Abstract:
Self-assembling segmented coiled tubing is a concept that allows the strength of thick-wall rigid pipe, and the flexibility of thin-wall tubing, to be realized in a single design. The primary use is for a drillstring tubular, but it has potential for other applications requiring transmission of mechanical loads (forces and torques) through an initially coiled tubular. The concept uses a spring-loaded spherical ‘ball-and-socket’ type joint to interconnect two or more short, rigid segments of pipe. Use of an optional snap ring allows the joint to be permanently made, in a ‘self-assembling’ manner.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional patent application Ser. No. 61/121,045 filed Dec. 9, 2008, which is incorporated herein by reference. 
    
    
     FEDERALLY SPONSORED RESEARCH 
     The United States Government has rights in this invention pursuant to Department of Energy Contract No. DE-AC04-94AL85000 with Sandia Corporation. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to drilling and drillstring equipment for oil and gas drilling, water well drilling, geothermal drilling, etc. 
     Most traditional drillstrings are constructed of straight sections of rigid pipe (i.e., ‘rigid tubulars’) interconnected (i.e., joined) by threaded joints. The pipe is typically manufactured with a thick wall section to allow it to convey large mechanical loads. 
     Coiled tubing is also used for drillstring tubulars. Its advantage is it can be transported to the drill site in long lengths (wrapped around a large spool) and readily deployed into the well. It is typically manufactured with a thinner wall than rigid pipe because it must be transported by wrapping the tubing around a spool (typical spool diameter ranges from 4-8 ft). It is deployed into the well by un-coiling it from the spool into a linear section, and then bending it over a gooseneck and down into the well. Coiled tubing typically has a wall thickness of 3/32- 3/16 inches thick, and outer diameter about 2-3 inches (e.g., 2.5 inches). Coiled tubing has material limitations in how tightly it can be wound on the spool. It also requires large forces to deploy it from the wound condition. 
     Traditional thick-walled jointed pipe offers the benefit of a tubular with greater strength; while thin-walled coiled tubing offers the benefit of rapid deployment. 
     The segmented coiled tubing concept of the present invention is a system that provides the benefits of both jointed pipe and coiled tubing. It eliminates the bending operation during unwinding, it can self-assemble, and it acts like rigid pipe once assembled. 
     Against this background, the present invention was developed. 
     SUMMARY OF THE INVENTION 
     Self-assembling segmented coiled tubing is a concept that allows the strength of thick-wall rigid pipe, and the flexibility of thin-wall tubing, to be realized in a single design. The primary use is for a drillstring tubular, but it has potential for other applications requiring transmission of mechanical loads (forces and torques) through an initially coiled tubular. The concept uses a spring-loaded spherical ‘ball-and-socket’ type joint to interconnect two or more short, rigid segments of pipe. Use of an optional snap ring allows the joint to be permanently made, in a ‘self-assembling’ manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form part of the specification, illustrate various examples of the present invention and, together with the detailed description, serve to explain the principles of the invention. 
         FIG. 1  is a representation of rigid tubulars (pipe segments), wound around a spool, in their axially displaced and rotated configuration, allowing the spherical joint to become active. 
         FIG. 2  is a cross section view through adjacent rigid pipe segments in the axially displaced and rotated configuration. Note: the snap ring is not shown. 
         FIG. 3  is a cross-section view through adjacent rigid pipe segments in a mated (assembled) configuration. 
         FIG. 4  is a cross section view through adjacent rigid pipe segments in the axially displaced and rotated configuration. Note: the snap ring is not shown. 
         FIG. 5  is a cross-section view through a rigid pipe segment. 
         FIG. 6  is a 3-D solid shaded isometric view of a rigid pipe segment. 
         FIG. 7  is a 3-D solid shaded isometric view of a spherical joint socket. 
         FIG. 8  is a 3-D solid shaded isometric view of a spherical ball joint connector comprising a ball mounted on a connecting link (note: coil spring is not shown). 
         FIG. 9  is a cross-section view through a rigid pipe segment showing two separate parts, A and B, which have been permanently joined together. 
         FIG. 10  is an exploded, isometric view of all the parts of the spherical joint for connecting two adjacent rigid pipe segments. Note: the coil spring and snap ring is not shown. 
         FIG. 11A  shows a rapid prototype model (plastic) showing adjacent tubulars mated together. 
         FIG. 11B  shows a connecting link including a coil spring and a ball. 
         FIG. 11C  shows a rigid pipe segment having male insert end, and a socket. 
         FIG. 12  is a rapid prototype (plastic) model showing the relative motion (rotation and axial displacement) of adjacent tubulars. 
         FIG. 13  is a cross-section view through adjacent rigid pipe segments in a mated (assembled) configuration. 
         FIG. 14  is a side view through adjacent rigid tubular segments in a mated (assembled) configuration. 
     
    
    
     LIST OF NUMBERED FEATURES REFERENCES IN FIGURES 
     
         
         
           
               8 —spool 
               10 —rigid pipe segment 
               12 —adjacent rigid pipe segment 
               13 —coil spring 
               14 —connecting link 
               16 —ball 
               17 —internal shoulder of rigid pipe segment for retaining spring 
               18 —socket 
               20 —internal snap ring groove 
               22 —external snap ring groove 
               24 —spherical joint 
               26 —snap ring 
               30 —front-facing contact surface of rigid pipe segment 
               32 —outer tapered sliding surface at insert end of socket 
               34 —inner sliding surface of rigid pipe segment 
               36 —rear-facing contact surface of socket 
               37 —internal spherical bearing surface of socket 
               39 —male insert end of rigid pipe segment 
               40 —internal spherical bearing surface of rigid pipe segment 
               41 —end plane of the rear end of second rigid pipe segment 
               42 —spring-retaining external shoulder (flange) of connecting tube 
               44 —internal bore of ball 
               50 —continuous tube insert 
               60 —rigid pipe segment 
               62 —rigid pipe segment 
               64 —rigid pipe segment 
               66 —spherical ball joint 
               68 —spherical ball joint 
               70 —slanted mating contact surface 
               72 —slanted mating contact surface 
             D 1 =larger inner diameter of rigid pipe segment 
             D 2 =smaller inner diameter of rigid pipe segment 
             D 3 =inner diameter of connecting tube 
           
         
       
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a representation of the present invention, comprising a series of short, rigid segments of pipe  10 ,  12  (i.e., rigid tubulars) interconnected by a hidden, spring-loaded spherical ‘ball-and-socket’ type joint  24 . The interconnected set of two (or more) rigid tubulars are circumscribed around the periphery of a spool  8  in a pre-assembled (i.e., displaced) configuration. Axial displacement of the spring-loaded spherical joint  24  allows rotation between adjacent segments  10  and  12  about an infinite number of axes; thereby allowing the segmented tube/pipe segments to be helically coiled on the spool. Activation of the spherical joints allow rotation of the individual pipe sections relative to one another, thereby allowing, for example, the individual pipe sections to circumscribe the periphery of a mounting spool in a piece-wise smooth fashion. 
       FIGS. 2, 3 and 4  show cross section views through adjacent rigid pipe segments in the axially-displaced (separated) and rotated configuration ( FIGS. 2 and 4 ), and the self-assembled (i.e., mated and locked) configuration ( FIG. 3 ). Note: the snap ring is not shown in  FIGS. 2 and 4 . The self-assembling segmented coiled tubing concept comprises a series of short, rigid pipe sections  10 ,  12  (for example, ranging from 6 to 8 inches long, but can be shorter, or much longer, if needed) having, for example, an outer diameter 2.5 inches, and wall thickness=⅜ to ½ inch thick, which are interconnected by spherical joint  24 . The pair of adjacent pipe segments  10 ,  12  can be axially displaced by pulling on spring-loaded connecting link  14 , thereby compressing coil spring  13 . 
     Spherical joint  24  comprises four pieces: connecting link  14 , coil spring  13 , spherical ball  16 , and socket piece  18 . In  FIGS. 2-4 , link  14  and ball  16  are shown as being hollow, with an inner diameter=D 3 . Axial displacement of the spherical joint  24  allows the spherical joint to become ‘active’ (i.e., free to rotate) by disengaging and separating the pair of mating contact surfaces  30  and  36 . Connecting link  14  comprises a spring-bias means  13  (e.g., a coil spring) for providing a restoring force to pull separated sections back together; for example, after the coiled tubulars have been unwound from the mounting spool; thereby making the unwinding process ‘self-assembling”. Spring  13  is limited (constrained) at one end by external shoulder (flange)  42  of tube  14 , and is limited (constrained) at the other end by internal shoulder  17  of pipe segment  10 . Hollow spherical ball  16  is attached to the other end of connecting link  14 , after link  14  has been inserted inside of the inner bore of the pipe segment  10 . Connecting link  14  can be a hollow tube. 
     Spherical joint  24  is “hidden”, meaning that when the adjacent rigid pipe segments  10  and  12  are mated together (assembled), the spherical joint is completely hidden from view, inside of the pipe segments. 
     The mating contact surfaces (front-facing surface  30 , and rear-facing surface  36 ) between adjacent segments  10 ,  12  can have interlocking contact areas  30  and  36  that allow (when touching) for transmission of mechanical thrust and bending moments along the axis of the mated sections. The interlocking mating surfaces can have, for example, an interlocking-type geometry that allows for transmission of torque between mated (assembled) sections. Examples of suitable interlocking-geometries include: semi-circle, semi-oval, sine-wave curve (i.e., wavy curve), spline-curve, fluted castellated curve, sawtooth curve, square-wave, gear-tooth design, or other similar interlocking geometries. 
     Optionally, the two mating contact surfaces  30  and  36  can be flat (planar), as shown in  FIG. 1 , with a non-interlocking geometry. In this example, the orientation of the flat contact surfaces  30  and  36  is perpendicular to the centerline axis of the rigid pipe segments. This allows the individual pipe segments  10 ,  12  to freely rotate about the centerline axis before, and after, being assembled (mated). In this option, no significant torque could be applied to the assembled tubulars (although compressive axial loads can be transmitted, and tensile axial loads can be transmitted if a snap ring is used). 
     A snap ring  26  (see  FIG. 3 ) can be used in the mated sections to ensure the permanence of the completed joint. Snap ring  26  fits into internal snap ring groove  20  on socket  18 , and then snaps into the external snap ring groove  22  in pipe segment  10  when assembled. The use of a snap ring also ensures the mated components do not slip relative to one another during torque transmission, by reacting the axial thrust generated by any inclined surfaces of the interlocking mating surfaces  30  and  36  that transmit the torque. 
     Optionally, a snap ring does not have to be used. In that case, the assembled joints would remain flexible and rotatable when pulled apart to displace the interlocking-geometry of the mating surfaces. This would allow the assembly to be repeatedly re-coiled around a spool, for example, if needed. However, reduced tensile strength of the drillstring would be expected without using the snap ring (when assembled). 
     Although not illustrated in the Figures, the design can also include an O-ring, or other type of fluid seal (which can be located, for example, between the snap ring and the inner shoulder of a pipe segment), whereby the internal volume of the mated sections could be sealed from the outer environment and used for fluid conveyance (liquid, gas), or other means. 
     In another embodiment (not illustrated) the interior volume of the spherical joint  24  (e.g., connecting link  14  and ball  16 ) is solid, not hollow or tubular. 
     In  FIG. 4 , the tapered external contact surface  32  at the male end of socket piece  18  is shaped to smoothly slide into the female end of the adjacent pipe segment  10  along matching interior sliding surface  34 . This surface can be lubricated, or made of a low-friction material, to prevent galling. 
     Additionally, or alternatively, the external bearing surface  34  of the tapered male end of socket  18 , and the matching internal bearing surface  34  inside the female end of rigid pipe segment  10  can have an internal fluted (straight-spline, gear-like) type of geometry that resists torsion. 
     The spherical joint connecting pieces  14 ,  16  and  18  can be made of steel, brass, aluminum, sintered bronze, plastic, ceramic, or other suitable material. The material can be the same, or different, than the rigid pipe sections. The individual pieces  14 ,  16  and  18  of spherical joint  24  can be made of the same, or different, materials. For example, tube  14  and ball  16  could be made of a plastic or polymer, while socket piece  18  could be made of metal. 
     Socket  18  can be attached to rigid pipe segment  12  in a variety of ways, including: threaded connection, brazed, welded, shrink-fit, friction welded, glued, and via a second snap-ring (not illustrated). Likewise, spherical ball  16  can be attached to connecting tube  14  in a variety of ways, including: threaded connection, brazed, welded, shrink-fit, friction welded, glued, and via a third snap-ring (not illustrated). 
     Bearing (sliding) surfaces can be treated with a low-friction surface treatment or coating, as needed, to prevent galling. 
     Spring  13  can be a coil spring, wave spring, or other type of spring, as is well known in the art. Alternatively, spring  13  can be an elastic rubber or polymeric material with similar spring resistance to a coil spring. 
     The self-assembling segmented coiled tubing concept of the present invention is different from rigid tubulars in that it includes self-assembling features. It is different from coiled tubing in that it extends the operating range for bending rates (e.g., allowing a much smaller radius of curvature) and extends the operating range for mechanical load transmission (both forces and torques). 
     Optionally, the rigid pipe segments  10 ,  12  can have a non-circular cross-section, such as a triangular, square, oval, or hexagonal cross-section. 
       FIG. 5  shows a cross-section view of pipe segment  12  and socket piece  18 . The interior spherical surface  37  of socket  18  and the interior spherical surface  40  of pipe segment  12  both circumscribe the same circle as the exterior surface of spherical ball  16  (not shown), including the normal manufacturing tolerances for allowing the inner and outer spherical surfaces to slide relative to each other. In other words, interior surfaces  37  and  40  define an interior, semi-spherical cavity (i.e., socket) for the holding ball  16 . The center ball  16  is aligned with the end plane  41  of the rear end of pipe segment  12 . Alternatively, the center of ball  16  can be slightly offset from the actual end of segment  12  by a few thousandths of an inch (i.e., segment  12  can be undercut). 
       FIG. 6  is a 3-D solid shaded isometric view of rigid pipe segment  10 . 
       FIG. 7  is a 3-D solid shaded isometric view of spherical joint socket piece  18 . Mating surface  36  is shown here as a sine-wave type interlocking shape with, for example, two ‘high’ spots and two ‘low’ spots. 
       FIG. 8  is a 3-D solid shaded isometric view of a spherical ball joint connector comprising a ball  16  mounted on a connecting link  14  (note: coil spring is not shown). The connecting tube  14  has a raised external shoulder  42  on the far end to retain the coiled spring. Ball  14  has a hollow interior bore  44 . 
     In  FIG. 9 , the rigid pipe segment  12  can optionally comprise two separately-machined parts A and B, where part A can be attached to part B in a variety of ways, including: threaded connection, brazed, welded, shrink-fit, friction welded, glued, and via a second snap-ring (not illustrated). 
       FIG. 10  is a 3-D solid-shaded, isometric, exploded view of all the parts ( 14 ,  18 ,  16 ) of the spherical joint connecting assembly  24  used for connecting two adjacent rigid pipe segments  10  and  12 . Note: coil spring  13  and snap ring  26  are not shown. 
       FIG. 11A  shows a rapid prototype model (plastic) showing adjacent tubulars mated together.  FIG. 11B  shows a connecting link including a coil spring and a ball.  FIG. 11C  shows a rigid pipe segment having male insert end, and a socket. 
       FIG. 12  is a rapid prototype (plastic) model showing the relative motion (rotation and axial displacement) of displaced adjacent tubulars. The compressed spring can be seen. 
       FIG. 13  is a cross-section view through adjacent rigid pipe segments in a mated (assembled) configuration. A continuous (i.e., non-jointed) tube  50  has been inserted through the central bore of the assembly. 
       FIG. 14  is a side view through three adjacent rigid tubular segments  60 ,  62 ,  64 , with spherical joints  66  and  68 , in a mated (assembled) configuration. The mating contact surfaces (e.g.,  70  and  72 ) are flat, but slanted at an angle, θ, with respect to the pipe&#39;s centerline, so that when the individual rigid segments  60 ,  62 ,  64  are aligned and connected with snap rings (not shown), the completed assembly is non-straight, depending on the angle of the slanted mating surface. 
     The particular examples discussed above are cited to illustrate particular embodiments of the invention. Other applications and embodiments of the apparatus and method of the present invention will become evident to those skilled in the art. It is to be understood that the invention is not limited in its application to the details of construction, materials used, and the arrangements of components set forth in the following description or illustrated in the drawings.