Abstract:
A wireline cable includes an electrically conductive cable core for transmitting electrical power, an inner armor layer disposed around the cable core, and an outer armor layer disposed around the inner armor layer, wherein a torque on the cable is balanced by providing the outer armor layer with a predetermined amount of coverage less than an entire circumference of the inner armor layer, or by providing the outer armor layer and the inner armor layer with a substantially zero lay angle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/497,142, filed May 9, 2012, which is a 371 of International Application No. PCT/US2010/049783, filed Sep. 22, 2010, which claims benefit of U.S. Provisional Patent Application Ser. No. 61/277,219, filed Sep. 22, 2009. Each of the aforementioned related patent applications is herein incorporated by reference. 
    
    
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     The invention is related in general to wellsite equipment such as wireline surface equipment, wireline cables and the like. 
     Deviated wells or wellbores often include extensive horizontal sections in additional to vertical sections. During oilfield operations, it can be particularly difficult to advance tool strings and cables along these horizontal sections. While tool strings descend by gravity in vertical well sections, tractor devices, which are attached to the tool strings are used to perform this task in the horizontal sections, such as those shown in  FIG. 1 . 
     In particular,  FIG. 1  illustrates a downhole tractor assembly  100  including a tractor  102  coupled to a tool string  104  and a cable  106  coupled to the tool sting  104  opposite the tractor  102 . In operation, the tractor  102  pulls the tool string  104  and the cable  106  along a horizontal well section, while a swivel connection  108  coupled between the tool string  104  and the cable  106  minimizes a rotation of the cable caused by a rotation of the tractor  102  and tool string  104 . 
     Several problems are associated with tractor or tractoring operations including torque imbalances in wireline cables that may lead to knotting or bird caging during sudden releases of cable tension. Uneven surfaces of wireline cables can abrade or saw into bends in well casings, which may damage the cable and well casing or cause the cable to become stuck. 
     A weight of the wireline cables imparts a drag on the tractor and the associated equipments such as a tool string and the like. The speed of travel of the tractor, therefore, is limited by the cable weight. The longer and/or more deviated the well, the more power the tractor requires in order to pull the weight of the cable and associated equipment. 
     A typical wireline cable with metallic armor wires on the outside diameter thereof has high friction with the wellbore including the casing and the like. Much of the power of the tractor, therefore, is used to overcome the friction between the cable and the wellbore. Due to the high friction between the cable and the wellbore a greater pulling power at the surface is also needed in the event of a tractor failure, wherein the cable is used as a life line to pull the tractor assembly out of the well. 
     Typical wireline cables have about 98% coverage in their outer armor wire strength member layer to fill the armor wire layer to be able to handle the cable and provide protection for the cable core. Due to this coverage, torque imbalances are inherent in this type of wireline cable, which may cause the cable to rotate during changes in the cable tension. 
     As the tractor travels down the well it may take a tortuous path and that can rotate the cable. To avoid rotating the cable, a swivel connection is used to connect the cable to the tool string to isolate the tool string from this type of torque. Because torque is generated in the cable when under tension, during a sudden release of that tension, the swivel allows the cable to spin, which can result in opening up of the outer armor wires (i.e. birdcaging) and may disadvantageously cause the cable to loop over itself within the casing. 
     Mono-cables with alloy armor wires typically comprise a single insulated copper conductor at the core for both electrical transmission and telemetry functions. With mono-cables, electric power is transmitted down the central, insulated power conductor and the electric power returns along the armor. However, with long length alloy cables, electrical power return on them is not possible as a galvanized steel armor package is utilized and the highly resistive nature of alloy wires, such as MP35N and HC-265, effectively precludes the production of long length mono-cables with alloy armors. In order to overcome the above issue, coaxial cables were introduced. With coaxial cables, the electrical power is transmitted down a central, insulated conductor, and returns along a serve layer of stranded copper wires covered by a thin layer of polymeric insulation located near the outer edge of the cable core. However, both mono-cables and coaxial cables have the same disadvantages during tractoring operations, as disclosed above. 
     It remains desirable to provide improvements in wireline cables and/or downhole assemblies. It is desirable, therefore, to provide a cable that overcomes the problems encountered with current cable designs. 
     SUMMARY 
     Embodiments disclosed herein describe a wireline cable and methods for use with tractors in deviated wells that, when compared to typical wireline cables, is not subject to torque imbalance during tension changes, has a lower coefficient of drag, and is lower in weight, with a high strength-to-weight ratio. 
     In an embodiment, a method comprises: providing a wireline cable, the cable including a cable core and a substantially smooth exterior surface; attaching a tractor to the wireline cable; and introducing the cable into a wellbore, wherein a torque on the cable is balanced and friction between the cable and the wellbore is minimized by the exterior surface. 
     In an embodiment, a cable comprises: an electrically conductive cable core for transmitting electrical power; an inner armor wire layer disposed around the cable core; and an outer armor wire layer disposed around the inner armor wire layer, wherein a torque on the cable is balanced by providing the outer armor layer with a predetermined amount of coverage of the inner armor wire layer. 
     In another embodiment, a cable comprises: an electrically conductive cable core for transmitting electrical power; an inner armor layer disposed around the cable core; and an outer armor layer disposed around the inner armor layer, wherein a torque on the cable is balanced by providing each of the inner armor layer and the outer armor layer with a lay angle of substantially zero. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a schematic representation of a downhole tractor assembly disposed in a wellbore according to the prior art; and 
         FIGS. 2-14  are a radial cross-sectional views, respectively, of embodiments of a wireline cable. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 2 , there is illustrated a torque balanced cable  200  for tractor operations according to a first embodiment of the present invention. As shown, the cable  200  includes a core  202  having a plurality of conductors  204 . As a non-limiting example, each of the conductors  204  is formed from a plurality of conductive strands  206  disposed adjacent each other with an insulator  208  disposed therearound. As a further non-limiting example, the core  202  includes seven distinctly insulated conductors  204  disposed in a hepta cable configuration. However, any number of conductors  204  can be used in any configuration, as desired. In certain embodiments an interstitial void  210  formed between adjacent insulators  208  is filled with a semi-conductive (or non-conductive) filler (e.g. filler strands, polymer insulator filler). 
     The core  202  is surrounded by an inner layer of armor wires  212  (e.g. high modulus steel strength members) which is surrounded by an outer layer of armor wires  214 . The armor wires  212  and  214  may be alloy armor wires. As a non-limiting example the layers  212 ,  214  are contra helically wound with each other. As shown, a coverage of the circumference of the outer layer  214  over the inner layer  212  is reduced from the 98% coverage found in conventional wireline cables to a percentage coverage that matches a torque created by the inner layer  212 . As a non-limiting example the coverage of the outer layer  214  over the inner layer is between about 60% to about 88%. The reduction in the coverage allows the cable  200  to achieve torque balance and advantageously minimizes a weight of the cable  200 . An interstitial void created in the outer layer  214  (e.g. between adjacent ones of the armor wires of the outer layer  214 ) is filled with a polymer as part of a jacket  216 . In the embodiment shown, the jacket  216  encapsulates at least each of the layers  212 ,  214 . As a non-limiting example, that jacket  216  includes a substantially smooth outer surface  218  (i.e. exterior surface) to minimize a friction coefficient thereof. It is understood that various polymers and other materials can be used to form the jacket  216 . As a further non-limiting example, the smooth outer jacket  216  is bonded from the core  202  to the outer surface  218 . In certain embodiments, the coefficient of friction of a material forming the jacket  216  is lower than a coefficient of friction of a material forming the interstices or interstitial voids of the layers  212 ,  214 . However, any materials having any coefficient of friction can be used. 
     In operation, the cable  200  is coupled to a tractor in a configuration known in the art. The cable  200  is introduced into the wellbore, wherein a torque on the cable  200  is substantially balanced and a friction between the cable  200  and the wellbore is minimized by the smooth outer surface  218  of the jacket  216 . It is understood that various tool strings, such as the tool string  104 , can be attached or coupled to the cable  200  and the tractor, such as the tractor  102 , to perform various well service operations known in the art including, but not limited to, a logging operation, a mechanical service operation, or the like. 
       FIG. 3  illustrates a torque balanced cable  300  for tractor operations according to a second embodiment of the present invention similar to the cable  200 , except as described below. As shown, the cable  300  includes a core  302 , an inner layer of armor wires  304 , an outer layer of armor wires  306 , and a polymeric jacket  308 . As a non-limiting example, the jacket  308  is formed from a fiber reinforced polymer that encapsulates each of the layers  304 ,  306 . As a non-limiting example, the jacket  308  includes a smooth outer surface  310  to reduce a frictional coefficient thereof. It is understood that various polymers and other materials can be used to form the jacket  308 . 
     An outer surface of each of the layers  304 ,  306  includes a suitable metallic coating  312  or suitable polymer coating to bond to the polymeric jacket  308 . Therefore, the polymeric jacket  308  becomes a composite in which the layers  304 ,  306  (e.g. high modulus steel strength members) are embedded and bonded in a continuous matrix of polymer from the core  302  to the outer surface  310  of the jacket  308 . It is understood that the bonding of the layers  304 ,  306  to the jacket  308  minimizes stripping of the jacket  308 . 
       FIG. 4  illustrates a torque balanced cable  400  for tractor operations according to a third embodiment of the present invention similar to the cable  200 , except as described below. As shown, the cable  400  includes a core  402  having a plurality of conductive strands  404  embedded in a polymeric insulator  406 . It is understood that various materials can be used to form the conductive strands  404  and the insulator  406 . 
     The core  402  is surrounded by an inner layer of armor wires  408  which is surrounded by an outer layer of alloy armor wires  410 . An interstitial void created in the outer layer  410  (e.g. between adjacent ones of the armor wires of the outer layer  410 ) is filled with a polymer as part of a jacket  412 . In the embodiment shown, the jacket  412  encapsulates at least each of the layers  408 ,  410 . As a non-limiting example, the jacket  412  includes a substantially smooth outer surface  414  to minimize a friction coefficient thereof. It is understood that various polymers and other materials can be used to form the jacket  412 . As a further non-limiting example, the jacket  412  is bonded to the insulator  406  disposed in the core  402 . In certain embodiments, the coefficient of friction of a material forming the jacket  412  is lower than a coefficient of friction of a material forming the insulator  406 . However, any materials having any coefficient of friction can be used. 
       FIG. 5  illustrates a torque balanced cable  500  for tractor operations according to a fourth embodiment of the present invention similar to the cable  400 , except as described below. As shown, the cable  500  includes a core  502  having a plurality of conductive strands  504  embedded in a polymeric insulator  506 . It is understood that various materials can be used to form the conductive strands  504  and the insulator  506 . 
     The core  502  is surrounded by an inner layer of armor wires  508 , wherein each of the armor wires of the inner layer  508  is formed from a plurality of metallic strands  509 . The inner layer  508  is surrounded by an outer layer of armor wires  510 , wherein each of the armor wires of the outer layer  510  is formed from a plurality of metallic strands  511 . As a non-limiting example the layers  508 ,  510  are contra helically wound with each other. An interstitial void created in the outer layer  510  (e.g. between adjacent ones of the armor wires of the outer layer  510 ) is filled with a polymer as part of a jacket  512 . In the embodiment shown, the jacket  512  encapsulates at least each of the layers  508 ,  510 . As a non-limiting example, that jacket  512  includes a substantially smooth outer surface  514  to minimize a friction coefficient thereof. 
       FIG. 6  illustrates a torque balanced cable  600  for tractor operations according to a fifth embodiment of the present invention similar to the cable  400 , except as described below. As shown, the cable  600  includes a core  602  having a plurality of conductive strands  604  embedded in a polymeric insulator  606 . It is understood that various materials can be used to form the conductive strands  604  and the insulator  606 . 
     The core  602  is surrounded by an inner layer of armor wires  608 , wherein each of the armor wires of the inner layer is formed from a single strand. The inner layer  608  is surrounded by an outer layer of armor wires  610 , wherein each of the armor wires of the outer layer  610  is formed from a plurality of metallic strands  611 . As a non-limiting example the layers  608 ,  610  are contra helically wound with each other. An interstitial void created in the outer layer  610  (e.g. between adjacent ones of the armor wires of the outer layer  610 ) is filled with a polymer as part of a jacket  612 . In the embodiment shown, the jacket  612  encapsulates at least each of the layers  608 ,  610 . As a non-limiting example, that jacket  612  includes a substantially smooth outer surface  614  to minimize a friction coefficient thereof. 
       FIG. 7  illustrates a torque balanced cable  700  for tractor operations according to a sixth embodiment of the present invention similar to the cable  300 , except as described below. As shown, the cable  700  includes a core  702  having a plurality of conductors  704 . As a non-limiting example, each of the conductors  704  is formed from a plurality of conductive strands  706  with an insulator  708  disposed therearound. In certain embodiments an interstitial void  710  formed between adjacent insulators  708  is filled with semi-conductive or non-conductive filler (e.g. filler strands, insulated filler). 
     The core  702  is surrounded by an inner layer of armor wires  712  which is surrounded by an outer layer of armor wires  714 . As a non-limiting example the layers  712 ,  714  are contra helically wound with each other. An outer surface of each of the layers  712 ,  714  includes a suitable metallic coating  713 ,  715  or suitable polymer coating to bond to a polymeric jacket  716  encapsulating each of the layers  712 ,  714 . As a non-limiting example, at least a portion of the jacket  716  is formed from a fiber reinforced polymer. 
     In the embodiment shown, an outer circumferential portion  717  of the jacket  716  (e.g. 1 to 15 millimeters) is formed from polymeric material without reinforcement fibers disposed therein to provide a smooth outer surface  718 . As a non-limiting example, the outer circumferential portion  717  may be formed from virgin polymeric material or polymer materials amended with other additives to minimize a coefficient of friction. As a further non-limiting example, a non-fiber reinforced material is disposed on the jacket  716  and chemically bonded thereto. 
       FIG. 8  illustrates a torque balanced cable  800  for tractor operations according to a seventh embodiment of the present invention similar to the cable  400 , except as described below. As shown, the cable  800  includes a core  802  having a plurality of conductive strands  804  embedded in a polymeric insulator  806 . It is understood that various materials can be used to form the conductive strands  804  and the insulator  806 . 
     The core  802  is surrounded by an inner layer of armor wires  808 . The inner layer  808  is surrounded by an outer layer of armor wires  810 . As a non-limiting example the layers  808 ,  810  are contra helically wound with each other. An interstitial void created in the outer layer  810  (e.g. between adjacent ones of the armor wires of the outer layer  810 ) is filled with a polymer as part of a jacket  812 . As a non-limiting example, at least a portion of the jacket  812  is formed from a fiber reinforced polymer. As a further non-limiting example, the jacket  812  encapsulates at least each of the layers  808 ,  810 . 
     In the embodiment shown, an outer circumferential portion  813  of the jacket  812  (e.g. 1 to 15 millimeters) is formed from polymeric material without reinforcement fibers disposed therein to provide a smooth outer surface  814 . As a non-limiting example, the outer circumferential portion  813  may be formed from virgin polymeric material or polymer materials amended with other additives to minimize a coefficient of friction. As a further non-limiting example, a non-fiber reinforced material is disposed on the jacket  812  and chemically bonded thereto. 
       FIG. 9  illustrates a torque balanced cable  900  for tractor operations according to an eighth embodiment of the present invention similar to the cable  400 , except as described below. As shown, the cable  900  includes a core  902  having a plurality of conductive strands  904  embedded in a polymeric insulator  906 . It is understood that various materials can be used to form the conductive strands  904  and the insulator  906 . The core  902  includes an annular array of shielding wires  907  circumferentially disposed adjacent a periphery of the core  902 , similar to conventional coaxial cable configurations in the art. As a non-limiting example, the shielding wires  907  are formed from copper. However, other conductors can be used. 
     The core  902  and the shielding wires  907  are surrounded by an inner layer of armor wires  908 . The inner layer  908  is surrounded by an outer layer of armor wires  910 . As a non-limiting example the layers  908 ,  910  are contra helically wound with each other. An interstitial void created in the outer layer  910  (e.g. between adjacent ones of the armor wires of the outer layer  910 ) is filled with a polymer as part of a jacket  912 . As a non-limiting example, at least a portion of the jacket  912  is formed from a fiber reinforced polymer. In the embodiment shown, the jacket  912  encapsulates at least each of the layers  908 ,  910 . 
     In the embodiment shown, an outer circumferential portion  913  of the jacket  912  (e.g. 1 to 15 millimeters) is formed from polymeric material without reinforcement fibers disposed therein to provide a smooth outer surface  914 . As a non-limiting example, the outer circumferential portion  913  may be formed from virgin polymeric material or polymer materials amended with other additives to minimize a coefficient of friction. As a further non-limiting example, a non-fiber reinforced material is disposed on the jacket  912  and chemically bonded thereto. 
       FIG. 10  illustrates a torque balanced cable  1000  for tractor operations according to a ninth embodiment of the present invention similar to the cable  200 , except as described below. As shown, the cable  1000  includes a core  1002  having a plurality of conductors  1004 . As a non-limiting example, each of the conductors  1004  is formed from a plurality of conductive strands  1006  with an insulator  1008  disposed therearound. In certain embodiments an interstitial void  1010  formed between adjacent insulators  1008  is filled with semi-conductive or non-conductive filler (e.g. filler strands, insulator filler). As a further non-limiting example, a layer of insulative material  1011  (e.g. polymer) is circumferentially disposed around the core  1002 . 
     The core  1002  and the insulative material  1011  are surrounded by an inner layer of armor wires  1012  which is surrounded by an outer layer of armor wires  1014 . A polymer jacket  1016  is circumferentially disposed (e.g. pressure extruded) on to the outer layer  1014  to fill an interstitial void between the members of the outer layer  1014 . As a non-limiting example, that jacket  1016  includes a substantially smooth outer surface  1018  to minimize a friction coefficient thereof. As shown, the jacket  1016  is applied only on the outer layer  1014  and does not abut the core  1002  or the layer of insulative material  1011 . In certain embodiments, the jacket  1016  is not chemically or physically bonded to the members of the outer layer  1014 . 
       FIG. 11  illustrates a torque balanced cable  1100  for tractor operations according to a tenth embodiment of the present invention. As shown, the cable  1100  includes a core  1102  having an optical fiber  1104  centrally disposed therein. A plurality of conductive strands  1106  are disposed around the optical fiber  1104  and embedded in an insulator  1108 . The core  1102  may comprise more than one optical fiber  1104  and/or conductive strands  1106  to define multiple power and telemetry paths for the cable  1100 . 
     The core  1102  is surrounded by an inner strength member layer  1110  which is typically formed from a composite long fiber reinforced material such as a UN-curable or thermal curable epoxy or thermoplastic. As a non-limiting example, the inner armor layer  1110  is pultruded or rolltruded over the core  1102 . As a further non-limiting example, a second layer (not shown) of virgin, UN-curable or thermal curable epoxy is extruded over the inner armor layer  1110  to create a more uniformly circular profile for the cable  1100 . 
     A polymeric jacket  1112  may be extruded on top of the inner strength member layer  1110  to define a shape (e.g. round) of the cable  1100 . An outer metallic tube  1114  is drawn over the jacket  1112  to complete the cable  1100 . As a non-limiting example, the outer metallic tube  1114  includes a substantially smooth outer surface  1115  to minimize a friction coefficient thereof. The outer metallic tube  1114  and the inner armor layer  1110  advantageously act together or independently as strength members. Each of the inner strength member layer  1110  and the outer metallic tube  1114  are at zero lay angles, therefore, the cable  1100  is substantially torque balanced. 
       FIG. 12  illustrates a torque balanced cable  1200  for tractor operations according to an eleventh embodiment of the present invention similar to the cable  1100 , except as described below. As shown, the cable  1200  includes a core  1202  having a plurality of optical fibers  1204  disposed therein. A plurality of conductive strands  1206  are disposed around the optical fibers  1204  and embedded in an insulator  1208 . The core  1202  may comprise more than one optical fiber  1204  and/or conductive strands  1206  to define multiple power and telemetry paths for the cable  1200 . 
       FIG. 13  illustrates a torque balanced cable  1300  for tractor operations according to a twelfth embodiment of the present invention similar to the cable  1100 , except as described below. As shown, the cable  1300  includes a core  1302  having a plurality of optical fibers  1304  disposed therein. A plurality of conductive strands  1306  are disposed around a configuration of the optical fibers  1304  and embedded in an insulator  1308 . 
     The core  1302  is surrounded by an inner strength member layer  1310  which is typically formed from a composite long fiber reinforced material such as a UN-curable or thermal curable epoxy or thermoplastic. As a non-limiting example, the inner armor layer  1310  is pultruded or rolltruded over the core  1302 . As a further non-limiting example, the inner armor layer  1310  is formed as a pair of strength member sections  1311 ,  1311 ′, each of the sections  1311 ,  1311 ′ having a semi-circular shape when viewed in axial cross-section. 
       FIG. 14  illustrates a torque balanced cable  1400  for tractor operations according to a thirteenth embodiment of the present invention similar to the cable  1100 , except as described below. As shown, the cable  1400  includes a core  1402  having an optical fiber  1404  centrally disposed therein. A plurality of conductive strands  1406  are disposed around the optical fiber  1404  and embedded in an insulator  1408 . The core  1402  is surrounded by an inner metallic tube  1409  having a lay angle of substantially zero. It is understood that the inner metallic tube  1409  can have any size and thickness and may be utilized as a return path for electrical power. 
     The polymeric materials useful in the cables of the invention may include, by nonlimiting example, polyolefins (such as EPC or polypropylene), other polyolefins, polyaryletherether ketone (PEEK), polyaryl ether ketone (PEK), polyphenylene sulfide (PPS), modified polyphenylene sulfide, polymers of ethylene-tetrafluoroethylene (ETFE), polymers of poly(1,4-phenylene), polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA) polymers, fluorinated ethylene propylene (FEP) polymers, polytetrafluoroethylene-perfluoromethylvinylether (MFA) polymers, Parmax®, any other fluoropolymer, and any mixtures thereof. The long fiber used in the composite of UN-curable or thermal curable epoxy or thermoplastic may be carbon fiber, glass fiber, or any other suitable synthetic fiber. 
     Embodiments disclosed herein describe a method and a cable design for use of a wireline cable comprising a torque balanced armor wire and very smooth, low coefficient of friction outer surface to be attached to a tractor that will reduce the weight the tractor has to carry, lower the friction the tractor has to overcome to pull the cable and the tool string through the wellbore and to avoid knotting and birdcaging associated with sudden loss of tension on the wireline cable in such operations. 
     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. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood as referring to the power set (the set of all subsets) of the respective range of values. Accordingly, the protection sought herein is as set forth in the claims below. 
     The preceding description has been presented with reference to presently preferred embodiments of the invention. Persons skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structures and methods of operation can be practiced without meaningfully departing from the principle, and scope of this invention. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.