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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND  
         [0001]    In the hydrocarbon research and recovery industry it is well known that operations are conducted well below the surface of the earth. Controlling such operations has traditionally included control lines comprising elongated metal tubes filled with hydraulic fluid, electric conductors, and/or optic fibers. The control lines must extend as far downhole as needed to provide communication and control with and over a downhole tool. Control lines that are loose on the surface of a tool are prone to be damaged. It is desirable therefore to provide retention of lines, although prior art methods and apparatus for such retention have not met all desired requirements.  
         SUMMARY  
         [0002]    A system for retaining an elongated member at a downhole tool comprises a key and a receiver structure at a downhole tool which is configured and dimensioned to receive at least one elongated member and a key.  
           [0003]    A method for retaining an elongated member at a downhole tool comprises positioning an elongated member in a receiver at the tool; positioning a key at said receiver and expanding the key to bear against the elongated member. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    [0004]FIG. 1 is a schematic side view of a receiver structure and a key for control line retention as disclosed herein;  
         [0005]    [0005]FIG. 2 is a side view of the key showing farther details;  
         [0006]    [0006]FIG. 3 is a top plan view of the key as shown in FIG. 2;  
         [0007]    [0007]FIG. 4 is an end view of the key as shown in FIG. 2;  
         [0008]    [0008]FIG. 4 a  is an alternate end view of the key;  
         [0009]    [0009]FIG. 5 is a cross-section view of the key as shown in FIG. 3 taken along section line  5 - 5 ;  
         [0010]    [0010]FIG. 6 is a cross-section view taken through a schematically illustrated tool having a receiver in four places thereon;  
         [0011]    [0011]FIG. 7 is a longitudinal section of a device shown in FIG. 6;  
         [0012]    [0012]FIG. 8 is a schematic cross-section view of a tool with a receiver structure, control lines, key and expander shown exploded therefrom; and  
         [0013]    [0013]FIG. 9 is the view of FIG. 8 with the expander urged into the key. 
     
    
     DETAILED DESCRIPTION  
       [0014]    With reference to FIG. 1 an assembly to retain a control line is illustrated generally at  10 . A receiver structure  12  is configured and positioned to receive a key  14 . As is visible in one side of receiver structure  12 , a control line profile  16  (a radi used corner square recess) is available to receive about half a control line while control line profile  18  on key  14  would receive the other half. That is to say that control line profiles  16  and  18  when nested define a channel within which a control line is retainable.  
         [0015]    Referring now to FIGS. 2, 3,  4 ,  4   a  and  5  more detailed drawings are introduced with respect to key  14 . It should be noted initially that FIG. 4 a  illustrates an alternate embodiment of key  40  to handle a single control line. Each of the other drawings illustrate a two control line embodiment. In FIG. 4 a , profile  17  will be understood to occupy the space that would otherwise be occupied by a control line. Key  14  is an elongate body constructed of durable material such as metal. In the embodiment specifically illustrated, there are two openings  19  having threads  20  for receiving set screws which are intended to help retain the key (key retainer) in the desired position when a device is assembled. It is to be understood that the number of set screws illustrated is not required, and that one or more set screws may be utilized if desired. In addition, it is not required that set screws be used at all. It is desirable that provision be made for retention of key  14 , the set screws being but one embodiment thereof. Other means for retention may include an interference fit of one or more of the exterior surfaces of the key against complementary one or more surfaces of the receiver structure.  
         [0016]    As it is intended that key  14  be expandable, slot  22  is provided in one embodiment of key  14  in order to allow the key to expand more easily. The slot  22  need only be long enough to facilitate the desired expansion. Key  14  may be expanded by driving any element (expander) having a greater width than slot  22  into that slot. In the illustrated embodiment, two plugs are shown to serve the desired purpose. One of skill in the art will recognize from the illustration that openings  24  are tapered pipe thread openings. As is also understandable by one of ordinary skill in the art, providing the initial diameter of the pipe thread similar to the diameter of the smallest section of the pipe plug (not shown) the key will be spread by the threading in of the plug to openings  24 . The taper is also well visible in FIG. 5. Further features of key  14  are illustrated in each of FIGS. 2, 4, and  5 . Namely, profile  18  is visible in each of the figures.  
         [0017]    Referring now to FIG. 6, receiver structure  12  and profile  16  will be visually understood. Also, referring back to FIG. 1, one of ordinary skill in the art will appreciate that key  14  is moved into receiver structure  12  through opening  26 . Referring to FIG. 7, advantageously receiver structure  12  is tapered on both ends  28  and  30  to reduce the possibility of the downhole tool  32  becoming jammed in the wellbore. In addition, the tapered edges  28  and  30  are helpful with respect to reducing impact on receiver structure  12 , thus reducing the chances that such receiver structure would be damaged during run-in.  
         [0018]    Referring to FIGS. 8 and 9 simultaneously, a completed construction of the device illustrates the cradling of the control lines  34  between profiles  16  and  18  respectively and key  14  in opening  26 . It should be noted that the tallest section of key  14  does not extend beyond the outside diameter  36  of receiver structure  12 . In FIG. 8, plug  38  is illustrated in exploded form above opening  24  whereas in FIG. 9 plug  38  has been threaded into opening  24  to spread key  14  into interference contact with control lines  34 . It should be noted by one of ordinary skill in the art that in FIG. 8 slot  22  has a first dimension whereas in FIG. 9 slot  22  has a larger dimension caused by the insertion of plug  38  and thereby the spreading of key  14 .  
         [0019]    The method for installing the device includes laying control lines within receiver structure  12 , and nesting them in profiles  16 . Key  14  is then tapped into place within opening  26  of receiver structure  12 . Slight insertion force might be required in the event that the control line is slightly bent, however the amount the force required to insert the key into the recess structure  12  is not significant. Once key  14  is fully inserted within recess  12  the two set screws (or other retention mechanism) are tightened to assure that key  14  stays in the desired position. Following securement of key  14  in its desired position, key  14  will be spread by any one of a number of means but as illustrated with two pipe thread plugs threaded into openings  24 . The plugs are desirably threaded in until their uppermost surfaces (as illustrated in FIG. 9) are below the uppermost surface (again as illustrated in the figures of key  14 ).  
         [0020]    An advantage of the illustrated embodiment is that it is entirely reusable since plugs  38  may be removed from key  14  at which point key  14  will return to its predeformed size. As is obvious from the foregoing statement, the expansion of key  14  is not beyond its elastic limit. Another advantage is that vibration created by well operations does not defeat or reduce the retaining capacity of the system.  
         [0021]    While preferred embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.

Summary:
A system for retaining an elongated member at a downhole tool comprises a key, a receiver at a downhole tool which is configurant to mention to receive at least one elongated member and a key.  
     A method for retaining an elongated member at a downhole tool comprises positioning an elongated member in a receiver at the tool, positioning a key at said receiver and expanding the key to bear against the elongated member.