Patent Application
20080053709
In one aspect, embodiments disclosed herein relate to protecting the bit body of a steel-bodied drag bit in the area surrounding the cutters. In particular, embodiments disclosed herein relate to a steel-bodied drag bit having such protection, to a method of manufacturing a steel-bodied drag bit with such protection, and to a method of modifying a steel-bodied drag bit to have such protection.
Generally, the embodiments disclosed herein include a steel body having at least one blade; at least one cutter pocket disposed on the at least one blade; at least one cutter disposed in the at least one cutter pocket; at least one recess disposed on at least a portion of the surface of the at least one cutter pocket, where the recess is adjacent a leading face of the at least one blade; and an erosion resistant material in the at least one recess.
As used in reference to the embodiments disclosed herein and the claims, the term cutter is not limited to any specific size, shape, form or material nor is the term cutter limited to cutters created for use in drill bits or other earth drilling applications. As used in reference to the embodiments disclosed herein and the claims, the term erosion resistant material means a material that is more erosion resistant than is the primary material from which the bit body is formed.
Referring to
As shown in
Steel bit bodies, such as those disclosed herein, may be formed in a machining process by a computer numerically controlled (“CNC”) lathe and mill, as known in the art. In this process, a steel bar may be turned to form the general profile of the bit; a drilling operation may form the orifices, cutter pockets, and recesses in the cutter pockets; and the blades and blade tops may be formed by milling. Alternatively, other embodiments may include a steel bit body formed by casting or any other suitable method. Further, one of ordinary skill in the art would recognize that the bit body characteristics such as the number and shape of the blades, the number and shape of the cutter pockets, and the number and placement of the orifices may be varied without departing from the scope of embodiments disclosed herein. The bit body characteristics shown in the illustrated embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.
In one embodiment, the recesses formed in the cutter pockets may be substantially concentric or coaxial with the cutter pocket in which they are formed. Alternatively, the recesses may be eccentric with respect to the cutter pocket in which they are formed. As described above, such recesses may be formed by a drilling operation at substantially the same time as the drilling of the cutter pockets in a machining process. Alternatively, such recesses may be formed by a milling operation performed subsequent to the time that the cutter pockets are formed. In various other embodiments, the recesses may be formed by various other processes known in the art including, for example, grinding, a shot peen, or a deburr tool.
Further, other embodiments may have recesses with different geometry and/or formed by different processes which may be performed at various stages of the bit manufacturing process. However, one of ordinary skill in the art would recognize that the method of forming the recesses, the geometry of the recesses, and the stage of the bit manufacturing process at which the recesses are formed may depend on the particular method used to form the bit body.
The length of the recesses, shown in
The thickness or depth of the recesses, shown in
The embodiment shown in
The erosion resistant material applied in the recesses disclosed herein may include, in various embodiments, one or more hard particles surrounded by a binder material. Hard metals such as oxides, nitrides, borides, carbides of Group IV, V, and VI metals and alloys thereof are examples of hard particles that may be used in the erosion resistant material disclosed herein. In a particular embodiment, the erosion resistant material may include tungsten carbide particles surrounded by a metal binder.
Various types of tungsten carbide may be used in the erosion resistant material, including cast tungsten carbide, macro-crystalline tungsten carbide, cemented tungsten carbide, and carburized tungsten carbide. The types, sizes, and percentages of the various carbide particles may be varied depending on the properties desired for the erosion resistant material in any particular application. Carbide combinations suitable for use in the erosion resistant material may include combinations similar to those in U.S. Pat. Nos. 4,836,307, 5,791,422, 5,921,330, and 6,659,206, which are herein incorporated by reference in their entirety.
In a particular embodiment, an erosion resistant material may have varying amounts of hard particles, with a binder alloy constituting the balance of the erosion resistant material. In some embodiments, the binder alloy may include a steel alloy or Group VIII metals such as Co, Ni, Fe, alloys thereof, or mixtures thereof.
In one embodiment, the erosion resistant material may include about 40 to 65 percent by weight spherical cast tungsten carbide and a balance of a nickel alloy, a Ni—Cr—Si—Fe—B alloy in a particular embodiment.
Many factors may affect the durability of the erosion resistant material. These factors include the chemical composition and physical structure (size, shape, and particle size distribution) of the hard particles, the chemical composition and microstructure of the binder metal or alloy, and the relative proportions of the hard particles to one another and to the binder metal or alloy. Due to the inverse relationship between wear resistance and fracture toughness, higher proportions of hard particles may increase the erosion and wear resistance of the erosion resistant material, while decreasing the fracture toughness of the erosion resistant material and weakening the bonding between the erosion resistant material and the steel bit body. Thus, one of ordinary skill in the art would recognize that by varying the type, size and amount of tungsten carbide particles (and thus also the amount of binder material), an erosion resistant material having the desired material properties for a particular drilling application may be selected.
Application of the erosion resistant material may be achieved by any suitable method known in the art. A welding process, such as arc or gas welding, both of which are well known in the art, may be used, for example, when the erosion resistant material includes tungsten carbide or other hard metals. Among the welding techniques that may be used to apply the erosion resistant material are a thermal spray process, an oxyacetylene welding process (OXY), plasma transferred arc (PTA), an atomic hydrogen welding (ATW), welding via tungsten inert gas (TIG), gas tungsten arc welding (GTAW) or other applicable processes as known by one of ordinary skill in the art.
In one embodiment, the erosion resistant material may be applied in the recesses so that it substantially fills the volume of a recess and is flush with the leading face of the blade. In this embodiment, the application of the erosion resistant material in the recesses may substantially preserve the cutter pocket geometry, and in effect, define the cutter pocket. Alternative embodiments may include recesses partially filled with erosion resistant material or erosion resistant material that completely fills the recesses and protrudes past the leading face of the blade.
In some embodiments, the erosion resistant material may be applied in the recesses before the cutters are placed in the cutter pockets. For example, this may be required in embodiments where the process of applying the erosion resistant material includes high temperature processing which would be detrimental to cutters containing temperature sensitive materials such as polycrystalline diamond or to the brazing material securing the cutters in the cutter pockets. Alternatively, in other embodiments, the cutters may be placed in the cutter pockets before the erosion resistant material is applied in the recesses.
When the erosion resistant material is applied in the recesses before the cutters are placed in the cutter pockets, a displacement, the use of which is well known in the art of drill bit manufacturing, that approximates the cutter geometry may optionally be placed in the cutter pockets. The use of displacements may preserve the cutter pocket geometry while the erosion resistant material is being applied to the recesses. As known in the art, displacements may be formed from any suitable material such as graphite or a ceramic material. After the erosion resistant material has been applied in the recesses, the displacements may be removed from the cutter pockets so that the cutters may be placed and secured in the cutter pockets.
The selection of an erosion resistant material may also depend on factors that are independent of the durability of the erosion resistant material. For example, the desired method of application of the erosion resistant material may limit the choice of erosion resistant materials. The selection of the application method may also depend on other various factors, such as, for example, compatibility with the erosion resistant material and the necessary amount of control over the placement of the erosion resistant material.
Likewise, the order of manufacture of the bit may also limit the choice of erosion resistant materials. If the cutters are to be brazed into the cutter pockets prior to the application of the erosion resistant material into the recesses, then the erosion resistant material, and its method of application, should be selected so as to avoid damage to the cutters or the braze joint. In the embodiment in which the cutter is brazed in the cutter pocket prior to the application of the erosion resistant material, the selection of the erosion resistant material may require that the erosion resistant material have a binder with a melting point lower than that of the braze material.
One of ordinary skill in the art should recognize that the composition of the erosion resistant material, the method of application of the erosion resistant material, and the ordering of steps of manufacturing the bit may be varied as required and should not be limited by the embodiments shown.
Additionally, while the present disclosure may make reference to exemplary lengths/depths/shapes of a recess in a cutter pocket of the present disclosure, one of ordinary skill in the art should recognize that such references have no limitation on the scope of the embodiments disclosed herein. Thus, it is expressly within the scope of the present disclosure that the recess disclosed herein may have any shape or size disposed in the cutter pocket of a steel bit body. For example, referring to
Additionally, as shown in
Embodiments disclosed herein may include one or more of the following advantages. A steel-bodied bit having erosion resistant material in the area surrounding the cutter pockets may be less susceptible to erosion of the bit body around the cutters than a conventional bit. Increased protection against erosion of the bit body may result in fewer lost cutters and fewer bit failures due to lost cutters. The increased protection may also make it more economical to rebuild steel-bodied bits. Reducing erosion in this area may also reduce the number of damaged bit features and the extent of the damage. Thus, minimizing the damage may reduce the amount of time required to rebuild bits, and therefore, make it more economical to rebuild bits.
Further, restrictions on the positioning and orientation of the orifices directing the flow of drilling fluid may also be lessened with increased protection against erosion. With increased erosion resistance near the cutters, orifices aiming drilling fluid directly or indirectly at the cutters may be less likely to erode the bit body around the cutters.
Aligning the leading face of the blade with the cutter edge which is adjacent the leading face of the blade may prevent drilling fluid flow patterns that promote erosion of the bit body around the cutters. The alignment may allow the drilling fluid to flow from the fluid courses and across the face of the cutter without an overhanging cutter edge deflecting the drilling fluid into the joint between the cutter and the bit body.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.
