CUTTER POCKET HAVING REDUCED STRESS CONCENTRATION
A method for forming a drag bit using displacements having a rounded end that creates a cutter pocket having a rounded rear portion. The displacement may comprise an insert on the rounded end that remains in the drag bit during and after formation. A cutter element may then be attached to the upper portion of the insert. The rounded shape of the insert provides a more even force distribution.
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This application claims priority to and the benefit of co-pending U.S. Provisional Application Ser. No. 60/946,300, filed Jun. 26, 2007, the full disclosure of which is hereby incorporated by reference herein.
BACKGROUND1. Field of Invention
The disclosure herein relates to contoured cutting teeth for use with a drilling bit. More specifically, the present disclosure concerns inserts having a spherical shaped rear portion disposed in a correspondingly formed pocket, wherein the pocket is situated on the cutting surface of a drag bit. The present disclosure also concerns a method for forming the pockets on the face of a drill bit.
2. Description of Prior Art
Earth boring bits for drilling wellbores into subterranean formations include roller cone bits and drag bits. The earth boring bits are typically connectable to a drilling system via a threaded connection disposed on the bottom portion of the bit. Drag type bits includes blades formed on the lower surface of the bit. The blades comprise a raised portion of material having a generally rectangular cross-section extending roughly from the center portion of the bit surface and radially outward along a side of the bit. Cutter pockets are formed on the upper surface of the blade, wherein the respective axes of the pockets are generally parallel with other pockets on the individual blade. Typically, the pockets comprise a hollowed out trough portion of the upper surface of the blade, wherein the pockets are formed to receive a cutting element therein.
The cutting elements can be attached in any number of ways, such as welding and brazing or other attachment means. The cutting element has a generally cylindrical shape with a cutting face on one end and planar on its other end. It is well known in the prior art to add polycrystalline diamond compact, i.e., PDC, on the face of the cutting element. The cutting element body is typically formed of a relatively hard material such as sintered tungsten carbide. The PDC layer may be mounted directly on the mounting body or on an intermediate carrier also generally made from a sintered tungsten carbide.
The bit body is usually comprised of either a tungsten carbide matrix or various forms of steel. Drilling systems typically utilize the weight on bit to press down into the rock that combined with the torque crushes the rock which causes the drilling action. Continued turning of the drill string pushes the teeth through the rock by the combined forces of the weight on bit and the torque.
Known displacements have planar ends that form cutter pockets with corresponding flat bottoms. During use of bit bodies having flat bottom cutter pockets, the geometry produces high stresses in the bit body adjacent the cutter pocket bottom. The high stresses can initiate cracking in the bit body thereby reducing bit life.
SUMMARY OF INVENTIONDisclosed herein is a drag bit and a method for creating a drag bit. In one embodiment, the drag bit comprises a blade on its cutting face, with a series of pockets on the blade formed using displacements. In one embodiment, the displacement comprises an insert on one end with removable displacement material on the other. The insert end opposite the displacement is rounded and oriented to be at the cutter pocket bottom while forming the bit. The insert and displacement converge at a planar surface. After the displacement material is removed from the insert, a cutting element may be attached to the end of the insert. Optionally, the displacement may comprise only removable displacement material with one or more rounded ends. A method is included herein for forming the pockets on the blade of the drag bit. The method involves forming the cutter pocket with the displacement having an insert with a rounded shaped end to form a rounded cutter pocket bottom, cleaning the removable portion of the displacement, and adding a cutting element to the end of the insert. Optionally, a method is disclosed wherein a fully removable displacement is used to form a cutter pocket with a rounded bottom. After casting a bit body using the displacement, the displacement(s) can be removed and a cutting element having a rounded bottom corresponding to the cutter pocket bottom can be affixed in the cutting pocket.
Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:
While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF INVENTIONThe present invention will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be through and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.
It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the invention is therefore to be limited only by the scope of the appended claims.
Disclosed herein is a device and method regarding forming cutter pockets and cutting elements of a drag bit. In one embodiment, a cutter pocket is formed using a displacement comprising removable displacement material and a non-removal insert having a rounded end. The displacement is oriented within a bit body casting form so when the bit body is formed, the rounded ended of the insert is integral within the bit body with the removable displacement between the insert and the bit outer surface. After removing the displacement material from the insert a cutting element can be attached to the insert's free end. Another way to form a rounded cutter element to bit body interface is to form a bit body using a rounded end displacement, wherein the entire displacement comprises removable material. In one embodiment, the cutter element(s) to bit body interface describes the contact surface between the cutter element and the bit body. The cutter element(s)/bit body interface also describes the forces and/or force distributions transferred between the cutter element(s) and the bit body. The interface can describe a single cutting element and bit body, a plurality of cutting elements and the bit body, or all cutting elements and the bit body. After casting the bit and then cleaning the displacement from the cutter pocket, a cutting element with a correspondingly rounded bottom can be affixed in the rounded bottom cutter pocket. One of the advantages of having a rounded cutter element to bit body interface is the forces experienced by the cutting element during cutting are transferred to the bit body through the insert (or cutter element) rounded end. A rounded interface has a greater area than traditional planar or flat bit body/cutting element interfaces, thus stresses imparted by the cutting element to the bit body are more evenly distributed throughout the bit body. More even stress distribution thereby minimizes stress concentrations in the bit body. Additionally, the improvement disclosed herein removes sharp corners in the cutter pocket rear portion. In contrast, some diamond fixed cutter bits have experienced primary cutter pocket cracking, especially for the cutters located proximate to the bit axis. These cracks initiate from the joint of the cutter pocket seat and propagate down towards the nozzle and/or front blade root.
In one embodiment, the displacements 16 in
After removing the front portion 44 of
With regard to the displacement 24 shown in
Claims
1. A method of forming a bit body for an earth boring drill bit comprising:
- combining bit body raw materials and a displacement having a rounded end into a bit body casting form;
- orienting the rounded end of the displacement to extend into the bit body materials; and
- processing the materials in the casting form to form a bit body, wherein the presence of the displacement extending into the bit body raw materials during the step of processing the materials forms a cutter pocket in the bit body.
2. The method of claim 1 further comprising, removing the displacement from the cutter pocket.
3. The method of claim 1, wherein the displacement comprises an insert portion not removable from the bit.
4. The method of claim 1, wherein the displacement comprises a portion formed from an erodible material and an insert portion comprising the rounded end.
5. The method of claim 4, wherein the insert is integrally formed in the bit body, the method further comprising removing the removable portion, and affixing a cutting element to the insert.
6. The method of claim 1, wherein the raw materials comprise tungsten and a binder.
7. The method of claim 2 further comprising, affixing a cutting element into the cutter pocket.
8. The method claim 1, further comprising combining a plurality of displacements into the casting form to thereby form a plurality of cutter pockets.
9. The method of claim 1, wherein the cutter pocket rounded bottom end has a shape selected from the group consisting of hemispherical, elliptical, and frusto-conical.
10. The method of claim 1, wherein the displacement comprises an erodible material.
11. The method of claim 10, wherein the displacement comprises material selected from the group consisting of graphite and silicone carbide, refractory materials, compressed particles, and combinations thereof.
12. The method of claim 1 further comprising, removing at least a portion of the displacement from the formed bit body, affixing a cutting element within the cutter pocket, coupling the bit body with insert to a drill pipe, boring a wellbore with the bit body and drill pipe.
13. An earth boring bit formed using a casting process, the b it attachable to a drill string for forming a subterranean wellbore, the bit comprising:
- a bit body;
- a blade extending from the bit body; and
- a cutter pocket having a rounded bottom end formed in the blade during the casting process, wherein the rounded bottom end is formed using a displacement having a rounded end.
14. The earth boring bit of claim 13, wherein the displacement is formed using an erodible material.
15. The earth boring bit of claim 13, wherein the displacement comprises an insert on the rounded end.
16. The earth boring bit of claim 13, wherein the displacement comprises a mid section and a rear portion having a rounded end.
17. The earth boring bit of claim 13, wherein the displacement rounded end is orientable in a bit body casting mold to form a cutter pocket having a rounded bottom.
18. The earth boring bit of claim 16, wherein the displacement mid section and rear portion comprises an erodible material.
19. The earth boring bit of claim 13, wherein the displacement comprises material selected from the group consisting of graphite and silicone carbide, refractory materials, compressed particles, and combinations thereof.
20. The earth boring bit of claim 13, wherein the rounded end has a shape selected from the group consisting of hemispherical, elliptical, and frusto-conical.
Type: Application
Filed: Jun 26, 2008
Publication Date: Jan 1, 2009
Applicant: BAKER HUGHES INCORPORATED (Houston, TX)
Inventors: Marc W. Bird (Houston, TX), Andy Oxford (Magnolia, TX)
Application Number: 12/147,179
International Classification: E21B 10/46 (20060101);