Patent Publication Number: US-2016231523-A1

Title: High temperature fiber optic cable

Description:
FIELD OF THE INVENTION 
     The invention relates to fiber optic cables, and more particularly, to fiber optic cables for use in high temperature or other harsh environments. 
     BACKGROUND 
     With advancements in the area of fiber optic sensors, particularly for use in harsh environments, such as in oil and gas wells, there is an increasing need for fiber optic cables that can survive harsh environments. For example, the harsh environment encountered in subterranean fiber optic sensing applications places demanding requirements on the design of fiber optic cables for use in the subterranean environment. Such a fiber optic cable may be used to interconnect a subterranean fiber optic sensor with instrumentation located at the surface of a well bore. 
     Subterranean environmental conditions can include temperatures in excess of 550° C., hydrostatic pressures in excess of 10 bar, vibration, and corrosive chemistry. Subterranean applications also lead to the requirement that the fiber optic cable be produced in lengths of 1000 m and longer while surviving and functioning in the harsh environments. 
     For certain high temperature applications, metal plating of optical fibers has been proposed to provide protection to the optical fibers, which are placed in metal sheathing. However, upon heating, some metals have been found to adhere to the interior of metal sheathing surrounding the optical fibers, resulting in breakage or other damage to the optical fibers in tensile loading upon cooling. Additionally upon repeated physical cycling of the optical fiber in the metal sheathing, some metal plating from the optical fibers has been found to wear away on the inside of the metal sheathing surrounding the optical fibers. 
     SUMMARY OF THE INVENTION 
     In some embodiments of the present disclosure, a fiber optic cable includes an outer tube, a ceramic fiber sleeve within the outer tube, and an optical fiber having a metal plating within the ceramic fiber sleeve. 
     In a method according to the present disclosure, a fiber optic cable is formed by placing a metal plated optical fiber in a ceramic fiber sleeve, and placing the ceramic fiber sleeve in an outer tube. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a side view of the fiber optic cable of the present disclosure. 
         FIG. 2  is a cross sectional view of the fiber optic cable of  FIG. 1 , taken through line A-A. 
         FIG. 3  is a perspective view of the fiber optic cable of  FIG. 1  within a well bore. 
     
    
    
     DETAILED DESCRIPTION 
     The fiber optic cables described herein may be used in harsh environments, particularly at high temperatures. Optical fibers contained in the fiber optic cables may not be exposed to significant damaging strain over a wide range of operating temperatures. 
     The fiber optic cables may generally include an optical fiber surrounded by a metal plating and a surrounding protective layer. The surrounding protective layer may include an outer tube received over the metal plated optical fiber, and a layer of ceramic material positioned between the outer tube and the metal plated optical fiber, the ceramic material maintaining the metal plated optical fiber generally centrally located within the outer tube and providing a mechanical link between the metal plated optical fiber and the outer tube to prevent relative movement between the fiber and the tube. 
     Referring now to  FIGS. 1 and 2 , a fiber optic cable  10  may include an outer tube  18 , a ceramic fiber sleeve  16  within the outer tube  18 , and an optical fiber  12 . The optical fiber  12  may be a polymer fiber within the ceramic fiber sleeve  16  without plating thereon. Alternatively, the optical fiber  12  may have a metal (e.g., gold, silver, etc.) plating  14  within the ceramic fiber sleeve  16 . The metal plating  14  may surround one or more optical fibers  12  in the ceramic fiber sleeve  16 . The diameter of the optical fiber  12  may be in the range of 0.01 mm to 0.2 mm, and in an exemplary embodiment may be 0.1 mm. Although the optical fiber  12  is described as being 0.01 mm to 0 2 mm in diameter, the diameter of the optical fiber  12  may vary over a large range, depending upon the materials used and the number of optical fibers  12  to be placed in the fiber optic cable  10 . Similarly, the outer diameter of the metal plating  14  of the optical fiber  12  may be in the range of 0.05 mm to 0.5 mm, and in an exemplary embodiment may be 0.01 mm. Although metal plating  14  is described as being 0.05 mm to 0.5 mm in diameter, the diameter of the metal plating  14  may vary over a large range, depending upon the number of optical fibers  12  to be placed in the fiber optic cable  10 . The metal plating  14  wall thickness may be selected to be sufficient for high temperature performance of the optical fiber  12 . 
     The fiber optic cable  10  may operate without the metal plating  14  adhering to the outer tube  18  in temperatures up to 550° C. However, the fiber optic cable  10  may be used over a wider temperature range, depending on the selection of ceramic material in a ceramic fiber sleeve  16 . Additionally, the ceramic fiber sleeve  16  may allow the optical fiber  12  and the metal plating  14  to relax and straighten with respect to an outer tube  18  due to differences in the coefficients of thermal expansion between the metal plated optical fiber  12  and the outer tube  18  and during spooling and deployment of the fiber optic cable  10 . The viscosity of the ceramic fiber sleeve  16  may widely vary, depending on the specific cable design, including the diameter of the metal plated optical fiber  12  and the number of optical fibers in the fiber optic cable  10 . The ceramic fiber sleeve  16  may also provide additional benefits of preventing chaffing of the metal plating  14  on the optical fiber  12  as a result of bending action during installation and vibration of the fiber optic cable  10 . The ceramic fiber sleeve  16  may also serve as an integrator of metal plated optical fiber surface roughness to avoid microbend losses in the optical fiber  12 . Suitable ceramic materials for use in the ceramic fiber sleeve  16  include 3M™ Nextel™ Braided Sleeving  312 , 3M™ Nextel™ Braided Sleeving  440 , other 3M™ Nextel™ Braided Sleeving, alumina magnesia silicate, any other material made of silica, or other ceramic based material that is stable at high temperatures. 
     Referring now to  FIG. 3 , the fiber optic cable  10  may be used in a wellbore  20  of and oil, gas, or other hydrocarbon bearing well. The optical fiber  12  may be selected to provide reliable transmission of optical signals between a first end  22  and a second end  24  of the fiber optic cable  10 , such as between a pulsed light source  26  and a light sensor assembly  28  positioned within the wellbore  20 . The light source  26  and/or the light sensor assembly  28  may be coupled with optical signal processing equipment either downhole or at the surface. Suitable optical fibers  10  may include fibers such as those used by distributed sensing vendors such as Quorex and Sensornet, any other distributed sensing optical fiber, or any other optical fiber suitable for use in a high temperature environment. Multiple optical fibers  12  may be included in a fiber optic cable, of which any two optical fibers  12  may be of the same type or of different types. Although the embodiments described use a single optical fiber  12  with metal plating  14 , it will be understood by those skilled in the art that more fibers may be used. The total number of fibers within the metal plating  14  or within the ceramic fiber sleeve  16  may be limited by the diameter of the metal plating or the ceramic fiber sleeve  16  such that sufficient space is provided within the outer tube  18  to prevent microbending of the optical fiber  12  during handing and deployment of the fiber optic cable  10 . 
     The metal plated optical fiber  12  may be surrounded by a ceramic fiber sleeve  16  and an outer tube  18 . For example, Ceramic Textiles and Composites (3M™ Nextel™  440  Braided Sleeving). The ceramic fiber sleeve  16  may provide a mechanical link between the metal plated optical fiber  12  and the outer tube  18  to prevent the metal plated optical fiber  12  from sliding under its own weight within the outer tube  18 . Additionally, the ceramic fiber sleeve  16  may keep the metal plated optical fiber  12  generally centered within the outer tube  18  and protect the optical fiber  12  and metal plating  14  from damage due to vibration. Suitable ceramic materials may include materials that are non-wetting to molten metal, so as to provide a barrier to prevent the metal plated optical fiber  12  from adhering to the outer tube  18  at high temperatures. In addition, suitable ceramic materials may include materials that reduce friction between the metal plating  14  and the outer tube  18 , or other materials providing benefits in view of the present disclosure. For example, ceramic materials may include boron nitride or other suitable materials. The fibers of the ceramic fiber sleeve  16  may be braided, tied, or otherwise woven together, such that the ceramic fiber sleeve  16  includes woven ceramic fibers. Woven ceramic fibers may be prefabricated or ceramic fibers may be braided around metal plated optical fiber  12  inline. Depending on the construction and the desired application, the ceramic fiber sleeve  16  may have varying degrees of stiffness. For example, the ceramic fiber sleeve  16  may be flexible. 
     In one exemplary embodiment, the ceramic fiber sleeve  16  is placed between a 0.05-0.125 mm diameter metal plated optical fiber  12  and an 2.8 mm inner diameter outer tube  18  having a 2.8 mm inner diameter and a 3.2 mm outer diameter, in which case, the ceramic fiber sleeve  16  may have a thickness in the range of 1 mm to 2.8 mm, preferably 1.6 mm. Although a range of ceramic fiber sleeve  16  thickness is described, any suitable thickness of ceramic fiber sleeve  16  may be used, depending of the dimensions of the metal plated optical fiber  12  and outer tube  18 , to provide the desired mechanical protection of the metal plated optical fiber  12  and/or to provide the mechanical linkage between the metal plated optical fiber  12  and the outer tube  18  to prevent relative movement therebetween. 
     The outer tube  18  may be manufactured of a heat and/or corrosion resistant material. For example, the outer tube  18  may be manufactured of stainless steel, Incolloys, or other metals. The outer tube  18  may be provided in a standard diameter (after draw down if applicable), such as 3.2 mm outer diameter and 2.8 mm inner diameter, and may have a diameter in the range of 1 mm to 8 mm. The outer tube  18  may have a wall thickness in the range of 0.1 mm to 2 mm. 
     The optical fiber  12  may be coated/plated with metal via painting, electroplating, or other methods useful for applying metal to an optical fiber. After the optical fiber  12  has been coated/plated with the metal plating  14 , the metal plated optical fiber  12  may be placed in the ceramic fiber sleeve  16  and the ceramic fiber sleeve  16  may be placed in the outer tube  18 . Placing the metal plated optical fiber  12  in the ceramic fiber sleeve  16  may be via threading the metal plated optical fiber  12  through the ceramic fiber sleeve  16 , which may be formed in advance of placing the metal plated optical fiber  12  therein. Such threading of the optical fiber  12  into the ceramic fiber sleeve  16  may be done manually or automated, and may involve inserting a wire or other tension member into the ceramic fiber sleeve  16 , attaching the tension member to the metal plated optical fiber  12 , and applying tension to the tension member, thus pulling the metal plated optical fiber  12  into the ceramic fiber sleeve  16 . Alternatively, the ceramic fiber sleeve  16  may be formed about the metal plated optical fiber  12  via braiding or winding ceramic fibers or a sheet formed of ceramic fibers around the metal plated optical fiber  12  while simultaneously forming the ceramic fiber sleeve  16 , or by otherwise encasing the metal plated optical fiber  12  within the ceramic fiber sleeve  16 . For example, the ceramic fibers may be braided about the metal plated optical fiber  12  in a manner similar to that used to form a woven copper shield about a plastic sheath in a coaxial cable. In various methods of placing the metal plated optical fiber  12  in the ceramic fiber sleeve  16 , a lubricant may be used to reduce friction between the metal plated optical fiber  12  and the ceramic fiber sleeve  16 . Suitable lubricants may include boron nitride, other high temperature ceramic lubricant powders, or other friction reducers. The lubricant may be applied to the exterior of the metal plating  14  of the optical fiber  12 , to the interior of the ceramic fiber sleeve  16 , or both. 
     Placing the ceramic fiber sleeve  16  in the outer tube  18  may be via threading the ceramic fiber sleeve  16  through the outer tube  18 , which may be formed in advance of placing the ceramic fiber sleeve  16  therein. Such threading of the ceramic fiber sleeve  16  into the outer tube  18  may involve a process similar to that described above for threading of the optical fiber  12  into the ceramic fiber sleeve  16 . Alternatively, the outer tube  18  may be formed about the ceramic fiber sleeve  16  via TIG weld, laser weld, or other suitable process for joining the outer tube  18  over the ceramic fiber sleeve  16  while simultaneously forming the outer tube  18 . In various methods of placing the ceramic fiber sleeve  16  in the outer tube  18 , a lubricant may be used to reduce friction between the ceramic fiber sleeve  16  and the outer tube  18 . Suitable lubricants may include boron nitride, or other friction reducers. The lubricant may be applied to the exterior of the ceramic fiber sleeve  16 , the interior of the outer tube  18 , or both. Application of the lubricant may involve sprinkling of a fine powder as the threading takes place. 
     Systems and methods may include the use of the fiber optic cables  10  described above. One such system may include the outer tube  18 , the ceramic fiber sleeve  16  within the outer tube  18 , and a metal plated optical fiber  12  within the ceramic fiber sleeve  16 . The system may also include the pulsed laser light source  26  at the first end  22  of the optical fiber  12  and the light sensor assembly  28  at the second end  24  of the optical fiber  12 . The pulsed laser light source may be configured to transmit light pulses from the first end  22  of the optical fiber  12  to the light sensor assembly  28  at the second end  24  of the optical fiber  12  and the light sensor assembly  28  may be configured to receive light pulses from the pulsed laser light source  26 . The light sensor assembly may be coupled with the optical signal processing equipment either downhole or at the surface. The optical signal processing equipment may be configured to process signals received by the light sensor assembly  28  to determine a variety of values for variables such as temperature, pressure, strain, sound or other conditions for which a measurement is desired in conjunction with optical fibers. 
     The fiber optic cables  10  described above may be used to measure a value of a variable. For example, a method of measuring a value of a variable may include providing the optic cable  10  including the optical fiber  12 , allowing the pulsed laser light source  26  to transmit light pulses from the first end  22  of the optical fiber  12  to the light sensor assembly  28  located at the second end  24  of the optical fiber  12 . The method may also include allowing the light sensor assembly  28  to receive light pulses from the pulsed laser light source  26 , and, based on the received light pulses, the method may include calculating the value of the variable. Such calculation may be done via the optical signal processing equipment or otherwise. In some applications, the variable for which a value is to be measured is temperature. More particularly, the value to be measured may be a temperature in excess of 750° C. or even a temperature in excess of 2400° F. 
     Those of skill in the art will appreciate that many modifications and variations are possible in terms of the disclosed embodiments, configurations, materials, and methods without departing from their scope. Accordingly, the scope of the claims and their functional equivalents should not be limited by the particular embodiments described and illustrated, as these are merely exemplary in nature and elements described separately may be optionally combined.