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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
     The present invention relates to a penetrator assembly for establishing communication between a tubing hanger and a surrounding christmas tree or wellhead housing. More particularly, the invention relates to such a penetrator which comprises at least one retractable member and a valve member which, upon retraction of the retractable member, will sever a data line extending from the tree or wellhead housing, through the penetrator assembly, and into the tubing hanger. 
     Monitoring of downhole conditions has traditionally been accomplished with electronic transducers. These are sited at regular intervals along the length of the tubing and also at reservoir level, and are used to monitor parameters such as temperature, pressure and stress levels. The disadvantage of this system is the difficulty in maintaining electrical contact in the environment which is being monitored. This can lead to erroneous information on the downhole situation, and therefore lost time. 
     More recently, the advent of fiber optic diagnostic systems has substantially reduced this disadvantage. A fiber optic loop is fed downhole, and a signal sent and received at opposing ends. The generated and received signals are compared using a decoder, and the downhole conditions are interpreted, providing a faster, more reliable monitoring method. 
     The monitoring line must pass downhole from outside the well, usually through the christmas tree to inside the tubing hanger, such that pressure integrity is not compromised. Any such access into the well requires a gas tight pressure seal to be set up around the line. During operations such as workovers, the fiber optic line presents a further problem. The line is usually routed through the completion in a way that will cause it to be broken if the tubing hanger and attached tubing string is pulled. The time involved in retrieving the line prior to pulling the tubing hanger renders the option of line retrieval impractical. Retrieval also presents another problem in that the line feed path must be sealed afterwards. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention there is provided a pressure barrier for retaining well fluid separate from a surrounding environment, characterized in that the barrier comprises a valve through which a data line extends between the environment and the well interior, the valve being sealably closable to sever the line. The line itself is relatively inexpensive to replace, and any pieces of sheared line remaining downhole can be flushed out before installation of a replacement line. When closed, the valve will maintain the pressure integrity of the barrier. This system has the benefit of minimizing costs, since it is much faster and easier to shear the line and seal its path into the well simply by closing the valve, than it is to retrieve the line and then plug its vacated path into the well. Although the invention is beneficial for use with fiber optic lines, it may also be employed in conjunction with any relatively small diameter line (electrical, optical or other) capable of being severed by a valve and which is relatively inexpensive to replace. 
     The valve may comprise a valve housing having a valve closure member movably received therein, the line passing through aligned apertures in the housing and closure member, movement of the closure member to close the valve causing the apertures to move out of alignment and sever the line. 
     Preferably the pressure barrier comprises a penetrator incorporating the valve and movable between a position in which the penetrator engages an interior well component and a position in which the penetrator is disengaged from the component, allowing the component to be pulled from or installed in the well. The component may include a further valve through which the line passes. Preferably the or each valve is closeable upon disengagement of the penetrator from the component. For example, the valve or valves may comprise poppet valves having sufficient closure bias to sever the line. The valves may be arranged to be opened by engagement of the penetrator with the component. 
     The invention and its preferred features and advantages are described below with reference to an illustrative embodiment shown in the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a horizontal sectional view of parts of a christmas tree or wellhead, a tubing hanger and a multiple penetrator assembly embodying the invention; 
     FIG. 2 is an enlarged sectional view on arrow A in FIG. 1 showing the penetrator assembly poppet valves in the open condition; 
     FIG. 3 is a further enlarged sectional view corresponding to FIG. 1, showing the left hand (open) poppet valves in more detail; and 
     FIG. 4 is a view corresponding to FIG. 3 but showing the poppet valves in the closed condition. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is shown a christmas tree or wellhead  10  (hereinafter “tree”) surrounding a tubing hanger  12 . A multiple horizontal penetrator assembly  14  modified to incorporate poppet valves in accordance with a preferred embodiment of the invention has male parts  16   a ,  16   b  mounted to the tree for co-operation with corresponding female parts  18   a ,  18   b  in the tubing hanger. Penetrator assemblies as such are well known and are normally used to provide electrical or hydraulic connections between a tubing hanger and a surrounding wellhead or tree. See, for example, U.S. Pat. No. 5,941,574. The general construction and operating principles of such penetrators, as distinct from the various modifications discussed below, do not form part of the present invention and will not be further described in detail. 
     The male parts  16   a ,  16   b  are axially movable in known manner to engage with or disengage from the female parts  18   a ,  18   b . Part  16   a  is shown engaged with part  18   a  and parts  16   b  and  18   b  are shown disengaged. When disengaged, the male and female parts  16   a ,  16   b  and  18   a ,  18   b  respectively, lie on opposite sides of the generally cylindrical boundary surface  20  between the tubing hanger  12  and tree  10 , allowing the tubing hanger to be run into or retrieved from the tree without interference. The male parts  16   a ,  16   b  extend through suitable sliding seals or packings  22 , so as to maintain the pressure integrity of the tree  10 . 
     Lengths of fiber optic line  24   a ,  24   b  extend through the hollow interiors of the male parts  16   a ,  16   b,  through the female parts  18   a ,  18   b,  as described in more detail below, and downhole through vertical bores  26  in the tubing hanger  12 . The lengths  16   a ,  16   b  may comprise opposite ends of a single loop extending down through one of the parts  16   a ,  16   b  and up through the other. The loop may be installed by attaching to the end of the line a small ball or “bullet” having a larger diameter than the line. The bullet is of a suitable size and shape to pass freely along a circulation path extending downhole through one of the penetrator parts  16   a  or  16   b  and then back out of the well through the other. The bullet and attached line are pumped through the ports and passageways forming the circulation path, with fluid drag on the line and bullet pulling them along. The additional drag on the larger diameter bullet maintains sufficient tension on the line leading end to prevent kinking. The ends of the line are housed in metal conduits  28   a ,  28   b  connected by pressure tight joints to the male parts  16   a ,  16   b.  The line ends  24   a ,  24   b  exit the conduits  28   a ,  28   b  through suitable pressure tight glands (not shown), thereby maintaining the pressure integrity of the well. 
     As shown in mare detail in FIGS. 2-4, the female parts  18   a,    18   b  and the inner ends of the male parts  16   a,    16   b  are adapted to form double poppet valve assemblies  30   a ,  30   b  respectively. The female parts each comprise a valve housing  31 , and the male parts a corresponding housing  34 . Poppets  32  having short noses  38  are slidable in the housings  31  and poppets  40  having longer noses  42  are slidable in the housings  34 , against the action of respective bias springs  44 . The poppets  32 ,  40  each have an axial bore  46  with a plug  47  containing a smoothly joined series of drillings  49  juxtaposed to an oblique radial bore  48  in the poppets  32 ,  40 . The housings  31 ,  34  each have an oblique radial born  50 . A series of intercommunicating drillings  52 ,  54 ,  56 ,  58  are provided in the tubing hanger and tree. The drillings  52 ,  56  have suitably shaped plugs  60 ,  62  so that together with the drillings  54 ,  58  they form a single smoothly radiused passageway having an inner end in alignment with the bore  50  in the valve housing  31 . 
     When the male parts  16   a ,  16   b  are extended towards the female parts  18   a ,  18   b,  the noses  38 ,  42  engage each other and the poppets are pushed back against their respective bias springs  44 . In this position (FIG. 3) the respective poppet and valve housing bores  48  and  50  are brought into alignment, and the outer end of drilling  56  is aligned with the bore  50  in valve housing  34 . The drillings in the plugs  47  are likewise moved adjacent to the inner ends of the bores  48 . The line  24   a  can now be pumped through the plug  47  and bore  48  in poppet  40 , bore  50  in valve housing  34 , drillings  56 ,  58 ,  54 ,  52 , bore  50  in valve housing  31 , bore  48  and plug  47  in poppet  32 , and downhole through bore  26 . A proportion of the fluid used to pump the line downhole and back up again may flow into the cavity defined at the tubing hanger/tree interface  20 , but sufficient flow will be established along the desired pathway for installation of the line. 
     When the penetrator male part is retracted (FIG. 4;  16   b  FIG.  1 ), the bias springs  44  extend the poppets  32 ,  40  in their respective housings  31 ,  34 . The bores  48  in each of the poppets  32 ,  40  are thereby moved out of alignment with the bores  50  in each valve housing  31 ,  34 , shearing the line  24   b  into three parts  24   b ′,  24   b ″,  24   b ″′. The bores  48  also move away from the plugs  47 . 
     Furthermore, with the penetrators retracted, shoulders  33  on the poppets  32 ,  40  seal against corresponding shoulders  35  on the valve housings  31 ,  34 . Annular seal elements  64  in the valve housings  31 ,  34  on either side of the bores  50  seal against the respective poppets  32 ,  40  to close off the bores  50 . The double poppet valve arrangements  30   a ,  30   b  thus provide a double pressure barrier between the external environment and the tubing annulus connected to the bores  26 . Valve housing  31  is sealed within the tubing hanger body  12  and valve housing  34  is sealed to the male penetrator parts  16   a ,  16   b  by annular seal elements  66 . The penetrator male parts  16   a ,  16   b  are slidable in the packings  22  to maintain the tree pressure integrity as previously discussed. 
     With all the penetrator male parts retracted in the manner of part  16   b , FIGS. 1 and 4, the tubing hanger  12  and the attached line parts  24   b ′″ can be pulled from the tree  10 . Poppet  40  and valve housing  34  provide a pressure barrier in the tree  10 , allowing the line parts  24   b ′ to be stripped from the penetrator male parts  16   b  and conduits  28   b  in safety. The short intermediate parts  24   b ″ of the lines  24   b  are allowed to fall into the production casing, to be flushed out later. A replacement line is readily installed with the penetrator male parts returned to the extended position ( 16   a , FIG. 1; FIG. 3) for example using a line feeding reel in a pressure tight housing sealingly connected to the conduits  28   a ,  28   b.    
     It should be recognized that, while the present invention has been described in relation to the preferred embodiments thereof, those skilled in the art may develop a wide variation of structural and operational details without departing from the principles of the invention. Therefore, the appended claims are to be construed to cover all equivalents falling within the true scope and spirit of the invention.

Summary:
A preferably fiber optic line passes into a well interior through a pressure barrier such as a tree or wellhead housing, via a modified horizontal penetrator assembly. The penetrator assembly comprises double poppet valve assemblies arranged to open upon engagement of the penetrator with an interior well component such as a tubing hanger. Retraction of the penetrator closes the poppet valves, sealing the pressure barrier, severing the line and allowing the tubing hanger to be pulled. A replacement line is readily installed through the open poppet valve assemblies.