Abstract:
Systems and methods are provided for swellable material activation and monitoring in a subterranean well. A sensor system for use in a subterranean well includes a swellable material, and at least one sensor which is displaced to a wellbore surface in response to swelling of the swellable material. Another sensor system includes a sensor which detects swelling of a swellable material. A swellable well tool system includes a base pipe, a swellable material on an exterior of the base pipe, and eccentric weighting for inducing rotation of the swellable material about a longitudinal axis of the base pipe.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an example described below, more particularly provides a drill bit with an extended life seal. 
       BACKGROUND 
       [0002]    Drill bits used to drill wellbores have to operate in an extremely hostile environment. As a result, such drill bits are highly specialized for their purpose. One such drill bit is of the type known as a roller cone bit, in which cutting elements are mounted on cones which rotate as the drill bit is rotated downhole to drill a wellbore. 
         [0003]    To facilitate rotation of the cones, bearings are provided between the cones and a body of the bit, and lubricant is provided for the bearings. To prevent external debris from damaging the bearings or otherwise causing excessive wear in the rotating cones, and to prevent escape of the lubricant, seals are also provided in such bits. 
         [0004]    Unfortunately, in the harsh downhole environment, seals in drill bits tend to fail (e.g., permit excessive wear, no longer exclude debris, fail to contain the lubricant, etc.) sooner than is desired. Drilling operations could be made much more economical and expeditious if drill bit seals had longer lives. 
       SUMMARY 
       [0005]    In the disclosure below, a drill bit and seal configuration therefor are provided which bring improvements to the art of sealing in drill bits. One example is described below in which a drill bit seal has its greatest contact pressure areas most closely positioned adjacent cooling fluid. Another example is described below in which areas of highest friction between the seal and a seal surface are concentrated at opposite sides of the seal. 
         [0006]    In one aspect, an improved drill bit for drilling a wellbore is provided by the present disclosure. The drill bit includes a seal surface, a seal which engages the seal surface, and a groove which compresses the seal greater on opposite axial sides of a central portion of the seal than at the central portion of the seal. 
         [0007]    In another aspect, a drill bit for drilling a wellbore is provided which includes a seal surface, a seal having a first cylindrical surface which engages the seal surface, and a second cylindrical surface opposite the first surface. The seal is retained in a groove. The groove has a third cylindrical surface which engages the second surface of the seal. The groove simultaneously biases the seal toward the seal surface on opposite axial sides of the third surface. 
         [0008]    In yet another aspect, a drill bit for drilling a wellbore is provided which includes a seal surface and a seal which engages the seal surface. The seal has right cylindrical shaped inner and outer diameter surfaces. A contact pressure between the seal surface and the seal is greater on opposite axial sides of a central portion of a contact area between the seal and the seal surface than at the central portion of the contact area. 
         [0009]    These and other features, advantages and benefits will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative examples below and the accompanying drawings, in which similar elements are indicated in the various figures using the same reference numbers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is an elevational view of a drill bit embodying principles of the present disclosure; 
           [0011]      FIG. 2  is a cross-sectional view through one arm of the drill bit of  FIG. 1 ; 
           [0012]      FIG. 3  is an enlarged scale cross-sectional view through a seal embodying principles of the present disclosure; 
           [0013]      FIG. 4  is a further enlarged scale cross-sectional view through one side of the seal, as indicated by detail “ 4 ” in  FIG. 3 ; 
           [0014]      FIG. 5  is a still further enlarged scale cross-sectional view of the seal as installed in a circumferential groove formed in a roller cone of the drill bit; and 
           [0015]      FIG. 6  is a cross-sectional view of the seal as installed in the assembled drill bit, the seal engaging a seal surface on the arm of the drill bit, and a profile being shown of contact pressure applied between the seal and the seal surface. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Representatively illustrated in  FIG. 1  is a drill bit  10  which embodies principles of this disclosure. The drill bit  10  is of the type known to those skilled in the art as a roller cone bit or a tri-cone bit, due to its use of multiple generally conical shaped rollers or cones  12  having earth-engaging cutting elements  14  thereon. 
         [0017]    Each of the cones  12  is rotatably secured to a respective arm  16  extending downwardly (as depicted in  FIG. 1 ) from a main body  18  of the bit  10 . In this example, there are three each of the cones  12  and arms  16 . 
         [0018]    However, it should be clearly understood that the principles of this disclosure may be incorporated into drill bits having other numbers of cones and arms, and other types of drill bit configurations. The drill bit  10  depicted in  FIG. 1  is merely one example of a wide variety of drill bits which can utilize the principles described herein. 
         [0019]    Referring additionally now to  FIG. 2 , a cross-sectional view of one of the arms  16  is representatively illustrated. In this view it may be seen that the cone  12  rotates about a journal  20  of the arm  16 . Bearings  22  are used between the cone  12  and the journal  20  to secure the cone on the arm. 
         [0020]    Lubricant is supplied to the interface between the cone  12  and the journal  20  from a chamber  24  via a passage  26 . A pressure equalizing device  28  ensures that the lubricant is at substantially the same pressure as the downhole environment when the drill bit  10  is being used to drill a wellbore. 
         [0021]    A seal  30  is used to prevent debris and well fluids from entering the interface between the cone  12  and the journal  20 , and to prevent escape of the lubricant from the interface area. As the cone  12  rotates about the journal  20 , the seal  30  preferably rotates with the cone and seals against an outer surface of the journal, as described more fully below. 
         [0022]    Referring additionally now to  FIG. 3 , an enlarged scale cross-sectional view of the seal  30  is representatively illustrated, apart from the remainder of the drill bit  10 . In this view it may be seen that the seal  30  is generally annular shaped, with an inner diameter d, an outer diameter D, an axial width W, and a radial width R. 
         [0023]    A further enlarged scale cross-sectional view of one side of the seal  30  is representatively illustrated in  FIG. 4 . In this view it may be seen that the seal  30  has radii R 1  straddling an inner right cylindrical surface  32 , and radii R 2  straddling an outer right cylindrical surface  34 . 
         [0024]    The surfaces  32 ,  34  preferably have their right cylindrical shapes to provide stability to the seal  30  during use in the extremely harsh downhole environment. However, the surfaces  32 ,  34  could have some curvature, angularity or other non-cylindrical geometric shape, in keeping with the principles of this disclosure. 
         [0025]    Note that the seal  30  is also preferably axially symmetrical, for example, its opposite axial sides  36  are substantially identical, the radii R 1  are identical to each other, and the radii R 2  are identical to each other. Thus, the seal  30  cannot easily be installed incorrectly. 
         [0026]    Preferably, the radii R 1  are greater than or equal to 0.1 times the axial width W of the seal  30 , and less than or equal to 0.3 times the axial width. However, other dimensions for the radii R 1 , and other relative dimensions between the radii R 1  and the axial width W, may be used if desired. 
         [0027]    Preferably, the radii R 2  are greater than or equal to 1.4 times the radii R 1 , and less than or equal to 2 times the radii R 1 . However, other dimensions for the radii R 2 , and other relative dimensions between the radii R 1  &amp; R 2 , may be used if desired. 
         [0028]    The preferred dimensions described above are expected to produce beneficial results for the seal  30  as used in the drill bit  10 . When used in other types of drill bits, however, the optimum dimensions could be different, so the dimensions should be evaluated for each specific application. 
         [0029]    Referring additionally now to  FIG. 5 , the seal  30  is representatively illustrated after having been installed in a circumferential groove  38  formed in the cone  12 . The groove  38  in this example performs more functions than just retaining the seal  30  and providing a seal surface against which the seal seals. The groove  38  also cooperates with the seal  30  to produce a unique profile of contact pressure between the seal and the journal  20 . 
         [0030]    As depicted in  FIG. 5 , the groove  38  has radii R 3  straddling an outer cylindrical surface  40 . The groove surface  40  contacts the outer surface  34  of the seal  30 . 
         [0031]    Note that the radii R 3  are preferably greater than the radii R 2  on the seal  30 . In other examples, the radii R 3  could be equal to the radii R 2 , but preferably the radii R 3  are not less than the radii R 2 . 
         [0032]    It will be appreciated that, when the seal  30  is radially compressed in the groove  38 , the radii R 3  will engage the seal (at the radii R 2 ), with the result that the seal will be compressed more near its opposite sides  36  than in a central portion  42  of the seal. This will also cause a greater contact pressure between the seal  30  and the journal  20  near the opposite sides  36  of the seal, as compared to at the central portion  42  of the seal. 
         [0033]    Referring additionally now to  FIG. 6 , the seal  30  is representatively illustrated after the cone  12  (with the seal in the groove  38  therein) has been installed on the journal  20 . The seal  30  now sealingly engages a cylindrical seal surface  44  on the journal  20 , and the seal is radially compressed between the seal surface and the outer surface  40  of the groove  38 . 
         [0034]    The radii R 3  of the groove  38  compress the seal  30  near its outer sides  36  to a greater extent than the seal is compressed at its central portion  42 . Thus, contact pressure between the seal  30  and the seal surface  44  is greater on opposite sides of a central portion of the contact area between the seal and the seal surface, as compared to at the central portion of the contact area. 
         [0035]    Although the radii R 3  are described above as a feature of the groove  38  which increases compression of the seal  30  on opposite axial sides of its central portion  42 , other features could be used instead of, or in addition to, the radii R 3 . For example, the groove  38  could have chamfers or other types of features on opposite sides of the surface  40  for increasing compression of the seal  30 , the surface  40  itself could be contoured in a manner which increases compression of the seal on opposite sides of its central portion  42 , etc. 
         [0036]    Preferably, the axial length of the surface  34  between the radii R 2  on the seal  30  is greater than the axial length of the surface  40  between the radii R 3  of the groove  38 , so that the radii R 3  initially contact the seal when it is installed in the groove, in order to enhance the compression of the seal on opposite sides of its central portion  42 . However, this relationship between the axial lengths of the surfaces  34 ,  40  is not necessary in keeping with the principles of this disclosure. 
         [0037]    The compressive biasing forces applied to the seal  30  by the radii R 3  of the groove are responsible for the increased compression of the seal on opposite axial sides of the central portion  42 . This increased compression results in the increased contact pressure depicted in the graph in  FIG. 6 . 
         [0038]    Note that the contact pressure increases very rapidly (at  46  and  48  in the graph) at the opposite edges of the contact area between the seal  30  and the seal surface  44 . This large contact pressure slope enables maximum contact pressure (at  50  and  52  in the graph) to be achieved very near the opposite edges of the contact area. 
         [0039]    One benefit of the maximum contact pressure  50 ,  52  being near the opposite edges of the contact area is that this helps to exclude debris (such as sand, etc.) and fluid from getting under the seal  30 , or between the seal and the seal surface  44 . Another benefit is that, since higher contact pressure results in greater friction and heat production, the greatest friction is in an area of the seal  30  which is most directly exposed to fluids (lubricant on one side, and drilling fluid on the other side) which will operate to provide cooling for the seal. 
         [0040]    By excluding debris and cooling the seal  30  at its areas of maximum contact pressure against the seal surface  44 , the service life of the seal is substantially increased. This can also result in decreased wear of the seal surface  44 . 
         [0041]    Preferably, the minimum contact pressure (at  54  in the graph) between the maximum contact pressures  50 ,  52  near the opposite edges of the contact area is between approximately 20 and 80% of the maximum contact pressures. Most preferably, the minimum contact pressure  54  is less than 60% of the greatest of the maximum contact pressures  50 ,  52 . However, other relative contact pressure relationships may be used, if desired. 
         [0042]    Another benefit of the seal  30  and groove  38  configuration described above is that the contact pressure profile is substantially symmetrical axially. This helps to stabilize the seal  30  in use (e.g., when the seal is rotating about the journal  20 ). 
         [0043]    Yet another benefit of the seal  30  and groove  38  configuration is that the other benefits remain, even as the seal wears in use. Thus, although the opposite edges of the contact area between the seal  30  and the seal surface  44  may get closer to each other as the seal wears away due to friction, the contact pressure near the opposite edges of contact is still greater than contact pressure in the middle of the contact area. 
         [0044]    One reason for this is that the seal surface  32  which contacts the seal surface  44  is right cylindrical shaped, instead of having bumps, ridges, etc. formed thereon to produce the increased contact pressure. Seals which produce increased contact pressure due to such bumps, ridges, etc. on the seals lose the ability to do so once the bumps, ridges, etc. are worn away. 
         [0045]    In contrast, the seal  30  and groove  38  produce the increased contact pressure between the seal and the seal surface  44  due to the groove compressing the seal more near its opposite sides  36  than at its central portion  42 . As a result, this increased contact pressure remains, even though the seal may experience wear during use. 
         [0046]    Another reason for the contact pressure near the opposite edges of contact remaining greater than contact pressure in the middle of the contact area, even though the seal  30  may wear in use, is that the seal is preferably made of a single material, rather than relying on different materials to produce respective different contact pressures or other sealing characteristics in the contact area. Seals which do rely on such different materials to produce enhanced sealing characteristics lose the ability to do so if the different materials wear away during use. However, it should be understood that the seal  30  could utilize more than one material, in keeping with the principles of this disclosure. 
         [0047]    The seal  30  is preferably made of a material such as HNBR, in which case the maximum contact pressures  50 ,  52 , as assembled, may be approximately 200-450 psi (˜1380-3105 kpa), and the material may have a hardness of approximately 80±5 durometer. However, other materials (such as NBR, FKM, fluorocarbon elastomers, etc.), other maximum contact pressures and other material hardnesses may be used in keeping with the principles of this disclosure. 
         [0048]    Preferably, the surfaces  32 ,  34  of the seal  30  are right cylindrical shaped. The surfaces  40 ,  44  of the groove  38  and journal  20 , respectively, are also preferably right cylindrical shaped. However, other shapes may be used for these surfaces, if desired. 
         [0049]    A further benefit of the seal  30  and groove  38  configuration described above is that the seal should not wear appreciably between the areas of greatest contact pressure  50 ,  52 . This is due to the fact that substantially less contact pressure (e.g., at  54  in the  FIG. 6  graph) is experienced between the maximum contact pressures  50 ,  52 , and so less friction and wear is also experienced in this area. 
         [0050]    It may now be fully appreciated that the above disclosure provides many advancements to the art of sealing in drill bits used for drilling wellbores. The seal  30  described above should have longer life and greater effectiveness, leading to reduced expenditures of time and money in drilling operations. 
         [0051]    The above disclosure in particular describes a drill bit  10  for drilling a wellbore. The drill bit  10  includes a seal surface  44 , a seal  30  which engages the seal surface  44 , and a groove  38  which compresses the seal  30  greater on opposite axial sides of a central portion  42  of the seal  30  than at the central portion  42  of the seal  30 . 
         [0052]    A contact pressure between the seal surface  44  and the seal  30  may be greater on opposite axial sides of a central portion of a contact area between the seal  30  and the seal surface  44  than at the central portion of the contact area. Minimum contact pressure  54  between the seal surface  44  and the seal  30  at the central portion of the contact area may be approximately 20-80% of a maximum contact pressure  50  or  52  between the seal surface  44  and the seal  30  on the opposite sides of the central portion of the contact area. Minimum contact pressure  54  between the seal surface  44  and the seal  30  at the central portion of the contact area may be less than 60% of a maximum contact pressure  50  or  52  between the seal surface  44  and the seal  30  on the opposite sides of the central portion of the contact area. 
         [0053]    The seal  30  may engage the seal surface  44  at a first surface  32  of the seal  30 , and the seal  30  may further have first radii R 1  straddling the first surface  32 . The first surface  32  may have a right cylindrical shape. 
         [0054]    The seal  30  may engage the groove  38  at a second surface  34  of the seal  30 , and the seal  30  may further have second radii R 2  straddling the second surface  34 . The second surface  34  may have a right cylindrical shape. 
         [0055]    The groove  38  may engage the seal  30  at a third surface  40  of the groove  38 , with the groove  38  further having third radii R 3  straddling the third surface  40 . The third radii R 3  are preferably greater than or equal to the second radii R 2 . 
         [0056]    The second radii R 2  may be greater than or equal to 1.4 times the first radii R 1 , and the second radii R 2  may be less than or equal to 2 times the first radii R 1 . The first radii R 1  may be greater than or equal to 0.1 times an axial width W of the seal  30 , and the first radii R 1  may be less than or equal to 0.3 times the axial width W of the seal  30 . 
         [0057]    An axial width of the third surface  40  between the third radii R 3  may be less than an axial width of the second surface  34  between the second radii R 2  prior to engagement of the seal  30  with the seal surface  44 . 
         [0058]    Also described by the above disclosure is a drill bit  10  for drilling a wellbore, with the drill bit  10  including a seal surface  44 , a seal  30  having a first cylindrical surface  32  which engages the seal surface  44 , and a second cylindrical surface  34  opposite the first surface  32 , and a groove  38  in which the seal  30  is retained. The groove  38  has a third cylindrical surface  40  which engages the second surface  34  of the seal  30 . The groove  38  simultaneously biases the seal  30  toward the seal surface  44  on opposite axial sides of the third surface  40 . 
         [0059]    Radii R 3  at the opposite axial sides of the third surface  40  may simultaneously contact and compress the seal  30  on opposite axial sides of a central portion  42  of the seal  30 . 
         [0060]    The first surface  32  may have a right cylindrical shape prior to engagement with the seal surface  44 . The seal  30  may be made of only a single material. Opposite axial sides of the seal  30  may be symmetrically shaped relative to each other. 
         [0061]    The above disclosure also describes a drill bit  10  for drilling a wellbore, in which the drill bit  10  includes a seal surface  44  and a seal  30  which engages the seal surface  44 . The seal  30  has right cylindrical shaped inner and outer diameter surfaces  32 ,  34 . A contact pressure between the seal surface  44  and the seal  30  is greater on opposite axial sides of a central portion of a contact area between the seal  30  and the seal surface  44  than at the central portion of the contact area. 
         [0062]    It is to be understood that the various examples described above may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of the present disclosure. The embodiments illustrated in the drawings are depicted and described merely as examples of useful applications of the principles of the disclosure, which are not limited to any specific details of these embodiments. 
         [0063]    Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to these specific embodiments, and such changes are within the scope of the principles of the present disclosure. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims and their equivalents.