Patent Application
20060032673
Not Applicable.
Not Applicable.
1. Field of the Invention
The invention relates generally to seal assemblies for sealing between a rotating and a static member. In one aspect, and more particularly, the invention relates to seals for rolling cone bits as used to drill boreholes for the ultimate recovery of oil, gas or minerals. Still more particularly, the invention relates to elastomeric seals that seal and protect the bearing surfaces between the rolling cone cutters and the journal shafts on which they rotate.
2. Description of the Related Art
An earth-boring drill bit is typically mounted on the lower end of a drill string. With weight applied to the drill string, the drill string is rotated such that the 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. 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 of journal segment legs. The rolling cones are mounted on bearing pin shafts (also called journal shafts or pins) that extend downwardly and inwardly from the journal segment legs. As the bit is rotated, 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. Liquid drilling fluid is normally used for oil and gas well drilling, whereas compressed air is generally used as the drilling fluid in mining operations.
Seals are provided in glands formed between the rolling cones and their journal shafts to prevent lubricant from escaping from around the bearing surfaces and to prevent the cutting-laden, and thus abrasive, drilling fluid from entering between the cone and the shaft and damaging the bearing surfaces. When cuttings are conveyed into the seal gland, they tend to adhere to the gland and/or seal component surfaces, and may cause undesirable increased deflection and wear to the seal components. Moreover, the cuttings can accelerate abrasive wear of all seal components and of the bearing surfaces.
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 before reaching the targeted formation. This is the case because each time the drill bit wears out or fails as a borehole is being drilled, the entire string of drill pipes, which may be miles long, must be retrieved from the borehole, section by section, in order to replace the bit. 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. The amount of time required to make a round trip for replacing a bit is essentially lost from drilling operations. As is thus obvious, this process, known as a “trip” of the drill string, requires considerable time, effort and expense. 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).
The durability of a bit and the length of time that a drill bit may be employed before it must be changed depends upon numerous factors. Importantly, the seals must function for substantial periods under extremely harsh downhole conditions. The type and effectiveness of the seals greatly impact bit life and thus, are critical to the success of a particular bit design.
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, and high temperatures.
As previously mentioned, the bearing surfaces in typical bits are lubricated, and the lubricant is retained within the bit by the seals. The seal is typically in the form of a ring, and includes a dynamic seal surface, that is placed in rotating contact against a non-rotating surface, and a static seal surface that engages a surface that is stationary with respect to the seal ring. Although the bit will experience severe and changing loading, as well as a wide range of different temperature and pressure conditions, the dynamic and static seal surfaces must nevertheless remain sealingly engaged in order to prevent the lubricant from escaping and/or cuttings from entering the lubricated areas. These seals should perform these duties throughout the life of the bit's cutting structure.
In one typical arrangement, the seal includes a static seal surface adapted to form a static seal with the interior surface of the roller cone, and a dynamic seal surface adapted to form a dynamic seal with the journal shaft upon which the roller cone is rotatably mounted. The seal must endure a wide range of temperature and pressure conditions during the operation of the drill bit and still prevent lubricants from escaping and/or contaminants from entering the journal bearing. Elastomer seals known in the art are conventionally formed from a single type of rubber or elastomeric material, or may be made of two or more materials bonded together.
The rubber or elastomeric material selected to form the seal for the journal bearings has a particular hardness, modulus of elasticity, wear resistance, temperature stability, and coefficient of friction, among other properties. Additionally, the particular geometric configuration of the seal (along with the dimensions of the seal gland) produces a selected amount of seal deflection that defines the contact pressure and seal footprint applied by the dynamic and static seal surfaces against respective journal bearing and roller cone surfaces.
The wear, temperature, and contact pressures encountered at the dynamic seal surface are different than those encountered at the static seal surface. Therefore, the type of elastomeric material and the geometry that is selected to form each seal surface is aimed at satisfying the particular operating conditions experienced by the different dynamic and static seal surfaces.
In certain prior art bits, the elastomeric seal rings are generally adapted to form static seals on outer surfaces and dynamic seals on inner surfaces thereof In such bits, the OD seal surface is arranged to form a static seal with an adjacent and concentric surface of a seal gland (where the seal gland is formed on an internal surface of a roller cone). During operation, localized temperature increases, caused by inadequate lubrication or abrasive penetration, may result in the ID seal surface becoming static by sticking to the journal shaft, and the OD seal surface then becoming dynamic. When rotation occurs at the OD seal surface, which is usually formed from a relatively soft elastomer and has a relatively poor wear resistance, the OD seal surface experiences severe wear, and the seal may fail after a short time.
The service life of bits equipped with such elastomeric seals is generally limited by the ability of the seal material to withstand the different temperature and pressure conditions at each dynamic and static seal surface. Where such seal components experience damage, the lubricant is able to escape, and cutting-laden drilling fluid is allowed to enter the seal gland causing still further deterioration and damage to the seal components. Eventually, enough cuttings may pass into the journal gap and/or enough lubricant may be lost from the bearing area such that rotation of the cone cutter is impeded and drilling dynamics are changed, eventually requiring the bit to be removed from the borehole. Accordingly, protecting the integrity of the seal is of utmost importance.
Additionally, to provide the appropriate sealing pressure and contact footprint, it is imperative that the seal and the seal gland be precisely manufactured. For example, if the gland is too large or the seal too small, the appropriate squeeze on the seal will not be provided and, in turn, the desired seal footprint and sealing pressure on the journal surface will be lacking. In such instances, the seal will not perform its intended function and the bit may prematurely fail. Likewise, if the seal is too large or the gland too small, an excessive sealing pressure and footprint may result, causing excessive heating and thermal failure of the seal. Once again, this can lead to bit failure. Accordingly, for these reasons, the seals must be precisely molded and the seal glands precisely machined to create the desired contact pressure and footprint on the journal shaft.
The requirement for the elastomeric seal to provide the precise contact pressure and footprint against the adjacent sealing surfaces creates difficulties for bit manufacturers. For example, an optimal seal design for a particular application may indicate that an elastomeric seal with a non-conventional or complex geometric profile be employed in the bit. This, in turn, may require a difficult-to-machine seal gland be formed in order to retain the non-conventional seal. In this instance, manufacturing the bit could be extremely expensive or even cost prohibitive, requiring that a compromise be made by the bit designer in which the bit design would surrender certain features desirable for good seal performance in order to ease manufacturing difficulties. As another example, for a given size of bit, the different rock formations and depth of borehole in which the bits are used may dictate different sealing pressures and footprints for these bits. Even for the same size bit, the manufacturer may be required to machine many types of seal glands for the same size of seals and bits, resulting in an increase in manufacturing cost. Still further, bit manufacturers make and inventory a wide variety of bit designs and, for each such design, there may be a relatively large number of sizes of such bits. In turn, the differing bit sizes require the manufacturer to make and inventory a relatively large number of cone cutters and seals. Depending upon the application and the particular design, the manufacturer may be required to manufacture a large number of 0-ring seals and corresponding seal glands to meet its various requirements. In turn, this leads to the manufacturer being required to make and inventory a large number of seals of substantially similar construction and materials, but of a myriad of cross- sectional areas. Assembly of such bits must be carefully accomplished to be sure of identifying correctly the precise seal that is required for a particular bit that is being manufactured, and ensuring that the appropriate seal is installed in the seal gland. The manufacturing is further complicated and made more expensive by the requirement that this large number of differently-sized seal rings be molded and, once completed, retained in inventory. Similarly, a variety of different milling programs or procedures must be maintained in order to properly machine the correct seal gland for the particular cone being manufactured.
It is therefore desirable that a new, long lasting and effective seal assembly be devised that maintains the appropriate contact pressure and footprint, to provide the appropriate seal on the static and dynamic sealing surfaces. In addition, it would be desirable that the seal assembly allow drill bit manufacturers to manufacture a wide range of bit sizes while minimizing or reducing the number of different sized seals and seal glands that must be made and kept in inventory.
In one embodiment, a seal assembly for a drill bit includes an elastomeric annular sealing seal and an auxiliary annular seal member engaging the sealing seal, the sealing seal and the auxiliary seal member being disposed in a seal gland of the bit and collectively establishing a dynamic and a static seal.
In another embodiment, a drill bit includes a cone cutter rotatably mounted on a journal shaft, an elastomeric sealing seal disposed about the journal shaft in a seal gland, where the sealing seal includes a dynamic sealing surface for dynamically engaging the journal shaft and a static seal surface opposite from the dynamic sealing surface. The drill bit further includes at least one auxiliary annular seal member disposed about the journal shaft in the seal gland and engaging both the seal gland and the static surface of the sealing seal.
The drill bit and seal assemblies may include one or more auxiliary annular seal members in the seal gland engaging the static sealing surface of the sealing seal. The auxiliary seal members may include a seal engaging surface that is non-linear and, in certain embodiments, may be shaped to generally conform to the shape of the static sealing surface of the sealing seal. The seal engaging surface of the auxiliary seal member may be convex and receive a concaved outer surface of the sealing seal. The auxiliary annular seal members may be generally L-shaped in cross-section, circular or may include other shapes and may be of varying sizes. For example, in certain embodiments, the auxiliary annular seal member may itself have a convex seal-engaging surface that engages a convex surface of the sealing seal. More than one auxiliary seal member may be employed in a seal assembly.
In certain embodiments, the seal assembly and bit include a local lubricant reservoir adjacent to the sealing seal and bounded, in part, by the sealing seal and the auxiliary annular seal member.
In certain embodiments, where the auxiliary seal member includes an extending leg portion, the leg portion may extend to a location that is short of the journal surface of the cone cutter so as to leave a gap between the auxiliary seal member and the journal surface, the gap helping to form a localized lubricant reservoir.
In embodiments where a plurality of auxiliary seal members are employed, some of the plurality of auxiliary seal members comprise elastomeric materials that differ in properties, such as hardness and modulus of elasticity. The plurality of annular seal members are not bonded to one another and are not bonded to the sealing seal, but instead, the annular seal members and the sealing seal are all separate annular elements pressed into engagement with one another.
In certain embodiments, the auxiliary annular seal member includes a seal engaging surface, at least a portion of which has a shape that generally conforms to the outer surface of the sealing seal. The auxiliary annular seal members further may include a gland engaging surface having a shape that generally conforms to the shape of the seal gland.
Embodiments described herein thus comprise a combination of features and advantages directed to 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:
Referring first to
Bit 10 further including nozzles 9. Nozzles 9 are disposed in the bit body 12 so as to transmit a flow of drilling fluid from the interior of the drill bit 10 to a wellbore (not shown) and to a space proximate the roller cones 14-16. The flow of drilling fluid serves to cool the drill bit 10, clean the cutting elements 26, and to transport formation cuttings from the bottom of the wellbore to a wellbore annulus (not shown) and, subsequently, to the surface.
It is to be understood that seal assemblies are described herein with respect to a three cone bit for purposes of example only, and that the seal assemblies described herein may be employed in single cone bits, as well as in bits having two or more cones. Likewise, the seals described herein may have application beyond drill bits, and may be used wherever a shaft seal is required to seal between a rotatable member mounted on the shaft and a member that is stationary relative to the rotatable member.
As best shown in
Referring still to
Journal pin 18 includes a bearing surface 42 that is substantially concentric to bearing surface 30 in cone 14. Bearing surface 42 includes a groove 43 for receiving locking balls 37. A ball passageway 36 intersects groove 43 and forms a means by which locking balls 37 are placed into cone 14 during assembly. The locking balls retain cone 14 on the journal pin 18. After the balls 37 are in place, ball retainer 39 is inserted through ball passageway 36 and an end plug 38 is welded or otherwise secured to close off the ball passageway 36.
Journal pin 18 further includes a reduced diameter portion 47 and end-surface 44. Bearing surface 42 of pin 18 and bearing surface 30 of cone 14 may include cylindrical inlays 48, 49, respectively, that are disposed in grooves formed in the respective parts for reducing friction, such inlays being made, for example, of aluminum bronze alloys. A nose bushing 45 is disposed about reduced diameter portion 47 of pin 18. Cone 14 is disposed over the pin 18 with nose button 46 positioned between end-surface 44 and the end portion 31 of central bore 28. Seal assembly 50, shown schematically in
The bearing structure described and shown
The bearing surfaces 30, 42 between the journal pin 18 and the cone 14 are lubricated by grease. The grease is applied so as to fill the regions adjacent to the bearing surfaces and to fill various interconnected passageways such that, upon bit assembly, air is essentially excluded from the interior of the bit. The bit includes a grease reservoir 19, including a pressure compensation subassembly 29 and a lubricant cavity 20 which is connected to the ball passageway 36 by lubricant passageway 21. The grease is retained in the bearing structure and the various passageways, including diagonal passageway 35 and passageways 21, 36, by means of seal assembly 50. Likewise, seal assembly 50 prevents drilled cuttings and abrasive drilling fluid from passing seal assembly 50 and washing out the lubricant and damaging the bearing surfaces. Details of the grease fill passage and system, as well as a typical grease system pressure compensation mechanism may be found, for example, in U.S. Pat. No. 6,170,830 issued to Cawthorne et al. and assigned to the assignee of the present invention. The lubricating grease reduces the friction and, as a result, the operating temperature of the bearings in the drill bit 10. Reduced friction increases drill bit performance and longevity, among other desirable properties.
As shown in
Referring now to
Sealing seal 60 generally includes an annular or ring-shaped seal body 62 having sealing surfaces on the inner and outer diameters thereof. The embodiment shown in
Referring still to
Likewise, in this embodiment, portion 69 of seal body 62 may be made from an elastomeric material having the following properties: a durometer hardness Shore A within the range of about 60 to 80; a modulus of elasticity at 100 percent elongation of from about 300 to 900 psi (2 to 5 megapascals); a minimum tensile strength of from about 1100 to 4600 psi (7 to 28 megapascals); elongation of from about 200 to 1000 percent; die C tear strength of at least 100 lb/in. (1.8 kilogram/millimeter); and a compression set after 70 hours at 100° C. of less than about 15 percent.
Auxiliary seal 70 is an annular member having a generally L-shaped cross-section. Auxiliary seal member 70 includes base portion 71 and a leg portion 72. Auxiliary seal 70 further includes a gland-engaging surface 73 and a seal-engaging surface 74. Seal-engaging surface 74, in this embodiment, is concave and shaped to generally conform to the curved shape of side surface 67 of sealing seal 60. Auxiliary seal 70 is disposed in seal gland 34 with base portion 71 engaging bottom surface 51 of seal gland 34 and with leg portion 72 engaging side wall 53. In this arrangement, leg portion 72 is engaging the seal gland side wall 53 that is closest to groove 32 (
In the embodiment shown in
In the embodiments described herein, the auxiliary seal member 70 is not bonded or otherwise attached to the sealing seal 60, but instead constitutes a separate seal element. In this way, the present seal assembly is distinguished from prior art annular seals that, rather than employing separate auxiliary seal members, simply used a single annular seal made from different materials bonded or molded together. In the embodiments described herein in which the auxiliary seal is a separate element, detrimental stresses at the interface between the different materials are avoided. In the instance of differing materials that are bonded together to form a single annular seal element as conventional in the prior art, due to the different materials and their differing thermal characteristics, stresses are imposed at the interface that can detrimentally affect the life of the seal and thus the life of the drill bit.
In the embodiment shown in
Suitable elastomeric materials useful for forming auxiliary seal 70 and portions 68 and 69 of sealing seal 60 include those selected from the group of fluoroelastomers including those available under the trade name Advanta manufactured by DuPont, carboxylated elastomers such as carboxylated nitrites, highly saturated nitrile (HSN) elastomers, nitrile-butadiene rubber (HBR), highly saturated nitrile-butadiene rubber (HNBR) and the like.
In the embodiment of
It is desirable that the thickness T of base portion 71 (measured radially relative to journal pin 18) is dimensioned so as to provide the appropriate “squeeze” or pressure on sealing seal 60 when cone 14 is assembled on journal pin 18. As shown in
In a similar manner, varying the thickness of leg portion 72 also affects the space available for axial motion of sealing seal 60 relative to seal gland 34. Too much void space would detrimentally affect the sealing seal's ability to remain static with respect to cone 14, however some space is desirable to allow for thermal expansion of seal 60. Selecting an auxiliary seal member 70 with a thicker leg 72 may permit a relatively small sealing seal 60 to be employed in a relatively large seal gland and still provide the necessary contact pressure and frictional force to seal effectively and resist rotation. The auxiliary seal member 70 may be fashioned to energize sealing seal 60 in a bi-directional manner and to provide geometric adjustments necessary to make a given sized and configured sealing seal 60 compatible in a number of differently-sized seal glands.
Upon assembly of drill bit 10, auxiliary seal member 70 is positioned within seal gland 34 of cone 14. Sealing seal 60 is disposed in seal gland 34 so that it engages seal-engaging surface 74 of auxiliary seal 70. Thereafter, journal pin 18 is disposed in cone bore 28 with pin 18 passing through and engaging ID seal surface 64 of sealing seal 60. As previously described, locking balls 37 may then be inserted in order to lock cone 14 on journal pin 18.
The dimensions of seal gland 34, auxiliary seal member 70 and sealing seal 60, and the elastomeric qualities of sealing seal 60 and auxiliary seal member 70 determine the amount of “squeeze” applied to sealing seal 60 and, in turn, define the dimension of seal footprint F and the contact pressure exerted between the ID seal surface 64 and the journal surface 42. In addition, the shape, dimensions and material properties of auxiliary seal 70 and sealing seal 60 determine the frictional force applied to sealing seal 60. It is generally desired that seal 60 remain static with respect to auxiliary seal member 70 and seal gland 34, and that seal member 60 form a dynamic seal between ID seal surface 64 and journal surface 42. The materials of auxiliary seal 70 and sealing seal 60 may be selected such that greater (or lesser) frictional force exists between these members. The greater force is desired to ensure that sealing seal 60 remains static with respect to auxiliary seal member 70.
Lengthening leg 72, and thereby shortening gap G, increases the contact area between seal member 60 and auxiliary seal 70 and thereby tends to increase the frictional force and enhance the ability of auxiliary seal 70 and sealing seal 60 to remain static with respect to each other. Likewise, lengthening leg 72 can ensure that auxiliary seal member 70 remains static with respect to cone 14. As will be understood, shortening leg 72 has the opposite effect, and although it would increase gap G and provide greater space for lubricant, it would decrease the area of contact between the sealing seal 60 and the auxiliary seal member 70. Accordingly, selecting the height of leg 72 (and thus length of gap G), thickness T of base 71 and the materials of sealing seal 60 and auxiliary seal 70, in some cases, presents a compromise between competing design choices.
The use of auxiliary seal 70 in conjunction with the sealing seal 60 in a seal gland 34 also provides significant advantages in manufacturing. First, with the selection of an appropriately dimensioned auxiliary seal 70, an identical sealing seal may be employed in seal glands having varying dimensions. This may best be understood by first referring to
Referring now to
By contrast, by employing the concept of an auxiliary seal member 70, a manufacturer may adopt a single sealing seal and affect the appropriate seal for many different sized drill bits merely by varying the size and elastomeric qualities of the auxiliary seal 70 that is employed. Referring to
In a similar manner, and referring to
Referring now to
As compared with the embodiment shown in
Another alternative seal arrangement is shown in
The sealing assemblies of the present design are not limited to seal glands having generally rectangular cross-sections. As shown in
Another alternative embodiment is shown in
Referring to
Referring now to
Referring now to
The various preferred embodiments of the invention that have been showed and described are exemplary only, and are not limiting. Many variations and modifications of the embodiments 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.
