Abstract:
A cable which includes conductor bundles prepared from at least one optical fiber positioned either centrally or helically about the center axis of the bundle, metallic conductors helically positioned around the bundles center axis, and a polymeric insulation material. A method of making a cable including forming a conductor bundle by placing helically positioned conductors and optical fibers about the periphery of a central optical fiber or metallic conductor, encasing the conductors, optical fibers, in a polymeric insulation material, and grouping the conductor bundles together.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to electrical and/or optical cables and, in particular to wireline cables having optical fiber(s) therein.  
         [0003]     2. Description of the Related Art  
         [0004]     In the petroleum industry, wireline cables are used to support tools, provide power, and collect data downhole from well-bores. In the case of data collection, the use of optical fibers in electric and/or optical cable offers the potential to carry greater amounts of information than conventional conductors. This is important since at a set diameter, factors such as maximizing data transfer, cable strength, power capacity, and environmental durability are critical to optimum cable design. Optical fibers present certain difficulties such as degradation due to hydrogen exposure, particularly at high temperatures, lack of comparable stretch/strain characteristics as compared with other cable elements, the possibility of volatilization of volatile organic compounds (VOCs) in coatings or other polymeric protective layers on the optical fibers, and hydrolytic attack against glass in the presence of water.  
         [0005]     Electrical and/or optical cables, such as those used in oilfield wireline operations, often include members that provide tensile strength to the cables. Historically, one or more layers of wire comprising a plough or ferritic steel are applied to the outer surfaces of such cables to form strength members. Metallic strength members in cables stretch under load and then return to their original length. Polymeric (un-crosslinked) materials in wireline cables stretch but do not return to their original lengths. Existing designs for fiber optic conductors used in wireline cables have incorporated several measures to protect the fiber optic elements. For example, Schlumberger&#39;s patent “Fiber Optic Cable and Core” (U.S. Pat. No. 4,375,313) places helically wound optical fibers around a polymeric core with additional polymeric material applied over the optical fibers. In this type of design, the polymeric material stretches along with the strength members, and the optical fibers&#39; helical configuration allows them to extend with that stretch. However, when the elongation stress is removed from the cable the polymeric material does not return to its original length, which leads to local stress points and causes signal attenuation. Optical fibers have markedly different deformation characteristics than a cable&#39;s metallic strength members and limited ability to stretch. Thus, a typical mechanical limitation for acceptable performance of optical fiber based cables is the amount of stretch a cable can withstand. The present invention provides cables comprising optical fiber(s) in conjunction with metallic conductors in configurations that avoid mechanical and durability limitations present in the prior art.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     In one aspect of the present invention, a cable is provided which includes conductor bundles prepared from at least one optical fiber positioned either centrally or helically about the center axis of the bundle, metallic conductors helically positioned around the bundles center axis, and a polymeric insulation material.  
         [0007]     In another aspect of the present invention, provided is a cable including a conduit formed from keystone shaped metallic conductors, which surrounds one or more optical fibers and an interstitial filler of low-volatility grease or any suitable gel, and an insulation layer disposed around the tube.  
         [0008]     All of the cable of the invention may optionally include jackets that in a first case surround outer conductors of the conductor bundles and are encased with a polymeric insulating material, or in a second case, the jackets encase the outer periphery of polymeric insulating material.  
         [0009]     A method for making a cable is also provided. The method includes forming a conductor bundle by placing helically positioned conductors and optical fibers about the periphery of a central optical fiber or metallic conductor, encasing the conductors, optical fibers, in a polymeric insulation material, and grouping the conductor bundles together.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a cross-sectional view of a typical prior art cable design.  
         [0011]      FIG. 2  is a cross-sectional view of a prior art optical fiber based cable design.  
         [0012]      FIG. 3  is a cross-sectional view of a first illustrative embodiment of a cable conductor bundle according to the present invention.  
         [0013]      FIG. 4  is a cross-sectional view of a second illustrative embodiment of a cable conductor bundle according to the present invention.  
         [0014]      FIG. 5  is a cross-sectional view of a third illustrative embodiment of a cable conductor bundle according to the present invention.  
         [0015]      FIG. 6  is a cross-sectional view of a fourth illustrative embodiment of a cable according to the present invention.  
         [0016]      FIG. 7  is a cross-sectional view of a fifth illustrative embodiment of a cable conductor bundle according to the present invention.  
         [0017]      FIG. 8  is a cross-sectional view of a sixth illustrative embodiment of a cable conductor bundle according to the present invention.  
         [0018]      FIG. 9  is a cross-sectional view of a seventh illustrative embodiment of a cable conductor bundle according to the present invention.  
         [0019]      FIG. 10  is a cross-sectional view of an eighth illustrative embodiment of a cable conductor bundle according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]     Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.  
         [0021]     The present invention relates to the wireline cables having optical fiber(s) used in conjunction with metallic conductors and uses thereof, particularly for oilfield applications. In general, the metallic conductors are insulated. Commercially available metallic conductors may be used in the present invention. In some embodiments, the metallic conductors are copper. Any cross sectional shape of metallic conductors may be used in the cables of the present invention. Examples of shapes include, but are not limited to, triangular, round, irregular, square, rhombic, trapezoidal, flat, cigar, oval, arch, rectangular, keystone, teardrop, wedge, and the like.  
         [0022]     Any commercially available optical fibers may be used in the present invention. The optical fibers may be single-mode fibers or multi-mode fibers, which are either hermetically coated or non-coated. When hermetically coated, a carbon or metallic coating is typically applied over the optical fibers. Optionally, a further secondary coating, such as, but not limited to, acrylic coatings, silicon/PFA coatings, or polyimide coatings, may be applied over the hermetic coating. An optical fiber may be placed in any location in a standard wireline cable core configuration. Optical fibers may be placed centrally or helically in the cable.  
         [0023]     Placing optical fibers in various positions and areas of the cable creates a wide variety of means to monitor well bore activity and conditions. When the optical fiber is placed in a helical position inside the cable, measurements of downhole physical properties, such as temperature or pressure, among many others, are quickly acquired. Conversely, placing the optical fiber in a central position upon the center axis of the cable allows for strain measurements, although this position may not enable quick physical property measurements.  
         [0024]     Optical fibers are desirable for high data rate transfer, for example 10 Mbps to 1 Gbps versus typically 500 kbps to 1 Mbps for copper conductors. Optical fibers may also enable better separation of power and data transmission, as well as avoiding cross-talk problems associated with metallic conductors.  
         [0025]     A typical technique to introduce optical fibers into wireline cables is using a metal (i.e. stainless steel) tube to contain the optical fibers, as optical fibers are fragile and prone to damage and degradation. Where metallic tubes are used to protect the fibers, the tubes must be strong enough to withstand pressures of up to 207 MPa and temperatures of 320° C. Unfortunately, the size required for this strength and durability deprives valuable space from wireline cable designs, thereby displacing conductor space. Also, such tubes may be damaged when they are pulled over sheaves at very high pull loads. The present invention allows optical fibers to be put in the helical or central conductor of any wireline cable configuration without the need for a metallic tube.  
         [0026]     Also, metallic tubes have limited fatigue life and elastic stretch, typically no more than 0.4%. As the present invention eliminates the need for metal tubes, stretch length may be increased to greater than 1.5%. Further, the use of metallic tubes limits the number of optical fibers that can be contained in a cable. As the present invention eliminates the need for a metal tube, the number of optical fibers may be increased while maintaining or increasing power capacity.  
         [0027]     Also, often optical fibers require splicing when the cable is damaged downhole. When, optical fibers are encased in a metal tube, splicing is not practically feasible. The present invention also overcomes this limitation and enables splicing of the optical fiber at any point along the wireline cable.  
         [0028]     In the embodiments according to the present invention, optical fibers or metallic conductors are placed at the center of helically wrapped conductor bundles. This central metallic conductor or optical fiber is then wrapped with helically positioned metallic conductors and/or optical fibers to create larger conductor bundles, and a polymeric insulation material may encase the bundle. The conductor bundles may then be combined with other conductor bundles to form a cable. In variations of this design, the optical fiber/metallic conductor bundles may be combined with separate helical optical fibers. Metallic wires of any suitable size, or even yarns may be included in the bundles or cables formed from the bundles. Wires and yarns provide compression resistance, and wires may supply additional current capacity. Preferably, the metallic wires are copper conductors. Various configurations of these embodiments may be used to provide attributes such as enhanced packing efficiency, more metallic conductor capacity, greater numbers of optical fibers, and improved stretch characteristics.  
         [0029]     Embodiments of the present invention typically include one or more polymeric insulation materials surrounding outer conductors of a conductor bundle that is capable of withstanding high temperatures. Such materials may include, but are not necessarily limited to, the polyaryletherether ketone family of polymers (PEEK, PEKK), polyolefins (EPC, TPX), fluoropolymers (ETFE, PFA, MFA), or the like. The polymeric insulation material may also be a stacked dielectric, such as those described in U.S. Pat. No. 6,600,108 (Mydur, et al.), hereinafter incorporated by reference.  
         [0030]     Interstitial fillers may further be included in embodiments of the present invention. Interstitial fillers typically occupy those interstitial spaces between the central or outer conductors/optical fibers within a conductor bundle. Interstitial fillers may also occupy interstitial spaces formed between a plurality of conductor bundles, or even between conductor bundles and an outer jacket, such as a tape jacket. Examples of suitable interstitial fillers include ethylene propylene diene monomer (EPDM), nitrile rubber, polyisobutylene, low volatility grease (such as Krytox®), fluoroelastomers, metallic conductors, wires, yarns (TFE, cotton, polyester), any suitable gel, or any combination thereof.  
         [0031]      FIG. 1  depicts a cross-section of a typical cable design used for downhole applications. The cable  100  includes a central conductor bundle  102  having multiple conductors and an outer polymeric insulating material. The cable  100  further includes a plurality of outer conductor bundles  104 , each having several metallic conductors  106  (only one indicated), and a polymeric insulating material  108  (only one indicated) surrounding the outer metallic conductors  106 . Commonly, the metallic conductor  106  is a copper conductor. The central conductor bundle  102  of a typical prior art cables, is essentially the same design as the outer conductor bundles  104 . A tape and/or tape jacket  110  made of a material that may be either electrically conductive or electrically non-conductive and that is capable of withstanding high temperatures encircles the outer conductor bundles  104 . The volume within the tape and/or tape jacket  110  not taken by the central conductor bundle  102  and the outer conductors  104  is filled by a filler  112 , which may be made of either an electrically conductive or an electrically non-conductive material. A first armor layer  114  and a second armor layer  116 , generally made of a high tensile strength material such as galvanized improved plow steel, alloy steel, or the like, surround and protect the tape and/or tape jacket  110 , the filler  112 , the outer conductor bundles  104 , and the central conductor bundle  102 .  
         [0032]      FIG. 2  illustrates a prior art optical fiber based cable designed for oilfield use. The cable  200  replaces the central conductor bundle  102  of  FIG. 1  with a metallic tube  202  containing one or more optical fibers  204  (three shown). The optical fibers  204  are encased in a metal tube  202 , designed to protect the optical fibers  204 . Further, the cable  200  commonly includes interstitial fillers  206  (only one indicated), such as a yarn, to provide compression resistance. While the metal tube  202  offers limited protection, metal tubes are known to be susceptible to mechanical damage, such as plastic stretching, bundling, or cracking, which then leads to cable failure from exposure to conditions presented during downhole deployment. The present invention overcomes this limitation by eliminating the need for such designs.  
         [0033]      FIG. 3  illustrates, in cross section, a first embodiment of an optical fiber conductor bundle according to the present invention. The conductor bundle  300  includes an optical fiber  302  centrally positioned on the center axis of the conductor bundle  300 , and a plurality of metallic conductors  304  (only one indicated) helically positioned around the optical fiber  302 . A polymeric insulating material  306  surrounds the metallic conductors  304 . Further, the volume between the optical fiber  302  and metallic conductors  304  may be filled with an interstitial filler  308 . The conductor bundle  300  may serve as a central conductor bundle, such as the conductor bundle  102  of cable  100  as depicted in  FIG. 1 . Also, the conductor bundle  300  may be positioned in a cable as one or more outer conductor bundles, for example, by replacing the outer conductor bundles  104  in  FIG. 1 .  
         [0034]      FIG. 4  is a cross-sectional view of a second illustrative embodiment of the present invention. The conductor bundle  400  has a plurality of optical fibers  402  (only one indicated) positioned at zero lay angle or any suitable lay angle relative to the center axis of cable  400 , and a plurality of metallic conductors  404  (only one indicated) surrounding the optical fibers  402 , wherein the metallic conductors are positioned at any suitable helical angle. Conductor bundle  400  further contains interstitial fillers  406  (only one indicated), which are preferably yarns, more preferably TlE yarns, as interstitial fillers to round out the center of the conductor bundle  400  and provide compression resistance. The metallic conductors  404  are encased in a polymeric insulating material  408 . As is the case with conductor bundle  300  in  FIG. 3 , conductor bundle  400  may serve as a central and/or outer conductor bundle when used to prepare a cable.  
         [0035]      FIG. 5  represents by cross-section a third illustrative embodiment of a cable according to the present invention. A conductor bundle  500  is formed from keystone shaped metallic wires  502  to form a conductor with a space for optical fibers  504  (only one indicated) and other components at the center of the conductor bundle  500 , as well as providing a compression and collapse resistant conduit that protects the optical fibers  504 . The keystone shaped metallic wires  502  preferably are copper wires, and may be coated with a nickel coating, or any suitable coating, for environmental resistance. One or more optical fibers  504  are then contained in the collapse resistant conduit formed by the keystone shaped wires  502 . The optical fiber(s)  504  may be positioned upon or parallel to the center axis, and orientated at a zero lay angle, or any suitable helical angle. The volume between the optical fiber(s)  504  and keystone shaped metallic wires  502  may be filled with interstitial fillers  506 . Preferably, the interstitial filler  506  is a low volatility compression resistant grease  506 , such as Krytox®, any suitable gel material, or any other low volatility interstitial filler. Further, other interstitial fillers  508 , such as yarns (only one indicated), preferably TFE yarns, may be run in the tube as well. Small copper conductors  510  (only one indicated) may be served around keystone shaped metallic wires  502 , and a polymeric insulation material  512  may be extruded over the exterior to encase and protect the conductor bundle  500 .  
         [0036]      FIG. 6  depicts, in cross-section, a fourth illustrative embodiment of the present invention. The conductor bundle  600  is a composite of smaller conductor bundles containing optical fibers. The conductor bundle  600  includes a central conductor bundle  602  and a plurality of outer conductor bundles  604  (only one indicated). The optical fibers and metallic conductors of the central conductor bundle  602  and outer conductor bundles  604  are configured as described by conductor bundle  300  as depicted in  FIG. 3 , with the exception that they do not have a polymeric insulating material  306  disposed about the outer conductors  304 . Metallic conductors  606  (only one indicated) and  608  (only one indicated) are disposed about the interstitial space of the conductor bundle  600  to provide additional compression resistance and conductor capacity. A polymeric insulation material  610  encases the outer conductor bundles  604  and metallic conductors  608 . The conductor bundle  600  may be used as both central and outer conductor bundles in the configuration of a cable.  
         [0037]     In the embodiment illustrated in  FIG. 7 , the conductor bundle  700  includes optical fibers  702  helically positioned around a central metallic conductor  704 . A plurality of metal conductors  706  (only one indicated) helically surround the central metallic conductor  704 . The metal conductors  706  and optical fibers  702  are surrounded with a polymeric insulation material  708 . The interstitial space  710  formed between the central metallic conductor  704 , the metal conductors  706 , and optical fibers  702 , may further be filled with an interstitial filler. The conductor bundle  700  may be used as central and outer conductor bundles in the configuration of a cable.  
         [0038]     Referring to  FIG. 8 , which illustrates a sixth embodiment of the present invention, conductor bundle  800  includes a central optical fiber  802  positioned on the central axis of the conductor bundle  800 . One or more optical fibers  804  (only one indicated) and a plurality of metal conductors  806  (only one indicated) are positioned helically around the central optical fiber  802 . The conductor bundle further includes polymeric insulation material filler  808 . The interstitial space  810  formed between the central optical fiber  802 , the metal conductors  806 , and optical fibers  804 , may further be filled with an interstitial filler. The conductor bundle  800  may be employed in cable configuration as central and outer conductor bundles.  
         [0039]      FIG. 9  depicts, in cross-section, a seventh illustrative embodiment of the present invention. The conductor bundle  900  may include any combination of optical fibers  902 , metallic conductors  904  (only one indicated), polymeric insulating material  906 , or other components according to the invention. Further, the conductor bundle  900  includes a jacket  908  placed around the outer periphery of the metallic conductors  904 . The jacket  908  may become part of the conductor and also protects the fiber optics from hydrogen, water and other chemical attack. The jacket  908  may be an extrusion of tin and gold alloy solder, any other extrudable metal or metal alloy, or a metallic wrap. The jacket  908  may also be a welded metallic tube that is drawn and shaped around the outer periphery of the metallic conductors  904 . Carbon nanotubes may also be deposited over the jacket  908  as further protection against hydrogen attack. Further, when a metallic wrap forms the jacket  908 , the seams of the metallic wrap may be overlapped or crimped for additional protection against water and chemical incursion. The polymer insulation material  906  is extruded over the jacket  908  to create a fiber optic and electrically insulated conductor. The jacket  908  can be included in any conductor bundle of the present invention.  
         [0040]     Referring to  FIG. 10 , which illustrates an eighth embodiment of the present invention. The conductor bundle  1000  according to the present invention may further include a jacket encasement  1002  encasing the polymeric insulating material  1004 , where the jacket encasement  1002  provides further protection for the conductor bundle  1000 . The conductor bundle can include metallic conductors  1006  (only one indicated), optical fibers  1008  (only one indicated), interstitial fillers  1010  (only one indicated), a polymeric insulating material  1004 , or any other components in accordance with the invention. Copper or other metallic tape may be used to form the jacket encasement  1002 . The jacket encasement  1002  may also be an extrusion of tin and gold alloy solder, any other extrudable metal or metal alloy, or welded metallic tube that is drawn and shaped around the outer periphery of the polymeric insulating material  1004 . When metallic tape is used, the seams of the tape may optionally be overlapped or crimped, and the outer surface of tape may be coated to enhance sealing properties.  
         [0041]     It may also be desirable in certain situations to serve an additional layer of metallic conductors over the outer conductors of a conductor bundle. The additional layer of conductors may be positioned in the same direction or opposite direction as the outer layer. The additional layer of conductors may be positioned at zero lay angle, or any suitable lay angle.  
         [0042]     While particular cable and conductor bundle configurations have been presented herein, cables and conductor bundles having other quantities and configurations of conductors and conductor bundles are within the scope of the present invention. The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.