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BACKGROUND 
   The present invention relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a hydraulically set concentric packer with multiple umbilical bypass through a piston of the packer. 
   It has long been desired to provide a convenient and economical method of extending umbilicals (such as hydraulic, electrical and/or fiber optic lines) through packers in subterranean wells. The lines could merely pass through the interior of an inner mandrel of a packer, but then the lines would interfere with flow and access through the packer, and the lines would be exposed to damage from tools, abrasive fluids, etc. passing through the packer. 
   One proposed solution to this problem is to install a sleeve within the mandrel, and position the lines between the sleeve and the mandrel. The sleeve would protect the lines from damage. Unfortunately, the presence of the sleeve restricts flow and access through the packer. 
   Another proposed solution is to extend the lines through a sidewall of the inner mandrel or an outer housing of the packer. However, this requires the mandrel or housing to have an increased wall thickness, which reduces the available cross-sectional area in the packer for flow area or, in the case of a hydraulically set packer, for actuator piston area. If the actuator piston area is reduced, then the available setting force is consequently reduced. 
   To provide sufficient piston area where the lines are extended through the outer housing, the housing may be provided with an eccentric bore (i.e., greater wall thickness on one side as compared to an opposite side of the housing). Unfortunately, this either requires the inner mandrel to be offset to one side in the housing (which in turn causes tubing connected above and below the packer to be laterally offset), or requires that the piston also be eccentrically formed. Each of these is undesirable for operational and/or manufacturing cost reasons. 
   Therefore, it will be appreciated that there is a need for improved ways of extending lines through packers and through actuators for packers. These improvements could find use in other applications, as well. 
   SUMMARY 
   In carrying out the principles of the present invention, in accordance with an embodiment thereof, a packer and an associated actuator are provided which conveniently and economically provide for extending lines through the packer and/or actuator in a well. 
   In one aspect of the invention, a packer for use in a subterranean well is provided. The packer includes a piston which displaces to set the packer in the well. A line, such as a hydraulic, electrical or fiber optic line, extends through the piston. The piston preferably has concentric inner and outer diameters, and is concentric with an inner mandrel and an outer housing of the packer. 
   In another aspect of the invention, a packer for use in a subterranean well includes a piston and an outer housing. The outer housing is sealingly engaged with the piston and reciprocably disposed relative to a seal element. Displacement of the outer housing relative to the piston outwardly extends the seal element. A line extends through a wall of the piston. 
   In yet another aspect of the invention, an actuator for a well tool positioned in a subterranean well is provided. The actuator includes a piston reciprocably disposed in the actuator, such that displacement of the piston in response to a pressure differential across a wall of the piston is operative to cause actuation of the actuator. A line extends through the piston wall. 
   These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic partially cross-sectional view of a well tool system embodying principles of the present invention; 
       FIGS. 2A  &amp; B are enlarged scale quarter-sectional views of successive axial sections of a packer used in the system of  FIG. 1 , the packer embodying principles of the invention; 
       FIG. 3  is a further enlarged scale quarter-sectional view of the packer, taken along line  3 — 3  of  FIG. 2B ; and 
       FIGS. 4A–C  are quarter-sectional views of successive axial sections of another packer used in the system of  FIG. 1 , the packer embodying principles of the invention. 
   

   DETAILED DESCRIPTION 
   Representatively illustrated in  FIG. 1  is a well tool system  10  which embodies principles of the present invention. In the following description of the system  10  and other apparatus and methods described herein, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used for convenience in referring to the accompanying drawings. Additionally, it is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of the present invention. 
   As depicted in  FIG. 1 , a production tubing string  12  has been installed in a wellbore  14  for the purpose of producing fluid from a formation or zone  16  intersected by the wellbore. Note that it is not necessary in keeping with the principles of the invention for a production tubing string to be used, or for fluid to be produced from a formation. Other types of tubular strings could be used, fluid could be injected instead of, or in addition to, being produced, etc. Thus, it is to be clearly understood that the system  10  is described herein as merely one example of the vast number of applications for the principles of the invention, which are not limited in any way to the details of the system  10 . 
   A flow control device  18  (such as a valve or choke) is interconnected in the tubing string  12  to regulate flow of the fluids between the formation  16  and the interior of the tubing string. Operation of the flow control device  18  is monitored and controlled from a remote location (such as the earth&#39;s surface or another location in the well) via lines  20  which extend between the remote location and an actuator  22  for the flow control device. For example, the lines  20  could include one or more hydraulic lines to hydraulically operate the actuator  22  or, if the actuator is electrically operated, the lines could include one or more electrical lines. 
   The actuator  22  could include a position sensor to monitor the position of a closure member (such as a sliding sleeve or choke device) of the flow control device  18 . Other sensors, such as temperature sensors, pressure sensors, etc., could be used. The lines  20  could include one or more fiber optic lines to operate the sensors and/or to transmit data from the sensors. Electrical lines could be used for this purpose, as well. 
   It is not necessary for the lines  20  to be connected only to the actuator  22 . The lines  20  could also, or alternatively, be connected to a sensor  24  apart from the actuator  22 . Thus, it should be clearly understood that the lines  20  can be of any type, can be used for any purpose, and can be connected to any type of well tool, in keeping with the principles of the invention. 
   An annulus  26  formed radially between the tubing string  12  and the wellbore  14  is closed off or blocked above and below the flow control device  18  by packers  28 ,  30  interconnected in the tubing string and set in the wellbore. Since at least the upper packer  28  is positioned between the flow control device  18  and the remote location, it is desired for the lines  20  to extend through the packer, without compromising the function of the packer, and without causing extraordinary inconvenience and expense. The lines  20  could also extend through the lower packer  30 , for example, to another flow control device, sensor, etc. below the lower packer, in which case the convenient and economical extension of the lines through the lower packer would also be desirable. 
   The system  10  accomplishes these objectives by providing the packers  28 ,  30  and their associated actuators with a unique method of extending the lines through the packers and their actuators. Examples are described below, but it should be clearly understood that the principles of the invention are not limited to the details of these specific examples. 
   Referring now to  FIGS. 2A  &amp; B, an enlarged quarter-sectional view of the packer  28  is representatively illustrated. In this view, the manner in which a hydraulic line  32 , which has another line  34  therein, extends through the packer  28  can be seen. For example, the line  34  could be an electrical line or a fiber optic line within the hydraulic line  32 . Note that any number of lines, and any types of lines, can extend through the packer  28  in keeping with the principles of the invention. 
   The packer  28  includes an inner tubular mandrel  36  having threaded connections at each end for interconnection in the tubing string  12 . A tubular outer housing  38  is reciprocably disposed relative to an annular piston  40 . The piston  40  is sealingly received in a bore  42  of the housing  38 , and is positioned radially between the mandrel  36  and the housing. The piston  40  is sealingly and rigidly attached to the exterior of the mandrel  36 . 
   An annular seal element  44  is positioned above the housing  38 , between an upper end of the housing and a downwardly facing shoulder  46  on a connector sub  48 . The connector sub  48  is sealingly and rigidly attached to the exterior of the mandrel  36 . 
   The lines  32 ,  34  extend longitudinally through an opening  50  formed through the connector sub  48 . A compression ferrule-type tubing fitting  52  sealingly secures the line  32  to the connector sub  48 . Another such fitting  56  sealingly secures the line  32  at a lower end of the piston  40 . The lines  32 ,  34  extend longitudinally through an opening  60  formed through the piston  40 . 
   To set the packer  28 , a pressure differential is applied longitudinally across a wall  62  of the piston  40 . For example, pressure within the mandrel  36  may be increased by applying pressure to the tubing string  12  at the surface. This pressure is communicated to an upper end of the piston  40  via an opening  64  formed through a sidewall of the mandrel  36 . A lower end of the piston  40  is exposed to pressure in the annulus  26  about the packer  28  via another opening  66  formed through a sidewall of the housing  38 . 
   The difference in pressure across the wall  62  of the piston  40  biases the piston (and mandrel  36 ) downwardly relative to the housing  38 . Alternatively, it could be considered that the difference in pressure biases the housing  38  upwardly relative to the piston  40  (and mandrel  36 ). Shear pins, shear screws, etc. or other conventional releasing devices may be used to prevent relative displacement between the housing  38  and the piston  40  until a predetermined pressure differential is achieved. 
   When the housing  38  displaces upwardly relative to the piston  40 , the seal element  44  will be axially compressed between the upper end of the housing and the shoulder  46 . This axial compression will cause the seal element  44  to extend radially outward into sealing contact with the wellbore  14 , thereby setting the packer  28 . An internally toothed ratchet device  68  grips the exterior of the piston  40  and prevents the housing  38  from displacing downwardly once it has displaced upwardly relative to the piston. 
   Another compression ferrule-type tubing fitting  54  is connected to the ring  58 . However, instead of securing the line  32  to the ring  58 , the fitting  54  sealingly secures a tube  70  to the ring. The tube  70  extends downwardly from the fitting  54  and into the opening  60  in the piston  40 . The tube  70  is sealingly and reciprocably received in the opening  60 . 
   The lines  32 ,  34  extend longitudinally through the tube  70 . As the housing  38  displaces upward relative to the piston  40 , the ring  58 , fitting  54  and tube  70  can also displace upward with the housing. However, since the tube  70  is sealed in the piston  40 , the tube&#39;s wall continues to isolate pressure on the top of the piston (communicated from the interior of the mandrel  36  via the opening  64 ) from pressure in the opening  60 , and from pressure in the annular space  72  above the ring  58  and radially between the mandrel  36  and the housing  38 . 
   Note that the piston  40  has an outer diameter PD which is concentric with an inner diameter Pd of the piston. Each of these diameters PD, Pd is also concentric with inner and outer diameters Md, MD of the mandrel  36 . Similarly, each of these diameters Pd, Pd, MD, Md is concentric with inner and outer diameters Hd, HD of the housing  38 . 
   Thus, the packer  28  does not require any of the mandrel, housing and piston  36 ,  38 ,  40  to be eccentric with respect to any of the others in order for the lines  32 ,  34  to extend through the packer. Yet, the piston  40  is provided with a relatively large piston area and the lines  32 ,  34  are protected within the packer  28 , without restricting flow or access through the mandrel  36 . 
   Referring additionally now to  FIG. 3 , a quarter-sectional view of the packer  28  is representatively illustrated, taken along line  3 — 3  of  FIG. 2B . In this view it may be seen that the packer  28  can include additional lines  74 ,  76 ,  78 ,  80  extending through the wall  62  of the piston  40 . These lines  74 ,  76 ,  78 ,  80  can be any types of lines, and any number of lines may be used. 
   Referring additionally now to  FIGS. 4A–C , a quarter-sectional view of the packer  30  is representatively illustrated. The packer  30  is similar in many respects to the packer  28  described above, and so elements shown in  FIGS. 4A–C  which are similar to those described above are indicated using the same reference numbers. 
   One substantial difference between the packers  28 ,  30  is that the packer  30  includes slips  82  (only one of which is visible in  FIGS. 4B  &amp; C) for anchoring the packer in the wellbore  14 . Another substantial difference is that a piston  84  of the packer  30  is not rigidly attached to an inner mandrel  86 . Instead, the piston  84  displaces downwardly relative to the mandrel  86  when the packer  30  sets. 
   This downward displacement of the piston  84  relative to the mandrel  86  pushes an upper wedge  88  downward also, causing the slips  82  to be displaced radially outward by inclined surfaces on the upper wedge and on a lower wedge go at a lower end of the slips. The upper wedge  88  is prevented from displacing upward by an internally toothed ratchet  94  once the upper wedge has displaced downwardly relative to the mandrel  86 . 
   Yet another substantial difference is that the packer  30  includes an anti-preset device  92  which prevents setting of the packer until an appropriate pressure level is applied to an upper side of the piston  84  via the opening  64 . Once the pressure level is attained, the device  92  releases and permits the packer  30  to be set. This prevents external loads applied to the packer  30  during run-in from causing the packer to set prematurely. 
   Note that the packer  30  includes a ring  96  which is somewhat similar to the ring  58  of the packer  28 . One or more shear screws  98  releasably secures the ring  96  in position. However, when pressure transmitted to the top of the piston  84  via the opening  64  exceeds pressure in the annulus  26  by a predetermined amount, the screws shear and the ring  96  displaces upward, thereby releasing the anti-preset device  92 . 
   As with the packer  28 , the packer  30  has a concentric piston  84 , mandrel  86  and outer housing  100 . The line  32  extends through the piston  84  within the tube  70 , which isolates pressure in the interior of the tubing string  12  (applied to the top of the piston  84  and the exterior of the tube via the opening  64 ) from pressure in the annulus  26  (applied to the bottom of the piston and to the interior of the tube). 
   Although the above descriptions of the packers  28 ,  30  have indicated that tubing pressure is used to set the packers, it will be readily appreciated that other pressure sources could be used. For example, a propellant could be used, the packers could alternatively be set mechanically (such as by manipulation of the tubing string  12 ), etc. Furthermore, the packers  28 ,  30  could be released using a shear ring, rotation of the tubing string  12 , by milling or cutting, shifting a sleeve, punching a port through the mandrels  36 ,  86  and applying pressure to a chamber, etc., or by any other method. 
   Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the invention, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to these specific embodiments, and such changes are contemplated by the principles of the present invention. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims and their equivalents.

Summary:
A hydraulically set concentric packer with multiple umbilical bypass through the piston. In a described embodiment, a packer for use in a subterranean well includes a piston which displaces to set the packer in the well, and a line extending through the piston. The piston has concentric inner and outer diameters, and is concentric with an inner mandrel and an outer housing of the packer.