US 20080023225 A1
Apparatus and method for monitoring the wear of a downhole tool, and providing indication of the degree of wear to an operator at the well surface. Rotating torque can exhibit a drop when wear of the cutting element matrix progresses to wear pads within the matrix. Other wear indicators can also be built into the cutting element matrix. Progression of wear down to the indicator can be directly measured at the well surface, or relayed to the surface via a downhole communication system.
1. A system for monitoring wear of a downhole tool, comprising:
a working profile formed on a downhole tool, said working profile being adapted to perform work on a structure downhole in a well bore;
a wear resistant pad within said working profile, said wear resistant pad being initially protected from physical contact with said downhole structure by said working profile;
a torque sensor adapted to measure the torque required to rotate said downhole tool;
where said wear resistant pad is adapted to cause a drop in said torque upon sufficient progression of wear of said working profile to bring said downhole structure into contact with said wear resistant pad.
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6. A method for monitoring wear of a downhole tool, comprising:
providing a wear resistant pad in a working profile of a downhole tool;
providing a torque sensor adapted to measure an operating parameter of said downhole tool;
operating said downhole tool to perform work downhole in a wellbore;
bearing weight with said wear resistant pad when wear of said working profile has progressed sufficiently to expose said wear resistant pad to contact with a downhole structure; and
sensing a drop in the torque required to rotate said downhole tool with said torque sensor.
This application is a divisional of U.S. patent application Ser. No. 11/120,655, filed on May 2, 2005, and entitled “Wear Indication Apparatus and Method”, which relies upon U.S. Provisional Pat. App. No. 60/571,246, filed on May 13, 2004, and entitled “Wear Indication Apparatus and Method.”
1. Field of the Invention
This invention is in the field of methods and apparatus used to perform downhole work in a well bore with a tool having a working profile which wears away during use, such as a mill, cutter, or drill bit.
2. Background Art
In the drilling, completion, and workover of oil and gas wells, it is common to perform work downhole in the well bore with a tool which has some sort of wearable working profile interfacing with a downhole structure. Examples would be milling a downhole metal object with a milling tool, performing a washover operation with a rotary shoe, cutting through a tubular with a cutting tool, or drilling through formation with a drill bit. During the performance of these operations, it is common for the working profile of the tool, such as the cutting elements mounted on its lower or outer face, to wear away. As this wear progresses, the effectiveness of the tool decreases.
It is desirable to pull the tool from the well and replace it, when the working profile has experienced a given amount of wear. The degree of wear at which it is desirable to replace the tool depends upon the type of tool and the operation being performed. Unfortunately, it is difficult or even impossible for the well operator at the Earth's surface to know accurately when this given amount of wear has occurred. Often, the decision as to when to pull the tool depends substantially upon the experience of the operator. That is, the operator must estimate the amount of tool wear based on whatever is known about the time the operation has been underway, the weight on the tool, the type of downhole structure being worked, the cuttings found in the drilling fluid, or a gradual change in work string torque. None of these parameters provides a definitive indication that the wear in the working profile has progressed to a specific degree at which the operator desires to pull the tool. Pulling a tool prematurely adds unnecessary trips out of the well, adding to rig time. Pulling the tool too late gradually decreases the effectiveness of the downhole operation, also adding to rig time.
It is desirable to have a means for determining in a definitive way when the wear of the working profile of the downhole tool has progressed to a known degree, thereby allowing the operator to make an informed decision about replacing the tool.
The present invention provides a wear indicator imbedded in the working profile at a depth protecting the wear indicator from contact with the downhole structure which is to be the target of the work performed by the working profile. As the work progresses, the working profile wears away until the wear indicator is exposed to contact with downhole structure, such as an object being milled or cut, or the formation being drilled. Upon exposure, the wear indicator changes some operating parameter related to the downhole tool, and this change in the operating parameter is detected by the operator or by a control system, definitively indicating a specific amount of wear of the working profile. Multiple wear indicators can be provided at multiple depths within the working profile, to provide definitive indications of progressive levels of wear of the working profile.
The wear indicator can take various forms. For example, a pressurized fluid path can be formed within the working profile, terminating beneath the surface. The fluid path can be pressurized, for instance, by the drilling fluid being pumped through the tool. When wear of the working profile progresses to the point that the fluid path is breached, this provides an additional flow path for the fluid out of the tool. This results in a measurable pressure drop in the fluid, which can be detected to provide a clear indication that the selected degree of wear has occurred. In this case, the pressurized fluid path imbedded in the working profile is the wear indicator, the fluid pressure is the pertinent operating parameter being monitored, and the sensor monitoring the fluid pressure might be a pressure gage.
As another example, wear resistant pads can be imbedded within the working profile as wear indicators. When wear of the working profile progresses to the point that the wear resistant pads contact the downhole structure and bear part of the weight, this significantly limits the milling or cutting action of the tool, resulting in a measurable drop in the torque required to rotate the tool, which can be detected to provide a clear indication that the selected degree of wear has occurred. In this case, the wear resistant pads imbedded in the working profile constitute wear indicators, the required rotating torque is the pertinent operating parameter being monitored, and the sensor monitoring the rotating torque might be a torque meter.
As still another example, a quantity of a discernible material can be encapsulated within the working profile. The discernible material can be, for example, a magnetic powder, a chemical tracer, or a visible material which contrasts with the drilling fluid returning to the surface of the well. When wear of the working profile progresses to the point that the encapsulated material deposit contacts the downhole structure and escapes from the working profile, the discernible material enters the fluid flowing through the tool and returns to the surface. The escape of this material from the working profile can be detected to provide a clear indication that the selected degree of wear has occurred. In this case, the capsule of discernible material imbedded in the working profile constitutes a wear indicator, the magnetic, chemical, or visible property of the material is the pertinent operating parameter being monitored, and the sensor monitoring this property would be the appropriate instrumentation or simply visual observation.
These changes in the operating parameters of the tool, initiated by the wear indicators, can be detected at the well surface by operator observation of instrumentation such as a pressure gage, a torque meter, or a sensor in the drilling fluid, or by observation of the drilling fluid itself. Alternatively, the operating parameter change can be detected by a sensor which outputs a signal to a control system. Further, the changes in the operating parameters can be detected by a downhole instrument which then relays a wear signal to the surface. Multiple types of wear indicators might be combined in a given tool.
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 shown in
As seen in
When the working profile 14 has worn down as shown in
As the downhole structure wears away the working profile 14, the downhole structure will eventually breach the material capsule 28. This releases the discernible tell-tale material from the tool 10. The discernible material can be detected either directly by an operator or by some kind of instrumentation, and this provides a definitive indication that wear of the working profile 14 has progressed to the point where the tool 10 should be replaced. So, the material capsule 28 provides another type of wear indicator which can give a discernible and definitive indication of the wear of the working profile. The pertinent operating parameter, the discernible property of the material, can be monitored by any means known in the art, such as a magnetic sensor, a chemical sensor, or by operator observation. The material capsule 28 can be used separately, or in combination with any of the other types of wear indicator.
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.