Abstract:
Subsea wells have a variety of proprietary well head configurations that require sophisticated locking and sealing profiles that allow the well bore to be sealed off and the production of hydrocarbons to be safely controlled. A universal tubing hanger and lockdown assembly uses a sealing apparatus to annularly seal the well bore. When compressed, a multi-piece stacked sealing system employs rigid and elastic members to seal the well bore annulus in both the top-down and bottom-up directions. Top-down pressure containment is needed for appropriate well system testing and bottom-up pressure containment is necessary to control the internal pressure of the well.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon U.S. provisional patent application No. 61/176,441, filed on May 7, 2009, the priority of which is claimed. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to a system and method of using same to seal a well bore such that the production of hydrocarbons may be safely controlled. More specifically, the invention relates to a multi-piece stacked sealing system and method for using same to seal the annulus between a production casing and a tubing hanger. 
         [0004]    2. Description of the Related Art 
         [0005]    A typical subsea wellhead assembly includes a wellhead housing installed at the sea floor. With a drilling blowout preventer (BOP) stack installed on the wellhead housing, the well bore is drilled while successively installing concentric casing strings in the well bore. Typically, each successive casing string is cemented at its lower end and includes a casing hanger sealed with a mechanical seal assembly at its upper end in the wellhead housing. 
         [0006]    In order to produce the cased well, a production tubing string and tubing hanger are typically run into the well bore through the BOP stack and the tubing hanger is landed, sealed and locked in the wellhead housing and/or casing hanger. Upon sealing the bore(s) extending through the tubing hanger, the BOP stack is removed and a Christmas tree is lowered onto the wellhead housing. A Christmas tree is an oilfield term understood to include the control valves and chokes assembled at the top of a well to control the flow of oil and gas. It is vitally important to the operation and safety of the well that the proper connections are remotely formed between the Christmas tree, the wellhead housing, and the tubing hanger. 
         [0007]    In a conventional completed well system, the Christmas tree is connected to the top of the wellhead housing over the tubing hanger. The tubing hanger supports at least one production tubing string which extends into the well bore. The tubing hanger provides a production bore within the tubing string and a conduit that communicates with the annulus surrounding the tubing string and inside the innermost or production casing string. In addition, the tubing hanger comprises at least one vertical production bore for communicating fluid between the tubing string and a corresponding production bore in the Christmas tree, and typically at least one vertical annulus bore for communicating fluid between the tubing annulus and a corresponding annulus bore in the Christmas tree. The tubing hanger may additionally include one or more service and control conduits for communicating control fluids and well chemicals through the tubing hanger or electrical power to devices or positions located in or below the tubing hanger. 
         [0008]    A tubing hanger conventionally is sealed and rigidly locked into the wellhead housing or component in which it is landed. In a well having a conventional Christmas tree, the tubing hanger is landed in the wellhead housing. The tubing hanger typically includes an integral locking mechanism which, when activated, secures the tubing hanger to the wellhead housing or a profile in the casing hanger. The locking mechanism ensures that any subsequent pressure from within the well acting on the tubing hanger will not cause the tubing hanger to lift from the wellhead housing thereby resulting in an unsafe condition. 
         [0009]    There are a limited number of subsea wellhead equipment manufacturers worldwide. Currently, the primary manufacturers of subsea wellhead housings are ABB Vetco Gray, Cooper Cameron Corp., Dril-Quip, FMC, and Kvaerner. Each of the primary manufacturers has its own proprietary wellhead housing and casing hanger designs, dimensions, and details. Quite frequently, a well is completed on Manufacturer A&#39;s wellhead housing and casing hangers using a tubing hanger and/or Christmas tree from Manufacturer B. However, since Manufacturer A&#39;s housing and casing hanger design are proprietary, Manufacturer B may not be able to connect its Christmas tree to Manufacturer A&#39;s housing without a license from Manufacturer A at a fee in order to design Manufacturer B&#39;s equipment to properly interconnect and mate with Manufacturer A&#39;s wellhead housing and casing hanger. This results in a substantial amount of additional engineering and costs or additional equipment (such as a tubing spool) when electing to purchase Manufacturer B&#39;s equipment for use with Manufacturer A&#39;s wellhead housing. Since each wellhead housing/system manufacturer has multiple models of housings and casing hangers with different proprietary details, it is not practical or economical for other manufacturers to build up an inventory of equipment for installation on other manufacturers&#39; wellhead equipment. In addition to the added costs, it also increases, the delivery time which is often vitally important to the well owner. 
         [0010]    A tubing hanger assembly adapted for positioning in the wellhead housing independently of any proprietary details of the wellhead housing has recently been disclosed by Broussard in U.S. Pat. No. 7,419,001, which is incorporated herein by reference. The tubing hanger suspension assembly disclosed in U.S. Pat. No. 7,419,001 includes a tubing hanger housing which is positioned in the wellhead housing and further includes a sealing and lockdown mechanism capable of providing sealing and load support of the production tubing in the production casing string. 
         [0011]      FIG. 1  shows a universal tubing hanger suspension assembly  80  according to a preferred embodiment of U.S. Pat. No. 7,419,001. The tubing hanger suspension assembly  80  includes a string of production tubing  122  connected to a tubing hanger housing  124 . The production tubing  122  defines a production tubing bore  122   a  extending axially through the tubing  122 . The tubing hanger housing  124  includes production bore  124   a  in fluid communication with the production tubing bore  122   a . The production bore  124   a  extends substantially vertically through the tubing hanger housing  124 . The production tubing string  122  typically extends down to the production zone Z. The production tubing string  122  includes a subsurface safety valve  126  at a desired depth with the well bore B. The tubing hanger housing  124  also includes an annulus passageway  124   b  extending through the tubing housing hanger  124 . Included in the tubing housing assembly  124  is an annulus isolation valve  128  arranged and designed to seal and close off the annulus passageway  124   b.    
         [0012]    The universal tubing hanger suspension assembly  80  includes a tubing hanger lower assembly  82  at a lower end of the tubing hanger housing  124 . The lower assembly  82  may be connected to or integral with the tubing hanger housing  124 . The lower assembly  82  includes a sealing and lockdown assembly  134 . The lower assembly  82  is preferably a tubular member having a throughbore, such as a pipe or a mandrel having a bore therethrough. The tubing hanger lower assembly  82  extends around the production tubing string  122  with a production annulus  132   a  defined therebetween. While production string  122  preferably has a length such that its lower end extends approximately to the production zone Z, the tubing hanger lower assembly  82  preferably has a length substantially less than the length of the tubing string  122 . 
         [0013]    The sealing and lockdown assembly  134  is carried by the tubing hanger lower member  82 . The sealing/lockdown assembly  134  is located near the lower end of the tubing hanger lower member  82 . An enlarged view of the sealing/lockdown assembly  134  is shown in  FIG. 1A . The sealing/lockdown assembly  134  includes an enlarged outside diameter tubular portion  136  which is slightly less than the inside diameter of the production casing  118 . The sealing/lockdown assembly  134  includes a sealing apparatus  138  and a movement prevention locking apparatus or lockdown apparatus  140 . The sealing apparatus  138  and the lockdown apparatus  140  may be contained within a unitary assembly or may be separate assemblies. In wells having a subsurface safety valve  126  ( FIG. 1 ), the sealing apparatus  138  is positioned in the casing string  118  above the subsurface safety valve  126  and the lockdown apparatus  140  will also be above the subsurface safety valve  126 . 
         [0014]    The lockdown apparatus  140  includes elements or slips, which may be metallic or nonmetallic, adapted to engage the interior of the production casing  118 . When engaged, the lockdown apparatus  140  engages the interior of the casing  118  and “fixes” or prevents axial (i.e., vertical or up and down) movement of the tubing hanger suspension assembly  80  ( FIG. 1 ) relative to the production casing  118 . 
         [0015]    The sealing apparatus  138  includes a sealing element, which may be made of elastomers or other elastic materials (including composites) or a metal seal, adapted to form an annular seal between the production casing  118  and the tubular portion  136 , as for example, by compression. The sealing apparatus  138  and the lockdown apparatus  140  may be independently activated or jointly activated. As shown in  FIG. 1A , the activation and de-activation of the lockdown apparatus  140  and the sealing apparatus  138  is hydraulically controlled through ports  142   a  and  142   b . However, the activation and de-activation may also be accomplished electronically, mechanically, or electrically. 
         [0016]    The sealing and lockdown assembly  134  is activated, preferably hydraulically, via the hydraulic control lines to force the lockdown apparatus  140  into tight locked engagement with the production casing  118 . The engaged lockdown apparatus  140  prevents or substantially prevents relative vertical movement between the lower tubular member  82  and the production casing  118 . The sealing and lockdown assembly  134  may comprise a set of slips having metal elements which grip the production casing  118 . An elastomeric or other elastic-type seal is compressed by the set slips to form a fluid-tight seal. Typically, the sealing and lockdown assembly  134  is a modified packer assembly of the type conventionally used in wells to isolate production zones, etc. However, disclosed hereinafter are implementations of a multi-piece stacked sealing system designed to be used in place of the sealing apparatus  138  disclosed in U.S. Pat. No. 7,419,001, to compliment the tubing hanger lockdown and seal assembly  134  disclosed therein, or to provide independent annular sealing between tubulars, i.e., in a well bore. U.S. provisional patent application No. 61/176,441, upon which this application is based, is incorporated herein by reference. 
       BRIEF SUMMARY OF THE INVENTION 
       [0017]    A multi-piece stacked sealing system (i.e., a multi-piece stacked seal system) arranged and designed to seal the annulus between tubular members, and more preferably, between production casing (i.e., outer tubular) and a tubing hanger (i.e., inner tubular) is disclosed. The system is preferably carried by a tubing hanger assembly and can either be a stand alone system or comprise a part of a sealing and locking mechanism assembly typically associated with a tubing hanger assembly. However, the system may also be used to seal annular spaces between a variety of tubulars. In a preferred implementation, the system comprises a plurality of rigid members (i.e., tapered rings composed of a rigid material), a plurality of elastic members (i.e., tapered rings composed of an elastic or elastomeric material), an upper support ring, and a lower support ring, each positioned around the circumference of the tubing hanger assembly. The plurality of rigid members are preferably stacked between the upper and lower support rings with the plurality of elastic members interposed therebetween such that the tapered surfaces of the rigid members, the elastic members, and the upper and lower support rings compliment each other. 
         [0018]    The system is activated by applying an axial downward force on the upper support ring by several methods including, but not limited to, hydraulic, mechanical, electronic, or electrical methods. This compressive force in turn compresses the spaces between the rigid members (i.e., rigid tapered rings) stacked around the tubing hanger and further compresses the elastic members (i.e., elastic tapered rings) disposed there in between. Compression of the elastic members causes their temporary deformation and forces the elastic members into sealing contact with the inner wall of the production casing, thereby sealing the annulus between the tubing hanger and the production casing. Once compressed, the rigid members are physically stopped by each other (i.e., they will not travel past each other), therefore, the system cannot be over-compressed. Similarly, the compressed elastic members are prevented from being extruded through any space between the inner wall of the production casing and the rigid members during activation/compression of the system by the counteracting compression forces that are imparted to the elastic members disposed between adjacent rigid members. De-activation of the system may be accomplished by removing or reducing the downward axial force applied to the upper support ring. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    By way of illustration and not limitation, the invention is described in detail hereinafter on the basis of the implementations represented in the accompanying figures, in which: 
           [0020]      FIG. 1  is a schematic sectional elevation view illustrating a universal tubing hanger suspension assembly comprising a tubing hanger lower assembly which carries a sealing and lockdown assembly; 
           [0021]      FIG. 1A  is an enlarged schematic sectional elevation view of the sealing and lockdown assembly of the tubing hanger suspension assembly of  FIG. 1 ; 
           [0022]      FIG. 2  is an enlarged schematic sectional elevation view illustrating a preferred implementation of the multi-piece stacked sealing system, in an non-actuated or non-sealing state, carried by the tubing hanger lower assembly and disposed between the tubing hanger lower assembly and production tubing; 
           [0023]      FIG. 3  is an enlarged schematic sectional elevation view illustrating a preferred implementation of the multi-piece stacked sealing system of  FIG. 2  in which the multi-piece stacked sealing system has been actuated to seal the annulus between the tubing hanger lower assembly and the production tubing; and 
           [0024]      FIG. 4  illustrates an enlarged schematic sectional view of the multi-piece stacked sealing system of  FIG. 2  illustrating the elastic member disposed adjacent to a top rigid member. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    As generally shown in  FIG. 2 , a preferred implementation of the invention is a multi-piece stacked sealing system  10  (i.e., a multi-piece stacked seal system) carried by a tubing hanger lower assembly  82  of a universal tubing hanger suspension assembly  80  ( FIG. 1 ). The multi-piece stacked sealing system  10  is preferably arranged and designed to seal the annulus between the tubing hanger lower assembly  82  and the production casing  118 . The multi-piece stacked sealing system  10  preferably comprises a plurality of rigid rings or members  20 , a plurality of elastic rings or members  40 ,  44 ,  46 , coiled springs  60 ,  62 , an upper support ring  22  carrying a U-cup seal  70 , and a lower support ring  24  carrying a U-cup seal  70 . The plurality of rigid members  20 , the upper support ring  22 , and the lower support ring  24  are preferably composed of a metallic material such as, but not limited to, steel; however various rigid nonmetallic and composite/mixed composition materials known to those of skill in the art may also be used. 
         [0026]    Each of the rigid members  20  is a ring-like structure designed with an inner wall  26  having an inner diameter slightly larger than the outer diameter of the tubing hanger lower assembly  82  such that the rigid members  20  may be carried by the tubing hanger lower assembly  82 . The rigid members  20  preferably have an outer diameter slightly smaller than the inner diameter of the production casing  118 ; however, the outer diameter of the rigid members  20  may be designed to contact the inner wall  92  of the production casing  118  regardless of whether the multi-piece stacked sealing system  10  is actuated or as a direct result of the actuation of the multi-piece stacked sealing system  10 . Rigid members  20  are preferably designed such that in cross-section, as shown in  FIG. 2 , the members  20  have a generally triangular shape (i.e., tapered on its top (upper) and bottom (lower) sides to form an outwardly distal apex/vertex) with each vertex preferably being flat (i.e., not pointed). 
         [0027]    The rigid members  20  are preferably stacked or disposed around the tubing hanger lower assembly  82  between an upper support ring  22  and a lower support ring  24  such that the inner wall  26  of the rigid members  20  is disposed adjacent to the outer surface  86  of the tubing hanger lower assembly  82 . The rigid members  20  are preferably designed to move/slide axially about the outer surface  86  of the tubing hanger lower assembly  82 . As previously discussed, the rigid members  20  have a generally triangular shape in cross-section and it is preferred to have the rigid members  20  oriented about the tubing hanger lower assembly  82  such that the apex  28  of this generally triangular shape in cross section is disposed towards the production casing  118 . In other words, rigid rings or members  20  each have a top (upper) surface and a bottom (lower) surface that are tapered toward a common circular (i.e., circumferential) apex  28 . When viewed in cross-section, this apex  28  may have a shape that is pointed (not shown) or flat ( FIGS. 2-4 ). There are two rigid members  20  shown in  FIG. 2 , however, additional rigid members (not shown) may be stacked above or below but between the upper  22  and lower  24  support rings. A space  30  is preferably disposed between each of the rigid members  20  and between the rigid members  20  and the upper  22  and lower  24  support rings. 
         [0028]    The upper support ring  22 , positioned around the circumference of the tubing hanger lower assembly  82  (i.e., inner tubular), has a U-cup seal  70  disposed in its inner wall  32  ( FIG. 4 ), which is arranged and designed to seal between the upper support ring  22  and the tubing hanger lower assembly  82 . Similarly, the lower support ring  24 , also positioned around the circumference of the tubing hanger lower assembly  82  (i.e., inner tubular), has a U-cup seal  70  disposed in its inner wall  34 , which is arranged and designed to seal between the lower support ring  24  and the tubing hanger lower assembly  82 . These top and bottom [ ]-cup seals  70  are preferably interchangeable and replaceable. While a U-cup seal is one preferred type of seal, other types of seals well known to those skilled in the art, including but not limited to O-ring and polypack seals, may also be preferably used. When viewed in cross-section ( FIGS. 2-3 ), the upper support ring  22  preferably has a tapered lower surface and the lower support ring  24  preferably has a tapered upper surface. As viewed in cross-section, the respective vertices of the upper and lower support rings, which are adjacent to the outer surface  86  of the tubing hanger lower assembly  82  and elastic member  44 ,  46 , are preferably flat (i.e., not pointed) so as to compliment the vertices of the elastic members  44 ,  46 . 
         [0029]    The elastic members  40 ,  44 ,  46  are preferably composed of a thermoplastic elastomer such as, but not limited to, an engineering thermoplastic elastomer. The thermoplastic elastomer is selected such that: (1) it is rigid under no axial loading and has a durometer between Shore 30D to 82D, more preferably between Shore 40D and 60D and most preferably between Shore 52D to 55D, and (2) under axial loading greater than approximately 50,000 lbf, but more preferably under axial loading greater than approximately 15,000 lbf, it becomes more fluid-like and capable of being deformed. Engineering thermoplastic elastomers composed, at least in part, of polyester, such as DuPont Hytrel® (thermoplastic polyester elastomer), and more specifically Dupont Hytrel® 5555HS, are a preferred material for constructing the elastic members  40 ,  44 ,  46 . However, other thermoplastic polyester elastomers may also be used. A preferred material may also have some or all of the following characteristics: 
         [0000]                                            Characteristic   Range                           Hardness (Shore D)   40 to 72           Specific Gravity   1.17 to 1.25           T m  (° C.)   170 to 232           Vicat Softening Point   112 to 203           Tensile Strength (MPa)   30 to 52           Flexural Modulus (MPa)    48 to 517           Elongation (%)   420 to 560                        
An advantage of using a preferred elastomeric material is that the multi-piece stacked sealing system  10  may be activated or energized to deform the elastic members  40 ,  44 ,  46  at a much lower axial compression force.
 
         [0030]    As shown in  FIG. 2 , the elastic members  40 ,  44 ,  46  are ring-like structures designed with an outer wall  42  having an outer diameter slightly smaller than the inner diameter of the inner wall  92  of the production casing  118 . The elastic members  40 ,  44 ,  46  are preferably designed such that in cross-section, as shown in  FIG. 2 , the elastic members  40 ,  44 ,  46  have a generally triangular shape (i.e., tapered on its top and bottom sides to form an inwardly distal apex). It is preferred to have the elastic members  40 ,  44 ,  46  oriented about the tubing hanger lower assembly  82  such that the apex  48  of this generally triangular shape in cross section is disposed towards the tubing hanger lower assembly  82 . In other words, elastic rings or members  40 ,  44 ,  46  each have a top (upper) surface and a bottom (lower) surface that are tapered toward a common circular (i.e., circumferential) apex  48 . When viewed in cross-section, this apex  48  may have a shape that is pointed (not shown) or flat ( FIGS. 2-4 ). While the elastic members  40 ,  44 ,  46  are interposed to compliment the tapered surfaces of the rigid members  20  and the upper  22  and lower  24  support rings, the elastic members  40 ,  44 ,  46  are preferably designed not to be flush with the tubing hanger lower assembly  82  so as to provide the space  30  previously described. As shown, the elastic members  40 ,  44 ,  46  are designed to be interposed between rigid members  20  and between the rigid members  20  and the upper  22  and lower  24  support rings, such that the elastic members  40 ,  44 ,  46  are also carried by the tubing hanger lower assembly  82 . Preferably, the plurality of rigid members  20  are stacked between the upper  22  and lower  24  support rings (and around the circumference of the tubing hanger) with the plurality of elastic members  40 ,  44 ,  46  interposed therebetween such that the tapered surfaces of the rigid members  20  and the elastic members  40 ,  44 ,  46  compliment each other. 
         [0031]    The ring-like elastic member  44  disposed adjacent to the upper support ring  22  has an upper spring  60  that is shaped in the form of a ring and disposed therein preferably within a notch or recessed groove  64  formed in an upper most surface  52 . Similarly, the ring-like elastic member  46  disposed adjacent to the lower support ring  24  has a lower spring  62  that is shaped in the form of a ring and disposed therein preferably within a notch or recessed groove  66  formed in a lower most surface  54 . An enlarged schematic sectional elevation view of the elastic member  44  disposed adjacent to the upper support ring  22  is shown in  FIG. 4 . The notch  64  formed in the upper most surface  52  of the elastic member  44  provides integral structures to elastic member  44 , similar to lips, on either side of the notch  64 . As shown in  FIG. 4 , the integral structure of the elastic member  44  closest to the tubing hanger lower assembly  82  forms an upper inner lip  58  and the integral structure of the elastic member  44  closest to the production casing  118  forms an upper outer lip  56 . An unactuated, ring-shaped spring  60  is disposed in the notch  64 . The upper spring  60  is designed to move radially outwardly in response to pressure applied axially to the upper support ring  22 . The outward radial movement of the spring  60  is further designed to apply pressure and thereby move the upper outer lip  56  radially outwardly and into sealing contact with the inner wall  92  of production casing  118 . While a close-up illustration of the elastic member  46  disposed adjacent to the lower support ring  24  is not shown, one skilled in the art will recognize that it would appear similar to that shown in  FIG. 4  except flipped top to bottom. 
         [0032]    In a preferred method of using the invention, a universal tubing hanger suspension assembly  80  ( FIG. 1 ) is placed within the wellhead housing such that the multi-piece stacked sealing system  10  carried by the tubing hanger lower assembly  82  is positioned proximate to the portion of the production tubing  118  (i.e., outer tubular) to be annularly sealed.  FIG. 2  shows the multi-piece stacked sealing system  10  prior to activation and  FIG. 3  shows the multi-piece stacked sealing system  10  after activation. The multi-piece stacked sealing system  10  may be activated/actuated hydraulically by applying hydraulic fluid into a cavity (not shown) arranged and designed to exert a downward axial force against the upper support ring  22 , e.g., through downward axial movement of ring-like member  76 . As shown in  FIGS. 2-4 , ring-like member  76  is representative of a hydraulically-actuated piston-type device. Such hydraulic mechanisms and actions are well known to those skilled in the art and several hydraulic actuators are known that may be equally employed to activate/actuate the multi-piece stacked sealing system  10 . Those skilled in the art will readily recognize that activation/actuation may also be effected electronically, mechanically, or electrically through a variety of methods and devices arranged and designed to apply a downward axial force upon the multi-piece stacked sealing system  10 . 
         [0033]    Starting with  FIG. 2 , upon activation/actuation, the upper support ring  22  of the multi-piece stacked sealing system  10  is forced downwardly in an axial direction by the downward axial movement of ring-like member  76  toward the rigid members  20  and the lower support ring  24 , thereby compressing the upper support ring  22 , the rigid members  20 , and the lower support ring  24  together. The compression of these members  20  and rings  22 ,  24  closes the spaces  30  therebetween such that they contact each other but are positively stopped by each other (i.e., there is no over travel). Thus, the multi-piece stacked sealing system  10  is preferably activated or energized (and unlocked) by axially moved internal components but the system  10  cannot be over compressed. It should be noted that lower support ring  24  is preferably designed to move/slide axially about the outer surface  86  of the tubing hanger lower assembly  82 . However, as shown in  FIGS. 2 and 3 , the downward axial movement of lower support ring  24  is stopped by tubing hanger lower assembly  82 . This permits the members  20  and rings  22 ,  24  to be compressed together via the downward axial force applied to upper support ring  22 , e.g., by ring-like member  76 . Alternatively, but not shown, the downward axial movement of lower support ring  24  may be stopped by an actuated element or slip of lockdown apparatus  140 , such as that shown in and described in relation to  FIGS. 1 and 1A . Further still, lower support ring  24  may be coupled to tubing hanger lower assembly  82  so as to prevent any downward axial movement. 
         [0034]    As shown in  FIG. 3 , the compression of these member(s)  20  and rings  22 ,  24  also compresses the plurality of elastic members  40 ,  44 ,  46  interposed therebetween, which in turn forces these elastic members  40 ,  44 ,  46  to deform into sealing contact with the inner wall  92  of the production casing  118 . This deformation and general outward radial movement of elastic members  40 ,  44 ,  46 , caused by their compression between the tapered surfaces of the rigid members  20  (and upper/lower support rings  22 ,  24 ), creates the spaces  38  as shown in  FIG. 3 . The composition of the elastic members  40 ,  44 ,  46  is selected to ensure deformation of the elastic members  40 ,  44 ,  46  into sealing contact with the inner wall  92  of production casing  118 , including production casing having an irregular surface, such as one marred, gashed, pitted, or out of round. The elastic member  44  adjacent to the upper support ring  22  is prevented from being extruded downwardly between the inner wall  92  of production casing  118  and the rigid member  20  by an equal or near equal counter force provided by the compressed, adjacently positioned elastic member  40 . Similarly, the elastic member  46  adjacent to the lower support ring  24  is prevented from being extruded upwardly between the inner wall  92  of production casing  118  and the rigid member  20  by an equal or near equal counter force provided by the compressed, adjacently positioned elastic member  40 . While  FIGS. 2 and 3  show only one elastic member  40  between rigid members  20 , additional elastic members  40  could be positioned between additional rigid members  20  in a similar alternating arrangement. The compression of these additional elastic members (not shown) would similarly prevent, by providing an equal or near equal counter force, the extrusion of adjacently positioned elastic members between the inner wall  92  of production casing  118  and the additional rigid members (not shown). 
         [0035]    As best shown in  FIG. 3 , compression of elastic member  44  by upper support ring  22  causes upper inner lip  58  ( FIG. 4 ) to compress and move upper spring  60  radially outward toward the inner wall  92  of the production casing  118 . The radial outward movement of spring  60  forces upper outer lip  56  ( FIG. 4 ) into sealing contact with the inner wall  92  of the production casing  118 . An advantage of the spring  60  is that it stores the kinetic energy of the axial compression of multi-piece stacked sealing system  10 ; thereby retaining the compression force against upper outer lip  56  ( FIG. 4 ) in sealing contact with the inner wall  92  and preventing or minimizing further deformation or creep of the elastic member  44 . As best shown in  FIG. 3 , compression of elastic member  46  by lower support ring  24  causes lower inner lip  59  to compress and move lower spring  62  radially outward toward the inner wall  92  of the production casing  118 . The radial outward movement of spring  62  forces lower outer lip  57  into sealing contact with the inner wall  92  of the production casing  118 . The spring  62  also retains the compression force against lower outer lip  57  in sealing contact with the inner wall  92 ; thereby preventing or minimizing further deformation or creep of the elastic member  46 . As will be readily apparent to one skilled in the art, when additional axial pressure is applied to the multi-piece stacked sealing system  10  either upwardly or downwardly, the compression of the elastic members  40 ,  44 ,  46  between the inner wall  92  of the production casing  118  and the tubing hanger lower assembly  82  increases, thereby improving the leak resistance of the multi-piece stacked sealing system  10 . 
         [0036]    As will be readily recognized by those skilled in the art, deactivation or unlocking of the multi-piece stacked sealing system  10  is accomplished by removing the downward axial force caused to be exerted upon the upper support ring  22 , e.g., by member  76 . The absence of this downward axial force will allow the elastic members  40 ,  44 ,  46  to resume their former shape, thereby expanding the rigid members  20  (and upper support ring  22 ) axially. While the previous implementations generally describe the activation/actuation of the system  10  using an axial downward force applied to the upper support ring  22  with the lower support ring  24  held stationary, an alternative implementation may activate/actuate the system  10  using an axial upward force applied to the lower support ring  24  with the upper support ring  22  held stationary. Based on the disclosure herein, such alternative implementation is within the knowledge of those skilled in the art. 
         [0037]    The Abstract of the disclosure is written solely for providing the United States Patent and Trademark Office and the public at large with a means by which to determine quickly from a cursory inspection the nature and gist of the technical disclosure, and it represents solely a preferred implementation and is not indicative of the nature of the invention as a whole. 
         [0038]    While some implementations of the invention have been illustrated in detail, the invention is not limited to the implementations shown; modifications and adaptations of the above implementations may occur to those skilled in the art. Such modifications and adaptations are in the spirit and scope of the invention as set forth in the claims: