Abstract:
A seal structure is provided for a downhole tool. In a described embodiment, a seal structure includes a seal support ring having at least one annular groove formed thereon and a longitudinal axis. At least one seal is included in the seal structure. The seal is disposed at least partially in the groove, and the seal is bonded to the ring. An annular recess is positioned longitudinally between opposing side walls of the groove. The recess may be formed in a body of the seal.

Description:
BACKGROUND 
     The present invention relates generally to sealing means for downhole tools and, in an embodiment described herein, more particularly provides a seal structure for a downhole tool. 
     It is well known that significant problems are typically encountered when an attempt is made to sealingly engage a seal bore in a downhole tool in an abrasive environment. Such an abrasive environment may exist, for example, in a fracturing or gravel packing job. These problems are multiplied when such sealing engagement must be performed multiple times downhole. 
     FIGS. 1A &amp; B illustrate a representative example of such a situation. A prior art seal structure  10  is disposed externally on a mandrel  12  of a downhole tool. The seal structure  10  includes a seal support ring  14  and two seals  16  disposed in open-sided grooves  18  formed externally on the ring. The seals  16  are bonded to the ring  14  in the grooves  18 . 
     It is desired to have the seal structure lo enter a seal bore  20  and effect a pressure bearing seal between the mandrel  12  and the seal bore. Unfortunately, sand  22 , or another abrasive material, such as synthetic proppant, etc., has accumulated between the mandrel  12  and the seal bore  20 . When the seal structure  10  enters the seal bore  20 , the sand  22  is compressed between the seals  16  and the seal bore, as may be seen in FIG.  1 B. 
     Compression of the sand  22  between the seals  16  and the seal bore  20  may not cause immediate failure of the seals. However, with repeated cycles of the seal structure  10  entering and withdrawing from the seal bore  20 , the seals will eventually deteriorate. 
     This problem appears to be exacerbated where a relatively large degree of compression is experienced in the seals  16  when they enter the seal bore  20 . Note that the seals  16  fill the grooves  18  and so, when the seals enter the smaller diameter seal bore  20 , they are compressed inwardly against walls of the grooves, as well as being significantly compressed against the seal bore and the sand  22  between the seals and the seal bore. An improved seal structure should provide space for the seals to deflect inwardly when a seal bore is entered, so that compression of the seals against the seal bore is reduced. 
     Another problem experienced in these situations is high “stabbing” force. That is, the force which must be exerted against the seal structure  10  to urge it into the seal bore  20 . In general, high stabbing forces are to be avoided, since they are known to cause seal damage, they may cause operational problems, etc. An improved seal structure should reduce the stabbing force needed for the seal structure to enter a seal bore. 
     SUMMARY 
     In carrying out the principles of the present invention, in accordance with an embodiment thereof, a seal structure is provided which solves the above problems in the art. 
     In one aspect of the invention, a seal structure for a downhole tool is provided which includes a seal support ring and a seal. The seal support ring has at least one annular groove formed thereon. The seal is disposed at least partially in the groove, the seal is bonded to the ring, and the seal has an annular recess formed thereon. 
     The recess may have a variety of cross-sectional shapes. In addition, the recess may be positioned in various portions of the seal body. Furthermore, there may be multiple seals disposed in multiple respective grooves on the ring. 
     In another aspect of the invention, another seal structure for a downhole tool is provided. The seal structure includes a seal support ring having at least one annular groove formed thereon and a longitudinal axis. A seal is disposed at least partially in the groove, and the seal is bonded to the ring. An annular recess is positioned longitudinally between opposing side walls of the groove. 
     Again, the recess may have a variety of cross-sectional shapes, the recess may be positioned in various portions of the seal body, and there may be multiple seals disposed in multiple respective grooves on the ring. In addition, the recess may be formed in a body of the seal. 
     In yet another aspect of the invention, another seal structure for a downhole tool is provided which includes a seal support ring, at least four seals and at least two recesses. The seal support ring has first, second, third and fourth spaced apart annular grooves formed on a surface thereof. First, second, third and fourth seals are bonded in respective ones of the first, second, third and fourth grooves, with the second and third seals being disposed between the first and fourth seals. A first annular recess is positioned between opposing side walls of the second groove, and a second recess is positioned between opposing side walls of the third groove. 
     These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A &amp; B are quarter-sectional views of a prior art seal structure for a downhole tool; 
     FIG. 2 is an enlarged scale quarter-sectional view of a first seal structure embodying principles of the present invention; 
     FIG. 3 is an enlarged scale quarter-sectional view of a second seal structure embodying principles of the present invention; 
     FIG. 4 is an enlarged scale quarter-sectional view of a third seal structure embodying principles of the present invention; and 
     FIG. 5 is an enlarged scale quarter-sectional view of a fourth seal structure embodying principles of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Representatively illustrated in FIG. 2 is a seal structure  30  which embodies principles of the present invention. In the following description of the seal structure  30  and other apparatus and methods described herein, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used only for convenience in referring to the accompanying drawings. Additionally, it is to be understood that the various embodiments of the present invention described herein 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 invention. 
     The seal structure  30  includes a seal support ring  32  and two seals  34  disposed in annular grooves  36  formed externally on the ring  32 . Of course, the seals  34  and grooves  36  could be internally formed on the ring  32 , if desired for a particular application, such as for sealing engagement with a cylindrical member within the ring. The seals  34  are bonded to the ring  32  in the grooves  36 . 
     Note that each of the seals  34  is positioned between opposing side walls  38  of the respective groove  36 . Specifically, the side walls  38  are on longitudinally opposite sides of the each of the seals  34 , relative to a longitudinal axis of the ring  32 . Thus, the seals  34  are retained between the side walls  38  of the grooves  36 . 
     A recess  40  is positioned between the side walls  38  of each of the grooves  36 . The depicted recesses  40  are generally rectangular in cross-section and are formed in the bodies of the seals  34  approximately midway between the side walls  38  of each of the grooves  36 . However, it is to be clearly understood that the recesses  40  may be otherwise shaped, may be otherwise positioned and may be formed in other components of the seal structure  30 , without departing from the principles of the present invention. 
     It may now be appreciated that the recesses  40  provide space for the seals  34  to displace inwardly toward the grooves  36 , without excessive compression of the seals. This reduced compression of the seals  34  reduces deterioration of the seals due to compressed abrasive material, and reduces the stabbing force needed for sealing engagement. 
     Referring additionally now to FIG. 3, another seal structure  50  embodying principles of the present invention is representatively illustrated. The seal structure  50  is similar in many respects to the seal structure  30  described above, and so elements of the seal structure  50  which are similar to those described above are indicated in FIG. 3 using the same reference numbers. 
     The seal structure  50  includes seals  52  disposed in the grooves  36  between respective ones of the side walls  38 . The seals  52  are bonded to the ring  32  in the grooves  36 . However, recesses  54  are formed in the seals  52  which differ substantially from the recesses  40  formed in the seals  34 . 
     The recesses  54  are generally semi-circular in cross-section. Thus, the recesses  54  each have a concave radiused internal surface. In addition, the recesses  54  are each adjacent one of the side walls  38  of its respective groove  36 , rather than being centrally positioned between the side walls. 
     Referring additionally now to FIG. 4, another seal structure  60  embodying principles of the present invention is representatively illustrated. The seal structure  60  is similar in many respects to the seal structure  50  described above, and so elements of the seal structure  60  which are similar to those described above are indicated in FIG. 4 using the same reference numbers. 
     In the seal structure  60 , the radiused recesses  54  are positioned in the bodies of the seals  52  approximately midway between side walls  38  of the respective grooves  36 . Otherwise, the seal structure  60  is the same as the seal structure  50 . However, due to the different positioning of the recesses  54 , the seals  52  of the seal structure  60  may react differently to a pressure differential applied thereacross. 
     Referring additionally now to FIG. 5, another seal structure  70  embodying principles of the present invention is representatively illustrated. The seal structure  70  includes a seal support ring  72  and four seals  74 ,  76 ,  78 ,  80  disposed and bonded in four respective annular grooves  82 ,  84 ,  86 ,  88  formed externally on the ring. Of course, the seals  74 ,  76 ,  78 ,  80  and grooves  82 ,  84 ,  86 ,  88  could be internally disposed on the ring  72 , in keeping with the principles of the present invention. 
     The outer seals  74 ,  80  may be configured as “wiper” rings. That is, the seals  74 ,  80  may be designed to wipe a seal surface free of abrasive material, debris, etc., before the inner seals  76 ,  78  contact the seal surface. Alternatively, or in addition, the outer seals  74 ,  80  may serve as initial seals for resisting a pressure differential, so that each of the inner seals  76 ,  78  resists the pressure differential after the respective one of the outer seals  74 ,  80  has failed. 
     Note that only the inner seals  76 ,  78  are positioned between opposing side walls  90 ,  92  of the respective inner grooves  84 ,  86 . The outer grooves  82 ,  88  do not have opposing side walls. 
     An annular recess  94  is formed in a body of the seal  76 , so that the recess  94  is positioned between the seal body and the upper side wall go of the groove  84 . The recess  94  is generally rectangular in cross-section. 
     A similar annular recess  96  is formed in a body of the seal  78 . However, the recess  96  is positioned between the seal  78  body and the lower side wall  92  of the groove  86 . The difference in positionings of the grooves  94 ,  96  is due to the different directions in which a pressure differential will act on the seals  76 ,  78  in a preferred use of the seal structure  70 . However, it is to be clearly understood that the recesses  94 ,  96  may be positioned other than as depicted in FIG. 5, without departing from the principles of the present invention. 
     Note that, in the seal structures  30 ,  50 ,  60 ,  70  described above, the seals  34 ,  52 ,  74 ,  76 ,  78 ,  80  may be formed of materials which are able to withstand high temperatures and otherwise hostile environments. One such hostile environment is use with heavy metal completion fluids, such as zinc bromide, and temperatures above 275° F. 
     For example, the outer seals  74 ,  80  of the seal structure  70  may be of a nitrile material and the inner seals  76 ,  78  may be formed of a fluorocarbon material (such as Fluorel™, Viton™, etc.). The nitrile material provides strength, so that the outer seals  74 ,  80  may act as wipers, as well as seals, and the fluorocarbon material provides enhanced chemical and temperature resistance. 
     The seal materials may be elastomers, they may be non-elastomeric, or a combination of these. Note that any seal material may be used, without departing from the principles of the present invention. 
     Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the invention, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to these specific embodiments, and such changes are contemplated by the principles of the present invention. 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.