A deep water subsea tree completion having a distributed temperature sensing system. In a described embodiment, a method of installing an optical fiber in a well includes the steps of: conveying an optical fiber section into the well; and monitoring a light transmission quality of the optical fiber section while the section is being conveyed into the well.

BACKGROUND  
       [0001]     The present invention relates generally to operations performed and equipment utilized in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides methods and apparatus for distributed temperature sensing in deep water subsea tree completions.  
         [0002]     Distributed temperature sensing (DTS) is a well known method of using an optical fiber to sense temperature along a wellbore. For example, an optical fiber positioned in a section of the wellbore which intersects a producing formation or zone can be used in determining where, how much and what fluids are being produced from the zone along the wellbore.  
         [0003]     Installation of DTS systems in deep water subsea tree completions could be made less risky and, therefore more profitable, if a fault in a light path of the optical fiber could be identified prior to final installation of the optical fiber in the well. This would enable the fault to be remedied before the riser is removed and the tree is installed. Presently, faults in the optical fiber light path are discovered after the tree is installed, at which time it is very difficult, expensive and sometimes cost-prohibitive, to troubleshoot and repair the faults.  
         [0004]     For these reasons and others, it may be seen that it would be beneficial to provide improved methods and apparatus for installation of distributed temperature sensing systems in deep water subsea tree completions. These methods and apparatus will find use in other applications, and in achieving other benefits, as well.  
       SUMMARY  
       [0005]     In carrying out the principles of the present invention, in accordance with an embodiment thereof, an optical fiber installation system and method are provided which decrease the risks associated with distributed temperature sensing in deep water subsea tree completions. The system and method enable a light transmission quality of an optical fiber installation to be monitored while the optical fiber is being installed, thereby permitting faults to be detected quickly.  
         [0006]     In one aspect of the invention, a method of installing an optical fiber in a well is provided. The method includes the steps of: conveying an optical fiber section into the well; and monitoring a light transmission quality of the optical fiber section while the section is being conveyed into the well.  
         [0007]     In another aspect of the invention, a method of installing an optical fiber in a well includes the steps of: conveying an assembly at least partially into the well with an optical fiber section attached to the assembly, the assembly being conveyed on another assembly; monitoring a light transmission quality of the optical fiber section during the conveying step by transmitting light through the optical fiber section; and then disconnecting the assemblies.  
         [0008]     In yet another aspect of the invention, an optical fiber well installation system is provided. The system includes a first assembly conveyed at least partially into the well by a second assembly. An optical connector is attached to each of the first and second assemblies. The optical connectors are connected in order to transmit light through the connected optical connectors between a first optical fiber section attached to the first assembly and a second optical fiber section attached to the second assembly. A light transmitting quality monitor may be connected to the second optical fiber section while the second assembly conveys the first assembly into the well.  
         [0009]     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 a representative embodiment of the invention hereinbelow and the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a schematic partially cross-sectional view of an optical fiber installation system embodying principles of the present invention; and  
         [0011]      FIG. 2  is a schematic partially cross-sectional view of the system of  FIG. 1 , in which additional steps of an optical fiber installation method have been performed. 
     
    
     DETAILED DESCRIPTION  
       [0012]     Representatively illustrated in  FIG. 1  is an optical fiber installation 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.  
         [0013]     In the system  10  and associated method, a completion assembly  12  is installed in a wellbore  14 . The completion assembly  12  may be gravel packed in the wellbore  14 , in which case the assembly may include a tubular completion string  16  with a well screen  20  suspended below a packer  18 . However, it is to be clearly understood that other types of assemblies and other types of completions may be used in keeping with the principles of the invention.  
         [0014]     The assembly  12  further includes a section of optical fiber  22  extending downwardly from an optical connector  24  attached at an upper end of the assembly, through the packer  18 , and exterior to the screen  20  through a portion of the wellbore  14  which intersects a formation or zone  26 . The section  22  could instead, or in addition, be positioned internal to the screen  20 , as depicted for section  30 , which extends downwardly from the connector  24  and into the interior of the string  16 . The section  22  could also, or alternatively, be positioned external to a casing string  32  lining the wellbore  14 , or could be otherwise positioned, without departing from the principles of the invention.  
         [0015]     The zone  26  is in communication with the intersecting portion of the wellbore  14  via perforations  28 . Other means could be provided for communicating between the zone  26  and wellbore  14 , for example, the portion of the wellbore intersecting the zone could be completed open hole, etc.  
         [0016]     The section  22  is used in the system  10  for distributed temperature sensing in the wellbore  14 . For example, the section  22  may be used to determine the temperature of fluid flowing between the zone  26  and the wellbore  14  in the portion of the wellbore intersecting the zone. The temperature of the fluid may be determined at distributed locations along the intersection between the wellbore  14  and the zone  26 , in order to determine where, how much and what fluids are being produced from, or injected into, the zone along the wellbore.  
         [0017]     A production tubing assembly  34  is conveyed into the wellbore  14  by use of a work string assembly  36  to suspend the production tubing assembly from a rig (not shown) positioned above a subsea wellhead  38 . The production tubing assembly  34  is conveyed by the work string assembly  36  through a riser  40  connecting the rig to the wellhead  38 , through the wellhead, and into the wellbore  14 . The work string assembly  36  includes a tubular work string  42  having a releasable connection  44  at a lower end.  
         [0018]     The production tubing assembly  34  includes a production tubing string  46  having an anchor  48  at an upper end, a seal  50  at a lower end, and a telescoping travel or extension joint  52  between the ends. As schematically depicted in  FIG. 1 , the anchor  48  is a tubing hanger which engages a shoulder  54  to secure the tubing string  46  in the wellbore  14 . The releasable connection  44  is a hanger running tool which, for example, uses a releasable latch to disconnect the work string  42  from the tubing string  46  after the tubing hanger  48  has been “set” by engaging the shoulder  54 .  
         [0019]     Other types of anchors and other means of setting anchors may be used in keeping with the principles of the invention. For example, the anchor could include slips which grip the wellbore  14  to set the anchor, the anchor could include a latch which engages a corresponding profile, etc.  
         [0020]     The travel joint  52  permits the seal  50  to engage a seal bore  56  at an upper end of the completion string  16  prior to the anchor  48  engaging the shoulder  54 . After the seal  50  is received in the seal bore  56 , the travel joint  52  allows the tubing string  46  to axially compress somewhat as the anchor  48  continues displacing downwardly to engage the shoulder  54 . This configuration is depicted in  FIG. 2 , wherein it may be seen that the seal  50  is sealed in the seal bore  56 , and the anchor  48  is engaged with the shoulder  54 .  
         [0021]     When the work string  42  has been disconnected from the tubing string  46 , the work string is retrieved from the well. The riser  40  is removed, and a tree  58  is installed on the wellhead  38  to connect the well to a pipeline  60 . Note that, if a fault is discovered in the system  10  after the tree  58  is installed, it will be very difficult, time-consuming and, therefore, expensive to troubleshoot and repair the system.  
         [0022]     However, in a very beneficial feature of the system  10 , faults in the system can be detected during installation when the faults are far easier to troubleshoot and repair. As depicted in  FIG. 1 , the work string  42  has a section of optical fiber  62  attached thereto. The optical fiber section  62  is coupled to an optical connector  64  at the lower end of the work string  42 .  
         [0023]     The optical connector  64  is connected to another optical connector  66  at an upper end of the production tubing string  46 . Preferably, the connector  66  is positioned above the anchor  48 , for convenient connection to the connector  64 , and for reasons that are described more fully below. Another optical fiber section  68  is coupled to, and extends between, the connector  66  and another optical connector  70  at a lower end of the tubing string  46 .  
         [0024]     As the tubing string  46  is conveyed into the wellbore  14  by the work string  42 , the upper optical fiber section  62  is optically connected to the section  68  via the connected connectors  64 ,  66 . A light transmitting quality (such as an optical signal transmitting capability, or optical signal loss) of the sections  62 ,  68  and/or connectors  64 ,  66  may be monitored by connecting a monitor  72  to the section  62  and transmitting light from the monitor, through the section  62 , through the connectors  64 ,  66 , and into the section  68 . For example, the monitor  72  may include a light transmitter (such as a laser) for transmitting light into the section  62 , an electro-optical converter (such as a photodiode) for receiving light reflected back to the monitor and converting the light into electrical signals, and a display (such as a video display or a printer) for observing measurements of the light transmitting quality indicated by the signals.  
         [0025]     If there is a fault in the sections  62 ,  68  or connectors  64 ,  66 , the monitor  72  can detect the fault before or after the anchor  48  is set, and preferably before the work string  42  is disconnected from the tubing string  46 . Of course, it would be very beneficial to detect a fault before the anchor  48  is set, since the tubing string  46  could fairly easily be retrieved from the well for repair at that point. It would also be beneficial to use the monitor  72  to verify the light transmitting quality of the sections  62 ,  68  and connectors  64 ,  66  after the anchor  48  is set, for example, to check for faults which may have occurred due to the anchor setting process, or due to other causes. Furthermore, it is desirable to use the monitor  72  to measure the light transmitting quality of the system  10  prior to disconnecting the work string  42  from the tubing string  46 , and retrieving the work string from the well.  
         [0026]     The monitor  72  may also be used to measure the light transmitting quality of the optical fiber section  22  after the connector  70  has been connected to the connector  24 . This connection between the connectors  24 ,  70  is made when the tubing string  46  is conveyed into the wellbore  14  and the lower end of the tubing string engages the upper end of the completion string  16 . This engagement connects the connectors  24 ,  70  and optically connects the sections  68 ,  22 . For example, a rotationally orienting latch  74  may be used at the lower end of the tubing string  46  to align the connectors  24 ,  70  when the tubing string engages the completion string  16 .  
         [0027]     By monitoring the light transmitting quality of the connectors  24 ,  70  using the monitor  72 , the optical connection between the sections  68 ,  22  may be verified before the anchor  48  is set. If the light transmitting quality of the connection between the connectors  24 ,  70  is poor, indicating that the connectors may not be fully engaged, or that debris may be hindering light transmission between the connectors, etc., then the connectors  24 ,  70  may be repeatedly disengaged by raising the tubing string  46 , and then re-engaged by lowering the tubing string, until a good light transmitting quality through the connectors is achieved.  
         [0028]     Of course, in this process a fault may be detected in another part of the system  10 . For example, a fault could be detected in the section  22  while the light transmitting quality of the connectors  24 ,  70  is being monitored. Thus, it may be seen that the light transmitting quality of any element of the system  10  may be monitored while the light transmitting quality of any other element, or combination of elements, is monitored at the same time.  
         [0029]     After the light transmitting quality of each of the sections  68 ,  22  and/or connections between the connectors  24 ,  70  and/or connectors  64 ,  66  have been verified, the work string  42  is disconnected from the tubing string  46 . The disconnection of the work string  42  may be accomplished in any manner, such as by raising the work string, rotating the work string, etc. If the work string  42  is to be rotated, then an optical swivel (not shown) may be used on the work string to permit at least a portion of the work string to rotate relative to the connector  64 . A suitable optical swivel is the Model 286 fiber optic rotary joint available from Focal Technologies Corporation of Nova Scotia, Canada.  
         [0030]     This disconnection of the work string  42  from the tubing string  46  also disconnects the connectors  64 ,  66  from each other. The work string  42  is then retrieved from the well. The riser  40  is removed and the tree  58  is installed as depicted in  FIG. 2 .  
         [0031]     The tree  58  has another optical fiber section  76  extending through it between an optical connector  78  and another monitor  80 . The monitor  80  may actually be a conventional distributed temperature sensing optical interface, which typically includes a computing system for evaluating optical signals transmitted through an optical fiber in a well. Thus, by connecting the connectors  78 ,  66 , the section  76  is placed in optical communication with the section  22 , permitting distributed temperature sensing in the portion of the wellbore  14  intersecting the zone  26 . The positioning of the connector  66  above the anchor  48  enables convenient connection between the connectors  78 ,  66  when the tree  58  is installed.  
         [0032]     The monitor  72  may also be a conventional distributed temperature sensing optical interface which is used to monitor the light transmitting quality of the system  10  during installation. The monitor  72  may be the same as the monitor  80 , or it may be a different monitor, or different type of monitor.  
         [0033]     Note that the connectors  24 ,  70 ,  64 ,  66 ,  78  are preferably optical connectors of the type known to those skilled in the art as “wet mate” or “wet connect” connectors. These types of connectors are specially designed to permit a connection to be formed between the connectors in a fluid. In the wellbore  14 , the connectors  24 ,  70  are optically connected in fluid, the connectors  64 ,  66  are initially connected and then are disconnected in fluid, and the connectors  66 ,  78  are optically connected in fluid.  
         [0034]     In a manner similar to that described above in which a light transmitting quality of the sections  62 ,  68  and/or connectors  64 ,  66  on the tubing string  46  and work string  42  are monitored during installation of the tubing string, a light transmitting quality of the section  22  and/or  30  and/or connector  24  may be monitored during installation of the completion assembly  12 . For example, the completion assembly  12  could be installed using the work string  42  or another string and, during this installation, light could be transmitted through the section  22  and/or  30  and/or connector  24  (and a connector connected to the connector  24 , and a optical fiber section on the work string, etc.) to monitor a light transmitting quality of these elements. The work string used to install the completion assembly  12  could be a gravel packing string, and the light transmitting quality of the section  22  and/or  30  and/or connector  24  (and a connector connected to the connector  24 , and a optical fiber section on the work string, etc.) could, thus, be monitored during and/or after the gravel packing operation.  
         [0035]     Although the monitoring of a light transmitting quality of a specific number of optical fiber sections  22 ,  30 ,  62 ,  68 ,  76  and associated connectors  24 ,  64 ,  66 ,  70 ,  78  has been described above, it will be readily appreciated that any number of optical fiber sections and connectors may be used, in keeping with the principles of the invention. For example, the tubing string  34  could be installed in multiple trips into the wellbore  14 , in which case additional optical fiber sections and connectors may be used on the separately installed portions of the tubing string, each of which could be monitored during its installation. As another example, formations or zones in addition to the single zone  26  described above could be completed using separate completion assemblies, each of which may have its associated optical fiber section(s) and connector(s), and each of the optical fiber sections and connectors may be monitored during installation. As yet another example, the tubing string  34  and completion assembly  12  could be installed in a single trip into the wellbore  14 , in which case there may be no need for the separate optical fiber sections  68  and  22  and/or  30 , or connectors  24 ,  70 .  
         [0036]     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.