Patent Abstract:
A body having a bore thereThrough for insertion of capillary tubing. A first means slidably coupled into the bore of the body frictionally restrains movement of the tubing by hydraulically engaging the periphery of the tubing with a compressible elastomeric sealing member. A second means slidably coupled into the bore of the body prevents movement of the tubing in the bore of the body by manually engaging the periphery of the tubing with a compressible elastomeric sealing member. A third means suspends the tubing in the bore of the body by manually engaging a plurality of suspension slips around the periphery of the tubing.

Full Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    The present invention relates to a pack-off method and apparatus for wellheads and, more particularly, but not by way of limitation, to a system for and method of controlling the movement of small diameter tubing into and out of natural gas wells incorporating a dual packing assembly for a more secure long-term sealing in the pack-off head.  
           [0003]    2. History of Related Art  
           [0004]    A well known practice that is common in the oil and gas industry is to use wellhead devices which will confine pressure in a well around a member such as a polished rod or wireline extending into a well during emergency conditions, as well as when it is necessary for servicing the well. It is well known for example that the production rates from natural gas wells can be adversely affected by corrosion and the buildup of such substances as scale, paraffin and salt. Producers have traditionally treated the wells by inserting chemicals and soap sticks at the wellhead and relying on gravity to carry the treating agent down the well to where it is needed. Recently a much more effective treatment means has been developed. Small diameter tubing is inserted into the well and the treating chemical is pumped down this capillary tubing, usually ¼ or ⅜ inch (sometimes ⅝ inch), under pressure and allowed to enter the well where it can do the most good. A check valve at the lower end of the tubing controls the release of the treating chemical and prevents well pressure from escaping up the capillary tubing.  
           [0005]    A service rig is employed to insert or Asnub in@ the capillary tubing while the well remains pressurized. In this way, the service company does not Akill the well@ by pumping water and/or mud into the well casing to build up a hydrostatic pressure head which contains the well pressure. Accordingly, the wellhead must have a means for sealing around the capillary tubing both during insertion or removal from the well and also on a long-term basis while the well is producing with the capillary tubing in place.  
           [0006]    In operation, the insertion of the tubing can be problematic and has been analogized to Apushing on a string,@ due to the upward force or thrust within the well. When the weight of the tubing is less than the upward force or thrust in the well due to the pressure therein acting on the tubing, problems can occur. Once a sufficient depth is reached during tube insertion resulting in the weight of the tubing being sufficient to overcome the upward force or thrust, the so-called “balance point” has been crossed. Likewise, when retrieving the tubing, the same phenomenon can occur as the weight of the tubing depending from the wellhead within the well decreases to the point that the weight is not sufficient to overcome the upward force or thrust placed there against.  
           [0007]    Although systems are available for controlling the capillary tubing being inserted through a wellhead, problems exist when the tubing is above the balance point as referenced above. Typically, a spool of capillary tubing is disposed adjacent the wellhead in conjunction with a means for guiding the tubing into and through the wellhead. Such spools and guiding mechanisms are powered, and if for some reason, the power unit providing the appropriate power were to fail, the possibility exists that an operator could lose control of the tubing when it is above the balance point. While it is known in the art to use sealing members around the capillary tubing for insertion into the well, problems ensue in securely retaining the tubing within the sealing members while performing the above-referenced operations. Specifically, loss of hydraulic pressure due to a leakage of the hydraulic fluid used to engage the sealing members can weaken the integrity of the sealing mechanism, thereby causing a loss of control of the movement of the capillary tubing.  
           [0008]    For the above mentioned reasons, a reliable method of and apparatus for tubing securement is greatly needed, particularly if it could be quickly actuated prior to damage or danger to the operators. The present invention provides a means for quickly regaining control of tubing within a wellhead that has for one reason or the other not been secured by the conventional, compressible pack-off and securing mechanism currently in use. Although slip caps, used in conjunction with manual slips functioning as locking chucks having serrated teeth extending inwardly toward the capillary tubing may be used to permanently secure tubing, such mechanisms, which require manual actuation and/or twisting with a wrench to impart threaded induced movement therefrom, is not feasible and clearly provides safety issues for the operator. It would be a distinct advantage to provide a second redundant sealing mechanism capable of reliable operation in the event of a capillary tubing control problem.  
           [0009]    The present invention addresses such problems by utilizing a combination of manual and hydraulic compressible seals in addition to a mechanical locking mechanism capable of withstanding the wellhead pressures.  
         SUMMARY OF INVENTION  
         [0010]    The present invention relates to a dual pack-off method and apparatus for wellheads. More particularly, the present invention relates to a system and method for controlling the movement of small diameter tubing into and out of wells while providing means for preventing the tubing from being blown out of the well. In one aspect, the invention includes a wellhead pack-off system for controlling the movement of small diameter tubing into and out of a well, comprising a body with a bore extending therethrough for insertion of the tubing, hydraulic sealing means slidably coupled into the bore of the body for frictionally restraining vertical movement of the tubing by hydraulically engaging the periphery of the tube with an upper compressible elastomeric sealing member, and manual sealing means slidably coupled into the bore of the body for frictionally restraining upward vertical movement of the tubing in the bore of the body by manually engaging a redundant lower compressible elastomeric sealing member around the periphery of the tubing.  
           [0011]    In another aspect of the invention, the body is divided into an upper body, an intermediate body, and a lower body. Further, the upper body is in threaded engagement with the intermediate body, and the intermediate body is in threaded engagement with the lower body. The upper body further comprises a threaded aperture extending through the sidewall thereof. The upper body also comprises the hydraulic sealing means having a plunger in axial alignment with the bore of the body, an upper spring in axial alignment with the plunger, an upper bushing set disposed within the lower end of the plunger, a conically shaped lower bushing set in axial alignment with the upper bushing set, and an upper compressible elastomeric sealing member in axial alignment with the upper and lower bushing set and disposed therebetween. The flow of hydraulic fluid through the first aperture of the upper body imparts a downward force to the plunger, which compresses the spring and forces the upper bushing set into the lower bushing set, thereby compressing the upper sealing member disposed therebetween. The abutting engagement of the upper sealing member and the conically shaped lower bushing set imparts radially inwardly motion to the upper sealing member . The radially inwardly movement of the upper sealing member forms a seal around the capillary tubing extending through the bore of the body.  
           [0012]    The intermediate body and the lower body comprise the manual sealing means having a piston in axial alignment with the bore of the body, a lower spring in axial alignment with the piston, a lower flat bushing in axial alignment with the piston, a conical bushing in axial alignment with the lower flat bushing, and a lower compressible elastomeric sealing member in axial alignment with the conical and lower bushing and disposed therebetween. In a manner similar to the actuation of the first means, a nut in threaded engagement with the lower body engages push rods positioned in the lower body and in abutting engagement with the piston. The engagement of the push rods and the piston imparts an upward force to the piston, which compresses the lower spring and forces the lower flat bushing into the conical bushing, thereby compressing the lower sealing member disposed therebetween. The abutting engagement of the lower sealing member and the conical bushing imparts radially inwardly motion to the lower sealing member. The radially inwardly movement of the lower sealing member forms a seal around the capillary tubing extending through the bore of the body.  
           [0013]    In still another aspect of the invention, the upper body further comprises suspension means for suspending the tubing by engaging a plurality of suspension slips around the periphery of the tubing. The suspension means further comprises a slip cap in threaded engagement with the upper body for engaging the suspension slips with the tubing.  
           [0014]    In a further aspect, the present invention provides a combination of three sealing means, including a hydraulic sealing means for controlling the capillary tubing while is being inserted or removed from the wellhead under pressure, suspension means for suspending the tubing from the wellhead for a prolonged period of time, and manual sealing means for long-term sealing around the capillary tubing. The advantages of providing a redundant manual sealing means are extra safety due to a redundant sealing means, reliability due to mechanical compression of the lower sealing member, and quick and easy adjustment of the manual sealing means. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The present invention will now be described in more detail with reference to preferred embodiments of the present invention, given only by way of examples, and illustrated in the accompanying drawings in which:  
         [0016]    [0016]FIG. 1 is a perspective view of a typical wellhead installation showing the insertion of capillary tubing;  
         [0017]    [0017]FIG. 2 is an enlarged, side-elevational, full cross-sectional view of the capillary tubing pack-off of the present invention with portions thereof cut away for illustrating the assembly thereof;  
         [0018]    [0018]FIG. 3 is a side-elevational, full cross-sectional view of the intermediate body of the capillary tubing pack-off of FIG. 2, illustrating one aspect of the fabrication thereof;  
         [0019]    [0019]FIG. 4 is a side-elevational, full cross-sectional view of the intermediate cap of the capillary tubing pack-off of FIG. 2, illustrating one aspect of the fabrication thereof;  
         [0020]    [0020]FIG. 5 is a side-elevational, full cross-sectional view of the piston for the capillary tubing pack-off of FIG. 2;  
         [0021]    [0021]FIG. 6 is a side-elevational, full cross-sectional view of the lower compressible elastomeric sealing member for the capillary tubing pack-off of FIG. 2;  
         [0022]    [0022]FIGS. 7A and 7B are top plan and side-elevational, full cross-sectional views, respectively, of the lower bushing for the capillary tubing pack-off of FIG. 2;  
         [0023]    [0023]FIG. 8 is a side-elevational, full cross-sectional view of the conical bushing for the capillary tubing pack-off of FIG. 2;  
         [0024]    [0024]FIG. 9 is a side-elevational view of the spring for the capillary tubing pack-off of FIG. 2;  
         [0025]    [0025]FIG. 10 is a side-elevational view of a push rod for the capillary tubing pack-off of FIG. 2;  
         [0026]    [0026]FIG. 11 is a side-elevational, full cross-sectional view of the nut for the capillary tubing pack-off of FIG. 2; and  
         [0027]    [0027]FIG. 12 is a side-elevational, full cross-sectional view of the jam nut for the capillary tubing pack-off of FIG. 2. 
     
    
     DETAILED DESCRIPTION  
       [0028]    It has been discovered that a wellhead pack-off incorporating a manual back-up sealing means of the compressible elastomer variety in the configuration set forth and described below may enhance the operational efficiencies surrounding the insertion or removal of capillary tubing into or out of a well under pressure. The manual sealing means of the present invention also provides a means for suspending the capillary tubing from the wellhead for a prolonged period of time. This system feature provides a definite advantage in those instances when the operators wish to hang off the tubing and leave the job site. The wellhead pack-off of the present invention is specifically adapted for providing a reliable, redundant seal that is mechanically compressed in order to provide a reliable, long-term seal of the capillary tubing at the welhead.  
         [0029]    Referring first to FIG. 1, there is shown a typical installation by a service rig  6  of capillary tubing  7  at a wellhead  8  utilizing a conventional pack-off  9  specifically adapted for the receipt of the capillary tubing therethrough. The wellhead  8  as shown herein utilizes the typical hardware associated with wellheads, including the wellhead pack-off  9  disposed in an upper portion thereof with the capillary string extending therefrom. It is known in the industry to use wellhead pack-off devices for controlling the capillary tubing while the well remains pressurized. As said above, there are many advantages to the utilization of capillary tubing. The well operator&#39;s expectations from the use of such tubing includes obtaining incremental increases in production and reserves, and the elimination of production fluctuations associated with soaping, flaring, and stop cocking. The use of capillary tubing also has been shown to reduce downtime and time requirements to maintain production while improving efficiency and effectiveness of chemical treatments and applications. In wells with liquid loading, the benefits of capillary strings include the improvement of system dynamics and minimization of reservoir damage. The present invention facilitates the above advantages by providing a reliable, redundant seal for increasing the reliability of the wellhead pack-off as set forth and described below.  
         [0030]    Referring now to FIG. 2, there is shown an enlarged side-elevational, full cross-sectional view of a capillary tubing pack-off  10  incorporating the principles of the present invention. The presence of a capillary tube is not shown for purposes of clarity. The pack-off  10  includes an upper body portion  11 , an intermediate body portion  100 , and a lower body portion  170  in axial alignment with the central axis  90 . The upper body portion  11  includes a slip cap  12  disposed on the first terminal end  13  thereof, and a plurality of manual upper slips  14  (preferably 3) disposed therein. The upper slips  14  are formed with serrated teeth  15  facing radially inwardly therefrom for engagement of capillary tubing (not shown) extending through the capillary tubing pack-off  10 . The upper body portion  11  further comprises a plunger  16  having a threaded portion  17  formed on an upper end  18  thereof and adapted for threadably engaging the slip cap  12  as shown herein. The upper body portion  11  also comprises a cap  20  adapted for receiving the plunger  16  therein in reciprocal mounting relationship therewith. The plunger  16  reciprocates relative to the cap  20  and maintains sealing engagement therewith by virtue of upper and lower o-rings  22  and  24 , respectively. The upper o-ring  22  is disposed in an o-ring groove  26  formed in upper end  28  of the cap  20 . The lower o-ring  24  is disposed in an o-ring groove  30  formed around middle section  32  of the plunger  16 . The o-rings  22  and  24  are preferably sandwiched between back-up rings  34 . As referenced herein, the construction and operation of the upper body portion  11 , as herein set forth, shown and described, is conventional in the art, as is the use of the aforesaid backup rings and o-rings. For purposes of specificity, the o-rings  22  and  24  of the 90 Duro Nitrile variety have been found acceptable. Likewise, the back-up rings  34  of 90 Duro Nitrile have also been found acceptable.  
         [0031]    Still referring to FIG. 2 and, in particular to the upper body portion  11  of the pack-off  10 , a brief description of the construction, assembly, and actuation thereof will be set forth, described and shown for purposes of specificity. As referenced above, the upper body portion  11 , as herein described, does not, in and of itself, comprise the inventive aspect of the present invention. A pack-off assembly incorporating the features of the upper body portion  11  shown herein is embodied in a Type CLS Packoff sold by the Assignee of the present invention. In that regard, the cap  20  is constructed with a threaded aperture  36  disposed between the o-rings  22  and  24  for purposes of communicating hydraulic fluid into a cavity  38  defined between the o-rings  22  and  24  and between an inside surface  40  of the cap  20  and an outside surface  42  of the plunger  16 . The pressure of hydraulic fluid within the cavity  38  provides a force acting upon the plunger  16  and imparting movement thereto against an upper spring  44  defined in a cavity  46 , which is disposed between the cap  20  and the plunger  16 . Movement of the plunger  16  in the direction of arrow  50  imparts movement against a steel upper bushing set  52 , which is disposed in abutting engagement against upper end  57  of an upper compressible elastomeric sealing member  54 . Lower end  56  of the upper sealing member  54  is formed in a conical configuration and lies in abutting engagement with a lower bushing set  58 . The upper sealing member  54  is of generally cylindrical construction, having a central bore  55  formed therethrough adapted for receiving the capillary tube axially therein. Compression of the upper sealing member  54  will impart enhanced sealing engagement of said capillary tube (not shown) within said cylindrical bore  55 . Such sealing operations are well accepted in the industry. For purposes of specificity, the upper sealing member  54  of the 70 Duro Nitrile variety have been found acceptable. The present invention as described below does, however, provide an advance over the prior art systems by incorporating a second, redundant lower elastomeric sealing member disposed beneath upper elastomeric sealing member  54 . The advantages of the manually actuatable redundant lower sealing member will be defined in more detail below.  
         [0032]    Still referring to FIG. 2, there is shown, as referenced above, a central body  99  of the intermediate body section  100 . The central body  99  has disposed therein a lower compressible elastomeric sealing member  102  having a central bore  104  formed therethrough and adapted for receiving a capillary tubing therein. The lower sealing member  102  is disposed within a cylindrical cavity  106  formed within the central body  99 . Within an upper end  108  of the cavity  106 , and on opposite ends thereof, is disposed a conical bushing  110  and a lower flat bushing  112 . Between the bushings  110  and  112  is disposed the lower sealing member  102 , the compression of which is regulated by a piston  114  bearing against the flat bushing  112 . The position of the piston  114  is controlled by a lower spring  116  urging the piston  114  downwardly in a direction  118  from the lower sealing member  102 . A plurality of push rods  120  bearing against an underneath side  122  of a outwardly extending hip portion  124  of the piston  114  urge the piston  114  upwardly in a direction  119  toward the lower sealing member  102 . The lower spring  116  is defined in a cavity  117  between the inner surface of the cap  134  and the outer surface of the piston  114 . The push rods  120  bear against the underneath side  122  and urge the piston  114  upwardly into the flat bushing  112 . The push rods  120 , of which six are preferably utilized in accordance with the preferred embodiment of the present invention shown herein, (other numerical combinations can be used) are positioned by a nut  126  positioned around a lower base  128  of the cap  134  of pack-off  10  and in threaded engagement therewith. Threads  130  are shown disposed between the lower base  128  and the nut  126 , with a jam nut  132  disposed therebeneath also in engagement with threads  130 . Finally, it may be seen that the lower spring  116 , piston  114  and push rods  120  are all contained within intermediate cap  134  of the intermediate body portion  100 . The intermediate cap  134  is in threaded engagement on an upper end  136  to a lower portion  138  of the central body  99  around which threads  140  are formed. The threaded engagement between the lower portion  138  of the central body  99  and the upper end  136  of the intermediate cap  134  is for the securement of the piston  114  axially disposed beneath lower sealing member  102  for the compression thereof.  
         [0033]    Referring still to FIG. 2, and more particularly to the intermediate body portion  100  thereof, the piston  114  includes an axial bore  150  having a diameter larger than that of the capillary tubing which extends through the axial bore  104  of the lower sealing member  102 . Likewise, an axial bore  152  is formed in the lower base  128  of the cap  134  therein providing an even greater diameter. To contain the gas or fluid pressure therein, o-rings  154  and  156  are disposed on opposite ends of the piston  114 , as shown herein. The o-rings  154  and  156  permit a degree of reciprocal movement of the piston  114  between the central body  99  and the lower base  128  to facilitate the manual adjustment of said piston. Finally, end  160  of the lower base  128  is constructed with threads  162  formed therearound for securement to the wellhead for the operation herein described.  
         [0034]    Referring now to FIG. 3, there is shown a side-elevational, full cross-sectional view of the central body  99  of the intermediate body portion  100  of FIG. 2. All other elements of the capillary pack-off  10  illustrated in FIG. 2 in association therewith have been removed for purposes of clarity. In this particular view, the fabrication of the central body  99  can be more clearly understood as well as certain functional aspects thereof. What is clearly shown herein is a multi-chambered axial bore  300  of the central body  99  facilitating the receipt of the above-referenced elements therein for the operation thereof, and in axial alignment with central axis  90 . The bore  300  includes cylindrical cavity  305  and cylindrical cavity  106  oppositely disposed about a cylindrical region  310  sandwiched therebetween. The inside diameter of bore  300  is decreased from the cylindrical cavity  305  to the cylindrical cavity  106 , with an inner lip  301  defining the cylindrical region  310 , which provides communication between the cylindrical cavity  305  and the upper end  108  of the cylindrical cavity  106 . As described above, various bore diameters may be preferable for receipt, adaptation and operation of the various elements described, set forth and shown in FIG. 2.  
         [0035]    Still referring to FIG. 3, the lower-portion  138  of central body  99  is larger in diameter than, and extends from an upper section  330  at an acute angle relative thereto. Furthermore, the lower outer surface of lower portion  138  is provided with threads  140  for threaded engagement with intermediate cap  134 . Likewise, the upper outer surface of the section  330  is provided in a threaded configuration  325  for threaded engagement with the cap  20 .  
         [0036]    Referring now to FIG. 4, there is shown a side-elevational, full cross-sectional view of the intermediate cap  134 , which comprises the upper portion  136  and the lower base  128 . The end  160  of the lower base  128  comprises lower body portion  170  of FIG. 2. All other elements of the capillary pack-off  10  illustrated in FIG. 2 in association therewith have been removed for purposes of clarity. In this particular view, the fabrication of the cap  134  can be more clearly understood as well as certain functional aspects thereof. What is clearly shown herein is a multi-chambered axial bore  400  of the cap  134  facilitating the receipt of the above-referenced elements therein for the operation thereof, and in axial alignment with central axis  90 . The axial bore  400  includes cylindrical chamber  405  axially aligned with the axial bore  152 . The axially aligned chamber  400  and bore  152  are oppositely disposed about a cylindrical region  415  sandwiched therebetween. The inside diameter of the bore  400  is decreased from the chamber  405  to the axial bore  152 . The cylindrical region  415  provides communication between the axial bore  152  and the chamber  405  formed upwardly thereof. A plurality of apertures  410  are formed parallel to the central axis  90  in collar  411  of the cap  134  in communication with the chamber  405  for receipt of the plurality of push rods  120 , described in further detail below. Furthermore, the collar  411  of the upper portion  136  of the cap  134  abuts and provides a stop for the push rods  120 , preventing further movement of the push rods  120 . As described above, the various bore diameters are necessitated for receipt, adaptation and operation of the various elements described, set forth and shown in FIG. 2.  
         [0037]    Still referring to FIG. 4, the outer surface of lower base  128  is provided in the threaded configuration  130  for threaded engagement with the nut  126  and the jam nut  132 . The end  160  of the lower base  128  is further formed with the threads  162  formed circumferentially therearound adapted for threadably engaging mating wellhead equipment of conventional nature of the types set forth and shown in FIG. 1. Likewise, the sidewalls of the cavity  405  are provided with internal threads  140  for threaded engagement with the lower portion  138  of the central body  99 .  
         [0038]    Referring now to FIG. 5, there is shown a side-elevational, full cross-sectional view of the piston  114  of FIG. 2. The central bore  150  is formed concentrically about the axis  90 . The piston  114  is formed with the hip portion  124  and an upper portion  505 , with an angled surface  506  therebetween extending at an acute angle relative to the upper portion  505 . A lower portion  515  extends rearward of the underside  122  of the hip portion  124  . The upper portion  505  and the lower portion  515  are adapted to receive the o-rings  156  and  154  in o-ring slots  556  and  554 , respectively. The upper portion  505  further includes a terminal end  520  abutting the lower sealing member  102 . The actuation of the piston  114  within the capillary tubing pack-off  10  will be described in more detail below.  
         [0039]    Referring to FIG. 6, there is shown a side-elevational, full cross-sectional view of the lower sealing member  102 . The central bore  104  is formed concentrically about the axis  90 . The lower sealing member  102  includes an upper angulated surface  600  in abutting engagement with the conical busing  110 , and a lower surface  605  in abutting engagement with the lower bushing  112 . As discussed below, the lower sealing member  102  frictionally restrains movement of the capillary tubing (not shown) extending through central bore  104  by forming a seal around the circumference of the capillary tubing in reaction to a force imparted by the piston  114 .  
         [0040]    Referring now to FIGS. 7A and 7B in combination, there is shown a top plan and a side-elevational view of lower bushing  112 . The central bore  104  is formed concentrically about the axis  90 . The low bushing  112  further comprises chamfered edges  712  and  714 . Furthermore, the lower flat bushing  112  includes a top surface  710  abutting the lower surface  605  of the lower sealing member  102  and a lower surface  705  abutting the upper terminal end  520  of the piston  114 .  
         [0041]    Still referring to FIGS. 7A and 7B in combination, there is shown below the plane of the lower surface  705  a plurality of grooves  701 . The grooves  701  allow well pressure to reach the outer perimeter of end  520  of piston  114 . This allows pressure to act over the entire area of end  520 , so that piston  114  is pressure balanced. If the piston  114  is pressure balanced, the spring  116  can force the piston  114  downwards to relax the compression of the lower sealing member  102  when it is time to pull the tubing our of the well for servicing.  
         [0042]    Referring now to FIG. 8, there is shown a side-elevational, full cross-sectional view of the conical bushing  110 , having the central bore  104  formed concencentrically about the axis  90 . The central bore  104  is in communication with the cylindrical region  310  of the central body  99 . The conical bushing  110  is contained in the upper portion  108  of the cylindrical cavity  106  of the central body  99  The conical bushing  110  includes a conically-shaped lower surface  805  in abutting engagement with the upper angulated surface  600  of lower sealing member  102 , and a flat upper surface  810  in abutting engagement with the lower portion of the lip  301  of the central body  99 . The function of conical bushing  110  will be discussed in more detail below.  
         [0043]    Referring to FIG. 9, there is shown a side-elevational view of the lower spring  116 . The spring  116  includes a central bore  900  in axial alignment with central axis  90 , and is defined in the cavity  117 . The spring  116  comprises a top surface  910  abutting the lower surface  350  of the lower portion  138  of the central body  99  and a bottom surface  905  in abutting engagement with the topside of the hip portion  124  of the piston  114 . The function of the spring  116  will be discussed in more detail below.  
         [0044]    Referring now to FIG. 10, there is shown a side-elevational view of one of the plurality of push rods  120  (preferably 6). The push rods  120  include a first end  915  abutting the underside  122  of the hip  124  of the piston  114 , and a surface  916  abutting the collar  411  of the sidewall of cylindrical chamber  405 , as shown in FIG. 4. The push rods  120  further include a body portion  919  which extend through the aperture  410 , as shown in FIG. 4, and abut the nut  126  at a lower end  917 .  
         [0045]    Referring now to FIG. 11, there is shown a side-elevational, full cross-sectional view of nut  126 . The nut  126  includes a central bore  940  in axial alignment with central axis  90 . The sidewalls of bore  940  include threads  951  for threaded engagement with the threads  130  of the lower base  128  of the cap  134 . The nut  126  further includes a top side  942  abutting the lower end  917  of the push rods  120 , and an underside  941  abutting the jam nut  132 . The outer surface  943  of the nut  126  is provided in a knurled configuration for facilitating engagement of the threads  951  with the threads  130  of the lower base  128 . As discussed below, the nut  126  of the present invention provides the mechanical actuation of piston  114  which imparts an upward force to lower sealing member  102  to frictionally restrain the &#39;capillary tubing extending along the axis  90  through central bore  940 .  
         [0046]    Referring to FIG. 12, there is shown a side-elevational, full cross-sectional view of the jam nut  132 . The jam nut  132  includes a central bore  950  in axial alignment with central axis  90 . The sidewalls of bore  950  are provided in a threaded configuration  954  for threaded engagement with the threads  130  of the lower base  128 . The outer surface  953  of the jam nut  132  is provided in a knurled configuration for facilitating engagement of the threads  954  with the threads  130  of the lower base  128 . A top surface  952  abuts the lower end  941  of nut  126 . As further described below, the jam nut  132  prevents slippage between the threads  954  of the nut  126  and the threads  130  of the lower base  128 .  
         [0047]    In operation, the redundant pack-off assembly of the pack-off assembly  10  of the present invention utilizes two temporary pack-off, sealing and securing systems for controlling the capillary tubing extending through capillary pack-off  10 . While the upper body portion  11  facilitates the hydraulic actuated sealing of a capillary tube, the intermediate body portion  100  provides a redundant seal.  
         [0048]    During the snubbing operation, the upper body portion  11  is regulated by the flow of hydraulic fluid through the aperture  36  from a hand pump or from a pump on a rig. The hydraulic pressure causes the plunger  16  to apply a variable compressive load to the upper sealing member  54 . The flow of hydraulic fluid through the aperture  36  of the upper body portion  11  imparts a downward force to the plunger  16 , which compresses the upper spring  44  and forces the upper bushing set  52  into the lower bushing set  58 , thereby compressing the upper sealing member  54  disposed therebetween. The abutting engagement of the upper sealing member  54  and the conically shaped lower bushing set  58  imparts radially inwardly motion to the upper sealing member  54 . The radially inwardly movement of the upper sealing member  54  forms a seal around the capillary tubing extending through the pack-off  10  of the present invention, thus frictionally restraining movement thereof.  
         [0049]    The intermediate body  100  comprises the redundant, lower compressible sealing member  102 . The lower sealing member  102  is, as described above, mechanically compressed via the nut  126  in order to provide a longer term seal than that potentially provided by the upper sealing member  54  of the upper body portion  11 . The jam nut  132  prevents the nut  126  from coming loose and releasing the lower compressible member  102 . In a manner similar to the actuation of the upper sealing member  54 , the nut  126  in threaded engagement with the lower base  128  of cap  134  engages the push rods  120  positioned in the collar  411  of the cap  134  and in abutting engagement with the piston  114 . The engagement of the push rods  120  by the nut  126  imparts an upward force to the piston  114 , which compresses the lower spring  116  and forces the lower flat bushing  112  into the conical bushing  110 , thereby compressing the lower sealing member  102  disposed therebetween. The abutting engagement of the lower sealing member  102  and the conical bushing  110  imparts radially inwardly motion to the lower sealing member  102 . The radially inwardly movement of the lower sealing member  102  forms a seal around the capillary tubing extending through the pack-off  10  of the present invention, thus frictionally restraining movement thereof.  
         [0050]    As described above, any leak of hydraulic fluid from the upper body portion  11  can compromise the integrity of the securing and sealing mechanism of the upper compressible elastomeric sealing member  54 . By utilizing the redundant, mechanically actuatable lower compressible elastomeric sealing member  102 , operators at the wellhead can egress from the job site and have a much higher level of confidence of the integrity of the pack-off unit  10  of the present invention because they will be relying upon a mechanical, long term sealing system which inherently has greater reliability and is not subject to potential pressure loss. Moreover, if the upper sealing member  54  exhibits any leaking, it is quick and easy to snug the lower sealing member  102  by rotation of the nut  126  to stop a leak. Such actuation can occur manually without having to bring in an additional pump and/or going through any more complex procedures than a simple rotation of a threaded member. The advantages of providing a redundant manual sealing means are extra safety due to a redundant sealing means, reliability due to mechanical compression of the lower sealing member, and quick and easy adjustment of the manual sealing means.  
         [0051]    Furthermore, when lowering tubing into the well or pulling tubing out of the well, the manual upper slips  14  described above which are actuated by the slip cap  12  are typically not in place on the capillary tubing pack-off  10  of the present invention. The slips  14  are placed into the upper end  18  after the desired amount of tubing has been inserted into the well. What is in place is the hydraulic actuation of the upper sealing member  54  and the manual actuation of the lower sealing member  102  as discussed above which permits sealing and securement of the capillary tube as long as the pressures within the well do not exceed that capable of being handled by such compressible members. Due to the fact that the upper and lower sealing members  54  and  102  are, however, elastomeric, it includes a relatively smooth surface for creating an effective seal thereagainst to prevent fluids from within the well to escape therefrom.  
         [0052]    It should be noted that the specification of the o-rings presented herein are for purposes of illustrating the requirement for sealing, as is typical in most hydraulic actuation systems due to the high pressures involved in the system, the multiple use of o-rings is deemed a preferred embodiment.  
         [0053]    Although a preferred embodiment of the invention as been illustrated in the accompanying drawings and described in the foregoing specification, the wellhead is capable of numerous rearrangements and modifications of parts and elements without departing from the spirit of the invention.

Technology Classification (CPC): 4