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 an elastomeric compressible 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 hydraulically actuating a plurality of slips to impart select engagement of the periphery of the tubing for its securement therein. 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.

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 while providing means for preventing the tubing from being blown out of the well.  
           [0003]    2. History of Related Art  
           [0004]    It is a common and well known practice in the oil and gas industry 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 substances such 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 {fraction (1/4 )} or {fraction (3/8)} inch (sometimes {fraction (5/8)} 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 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 while it is being inserted or removed 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 pressure 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 in the well, 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.  
           [0008]    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 an hydraulically actuated mechanism capable of reliable operation in the event of a capillary tubing control problem.  
         SUMMARY OF INVENTION  
         [0009]    The present invention relates to a 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 therethrough for insertion of the tubing, first means slidably coupled into the bore of the body for preventing movement of the tubing by hydraulically engaging a plurality of slips around the periphery of the tubing, and second means slidably coupled into the bore of the body for frictionally restraining movement of the tubing by hydraulically engaging the periphery of the tubing with a compressible elastomeric sealing member.  
           [0010]    In another aspect of the invention, the body includes an upper unit and a lower unit. The lower unit is in threaded engagement with the upper unit. The upper unit comprises a first, second and third threaded aperture in communication with the bore of the upper unit. The upper unit further comprises the first means having a hollow cylindrical piston slidably coupled within the bore of the upper unit and in axial alignment therewith, a plurality of slips coupled to the piston and having serrated teeth for engagement or disengagement of the tubing, a slide member slidably coupled within the first aperture and extending therethrough for disengaging the plurality of slips from around the periphery of the tubing, and a plug, adapted for threaded engagement with the first aperture and disposed atop the slide for positioning the slide relative to the sidewall of the bore of the upper body. The flow of hydraulic fluid through the third aperture imparts an upward force to the piston thereby imparting a radially inwardly motion to the plurality of slips due to the inclined side walls of the bore of the upper unit so as to cause engagement of the plurality of slips with the tubing. Similarly, the flow of hydraulic fluid through the second aperture imparts a downward motion to the piston thereby imparting a radially outwardly motion to the plurality of slips due to engagement of the plurality of slips with the slide.  
           [0011]    The lower unit further comprises a threaded aperture in communication with the bore of the lower unit. The lower unit also comprises the second means having a plunger in axial alignment therewith, a 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 a compressible elastomeric sealing member in axial alignment with the upper and lower bushing set and disposed therebetween. The flow of hydraulic fluid through the aperture of the lower unit 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 sealing member disposed therebetween. The abutting engagement of the sealing member and the conically shaped lower bushing set imparts radially inwardly motion to the sealing member. The radially inwardly movement of the sealing member forms a seal around the capillary tubing extending through the bore of the body.  
           [0012]    In still another aspect of the invention, the upper unit 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 unit for engaging the suspension slips with the tubing.  
           [0013]    In a further aspect, the invention provides an extra set of slips that can be quickly engaged around the capillary tubing described above, to arrest upward movement in an emergency situation. A double-acting hydraulic piston is used to move the slips upwards into an engaged position to halt the upward movement of the tubing. After the crew regains control, hydraulic pressure can be applied to the opposite side of the piston to move the slips downwardly and outwardly into a position that allows free upward or downward motion of the capillary tubing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    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:  
         [0015]    [0015]FIG. 1 is a perspective view of a typical wellhead installation showing the insertion of capillary tubing;  
         [0016]    [0016]FIG. 2 is an enlarged, side-elevational, cross-sectional view of the capillary tubing pack-off of the present invention with portions thereof cut away for illustrating the assembly thereof;  
         [0017]    [0017]FIG. 3 is a side-elevational, full cross-sectional view of the upper body of the capillary tubing pack-off of FIG. 2, illustrating one aspect of the fabrication thereof;  
         [0018]    [0018]FIG. 4 is a side-elevational view of the piston for the capillary tubing pack-off of FIG. 2;  
         [0019]    [0019]FIGS. 5A and 5B comprise a side-elevational, full cross-sectional and frontal view, respectively, of the piston shown in FIG. 4;  
         [0020]    [0020]FIGS. 6A, 6B and  6 C are multiple views of the fabricated slip of the capillary tubing pack-off of FIG. 2 illustrating various aspects of the fabrication thereof;  
         [0021]    [0021]FIGS. 7A and 7B are top plan and side-elevational views, respectively, of the plug of the capillary tubing pack-off of FIG. 2;  
         [0022]    [0022]FIGS. 8A through 8C comprise multiple views of the slide for the capillary tubing pack-off of FIG. 2; and  
         [0023]    [0023]FIGS. 9A through 9C comprise multiple views of a perspective, cross-sectional view of the upper body portion of the capillary tubing pack-off of FIG. 2 with portions thereof cut away for illustrating the engagement and disengagement of the slips within the capillary tubing pack-off of FIG. 2. 
     
    
     DETAILED DESCRIPTION  
       [0024]    It has been found that a wellhead pack-off incorporating hydraulically actuated sealing means 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 hydraulically actuated sealing means of the present invention also provides a means for suspending the capillary tubing from the wellhead for a prolonged period of time. As described below, and as set forth and shown in the drawings, the wellhead pack-off of the present invention provides a set of hydraulically activated slips specifically adapted for restraining the capillary tubing if it begins to be blown out of the well under pressure.  
         [0025]    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 prior art 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 prior art to use wellhead pack-off devices for controlling the capillary tubing while the well remains pressurized. As set forth 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. Also, the use of capillary tubing have 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 tubing include the improvement of system dynamics and minimization of reservoir damage. The present invention facilitates the above advantages by increasing the reliability of the wellhead pack-off as set forth and described below.  
         [0026]    Referring now to FIG. 2, there is shown an enlarged side-elevational, partially-cross-sectional view of the capillary tubing pack-off  10  of the present invention. The presence of a capillary tube is not shown for purposes of clarity. The pack-off  10  includes an upper unit  500  and a lower unit  501  adapted for receiving a capillary tube axially therethrough, and in axial alignment with a central axis  100 . Upper unit  500  includes a slip cap  12  disposed on the first terminal end  13  thereof. A plurality of manual upper slips  14  are disposed within the slip cap  12  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 unit further comprises a body  16  having a threaded portion  17  adapted for threadably engaging the slip cap  12  as shown herein. The body  16  is constructed for receipt of a plurality of hydraulic lower slips  18  disposed along an inclined surface  19  formed therein. A threaded aperture  21  is formed in cylindrical wall  23  of the body  16  adapted for receipt of a slide  22  and a plug  20  therein. A separate aperture  21 , slide  22 , and plug  20  is provided for and adapted for engagement with each of the plurality of lower slips  18  in a manner described in more detail below.  
         [0027]    Still referring to FIG. 2, there is shown the body  16  of upper unit  500  constructed with the cylindrical wall  23 , within which is disposed, for reciprocation therein, a piston  24 . The piston  24  is disposed in sealing engagement with a cylindrical wall  23  through an o-ring  26  disposed therebetween. A second o-ring  28  is disposed in a groove  27  of an upstanding cylindrical boss  29  formed around the piston  24  that is described in more detail below. Likewise, a third o-ring  30  is disposed between an inside surface  31  of the body  16  and an upper internal surface of a cap  32 . The cap  32  forms the upper region of lower unit  501  and is constructed with an outwardly facing thread portion  34  adapted for engagement with an inwardly facing threaded surface  36  of the lower end of body  16 . The cap  32  is configured for receiving a lower end  40  of piston  24  with an o-ring  41  disposed therebetween. Axially disposed within the cap  32  is a reciprocating plunger  42  sealed thereagainst through an o-ring  43 . Likewise a second o-ring  45  is disposed around an upper boss  44  of the plunger  42  for sealing against the inside of the cap  32 . The plunger  42  is also constructed with a reduced neck portion  50  adapted for receiving a spring  52  therearound. The spring is disposed in space  54  formed between the plunger  42  and the inside surface of the cap  32  for purposes of biasing the plunger  42  upwardly. A threaded aperture  46  is formed in the sidewall of cap  32  and permits hydraulic fluid to enter and egress space  47 , formed between intermediate portion  48  of plunger  42  and the sidewall of cap  32 . Furthermore, the space  47  is separated from the space  54  by upper boss  44  and sealed thereagainst by second o-ring  45 .  
         [0028]    Referring still to FIG. 2, and, in particular, further aspects of the lower unit  501  of the capillary tubing pack-off  10  of the present invention, a steel upper bushing set  56  is disposed within a lower end  58  of the plunger  42 . The steel upper bushing set  56  is formed with a radially extending neck region  60  that abuts the terminal end of the plunger  42  on a first side and abuts an elastomeric compressible sealing member  64 , preferably formed of rubber or the like, on the opposite side thereof. The sealing member  64  is disposed in axial alignment with the steel upper bushing  56  and within the walls of an extended base  66 . Extended base  66  is formed with a lower base portion  68  forming a shoulder  70  facing upperwardly therefrom toward the sealing member  64  and upon which a lower bushing set  74  is disposed. It may be seen that the lower bushing set  74  is sandwiched between the shoulder  70  and an angulated surface  76  of the sealing member  64 . The angulated surface  76  is formed at angle that matingly engages in abutting relationship therewith angulated surface  78  of the lower bushing set  74 , also preferably formed of steel. The lower base portion  80  of the extended base  66  is further formed with threads  82  formed circumferentially therearound adapted for threadably engaging mating wellhead equipment.  
         [0029]    The above provides a description of the general assembly of the capillary tubing pack-off  10  of the present invention. A description of many of the individual elements forming portions thereof will be described in more detail below. What is common in the assemblage, however, of the above-described elements is the fact that a central aperture  100  is formed therethrough, as indicated by the phantom line of central axis  100  therein. The aperture along axis  100  is adapted for receipt of capillary tubing therein, as referenced above. Actuation of the capillary tubing pack-off  10 , in the manner described herein, allows selective engagement and disengagement of the capillary tubing disposed within the capillary tubing pack-off for purposes of installing, removing, and locking capillary tubing within a well.  
         [0030]    Referring now to FIG. 3, there is shown a side-elevational, full cross-sectional view of the body  16  of FIG. 2, with all other elements of the capillary pack-off  10  illustrated in FIG. 2 in association therewith removed for purposes of clarity. In this particular view, the fabrication of the body  16  can be more clearly understood as well as certain functional aspects thereof. For example, body  16  includes the threaded apertures  21  (preferably three) adapted for receiving the slides  22  and the plugs  20  (shown as FIG. 2) therein. The construction and operation of the threaded apertures  21  and slides  22  will be described in more detail below. What is clearly shown herein is the multi-chambered axial bore  102  of the body  16  facilitating the receipt of the above-referenced elements therein for the operation thereof, and in axial alignment with central axis  100 . The bore  102  includes first and second conical sections  104  and  106  oppositely disposed about a cylindrical region  108  sandwiched therebetween. An aperture  110  is formed in a sidewall body  16  in communication with chamber  106 . The Aperture  110  provides a means of visually confirming that the slips  18  are in position to engage the capillary tubing, while the aperture  21  provides outside communication into a cylindrical chamber  112  disposed contiguous to the conical section  106 . A conical transition section  114  provides communication between the chamber  112  and a cylindrical chamber  116  formed upwardly of a cylindrical region  118 . The inside diameter of the body  16  is increased to provide a cylindrical region  120  above and in communication with a lower-most region  122 . The sidewalls of the lower-most region  122  form inwardly facing threaded surface  36  for threaded engagement with cap  32 . 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.  
         [0031]    Still referring to FIG. 3, the sidewall of the body  16  includes a first threaded aperture  204  providing communication into the region  116  while a second threaded aperture  202  provides communication into the chamber  118 . Finally, the walls of the lower-most region  122  are formed with the threads  36 , referenced above.  
         [0032]    Referring now to FIG. 4, there is shown a top plan view of the piston  24  of FIG. 2. The piston  24  is constructed with an upper body portion  130  formed with slots  132  (preferably three) therein. The slot  132  is adapted for receiving the slides  22  and the lower slips  18 , as represented in phantom. Likewise, the piston  24  is constructed with a groove  134  adapted for receiving o-ring  26  as shown in FIG. 2. An o-ring may also be mounted around the piston  24  within the boss  29  extending therearound and adjacent to intermediate portion  90  of the piston  24 . An o-ring groove  142  is also formed in the lower end  40  of the piston  24 .  
         [0033]    Referring to FIGS. 5A and 5B in combination, there is shown a side-elevational, partially cross-sectional and frontal view, respectively, of the piston  24  of FIG. 4. The slots  132 , as shown in FIG. 4, may be seen to comprise an elongated section thereof exposing a central bore  144  therein. The central bore  144  is formed concentrically about the axis  100 , as is central chamber  146  formed adjacent thereto. The reciprocal actuation of the piston  24  within the capillary tubing pack-off  10  will be described in more detail below.  
         [0034]    Referring now to FIG. 6A, there is shown an enlarged top plan view of one hydraulic lower slip  18  (preferably of the set of three, although other numerical combinations may be used). The slip  18  includes a frontal face  150  and a rear face  152  wherein an angled body portion  154  extends therebetween. A key section  156  is disposed rearwardly thereof and extends therefrom by neck region  158 .  
         [0035]    Referring now to FIG. 6B, there is shown a side-elevational view of the hydraulic lower slip  18 , illustrating aspects in the manufacturing thereof. The neck region  158  of the key section  156  may be seen relative to the surface  152 . The slip  18  is formed with a plurality of serrated teeth  15 , which teeth may be of similar shape as those set forth and described relative to the manual upper slips  14  described above. The key section  156  has an angled rear surface  157  for sliding engagement with slide  22 , described in more detail below.  
         [0036]    Referring now to FIG. 6C, there is shown an end-elevational view of the hydraulic lower slip  18  illustrating other aspects of the manufacture thereof. As will be seen, the serrated teeth  15  comprise a relatively small section of the hydraulic lower slip  18  and are disposed inwardly in a position adapted for engagement with the capillary tubing placed therethrough as will be described in more detail below.  
         [0037]    Referring now to FIGS. 7A and 7B in combination, there is shown a top plan and a side elevational view of one plug  20  (preferably 3) of the capillary tubing pack-off of FIG. 2. The plug  20  is constructed with a threaded side portion  160  adapted for threaded engagement with the threaded aperture  21  formed in the capillary tubing pack-off  10 . As shown in FIG. 2, the plug  20  is disposed atop the slide  22  for positioning the slide  22  relative to the sidewall of the cylindrical chamber  112  of the body  16  of the capillary tubing pack-off  10 . The placement of the slide facilitates the actuation of the hydraulic lower slips  18 , as will be described in more detail below.  
         [0038]    Referring now to FIGS. 8A through 8D in combination, there is shown one of the above-referenced slides  22 . In these particular views, the manufacturing of the slide may be more clearly seen and, in particular, the construction of the angulated surface therein facilitating engagement with the angled surface  157  of the lower slips  18  discussed above.  
         [0039]    Referring specifically now to FIG. 8A, there is shown a side elevational view of the slide wherein angulated surface  170  is shown to be disposed across body section  172  for facilitating sliding engagement with the angled rear surface  157  of the hydraulic lower slip  18 , as represented in phantom. Body section  172  is disposed beneath a head section  174  having a threaded aperture  176  formed therein. The threaded aperture  176  enables the slide  22  to be extracted with a bolt (not shown) after removing the plug  20 .  
         [0040]    Referring now to FIG. 8B, a top plan view of the slide  22  of FIG. 8A is set forth and shown. The aperture  176  is most clearly shown in this particular view while the angulated surface  170  of body section  172  is shown in phantom.  
         [0041]    Referring now to FIG. 8C, the slide  22  of FIG. 8A is shown in a bottom plan view wherein the body portion  172  is shown to be formed with the slide surface  170  shown in phantom and the shape of which is most clearly set forth and illustrated as it is disposed beneath the larger head section  174 .  
         [0042]    Referring now to FIGS. 9A through 9C in combination, there is shown a perspective view of a cutaway portion of the piston  24  and the body  16 , with one of the slides  22 , and slips  18 , contained therein, illustrating the engagement one with the other for purposes of description of the operation thereof within the capillary tubing pack-off  10 . In these particular views, the engagement of the hydraulic lower slip  18  by slide  22  may be more clearly seen during retraction of the slip  18  by piston  24  in direction of arrow  201 .  
         [0043]    Referring specifically now to FIG. 9A, there is shown the piston  24  and the slip  18  in an engaged position, with the slide  22  inserted through the threaded aperture  21  and slot  132  of piston  24 . The plug  20  is not shown for purposes of clarity.  
         [0044]    In the engaged position, forward motion of the piston  24  induces forward movement of the slip  18  by virtue of the interlocking relationship thereof, whereby the angulated surface  154  bears against the angulated surface  19  of the body  16 , imparting inwardly radially directed motion to the slip  18 , as depicted by arrow  155 . The inwardly radial direction of movement of the slip  18  along the direction of the arrow  155  will cause the teeth  15  thereof to bear against capillary tubing (not shown) extending axially therethrough.  
         [0045]    Referring to FIG. 9B, there is shown the same view as in FIG. 9A, illustrating a transitional stage during retraction by the piston  24  of the slip  18 . As discussed above, movement along the arrow  201  will impart a radially outwardly motion to the slip  18 . During a portion of this retraction, however, the teeth  15  remain engaged with the tubing due to the radially inwardly force imparted by the angulated surface  19  of the body  16  to the angulated surface  154  of the slip  18 .  
         [0046]    Referring now to FIG. 9C, there is shown the same view as in FIGS. 9A and 9B, illustrating the engagement of slide  22  and slip  18  by the motion of the slip  18  imparted by the piston  24  during retraction in the direction of arrow  201 . It may be seen that the angulated surface  170  of the slide  22  engages the slip  18  across the angulated surface  157  thereof. Movement of the piston  24  induces the angulated surface  157  of the slip  18  to abut the angulated surface  170  of the slide  22 , whereby the slip  18  is induced to move radially outwardly along the surface  170  of the side  22  disengaging teeth  15  from the tubing, as depicted by arrow  159 .  
         [0047]    While the construction and operation of the capillary tubing pack-off of the present invention may be clearly set forth and shown herein, the assembly thereof also should be addressed. The interlocking engagement between the slips  18  and the piston  24  necessitates assembly one with the other within the body  16  of the capillary tubing pack-off  10  for subsequent insertion of the slide  22  for positioning therebetween. As referenced above, the function of the slide  22  is to impart radially outwardly movement of the slip  18  during the retraction thereof in the direction of arrow  201  by virtue of the angled surface  157  of slip  18  engaging surface  170  of slide  22 .  
         [0048]    Referring back now to FIG. 2, the overall operation of the capillary tubing pack-off  10  of the present invention will now be more clearly described. The capillary tubing pack-off  10  basically comprises the lower unit  501  and the upper unit  500 . The lower unit  501  comprises a first clamping means using the sealing member  64 . The upper unit  500  comprises a second clamping means using the plurality of hydraulic lower slips  18  and a third clamping means using the manual slips  14 .  
         [0049]    Referring still to FIG. 2, and in particular to the lower unit  501 , which has been described in detail above. The lower unit  501  serves to provide a first clamping means for controlling the movement of small diameter tubing into and out of wells by providing an hydraulically actuatable clamping mechanism working in conjunction with a conventional elastomeric compression pack-off. The use of hydraulically actuated elastomeric pack-offs to seal capillary tubing is known in the art. In that regard, lower unit  501  includes a conventional hydraulically actuated pack-off. It may be seen that hydraulic fluid injected through port  46  into space  47  of the capillary tubing pack-off lower unit  501  will cause movement of the plunger  42  therein against spring  52  and against the upper bushing  56  which bears against sealing member  64 . Sealing member  64  is constructed with an angulated surface  74  which bears against angulated surface  76  of the lower bushing  78  whereby radially inwardly directed expansion is imparted for engaging capillary tubing disposed therein. As stated above, this type of hydraulic actuation utilizing a plunger and a compressible member is accepted in the industry. What is not of standard acceptance is the use of means for actuation of a series of mechanical locking members such as the hydraulic lower slips  18  having teeth  15  formed along an inner surface thereof (shown in FIG. 6A- 6 C) for engagement of the capillary tubing extending therethrough. In the lower unit  501  of FIG. 2, a first clamping mechanism is provided by the sealing member  64 . The sealing member  64  provides the requisite sealing of the capillary tubing and a degree of securement thereagainst. In high pressure situations, it is, however, potentially problematic to have the sole means for securing capillary tubing the sealing member  64  for which only a smooth frictional surface is afforded therewith. For this reason, in the upper unit  500 , a second clamping mechanism is provided by the hydraulic lower slips  18  which greatly improve the reliability, safety and efficiency of such wellhead operations.  
         [0050]    Referring specifically now to the upper unit  500  and the operation of the second claimping means comprising the plurality of slips  18  described above in FIG. 2, the slips  18  may be used (preferably three) to arrest the upward motion of the capillary tubing in an emergency situation. The slips  18  are positioned by virtue of the piston  24  that is hydraulically actuated to move in a first upward direction along arrow  200  in response to hydraulic fluid flowing through the aperture  202  and bearing thereagainst. The aperture  204  allows expulsion of any hydraulic fluid contained in cavity  206  defined therebeneath and around the upper region of piston  24 . Movement of the piston  24  in the direction of arrow  200  then imparts movement to the slips  18  disposed axially against the end  133  of the piston  24 . It may be seen that the slot  132  (FIGS. 4 and 5), provided for each of the plurality of slips, permits an abutting relationship between the end  133  of the piston  24  (shown in FIG. 4) and the surface  152  of the slip  18  (shown in FIGS. 6A and 6B). Movement of the piston  24  in the direction of the arrow  200  thus imparts movement of the slips  18  in the same direction, which by virtue of the angled interface along the surface  19  induces the slips  18  to move radially inwardly in a clamping action, similar to the jaws of a chuck, against an object such as a capillary tube extending axially through the capillary tubing pack-off  10 . The teeth  15  then are positioned to physically engage the surface of the capillary tube for securement thereof actuated by the hydraulic pressure imparted thereto. Likewise, release of the hydraulic fluid through the aperture  202  while hydraulic fluid is injected through the aperture  204  will cause the piston  24  to move in the direction of the arrow  201 , and the movement will likewise cause movement of the slips  18  in the direction of the arrow  201  by virtue of the interlocking relationship therebetween. As discussed above in relation to FIGS. 9A through 9C, the teeth  15  of the slips  18  continues to engage the surface of the capillary tube due to the radially inwardly force exerted on the angled surfaces  154  of the slips  18 , until angled surfaces  170  of the slides  22  (one slide is provided for each slip) engage the angled surfaces  157  of the slips  18 , thereby imparting a radially outwardly motion to the slips  18 , disengaging the teeth  15  from the surface of the capillary tubing.  
         [0051]    Referring still to FIG. 2, and, in particular to the third clamping mechanism set forth and described above in the upper unit  500  comprising the manual upper slips  14  which may be provided in a series of two or more (preferably three) and are manually positioned for claimping action relative to the slip cap  12 . In operation, however, 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, although they are positioned around the capillary tubing being fed thereto. The third clamping mechanism is utilized once the capillary tubing reaches a certain depth and is cutoff from the tubing reel on the service rig to suspend the tubing and prevent it from being pulled down by gravity. In an emergency situation, however, there are generally two means available to an operator to control the movement of capillary tubing in the pack-off  10  of the present invention. The first clamping means, as discussed above, is the hydraulic actuation of the sealing member  64  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 sealing members. If the well pressure become great enough, the operator of the pack-off  10  of the present invention is able to connect and have available to him the ability to immediately hydraulically actuate a mechanical chuck in the form of the plurality of hydraulic lower slips  18  described above for secured engagement of the capillary tubing extending through the pack-off  10 .  
         [0052]    It should also 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.