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BACKGROUND 
     As the worldwide demand for oil and gas has continued to escalate, the systems used to control and monitor the production of oil and gas wells have continued to increase in sophistication and complexity. It is not uncommon for wells to have a significant number of production zones, and to incorporate multiple sets of monitoring and control systems, each requiring separate sets of communication and control lines between the surface and the downhole equipment located within each production zone. Such communication and control lines may include hydraulic lines, copper electrical lines, and optical fiber lines, just to name a few examples. While techniques do exist for attaching multiple lines to production tubing as they are introduced into the well during the well completion process, the use of expansion joints along the length of the production tubing may limit or even preclude the use of multiple lines. 
     Expansion joints are necessary in extreme environments that subject the production tubing to significant expansion and compression forces such as those found, for example, in offshore wells or in deep wells where the production tubing can be subjected to large variations in temperature both in the surrounding strata and in the product being extracted through the tubing. These temperature variations over very large lengths of production tubing can produce significant variations in tubing length, thus necessitating the use of expansion joints over the length of the production tubing to relieve the stresses created and to avoid damaging the tubing and any production equipment coupled to the tubing. 
     Existing systems using a single control/communication line, such as a ¼″ hydraulic control line attached to the outside of the production tubing from the surface to the downhole equipment being controlled (e.g., a downhole safety valve), are sometimes configured to account for the variations in tubing length at the expansion joint by coiling the control line around the joint, thus allowing the line to coil and uncoil as the joint correspondingly contracts and extends. While it is possible to incorporate such line coils around expansion joints when using a single control/communication line, such coiling may not work with systems that require even as few as two or three lines. This is due to the fact that over time, as the joint contracts and extends, the control/communication lines will tend to become entangled, which over time can damage the lines. If the lines are damaged, it may become necessary to shut the well down and set up a “workover” rig to remove the production tubing and replace the damaged lines. Such repairs are extremely expensive, both in terms of the direct costs of performing the repairs, as well as in terms of lost production due to the significant amount of time it takes to perform the repairs. 
     SUMMARY 
     An expansion joint with one or more communication medium bypass paths is described herein. At least some illustrative embodiments include a first axially flexible cylinder, one or more additional axially flexible cylinders positioned within the first cylinder, a first annular member positioned at a first end of, and coupled to, the first cylinder and the one or more additional cylinders (the first annular member including one or more apertures through said member), and a second annular member positioned at a second opposite end of, and coupled to, the first cylinder and the one or more additional cylinders (the second annular member including one or more apertures through said member). All cylinders concurrently extend and contract in axial length when the first and second annular members are respectively moved away from and towards each other. Annular spaces formed by each of the one or more additional cylinders and an externally adjacent cylinder, together with corresponding apertures of each of the first and second annular members, each provides at least one path for at least one communication medium. 
     At least some other illustrative embodiments include a downhole production tubing system that includes a plurality of tubing segments coupled to each other to provide at least part of a path between one or more production zones within a well and the surface above the well, and an expansion joint that couples at least two of the plurality of tubing segments together. The expansion joint includes a first axially flexible cylinder, one or more additional axially flexible cylinders located within the first cylinder, a first annular member positioned at a first end of, and coupled to, the first cylinder and the one or more additional cylinders (the first annular member including one or more apertures through said member), and a second annular member positioned at a second opposite end of, and coupled to, the first cylinder and the one or more additional cylinders (the second annular member including one or more apertures through said member). All cylinders concurrently extend and contract in axial length when the first and second annular members respectively move away from and towards each other in response to expansions and contractions of at least one of the tubing segments. Annular spaces formed by each of the one or more additional cylinders and an externally adjacent cylinder, together with corresponding apertures of each of the first and second annular members, each provides at least one path for at least one communication medium used for communication between surface equipment and downhole equipment. 
     Other illustrative embodiments of an expansion joint include means for flexibly encapsulating at least one communication medium (the means for encapsulating extending and contracting in a longitudinal direction) and means for securing each of two ends of the means for encapsulating (each end opposed to the other along the longitudinal direction, and each means for securing including at least one means for traversing the corresponding means for securing). Each of the means for securing moves away and towards each other as the means for encapsulating respectively extends and contracts. The means for encapsulating, in conjunction with the at least one means for traversing of each of the means for securing, provides a path through the expansion joint for the at least one communication medium. 
     Still other illustrative embodiments of a downhole production tubing system include a plurality of tubing segments coupled to each other to provide at least part of a path between one or more production zones within a well and the surface above the well, and an expansion joint that couples at least two of the plurality of tubing segments together. The expansion joint includes means for flexibly encapsulating at least one communication medium (the means for encapsulating extending and contracting in a longitudinal direction), and means for securing each of two ends of the means for encapsulating (each end opposed to the other along the longitudinal direction, and each means for securing including at least one means for traversing the corresponding means for securing). Each of the means for securing moves away and towards each other as the means for encapsulating respectively extends and contracts in response to expansions and contractions of at least one of the tubing segments. The means for encapsulating, in conjunction with the at least one means for traversing of each of the means for securing, provides a path through the expansion joint for the at least one communication medium used for communication between surface equipment and downhole equipment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of at least some illustrative embodiments, reference will now be made to the accompanying drawings in which: 
         FIG. 1  shows a simplified diagram of a production well that incorporates several expansion joints along the production tubing, in accordance with at least some illustrative embodiments; 
         FIG. 2A  shows a detailed view of the expansion joint of  FIG. 1 , in accordance with at least some illustrative embodiments; 
         FIG. 2B  shows the expansion joint of  FIG. 1  in various states ranging from fully contracted to fully extended, in accordance with at least some illustrative embodiments; 
         FIG. 3  shows a cross-sectional view of the expansion joint of  FIG. 1  incorporating two hydraulic paths through the joint, in accordance with at least some illustrative embodiments; 
         FIG. 4  shows a cross-sectional view of the expansion joint of  FIG. 1 , incorporating both a hydraulic path and an optical fiber path through the joint, in accordance with at least some illustrative embodiments; and 
         FIG. 5  shows a cross-section view of the expansion joint of  FIG. 1 , incorporating two hydraulic paths and a third optical fiber path through the joint, in accordance with at least some illustrative embodiments. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a simplified completed production well  100  using a production tubing  102  that includes tubing segments  102 A,  102 B,  102 C,  102 D and  102 E, and expansion joints  200 A and  200 B constructed in accordance with at least some illustrative embodiments. The well includes surface casing  124 , secured in place by cement  126 , and production casing  120 , concentrically located within surface casing  124  and secured in place by cement  122 . Production tubing  102  runs the length of production well  100 , from the surface through production zones A and B. Packers  107 A and  107 B are secured to both the inside of production casing  120  and the outside of production tubing  102 , and serve to isolate each production zone. Chokes  108 A and  108 B operate to control the flow of product originating from the perforations within each production zone (perforations  110 A within zone A, and perforations  110 B within zone B, respectively) through production tubing  102 . In the example of  FIG. 1 , choke  108 A is hydraulically controlled via hydraulic control line  106 , and choke  108 B is similarly hydraulically controlled via hydraulic control line  104 . 
     Because production tubing  102  is secured at the top of production casing  120  and at each of packers  107 A and  107 B, expansion and/or contraction of the production tubing (e.g., due to thermal variations along the length of the tubing) can produce significant stress forces on the production tubing and the control lines. To help alleviate such stress forces, expansion joints  200 A and  200 B are inserted along the length of production tubing  102 . Expansion joint  200 A is inserted between tubing segments  102 A and  102 B, and operates to alleviate the stress forces that may develop along production tubing  102  and control lines  104  and  106  between the top of production casing  120  and packer  107 A. Similarly, expansion joint  200 B is inserted between tubing segments  102 C and  102 D to alleviate the stress forces that develop along production tubing  102  and control line  104  between packer  107 A and  107 B. 
     As is evident from  FIG. 1 , the hydraulic fluid within hydraulic control line  104  passes through both expansion joints  200 A and  200 B. Likewise, hydraulic fluid within hydraulic control line  106  passes through expansion joint  200 A. In at least some embodiments, these control lines are constructed of ¼″ metal tubing and are secured to the exterior of production tubing  102 . Control line segments  104 A,  104 B,  106 A and  106 B each couple to expansion joint  200 A, while control line segments  104 C and  104 D couple to expansion joint  200 B. Each expansion joint shown provides a separate, isolated path for the fluid of each control line to which it is coupled, as is described in more detail below. 
       FIG. 2A  illustrates a detailed, cutaway view of an expansion joint  200 , constructed in accordance with at least some illustrative embodiments. Joint  200  includes a telescoping tubular assembly that includes tubular members  213  and  215 . Tubular member  213  has a smaller diameter than tubular member  215 , is concentrically located within tubular member  215 , and is able to move along the central axis of expansion joint  200 . Tubular member  213  includes annular members  211  and  217 , and annular member  217  includes apertures  209  through the annular member to permit fluid flow from one side of the annular member to the other as tubular member  213  moves within tubular member  215 . The travel of tubular member  213  is limited by annular member  217  when expansion joint  200  is fully extended and by annular member  211  when expansion joint  200  is fully contracted. When expansion joint  200  is either fully contracted or fully extended, the forces exerted on the expansion joint (either compressive or tensional) are transferred along tubular members  213  and  215 .  FIG. 2B  illustrates expansion joint  200  while fully contracted, partially extended and fully extended. 
     Continuing to refer to  FIG. 2A , tubular member  215  includes annular member  210  and threaded end  216 , and tubular member  213  further includes threaded collar  218  (threads not shown). Threaded end  216  and threaded collar  218  enable expansion joint  200  to be coupled to tubing segments as shown in  FIG. 1 . Each of annular members  210  and  211  of  FIG. 2A  radially extend beyond the outer diameter of tubular member  215 , allowing each of flexible hollow cylinders  202 ,  204  and  206  to be positioned outside of tubular member  215  and attached to both annular members  210  and  211 . In the example of  FIG. 2A , the flexible cylinders are implemented using bellowed walls. Such bellows may be manufactured using any of a number of techniques (e.g., welding together individual rings). Further, the flexible cylinders may also be implemented using structures other than bellows, and using flexible geometric shapes other than a flexible cylinder. 
     Each pair of adjacent flexible cylinders, together with annular members  210  and  211 , form annular spaces between the cylinders and annular members. In at least some illustrative embodiments, the cylinders are each hermetically coupled to the annular members (e.g., using continuous welds around the entire circumference of the joints between the cylinder ends and the annular members). In such embodiments, the resulting annular space is used to transfer fluids, such as the hydraulic fluid passing through control lines  104  and  106  of  FIG. 1 . The transfer of fluids to these annular spaces is accomplished by including apertures within each of annular members  210  and  211  that pass through each member and are aligned with the annular spaces between the flexible cylinders. In the example of  FIG. 2A , these apertures ( 212 A,  212 C,  214 A and  214 C) are extended using threaded tubing attached to the annular members (e.g., ¼″ tubing similar to that used for control lines  104  and  106  of  FIG. 1 ). 
       FIG. 3  illustrates a cross-sectional view of the expansion joint of  FIG. 1 , constructed in accordance with at least some illustrative embodiments. The illustrated expansion joint includes two separate fluid paths that are kept isolated from each other. The first path flows through aperture  214 A in annular member  210 , annular space  214 B between flexible cylinders  202  and  204 , and aperture  214 C in annular member  211 . The second path flows through aperture  212 A in annular member  210 , annular space  212 B between flexible cylinders  204  and  206 , and aperture  212 C in annular member  211 . In at least some illustrative embodiments, the apertures associated with a given flow in each of the annular members are radially located on opposite sides of the cylinder to evenly distribute the fluid flow throughout the annular space. Other positions for, and numbers of, such apertures may also be suitable to implement the claimed expansion joint. 
     As can be seen from  FIGS. 2B and 3 , as the expansion joint extends and contracts, the bellows of the cylinders respectively move radially inwardly and outwardly. This movement, together with the overall radial flexibility of the cylinder walls and the large volume of the annular space relative to the diameter of the control lines, allows the volume of the annular space to remain relatively constant and produces little if any pressure variations in the fluid within the control lines coupled to the expansion joint as the joint extends and contracts. Further, because such movements within the production tubing are gradual over time, any pressure variations that do occur can be compensated using a variety of known pressure control systems and methods. 
     Also, as the expansion joint extends and contracts, and tubular member  213  extends beyond or contracts into tubular member  215 , it is important to maintain the pressure integrity of the telescoping tubular assembly. In at least some illustrative embodiments, at least one seal  224  is located within a groove at the end of tubular member  215  nearest to annular member  211  and around the exterior of tubular member  213  where it protrudes out from tubular member  215 , as shown in  FIG. 3  (as well as  FIGS. 4 and 5 ). Such a seal operates to contain the fluid passing through the expansion joint to the interior of tubular members  213  and  215 , and prevents the loss of pressure and fluid as the expansion joint extends and contracts. 
     Although the embodiments described above illustrate the transfer of hydraulic fluid through the expansion joints, other communication media may also be routed through the expansion joint. For example,  FIG. 4  illustrates a cross-sectional view of an expansion joint that allows both hydraulic fluid and an optical fiber to be routed through the same joint, in accordance with at least some illustrative embodiments. In a manner similar to the example of  FIG. 3 , hydraulic fluid in the example of  FIG. 4  is routed through apertures  212 A and  212 C, as well as annular space  212 B. But an optical fiber  214 D is routed through aperture  214 A, annular space  214 B and aperture  214 C in the example of  FIG. 4 , rather than hydraulic fluid. Optical fiber  214 D is coiled within annular space  214 B so as to allow the fiber to adjust to the changes in the length of the expansion joint without substantially stressing the fiber with tensional forces as the joint extends, and to avoid exceeding the bend radius of the fiber as the joint contracts. In at least some illustrative embodiments of the expansion joint of  FIG. 4  optical fiber  214 D is routed outside the expansion joint within a protective tubing (e.g., ¼″ tubing similar to that used for control lines  104  and  106  of  FIG. 1 , but not shown in  FIG. 4 ) which runs along the outside of production tubing  102  as shown in  FIG. 1  and protects the optical fiber from the extreme conditions present in the downhole environment 
     In at least some illustrative embodiments, spacers are positioned between the cylinder walls within the annular space to prevent the walls from crushing a communication medium routed through the annular space. In the example of  FIG. 4 , spacers  222  are attached to the inside of flexible cylinder  202  such that as the expansion joint contracts, and portions of the bellowed wall of cylinder  202  move closer to portions of the bellowed wall of cylinder  204 , the walls are kept at a minimum distance (i.e., approximately the thickness of spacer  222 , accounting for some possible compression of the spacer), which protects the fiber from either being crushed or flexed beyond its bend radius. While small rectangular spacers are shown in  FIG. 4 , any number of spacers of different sizes and shapes may be suitable for use in at least some illustrative embodiments. Such spacers may also be used within an annular space used to route a fluid (e.g., annular space  212 B) so as to further limit changes in the overall volume of the annular space as the expansion joint extends and contracts. 
     Additionally, while the example of  FIG. 4  shows two annular spaces, one routing a hydraulic fluid and the other routing an optical fiber, any number of annular spaces (limited only by the physical space limitations imposed by the dimensions of a given expansion joint), any number and combination of different types of communication media, and any type of communication media may be suitable for use in at least some illustrative embodiments. Such communication media include, but are not limited to, fluids, optical media, electrical conductors, radio frequency waveguides, acoustical media, and ultrasonic media, just to name a few examples. 
     In another illustrative embodiment shown in  FIG. 5 , the two annular spaces  212 B and  214 B both provide fluid paths through the expansion joint. Optical fiber  216 D provides a third communication medium and is routed through the expansion joint via aperture  216 A, annular space  216 B (between the innermost flexible cylinder and the telescoping tubular assembly) and aperture  214 C. As in the example of  FIG. 3 , optical fiber  216 D of  FIG. 5  is coiled within annular space  216 B so as to allow the fiber to adjust to the changes in the length of the expansion joint without substantially stressing the fiber with tensional forces as the joint extends, and to avoid exceeding the bend radius of the fiber as the joint contracts. In a manner similar to the example of  FIG. 4 , in at least some illustrative embodiments of the expansion joint of  FIG. 5  optical fiber  214 D is routed outside the expansion joint within a protective tubing (e.g., ¼″ tubing similar to that used for control lines  104  and  106  of  FIG. 1 , but not shown in  FIG. 5 ) which runs along the outside of production tubing  102  as shown in  FIG. 1 . 
     To avoid subjecting the flexible cylinder walls to additional stresses caused by pressure differences between the region external to the expansion joint and the region between the innermost flexible cylinder and the telescoping tubing, at least some illustrative embodiments include any of a number of pressure equalization apertures through either or both annular rings  210  and  211  to allow fluid flow between the exterior of the expansion joint and the interior of the innermost cylinder (but external to the tubing). These are shown as apertures  220  in  FIGS. 3 ,  4  and  5 . While shown as straight, cylindrical apertures, various other shapes and routings may also be suitable to form the apertures. Also, while four such apertures are shown relatively positioned at opposite sides of annular rings  210  and  211  in  FIGS. 3 and 4  (and two apertures in  FIG. 5 ), any number of apertures in any of a variety of relative positions may be suitable implementations of the apertures  220 . 
     The above discussion is meant to illustrate the principles and at least some embodiments. Other variations and modifications will become apparent to those of ordinary skill in the art once the above disclosure is fully appreciated. For example, while some of the embodiments describe the use of communication media to operate chokes positioned along a production tubing within a well, the communication media may be used for any type of information exchange between any type of equipment, in any direction, both inside and outside the well. Further, such exchanged information may be used for controlling downhole equipment from the surface, for reporting status and/or data from downhole equipment to the surface, or for exchanging information between multiple pieces of downhole equipment located at different points along the length of the well. It is intended that the following claims be interpreted to include all such variations and modifications.

Summary:
An expansion joint with one or more communication medium bypass paths is described herein. At least some illustrative embodiments include a first axially flexible cylinder, one or more additional axially flexible cylinders positioned within the first cylinder, and first and second annular members each positioned at a opposite ends of, and each coupled to, the first cylinder and the one or more additional cylinders (the first and second annular members each including one or more apertures through each member). All cylinders concurrently extend and contract in axial length when the first and second annular members are respectively moved away from and towards each other. Annular spaces formed by each of the one or more additional cylinders and an externally adjacent cylinder, together with corresponding apertures of each of the first and second annular members, each provides at least one path for at least one communication medium.