent interior bore of the cone cutter. Under load, however, the lubricant can experience thermal breakdown, a condition in which the chemical composition of the lubricant is altered due to thermal and mechanical stresses, and its lubricating properties are depleted. Maintaining adequate lubrication of the bearings requires the periodic replacement of old, degraded lubricant with new lubricant that is stored in a grease reservoir within the bit. Regularly supplying fresh lubricant into the journal gap will help lengthen the useful life of the cone cutter assembly and of the bit. Consequently, the frequency with which the bit must otherwise be replaced due to bit failure or loss of an acceptable ROP may be reduced by providing proper lubrication of the cone cutters.
Seals are provided in the journal gap between the rolling cones and their respective journal pins to prevent lubricant from escaping from around the bearing surfaces and to prevent the cutting-laden, abrasive drilling fluid present in the borehole from entering the gap between the cone and the journal pin. If cuttings are conveyed into the journal gap, they tend to adhere to the seal ring and/or seal component surfaces and may cause deformation, damage and/or slippage of the seal components. Moreover, the cuttings and other dirt or debris present can accelerate abrasive wear of all seal components and of the bearing surfaces themselves. Thus, the integrity of the seal for maintaining lubricant between the journal pin and rotating cone cutter also impacts the durability of a bit and the length of time that a drill bit may be employed before it must be changed.
A common seal is formed by an elastomeric ring (commonly called an “O-ring”). Other conventional seals employ one or more rings made of various materials. Without regard to construction, the seal will include a dynamic seal surface, which is placed in rotating contact against another surface—generally the journal pin. The sealing ring also includes a static seal surface, which is placed in contact against a stationary surface—generally the rotating cone cutter. Although the bit will experience severe and varying loads, as well as a wide range of different temperature and pressure conditions, the dynamic and static seal surfaces must remain sealingly engaged to prevent the lubricant from escaping and/or contaminants from entering the lubricated areas, and should perform these duties throughout the life of the bit's cutting structure.
As previously mentioned, the integrity of a seal can be compromised by cuttings, dirt and other debris that may become wedged between various dynamic and static seal surfaces. As the cone cutter rotates during operation, the seal is subjected to extreme pressures, temperatures and vibration, and may expand or contract. The cone cutter will tend to experience axial movement, which can cause the seal ring to “roll” along its annular axis, allowing debris to collect between the ring and an adjacent surface. In addition axial movement and rolling about the journal pin axis, the cone cutter will tend to experience radial movement, or rocking about the pin due to clearances inherent between the cone cutter and journal pin. The rocking is generally facilitated by clearances in the ball races.
Excessive axial movement may exacerbate the rolling or sliding movement of the ring and debris collection in the seal. The debris may compromise the integrity of the seal, allowing lubricant to escape out of the journal gap and into the borehole. If enough lubricant escapes from the journal gap, temperatures within the gap could rise to unacceptable levels, putting even greater thermal stress on the remaining lubricant and the elastomeric seal components. Potentially worse, enough debris may pass into the journal gap and/or enough lubricant may escape the gap to impede rotation of the cone cutter. As a result, drilling dynamics may be changed by a bearing and/or seal failure, eventually requiring the bit to be removed from the borehole. Accordingly, protecting the integrity of the seal is of utmost importance.
Conventional rolling cone bits include lubricant systems within their journal segments for communicating lubricant from a reservoir to the bearing surfaces of the journal gap. Some such systems employ the axial movement of the cone cutter as part of a pumping mechanism for supplying stored lubricant to the bearing surfaces. However, it is believed beneficial to control the rate of axial movement of the cone cutter. When in an extended state, the cone cutter extends the journal gap in the axial direction. The cone cutter tends to quickly retract, slamming the surfaces of the cutter into the thrust face, the annular end face of the journal pin, and the spindle pin face, the end face of the reduced-diameter spindle pin. In downhole operation, this is a largely uncontrolled vibration that can not only damage the impacting faces of the cutter and the journal pin, but also the seal, at least in part by allowing a faster and/or greater magnitude of annular roll. Consequently, it is desired to dampen the axial vibration of the cone cutter on the journal pin while still maintaining adequate lubrication cycling throughout the journal gap and bearing surfaces.
Described herein is a lubricant pump and cone movement dampener system for an earth-boring bit. The system of the preferred embodiments includes a journal pin having a first journal surface, a cone cutter disposed over the journal pin and having a second journal surface, and a circumferential ball race formed between the first and second journal surfaces. The system of the preferred embodiments further includes a grease passage in fluid communication with the ball race and passing through the journal pin. An axial bore is disposed through the end of the spindle pin and is in fluid communication with the grease passage. A unidirectional valve disposed within the axial bore allows lubricant movement out of the axial bore and into the journal gap, formed by the exterior of the journal pin and the adjacent interior bore of the cone cutter, when the cone moves axially away from the bit body. The valve is configured to prevent the flow of lubricant in the opposite direction, thereby providing a dampening effect as the cone cutter tends to move axially back toward the bit body.
Embodiments described herein thus comprise a combination of features and advantages that overcome some of the deficiencies or shortcomings of prior art seal assemblies and drill bits. The various characteristics mentioned above, as well as other features and characteristics described in more detail below, will be readily apparent to those skilled in the art upon reading the following detailed description of preferred embodiments, and by referring to the accompanying drawings.
For a more detailed description of the preferred embodiments of the present invention, reference will now be made to the accompanying drawings, wherein:
The preferred embodiments of the present invention disclose a lubricant pump and cone movement dampener system for improving lubricant cycling and cone movement dampening within an earth-boring bit.
Each cutter cone 104 is in the form of a generally conical steel body having a central bore or cavity 126 for receiving journal pin 118 and having cemented tungsten carbide inserts 108 pressed into holes on the external surface. For long life, the inserts 108 may be tipped with a polycrystalline diamond layer. Such tungsten carbide inserts 108 provide the drilling action by engaging a subterranean rock formation as the rock bit 100 is rotated. Some types of bits have teeth milled on the outside of the cone rather than employing carbide inserts as cutting elements. Such bits are typically referred to as “milled-tooth” or “steel tooth” bits.
The cavity 126 in the cone 104 typically contains a cylindrical bearing surface 128 concentric to pin bearing surface 133. Disposed about the bearing surface 133 of the pin 118 is a floating journal sleeve 132. Collectively, sleeve 132 and journal bearing surfaces 133 and 128 provide the main bearing surface for the cone 104 on the bit body 102. Other types of bits, particularly for higher rotational speed applications, may include roller bearings instead of the journal bearings illustrated herein.
A plurality of locking balls 142 are fitted into complementary ball races 144, which are annular, hemispherically shaped indentions or grooves in the cone 104 and on the journal pin 118. Upon assembly of the cone 104 on journal pin 118, balls 142 are inserted through a ball passage 146, which extends through the journal pin between the ball races 144 and the exterior of the rock bit 100. A cone 104 is first fitted on the journal pin 118, and then the locking balls 142 are inserted through the ball passage 146. The balls 142 carry any thrust loads tending to remove the cone 104 from the journal pin 118, and thereby retain the cone on the journal pin. The balls 142 are retained in the races 144 by a ball retainer 148 that is inserted through the ball passage 146 after the balls are in place in the ball race. The ball retainer 148 may be of such diameter as to not completely fill the ball passage 146, allowing a portion of the ball passage diameter to serve as a grease passage 150 for communicating lubricant to the ball races 144 and journal bearing surfaces 128, 133. A plug 154 is then welded or otherwise secured into the end of the ball passage 146 to keep the ball retainer 148 in place. Although shown as the same passage, it will be understood that an alternative embodiment may include a grease passage 150 distinct from ball passage 146, while still maintaining fluid communication with a leg grease passage 156 and ball race 144.
The bearing surfaces 128, 133 between the journal pin 118 and the cone 104 are lubricated by a grease or other lubricant. Preferably, upon assembly of the rock bit 100, the interior of the bit is evacuated, and lubricant is introduced through a fill passage (not shown). The lubricant thus fills the regions adjacent the bearing surfaces 128, 133 plus various passages and a grease reservoir subassembly 164, and air is essentially excluded from the interior of the rock bit 100. The reservoir subassembly 164 comprises a cavity 112 in the rock bit body 102 and is connected to the ball passage 146 by a leg grease passage 156 (not to be confused with a grease passage 150 present in the journal pin 118). Lubricant also fills the portion of the ball passage 146 adjacent the ball retainer 148 and journal gap 160. The journal gap 160 is the narrow space between cone cutter 104 and journal pin 118. Lubricant is retained in the journal gap 160 by a resilient seal in the form of a journal seal ring 162 between the cone 104 and journal pin 118. Journal gap 160 is not limited to the area adjacent to journal sleeve 132, but extends along journal pin 118 to lower end 122.
A reservoir subassembly 164 is disposed in cavity 112. The subassembly comprises a reservoir canister 166 with a vent passage 174 at its inner end. A flexible rubber reservoir bellows 170 extends into the cup from its outer end. The reservoir bellows 170 is held into place by a reservoir end cap 172 having a vent passage 174. The reservoir subassembly 164 is retained in position by a snap ring 176. Although a rotary cone drill bit having a pressure compensation subassembly is shown, it will be understood that some rotary cone drill bits are configured without pressure compensation subassemblies. For example, rotary cone drill bits used in mining operations, i.e., mining bits, are used in operating conditions different from that of rock bits where pressure compensation is not necessary.
When the rock bit is assembled, the ball race 144, the journal gap 160, the axial bore 202 (described below), the leg grease passage 156, and cavity 112 outside the reservoir bellows 170 are all filled with lubricant. If the volume of the lubricant expands due to heating, for example, the reservoir bellows 170 of subassembly 164 contracts to provide additional volume in the sealed lubricant system, thereby preventing accumulation of excessive pressures. High pressure in the lubricant system can damage the seal ring 162 and permit abrasive-laden drilling fluid to enter the journal gap 160 and damage bearing surfaces 128, 133. Conversely, if the lubricant volume should contract, the reservoir bellows 170 can expand to prevent low pressures in the sealed lubricant system, which could cause flow of abrasive and/or corrosive substances past the seal ring 162. If desired, a pressure-relief check valve (not shown) can also be provided in the reservoir subassembly 164 for relieving over-pressures in the lubricant system that could damage the seal ring 162.
Referring now to
In this embodiment, the axial bore 202 includes a counterbore 208, an area of enlarged diameter for seating and maintaining position of the unidirectional valve 204. As shown in this embodiment, the unidirectional valve 204 is a ball-spring type valve. As shown, a ball 210 fitted in the counterbore 208 is pushed toward the shoulder 212 formed at the intersection of the counterbore and axial bore 202. Lubricant flowing into the counterbore 208 from the journal gap 160 presses the ball against shoulder 212, maintaining the closed position of the ball until the pressure of lubricant flow in opposite direction is sufficient to unseat the ball and open the valve 204. A spring 214 fitted in the counterbore 208 also helps maintain the closed position of the ball 210. The force of the spring 214 against the ball 210 reduces response time for opening and closing valve 204, thereby dampening cone movement.
The spring 214 is preferably held in the counterbore 208 by a retaining mechanism 206. Preferably, the retaining mechanism 206 is a snap ring or other similar device that allows the spring 214 to maintain its terminal end position while still allowing lubricant to flow out of the axial bore 202. However, it will be understood that while a ball valve and counterbore have been shown, any other suitable unidirectional valve may be fitted within the axial bore 202 without the need for a counterbore. A seal, generally in the form of a journal seal ring 162 is disposed between the journal surfaces 128 and 133 to prevent egress of the lubricant into the earthen borehole and prevent or retard entry of contaminants and debris into the journal gap 160.
A certain amount of axial cone movement occurs in the rolling cone cutters as a result of the formation forces acting on the cutter elements of the cone cutter. As such forces cause the cone cutter 104 to move axially along the journal pin 118 in a direction and away from leg 116, lowered pressure within the journal gap 160 will induce flow of more lubricant out of the axial bore 202 and ball race 144 into journal gap 160. As the cone cutter 104 is pushed back towards leg 116 along the journal pin 118, as caused by formation forces acting on other rows of cutter elements, lubricant is forced out of journal gap 160. Because valve 204 is unidirectional, it prevents lubricant exiting gap 160 from passing through axial bore 202. Thus, lubricant that is forced out of journal gap 160 can only exit gap 160 via ball race 144. This cycle of lubricant motion into and out of the journal gap 160 allows heated lubricant to be evacuated from the gap and for fresher, cooler grease to enter the gap. Lubricant cycling ensures a longer life of the lubricant, and consequently, contributes to the longer life of the bit and more efficient and cost-effective drilling operations.
Additionally, the placement and function of the unidirectional valve 204 in the journal pin 118 forces the lubricant that is originally conducted into gap 160 via bore 202 to pass through the tortuous path of the narrow journal gap 160 from the end of spindle pin 120 to ball race 144 to find another point of egress (i.e. grease passage 150) as the cone cutter moves axially back toward leg 116. With valve 204 closed, lubricant present in the journal gap 160 is pushed into the ball races 144, from which it enters into grease passage 150 before cycling back into axial bore 202. Overall, lubricant flow is generally unidirectional throughout the axial bore 202 of cone movement dampener 200, largely cycling out of the axial bore 202, into the journal gap 160, and back into the grease passage 150 (via ball races 144) where it may thereafter enter the axial bore 202 again. Although grease passage 150 is in fluid communication with leg grease passage 156 leading to the grease reservoir (not shown in
The presence of cycling lubricant in the journal gap 160 has a cushioning effect, such that axial movement of the cone cutter 104 back towards the journal pin 118 is dampened. Under conventional operating conditions, the cone cutter 104 would tend to oscillate axially in a rapid fashion along journal pin 118. When fitted with the lubricant pump and cone movement dampener 200 of the preferred embodiments, the speed at which the cone cutter 104 can oscillate is reduced. This is especially desired during the retraction phase, when the cone 104 moves towards the journal pin 118. Instead of rapidly slamming into the faces of the journal pin 118 and spindle pin 120, the cone cutter 104 approaches these faces more slowly due to the presence of lubricant that has been pumped into journal gap 160 via valve 204. When the cone is forced back along journal pin 118 toward leg 116, the cone movement is retarded as the lubricant pumped into the gap 160 through passageways 150 (of area A1) and 202 (of area A2) can be forced out of gap 160 only through grease passage 150. With the total area available for communicating the lubricant thus decreased, cone movement is slowed. Consequently, less physical wear is possible on the impacting faces. In addition, the slowed axial movement of the cone cutter 104 relative to the journal pin 118 contributes to less rolling and movement of the seal rings 44. As previously mentioned, rapid movements of the cone may cause excessive movement or roll of seal rings 162 in the axial direction, which may allow debris to become wedged between the seal ring 162 and an adjacent surface, reducing the integrity of the seal. The rapid cycling of an undampened cone 104 may allow the seal ring 162 to move back over and cover the debris, thus trapping the debris and possibly compacting it. Compacted debris may collect and become hard enough to physically damage the seal ring 162, further impacting the integrity of the seal.
While various preferred embodiments of the invention have been showed and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments herein are exemplary only, and are not limiting. Many variations and modifications of the apparatus and methods disclosed herein are possible and within the scope of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims.
The present application claims the benefit of 35 U.S.C. 111(b) provisional application Ser. No. 60/497,178 filed Aug. 22, 2003, and entitled Lubricant Pump and Cone Movement Dampener.
| Number | Date | Country | |
|---|---|---|---|
| 60497178 | Aug 2003 | US |
