Abstract:
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. A pressurized fluid path within the cutting element matrix can exhibit a pressure drop when wear of the matrix progresses into the fluid path, or rotating torque can exhibit a drop when wear of the matrix progresses to wear pads within the cutting element 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.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application relies upon U.S. Provisional patent application No. 60/571,246, filed on May 13, 2004, and entitled “Wear Indication Apparatus and Method.” 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable  
       BACKGROUND OF THE INVENTION  
       [0003]     1. Field of the Invention  
         [0004]     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.  
         [0005]     2. Background Art  
         [0006]     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.  
         [0007]     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&#39;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.  
         [0008]     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.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     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.  
         [0010]     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.  
         [0011]     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.  
         [0012]     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.  
         [0013]     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.  
         [0014]     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: 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0015]      FIGS. 1 and 2  are section views of a prior art mill;  
         [0016]      FIG. 3  is an end view of a prior art mill;  
         [0017]      FIG. 4  is an end view of a mill according to the present invention;  
         [0018]      FIG. 5  is a section view of the mill of  FIG. 4 , showing penetration of the wear indicator by a downhole structure;  
         [0019]      FIGS. 6 and 7  are section views of a second embodiment of the present invention, before and after breaching of the fluid pressure wear indicators, and before and after contact with the wear resistant pad type wear indicators; and  
         [0020]      FIG. 8  is a section view of a third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     As shown in  FIGS. 1 through 3 , a prior art mill M is lowered through a casing C into contact with a downhole structure to be milled away, such as a tubular element T. The typical mill M would have a fluid path FP for drilling or milling fluid, and the fluid would be conducted to the working surface of the working profile WP of the mill M via fluid nozzles as known in the art, which are only partially shown here. The mill M is typically rotated, in order to mill away the tubular element T with the working profile WP. The working profile WP can be a matrix of cutting elements formed on the lower face of the mill M, which is in this case represented as an end mill or junk mill. For purposes of the present invention, the tool could also be a rotary shoe, any kind of cutter, or even a drill bit. Similarly, the working profile could be any kind of profile mounted or formed on the tool for purposes of performing work on any kind of downhole structure, including an earth formation.  
         [0022]     As seen in  FIGS. 2 and 3 , as the mill M is rotated, it will mill away a portion of the tubular element T, but at the same time, the tubular element T will wear a groove G through the cutting element matrix which constitutes the working profile WP. When the top of the tubular element T contacts the body of the mill M, the cutting or milling action essentially stops. At this point, there is little or no indication for the operator that milling has ceased. For other types of structure being milled or drilled, the wear pattern formed in the working profile would be different from the circular groove shown, but the principle is the same.  
         [0023]      FIG. 4  shows an end view of a first embodiment of a tool  10  according to the present invention.  FIG. 5  shows the tool  10  in operation. The tool  10  has a body  12 , on which is formed a working profile  14  in the form of a matrix of cutting elements. As the tool  10  is rotated, the leading face  16  of the working profile  14  contacts the tubular element T, and the working profile  14  mills away the tubular element T. As mentioned above, at the same time, the tubular element T will wear a circular groove in the working profile  14 . A rectangular, closed-end, fluid passage  21  is formed within the working profile  14 , imbedded below the leading surface  16  of the working profile  14 . That is, the working profile  14  initially separates the fluid passage  21  from contact with the downhole structure, represented in this case by the tubular element T. Thus, the fluid passage  21  is represented as dashed lines in  FIG. 4 , and the nozzles  19  are shown leading from the fluid path  18  to the leading face  16 .  FIG. 4  indicates just one example of how the fluid passage  21  can be imbedded within the working profile  14 , without interfering with the normal flow through the nozzles  19 . The fluid passage  21  could be a tube imbedded within the working profile  14 , or it could simply be a cavity formed therein by any known means.  
         [0024]      FIG. 5  shows that the fluid passage  21  is actually connected in fluid flow communication to the fluid path  18  and forms a dead-end part thereof. As the tubular element T wears a groove into the working profile  14 , the tubular element T will eventually breach the fluid passage  21 . This provides an additional outlet from the fluid path  18 , in addition to the nozzles  19 . Opening of this additional fluid outlet causes a noticeable drop in the backpressure in the fluid path  18 , 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 fluid passage  21  provides one type of wear indicator which can give a discernible and definitive indication of the wear of the working profile. The pertinent operating parameter, the fluid pressure, can be monitored by any means known in the art, such as a pressure gage.  
         [0025]      FIGS. 6 and 7  show a second embodiment of the tool  10 , which actually includes two additional types of wear indicators. That is, a plurality of closed fluid passages  20 , in this case a plurality of branches, are embedded within the cutting profile  14 . As with the rectangular fluid passage  21 , these fluid branches  20  could be tubes  22  imbedded within the working profile  14 , or they could simply be passages formed therein by any known means. These fluid branches  20  function in a similar fashion to the fluid passage  21 . Also shown in this embodiment is another type of wear indicator, namely a plurality of pads  24  of wear resistant material.  
         [0026]     When the working profile  14  has worn down as shown in  FIG. 7 , to the point where the wear resistant pads  24  contact the downhole structure, the wear resistant pads  24  begin carrying a substantial portion of the weight on the tool  10 . This essentially prevents any further milling or cutting action, and as a result, the torque required to rotate the tool  10  is significantly reduced. This discernible reduction in rotating torque can be sensed by any means known in the art, such as a torque meter. The reduced torque meter reading constitutes a definitive indication that the working profile  14  has worn to a point where replacement of the tool  10  is required. So, the wear resistant pads  24  provide 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 rotating torque, can be sensed or monitored by any means known in the art. The wear resistant pads  24  can be used in combination with the fluid branches  20 , or in combination with a rectangular fluid passage  21 , or any of these can be used separately.  
         [0027]      FIG. 8  shows a third embodiment of the tool  10 , which also includes two types of wear indicator. As with the embodiment shown in  FIGS. 6 and 7 , the wear resistant pads  24  are shown here, and they function in the same way as described above. Additionally, this embodiment shows a capsule  28  of a discernible medium or material, which functions as a tell-tale agent. As with the rectangular fluid passage  21 , the capsule  28  could be a tubes  30  imbedded within the working profile  14 , or it could simply be a passage formed therein by any known means. The discernible material might be a magnetic powder, a chemical agent, or any other material which contrasts in some way, such as visibly, with the drilling or milling fluid being pumped through the tool  10 . Other discernible properties might also be used, with the key point being that they are discernible to an observer or to some type of instrumentation, once they are released from the tool  10 .  
         [0028]     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.  
         [0029]     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.