Abstract:
A simple threaded end connector is easily attached to the end of a tube. One embodiment of the threaded end connector attaches to the end of a coiled tubing string so to allow the coiled tubing string to easily connect to a variety of threaded downhole tools

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application, pursuant to 35 U.S.C. 111(b), claims the benefit of the earlier filing date of provisional application Ser. No. 61/626,449 filed Sep. 27, 2011, and entitled “Means of Attachment of a Threaded End Connector to an End of a Tubing.” 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a device and method for attaching a threaded end connector to the end of a tube. More particularly, the invention relates to a device and method for attaching a threaded end connector to the end of a coiled tubing string so that it can connect to a variety of drillstring components. 
         [0004]    2. Description of the Related Art 
         [0005]    Coiled tubing offers a rapid and cost effective way to deploy and retrieve tools used in well drilling and servicing. Previously, the attachment of such tools or threaded adapters to the bottom end of a coiled tubing string has utilized either mechanical means or simple annular welds. Annular fillet or butt welds between the tubing and a tool or threaded adapter are difficult to reliably produce and can be subject to fatigue from bending. Allowable fillet weld sizes for connecting tubing to adapters are insufficient to develop the full axial and torsional strengths needed of the tubing. 
         [0006]    One commercially available mechanical connection means, the External Dimple Connector, sold by Weatherford International Ltd., is engaged over the coiled tubing with a close slip fit and uses elastomeric seal rings to seal the annular gap. Multiple radially oriented grub screws, positioned in a regularly spaced pattern in the annular external wall of the Weatherford connector, move inwardly to plastically deform the tubing wall to create sufficient interlocking to provide the desired axial and torsional load capacity. However, this design can be ineffective if the elastomeric seals are damaged or deteriorate. An additional weakness of this type of connector can result if the grub screws are screwed in too little, resulting in an inadequate load capacity. 
         [0007]    Weatherford International Ltd. also offers an Internal Dimple Connector. That connector also uses elastomeric seals to seal the annular gap between the tubing bore and the connector. The Internal Dimple Connector has multiple external semispherical pits into which a separate tool is used to plastically deform the tubing wall into each of the pits in response to radially inward thrusts applied by individual spherical ended screws. This type of connector also is sensitive to seal damage or deterioration. Because coiled tubing is typically formed with an internally protruding weld bead parallel to the tube axis, there is a likelihood of damage to the annular seals from contact with the weld bead, even if the tubing bore is reamed. 
         [0008]    A third type of threaded adapter is the Coil Tubing Connector TT0740-375 from Thru-Tubing Technology. This connector also uses elastomeric seals to seal the annular gap between the tubing exterior and the connector bore. The connector consists primarily of two tubular bodies which are joined by a threaded connection. Axial and torsional gripping is provided by engagement of a deformable internally toothed, externally tapered annular slip retained in a frustroconical pocket of a first half of the connector. The second half of the connector abuts the lower end of the slip. Tightening the threaded connection between the first and second halves of the connector causes the slip to be axially compressed into the frustroconical pocket so that it is forced radially inwardly into engagement with the tubing. Radial set screws are used to prevent backing off of the threaded connection between the two halves of the connector. High friction in the threaded interconnection of the two connector halves can lead to inadequate axial capacity, and the elastomeric seals are subject to installation damage and deterioration. 
         [0009]    A need exists for additional tubing connectors which can offer high axial and torsional strength along with reliable sealing between the connector and the tubing to which it is mounted. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention relates to a device and method for attaching a threaded end connector to the end of a tube. More particularly, the invention relates to a device and method for attaching a threaded end connector to the end of a coiled tubing string so that it can connect to a variety of drillstring components. 
         [0011]    One embodiment of the present invention includes a threaded tubing end assembly comprising: a) a tubing having a transverse first end, a tubing through bore, a weld seam internally extending into the tubing through bore, and a through slot extending axially from the first end to a predetermined length, wherein the through slot is located in a side of the tubing opposite the weld seam; b) a threaded adapter having an adapter through bore, and an adapter body having a threaded first end, and an opposed second end with an external transverse shoulder surrounding a reduced diameter elongated shank extending from the second end, wherein the elongated shank has an external longitudinal slot sized to accommodate the internally extending weld seam of the tubing; c) a circumferential weld sealingly connecting the first end of the tubing to the transverse external shoulder of the threaded adapter, when the tubing through bore is positioned around the shank of the adapter so that the first end of the tubing abuts the transverse external shoulder of the adapter and the tubing weld seam is accommodated in the longitudinal slot of the adapter; and d) a longitudinal weld filling the axially extending through slot of the tubing and providing a structural connection between the tubing and the elongated shank. 
         [0012]    A second embodiment of the present invention includes a threaded tubing end assembly comprising: a) a tubing having (i) a transverse first end with an internal chamfer, (ii) a tubing through bore, (iii) a weld seam internally extending into the tubing through bore, and (iv) a through slot extending axially from the first end of the tubing to a predetermined length, wherein the through slot is located in a side of the tubing opposite the weld seam; b) a threaded adapter having (i) an adapter through bore, and (ii) an adapter body having a threaded first end with a first transverse external shoulder, an opposed second end having a second transverse external shoulder and a reduced diameter elongated shank attached to the second end, wherein the shank has an external longitudinal slot extending an entire length of the shank and sized to accommodate the internally extending weld seam of the tubing, and wherein the elongated shank has a substantially constant external diameter sized to be a close fit with the tubing through bore when the tubing weld seam is accommodated in the longitudinal slot; c) a circumferential weld sealingly connecting the first end of the tubing to the second transverse external shoulder of the adapter body, when the tubing through bore is positioned around the elongated shank of the adapter so that the first end of the tubing abuts the second transverse external shoulder of the adapter body and the tubing weld seam is accommodated in the longitudinal slot of the elongated shank; and d) a longitudinal weld filling the axially extending through slot of the tubing and providing a structural connection between the tubing and the elongated shank on a side of the shank opposite the longitudinal slot. 
         [0013]    Another embodiment of the present invention includes a method for attaching a threaded adapter to a tube comprising the steps of: (a) cutting a through slot through a first side of a tube opposite a weld bead that protrudes into a through bore of the tube, wherein the through slot axially extends from a transverse end of the tube for a predetermined length; (b) aligning the tube weld bead with an external longitudinal slot that extends along one side of an elongated shank of a threaded adapter; (c) sliding the transverse end of the tube over the elongated shank of the threaded adapter so that the transverse end of the tube abuts a transverse shoulder of the threaded adapter and the tube weld bead is positioned within the shank longitudinal slot, wherein the transverse shoulder surrounds an interior end of the elongated shank; (d) connecting the transverse end of the tube to the transverse shoulder of the adapter with a circumferential weld; and (e) connecting the shank of the threaded adapter to a side of the tube opposite the tube weld bead with a longitudinal weld filling the axially extending through slot. 
         [0014]    Yet another embodiment of the present invention includes a method for attaching a threaded adapter to a tube comprising the steps of: (a) obtaining a threaded adapter having an adapter through bore, and an adapter body having a threaded first end, an opposed second end with a reduced diameter elongated shank attached to the second end and a transverse external shoulder surrounding the shank on the second end, wherein the shank has an external longitudinal slot extending a length of the shank; (b) preparing an outer tubing end of a coiled tubing string by providing a transverse end of the outer tubing end and cutting an axially extending through slot for a predetermined length through a first side of the outer tubing end opposite a weld bead that protrudes into a through bore of the coiled tubing; (b) aligning the tube weld bead with the external longitudinal slot that extends along one side of the elongated shank of the threaded adapter; (c) sliding a tubing through bore along the length of the elongated shank of the threaded adapter so that the transverse end of the tubing abuts the transverse shoulder of the threaded adapter and the tube weld bead is positioned within the shank longitudinal slot; (d) connecting the transverse end of the tube to the transverse shoulder of the adapter with a circumferential weld; and (e) connecting the shank of the threaded adapter to a side of the tube opposite the tube weld bead with a longitudinal weld filling the axially extending through slot. 
         [0015]    The foregoing has outlined rather broadly several aspects of the present invention in order that the detailed description of the invention that follows may be better understood and thus is not intended to narrow or limit in any manner the appended claims which define the invention. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing of the structures for carrying out the same purposes as the invention. It should be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
           [0017]      FIG. 1  is an oblique view of the first embodiment of the present invention, wherein a connector with a male distal thread at a first end is welded at its second end to one end of a coiled tubing string. 
           [0018]      FIG. 2  is an oblique view of the end of the coiled tubing string which is to be joined to the threaded connector of  FIG. 1 , wherein the tubing end is provided with an elongated through slot parallel to the axis of the tubing. The slot serves as a weld preparation for making the connection of the tube to the threaded end connector. 
           [0019]      FIG. 3  is an oblique view of the male threaded end connector of the first embodiment of the present invention, wherein the connector has a male distal thread at a first end and is configured to be welded to a coiled tubing at its second end. 
           [0020]      FIG. 4  is a longitudinal sectional view of the cojoined threaded male end connector and tubing end of  FIG. 1 , wherein the section is taken through the aligned and welded slots of the joined parts. 
           [0021]      FIG. 5  is an oblique view of a second embodiment of the female threaded end connector attached to an end of a coiled tubing. 
           [0022]      FIG. 6  is an oblique view of the female threaded end connector of the second embodiment. 
           [0023]      FIG. 7  is a longitudinal sectional view of the cojoined threaded female end connector and tubing end of  FIG. 5 , wherein the section is taken through the aligned and welded slots of the joined parts. 
           [0024]      FIG. 8  is a transverse sectional view of the longitudinal weld connecting the tubing and the male threaded end connector of  FIG. 4 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    The materials of the present invention typically are high strength low alloy carbon steels, such as AISI 4130 for the threaded portion of the threaded end fitting. The coiled tubing typically will have a yield strength of approximately 80,000 psi. The weld metal will be selected to be compatible with both the threaded end fitting and the coiled tubing. In service, the threaded end fittings of the present invention normally will be located on the lower end of the coiled tubing string. When describing orientations of the components of the present invention, it is assumed herein that “upward” is on the tubing side of the tubing to adapter connection, while “downward” is on the adapter side of the connection. 
       First Embodiment 
       [0026]    Referring to  FIG. 1 , a first embodiment  10  of the present invention is seen in an oblique view. The male threaded end adapter assembly  10  consists of a prepared coiled tubing end  11 , a male threaded end fitting  16 , a longitudinal weld  23 , and a circumferential weld  24 . 
         [0027]    The tubing end  11 , shown joined to the end fitting  16  in  FIG. 1  and by itself in  FIG. 2 , typically has a relatively thin wall and a substantially circular cross-section. The lower tubing end  11  is preprepared for attachment to the male end adapter  10  by: (a) squaring the lower end of the tubing end  11 , (b) cutting a long narrow through slot  12  of a predetermined length with parallel sides and a rounded end  13  parallel to the tube axis from the transverse lower tubing end, and (c) providing an internal end chamfer sufficiently large that end abutment is ensured between the lower tubing transverse end and a transverse external shoulder  25  of the male threaded end fitting  16  or a female threaded end fitting  30 . The internal chamfer ensures that a sound circumferential fillet seal weld  24  can be made between the abutted parts. 
         [0028]    The manufacture of coiled tubing generally includes bending a metal strip about an axis parallel to its longitudinal axis so that it has a circular cross-section. The abutting edges of the rounded metal strip are then welded with a longitudinal weld seam to connect the two adjacent edges of the rounded metal strip. The longitudinal weld generally leaves an inwardly extending longitudinal weld bead  15  along the length of the tubing. Thus, the interior cylindrical surface  14  of the tubing end  11  will typically exhibit the inwardly extending longitudinal seam weld bead  15 . Although the size and shape of the longitudinal seam weld bead will vary, it generally has an arcuate surface projecting inwardly, that is relatively narrow and has a width approximately equal to or less than the thickness of the tubing. The inward projection of the weld bead  15  is typically about half of its width in the circumferential direction. 
         [0029]      FIG. 3  is an oblique view which shows the male threaded end adapter  16 . From its lower end, the exterior of the male threaded end adapter  16  has an external tapered male thread  17 , a downwardly facing external transverse sealing shoulder, an enlarged cylindrical main body  26 , a transverse upwardly facing shoulder  25 , and a constant diameter elongated shank  18 . Adapter  16  has a coaxial through bore  27  to permit fluid flow. The length of the elongated shank  18  will vary but should be at least as long as or longer than the slot  12  in the prepared tubing end  11 . Typically, the length of shank  18  is on the order of two to four times the diameter of the tubing end  11 . The shank  18  is made to have a close slip fit to the through bore of the tubing end  11  when interference with the interior longitudinal weld bead  15  is avoided by engagement of the weld bead  15  in the longitudinal slot  19  in the shank  18 . 
         [0030]    The male thread  16  is selected to be compatible with comatable drillstring components, such as downhole motors and the like. The connection of the male threaded adapter  16  to any comatable drillstring components relies on an intimate compressive abutment between its downwardly facing external transverse sealing shoulder and a corresponding upwardly facing shoulder of a comating female connection. 
         [0031]    In order to avoid excess stress concentration, a fillet weld is provided between the upwardly facing external transverse shoulder  25  and the shank  18  of adapter  16 . The size of the fillet is slightly less than the internal chamfer at the end of the tubing  11 . The elongated shank  18  of end adapter  16  has an external slot  19  parallel to its axis extending from its upper end to adjacent the upwardly facing external transverse shoulder  25  of the adapter  16 . Slot  19  has a width and depth sufficient to readily accommodate the internal weld bead of the tubing without interference and also has a rounded internal end  20  adjacent shoulder  25 . 
         [0032]    The connection of the tubing  11  and the male threaded end adapter  16  is made by first aligning the internal weld bead  15  of the prepared tubing end  11  with the slot  19  in the shaft  18  of the end adapter  16 , then inserting the end adapter  16  into the tubing end  11  until the lower end of the tubing end  11  abuts the upwardly facing shoulder  25  of the threaded end adapter. When this action is complete, the internal weld bead  15  of the tubing is contained within the slot  19 , as seen in  FIG. 8 , and at least partially anchored against axial movement. 
         [0033]    Since tubing slot  12  is opposed to the longitudinal weld seam  15 , when the slot  19  of the shank  18  contains the weld bead  15 , the tubing slot  12  is on the opposite side of the tubing end  11  from the shank contained weld bead. The slot  12  is then completely filled by weld  23  so that a sealing structural connection is produced between the tubing end  11  and the adapter  16 . The weld  23  is made so that its outer surface is convex. Weld  23  is readily made and provides substantial axial and torsional strength to the joint between tubing  11  and adapter  16 . 
         [0034]    Following the making of weld  23 , a circumferential fillet weld  24  is made at the abutted junction of the end of the tubing  11  and the upwardly facing transverse shoulder  25  of the adapter  16 . While the circumferential fillet weld  24  does contribute both axial tension and torsion capacity to the connection between the tubing  11  and the adapter  16 , the primary requirement for the circumferential weld is that it completely seal between the two parts. The sizing of the two welds  23  and  24  is such that they possess a combined torsional and axial tension resistance greater than both the axial strength and the torsional strength of the coiled tubing. The interconnection of the tubing end  11  and the male threaded adapter  16  is fully sealed against leakage. 
       Second Embodiment 
       [0035]    The female thread adapter assembly  29 , shown in  FIG. 4 , of the second embodiment of the present invention is identical to the first embodiment  10  in all respects except that the female threaded adapter  30  has an internal tapered female thread  31 , rather than the male tapered thread  17  of the male threaded end fitting  16 . Both male and female threads are frequently used for connections in oilfield downhole tools. 
         [0036]    The same prepared tubing end  11  is used for both embodiments of the present invention. From its lower end, the exterior of the female threaded end adapter  30 , shown in  FIG. 6 , has a downwardly facing external transverse sealing shoulder, an enlarged cylindrical main body  32 , a transverse upwardly facing shoulder  36 , and a reduced constant diameter elongated shank  33 . The shank  33  has a close slip fit to the through bore of the tubing  11  when interference with the interior longitudinal weld seam  15  is avoided. 
         [0037]    Threaded adapter  30  has a coaxial through bore  34  to permit fluid flow and an internal tapered female thread  31  at its lower end. The length of the elongated shank  33  is somewhat more than that of the slot  12  in the prepared tubing end  11 . Typically, the length of shank  33  is on the order of two to four times the diameter of the tubing  11 . 
         [0038]    The female thread  31  is selected to be compatible with comatable drillstring components, such as downhole motors and the like. The connection of female thread adapter assembly  29  to any comatable drillstring components relies on an intimate compressive abutment between the downwardly facing external transverse sealing shoulder of adapter  30  and a corresponding upwardly facing shoulder of a comating male connection. 
         [0039]    In order to avoid excess stress concentration, a fillet is provided between the upwardly facing external transverse shoulder  36  and the shank  33  of adapter  30 . The size of the fillet is slightly less than the internal chamfer at the lower end of the tubing end  11 . The elongated shank  33  of end adapter  30  has an external slot  35  parallel to its axis extending from its upper end to adjacent the upwardly facing external transverse shoulder  36  of the adapter  30 . Slot  35  has a width and depth to readily accommodate the internal weld bead  15  of the tubing  11  without interference and also has a rounded internal end  20  adjacent shoulder  36 . 
         [0040]    The connection procedures for the female threaded adapter assembly  29  and the interconnection of the tubing end  11  and the female threaded adapter  30  are identical to those used for the male thread adapter assembly  10 . The connection of the tubing  11  and the female threaded end fitting  29  is made by first aligning the internal weld bead  15  of the tubing with the slot  35  of the end adapter  30 , then inserting the female threaded adapter  30  until the end of the tubing abuts the upwardly facing shoulder  36  of the adapter. Following this, tubing slot  12  is completely filled by welding so that a sealing structural connection is produced between the tubing  11  and the adapter  30 . The longitudinal weld  23  is made so that its outer surface is convex and extends slightly above the outer cylindrical surface of the tubing  11 . 
         [0041]    Following the making of weld  23 , a circumferential fillet seal weld  24  is made at the junction of the end of the tubing  11  and the upwardly facing transverse shoulder  36  of the adapter  30 . The sizing of the two welds  23  and  24  is such that they possess a combined torsional and axial tension resistance greater than both the combined axial strength and the torsional strength of the tubing  11 . 
         [0042]    The transverse sectional view of  FIG. 8  illustrates the connection of the male adapter assembly  10  to the tubing end  11 , but it can equally apply to the female threaded adapter assembly  29  if the external slot  35  in its elongated shank  33  is substituted for the corresponding items in the male threaded adapter  16 . 
       OPERATION OF THE INVENTION 
       [0043]    The threaded adapter assemblies  10  and  29  of the present invention basically are passive devices to which various comatably threaded devices are attached in order to enable various operations to be performed downhole in a well. The threaded connections between adapter assemblies  10  and  29  are made by fixedly gripping the outer cylindrical bodies  26  or  32  and then engaging appropriately threaded comating tools into full engagement at a predetermined torque. Releasing a threaded connection is done by firmly gripping the outer cylindrical bodies and applying sufficient torque to separate the connection. 
         [0044]    When a tool or device is deployed into a well on the lower end of a coiled tubing string which has attached one of the threaded adapter assemblies of the present invention, relatively high tension loads may have to be applied to the threaded adapter in order to free pipe that has been stuck in the well. Also, the threaded adapter may be subject to torsion loads during downhole operations. In such cases, the welds of the adapters readily provide tension and torsion capacities for the adapter assemblies equal to or greater than a simple fillet, butt, or groove weld can provide. The additional strength capacities provided by the addition of the longitudinal weld  23  also assist in avoidance of structural fatigue problems for the connections. 
       ADVANTAGES OF THE INVENTION 
       [0045]    The present invention permits the easy and reliable interconnection of the threaded end adapters to the outer end of a coiled tubing string so that the connection has both axial and torsional strength equal to or in excess of the strength of the tubing. Equivalent structural strength capacity is difficult or impossible to obtain reliably with only a single circumferential fillet weld or groove weld or butt weld. 
         [0046]    Inserting the shanks of the threaded end adapters into the tubing bore is simple and does not require vigorous hammering or otherwise forcing of the end adapters. The connecting welds are easy to make with conventional equipment, easily visually inspected, and can be made sufficiently strong and reliable to ensure reliable and fatigue resistant connections. Also, weld inspection is simple. 
         [0047]    The fabrication of the threaded adapters is simple and economical, and tubing end preparation does not require reaming or scarfing to remove the inwardly protruding seam weld. Reaming the tubing is difficult because of variations in tubing bore size and ovality, as well as being difficult to inspect. The tubing diameter tends to open up slightly when a longitudinal slot is cut through its wall, which further eases the installation of the adapter shank into the tubing bore. 
         [0048]    The above advantages result in a more reliable connection means which is less expensive, readily installed, and robust. 
         [0049]    Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. As may be understood readily by those skilled in the art, certain variations in the structure of the present invention may be made without departing from the spirit of the invention. For instance, the shape and dimensions of the component parts of the threaded adapters can be varied. These and other minor changes can be made without departing from the spirit of the invention.