Abstract:
A method that is usable with a well includes changing a connection between a first coiled tubing segment and a second coiled tubing segment while an upper end of the first coiled tubing section is out of the well and a portion of the first coiled tubing segment is deployed in the well. After the connection is changed, the method includes deploying the remainder of the first coiled tubing segment into the well or retrieving the portion of the first coiled tubing segment from the well.

Description:
[0001]     This application is a continuation-in-part of U.S. patent application Ser. No. 11/115,610, entitled, “TUBING CONNECTOR,” which was filed on Apr. 27, 2005, and is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND  
       [0002]     The invention generally relates to a technique and system for intervening in a wellbore using multiple reels of coiled tubing.  
         [0003]     Coiled tubing is used in a broad array of applications in oilfield operations such as drilling and completing oil and gas wells, conveying equipment, and performing maintenance on completed oil and gas wells. To deploy coiled tubing into a wellbore, the coiled tubing string is unreeled or unspooled from a coiled tubing reel, run over an injector gooseneck and inserted into a wellhead system for injecting the coiled tubing into the wellbore. To retract coiled tubing from a wellbore, the coiled tubing is reeled or spooled back out of the wellbore through the wellhead system over the gooseneck and onto the coiled tubing reel. It is known that bending and straightening the coiled tubing in well site operations and spooling the coiled tubing on a reel causes low cycle fatigue in the coiled tubing, which if left unchecked can lead to failure of the coiled tubing. The ability to unreel and reel coiled tubing as a continuous tubing string nevertheless offers attractive operational advantages over jointed pipe that requires connections at each relatively short length of pipe.  
         [0004]     It is not uncommon for the reel to contain ten thousand feet or more of coiled tubing, as the length of the tubing on the reel typically is a function of the deepest intervention in which the coiled tubing will be used. Furthermore, additional coiled tubing typically is added to the reel for purposes of creating spare tubing that may be cut off to remove a damaged section.  
         [0005]     Challenges typically arise in transporting the reel to the well site and handling the coiled tubing reel at the well site due to the size of the reel. Thus, there is a continuing need for better ways to deploy a coiled tubing string into a well and retrieve the string from the well.  
       SUMMARY  
       [0006]     In an embodiment of the invention, a method that is usable with a well includes changing a connection between a first coiled tubing segment and a second coiled tubing segment while an upper end of the first coiled tubing segment is out of the well and a portion of the first coiled tubing segment is deployed in the well. After the connection is changed, the method includes deploying the remainder of the first coiled tubing segment into the well or retrieving the portion of the first coiled tubing segment from the well.  
         [0007]     In another embodiment of the invention, a system that is usable with a well includes a first coiled tubing segment, a second coiled tubing segment and slips. The slips secure an upper end of the first coiled tubing segment when the first coiled tubing segment is partially deployed in the well to permit the second coiled tubing segment to be selectively connected to or disconnected from the first coiled tubing segment.  
         [0008]     In another embodiment of the invention, a method of deploying coiled tubing in a wellbore includes providing a coiled tubing connector having a body with a longitudinal bore therethrough, the body including a first end section and a second end section sections. Each end section includes a tapered external surface and a stiff section disposed between the first and the second end sections. The method also includes disposing the first end section within a first coiled tubing having a wall thickness and disposing the second end section within a second coiled tubing having a wall thickness different than the wall thickness of the first coiled tubing. The method further includes securing the stiff section to the inner diameter of each of the first and second coiled tubings, thereby forming a connected tubing and lowering the connected tubing into a wellbore.  
         [0009]     Advantages and other features of the invention will become apparent from the detailed description, drawing and claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0010]      FIG. 1  is a schematic diagram of a well according to an embodiment of the invention.  
         [0011]      FIG. 2  is a flow diagram depicting a technique to deploy coiled tubing in a well according to an embodiment of the invention.  
         [0012]      FIG. 3  is side view of a specific embodiment of a coiled tubing connector according to an embodiment of the invention, and in use to connect a section of coiled tubing to a tool string.  
         [0013]      FIG. 4A  is a side view of another specific embodiment of a coiled tubing connector according to an embodiment of the invention similar to the one shown in  FIG. 3  but shown not connected to any coiled tubings.  
         [0014]      FIG. 4B  is a side view of another specific embodiment of a coiled tubing connector according to an embodiment of the invention.  
         [0015]      FIG. 4C  is a side view of another specific embodiment of a coiled tubing connector according to an embodiment of the invention.  
         [0016]      FIG. 5  is side view of two coiled tubing connectors according to an embodiment of the invention, and in use to connect coiled tubing to a tool string.  
         [0017]      FIG. 6  is a side view of a specific embodiment of a coiled tubing connector according to an embodiment of the invention, and in use to connect two sections of coiled tubing to a tool string.  
         [0018]      FIG. 7A  is a strain diagram from a finite element model of a prior art internal coiled tubing connector having a flexible center section.  
         [0019]      FIG. 7B  is a strain diagram from a finite element model of an embodiment of a coiled tubing connector according to an embodiment of the invention.  
         [0020]      FIG. 8  is side view of another specific embodiment of a coiled tubing connector according to an embodiment of the invention, and in use to connect two sections of coiled tubing.  
         [0021]      FIGS. 9, 10  and  11  are side views of specific embodiments of a coiled tubing connector according to other embodiments of the invention and in use to connect a section of coiled tubing to a tool string.  
         [0022]      FIG. 12  is a schematic diagram illustrating a two piece coiled tubing connector according to another embodiment of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0023]     Referring to  FIG. 1 , an embodiment  10  of a well in accordance with the invention includes a wellbore  20 , which may or may not be cased by a casing string  22 . During the drilling, completion and maintenance of the well  10 , a coiled tubing string  30  may be run into the wellbore  20  to perform a specific function, and thereafter, the coiled tubing string  30  may be retrieved from the wellbore  20 . As a more specific example, to treat the well  10 , the coiled tubing string  30  may be run downhole inside the wellbore  20  for purposes of introducing a stimulation fluid.  
         [0024]     Unlike conventional arrangements, the coiled tubing string  30  is formed from relatively short, connected coiled tubing segments (segments of approximately 2000, 3000, 4000 or 5000 feet, as examples) instead of, for example, one relatively long continuous segment (a segment of 10,000 feet or more, for example) that spans the length of the intervention. To accomplish this, the coiled tubing is transported to the well in several reels  35  (one of which is depicted in  FIG. 1 ), each of which may contain one of the coiled tubing segments. Each coiled tubing segment that forms the coiled tubing string  30  may be a continuous length of coiled tubing, and connectors are used to concatenate the coiled tubing segments together for purposes of forming the string  30 . As further described below, the coiled tubing string  30  may contain tools that may be added at the end of the string  30  as well at intermediate locations of the string  30  due to the string&#39;s segmented design.  
         [0025]     In accordance with embodiments of the invention, each coiled tubing segment is transported to the well site on its own reel  35  and may have an attached connector at each end, which is constructed to mate with a connector of another coiled tubing segment or tool. Thus, in these embodiments of the invention, a two piece connector assembly (such as one female connector and one male connector) is used to join coiled tubing segments and add tools to the coiled tubing string  30 . In other embodiments of the invention, a one piece connector assembly may be used to connect coiled tubing segments and add tools to another segment or tool. Many variations are therefore contemplated and are considered to be within the scope of the appended claims.  
         [0026]     As a more specific example, in accordance with some embodiments of the invention, one end of the coiled tubing segment may have a female connector, and the other end of the coiled tubing segment may have a male connector. Thus, to join two coiled tubing segments together, the male and female connectors from the segments are mated together.  FIG. 1  depicts two exemplary coiled tubing segments in connection with the deployment or retrieval of the coiled tubing string  30  to/from the well  10 : an upper coiled tubing segment  30   a  that is located outside of the wellbore  20  and is partially wound around its associated reel  35 ; and a lower coiled tubing segment  30   b  that has previously been unwound from its associated reel (not shown), is partially disposed in the wellbore  20  and is connected at its lower end to another coiled tubing segment or tool. The upper coiled tubing segment  30   a  is attached at its lower end via its connector  70  to a mating connector  80 , which, in turn, is connected to the upper end of the lower coiled tubing section  30   b.    
         [0027]     For the state of the well  10  depicted in  FIG. 1 , the upper end of the lower coiled tubing segment  30   b  is engaged by slips  56 , which secure the upper end so that the connector  80  may be connected to or disconnected from the connector  70 , depending on whether the coiled tubing string  30  is being deployed in or retrieved from the wellbore  20 .  
         [0028]     The upper coiled tubing segment  30   a  is partially wound around its associated reel  35  and extends through a coiled tubing injector  50  and a gooseneck  40 . On the reel  35 , the end of the coiled tubing segment  30   a  is secured to an end connector  88  that is mated to a connector  78  that, in turn, is secured to a shorter coiled tubing segment  30   c , which is mounted to the drum of the reel  35 . The shorter coiled tubing segment  30   c  has a length that is sufficient to extend over the gooseneck  40  and the injector  50  to the position where the end connector  88  is secured by the slips  56 . Thus, when the coiled tubing segment  30   a  is deployed, the coiled tubing segment  30   c  unwinds from the reel  35  until the connectors  78  and  88  pass through the injector  50 , and the upper end of the coiled tubing segment  30   a  is secured by the slips  56 . At this point, the connectors  78  and  88  are disconnected, the shorter coiled tubing segment  30   c  is wound back on the reel  35 , the reel  35  containing the shorter coiled tubing segment  30   c  is removed; and subsequently, a coiled tubing segment (from another reel) may be unwound and run through the injector  56  and attached to the coiled tubing segment  30   a  in a similar manner. More coiled tubing segments may be added to the coiled tubing string  30  in a similar manner. The opposite process occurs for retrieving the coiled tubing string  30  from the well.  
         [0029]     In accordance with some embodiments of the invention, the connectors  70  and  78  may be female connectors, and the connectors  80  and  88  may be male connectors.  
         [0030]     To summarize, in accordance with some embodiments of the invention, a technique  100  (see  FIG. 2 ) to deploy coiled tubing in a well includes deploying (block  104 ) the next coiled tubing segment through the injector  50  and into the wellbore  22 . If a determination is made (block  108 ) that another coiled tubing segment is to be deployed, then the upper end of the uppermost partially deployed coiled tubing segment is secured (block  112 ) by the slips  56  so that the lower end of the next coiled tubing segment to be deployed is attached to the uppermost deployed coiled tubing segment, pursuant to block  114 . The technique  100  continues with block  104  to deploy the next coiled tubing segment so that the blocks  104 ,  108  and  112  are repeated for each coiled tubing segment.  
         [0031]     The coiled tubing string  30  may likewise be retrieved from the well in segments by a process that includes, for each coiled tubing segment that emerges from the well, engaging the upper end of the coiled tubing segment with slips, disconnecting the coiled tubing section from the coiled tubing section above, connected the coiled tubing section to a shorter coiled tubing section that is connected to the drum of a reel and then, winding the shorter coiled tubing section and now attached coiled tubing section from the well back onto the reel. This process continues until all coiled tubing segments have been wound onto their respective reels and thus, the coiled tubing string  30  has been retrieved from the wellbore  20 .  
         [0032]     As depicted in  FIG. 1 , among its other features, the well  10  may include a well tree  31  through which the coiled tubing string  30  passes and which seals off the region of the string  30  above the tree from the wellbore  20 . The well tree  31  may include, as examples, a lubricator and a blow out preventer (BOP) and may include ports to communicate fluids to and from the wellbore  20 .  
         [0033]     In addition to including coiled tubing sections, the coiled tubing string  30  may include various tools, depending on the particular embodiment of the invention. In this regard, the coiled tubing string  30  may include, for example, a bottom hole assembly (BHA) (not shown in  FIG. 1 ), which is attached to the bottom end of the coiled tubing string  30  and thus, is attached to the bottom end of the first coiled tubing segment that is deployed into the wellbore  20 . Because the coiled tubing string  30  is formed from multiple segments, a tool may also be incorporated into the coiled tubing string  30  at an intermediate position above the bottom end of the string  30 . In this regard, as depicted in  FIG. 1 , in accordance with some embodiments of the invention, a tool  60  may be disposed between the upper and lower ends of the coiled tubing string  30  for purposes of performing a particular function relating to the job being performed by the coiled tubing string  30 .  
         [0034]     For example, the tool  60  may be a swabbing tool for purposes of preventing a fluid that is injected via the coiled tubing string  30  at its lower end from reaching an upper section of the wellbore  20 . In this regard, the swabbing tool  60  may form an annular barrier around the exterior of the coiled tubing string  30  at a particular intermediate location of the coiled tubing string  30 . Thus, for example, if a particular zone of the well below the swabbing tool  60  is being treated with a stimulation fluid, the tool  60  prevents the stimulation fluid from reaching the region of the well above the tool  60 , where damage may possibly occur.  
         [0035]     As another example, a tool that is deployed on the coiled tubing string  30  may include one or more sensors for purposes of detecting when a particular fluid, such as a stimulation fluid, has reached the tool. In this regard, an operator at the surface of the well may monitor results that are communicated uphole from the tool for purposes of determining when to halt pumping of treatment fluid into the well via the coiled tubing string  30 . Other tools may be part of the coiled tubing string  30 , in accordance with other embodiments of the invention.  
         [0036]     Depending on the particular embodiment of the invention, a one piece connector assembly or a two piece connector assembly (as depicted in  FIG. 1 ) may be used to selectively connect two coiled tubing segments together. For example, referring to  FIG. 3 , a single piece coiled tubing connector  210  constructed in accordance with an embodiment of the invention may be used to connect a first section of coiled tubing  212  and a second section of coiled tubing  214 . The connector  210 , having a body  216  having a longitudinal bore  218  therethrough, includes a stiff section  227  and at least one end section  228 . Often stiff section  227  is provided between two end sections  228 , as is shown  FIG. 3 . In some embodiments, body  216  of connector  210  may be discontinuous, and in further embodiments, stiff section  227  is separable from one or more end sections  228 . In some embodiments of the invention, the body  216  of the connector  210  may be a continuous body in which one region of connector body  216  is stiff section  227  and other region or regions of connector body  216  are end section or sections  228 .  
         [0037]     The stiff section  227  of connector  210  has an outer diameter that it will fits snugly within the inner diameter of first and second sections of coiled tubing  212  and  214 . The exterior diameter of body  216  remains essentially constant throughout stiff section  227 , excepting in localized areas where a means, such as a groove or indentation, to effect a connection with coiled tubing  212  and  214  are present.  
         [0038]     In end sections  228  of body  216 , external diameter  229  of body  216  gradually decreases from the end  231  of the end section  228  proximate to the stiff section  227  towards the distal end  233  of the body  216 , such that the external diameter of end section  228  of body  216  is not engaged snugly within the interior diameter of coiled tubing  212  or  214 . When coiled tubing  212  and  214  is straight, end section  228  is not in contact with the inner diameter of the coiled tubing  212  or  214  owing to the decreasing external diameter  229  of end section  228 . This decreasing external diameter, referred to herein as tapered, may be constructed in any variety of ways that provides a smaller external diameter at the distal end  233  of end section  228 ; examples of ways by which a taper may be formed include but are not limited to a single angle, a series of short angle sectors, a constant radius, or a compound radius.  
         [0039]     As coiled tubing  212  is connected to connector  210  in stiff section  227  and coiled tubing  212  bends as is routine in coiled tubing deployment and operation, only a limited area of end section  228  will be in contact with the interior diameter of coiled tubing  212  as it bends owing to the decreasing exterior diameter  229  of end section  228 . In this way, there is a limited area of contact between coiled tubing  212 / 214  as it bends over the length of end section  228  and that limited area of contact translates along the length of end section  228  as coiled tubing  212  bends. As such, the stress point occurring at the point of contact translates along the end section  228  and overlapping coiled tubing  212 , thereby avoiding the formation of a specific point of stress concentration or hinge point. This characteristic is referred to herein as the restrictive bend feature.  
         [0040]     The restrictive bend feature avoids the formation of a hinge point resulting from stress repeatedly concentrating in areas. It is known that such hinge points create a weak point in coiled tubing connectors. By design, this restrictive bend feature provides a transition between the stiff section  227  of connector  10  and the coiled tubing  212  or  214  and distributes the strain in the coiled tubing over the length of end section  228  rather than in a localized hinge point. By such a strain distribution, the maximum stress imposed on any particular point of coiled tubing  212  or  214  overlapping end section  228  and the duration of time at which any particular point is subjected to that stress is reduced. This serves to improve the low cycle fatigue performance of the overall coiled tubing and connector configuration. Such a configuration is notably different from known flexible internal connectors and is counter to the conventional approach of providing a flexible middle section with stiffer section on either side. Thus the coiled tubing connector may be useful to provide a connection that is flexible on both ends and stiff in the middle.  
         [0041]     In various embodiments, the diameter of the internal surface of body  216  along longitudinal bore  218  in end section  228  may decrease in a similar manner to external diameter  229 , may remain the same throughout end section  228 , or may increase to form an internal tapered surface  230 . In embodiments in which the diameter of the internal surface of body  216  along longitudinal bore  218  in end section  228  remains the same or increases, the cross sectional wall thickness of body  216  in end section  228  decreases toward distal end  233  as a result of decreasing external diameter  229 . This decreasing wall thickness makes end section  228  more flexible at distal end  233  and increasingly less flexible along the length of end section  228  extending to the end of stiff section  227 . In this way, connector  210  is most flexible at the distal end  233  of end section  228  and has diminishing flexibility traversing toward stiff section  227  along the length of end section  228  such that the stiffest area of end section  228  is at end  231  adjacent to stiff section  227 .  
         [0042]     Connector  210  may be secured to the coiled tubing  212  and  214  in stiff section  227  by techniques suitable for use with internal connectors such as roll-on connectors, screws, crimping, and dimpling. In  FIG. 3 , the connection between stiff section  227  and coiled tubing  212  and  214  is shown made by indentations  222  on the outer surface of stiff section  227  receiving protuberances  220  on the coiled tubing  212  and  214 . Such indentations may be made a variety of ways such as surrounding the coiled tubing with a mold and pressing the mold to form indentations, using a push or screw to form the indentations, or using a pre-pattern of weaker points in stiff section  227  into which coiled tubing  212  or  214  may be easily pressed. In some embodiments, the exterior surface of stiff section  227  may be patterned in a manner to facilitate this connection with coiled tubing  212  and  214 . For example, indentations in the exterior surface of stiff section  227  may spread uniformly about the circumference in a localized area or along the length of stiff section  227 . Alternatively, depressions for receiving screws holes may be provided in the exterior surface of stiff section  227 ; such depressions may similarly be in a localized area or along the length of stiff section  227 .  
         [0043]     In addition, the pattern, shape, or depth of such indentations may be varied and in particular, be varied in such a manner that the stress during bending of the connection is distributed across the indentations and not concentrated in a limited localized area. Moreover this variation may be done in such a manner as to vary the relative snugness of the connection between connector  210  and coiled tubing  212  or  214  across stiff section  227  of connector  10  such that the connection between connector  210  and coiled tubing  212  or  214  is relatively snug near the ends of coiled tubing  212  or  214  and the connection is less snug in other areas of stiff section  227  of connector  210 . For example, dimple screws closest to the ends of coiled tubing  212  or  214  of the tubing can be tightened to a different depth compared to those screws furthest from the ends of coiled tubing  212  or  214 .  
         [0044]     Alternatively or in addition to indentations along the external surface of stiff section  227 , indentations may be provided on the internal surface of body  216  along longitudinal bore  218 . In this manner, a thinner wall section of body  216  is provided in desired locations at which coiled tubing  212  or  214  may be pressed or crimped to secure contact between connector  210  and coiled tubing  212  or  214 . In another embodiment, a groove may be provided around the circumference of stiff section  227  or a series of circumferential or partially circumferential grooves may be placed or staggered along the length of stiff section  227 . Various combinations of these techniques may also be used and are considered within the scope of the present invention.  
         [0045]     Connector  210  may preferably be provided with one or more seals  224  to prevent fluid leakage between the connector  210  and each of either or both of the coiled tubing  212 / 214 . These seals  224  may be of any known type, including but not limited to O-rings, chevron seals, T-seals, dynamic seals such as PolyPak™, and various other elastomeric devices.  
         [0046]     In some embodiments of the invention, the connector  210  may include an annular lip  226  disposed about the body  216  in the stiff section  227  and positioned such that it is disposed between the respective ends of the coiled tubings  212  and  214 . The diameter of annular lip  226  is the same or essentially equivalent to the outer diameter of coiled tubing  212  and  214 . As such, annular lip  226  does not preclude connector  10  from passing through the wellhead equipment. Annular lip  226  provides support for the end of the coiled tubing  212  or  214  or to reduce forces that cause flaring of tubing ends and also to contain and protect the tubing ends. As will be appreciated by those of skill in this art, the annular lip  226  functions to reduce deformation or “egging” of the ends of the coiled tubing  212  or  214  during use.  
         [0047]     In some embodiments, a flow control device, such as a check valve, may be used in conjunction with connector  210 . The flow control device permits fluid flow through in one configuration and restricts fluid flow through in another configuration. Methods of switching such flow control devices from one configuration to another configuration are well known and include, for example, exerting an axial external pressure on the connector, dropping a ball, or providing a control signal. Such embodiments are of particular use when the coiled tubing is under pressure, such as well pressure or fluid pressure. The flow control device may be placed within stiff section  227  of connector  210  (see  FIG. 9 ), within coiled tubing  212  (see  FIG. 10 ) or  214  adjacent to connector  210  (see  FIG. 10 ). A combination of internal and external flow control devices may be also used.  
         [0048]     In some embodiments of the invention, the connector  210  is utilized to connect coiled tubing  212  and  214  of different wall thicknesses and correspondingly different bending stiffnesses, advantageously eliminating the need to weld the coiled tubing sections having different wall thicknesses. For example, coiled tubing  212  has a wall thickness different than the wall thickness of coiled tubing  214 . The wall thickness of coiled tubing  212  may be greater than the wall thickness of coiled tubing  214  or the wall thickness of coiled tubing  214  may be greater than the wall thickness of coiled tubing  212 . Alternatively, the coiled tubings  212  and  214  have different wall thicknesses and substantially the same outer diameter. Alternatively, the coiled tubings  212  and  214  have different wall thicknesses only at those portions of the coiled tubings  212  and  214  where the coiled tubings  212  and  214  are joined by the connector  210 , such as end portions thereof or the like.  
         [0049]     As shown in  FIGS. 4A, 4B  and  4 C, the decreasing exterior diameter  229  of end section  228  can be constructed on the external surface of body  216  in a variety of ways, including but not limited to with a single angle, a series of short angle sectors, a constant radius or a compound radius. In some embodiments, the diameter of the internal surface of body  216  along longitudinal bore  218  may increase in end section  228  to form an internal tapered surface  230 . For example, in the specific embodiments shown in  FIG. 3 , end section  228  is shown having an outer tapered surface  229  and a tapered internal surface  230  in longitudinal bore  218 . This internal tapered surface  230  similarly may be constructed in a variety of ways, including but not limited to with a single angle, a series of short angle sectors, a constant radius, or a compound radius. In some embodiments, the manner in which decreasing exterior diameter  229  and internal tapered surface  230  are constructed may be the same and in some embodiments, the manner in which they are formed may be different. In the specific embodiment shown in  FIG. 4A , end section  228  includes an internal tapered surface  230  and a tapered outer surface of body  229 . In the embodiment shown in  FIG. 4B , end section  228  includes a plurality of outer tapered surfaces, or short angle sectors,  229 A,  229 B and  229 C, and internal surface  230  is not tapered. In the embodiment shown in  FIG. 4C , end section  228  includes a tapered outer surface  229  formed by a constant radius and internal surface  230  in the longitudinal bore  218  is not tapered.  
         [0050]     There is shown in  FIG. 5 a  coiled tubing connector  210  constructed in accordance with the present invention and in use to connect a first section of coiled tubing  212  and a tool string  213 . Connector  210  has a body  216  having a longitudinal bore  218  therethrough and comprises a stiff section  227  and an end section  228 . In some embodiments, connector  210  may disassembled by separating stiff section  227  may be separated from end section  228  and assembled by attached stiff section  227  to end section  228  by using any number of connection methods known for connecting while maintaining a flush exterior surface such as threading, patterned jointing, or lock and key.  
         [0051]     Stiff section  227  of connector  210  has an outer diameter that fits snugly within the inner diameter of coiled tubing  212 . The other end  241  of stiff section  227  connects to tool string  213 . Such a connection to tool string  13  may be made by any number of connection methods known for connecting while maintaining a flush exterior surface such as threading, patterned jointing, or lock and key. In end section  228 , the external diameter  229  of body  216  gradually decreases from end of the end section  228  proximate to the stiff section  227  towards the distal end  233  of the body  216 , such that the external diameter  229  of end section  228  at the distal end  233  of body  216  is not engaged snuggly within the interior diameter of coiled tubing  212 . When coiled tubing  12  is straight, end section  228  is not in contact with the inner diameter of the coiled tubing owing to its decreasing external diameter  229 . In this way, there is a limited area of contact between coiled tubing  212 / 214  as it bends over the length of end section  228  and that limited area of contact translates along the length of end section  228  as coiled tubing  212  bends. As such, the stress point occurring at the point of contact translates along the end section  228  and overlapping coiled tubing  212 , thereby avoiding the formation of a specific point of stress concentration or hinge point. The restrictive bend feature of end section  228  previously described is present in the embodiment shown in  FIG. 5 .  
         [0052]     A specific embodiment is shown in  FIG. 6  in which two coiled tubing connectors  210  constructed in accord with the present invention are shown to connect a first section of coiled tubing  212 , a tool string  213 , and a second section of coiled tubing  214 . Each coiled tubing connector  210  has a body  216  having a longitudinal bore  218  therethrough and comprises a stiff section  227  and an end section  228 . Each tubing connector  210  is connected to coiled tubing  212  or  214  at stiff section  227  and to tool string  213  at one end  241 . The first tubing connector  210  is connected at stiff section  227  to coiled tubing  212  and the second tubing connector  210  likewise is connected at stiff section  227  to coiled tubing  214 . Stiff sections  227  have an outer diameter that fits snugly within the inner diameter of coiled tubing  212 . End section  228  of each of the first and the second tubing connector  210  has an external diameter  229  that gradually decreases from the end  240  of the end section  228  proximate to the stiff section  227  towards the distal end  233  of the body  216 , such that the external diameter  229  of end section  228  at the distal end  233  of body  216  is not engaged within the interior diameter of coiled tubing  212  or  214  respectively when the coiled tubing is not bent.  
         [0053]     In some embodiments, first or second connector  210 , or both, may comprise a body  216  in which one region of the body  216  is stiff section  227  and another region of body  216  is end section  228 . In other embodiments, body  216  of the first or second connector  210 , or both, may disassembled by separating stiff section  227  from end section  228  and assembled by attached stiff section  227  to end section  228  using any number of connection methods known for connecting while maintaining a flush exterior surface such as threading, patterned jointing.  
         [0054]     Stiff section  227  of each the first and second connectors  210  have an outer diameter that fits snugly within respectively the inner diameter of coiled tubing  212  or  214 . End section  228  of each of the first and the second tubing connector  210  has an external diameter  229  that gradually decreases from the end  231  of the end section  228  proximate to the stiff section  227  towards the distal end  233  of the body  216 , such that the external diameter  229  of end section  228  at the distal end  233  of body  216  is not engaged within the interior diameter of coiled tubing  212  or  214  respectively when the coiled tubing is not bent. This restrictive bend feature of end section  228  previously described is included in the embodiment shown in  FIG. 6 .  
         [0055]     Each of the embodiments described has a reduction in the exterior diameter of end section  228 . When bending occurs in routine use, coiled tubing  212 / 214  bends until it contacts end section  228 . As bending continues, the contact point between coiled tubing  212 / 214  and end section  228  translates along the length of end section  228 , thereby avoiding a localized hinge point. In this way, connector  210  of the present invention undergoes lower strain during bending and as a result, suffers lower fatigue and has a longer useful life.  
         [0056]     Advantages of the connector described herein may be seen by referring to  FIGS. 7A and 7B  in which output from finite element modeling is shown.  FIG. 7A  illustrates the output of finite element modeling of a known internal coiled tubing connector having a flexible center section and stiff end sections; numerous areas of high strain concentration  250  are shown including an extended area of high strain concentration  250  in the flexible center section.  FIG. 7B  illustrates the output of finite element modeling having the same inputs as  FIG. 7B , except that the connector is modeled is of the present invention; few areas of high strain concentration  250  are shown for the present invention connector. As high strain concentration leads to diminished usage life or to greater risk of failure, the advantages of the connector described herein are apparent from a comparison of  FIG. 7B  to  FIG. 7A  from which is can be seen that connector  210  of the present invention undergoes less strain than the coiled tubing connector having a flexible center section.  
         [0057]     As shown in  FIG. 8 , in another specific embodiment, connector  210  may further be provided with a flow guide/debris barrier  232  disposed at each end of the connector  210 . The barrier  232  may include a body  234  with a tubular section  236  extending therefrom and adapted to fit within the bore  218  of the connector  210 . The body  234  may include a shoulder  238  designed to engage the tip of end section  228  of connector  210 . Body  234  may include an annular recess  244  for receiving an annular seal  242 . The body  234  may further include a tapered inner bore  240 . The debris barrier  32  functions to keep debris and solids, which could impede controlled bending, out of the restrictive bend area between external diameter  229  of end sections  228  and internal surface  230  of the coiled tubings  212 / 214 . Barrier  232  may be separate from the connector  210 , as shown, or it may be integral with the connector  210 . In various embodiments, barrier  232  may be rigid or flexible. An example of an integral flexible embodiment is an elastomeric cone molded to the end of connector  210 . Any combination of these techniques may be used. If barrier  232  is separate from connector  210  instead of integral with it, it may be held in position by a coiled tubing weld bead  246  on one side and connector  210  on the other side.  FIG. 8  further illustrates that connector  210  may include an anti-extrusion ring  248  adjacent seal  224 .  
         [0058]     Advantages of the connectors in accordance with embodiments of the invention include a tensile strength similar to the tensile strength of the coiled tubing; the capability of bending around a coiled tubing reel and an injector gooseneck during operation; a low cycle fatigue life similar to the coiled tubing; a pressure tight seal both from internal and external sources; and the ability to pass through a wellhead assembly.  
         [0059]     In some embodiments, a flow control device, such as a check valve, may be used in conjunction with connector  210 . The flow control device permits fluid flow through in one configuration and restricts fluid flow through in another configuration. Methods of switching such flow control devices from one configuration to another configuration are well known and include, for example, exerting an axial external pressure on the connector, dropping a ball, or providing a control signal. Such embodiments are of particular use when the coiled tubing is under pressure, such as well pressure or fluid pressure. The flow control device  260  may be placed within stiff section  227  ( FIG. 9 ) of connector  210  or within coiled tubing  212  ( FIG. 10 ) or  214  ( FIG. 11 ) adjacent to connector  210 . A combination of internal and external flow control devices may be also used.  
         [0060]      FIG. 12  depicts an embodiment of a two piece connector assembly for joining two coiled tubing segments together, in accordance with other embodiments of the invention. The two piece connector assembly includes a first connector  400  (an embodiment of the connector  70  of  FIG. 1 , for example), which mates with another connector  410  (an embodiment of the connector  80  of  FIG. 1 , for example). In some embodiments of the invention, each coiled tubing segment is transported to the well site with the connectors  400  and  410  (one secured to each end) already being in place on their respective coiled tubing segments.  
         [0061]     Each connector  400 ,  410  has the same general design, with an end connector distinguishing one connector  400 ,  410  from the other. For example, in accordance with some embodiments of the invention, the connector  400  is a female connector due to a female end connector  350  that mates with a male end connector  354  of the connector  410 . The opposite ends of the connectors  400  and  408  receive the respective coiled tubing sections  330   a  and  330   b , respectively. Each end connector  350 ,  354  is a non-rotating connector and may be one of numerous different types of connectors, depending on the particular embodiment of the invention. For example, in accordance with some embodiments of the invention, the end connectors  350  and  354  may be threaded connectors, and in other embodiments of the invention, as another non-limiting example, each end connector  350 ,  354  may be a crimp-type connector. Thus, many variations are contemplated and are within the scope of the appended claims.  
         [0062]     As depicted in  FIG. 12 , the connector  400  has a generally tapered exterior end surface  371 , which is inserted into the end of the coiled tubing section  330   a . The surface  371  establishes a sliding area of contact between the connector  400  and the coiled tubing section  330   a , to prevent a hinge point. Between the surface  371  and the end connector  350 , the connector  400  may include a profile for purposes of attaching the coiled tubing section  330   a  to a connector body  373 . As an example, as depicted in  FIG. 3 , in accordance with some embodiments of the invention, the connector body  373  includes indentations  360  which receive corresponding protuberances  370  of the coiled tubing section  330   a  when the coiled tubing section  330   a  is crimped into the connector body  373 .  
         [0063]     Apart from having the opposite-type end connector  354 , the connector  410  has a similar design to the connector  400 , in accordance with some embodiments of the invention. In this regard, as shown in  FIG. 3 , the connector  410  includes a connector body  383 , which has a tapered end surface  381  that is received into the coiled tubing section  330   b . Furthermore, the connector body  383  has indentations  380  that receive corresponding protuberances  382  when the coiled tubing section  330   b  is crimped into the connector body  383 .  
         [0064]     In accordance with some embodiments of the invention, a check valve may be disposed in one or both of the connectors  400  and  410  for purposes of maintaining fluid seal integrity of the coiled tubing string  330 . In this regard, it is possible that during its lifetime, the coiled tubing string  30  (see  FIG. 1 ) may possibly develop a pin hole leak beneath the well tree  31 . This leak, in turn, may cause the communication of well fluid from the annulus into the central passageway of the coiled tubing string  30 , thereby compromising the seal integrity of the well. As depicted in  FIG. 3 , in some embodiments of the invention, a flow control device, such as a check valve  390 , may be located in the connector  410  (i.e., the bottom connector), although the check valve may be located in the upper connector  400 , in accordance with some embodiments of the invention. A particular advantage of incorporating a flow control device, such as the check valve  390 , into the bottom connector  410  is that when the connectors  400  and  410  are separated at the slips  56  (see  FIG. 1 ), a seal is maintained on the central passageway of the coiled tubing string  30 . Additionally, should a leak develop, additional measures may be employed using the one-way communication path through the check valve  390 , such as injecting a kill fluid through the check valve  390  and into the central passageway of the deployed coiled tubing string, for example.  
         [0065]     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.