Abstract:
A sensing cable, including an outer cladding; and at least one sensing bundle contained within the cladding, each sensing bundle having a sensing fiber wrapped strain-transmissively by at least one strand. A method of sensing strain is also included.

Description:
BACKGROUND 
     Cables, particularly fiber optic cables, are used ubiquitously in the downhole drilling and completions industry. These cables are used for enabling a variety of downhole conditions and parameters, such as temperature, vibration, sound, pressure, strain, etc. to be monitored. Due chiefly to their pervasive use, there is an ever-present desire in the industry for alternate styles of sensing cables, particularly for enhancing the ability to more accurately sense a specific parameter such as strain. 
     SUMMARY 
     A sensing cable, including an outer cladding; and at least one sensing bundle contained within the cladding, each sensing bundle having a sensing fiber wrapped strain-transmissively by at least one strand. 
     A method of sensing strain including deploying a cable having at least one at least one sensing bundle contained within a cladding, each sensing bundle having a sensing fiber wrapped strain-transmissively by at least one strand; and transmitting strain to the fiber via the at least one strand. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG. 1  is a prospective view of a strain-sensing cable according to an embodiment disclosed herein with a cladding partially stripped off, 
         FIG. 2  is a cross-sectional view of the cable of  FIG. 1 ; and 
         FIG. 3  is a prospective view of a strain-sensing cable according to another embodiment disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
     Referring now to  FIG. 1 , a cable assembly  10  is illustrated. The assembly  10  includes at least one braid or bundle  12  for improving a strain-sensing capability of the cable  10 . Specifically, each of the bundles  12  includes a fiber  14  that is wrapped with or surrounded by a plurality of strands  16 . The fibers  14  are arranged for sensing one or more downhole conditions or parameters such as temperature, pressure, strain, acoustics, etc. In one embodiment, the fibers  14  are optical fibers. In a further embodiment, the fibers  14 , in the form of optical fibers, include fiber Bragg gratings for enabling the aforementioned sensing capabilities. 
     The strands  16  are included to facilitate the transfer of strain directly to the fibers  14  so that the cable  10  can be used, e.g., to measure strain in a tubular string or downhole component. To this end, the strands  16  are wrapped, wound, or secured, e.g., helically, spirally, circumferentially, etc., about each of the fibers  14 . The number of the strands  16  and the number of turns of the strands  16  per unit length of the fibers  14  may vary in different embodiments. In one embodiment, the strands  16  are stainless steel, although it is to be appreciated that other materials can alternatively be used that exhibit good strain transfer capabilities (e.g., resiliency, ductility, etc.) and resistance to downhole conditions (e.g., maintain good strain transmission to the fibers  14  in high temperature or high pressure environments, etc.). 
     Similar to the strands  16  being wrapped or wound about the fibers  14  in each of the bundles  12 , the bundles  12  in the embodiment of  FIG. 1  are wrapped or wound, e.g., helically, spirally, circumferentially, etc., about a core or central wire  18 . The gauge, material, properties, etc. of the central wire  18  can be selected for setting the properties of the cable  10 , such as ductility, flexibility, conformability, radial compression strength, tensile strength, etc. In the illustrated embodiment, the bundles  12  are interspaced about the central wire  18  with a plurality of tubes  20 . It should of course be appreciated that the tubes  20  could be optional in some embodiments and that any number of the tubes  20  and the bundles  12  could be included in any desired arrangement or pattern (e.g., a sequence that is alternating/non-alternating, repeating/non-repeating, randomized, etc.). An internal passageway through ach of the tubes  20  enables, e.g., one or more sensing fibers  22  (e.g., resembling the fibers  14  but without the strands  16 ) to be located within the tubes  20  for sensing a variety of non-strain related properties (e.g., temperature, pressure, acoustics, etc.). In one embodiment, the tubes  20  and the sensing fibers forming assemblies according to known fiber in metal tube (FIMT) techniques by sealing one or more fibers resembling the fibers  22  within the tubes  20 . According to known FIMT techniques, the tubes  20  may be filled with a gel or fluid to aid in the operation of the tubes  20  and/or the cable  10 . It is additionally noted that the tubes  20  also play a role in setting the properties and performance of the cable  10 , for example, by increasing the compressive strength of the cable  10  in order to avoid the cable  10  collapsing in high pressure downhole applications. It is to be appreciated that ones of the tubes  20  could be replaced with solid wires resembling the central wire  18 , that the central wire  18  could be hollow and resemble one of the tubes  20 , or other modifications could be made to the cable  10 . 
     The cable  10  includes a cladding or sheath  24  to further protect and set the properties of the cable  10  as well as to maintain the assembled arrangement of the components (e.g., to maintain the strands  16 , bundles  12 , and tubes  20  being wrapped around their corresponding components). Additionally, a cavity  26  formed by the empty space within the cladding  24  located between the bundles  12 , the central wire  18 , and/or the tubes  20 , can be filled with a polymer or other filler material, e.g., for achieving the aforementioned objectives of the cladding  24 . In one embodiment the filler material in the cavity  26  is a plastic elastomer, such as that marketed under the trade name Hytrel® and made commercially available from E. I. du Pont de Nemours and Company (DuPont). 
     An alternate embodiment is illustrated in  FIG. 3 , namely, a cable  10 ′. The components of the cable  10 ′ generally resemble those in the cable  10  and have thus been numbered in accordance with the above-discussed embodiment where appropriate. While the bundles  12  are spirally wrapped in the cable  10 , a plurality of bundles  12 ′ in the cable  10 ′ extends axially within the cladding  24  in a non-spiraling manner (but otherwise resemble the bundles  12 ). A plurality of tubes  20 ′ are also shown extending axially in a non-spiraling manner, but otherwise resemble the tubes  20  discussed above. For example, the bundles  12 ′ and/or the tubes  20 ′ in the cable  10 ′ may extend straight along the central member  18 , in parallel with the central member  18 , concentrically with the cladding  24  in lieu of the central member  18 , etc. It is noted that a cross-section of the cable  10 ′ would generally resemble the illustration of  FIG. 2 . The cable  10 ′ may have particular benefits, for example, in a shape-sensing application in which strain measurements by the fibers  14  are utilized in calculating or determining the shape of a component about or with which the cable  10  is installed. 
     While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.