Abstract:
An apparatus for storing cable along a tubular in a wellbore using a first retainer for attachment to the tubular at a first location and a second retainer for attachment to the tubular at a second location. Each retainer is constructed and arranged to reverse the direction of the cable and to at least partially retain the cable due to elastic forces therein. In one embodiment, the cable is formed into a plurality of loops, each having an upper end retained by the first retainer and a lower end retained by the second retainer.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     Embodiments of the present invention generally relate to an apparatus and method for storing cable in a wellbore. 
     Description of the Related Art 
     The installation and operation of permanent control or sensor systems in oil or gas wells (geothermal, CO2 injection wells, etc.) requires the use of cables between the surface of the well and the downhole wellbore equipment for supply of power, control and/or the provision of a conduit for communications. For example, cable may include electrical conductors, hydraulic lines, or fiber optic cables. In most cases, the cable runs along a string of tubulars, like production tubing from downhole equipment to the surface of the well where it extends through a liner hanger or other device that supports the weight of the string. Generally, it is desired to run the cable parallel to the axis of the wellbore tubing with clamps applied to support the cable and hold it parallel to the tubing. 
     It is also common to provide extra cable at an upper end of the tubing string, just below the liner hanger or tubing hanger, to facilitate access to and service of downhole equipment. The additional cable, known as a “service loop”, facilitates the replacement and rework of the downhole components as it provides personnel with extra cable. In one current technique, it is common to wrap numerous turns of the cable around the tubing in order to store it in the wellbore. In applications involving more than one cable, the cables are wound around the tubing side by side. 
     There are a number of difficulties associated with providing a service loop as described above. First, the cables are relatively stiff, so they resist being wound around the tubing and tend to “spring back” when released. In some instances, the cable (and any conductors therein) may break if bent beyond its elastic limit. This can require the involvement of multiple rig personnel when winding the cable. In a typical setting multiple individuals hold the excess cable while encircling the tubing numerous times in order to wrap the cable. The cable also has a minimum bending radius beyond which its mechanical integrity is compromised and great care must be taken not to bend the cable beyond this limit. Additionally, care must be taken to assure the cable is tightly wound around the tubing and does not overlap, as slack cable or overlaps increase the probability that the cable will be damaged during run-in. The process of unwrapping the cable is equally complex, as it must be unwound in a controlled manner to avoid entanglement or damage and to assure that any separate cable remaining on the tubing remains securely wound. 
     There is a need therefore, for an apparatus and method to store cable in a wellbore that overcomes the problems associated with prior art methods and apparatus. 
     SUMMARY OF THE INVENTION 
     The present invention generally teaches an apparatus for storing cable along a tubular in a wellbore using a first retainer for attachment to the tubular at a first location and a second retainer for attachment to the tubular at a second location. Each retainer is constructed and arranged to reverse the direction of the cable and to at least partially retain the cable due to elastic forces therein. In one embodiment, the cable is formed into a plurality of loops, each having an upper end retained by the first retainer and a lower end retained by the second retainer. 
     In another embodiment a method includes anchoring the cable at a first location on an outer wall of the tubular; extending a predetermined length of the cable along the outer wall in a direction substantially parallel to the axis of the tubular; anchoring the cable at a second location and; extending a second predetermined length in the direction of the first anchor location; whereby at each anchor location the cable is at least partially retained by elastic forces in the cable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a side view showing a portion of a tubular having a length of cable stored thereon in a plurality of loops. 
         FIG. 2  is a side view of the tubular illustrating an upper and lower retainer for retaining loops of the cable at an upper and lower end. 
         FIG. 3  is an enlarged view of the upper retainer illustrating formations formed thereon for retaining an upper portion of loops of cable. 
         FIG. 4  is a partial section view of the tubular showing a cover for covering the loops of cable. 
         FIG. 5  is an enlarged view of an upper portion of a retainer having pegs for retaining the loop. 
         FIG. 6  is another embodiment showing an upper portion of a retainer and formations for retaining a loop. 
         FIG. 7  illustrates an upper and lower plurality of loops disposed on a single tubular. 
         FIG. 8  illustrates a plurality of nested loops retained on a single length of tubular. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention generally teaches a method and apparatus for storing cable in a wellbore.  FIG. 1  is a side view showing a portion of a tubular having a length of cable stored thereon in a plurality of loops. In a typical application, a length of cable  5  is arranged at the upper end of a tubular string  20  and thereafter, the string is lowered and the length of cable  5  is retained in a plurality of non-intersecting loops  10  in the wellbore. While not shown in the figure, it will be understood that a first end of the length of cable extends towards the surface of the well, while an opposite end extends downward to a piece of equipment, like a pump. 
     The intent of the arrangement is to form the loops around the outer circumference of a tubular by offsetting the top of one loop from the bottom of the adjacent loops as depicted. The height “H” of the loops is determined based upon the amount of cable to be stored. The width “W” of the top and bottom portions of each loop are determined by the minimum bending radius “R” of the cable being stored. For the purposes of this disclosure, minimum bending radius is that radius into which a cable can be formed without damaging the cable. For example, a typical cable for powering a downhole component, like a pump, includes several copper conductors nested together and covered by a sheath. This arrangement necessarily results in a relatively stiff cable and one that has a limit to the shape it can assume without damaging the conductors. Likewise, the tubular used to carry and hold the pump at the bottom of the wellbore is necessarily of a diameter large enough to safely maintain the weight of the pump and convey pumped fluids to the surface of the well. The size and bending characteristics of the cable, as well as the circumference of the tubular, therefore determines the number of loops that can be formed therearound. For example, radius R illustrates a minimum bending radius for the cable  5  of  FIG. 1 . In one example, a typical tubular used to maintain an electric pump downhole has a circumference of 30 inches and a cable used to provide electrical power to the pump has a diameter of 1 inch and a minimum bending radius of 6 inches. Permitting a nominal amount of space between the loops, six loops can effectively be formed around the circumference of the tubular. 
       FIG. 2  is a side view of the tubular  20  and length of cable  5  and illustrates an upper and lower retainers for retaining loops  10  of the cable at an upper and lower ends. The retainers  30 A,  30 B can be installed at any location on the tubular, and their placement and separation determines the height “H” of loops of the cable  5 . In one embodiment, each retainer includes a fastener  35  that is cammed and permits the retainer to be tightened around the tubular. While the retainers in the embodiment shown are clamp-like, it will be understood that the retainers could operate any number of ways and be secured around the tubular with threads, welds, or any other pressure-inducing means. Further, the retainer may be constructed of any mechanically suitable material which retains its properties in a wellbore environment (e.g. steel, aluminum, other metal, or composites like injection molded resins, “plastics” etc.) 
     Visible in  FIG. 2  on each retainer are a plurality of formations  40  constructed and arranged to hold the top and bottom of each loop in a manner that avoids damage to the cable but utilizes the natural elasticity of the cable to aid in its retention in the retainer. In the embodiment shown, a main formation  45  is centered under each loop  10  at the top retainer  30 A and above each loop at the bottom clamp  30 B. The retainers are installed whereby each main formation  45  of the bottom retainer is rotationally distinct from its mating formation  45  on the upper retainer, thus encouraging the loops of cable to extend around the tubular. For example, in the embodiment of  FIG. 2 , the retainers are installed whereby the upper and lower main formations  45  are equally staggered around the circumference of the tubular  20 . 
     While the main formations  45  support the loops of cable at an upper and lower ends, side formations  50  operate to restrain the sides of each loop at an upper and lower end by acting against the elasticity of the loop  10 . In the embodiment shown, a single side formation  50  on each retainer  30 A,  30 B is utilized by two adjacent loops  10 . Additional side formations  50  are provided to facilitate the installation of the cable  5  and to retain the loops in the event the loops should slacken and their elasticity should urge them away from the main formation  45 . 
       FIG. 3  is an enlarged view of the upper retainer  30 A illustrating main  45  and side  50  formations thereon for retaining an upper portion of the loops  10  of cable  5 . The upper portions of three loops  10  are shown. The figure illustrates the design of the formations, particularly an undercut  55  provided in each formation  45 ,  50  to further retain the loops and prevent the cable  5  from extending outwards away from a surface of the tubular  20 . For example, the main formation  45  shown in this figure not only supports the loop  10  from below, but also retains the loop against a wall of the tubular  20 . Similarly, the side formations not only prevent the sides of the loop from extending outwards (due to their elasticity), but also retains them against the tubular wall. 
       FIG. 4  is a partial section view of the tubular  20  showing a cover  60  covering the loops  10  of cable  5 . The cover in the embodiment shown includes a hinge portion on one side (not shown) and a clamping arrangement  65  on an opposite side with a fastener. The cover  60  is constructed and arranged to extend around the tubular  20  in the area of the loops  10  to isolate the loops and retainers  30 A,  30 B from the wellbore therearound, thereby reducing the likelihood of damage to the cable  5  and associated hardware. The cover  60  is optional and it may be constructed and arranged to encompasses the upper and lower retainers as shown in the Figure, or may be “split” such that it only covers a section of cable fixed in the retainer. In other embodiments, the cover may be incorporated into the design of the retainer or may be a separate component. 
       FIG. 5  is an enlarged view of an upper portion of a loop  10  and various peg formations  60  for retaining the loop.  FIG. 5  is an alternative arrangement wherein the retainers are provided with the pegs  60  that work together to maintain an upper end of a loop  10  of cable  5  in its curved shape against its natural elastic tendency to straighten. The pegs  60  are arranged in two semicircles with a curved area therebetween to maintain an upper end of the loop. In the embodiment of  FIG. 5 , certain pegs are provided with an undercut  55  to support and retain the cable against a wall of the tubular  20 . 
       FIG. 6  is another embodiment showing a portion of an upper retainer  30 A having a main formation  75  and a corresponding formation  80  whereby a curved groove  85  is formed therebetween. As shown, an upper end of a loop  10  of cable  5  is supported in the curved groove  85 . Like the other embodiments, portions of each formation  75 ,  80  are undercut  55  to further retain the cable against movement away from the tubular wall. It will be understood that  FIGS. 3, 5 and 6  show the various arrangements at an upper end of a loop and that corresponding arrangements would typically be provided at a lower end of each loop retainer. 
     In a typical operation, a length of cable  5  is stored on a tubular  20  in the following manner. First, a selected section of tubular is exposed at the surface of the well, typically by retaining it temporarily with draw works or some temporary hanging mechanism. Thereafter, an upper and lower retainer  30 A,  30 B are installed with the distance therebetween determined by the amount of cable to be stored. In a typical case, the retainers are rotationally arranged so that the formations on each have an alternating relationship between top and bottom. The retainers are chosen based upon the circumference of the tubular, and the formations thereupon to retain the upper and lower ends of the loops  10  are chosen based upon the size and bending characteristics of the cable  5 . The loops are then formed one at a time by extending the cable around formations of the top retainer and around the formations of the lower retainer. The tubular can be rotated or an installer can move around the tubular as the loops are formed. 
       FIG. 7  illustrates an upper and lower plurality of loops  10 A,  10 B disposed on a tubular  20 . The purpose of  FIG. 7  is to illustrate that additional cable  5  can be stored on a single tubular by arranging the cable in two separate groups of loops  10 A,  10 B, one upper group and one lower group. In the embodiment, each group includes its own upper and lower retainers (not shown) with one end of the cable  11  at the lower group extending to downhole equipment and cable at the upper end  12  extending to the surface of the well. Another length of cable  13  extends between the upper group  10 A and lower group  10 B. In the embodiment of  FIG. 7 , the length of cable stored is doubled, making the arrangement especially useful in cases where the tubular has a relatively small diameter or in cases where additional cable needs to be stored. In this embodiment, the tubular would be typically held at a first position while the upper loops  10 A are arranged and thereafter, at a second position while the lower loops are arranged. While the upper  10 A and lower  10 B loops are shown as being equal in height “H 1 ”, “H 2 ”, they need not be. 
       FIG. 8  illustrates a plurality of nested loops  16 ,  17 ,  18  retained on a single length of tubular.  FIG. 8 , like  FIG. 7 , illustrates an arrangement whereby a number of loops of the same height “H” is multiplied by nesting the loops together. In this arrangement, however, upper and lower retainers (not shown) are equipped with multiple sets of the formations or pegs like those shown in  FIGS. 2-3, 5-6 , permitting the upper and lower ends of multiple loops to be stored in a manner that prevents the loops from intersecting with each other. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.