Not Applicable
1. Field of the Invention
This invention is in the field of tools used downhole, in oil or gas wells, to mill or otherwise cut metal objects in the borehole.
2. Background Art
In the drilling, completion, or re-work of an oil or gas well, it often becomes necessary to cut into or through a metal object which is located downhole in the well bore. This can be required, for instance, in cutting through the wall of a well casing, removing a packer, or milling away some other metal obstruction which may be present in the borehole. This type of cutting or milling operation is very different from the type of metal cutting operations typically found in a machine shop environment. The downhole metal cutting operation involves the rotation of a very large tool by a very heavy workstring, by comparison with the typical machine shop operation. The downhole cutting operation itself involves a great deal of vibration and even severe impact, between the cutting tool and the metal object being cut. In fact, much of the force of any such impact or vibration is typically brought to bear directly on the cutting insert or inserts which are mounted on the cutting face of the downhole cutting tool. These cutting inserts are essentially the “teeth” of the cutting tool. They are typically made of a very hard material, such as tungsten carbide.
The operator can not closely observe the downhole cutting operation and monitor the condition of the cutting insert or inserts. By contrast, the machine shop operator can closely observe the cutting operation as it progresses, and he can change the cutting insert regularly as its cutting surfaces degrade. Stopping the operation in the machine shop is typically significantly cheaper than pulling a downhole tool from the well bore and checking or changing the tool out. This means that the typical machine shop operation is always done with a basically fresh cutting insert in good condition.
The downhole operator, on the other hand, must simply rotate the workstring and rely upon fairly remote indicators of the performance of the tool, such as vibration and rate of penetration, to judge the progress of the cutting operation. As a result, as the cutting operation continues, the cutting insert on the face of the cutting tool usually wears away and disintegrates. It is common, in fact, to have multiple cutting inserts on a downhole cutting tool, with the inserts being arranged progressively across the cutting face of the tool. This is done so that, as each cutting insert wears away and disintegrates or falls off the tool, another adjacent cutting insert establishes contact with the work piece, thereby continuing the cutting action. This alleviates the need to pull the work string and replace the tool, or at least delays the necessity of replacing the tool.
An unfortunate aspect of this situation is that each cutting insert must remain effective in spite of having its original cutting geometry drastically changed as the cutting operation progresses; that is, the insert will not retain its original cutting edge for very long. If the cutting insert wears to such an extent that the cutting edge is gone, the portion of the insert contacting the work piece can act as a bearing surface. If the cutting insert can not cut effectively after having its original cutting edge worn away, the insert will not be an effective part of the tool, and it can even impede the action of nearby cutting inserts, by acting as a bearing surface, rather than as a cutting surface.
It is also known to provide a chip breaking feature on the forward face of a cutting insert for use in the downhole environment, which causes the insert to break off metal chips from the work piece at short lengths, allowing the chips to be more easily removed from the well bore by the flow of drilling fluid. So, as wear progresses across the insert face, through the chip breaking feature, the insert might cease to break off short chips and begin to produce long, thin metal turnings. The long thin turnings are not easily removed from the well bore by the flow of fluid, so this type of insert wear can lead to the clogging of the area around the cutting tool, preventing further penetration of the work piece. Further, if the chip breaking feature contributes in any way to the fragility of the insert body, it can cause the insert to disintegrate prematurely and fall off the cutting tool, resulting in a complete loss of the ability to cut, until the tool body wears sufficiently to allow the adjacent cutting insert to come into play.
It is desirable to have, therefore, a cutting insert which is sufficiently robust to withstand the impacts experienced in the downhole environment, and which is designed to break off short metal chips from the work piece, and to continue to present an effective cutting geometry to the work piece, even as the original cutting geometry of the insert gradually wears away.
The present invention, in summary, is a downhole cutting insert which has one or more lands on its cutting face, interspersed with one or more beveled surfaces, creating a robust cutting face on the insert. The juxtaposition of bevels with lands causes the insert to break off metal chips from the work piece at short lengths, allowing the chips to be more easily removed from the well bore by the flow of drilling fluid. Use of alternating multiple bevels and lands allows the insert to continue to effectively form short metal chips, even as the forward face and the edge of the insert gradually degrade.
The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which:
As illustrated in
The cutting inserts 20 can take various shapes, some of which will be designated as 20, 20A and 20B in the Figures discussed below. Other shapes can also be used without departing from the spirit of the present invention, as long as they exhibit the features described below.
As illustrated in
Each bevel 24 is angled forward, or in the direction 18 of rotation, above or forward of the outwardly adjacent land 22 by a distance 32, at an angle 34 from a plane orthogonal to the axis of the cutting insert 20. The angle 34 can be between approximately 20 degrees and approximately 70 degrees, with a preferred angle of approximately 45 degrees. Put another way, the bevel 24 is also angled relative to the axis of the cutting insert 20, by an angle between approximately 20 degrees and approximately 70 degrees, with a preferred angle of approximately 45 degrees. A representative raised distance 32 could be on the order of approximately 0.015 inch. It can be seen that, on the round insert 20A shown in
The distance 32 by which each bevel 24 rises above its outwardly adjacent land 22 terminates the bevel 24 either in the surface 26 or in an inwardly adjacent land 22, as shown in
While the particular invention as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages hereinbefore stated, it is to be understood that this disclosure is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended other than as described in the appended claims.
This application claims the benefit of U.S. Provisional Patent Application No. 60/525,577, filed on Nov. 26, 2003, and entitled “Flat and Bevel Chipbreaker Insert.”
Number | Date | Country | |
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60525577 | Nov 2003 | US |