Abstract:
An internal slip connector useful for attaching tools or other devices to the inside wall of a conduit, the connector having a mandrel with a head end, a threaded end, a reduced-diameter shaft section disposed between the head end and the threaded end, two abutting slip segments loosely disposed around the mandrel between the head end and an upper extending portion of the threaded end, and a nut threaded onto the mandrel below the slip segments. When tightened following insertion of the slip segments into the conduit, the nut causes the slip segments to slide radially outward along an oblique interface between them. Gripping surfaces disposed on the outside of the slip segments are thereby pressed into engagement with the inside wall of the conduit. The internal slip connector can be used with coiled tubing of various wall thicknesses and is easily released after loosening the threaded nut.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to apparatus useful for releasably securing one or more devices, especially well tools, to the free end of a conduit such as coiled tubing or pipe prior to running the conduit into a well bore. 
   2. Description of Related Art 
   The use of coiled tubing for running tools or other devices into the bore of an oil or gas well is well known. Coiled tubing is made of steel and is typically delivered to a well site on truck-mounted spools or reels and run into a well bore inside production tubing or casing that is already in place. Coiled tubing is made in various nominal diameters ranging, for example, from ¾ to 4½ inches, with nominal diameters of 1¼ inches to 2½ inches being quite common. Because coiled tubing is most often made by roll forming and welding a continuous strip of steel, a raised seam line often extends longitudinally down the inside wall of the tubing. Except for the seam line, the inside and outside wall surfaces of coiled tubing are typically smooth. 
   The use of external or internal slip connectors for releasably attaching well tools to coiled tubing and pipe is also well known. However, the conventional, commercially available slip connectors typically fit only a single wall thickness of tubing or pipe. Even for coiled tubing having a specified nominal diameter, the wall thickness and actual inside diameter can vary significantly depending upon factors such as manufacturer, material, use cycles, temperature, loading and the like. In the past it has been necessary, for example, to purchase and inventory as many as nine different sizes of slip connectors for use with coiled tubing having a nominal diameter of 1¼ inches. 
   Slip connectors are therefore needed that can be used easily and effectively with coiled tubing and pipe having different wall thicknesses for a given nominal diameter. 
   SUMMARY OF THE INVENTION 
   The invention disclosed herein is an internal slip connector that can be quickly and easily attached to, or released from, the inside wall of a conduit such as coiled tubing or pipe, and that is sufficiently adjustable to tightly engage the inside wall and withstand tensile loading without separation even where the wall thickness or the inside diameter vary significantly for a given nominal diameter. 
   According to a preferred embodiment of the invention, an internal slip connector is provided that is useful for attaching tools or other devices to the inside wall of a conduit, the connector comprising a mandrel with a head end, an externally threaded end opposite the head end, a reduced diameter shaft section disposed between the head end and the threaded end, and an axial bore; two cooperatively aligned slip segments disposed in loose sliding engagement around the mandrel between the head end and an upper extending portion of the threaded end; and a nut threaded onto the mandrel below the slip segments. When the nut is tightened following insertion of the slip segments into the conduit, the slip segments slide along an oblique interface where they abut each other and are canted apart slightly in opposite radial directions. A plurality of longitudinally spaced, arcuately extending teeth, wickers or other gripping surfaces disposed on the outside of the slip segments are thereby pressed into engagement with the inside wall of the conduit. The advancing movement of the threaded nut toward the mandrel head is stopped when the engagement force between the outer surface of the slip segments and the inside wall of the conduit is sufficiently great to support the weight of the tool or other device being attached to the conduit by the connector. A threaded collar is desirably provided below the threaded nut to act as a lock nut and also provide a threaded connection to tools or devices disposed below the connector. 
   Following use, the internal slip connector can be removed from the end of the conduit by loosening the threaded collar and nut, after which a minimal tensile force exerted between the conduit and connector will cause the slip segments to slide obliquely inward and out of engagement with the conduit wall, thereby releasing the connector from the conduit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The apparatus of the invention is further described and explained in relation to the following drawings wherein: 
       FIG. 1  is a simplified front perspective view of a preferred embodiment of the subject internal slip connector inserted inside the free end of a conduit prior to engagement of the slip segments with the conduit wall; 
       FIG. 2  is a perspective view as in  FIG. 1  but showing the internal slip connector removed from the free end of the conduit; 
       FIG. 3  is an exploded perspective view of the internal slip connector of  FIGS. 1 and 2 ; 
       FIG. 4  is an enlarged, cross-sectional elevation view of the internal slip connector and conduit taken along line  4 — 4  of  FIG. 1 , with the slip segments inserted into the free end of the conduit and coaxially aligned with the mandrel prior to engagement with the conduit wall; 
       FIG. 5  is a cross-sectional view taken along line  5 — 5  of  FIG. 4 ; 
       FIG. 6  is a detail view of structure from  FIG. 4 , showing the slip segments canted out of coaxial alignment with the mandrel and into engagement with the inside wall of the conduit; 
       FIG. 7  is a simplified front perspective view of a preferred embodiment of the subject internal slip connector inserted inside the free end of a conduit as in  FIG. 1 , but showing a segment of square tubing disposed around the connector and conduit; and 
       FIG. 8  is an enlarged, diagrammatic view identifying end points of the minimum and maximum transverse dimensions of the inside wall of the top slip segment as measured perpendicularly through the axial bore. 
   

   Like reference numerals are used to indicate like parts in all figures of the drawings. 
   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , internal slip connector  10  of the invention is shown with its top portion extending upwardly into the substantially cylindrical bore of a segment of coiled tubing  12 . Referring to  FIGS. 2 and 3 , in which coiled tubing segment  12  is exploded away from internal slip connector  10 , slip connector  10  further comprises collar  14 , threaded nut  16 , thrust washer  44 , slip segments  40 ,  42 , and mandrel  31  having head  26 , shaft  29  with a diameter reduced relative to the maximum transverse dimension of the head, threaded lower end  30  and an axial bore  32 . Coiled tubing  12  is generally cylindrical and comprises an inside wall  65  defining an axial bore  66 . Seam  64 , which is typically created when two edges are welded together during manufacture of the tubing, can project radially inward a small distance relative to the inside diameter of axial bore  66 . 
   The threaded length of threaded end  30  of mandrel  31  is desirably long enough to allow threaded nut  16  and collar  14  a sufficient range of travel to fully engage and disengage inside wall  65  of coiled tubing during use as described in greater detail below. According to one preferred embodiment of the invention, head  26  further comprises flat side  28  and downwardly facing flange surface  48 . Flat side  28  abuts against cooperatively aligned flat side  52  of upwardly projecting portion  50  of top slip segment  40  when internal slip connector  10  is assembled ( FIG. 2 ), and prevents slip segments  40 ,  42  from rotating relatively to mandrel  29 . 
   Top slip segment  40  preferably comprises a generally cylindrical body having an upwardly facing shoulder  46  that is generally perpendicular to inside wall  58  and is annular except where it steps upwardly at flat surface  52  of upwardly extending portion  50 . Oblique surface  60  abuts and engages a cooperatively aligned surface  68  of bottom slip  42 , and is preferably disposed at an angle ranging from about 45 to about 60 degrees to a plane perpendicular to the longitudinal axis through the mandrel. Although angles less than about 45 degrees and greater than about 60 degrees can also be used, they are less preferred for producing both the sliding engagement and the oppositely directed canting of slips  40 ,  42  that are desired during use of internal slip connector  10 . Bottom slip segment  42  also preferably comprises a generally cylindrical body having oblique surface  68  at its top and an annular bottom shoulder  80 . Bottom shoulder  80  is preferably substantially perpendicular to the inside wall of bottom slip segment  42 . Vertical groove  62  of top slip segment  40  and vertical groove  74  of bottom slip segment  42  are preferably cooperatively alignable with seam  64  and are configured to receive seam  64  of coiled tubing segment  12  into engagement with them to limit rotational movement between coiled tubing segment  12  and slip segments  40 ,  42  when slip segments  40 ,  42  are tightened into engagement with inside wall  65 . 
   Although the words “generally cylindrical” are used herein to describe the body of each of slip segments  40 ,  42 , it should be understood that the term “generally cylindrical” primarily characterizes the round outside shape of slip segments  40 ,  42  when they are stacked in vertical alignment as shown in  FIG. 2 . Where oblique surfaces  60 ,  68  are disposed in aligned, abutting relationship to each other, they cooperate to define an elongate structure that appears to be cylindrical in shape except for the outwardly facing surface elements that serve as gripping surfaces. A particularly preferred gripping surface comprises a plurality of downwardly and outwardly inclined surfaces  56 ,  72  that each terminate in axially spaced, arcuately extending teeth or ridges  54 ,  70  that “bite” into inside wall  65  of coiled tubing during tightening of threaded nut  16 . These outwardly facing gripping structures, sometimes referred to as “teeth” or “wickers,” are merely intended to be examples of satisfactory gripping structures for use in slip connectors  10  of the invention. It will be appreciated upon reading this disclosure, however, that other similarly effective gripping structures can likewise be used on the outwardly facing surfaces of slip segments  40 ,  42  to provide tight frictional engagement with inside wall  65  of coiled tubing segment  12  during use. Slip segments  40 ,  42  are desirably made of a type of steel that is hard enough to withstand excessive deformation when, for example, teeth or ridges  54 ,  70  are tightened into engagement with inside wall  65  of coiled tubing  12 . Satisfactory metals for use in making slip segments  40 ,  42  include P110 or 4140 steel, or an equivalent. P110 steel has a little higher tensile strength that 4140 and is therefore preferred. 
   The preferred shape of the internal bore of slip segments  40 ,  42  is further described and explained in relation to  FIG. 8 , which depicts a cross-sectional view through top slip segment  40  (taken below surface  46 ). The internal bore geometry of bottom slip segment  42  is preferably substantially the same. Referring to  FIG. 8 , inside wall  58  of top slip segment  40  is desirably oval-shaped, with points  94 ,  98  identifying the ends of the maximum transverse dimension measured perpendicularly through longitudinal axis  92  and with points  96 ,  100  identifying the minimum transverse dimension measured perpendicularly through longitudinal axis  92 . In this view, top slip segment  40  is rotated 90 degrees clockwise from the view shown in  FIGS. 2 and 3 , so that groove  62  is facing to the left side rather than forwardly. Although the language “oval-shaped” is used herein to describe a cross-sectional area that is elongated and facilitates more lateral movement in one direction relative to a centrally disposed mandrel than in a perpendicular direction in the same horizontal plane, it should be appreciated that such terminology is not intended necessarily to invoke the strict mathematical precision of an ellipse nor to preclude use of a more oblong bore having relatively parallel opposed sides disposed proximally to the mandrel. The functional purpose of the oval-shaped wall  58  is to facilitate some lateral movement of the slip segments in one direction while more closely limiting lateral movement in the perpendicular direction. This allows a portion of the gripping surfaces to engage the inside wall of the coiled tubing during tightening without excessive slack or wobbling that could result in misalignment or rotation between slip segments  40 ,  42 . As used herein, the term “gripping surfaces” is not intended to suggest adhesion but rather a tight frictional engagement in which the surface irregularities on the slip segments improve the “bite” achieved when the slips are forced into engagement with the inside wall of the coiled tubing. 
   Referring again to  FIGS. 2 and 3 , thrust washer  44  is preferably made of brass and is intended to provide wear surfaces between the top of threaded nut  16  and bottom shoulder  80  of bottom slip segment  42  as threaded nut  16  is rotated upwardly toward head  26  of mandrel  31 . One benefit of the present invention is that slip segments  40 ,  42  and thrust washer  44  are easily and conveniently replaceable between successive uses of mandrel  31 , collar  14  and threaded nut  16  if excessive wear or deformation occurs during use. 
   Referring to  FIG. 3 , threaded nut  16  preferably further comprises an unthreaded upper section  18  having an upwardly facing annular surface  36  and a bore  34  with an inside diameter slightly greater than the outside diameter of threaded end  30  of mandrel  31 . Annular flange member  20 , has an outer diameter substantially the same as the outside diameter of coiled tubing  12 , with an upwardly facing annular O-ring groove  35  for seating O-ring  37  prior to urging top shoulder  38  into abutting engagement with bottom end surface  82  of coiled tubing  12  prior to tightening threaded nut  16 . Internally threaded hex head section  22  is desirably provided below flange member  20  to facilitate use of a wrench in tightening nut  16  on threaded end  30  of mandrel  31 . 
   Cylindrical collar  14  is desirably provided for use as a lock nut to prevent threaded nut  16  from backing away from thrust washer  44  and lower slip segment  42  when under load, and for use in attaching other tools or devices to the coiled tubing beneath internal slip connector  10 . Such other tools or devices are preferably attached to collar  14  by threaded engagement, and the lower portion of collar  14  can be provided with either box threads (as in  FIG. 4 ) or with pin threads, as desired, or by any other known suitable means. 
   The operation of internal slip connector  10  is further described in relation to  FIGS. 4–6 . Referring to  FIG. 4 , mandrel head  26  and slip segments  40 ,  42  are shown fully inserted into coiled tubing  12 , with O-ring  37  providing sealing engagement between annular space  86  inside coiled tubing  12  and flange member  20 . Slip segments  40 ,  42  are coaxially aligned relative to longitudinal axis  92 , and ridges or teeth  54 ,  70  of are not engaging inside wall  65  of coiled tubing segment  12 . Collar  14  is threaded onto the bottom of threaded end  30  but is not yet tightened snugly against hex head  22 .  FIG. 5  is a cross-sectional view through  FIG. 4  and depicts the position of mandrel wall  24  relative to oval-shaped inside wall  58  of slip segment  40 . In  FIG. 5 , seam  64  is shown projecting inwardly from inside wall  65  of coiled tubing  12 , and is aligned with but not engaging vertical groove  62  of slip segment  40 . 
   The fully engaged position of internal slip connector  10  relative to coiled tubing segment  12  is shown in  FIG. 6 . In  FIG. 6 , hex head  22  has been rotated in a clockwise direction, causing unthreaded upper portion  18  to advance upwardly against thrust washer  44 , which has in turn caused bottom slip segment  42  to push upwardly against top slip segment  40 . As bottom slip segment  42  moves upwardly, oblique surface  68  slides along abutting oblique surface  60 . Then, because further upward movement of slip segment  40  is impeded by mandrel head  26 , ridges  70  near the top of bottom slip segment  42  and ridges  54  near the bottom of top slip segment  40  are canted outwardly into engagement with inside wall  65  of coiled tubing  12 . Additional pressure exerted by the threaded nut  16  on slip segments  40 ,  42  causes slip segments  42 ,  40  to wedge tightly together along abutting oblique surfaces  60 ,  68 , and causes ridges (teeth)  54 ,  70  to “bite” into even tighter frictional engagement with wall  65  of coiled tubing segment  12 . Once hex head  22  of threaded nut  16  is tightened to the desired extent, collar  14  is desirably tightened snugly against it and additional tools or devices to be suspended from internal slip connector  10  are also attached to the bottom of collar  14 . 
   It will be appreciated upon reading this disclosure that the preferred torque needed to reliably but releasably secure slip segments  40 ,  42  to coiled tubing  12  will depend upon many factors including, for example, the intended load to be suspended from internal slip connector  10 , the diameter and wall thickness of the coiled tubing  12 , the diameter and gauge of the threads on nut  16  and threaded end  30 , and the relative hardness of the materials used in making slip segments  40 ,  42  and inside wall  65  of coiled tubing  12 . For steel coiled tubing having a nominal diameter of 1.25 inches, a maximum typical design load is about 5000 pounds. In practice, nut  16  and collar  14  are tightened preliminarily and then a tensile load of about 1000 pounds is applied across the connection to “set” the teeth in wall  65  of coiled tubing  12 . Nut  16  and collar  14  are then further tightened and a tensile load of about 3000 to about 5000 pounds is applied to insure a firm connection. Nut  16  and collar  14  are then tightened again if necessary, and the coiled tubing operation can continue. After completion, collar  14  and nut  16  are loosened and sufficient tensile force is applied to disengage slip segments  40 ,  42  from inside wall  65  of the coiled tubing  12 . 
   In some cases, the material, diameter and wall thickness of coiled tubing  12  may cause concern that tightening the slip segments of internal slip connector  10  will deform coiled tubing  12 . In such cases, a segment of square tubing  90 , if positioned substantially as shown in  FIG. 7 , can be utilized to maintain dimensional stability of coiled tubing  12  during tightening. 
   Other alterations and modifications of the invention will likewise become apparent to those of ordinary skill in the art upon reading this specification in view of the accompanying drawings, and it is intended that the scope of the invention disclosed herein be limited only by the broadest interpretation of the appended claims to which the inventor is legally entitled.