Flexible Tubular Sub, and Method of Running a Tool String Into a Wellbore

Abstract

A flexible tubular sub comprising a cylindrical body. The tubular sub has a first end and an opposing second end, with each end having threads. The threads may be female threads used for connecting to respective male threads of a tandem sub that is associated with a perforating gun. The flexible tubular sub also comprises an elongated shaft. The shaft resides between the first and second ends, and has an outer diameter that is smaller than an outer diameter of the threaded ends. This serves to reduce a moment of inertia for the flexible tubular sub. The flexible tubular sub also includes a pair of transition sections. The transition sections reside between the shaft and each of the opposing first and second ends. A method of running a tool string such as a perforating gun assembly into a wellbore using the flexible sub is also provided. In this instance, the sub may be placed between adjacent perforating gun barrels.

I claim: 
     
         1 . A flexible tubular sub defining a cylindrical body, and comprising:
 a first end and an opposing second end, wherein each of the first and second ends comprises threads, and wherein each of the first and second ends has a first outer diameter;   an elongated shaft between the first and second ends as part of the cylindrical body, wherein the shaft has a second outer diameter that is smaller than the first outer diameter, thereby reducing a moment of inertia for the flexible tubular sub;   a bore extending between the first and second ends, with the bore being dimensioned to closely receive an electrical wire or data cable; and   a transition section residing between the shaft and each of the opposing first and second ends.   
     
     
         2 . The flexible tubular body of  claim 1 , wherein the cylindrical body has a consistent metal composition across its length. 
     
     
         3 . The flexible tubular body of  claim 1 , wherein the shaft is fabricated from steel, titanium, beryllium copper, or a metal alloy thereof. 
     
     
         4 . The flexible tubular body of  claim 3 , wherein the threads at each of the first and second ends comprises female threads configured to threadedly connect to an end of a perforating gun through a male-by-male tandem sub. 
     
     
         5 . The flexible tubular body of  claim 4 , having a length that is between one and five times the first outer diameter. 
     
     
         6 . A tool string, comprising:
 a first cylindrical wellbore tool comprising a rigid housing;   a second cylindrical wellbore tool also comprising a rigid housing; and   a flexible tubular sub defining a cylindrical body, with the cylindrical body residing between the first cylindrical wellbore tool and the second cylindrical wellbore tool, and comprising:
 a first end and an opposing second end, wherein each of the first and second ends defines a coupling having a first outer diameter that approximates an outer diameter of the adjoining first and second cylindrical wellbore tools; 
 an elongated shaft between the couplings, wherein the shaft has a second outer diameter that is smaller than the first outer diameter, thereby reducing a moment of inertia for the flexible tubular sub; 
 a bore extending between the first and second ends, dimensioned to closely receive an electrical wire or data cable; and 
 a transition section residing between the shaft and each of the opposing first and second ends. 
   
     
     
         7 . The tool string of  claim 6 , wherein:
 each of the first and second wellbore tools is a perforating gun;   the tool string is a perforating gun assembly; and   the outer diameter of each perforating gun is formed by a respective gun barrel housing.   
     
     
         8 . The tool string of  claim 7 , wherein the shaft is fabricated from steel, titanium, beryllium copper, or a metal alloy thereof. 
     
     
         9 . The tool string of  claim 7 , wherein:
 the threads at each of the first and second ends comprises female threads configured to threadedly connect to an end of an adjoining perforating gun through a male-by-male tandem sub; and   the flexible tubular sub has a length that approximates a length of each of the first and second wellbore tools.   
     
     
         10 . A method of running a tool string into a wellbore, comprising:
 providing a wellbore, wherein the wellbore has a deviated section;   running a tool string into the wellbore, the tool string comprising:
 a first cylindrical wellbore tool having a rigid housing; 
 a second cylindrical wellbore tool also having a rigid housing; and 
 a flexible tubular sub residing between the first and second wellbore tools and defining a cylindrical body, and comprising:
 a first end and an opposing second end, wherein each of the first and second ends has a first outer diameter that approximates an outer diameter of an adjoining wellbore tool; 
 an elongated shaft between the first and second ends, wherein the shaft has a second outer diameter that is smaller than the first outer diameter; 
 a bore extending between the first and second ends, dimensioned to closely receive an electrical wire or data cable; and 
 a transition section residing between the shaft and each of the opposing first and second ends; 
 wherein the central body has a second outer diameter that is smaller than the first outer diameter, thereby reducing a moment of inertia for the flexible tubular sub; and 
 
   passing the tool string through the deviated section.   
     
     
         12 . The method of claim  11 , wherein:
 the tool string is run into the wellbore at the end of an electric wireline; and   running the tool string into the wellbore and passing the tool string through the deviated section comprises pumping the tool string downhole using hydraulic pressure.   
     
     
         13 . The method of claim  11 , wherein:
 each of the first and second wellbore tools is a perforating gun;   the tool string is a perforating gun assembly; and   the outer diameter of each perforating gun is formed by a respective gun barrel housing.   
     
     
         14 . The method of  claim 13 , wherein the shaft is fabricated from steel, titanium, beryllium copper, or combinations thereof. 
     
     
         15 . The tool string of  claim 13 , wherein:
 the threads at each of the first and second ends of the cylindrical body comprises female threads configured to threadedly connect to an end of a tandem sub; and   each tandem sub comprises male-by-male ends, with a first male end being threadedly connected to an end of the flexible tubular sub, and a second male end being threadedly connected to an end of a perforating gun.