Abstract:
A cable protector includes a housing body which is adapted to fit in a pipe connector. The housing body has a central bore and an insert body is rotatably supported in the central bore. The insert body has a groove which is adapted to receive a cable.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to oil and gas wireline operations. More specifically, the invention relates to an apparatus for protecting a wireline from damage during a fishing operation. 
     2. Background Art 
     In oil and gas wireline operations, downhole tools, e.g., logging tools, are conveyed into and withdrawn from a wellbore using an armored electrical cable called a wireline. The downhole tools are typically tubular members that are threaded together to form a “tool string.” A cable head couples the wireline to the tool string. Occasionally, during operation, the tool string may become stuck in the wellbore. When the tool string gets stuck, a high tension is usually applied to the tool string to try to free the tool string from its stuck position. This high tension is applied to the wireline at the surface by a winch used to extend and retract the cable, and the wireline transmits the applied tension to the cable head. The cable head in turn transmits the tension to the tool string. The amount of tension available to free the tool string from its stuck position depends on the breaking strength of the cable, the profile and coefficient of friction of the wellbore, the position of the tool string inside the wellbore, and various other parameters, in particular the weight of the cable in the wellbore. 
     The connection between the cable head and the wireline typically includes a “weak point.” A weak point is a link designed to break when a predetermined amount of tension is applied to it. Normally, the weak point has the lowest breaking strength in the tool string. The weak point allows the cable to be separated from the cable head in the event that enough tension cannot be applied to the tool to free it. In situations where the tension required to free the tool string exceeds the breaking strength of the cable, the tool string must be “fished” out of the wellbore. To fish the tool string, the operator first latches onto the cable head or tool string using a fishing tool coupled to one end of a drill pipe and then applies tension to the wireline to break the weak point and release the wireline from the cable head. The wireline is first removed from the wellbore, and then the cable head and the tool string are pulled out of the wellbore by removing the drill pipe. 
     In a method of fishing known as the cut and thread method, the cable is used to guide the fishing tool to the stuck tool string. FIG. 1 shows a prior art setup from the rig floor up for a fishing operation. During normal wireline operations, the cable  2  is payed from a cable drum (not shown). The cable  2  is threaded through sheaves  4 ,  6  and then passed through the rotary table  8  into the wellbore (not shown). In order to allow the cable  2  to guide the fishing tool (not shown) to the stuck tool (not shown) in the wellbore (not shown), the cable  2  is cut near the rig floor. An overshot  10  is connected to the winch-side section  2   a  of the cable  2  threaded through the sheaves  4 ,  6 , and a spearhead  12  is connected to the downhole-side section  2   b  of the cable  2  that extends through the rotary table  8 . In the illustration shown, a drill pipe  14  is supported by slips (not shown) in the rotary table  8 . The fishing tool (not shown) is attached to the end of this drill pipe  14 . A clamp  15  is then mounted on the upper end of the drill pipe  14  to hold the spearhead  12  and prevent the spearhead  12  from falling through the drill pipe  14 . 
     The next step is to make up a drill pipe stand  16  and then connect the drill pipe stand  16  to the drill pipe  14 . Typically, the drill pipe stand  16  consists of three drill pipe “joints” threaded together. After connecting the drill pipe stand  16  to the drill pipe  14 , the drill pipe stand  16  is lowered through the rotary table  8  into the wellbore (not shown). This process of connecting a drill pipe stand to the uphole end of the drill pipe at the rotary table  8  and lowering the drill pipe stand through the rotary table  8  is repeated until the fishing tool (not shown) on the end of the drill pipe  14  reaches the stuck tool (not shown) in the wellbore (not shown). In the illustration, a drill pipe stand  16  is suspended above the drill pipe  14  by a power drive  18 . The power drive  18  is supported by the derrick  20  and rides on the guide rail  22 . Before connecting the drill pipe stand  16  to the drill pipe  14 , the winch-side cable section  2   a  is threaded through the drill pipe stand  16  until the overshot  10  engages with the spearhead  12 . After the tension on the cable  2  is increased, the clamp  15  is then removed to allow the drill pipe stand  16  to be connected to the drill pipe  14 . The power drive  18  is used to lower the drill pipe  14  having the new stand  16  connected thereto. 
     FIG. 2 shows the drill pipe stand  16  connected to the drill pipe  14 . To connect the drill pipes, the drill pipe stand  16  is rotated relative to the drill pipe  14  so that the threads in the bottom drill pipe  16   a  can engage with the threads in the drill pipe  14 . During this operation, the cable  2  is held in tension. The winch-side cable section  2   a  is also slanted with respect to the upper drill pipe  16   b  because the sheave  6  must be hung off to the side to give the power drive  18  room to operate. During normal wireline operations, the sheave  6  is typically held directly above the rotary table  8 . With the winch-side cable section  2   a  in this slanted position, the threads in the upper drill pipe  16   b  contact the wireline section  2   a  as the upper drill pipe  16   b  rotates. The effect is that the threads cut into the winch-side cable section  2   a , reducing the tensile strength of the cable  2  at the contact area. As more stands of drill pipe are made up and connected to the drill pipe  14  in the wellbore using the process described above, the threads on the drill pipe repeatedly contact the winch-side cable section  2   a  in the same area, further weakening the cable  2  at the contact area. As the degradation continues, a point is reached where the cable  2  breaks. Thus, a mechanism is needed for protecting the cable  2  while connecting stands of drill pipe to the drill pipe in the wellbore. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention relates to a cable protector which comprises a housing body having a central bore. The housing is adapted to fit in a pipe connector. An insert body is rotatably supported in the central bore. The insert body has a groove which is adapted to receive a cable. 
     In some embodiments, a roller is rotatably supported in the groove. The cable rides on the roller when there is relative movement between the cable and the housing body. In some embodiments, a wall of the housing body includes an opening which provides access to the central bore of the housing body. In some embodiments, the housing body has a threaded end portion for engagement with a threaded pipe. 
     Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 illustrate a prior art setup for a fishing operation. 
     FIG. 3 illustrates a setup for a fishing operation in accordance with one embodiment of the invention. 
     FIG. 4 is a front view of the cable protector shown in FIG.  3 . 
     FIG. 5 is a vertical cross section of the cable protector shown in FIG.  4 . 
     FIG. 6A is a top view of the insert shown in FIG.  5 . 
     FIG. 6B is a cross section of the insert shown in FIG.  6 A. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Various embodiments of the invention will now be described with reference to the accompanying figures. FIG. 3 shows a cable protector  24  installed on the drill pipe stand  16  (also previously shown in FIGS.  1  and  2 ). The purpose of the cable protector  24  is to protect the cable  2  (also previously shown in FIGS. 1 and 2) from damage as the drill pipe stand  16  is rotated. FIGS. 4 and 5 show an enlarged view and vertical cross section of the cable protector  24 , respectively. As illustrated, the cable protector  24  includes a housing body  26  which is generally tubular in shape. The housing body  26  has a central bore  28  (shown in FIG.  5 ). An opening  30  is provided in the wall of the housing body  26 . The opening  30  is connected to the central bore  28  and provides an entry into the central bore  28 . The lower portion  32  of the housing body  26  includes threads for engaging with a drill pipe, e.g., the drill pipe  16   b  shown in FIG.  3 . Apertures  34  are provided in the wall of the housing body  26  for engagement with handles (not shown). The handles facilitate handling of the housing body  26 . 
     The housing body  26  has an inner shoulder  36 . An insert  38  is supported on the inner shoulder  36 . The insert  38  is supported so as to freely rotate relative to the housing body  26 . A lubricant (not shown) is provided in between the housing body  26  and the insert  38  to reduce friction. FIG. 6A shows a top view of the insert  38 . FIG. 6B shows a section through the insert  38 . As shown in FIGS. 5,  6 A, and  6 B, the insert  38  includes an insert body  40  which is generally annular in shape. The insert body  40  has an opening  42  (shown in FIG. 6B) which can be aligned with the opening  30  (shown in FIG. 4) in the housing body  26 . A groove  44  is provided in the insert body  40 . In one embodiment, a roller  46  is rotatably supported in the groove  44 . In one embodiment, the insert body  40  includes apertures  48  (shown in FIG. 6B) through which a pin (not shown), for example, can be inserted through the roller  46  to allow the roller  46  to rotate freely within the groove  44 . Other means of rotatably supporting the roller  46  within the groove  44  can also be used. 
     A retaining plate  50  (shown FIG. 5) is mounted on the upper end  52  of the housing body  26  to retain the insert  38  within the housing body  26 . The retaining plate  50  is secured to the housing body  26 , for example, using bolts  54  (shown in FIG. 4) and nuts (not shown). The bolts  54  extend through apertures  55  in the retaining plate  50  and apertures  57  in the housing body  26 . The retaining plate  50  has a bore  56  that is generally coaxial with the bore  28  of the housing body  26 . The cable (such as  2  in FIG. 3) can be inserted into the housing body  26  through the bore  56  in the retaining plate  50 . Preferably, the inner surface  58  of the retaining plate  50  is shaped such that it does not present a sharp edge to the cable (not shown). The inner surface  58  may be tapered or rounded, for example. 
     Returning to FIG. 3, the cable protector  24  is installed on the drill pipe stand  16 . Initially, the drill pipe stand  16  is suspended above the drill pipe  14 . The drill pipe  14  is supported by slips (not shown) in the rotary table  8 . The cable section  2   a  is then threaded through the drill pipe stand  16  and connected to the cable section  2   b  extending through the drill pipe  14 . Typically, the connection is made by engaging the overshot  10  attached to the winch-side cable section  2   a  with a spearhead ( 12  in FIG. 1) attached to the downhole-side cable section  2   b . The cable section  2   a  is inserted into the drill pipe stand  16  through the insert  38  (shown in FIG. 5) of the cable protector  24 . The insert body  40  (shown in FIG. 5) is rotated if necessary to ensure that the winch-side cable section  2   a  is positioned over the roller  46  (shown in FIG. 5) within the groove  44  (shown in FIG.  5 ). 
     Upon connecting the cable sections  2   a  and  2   b , the drill pipe stand  16  is lowered onto the drill pipe  14  and rotated relative to the drill pipe  14  to make the threaded connection. As the drill pipe stand  16  rotates, the housing body  26  (shown in FIG. 5) also rotates because it is connected to the drill pipe stand  16 . The winch-side cable section  2   a  rides on the roller  46  (shown in FIG. 5) in the groove  44  (shown in FIG. 5) and tends to keep the insert body  40  (shown in FIG. 5) stationary while the housing body  26  rotates relative to the insert body  40 . In this way, contact is avoided between the winch-side cable section  2   a  and the drill pipe threads. After making the connection, the drill pipe stand  16  is lowered and the cable protector  24  is disengaged from the drill pipe stand  16 . The opening  30  (shown in FIG. 4) in the housing body  26  and the opening  42  (shown in FIG. 6A) in the insert body  40  are then aligned to allow the cable protector  24  to be removed from the cable  2 . The cable protector  24  can then be installed on another drill pipe stand. 
     The cable protector  24  has been described with respect to the winch-side cable section  2  riding on the roller  46  (shown in FIG. 5) as the housing body  26  (shown in FIG. 5) is rotated. In an alternate embodiment, the roller  46  may be removed from the groove  44 , but the winch-side cable section  2   a  will remain in the groove  44  as the housing body  26  rotates. The insert body  40  may be made of a soft metal, such as copper or lead, so that it does not damage the winch-side cable section  2   a.    
     The invention can provide general advantages. By installing the cable protector on a drill pipe stand and allowing the cable to ride on the roller as the drill pipe stand rotates, the possibility of cutting the cable is reduced because the cable no longer contacts the threads in the drill pipe. 
     While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.