Patent Publication Number: US-2005116469-A1

Title: Coiled tubing connector and method of manufacture

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention relates to a coiled tubing connector and a method of making such a connector.  
      Coiled tubing connectors are used for connecting coiled tubing to a tool, or to one end of a work string.  
      In oil drilling and other well operations, an operator uses coiled tubing for raising and lowering tools into the well bore. An operator attaches a tool/work string to the end of a reel of coiled tubing. By reeling out the coiled tubing the operator can insert the tool/work string to a desired location within the well. By retracting the coiled tubing an operator can remove the tool/work string from the well.  
      A coiled tubing connector may be subjected to significant tension, compression and torque forces within the well. The connector must not disconnect under these conditions.  
      A known type of coiled tubing connector is a so-called “external slip” connector.  
      This type of connector uses an arrangement of so-called “wicker” slips that grip the coiled tubing using a wedge-like action. An increase in tension results in an increase in grip.  
      Each wicker slip engages with the coiled tubing via a set of teeth. The holding capability of the connector relates to the “bite” of the teeth into the coiled tubing.  
      The wicker slips are hardened to ensure the engagement of the teeth with the coiled tubing. This excludes use of the external slip connector in certain harsh environments.  
      The wicker form, fit and size determine the outside diameter of the connector.  
      External slip connectors may be expensive and time-consuming to manufacture. Furthermore, manufacturing tolerances affect performance.  
      A second known type of coiled tubing connector is a so-called “external dimple” connector.  
      A connector of this type attaches to coiled tubing via a series of grub screws that engage pre-formed dimples in the outer surface of the tubing wall. The dimples are formed by using a tool. The tool places indents in positions corresponding to the grub screws on the connector.  
      The strength of the connector is limited by the shear strength of the grub screws.  
      A special tool is required to prepare the coiled tubing. As a consequence preparation and attachment of the connector is time-consuming.  
      The bore of the coiled tubing is significantly reduced in the region of the connector. Furthermore, the outside diameter of the connector is determined by the form and size of the grub screws.  
      Use of the connector in certain environments is restricted because of the materials from which the connector is constructed.  
      A further known type of coiled tubing connector is a so-called “roll-on” connector.  
      This type of connector includes a threaded portion that defines a plurality of pre-formed channels. The connector attaches to the internal bore of the coiled tubing via a threaded portion. An operator secures the connector to the coiled tubing by crimping the tubing onto the pre-formed channels using a crimping tool.  
      A disadvantage of this arrangement is that the bore of the connector is less than that of the coiled tubing.  
      The roll-on connector is also difficult to remove from the coiled tubing.  
      An “internal slip” connector is another type of known coiled tubing connector.  
      An operator secures this type of connector to the internal bore of the coiled tubing via a number of tapered slips.  
      The bore of the connector is significantly smaller than that of the coiled tubing.  
      A further type of known coiled tubing connector is a “dimple-on” connector.  
      This type of connector attaches to coiled tubing via a portion of the connector that includes mutually spaced dimples in its outer surface. An operator secures the connector to the coiled tubing by crimping the tubing into the pre-formed dimples using a crimping tool.  
      The bore of the connector is less than that of the coiled tubing.  
      In addition the dimple-on connector is sometimes difficult to remove from the coiled tubing.  
     SUMMARY OF THE INVENTION  
      According to a first aspect of the invention there is provided a coiled tubing connector comprising: 
          a first, hollow sub including an internal recessed portion, and an engagement portion adjacent to a first end of the sub;     at least one arcuate segment, with each said segment defining a protuberance extending radially from an inner surface thereof; and     a second, hollow sub including an engagement portion adjacent to a first end thereof,     the first sub being moveable on an exterior surface of a length of unwound coiled tubing;     each said protuberance being engagable with a corresponding circumferentially extending recess in the coiled tubing;     the second sub being moveable on the exterior surface of the coiled tubing; and     the engagement portion of the first sub being engagable with the engagement portion of the second sub to cause in use each said arcuate segment to be retained within the internal recessed portion of the first sub to thereby maintain engagement of each said radially extending protuberance with the circumferentially extending recess in the coiled tubing.        

      According to a preferred embodiment of the invention, the second sub includes an internal shoulder, the internal shoulder in use abutting a first end of the coiled tubing.  
      Respective sides of each arcuate segment may preferably in use abut the first end of the second sub and an internal shoulder of the first sub, thereby preventing axial movement of the engaged subs relative to the or each arcuate segment.  
      Conveniently the engagement portion of the first sub defines a screw thread, and the engagement portion of the second sub defines a complementary screw thread.  
      Preferably the second sub includes a second end, the second end defining a threaded portion that permits the attachment of a tool or a work string to the connector.  
      In an alternative embodiment the second sub includes a second end, the second end defining an arrangement that is substantially similar to the first end, the two similar ends permitting the in-line connection of two lengths of coiled tubing.  
      According to a second aspect of the invention there is provided a method of making a coiled tubing connector comprising the steps of: 
          (a) forming at least one circumferentially extending recess in the outer surface of a length of unwound coiled tubing;     (b) locating a first, hollow sub so as moveably to surround the coiled tubing;     (c) placing one or more arcuate segments of a split ring on the outer surface of the coiled tubing whereby a protuberance extending radially from an inner surface of at least one arcuate segment engages the circumferentially extending recess;     (d) locating a second, hollow sub so as moveably to surround the coiled tubing; and     (e) engaging the first and second subs together to retain each arcuate segment therebetween, thereby maintaining engagement of the or each radially extending protuberance with the circumferentially extending recess and locking the first and second subs against movement relative to the coiled tubing.        

      In a preferred embodiment of the method step (e) includes causing abutment of each arcuate segment against a first end of the second sub and an internal shoulder defined by the first sub, thereby preventing axial movement of the engaged subs relative to the or each arcuate segment.  
      Conveniently step (d) includes causing abutment of an internal shoulder defined by the second sub against the first end of the coiled tubing.  
      It is an advantage of the invention to provide a coiled tubing connector that only requires the use of a readily available tool to create and therefore is quick and simple to use.  
      It is a further advantage of the invention to provide a coiled tubing connector that is tailored to the strength of the coiled tubing and is not dependent upon the engagement of teeth for its holding capability.  
      Another advantage of the invention is to provide a coiled tubing connector that can be manufactured of a material that is appropriate for a particular (eg. downhole) environment; and manufactured inexpensively.  
      A further advantage of the invention is to provide a coiled tubing connector that is reusable.  
      It is a still further advantage of the invention to provide an easy, quick method of making a coiled tubing connector. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective, partially-sectioned view of a length of known coiled tubing unwound from its drum;  
       FIG. 2  is a perspective, partially-sectioned view showing a first sub according to a first embodiment of the invention positioned on the coiled tubing shown in  FIG. 1 ;  
       FIG. 3  is a perspective view of a split ring according to the first embodiment of the invention;  
       FIG. 4  is a perspective, partially-sectioned view of the  FIG. 2  arrangement including the split ring according to the first embodiment of the invention;  
       FIG. 5  is a perspective, partially-sectioned view of the first sub, the split ring, and a second sub according to the first embodiment of the invention and including the coiled tubing shown in  FIG. 1 ; and  
       FIG. 6  is a side-elevational, partially-sectioned view of a coiled tubing connector according to the first embodiment of the invention. 
    
    
     DESCRIPTION OF THE EMBODIMENTS  
      Referring to  FIG. 1 , a known, hollow coiled tubing for use in oil and gas wells is designated by the reference numeral  10 . The coiled tubing  10  is typically formed from carbon steel, corrosion resistant alloys, or titanium; and includes a circumferentially extending recess  11  in the outer surface thereof adjacent a first end  12 . In the preferred embodiment the recess  11  extends around the entire a circumference of the coiled tubing  10 . Other embodiments (not shown in the drawings) in which a recess or a plurality of recesses extend only part-way around the circumference of the tubing are also possible.  
      Referring to  FIGS. 2-6 , a preferred embodiment of coiled tubing connector is designated generally by the reference numeral  50  ( FIG. 6 ).  
      The connector  50  comprises a first sub  20  that is slidable on the exterior surface of the coiled tubing  10 . The first sub  20  includes an internal recessed portion  21  ( FIG. 2 ) and an engagement portion  22  at a first end  26  thereof.  
      The connector  50  also includes two arcuate segments  31 ,  32 .  FIG. 3  shows a preferred embodiment in which the two arcuate segments  31 ,  32  define a split ring  30 . Each arcuate segment  31 ,  32  includes a protuberance  33  extending radially from an inner surface thereof.  
      Each protuberance  33  is engagable with the circumferentially extending recess  11  in the coiled tubing  10  ( FIG. 4 ).  
      A greater or fewer number of segments may be used. Furthermore, not all of the segments need include radially extending protuberances.  
      The connector  50  also includes a second sub  40  that is slidable on the exterior surface of the coiled tubing  10  ( FIG. 5 ). The second sub  40  includes an engagement portion  41  adjacent to a first end  42  thereof.  
      The engagement portion  22  of the first sub  20  is engagable with the engagement portion  41  of the second sub  40 . Engaging the first and second subs  20 ,  40  together ( FIG. 6 ) retains the two arcuate segments  31 ,  32  within the internal recessed portion  21  of the first sub  20 . This in turn maintains engagement of the radially extending protuberances  33  with the circumferentially extending recess  11  in the coiled tubing  10 .  
      The engagement portions  22 ,  41  of each of the first sub  20  and the second sub  40  define screw threads  24 ,  43 . The second sub  40  screw thread  43  is complementary to the first sub  20  screw thread  24 . This permits the first and second subs  20 ,  40  to engage securely together. It also facilitates the removal of the connector  50  from the coiled tubing  10 , thereby allowing for the re-use of the connector  50 .  
      In this way the connector  50  is secured to the coiled tubing  10 .  
      The second sub  40  includes an internal shoulder  43  ( FIG. 5 ). In use the shoulder  44  abuts a first end  12  of the coiled tubing  10 . This allows the end  12  of the coiled tubing  10  to carry the axial loading on the second sub  40  as it is driven into a well bore. This removes the axial loading from the split ring  30  and recess  11 , thereby extending the fatigue life of the connector  50 .  
      Respective edges  34 ,  36  of the arcuate segments  31 ,  32  abut the first end  42  of the second sub  40  and an internal shoulder  23  of the first sub  20 . This prevents axial movement of the engaged subs  20 ,  40  relative to the arcuate segments  31 ,  32 . Such an arrangement also helps to extend the fatigue life of the connector  50 .  
      A second end  46  of the second sub  40  defines a threaded portion  47  ( FIG. 6 ). This portion  47  permits the attachment of a tool or a work string to the connector  50 .  
      Alternatively, the second end  46  of the second sub  40  defines an arrangement (not shown in the drawings) that is substantially similar to the first end of the second sub  40 . The two similar ends permit the in-line connection of two lengths of coiled tubing.  
      The preferred method of making the coiled tubing connector  50  of  FIG. 6  includes the following steps: forming a circumferentially extending recess  11  in the outer surface of a length of unwound coiled tubing  10 ; sliding a first sub  20  onto the coiled tubing  10  via first end  12  thereof (as shown in  FIG. 2 ); placing two arcuate segments  31 ,  32  that define a split ring  30  on the outer surface of the coiled tubing  10  whereby a protuberance  33  extending radially from the internal surface of each arcuate segment  31 ,  32  engages with the circumferentially extending recess  11  (as shown in  FIG. 4 ); sliding a second sub  40  onto the coiled tubing  10  via the first end  12  thereof, ensuring that the internal shoulder  44  defined by the second sub  40  abuts the first end  12  of the coiled tubing  10 ; and engaging the first and second subs  20 ,  40  together to retain the two arcuate segments  31 ,  32  therebetween, thereby maintaining engagement of each radially extending protuberance  33  with the circumferentially extending recess  11 .  
      An operator may use a modified coiled tubing cutter to form the circumferentially extending recess  11 . The cutter modification involves replacing the cutting blade with a wheel having a cross-section corresponding to the shape of recess required.  
      The preferred method also includes the step of causing abutment of the two arcuate segments  31 ,  32  against the first end  42  of the second sub  40  and the internal shoulder  23  defined by the first sub  20 . This prevents axial movement of the engaged subs  20 ,  40  relative to the two arcuate segments  31 ,  32 .