Abstract:
A fluid seal assembly consists of a seal element of compliant material that is retainingly carried by a seal carrier. The seal carrier includes one or more elements of relatively rigid material defining a sealing face with a seal-receiving groove intermpting the sealing face. The seal-receiving groove has groove-defining walls each of which has a proximal end at the sealing face and a distal end. The groove-defining walls serve as seal contact surfaces. The seal contact surfaces are configured such that the seal-receiving groove narrows toward its distal end. The seal-receiving groove has a depth and a breadth suitable for accepting the seal element, with the seal element projecting past the sealing face when compressed to be in contact with the seal contact surfaces.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates in general to seal assemblies, and in particular to seal assemblies for sealing tools or other devices against surfaces with large tolerances and with surface finishes typical of as-rolled steel. 
       BACKGROUND OF THE INVENTION 
       [0002]    An established method of configuring elastomeric seals, typical of O-ring type seals, to seal the gap between assembled first and second close-fitting solid components, separated by an extrusion gap, is to provide a resilient, compliant, and substantially incompressible seal element (mechanical properties characteristic of elastomers) in a generally rectangular seal groove of a controlled depth (defining the groove bottom surface) and width (defining the groove sidewall surfaces) placed in the first component, referred to herein as the seal carrier, adjacent to a seal surface provided in the second component, referred to herein as the workpiece. The unconstrained seal element depth is selected to exceed the sum of the groove depth and gap between the seal carrier and the seal surface of the workpiece, so that interference is created between the seal element and the groove bottom and workpiece seal surfaces of the assembled components. This interference tends to deform the compliant elastomer by compression in a direction normal to the seal surface and, due to its substantially incompressible bulk properties, elongation in the transverse direction. To accommodate the elongation, the seal groove width typically slightly exceeds the seal element&#39;s deformed width to volumetrically accommodate this deformation. This is typically desirable to promote pressure activation and avoid pressure entrapment in the cavities between the sidewall and the seal element. 
         [0003]    Configured thus, the seal element is forced into contact with the workpiece surface and the groove bottom where, as is known in the art, the initiation of the seal function is dependent on arranging the design parameters of geometry, surface roughness, elastomer compliance, and amount of interference to ensure that the initial contact stress distribution is sufficient to result in conforming contact both between the seal element and the workpiece surface and between the seal element and the seal groove bottom. However, the effectiveness of this type of seal in some applications is limited, especially where surface roughness of the workpiece is high and cannot be readily controlled, and where the extrusion gap tolerances are loose. In such applications, it can be difficult or impossible to arrange the available design parameters to provide the amount of interference required to achieve a reliable seal, within the allowable deformation limits of the available elastomeric materials with respect to material properties, and within seal load constraints. 
         [0004]    Also, the established method of installing an elastomeric seal is to stretch the seal element over the seal carrier into the fixed-geometry groove. This method of installation becomes increasingly difficult as the seal element thickness become large relative to the seal length. 
         [0005]    The present invention addresses the foregoing problems. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    In broad terms, the present invention provides a fluid seal assembly comprising a seal carrier made of relatively rigid material and defining a sealing face, with the sealing face being interrupted by a seal-receiving groove, for receiving a resilient seal element. 
         [0007]    The seal-receiving groove has groove-defining walls, each having a proximal end at the sealing face and a distal end (i.e., away from the sealing face). The groove-defining walls serve as seal contact surfaces. The groove-defining walls converge so as to narrow the seal-receiving groove toward its distal end. The seal-receiving groove has a depth and a breadth suitable for accepting the seal element such that the seal element projects beyond the sealing face when it is brought into contact with the seal contact surfaces. 
         [0008]    The above-described fluid seal assembly provides an alternative to prior art seal assemblies. It will be understood that having the seal element wedged into a converging seal-receiving groove facilitates provision of an effective seal through an increased range of sealing gaps. When not confined by contact with a workpiece, the seal element tends to move outwardly from the seal carrier to a neutral position (i.e., with no external force or pressure urging the seal element into the seal groove). This simplifies the replacement of worn seals. 
         [0009]    Although beneficial results may be obtained through the use of the fluid seal assembly as described above, in some configurations the seal element may tend to fall out of the seal carrier when it is not confined by contact with a workpiece and has moved to a neutral position. In such applications, it is preferred that the seal-receiving groove be narrowed at the sealing face by providing seal retention means associated with the proximal end of the seal-receiving groove. In preferred embodiments, the seal retention means is provided by configuring a proximal portion of at least one of the groove-defining walls to form an inwardly-projecting seal retention face at the proximal end of at least one of the seal contact surfaces (“inwardly-projecting” meaning, in this context, that the seal retention face is canted toward the opposing groove-defining wall). It will be understood that the seal retainer means may be provided in forms other than retention faces as described above. 
         [0010]    To ensure that the seal element is supported by the converging walls of the seal-receiving groove only, it is preferred that the maximum depth to which the seal element can extend into and contact the seal-receiving groove is less than the total depth of the seal-receiving groove, so as to define a clearance interval of the seal-receiving groove walls distal of the region of contact with the seal element. The space between the clearance intervals of the opposing groove walls define the bottom of the groove, and together with the seal, enclose an inner pressure chamber distal to both seal contact intervals. 
         [0011]    To promote pressure activation and prevent pressure entrapment, it is desirable to provide means to allow fluid pressure from the high-pressure side of the seal to communicate with the inner pressure chamber, i.e., bypass the seal contact region of the seal-receiving groove side wall positioned on the intended high-pressure side of the seal- receiving groove. Examples of possible means for providing such fluid communication with the inner pressure chamber include: providing a port extended from the sealing face through the seal carrier to the inner pressure chamber; notches provided across the contact interval of the seal-receiving groove wall on the high-pressure side; and similar notches provided in the seal face across the portion of its surface mating with the contact interval of the seal-receiving groove wall on the high-pressure side. Fluid can thus flow from the high-pressure side of the sealing face to communicate with the inner pressure chamber to pressurize the seal under the action of increased differential pressure, and to correlatively depressurize this region when differential pressure is decreased; thus, respectively, providing pressure activation and avoiding pressure entrapment. 
         [0012]    In axi-symmetric applications, as the cross-sectional area (or chord size or thickness) of a seal element is increased, it becomes more difficult to remove the seal element from the seal carrier by stretching, particularly where the thickness-to-diameter ratio is relatively large. In such cases, it is preferred that the seal carrier be formed with first and second components, with each seal carrier component comprising one of the groove-defining walls. This makes it possible to separate the first and second seal carrier components to facilitate removal of the seal element in cases where the thickness of the seal element makes removal by stretching difficult. 
         [0013]    As is known in the art, a seal element that is perfectly circular in cross-section can tend to roll under certain conditions of relative sliding between the workpiece and the seal carrier. An example of this tendency to roll is manifest in the well-known torsional failure mode of axi-symmetric O-ring seals deployed to seal the annulus between a piston sliding in a bore. The toroidal shape of these seals does not resist rotation about the toroidal axis, therefore allowing segments of the seal element to roll about the toroidal axis and accumulate twist that can lead to premature failure. In applications where there is concern about the seal element rolling, it is preferred that the seal cross-section be modified to resist rolling. Although the modified seal element can remain generally circular in cross-section, it is then preferred for the seal element to be provided with portions that are substantially flat in cross-section and that generally correspond to and mate with the seal contact surfaces of the seal-receiving groove. The engagement under pressure of the flat portions of the seal element with the flat seal contact surfaces will reduce rolling. However, resistance to rolling is more preferably achieved by providing the seal with a more non-circular cross-section so that its characteristic depth is greater than its width; i.e., elongate in the direction normal to the workpiece surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Embodiments of the invention will now be described with reference to the accompanying Figures, in which numerical references denote like parts, and in which: 
           [0015]      FIG. 1  is a schematic cross-section through a seal assembly in accordance with a first embodiment of the present invention, with a V-shaped seal-receiving groove. 
           [0016]      FIG. 2  is a schematic cross-section through a seal assembly in accordance with a second embodiment of the present invention, with a single seal retention face. 
           [0017]      FIG. 3  is a schematic cross-section through a seal assembly of the present invention, with each groove-defining wall having a seal-retention face. 
           [0018]      FIG. 4  is a schematic cross-section through the seal assembly of  FIG. 3 , shown as it would appear engaged with a workpiece with a large extrusion gap, and with a higher pressure applied to the bottom end of the assembly and a lower pressure applied to the upper end of the assembly. 
           [0019]      FIG. 5  is a schematic cross-section through the seal assembly of  FIG. 3 , shown as it would appear engaged with a workpiece with a small extrusion gap. 
           [0020]      FIG. 6  is a schematic cross-section through a variant of the seal assembly in  FIG. 4 , with high-pressure and low-pressure fluid ports, shown as it would appear engaged with a workpiece with a large extrusion gap, and with a pressure differential as in  FIG. 4 . 
           [0021]      FIG. 7  is a schematic cross-section through a variant of the seal assembly in  FIG. 6 , with high-pressure and low-pressure fluid ports provided integral to the seal element, shown as it would appear engaged with a workpiece with a large extrusion gap, and with a pressure differential as in  FIG. 6 . 
           [0022]      FIG. 8  is a cross-section through a circularly-configured seal assembly generally as shown in  FIG. 6 , with the seal-receiving groove being of toroidal configuration, and with the seal assembly disposed within and sealing against a tubular workpiece. 
           [0023]      FIG. 9  is a cross-section through a circularly-configured seal assembly generally as shown in  FIG. 6 , with the seal-receiving groove being of toroidal configuration, and with the seal assembly surrounding and sealing against a tubular workpiece. 
           [0024]      FIG. 10  is a cross-section through a tubular running tool with a seal assembly in accordance with an embodiment of the present invention mounted to the bottom end thereof, and shown as it would appear with the tubular running tool in the retracted position. 
           [0025]      FIG. 11  is a cross-section through the seal assembly of  FIG. 10 , shown disposed within and in sealing engagement with an axi-symmetric tubular workpiece with a comparatively large extrusion gap. 
           [0026]      FIG. 12  is a cross-section through the seal assembly of  FIG. 11 , shown disposed within and in sealing engagement with an axi-symmetric tubular workpiece with a comparatively small extrusion gap. 
           [0027]      FIG. 13  is an enlarged partial cross-section through the seal assembly of  FIG. 11 . 
           [0028]      FIG. 14  is an enlarged partial cross-section through the seal assembly of  FIG. 11 , shown as it would appear partially disassembled to allow removal and replacement of the seal element. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0029]    General Principles 
         [0030]    With reference to  FIGS. 1 through 6 , the general principles of the seal assembly of the present invention will now be described.  FIG. 1  is a schematic cross-section through a seal assembly  10   a  in accordance with one embodiment of the invention, shown in isolation from a workpiece. Seal assembly  10   a  comprises a seal carrier  40   a  and a resilient seal element  20 . Seal carrier  40   a  has a proximal face  12  and defines a generally V-shaped seal-receiving groove (or simply “seal groove”)  50   a,  for receiving seal element  20 . Seal groove  50   a  intercepts proximal face  12  and, in the embodiment of  FIG. 1 , reduces in width as it penetrates into seal carrier  40   a.  Seal groove  50   a  is defined by contact faces  42  and  44 , which are extended to form a pair of clearance faces  48 . These clearance faces or intervals at the distal ends of the seal-receiving groove walls extend distally of the region of contact with the seal element supporting the seal element. The clearance faces are shown herein as being contiguous with the V-shaped contact faces  42  and  44 , but may be variously configured in alternative embodiments. The length and angles of contact faces  42  and  44  of clearance faces  48  are selected in conjunction with the size and shape of seal element  20  to allow for inward displacement of seal element  20  into seal groove  50   a,  and also to allow seal element  20  to return to a neutral position when unloaded. 
         [0031]    As shown by way of example in  FIG. 1 , seal carrier  40   a  optionally incorporates a high-pressure fluid port  45  extending between proximal face  12  of seal carrier  40   a  and a selected location on a selected clearance face, such that the distal (i.e., inner) region of seal groove  50   a  is in fluid communication with a source of higher pressure. The purpose and function of high-pressure fluid port  45  will be described in greater detail later in this specification. 
         [0032]    Depending on the configuration of seal groove  50   a,  the seal groove geometry of seal assembly  10   a  may allow seal element  20  to come out of seal groove  50   a  completely when unloaded, and in such cases some means for retention may be required. Seal retention can be effected by hoop stress in seal element  20  in cases where the seal carrier and workpiece are generally axi-symmetric in shape. However, it may be desirable to have additional or alternative seal retention means, examples of which are illustrated in  FIGS. 2 through 6 . 
         [0033]      FIG. 2  is a schematic cross-section through a seal assembly  10   d  in accordance with a second embodiment of the invention, comprising a seal carrier  40   d  a seal-receiving groove  50   d  defined by a single seal retention face  43 , contact faces  42  and  44 , and pair of clearance faces  48 . In this embodiment, the angles of clearance faces  48  are not equal, and contact face  42  is configured such that it is normal to the seal surface of the workpiece (not shown). This embodiment of the seal assembly facilitates retention of seal element  20  within groove  50   b,  regardless of other three-dimensional aspects of the groove, such as axi-symmetric seals, which are typically reliant on hoop stress for seal retention. 
         [0034]      FIG. 3  is a schematic cross-section through a seal assembly  10   b  in accordance with a third embodiment of the invention. Seal assembly  10   b  comprises a seal carrier  40   b  having a seal-receiving groove  50   b  defined by two retention faces  41  and  43 , contact faces  42  and  44 , and pair of clearance faces  48 , with a seal element  20  disposed within groove  50   b.  This embodiment of the seal assembly facilitates retention of seal element  20  within groove  50   b,  regardless of the configuration of the seal groove, and independent of other three-dimensional aspects of the groove geometry. 
         [0035]      FIG. 4  illustrates seal assembly  10   b  installed in association with a workpiece  30  with a comparatively large extrusion gap G between the proximal face  12  of seal carrier  40   b  and contact face  31  of workpiece  30 . Seal groove  50   b  of seal carrier  40   b  has retention faces  41  and  43 , contact faces  42  and  44 , and pair of clearance faces  48 . Retention faces  41  and  43  collectively form a diverging wedge  47 , relative to the converging wedge provided by contact faces  42  and  44  collectively. The length and angle of retention faces  41  and  43  are selected in conjunction with the size and shape of seal element  20  to prevent loss of containment of seal element  20  during engagement and disengagement from workpiece  30 . As well, retention faces  41  and  43  function to position seal element  20  in a neutral position to ensure engagement with workpiece  30  over a range of gap widths G. 
         [0036]    Referring again to  FIG. 3 , seal element  20  is shown in a neutral position, and the maximum gap width at which initial seal engagement will occur is indicated by G 0 . Referring again to  FIG. 4 , gap G is less than G 0 , resulting in seal interference with the workpiece  30  as required to initiate a seal under pressure. 
         [0037]    Referring now to  FIG. 5 , seal assembly  10   b  is shown engaged with a workpiece  30  with a smaller extrusion gap G than in  FIG. 4 , forcing seal element  20  further into seal groove  50   b,  such that it comes out of contact with both retention faces  47  and increases contact with both contact faces  42  and  44 , but does not move deep enough to engage clearance faces  48 . 
         [0038]    Referring again to  FIG. 4 , the length and angle of contact faces  42  and  44  and clearance faces  48  are selected in conjunction with the size and shape of seal element  20  to allow for inward displacement of seal element  20  in a direction generally normal to contact face  31  of workpiece  30 , to accommodate a selected range of gap widths G. Also, the angles of contact faces  42  and  44  are selected with consideration of frictional forces to ensure that seal element  20  tends to return to its neutral position upon unloading, to prevent “sticking” of seal element  20  within groove  50   b.    
         [0039]    It will be generally apparent that the present invention provides a means to increase the amount or range of allowable interference or “squeeze” for a seal element of a given cross-section, thus enabling the seal to function over a larger range of gap widths G than would otherwise be possible with a seal element of similar cross-section retained in a seal groove having a conventional, generally rectangular geometry. It will be further apparent that this desirable functionality is achieved because the amount of distortional strain generated by a given incremental reduction in gap G (i.e., increase in interference) is less than would occur if this same amount of “squeeze” were imposed on a conventional  0 -ring of similar cross-section between the workpiece and a conventional seal-carrying groove. 
         [0040]    Referring still to  FIG. 4 , seal element  20  in this embodiment has a circular cross-section when unstressed, and is shown approximately as it would appear compressed and engaging contact surface  31  of workpiece  30  and contacting seal carrier  40   b  on contact faces  41 ,  42 ,  43  and  44 . However, it will be understood that seal elements for use with the present invention are not limited to this cross-section, and that other seal shapes may be selected to suit particular design requirements or preferences. Seal shapes can be selected with geometric features that provide any or all of the following improvements in functionality over a seal element of circular cross-section:
       Enhanced resistance to rotation and twisting during insertion, by providing flat surfaces that engage one or both contact faces, or, more preferably, by providing the seal element with a non-circular cross-section having its characteristic depth greater than its width; i.e., being elongate in the direction normal to the workpiece surface;   Reduced radial load during insertion, by providing a smaller contact area between the seal element and the contact faces; and   Increased or decreased initial contact pressure, by modifying contact radii and/or providing a flat contact interface between the seal element and the workpiece or the seal carrier.       
 
         [0044]    With reference to  FIGS. 3 through 5 , retention face pair  47 , contact faces  42  and  44 , and clearance faces  48  of seal assembly  10   b  are shown to be symmetrical top to bottom. However, it is to be understood that either or both of retention faces  47 , either or both of contact faces  42  and  44 , and either or both of clearance faces  48  can be non-symmetrical, as may be desirable in some cases. As such, deformation of seal element  20  is not necessarily limited to a direction normal to contact face  31  of workpiece  30 . 
         [0045]    Referring again to  FIG. 4 , seal element  20  is made of a sufficiently compliant (i.e., resilient) material such that, in the illustrated assembly, it comes into substantially conforming contact with contact faces  31 ,  41 ,  42 ,  43  and  44 , thereby creating five chambers as follows:
       outer LP (i.e., low-pressure) chamber  51 , on the LP side of the seal assembly between workpiece contact face  31  and proximal face  12  of seal carrier  40   b;      outer HP (i.e., high-pressure) chamber  52 , on the HP side of the seal assembly between workpiece contact face  31  and proximal face  12  of seal carrier  40   b;      inner LP chamber  53 , bounded by the LP side of seal element  20  and adjacent regions of contact faces  41  and  42 ;   inner HP chamber  54 , bounded by the HP side of seal element  20  and adjacent regions of contact faces  43  and  44 ; and   distal chamber  55 , bounded by a distal surface of seal element  20  and adjacent distal regions of contact faces  42  and  44 .       
 
         [0051]    A high-pressure fluid port  45  connects outer LP chamber  51  and distal chamber  55 , such that distal chamber  55  is exposed to a source of higher pressure HP acting on one side of the seal assembly (i.e., the lower side in  FIG. 4 ), while outer HP chamber  52  on the other side of the seal assembly is exposed to a source of comparatively lower pressure LP. It will be understood that although it is not directly linked to the source of higher pressure HP, inner HP chamber  54  can generally be assumed to be at the same higher pressure as a result of being surrounded by outer LP chamber  51  and distal chamber  55  which are at the higher pressure. 
         [0052]    It will also be understood that there may be some uncertainty as to whether seal element  20  will sealingly engage seal carrier  40   b  on retention face  41  or retention face  42 .  FIG. 6  illustrates a seal assembly  10   c  in accordance with an alternative embodiment in which this uncertainty is addressed by providing a low-pressure fluid port  46  connecting chambers  52  and  53 , thereby ensuring that chambers  52  and  53  are linked to the lower pressure side (LP) of seal element  20 . Conforming contact can remain between seal element  20  and all five contact faces  31 ,  41 ,  42 ,  43 , and  44  as geometry may allow, but with only faces  31  and  42  needing to be in sealing engagement with seal element  20 . 
         [0053]      FIG. 7  is a schematic cross-section through a seal assembly  10   e  of the present invention. Seal assembly  10   e  is a variant of the seal assembly in  FIG. 6  with a high-pressure fluid port  56  and a low-pressure fluid port  57  provided integral to seal element  20 . HP fluid port  56 , shown in  FIG. 7  as a groove through seal element  20 , connects high-pressure chambers  51 ,  54 , and  55 . LP fluid port  57 , shown as a groove through seal element  20 , connects low-pressure chambers  52  and  53 . Although HP fluid port  56  and LP fluid port  57  are each shown as a single groove, it is to be understood that seal element  20  may be provided with multiple such grooves or ports arranged along its length. 
         [0054]    The ported seal element provides fluid connectivity similar to the ported groove of the embodiment described with reference to  FIG. 6 . With the seal element thus configured, the seal retainer can be configured symmetrically about a seal groove centerline extending between the proximal and distal ends of the groove. Consequently, the unidirectional seal carrier becomes bidirectional, while the seal element becomes unidirectional. As such, to reverse the sealing direction, the seal element can be installed in the reverse orientation, which in this case would put the high-pressure port on the top and the low-pressure port on the bottom of the seal assembly (as viewed in  FIG. 7 ). It is to be understood that this seal element can be provided with only a high-pressure port to provide functionality similar to that described with reference to  FIGS. 1 through 5 . It is also to be understood that a seal element thus configured can be assembled with a seal carrier that also includes high-pressure and/or low-pressure ports as described with reference to  FIGS. 1 through 6 , without loss of unidirectional sealing function. 
         [0055]      FIG. 8  illustrates a circularly-configured embodiment of a seal assembly generally as shown in  FIG. 6 , with the seal-receiving groove being of toroidal configuration, with the seal assembly coaxially disposed within and sealing against a tubular workpiece, and with the seal assembly and workpiece having a common centerline (C/L). 
         [0056]      FIG. 9  illustrates an alternative circularly-configured embodiment of a seal assembly as in  FIG. 6 , with the seal-receiving groove being of toroidal configuration, and with the seal assembly coaxially surrounding and sealing against a tubular workpiece. 
         [0057]    Seal Assembly For Tubular Running Tool 
         [0058]      FIGS. 10 through 14  illustrate a preferred embodiment of the seal assembly of the present invention, incorporated into the lower end  101  of a tubular running tool  100 . As shown in  FIG. 10 , seal assembly  110  comprises an upper seal retainer  120 , a lower seal retainer  140 , a seal assembly retention element  160 , and a seal element  180 . Seal assembly  110  is shown in  FIG. 10  as it would appear with tubular running tool  100  in the retracted position (i.e., not engaging a tubular workpiece). In this case, seal element  180  is shown with a circular cross-section, with seal element  180  in its neutral, unstressed state partially protruding beyond both the upper and lower seal retainers  120  and  140 . It is to be understood that this is for the purpose of illustrating interference between upper seal retainer  120 , a lower seal retainer  140 , and seal element  180 , and that the assembled seal element  180  will be partially compressed by upper and lower seal retainers  120  and  140 . As such, where seal element  180  is thus fully restrained as illustrated in this view, seal element  180  will come into conforming contact with both upper and lower seal retainers  120  and  140 , and will sealingly engage upper seal retainer  120 . 
         [0059]      FIG. 11  is a cross-section through seal assembly  110  coaxially dispose within a tubular workpiece  200  having an internal surface  202 , and with seal element  180  in circumferential sealing engagement with internal surface  202 . The diameter of the internal surface  202  of workpiece  200  is at the upper end of a specified allowable range for seal assembly  110  (i.e., gap G is comparatively large). Upper seal retainer  120  has an upper face  121 , a lower face  122 , an inner face  123 , and an outer (or proximal) face  124 . Lower face  122  of upper seal retainer  120  has a plurality of vertically-oriented bolt holes  125  to facilitate connection to lower seal retainer  140 . Upper seal retainer  120  also has a downward-facing shoulder  131  and a double-faceted half seal groove  126 , defined by a retention face  128  near outer face  124  and a contact face  127 . Upper seal retainer  120  also has a plurality of radially-oriented pin holes  129  disposed on outer face  124  and connected to lower face  122  by relief ports  130 , which intercept half seal groove  126  at the convergence point of the retention face  128  and contact face  127 . 
         [0060]    Referring still to  FIG. 11 , lower seal retainer  140  has an upper face  141 , a lower face  142 , an inner face  143 , an outer face  144 , and a plurality of bolt holes  145  extending between lower face  142  and upper face  141 . Upper face  141  of lower seal retainer  140  has a double-faceted half seal groove  146 , comprising a retention face  147  and contact face  148 , near outer face  144 , and an upward-facing shoulder  158 . Upward-facing shoulder  158  of lower seal retainer  140  and downward-facing shoulder  131  of upper seal retainer  120  collectively form a pair of shoulders  150 . Lower face  142  of lower seal retainer  140  is in this case configured as a stabbing guide, generally frustoconical in shape, and configured to centralize a casing running tool (not shown in  FIG. 11 ) during insertion into proximal end  201  of workpiece  200 . 
         [0061]    Upper and lower seal retainers  120  and  140  are configured to be rigidly attached to one another such as, in the illustrated case, by a plurality of cap screws  190  threaded into holes  125  of upper seal retainer  120 , with heads shouldering in counter-bored holes  145  of lower seal retainer  140 . Tension in cap screws  190  is reacted through shoulder pair  150 . 
         [0062]    Seal element  180  is disposed between upper and lower seal retainers  120  and  140  in seal groove  153 . In the illustrated embodiment, seal element  180  is toroidal in shape; i.e., axi-symmetric with a circular cross-section. Although shown in a compressed state, seal element  180 , being made from a sufficiently resilient and compliant material, substantially conforms to the shape of seal groove  153 , and is radially confined by inside surface  202  of workpiece  200 . Seal groove  153  is defined by the pair of contact faces  148  and  127 , clearance faces  151 , and the pair of retention faces  152  and  128 , where the angular orientations of contact faces  127  and  148  are selected to provide both resilience-driven rebound (i.e., spring-back) and resistance to “sticking” of seal element  180 , where “sticking” is defined as the tendency of a seal element to remain in the radially inwardly displaced position within its seal groove upon removal of assembly  110  from workpiece  200 , rather than elastically rebounding to a neutral position. The angular orientations of retention faces  127  and  147  are selected to prevent loss of containment of seal element  180 , defined as the tendency of a seal element to come out of its seal groove during insertion into and extraction of the seal assembly from workpiece  200 . The pair of retention faces  152  are configured such that when seal element  180  is not under pressure, they urge or bias seal element  180  toward a neutral position. 
         [0063]    The radial position of the maximum height of seal groove  153  can be chosen in conjunction with the diameter of seal element  180  to provide a pre-stressing hoop compression or expansion of seal element  180  to bias it in favour of contact or retraction, as well as to locate seal element  180 . 
         [0064]    Referring still to  FIG. 11 , assembly retainer  160 , located internal to and coaxially with upper seal retainer  120  is provided separate from upper seal retainer  120 , and has upward-facing shoulder  161  at lower end  162  and thread element  163  at upper end  164 . It is to be understood that assembly retainer  160  can be integral with upper seal retainer  120 , and is shown in the illustrated embodiment as a separate component as may in some cases be necessary or desirable due to material strength and availability requirements. 
         [0065]    Disposed along outer surface  165  of assembly retainer  160  are circumferential grooves containing seal elements  166 ,  167  and  168 . Assembly retainer  160  is arranged such that seal elements  167  and  168  sealingly engage inner face  123  of upper seal retainer  120 , while seal element  166  and thread element  163  collectively sealingly and threadingly engage lower end  101  of tubular running tool  100  (not shown in  FIG. 10 ). 
         [0066]    In the illustrated embodiment, seal element  180  has a circular cross-section. However, it is to be understood that a seal assembly in accordance with the present invention is not limited to the use of a seal element with this cross-sectional profile. A seal element suitable for use with the seal assembly is not restricted to any particular shape or configuration, provided that it provides: a contact interface with the inside surface of the workpiece for a range of widths of gap G; a sufficiently small exposed contact angle relative to the axis of the tool to facilitate seal element displacement into the seal groove when installing the tool in workpiece  200 ; and contact interfaces with the retention and contact faces of upper and lower seal retainers  120  and  140  respectively. 
         [0067]      FIG. 12  is a cross-section through seal assembly  110 , positioned coaxially within and sealingly engaged with a workpiece  200 , with workpiece  200  having an inside diameter at the lower end of the allowable range (i.e., gap G is comparatively small). Seal element  180 , in conjunction with contact faces  128  and  148  and clearance faces  151 , allows for radial inward displacement of seal element  180  when the inside surface  202  of workpiece  200  has a diameter at the small end of the allowable range. Seal element  180 , which may have a circular cross-section when unstressed, is shown in this view compressed between seal retainers  120  and  140  and workpiece  200 . 
         [0068]    Referring again to  FIG. 11 , lower seal retainer  140  is provided with a plurality of fluid ports  149 , which allow fluid flow between outer surface  144  and upper surface  141  of lower seal retainer  140 , and to seal groove  153  internal to seal element  180 , thus providing pressure acting on the inside of seal element  180  as a further means to promote or enhance sealing engagement of seal element  180  on inside surface  202  of workpiece  200 . Seal groove  153  and fluid ports  149  may be filled with a grease or other substance having relatively high viscosity throughout the range of the tool&#39;s operating temperature in order to maintain relatively free communication of pressured fluid through ports  149 , which might otherwise be plugged with drilling mud or other solids containing fluids, thus hindering or preventing pressure equalization and proper function of seal assembly  110 . 
         [0069]    The function and operation of seal assembly  110  may be readily understood with reference to  FIG. 13 , which is an enlarged partial cross-section through seal assembly  110  and workpiece  200  as shown in  FIG. 12 . While it is shown in this view that seal element  180  contacts and engages upper and lower seal retainers  120  and  140  in four locations on faces  127 ,  128 ,  147 , and  148 , and also engages inside surface  202  of workpiece  200 , it is to be understood that if the diameter of inside surface  202  is small relative to the range of allowable inside diameters, resultant radial movement of seal element  180  may result in loss of seal engagement on surfaces  127  and  147 . As such, seal element  180  will engage only on faces  128  and  148 . Also as a result of this potentially intermittent contact, debris from inside surface  202  of the workpiece  200  can collect on surfaces  127  and  147 , such that upon subsequent engagement, sealability on  120  and  140  may be compromised. 
         [0070]    It is also to be understood that the high-pressure side of the seal is ported by fluid ports  149  to include chambers  155 ,  156 , and  157 , while the low-pressure side of the seal is ported by fluid ports  129  to include chambers  135  and  136 . Consequently, sealing engagement occurs on surfaces  128  and  202 . 
         [0071]    Referring now to  FIG. 14 , which shows the seal assembly  110  as it would appear partially disassembled to allow removal of seal element  180  and installation of a new seal element  180 . In this configuration the cap screws  190  of seal assembly  110  have been partially removed allowing additional separation between upper and lower seal retainers  120  and  140  respectively, in this position seal element  180  can be moved laterally in the seal groove  153  such that one side is located adjacent to the load shoulder pair  150  close to the mid-radius of the seal assembly, while the opposite end of seal element  180  is radially external to seal assembly  110  and can be removed provided seal element is of sufficiently low minor diameter and is fabricated from a sufficiently strong, flexible and compliant material typical of elastomers used for fluid seals. 
         [0072]    In summary, the seal assembly described above comprises a seal carrier having a seal-receiving groove defined by two sidewalls carrying an elastomeric seal element engageable with a seal surface of a workpiece to seal the gap between the seal carrier and the workpiece, wherein:
       the sidewalls (also referenced herein as contact faces) are configured such that the width of the seal groove decreases from its outer (or proximal) end toward its inner (or distal) end;   the elastomeric seal element is configured to be close-fitting with the contact faces, with the angular orientations of the two sidewalls relative to the seal surface of the workpiece being selected to allow the seal element to move in a direction generally normal to the seal surface while being compressed laterally between the contact faces; and   when assembled in conjunction with the workpiece, the undeformed shape of the elastomeric seal element is arranged to interfere collectively with the confining surfaces of the workpiece and sidewalls of the groove, giving rise to contact stresses on these confining surfaces that in turn tend to seal the gap between the workpiece and seal carrier.       
 
         [0076]    The geometric configuration of the seal groove is selected with consideration to anticipated friction forces, such that when the seal assembly is disengaged from the workpiece, the seal element moves outward from the seal groove toward its neutral position. Depending on the shape of the seal element and the seal groove geometry, it may be possible for the seal element to come out of the seal groove completely, in which case it will be desirable to provide seal retention means associated with the seal groove. 
         [0077]    In the case of certain axi-symmetric seals, where the seal groove and workpiece are circular or cylindrical, seal retention may be accomplished using the inherent hoop stiffness of the seal element. However, for applications where this means of retention is insufficient or unavailable (such as, for example, in face seal applications), at least one of the sidewalls of the seal groove may be provided with a seal retainer in the form of a second tapered face (referred to herein as a retention face). As such, the seal groove geometry is selected so that the width of the groove is smaller near the outer (or proximal) surface of the seal carrier, where an outermost region of at least one sidewall serves as a retention face, which tapers away from the retention face on the opposite groove sidewall, to a point of maximum width where the retention face intersects the inside facet of the seal groove sidewall, defined previously as the contact faces. 
         [0078]    The intersection point of the faces of the seal groove sidewalls defines a neutral position of the seal element; i.e., a position in which the seal element will be positioned when not under pressure or engaged on a workpiece. A neutral position is selected in conjunction with the seal element geometry to position the seal element to engage the workpiece and provide some initial contact engagement over the range of workpiece/seal carrier gap widths. The angles of the pair of retention faces relative to the seal surface of the workpiece is selected to position the seal element in a neutral position when not loaded and to prevent loss of seal containment by minimizing the seal groove opening width. 
         [0079]    The seal assembly of the present invention is unidirectional, while the groove geometry can be symmetrical. The assembly is arranged such that the groove internal to the seal element is ported to the high-pressure side of the seal. As such, the seal element sealingly engages the seal surface of the workpiece and the contact face on the low-pressure side of the seal. 
         [0080]    It is generally understood that the interference or “squeeze” limit for typical solid elastomeric seals, such as  0 -rings, is approximately 30%, before premature material breakdown of the seal element will occur. This is used as a measure of allowable distortional strain which the material can be expected to accommodate without failure. It will be apparent to one skilled in the art that seal assemblies with a reduced distortional-strain-to-gap-displacement ratio will accommodate an increase in the range of sealable gap widths without failure. In this context, “interference displacement” is defined as the difference between the unconstrained elastomeric seal located in the seal carrier and the seal surface of the workpiece, basically the magnitude that the gap size can be increased before the elastomer to seal surface contact is lost. 
         [0081]    An advantage provided by generally axi-symmetric seal assemblies in accordance with the present invention is the ability to easily remove and replace seal elements, as may be necessary, due to wear or damage. Typically, elastomeric seals are installed by stretching the seal element over the seal carrier into a fixed geometry groove. This becomes increasingly difficult as the seal element thickness increases relative to the seal length, because more hoop strain and correlatively more force is required. To address this problem, seal carrier in accordance with the present invention may optionally comprise upper and lower parts, such that the parts can be partially disassembled, and the geometry of the seal groove may be selected so that the seal element can be moved laterally and removed from the seal carrier without requiring the seal element to be stretched. 
         [0082]    It will be readily appreciated by those skilled in the art that various modifications of the present invention may be devised without departing from the scope and teaching of the present invention, including modifications which may use equivalent structures or materials hereafter conceived or developed. It is to be especially understood that the invention is not intended to be limited to any described or illustrated embodiment, and that the substitution of a variant of a claimed element or feature, without any substantial resultant change in the working of the invention, will not constitute a departure from the scope of the invention. It is also to be appreciated that the different teachings of the embodiments described and discussed herein may be employed separately or in any suitable combination to produce desired results. 
         [0083]    In this patent document, any form of the word “comprise” is to be understood in its non-limiting sense to mean that any item following such word is included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one such element. Any use of any form of the terms “connect”, “engage”, “couple”, “attach”, or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the subject elements, and may also include indirect interaction between the elements such as through secondary or intermediary structure. Relational terms such as “parallel”, “perpendicular”, “coincident”, “intersecting”, and “equidistant” are not intended to denote or require absolute mathematical or geometrical precision. Accordingly, such terms are to be understood as denoting or requiring substantial precision only (e.g., “substantially parallel”) unless the context clearly requires otherwise.