Patent Application
20090321146
1. Field of the Invention
The present invention relates generally to drill bits for drilling into a subterranean formation, and more specifically to drill bits for drilling into a subterranean formation that include a wear resistant diamond-like carbon (DLC) coating applied to one or more of the inner surfaces of the drill bit and methods for applying a wear resistant DLC coating to one or more interior surfaces of the drill bit, to reduce wear on the seal and the surface of the drill bit.
2. Description of Related Art
Rotary-type drill bits include both rotary drag bits and roller-cone bits. Typically, in a rotary drag bit, fixed cutting elements are attached to the face of the drill bit. In a roller-cone arrangement, the drill bit typically has three cones, each independently rotatable with respect to the bit body supporting the cones through bearing assemblies. The cones carry either integrally formed teeth or separately formed inserts that provide the cutting action of the bit into the earthen formation.
The roller cones are typically attached to a bearing shaft that extends in a generally inward and downward orientation relative to the leg of the drill bit. Rotation of the roller cone is generally about an axis defined by the bearing shaft. The roller cone typically contacts the bearing shaft at a plurality of interior surfaces of the roller cone. The force applied to the drill bit during drilling operations is transmitted through the drill bit and to the interior surfaces of the roller cone and the bearing shaft.
While the application of hardened and wear resistant coatings to the outer wear surfaces of drill bits, such as the cutting elements, is known in the art, application of wear resistant coatings to the interior wear surfaces of drill bits is only recently gaining attention. Prior art methods have thus far been directed to the application of wear resistant coatings in an effort to reduce wear between interior contacting metal-metal surfaces, which can lead to the deterioration of the interior of the roller cone and/or the bearing shaft it contacts, thus leading to the need to replace the drill bit.
A seal is typically positioned between the bearing pin and the outside environment and is designed to keep lubrication in and around the bearing space and keeps contaminants, including drilling fluids and cuttings, out of the bearing space. The seal should apply enough pressure or squeeze around the bearing pin to prevent loss of lubrication, while at the same time preventing the influx of drilling fluids, however, at the same time, the pressure should be minimized to reduce friction and wear of the seal. Over time, friction between the rotating seal and the seal gland can result in wear of both the seal gland and the seal, thereby causing a decrease in the seal squeeze and failure of the drill bit.
While the prior art has focused on the need to reduce wear between metal-metal surfaces on drill bits, it is also known that during extended use, elastomeric seals wear due to friction as a result of contact with the bearing shaft. Prior art methods to reduce wear of the seal and improve the lifetime thereof have generally focused on the materials used for the seal and seal composition additives for increasing wear resistance. Prior art additives utilized for increased life in seals include molybdenum disulfide, graphite, nitrides and other known compounds, however these have only met with limited success. Thus, there exists a need for reducing seal wear and improving overall seal lifetimes through manipulation of the physical properties of the bearing shaft metal.
The present invention provides a rotary-type drill bit for drilling subterranean formations and method for making the same. The bit according to the present invention includes a surface treatment for the interior portions of the drill bit to decrease seal and seal gland wear.
In one embodiment, a drill bit for drilling a subterranean formation is provided. The drill bit includes at least one leg and a cantilevered bearing shaft comprising a base formed on the at least one leg and having a substantially cylindrical surface extending from the base defining a longitudinal axis. A roller cone is disposed about the bearing shaft and is configured to rotate about the longitudinal axis. The roller cone includes an exterior surface for contacting the subterranean formation and an interior surface disposed about the bearing shaft. A sealing element is disposed circumferentially about the bearing shaft and is positioned between the interior surface of the roller cone and an exterior surface of the bearing shaft. At least a portion of the exterior surface of the bearing shaft that contacts the sealing element includes a diamond-like carbon coating.
In another embodiment of the present invention, a drill bit for drilling a subterranean formation is provided that includes at least one leg and a cantilevered bearing shaft that includes a base formed on the at least one leg and includes a substantially cylindrical surface extending from the base defining a longitudinal axis. A roller cone is disposed about the bearing shaft and is configured to rotate about the longitudinal axis. The roller cone includes an exterior surface for contacting the subterranean formation and an interior surface disposed about the bearing shaft. A sealing element is disposed circumferentially about the bearing shaft and is positioned between the interior surface of the roller cone and an exterior surface of the bearing shaft. The drill bit further includes a bearing sleeve secured to base of the bearing shaft, thereby forming a portion of the exterior surface of the bearing shaft that contacts the sealing element, wherein at least a portion of the exterior surface of the bearing sleeve that contacts the sealing element includes a diamond-like carbon coating.
In another embodiment, a drill bit for drilling a subterranean formation is provided. The drill bit includes at least one leg and a cantilevered bearing shaft that includes a base formed on the at least one leg and a substantially cylindrical surface extending from the base defining a longitudinal axis. The drill bit further includes a roller cone disposed about the bearing shaft, wherein the roller cone is configured to rotate about the longitudinal axis. The roller cone includes an exterior surface for contacting the subterranean formation and an interior surface disposed about the bearing shaft. A sealing element is disposed circumferentially about the bearing shaft and is positioned between the interior surface of the roller cone and an exterior surface of the bearing shaft. The drill bit includes a first bearing sleeve secured to base of the bearing shaft, thereby forming a portion of the exterior surface of the bearing shaft that contacts the sealing element, and a second bearing sleeve secured to the bearing shaft adjacent to the first bearing sleeve, thereby forming a portion of the exterior surface of the bearing shaft that contacts the interior surface of the roller cone. At least a portion of the exterior surface of the first bearing sleeve that contacts the sealing element includes a diamond-like carbon coating.
In another aspect, a method for reducing wear of an elastomeric seal in a drill bit is provided. The method includes the steps of providing a drill bit that includes at least one leg, a cantilevered bearing shaft that includes a base formed at the at least one leg and a substantially cylindrical surface extending from the base defining a longitudinal axis, wherein the bearing shaft having a lateral side surface, and a roller cone disposed about the bearing shaft. The roller cone is configured to rotate about the longitudinal axis, and includes an exterior surface that includes a plurality of cutting elements for contacting the subterranean formation and an interior surface disposed about the bearing shaft. An elastomeric shaft seal is positioned between the lateral side surface of the bearing shaft and the interior of the roller cone, and prevents the influx of unwanted fluids into an interior space defined by the interior surface of the roller cone and the bearing shaft. The method further includes the step of applying a wear resistant coating to the bearing shaft where it contacts the elastomeric shaft seal ring. In certain embodiments, the wear resistant coating includes diamond-like carbon.
a is a view showing the wear on a bearing shaft without a DLC coating after simulated use.
b is a view showing wear on a bearing shaft having a DLC coating after simulated use.
Although the following detailed description contains many specific details for purposes of illustration, one of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope and spirit of the invention. Accordingly, the exemplary embodiments of the invention described herein are set forth without any loss of generality to, and without imposing limitations thereon, the present invention.
Various materials known in the art can be used to provide surface treatments for the exterior surfaces of drill bits. Surface treatments can be applied to the exterior surface of the drill bits for a variety of reasons, such as increased life time of the exposed parts, and/or to reduce adhesion of various substances to the exterior surfaces of the drill bit. In contrast, the present invention relates to the application of surface treatments to the interior contacting surfaces of the drill bit. More specifically, the present invention is directed to the use of wear resistant coatings on the interior surface of the roller cone drill bits to reduce wear of the seal, resulting in increased life of both the metal surfaces and the seals.
One exemplary wear resistant surface coating is diamond-like carbon (DLC). DLC is a form of meta-stable amorphous carbon or hydrocarbon compound with physical properties very similar to those of diamond. Being amorphous, there are typically no grain boundaries. DLC coating is a carbon coating that includes a mixture of sp3 and sp2 hybridized carbon atoms. The sp3 hybridized carbons form a tetrahedral crystalline orientation found in diamond. The sp2 hybridized carbons have a planar crystalline structure, like that found in graphite. Technically, the sp3 hybridization means that the carbon reconfigures one s-orbital and three p-orbitals to form four identical sp3 orbitals having a tetrahedral configuration for bonding with the adjacent carbon atom. The sp2 hybridized orbital is derived from one s-orbital and two p-orbitals to form three sp2 orbitals, which are planar in orientation. DLC coatings have a certain percentage of both types hybridized carbons, depending upon how the material is prepared, thus the hardness of a DLC coating can be designed to be between that of diamond and graphite. The DLC coating has a hardness of between about 2000 and 5000 knoop, depending upon the amount of sp2 and sp3 hybridized carbons and other impurities present in the coating.
In certain embodiments, the proportions of sp2 and sp3 hybridized carbons in the DLC can be varied. A DLC coating having a higher concentration of sp3 hybridized carbon atoms typically has a greater hardness than the DLC coatings having a lower concentration of sp3 hybridized carbon atoms. Without wishing to be bound by any specific theory, it is believed that the graphitic sp2 carbons present in the DLC coating contribute lubricious properties to the coating, resulting in a smooth, corrosion resistant surface. While the greater concentration of sp2 carbon atoms typically results in a softer coating, it also has a higher lubricity. The exact combination of hardness and lubricity can be adjusted based upon the desired properties of the end product. In addition to carbon, DLC coatings can also include a variety of impurities, such as hydrogen and/or metal atoms. Hydrogen is typically present as a result of the process gas used during fabrication, because DLC coatings are deposited by the decomposition of a carbon compound and hydrogen compound. One suitable DLC precursor carbon compound is acetylene.
The diamond-like carbon coatings of the present invention can be applied by a variety of techniques, including but not limited to, physical vapor deposition, chemical vapor deposition, vacuum deposition and like processes. Physical vapor deposition processes can include evaporation, sputtering and laser ablation. Chemical vapor deposition (CVD) processes generally include the deposition of a solid from the vapor phase onto a substrate that optionally may be heated or pretreated by other means to enhance the reaction of the material being deposited with the substrate surface. In certain embodiments, DLC is applied from high energy carbon precursors that are produced by a plasma, sputter deposition, ion beam deposition, or the like. In other embodiments, the DLC layer can be applied by deposition from an RF (radio frequency) plasma, sustained in hydrocarbon gases, onto negatively biased substrate surface. The DLC coating can be applied directly to the surface being coated, or to a metal interlayer that has been applied to the surface being coated. Generally, the DLC coating can be applied to any substrate that is compatible with a vacuum deposition environment.
In one exemplary embodiment, the DLC coating can be applied in the following manner. DLC is applied by deposition from an RF (radio frequency) plasma, sustained in hydrocarbon gases, onto a negatively biased substrate surface. In this process, referred to as a plasma assisted chemical vapor deposition (PACVD), the substrate surface is typically heated by an electron current to a temperature that is below their lowest transformation temperature. Electrons from the electron current are attracted to the face of the substrate surface from a plasma beam in the center of the chamber. After heating, the substrate surface can be etched by argon ion bombardment or a like process. For this, the substrate surface is typically biased to a negative potential to attract argon ions from a plasma source. This process cleans the surfaces by etching.
After cleaning of the substrate surface has been completed, one or more metallic interlayers, such as chromium, can optionally be applied to the substrate surface from a sputter source. Sputtering is similar to etching, however a bias voltage is applied to the metal (e.g., chromium) target of several hundred volts. The substrate being coated with the metal serves as a negative electrode. Material is removed from the metal target surface by the impact of argon ions, and this material then condenses onto the target substrate surface. Depending upon the material of the substrate being coated, the optional metallic interlayer prepared in this manner can be used to increase adhesion of the DLC coating and can be formed of a variety of metals, such as titanium.
After the optional deposition of the metal interlayer on the surface of the substrate, acetylene or another carbon source can be introduced and a plasma can be ignited between substrate surface and the chamber walls. Decomposition of the carbon source results in the formation of individual carbon atoms that coat the substrate surface or the optional metallic interlayer of the substrate with DLC. DLC coatings are insulating, thus the plasma for the DLC cannot be a DC plasma, but must instead be an AC plasma. Typically an RF plasma is used. After coating the substrate with the DLC coating, the substrate is cooled and the deposition chamber vented. During the entire DLC coating process, the temperature in the deposition chamber is preferably maintained at below the lowest transformation temperature of the substrate.
In addition to the process of applying the DLC coating described above, other processes are suitable for the deposition of the DLC, including primary ion beam deposition of carbon items (IBD). Another process that may be suitable is sputter deposition of carbon, either with or without bombardment by an intense flux of ions (physical vapor deposition). Yet another technique is based on closed field unbalanced magnetron sputter ion plating, combined with plasma assisted chemical vapor deposition. The deposition can be carried out at approximately 200° C. in a closed field unbalanced magnetron sputter ion plating system.
The DLC, as applied, can have a thickness between approximately 0.5 μm and 100 μm. Preferably the DLC coating has a thickness of between approximately 1 μm and 10 μm. The optional intermetallic layer can have a thickness of between about 0.5 μm and 10 μm, and is preferably minimized.
In certain embodiments, multilayer compositions can be prepared. The multilayer composition is prepared by repeating the steps of applying the DLC coating to the surface being coated.
In certain embodiments, an alternate coating can be applied to the bearing shaft surface that contacts the seal. For example, in certain embodiments, a wear and corrosion resistant coating selected from hardfacing, Hardide™, TiN or SiC can be applied by known means to the bearing shaft surface. A lubricant layer, selected from Teflon, hexagonal boron nitride, graphite, tungsten disulfide or molybdenum disulfide, or a like material, can then be applied to the wear resistant coating.
In accordance with the present invention, a DLC coating can be applied to lateral surface 128 of bearing shaft 107, which contacts seal 116. Additionally, the DLC coating can be applied to any surface seal 116 contacts, such as back face plane 129 or forward face plane 130.
As described herein, methods for the preparation of drill bits that include a wear resistant surface are also provided. The wear resistant surface is generally applied to at least one of the contacting surfaces between the interior of the roller cone and the exterior of the bearing shaft.
Typically, the drill bit body is prepared as three separate pieces or “thirds”, which after assembly, are welded together to make the drill bit. The manufacture of a drill bit having wear resistant surfaces according to the methods described herein includes the steps of providing a third, wherein the third includes a drill bit leg and a cantilevered bearing shaft formed on the end the drill bit leg. The drill bit leg may then be masked off, leaving exposed only the surfaces to which the wear resistant coating is desired to be applied. The masked drill bit leg may then be positioned in a vacuum deposition chamber, and the desired materials may be deposited thereon. Preferably, at least a portion of the bearing shaft is left exposed and coated with a wear resistant coating. In certain embodiments, the chamber may be heated and maintained at a reduced pressure during the deposition. One preferred coating for the bearing shaft is a tungsten/tungsten carbide coating. Following deposition of a wear resistant coating of desired thickness, the drill bit leg having the wear resistant coating is removed from the deposition chamber, the masking is removed, and the drill bit is assembled. Assembly of the drill bit includes the steps of positioning a roller cone on the bearing shaft which has the wear resistant surface coating applied thereto, securing the roller cone to the bearing shaft by inserting the locking balls into the locking ball race, and welding three similarly configured thirds together to achieve the drill bit, such as for example, by electron beam welding.
In an alternate embodiment, the manufacture of a drill bit having wear resistant DLC surfaces according to the methods described herein can include the step of providing a masked bearing shaft, wherein the exposed surfaces of the bearing shaft are desired to be coated with the DLC coating. Preferably, the bearing shaft, to which the cone is attached when the drill bit is assembled, includes a DLC coating. The masked bearing shaft may be positioned in a vacuum deposition chamber, and the desired DLC material deposited thereon. In certain embodiments, the chamber is heated and maintained at an elevated pressure, during the deposition of the coating. Following deposition of a surface coating of desired thickness, the bearing shaft may be removed from the deposition chamber, the masking removed, and the drill bit assembled. During assembly, the roller cone is positioned on a bearing shaft which has a DLC coating applied to at least a portion of the exterior surface, and locking balls are inserted into a locking ball race, thereby securing the roller cone to the bearing shaft. Typically, the drill bit is prepared as the separate pieces or “thirds”, which after securely fastening the roller cones to the bearing shaft, are welded together to make the drill bit.
In certain embodiments, a sleeve can be installed on the bearing shaft, wherein the sleeve includes a wear resistant DLC coating applied to the exterior surface. Methods for application of the wear resistant coating on the surface of the sleeve are provided herein, and can include physical and chemical vapor deposition. Techniques for the use of bearing sleeves are described in U.S. Pat. Nos. 7,387,177 and 7,392,862, the disclosures of which are hereby incorporated in their entirety. In certain embodiments, the sleeve that includes a wear resistant coating can be secured to a bearing shaft that is adapted to receive said sleeve. Methods for affixing or securing the sleeve to the bearing shaft include welding, brazing, gluing, soldering, shrink fitting, pinning, splining, combinations thereof, or the like.
A 12.25 inch tri-cone drill bit not having a wear and corrosion resistant coating applied to the portion of the bearing shaft that contacts the elastomeric seal was run in a drilling field application. The drill bit was used to drill a borehole for a period of at least 34 hours, and was rotated at approximately 220 rpm or greater.
The uncoated drill bit showed significant wear on both the bearing shaft and the seal after completion of the run. As shown in
As used herein, squeeze is defined as: (seal width minus the gland width)/seal width. The loss of the width of the seal cross section is responsible for the loss of approximately 50% of the squeeze of the seal. The wear on the seal gland of the bearing shaft is responsible for a loss of approximately 68% of the squeeze of the seal. Overall, the combined wear on the seal and the bearing resulted in a loss of approximately all of the squeeze on the seal. Additionally, it should be noted that the bearing shaft wear is larger when compared with the seal wear. This suggests the wear reduction of the bearing shaft as described in this invention can significantly improve retention of seal squeeze and thus drill bit lifetime.
Furthermore, analysis of the fluids (grease) in the drill bit showed high contamination with drilling fluids. Specifically, while the increase of silicon present in the drill bit grease at the reservoir of the drill bit was relatively low, in contrast, the concentration of silicon at the bearing increased by a factor of approximately 15, relative to a normalized silicon concentration for an uncontaminated sample.
A second test was conducted to simulate normal usage of a rock drill bit, wherein two seal test fixtures, consisting of the portion of the bearing shaft that is in sliding engagement with the seal, one coated with a DLC coating about the bearing shaft where the seal contacts the bearing shaft and one uncoated, were submerged in drilling mud and operated. The drilling mud was maintained at a temperature of approximately 150° F. and the cones were rotated at a rate of about 240 rpm for 48 hours. Sand in the mud was injected into the gland with a pump to simulate an abrasive environment.
b shows a view of a DLC coated seal test fixture and
As used herein, recitation of the term about and approximately with respect to a range of values should be interpreted to include both the upper and lower end of the recited range.
As used in the specification and claims, the singular form “a”, “an” and “the” may include plural references, unless the context clearly dictates the singular form.
Although some embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereupon without departing from the principle and scope of the invention.
This application is a continuation-in-part of co-pending application Ser. No. 12/417,416, filed on Apr. 2, 2009, which is a continuation-in-part application of U.S. patent application Ser. No. 12/172,364, filed Jul. 14, 2008, which claims priority to and the benefit of U.S. Provisional Application Ser. No. 60/949,756, filed Jul. 13, 2007, and also claims priority to and the benefit of co-pending U.S. Provisional Application Ser. No. 61/041,621, filed Apr. 2, 2008, the full disclosures of which are hereby incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 60949756 | Jul 2007 | US | |
| 61041621 | Apr 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12417416 | Apr 2009 | US |
| Child | 12556325 | US | |
| Parent | 12172364 | Jul 2008 | US |
| Child | 12417416 | US |
