Abstract:
A tapered connector for a tubing string. The present invention includes a tapered connector used in interconnecting sections of the tubing string having differing outside diameters. The connector is preferably conical and fixedly attached to the tubing portions in various ways, such as welding. The tubing string can be injected into a well by using a tubing injector with gripper blocks having a V-shaped groove defined therein adapted for engaging the different diameter tubing sections and the tapered connector and methods of injecting are also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the use of coiled tubing in a well, and more particularly, to a tapered connector for joining lengths of coiled tubing with differing outside diameters. 
     2. Description of the Prior Art 
     After a well has been completed to produce oil or gas, it is necessary to periodically service the well. There are many occasions where the service procedure is carried out using coiled tubing. Such tubing is inserted into the wellhead through a lubricator assembly or stuffing box. Typically, this is necessary because there is a pressure differential at the surface of the well and the atmosphere, which may have been naturally or artificially created, that serves to produce oil or gas or a mixture thereof from the pressurized well. The tubing is inserted by an injector which generally incorporates a tubing guide, or gooseneck, and a plurality of gripper blocks for engaging the tubing and moving it through the injector. One such injector apparatus is shown in U. S. Pat. No. 5,553,668, assigned to the assignee of the present invention. 
     The tubing is relatively flexible and can therefore be cyclically coiled onto and off of a spool, or reel, by the injector which often acts in concert with a windlass and a power supply which drives the spool or reel. In the injector, the gripper blocks are attached to movable gripper chains. The gripper blocks sequentially grip the coiled tubing that is positioned therebetween. When the gripper chains are in motion, each chain has a gripper block that is coming in contact with the coiled tubing as another gripper block on the same gripper chain is breaking contact with the coiled tubing. This continues in an endless fashion as the gripper chains are driven to force the tubing into or out of the wellbore, depending on the direction in which the drive sprockets are rotated. 
     In the past, such coiled tubing has had a constant cross section. However, maintaining a constant diameter for the tubing can present some problems under certain circumstances. For example, it may be desirable to reduce the weight of the string, and this cannot be done if the string has a constant diameter. Further, a larger string causes more drag in the wellbore, particularly when the strings are being used in a horizontal or other deviated portion of the well. There is a need, therefore, for a tubing string with different sized portions. The present invention provides a solution to this problem by providing a string having a tapered connection therein between two lengths of tubing having differing diameters. This is accomplished by providing a tapered connector which provides an elongated tapering tubing string portion which is connected at opposite ends thereof to a larger tubing portion and a smaller tubing portion. 
     For example, a larger outside diameter tubing at the top of the string and a smaller outside diameter tubing at the bottom allow the coiled tubing string to be designed for longer lengths by reducing the hanging weight of the string and also reduces the percent of yield load on the larger diameter portion compared to a string having a single outside diameter. 
     The present invention also provides for use of a smaller outside diameter portion in a horizontal or deviated well formation, thus reducing the drag of the tubing while still having the larger diameter portion at the top of the string to push the string further into the well because of the decreased buckling of the large portion. 
     Another problem with constant diameter tubing relates to the key issue of pressure drop therethrough. If the wellbore size at the treatment area is small, then previously a small diameter length of tubing had to be used. The smaller diameter tubing could present significant pressure drop problems. The present invention solves this by allowing the use of larger outside diameter tubing close to the treatment zone with a smaller portion actually at the treatment zone. 
     All of these embodiments are possible due to the V-shaped groove design of the gripper blocks in the Halliburton injector system which allows tubing of varying outside diameters to be engaged by the same blocks. 
     SUMMARY OF THE INVENTION 
     The apparatus of the present invention utilizes one or more tapered connectors in a tubing string for use in servicing a well. Thus, the invention provides a tubing string for use with a tubing injector for injecting tubing into a wellbore wherein the string comprises at least a first tubular portion having a first tubing outside diameter, a second tubular portion having a second tubing outside diameter which is different than the first tubing outside diameter, and a tapered portion disposed between the first and second tubing portions. The tapered portion comprises a first end having a first end outside diameter substantially equal to the first tubing outside diameter and a second end having a second end outside diameter substantially equal to the second tubing outside diameter. The tapered portion is preferably substantially conical. 
     The tapered portion may be connected to the first and second tubing portions by a variety of means. For example, it can be crimped, swaged, screwed or welded to the connection. A first connector may be used interconnecting the first tubing portion and the first end of the tapered portion, and a second connector may be used interconnecting the second tubing portion and the second end of the tapered portion. These first and second connectors may be integrally formed with the tapered portion. Multiple tapered portions with connectors may be utilized in a tubing string to connect differing diameter tubings into a string for servicing a well. 
     In the preferred embodiment, the first and second connectors are substantially cylindrical. The first connector has a first connector outside diameter substantially equal to the first tubing outside diameter, and the second connector has a second connector outside diameter substantially equal to the second tubing outside diameter. 
     The present invention also includes a method of running tubing in a wellbore comprising the steps of (a) providing a tubing string having an outer surface with a plurality of outside diameters, and (b) injecting this tubing string into the wellbore. Step (a) comprises providing the tubing string with a tapered connector between adjacent tubing portions having different outside diameters. Step (b) comprises passing the tapered connector through a tubing injector for injecting the tubing into the wellbore. This injector is provided with a plurality of gripper blocks therein adapted for engaging and gripping the tapered connector and the different outside diameters of the tubing string as the tubing string is injected into the wellbore. 
     Stated in another way, the invention includes a method of running tubing into a wellbore comprising the steps of (a) positioning a tubing injector adjacent to a wellhead at an upper end of a wellbore, (b) positioning a tubing string through the injector, the tubing string being provided with an outer surface having more than one outside diameter, and (c) actuating the tubing injector for injecting the tubing string in the wellbore. Step (c) may include passing a tubing connector therethrough which interconnects the portions of the tubing string having different outside diameters. 
     Numerous objects and advantages of the invention will become apparent with the following detailed description of the preferred embodiment is read in conjunction with the drawings illustrating such embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically shows the tubing connector of the present invention interconnecting two portions of a tubing string having different outside diameters as the tubing string is passed through a tubing injector into a well. 
     FIG. 2 shows a detail of the engagement of gripper blocks in the tubing injector with the tubing string. 
     FIG. 3 is a cross section taken along lines  3 — 3  in FIG.  2 . 
     FIG. 4 is a longitudinal cross section of the tubing connector portion of the tubing string. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and more particularly to FIGS. 1 and 2, the tubing connector of the present invention is shown and generally designated by the numeral  10 . Connector  10  interconnects a first tubing section or portion  12  and a second tubing section or portion  14 . First tubing section  12 , second tubing section  14  and tubing connector  10  may all be said to form portions of a tubing string  16 . 
     Typically, tubing string  16  is supplied on a large drum or reel  18  and is typically several thousand feet in length. Tubing string  16  is in a relaxed but coiled state when supplied from drum  18 . Tubing string  16  is typically spooled from the drum  18  supported on a truck (not shown) for mobile operations. 
     An injector apparatus  20  is mounted above a wellhead  22  adjacent to a ground surface  23  on a superstructure  24 . Extending upwardly and away from superstructure  24  is a guide framework  26  having a plurality of pairs of guide rollers  28  and  30  rotatably mounted thereon. 
     Tubing string  16  is supplied from drum  18  and is run between rollers  28  and  30 . As tubing string  16  is unspooled from drum  18 , generally it will pass adjacent to a measuring device, such as wheel  32 . Alternatively, the measuring device may be incorporated in injector  20 , such as described in U.S. Pat. No. 5,234,053 to Connell, assigned to the assignee of the present invention. 
     Rollers  28  and  30  define a pathway for tubing string  16  so that the curvature of the tubing is slowly straightened as it enters injector  20 . There is enough play in rollers  28  and  30  to accommodate different-sized tubing diameters. As will be understood, tubing string  16  is preferably formed of a material which is sufficiently flexible and ductile that it can be curved for storage on drum  18  and later straightened. While the material is flexible and ductile, and will accept bending around a radius of curvature, it runs the risk of being pinched or suffering from fatigue failure should the curvature be severe. Rollers  28  and  30  are spaced such that straightening of the tube is accomplished so that the tubing is inserted into the well without kinks or undue bending. 
     Referring now to FIGS. 2 and 3, the details of the interaction between tubing string  16  and injector  20  will be discussed. Inside superstructure  24 , a pair of gripper chains  34  and  35  are driven by a corresponding pair of gripper chain drive sprockets  36  and  37 , respectively. Gripper chain drive sprockets  36  and  37  are mounted on drive shafts  38  and  39 , respectively and driven thereby by a prime mover (not shown) in a manner known in the art. The lower portion of gripper chains  34  and  35  are supported by gripper chain idler sprockets  40  and  41 , respectively mounted on idler shafts  42  and  43 . 
     Gripper chains  34  and  35  are of a kind known in the art, and each has a plurality of outwardly facing tubing gripper blocks  44  thereon. As best seen in FIG. 3, each gripper block  44  has a V-shaped groove  46  defined on the outer face thereof. The V-shape of groove  46  allows the blocks to automatically adjust for different diameters on tubing string  16 . That is, a larger outer surface  48  on tubing string  16  will be positioned further outwardly in groove  46  than a smaller diameter portion. Drive sprockets  36  and  37  and idler sprockets  40  and  41  are biased toward tubing string  16  in a manner known in the art so that gripper chains  34  and  35  generally conform to the outer surface of tubing string  16 . As seen in FIG. 2, when tapered connector  10  passes through injector  20 , gripper blocks  44  will grip along tapered outer surface  48  thereof. Gripper chains  34  and  35  are rotated in opposite directions so that the gripper blocks  44  on both which engage tubing string  16  move downwardly to force the tubing string into the well. This can be reversed to pull tubing string  16  out of the well. The V-shaped grooved surface of gripper blocks  44  in the Halliburton injector allow the differing outer surfaces of tubing string  16  to be substantially simultaneously engaged. 
     Referring now to FIG. 4, a cross section of the portion of tubing string  16  which includes tapered connector  10  is shown. Connector  10  is substantially conical in the preferred embodiment. Preferably, the maximum outer diameter  50  of tapered connector  10  is substantially the same as outside diameter  52  of first tubing section  12 . Similarly, the minimum outside diameter  54  of connector  10  is substantially the same as outside diameter  56  of second tubing section  14 . The upper end of tubing connector  10  is connected to first tubing section  12  by a first connector section  58 , and the lower end of tapered connector  10  is attached to second tubing section  14  by a second connector section  60 . In the illustrated embodiment, first and second tubing sections  12  and  14  and tapered connector  10  are metal, and first and second connector sections  58  and  60  are characterized by welded portions between tapered connection  10  and first and second tubing sections  12  and  14 , respectively. 
     Alternatively, tapered connector  10  can have an internal nose that is integral thereto at each end. The noses are inserted into first and second tubing sections  12  and  14 . The tubing sections then can be crimped or swaged onto the tapered connector. In still another embodiment, the tapered connector can be threadingly engaged with the first and second tubing sections  12  and  14 . Tapered connector  10  and first and second tubing sections  12  and  14  may be made of a non-metallic composite material. 
     In any of the embodiments of tapered connector  10 , the key feature is that the outer surface of tubing string  16  be relatively smooth so that tapered connector  10  provides a substantially even and gradual transition between first tubing section  12  and second tubing section  14 . In this way, tubing connector  10  will pass smoothly through injector  20  and be substantially uninterruptedly engaged by gripper blocks  44  so that tubing string  16  is injected into the well. 
     If desired, multiple tubing sections having different diameters can be connected as described hereinafter to produce a tubing string for treating a well. For example, a larger outside diameter tubing at the top of a string may be connected to a smaller outside diameter tubing which in turn is connected to a yet smaller outside diameter tubing by multiple tapered connectors to reduce the hanging weight of the string and thereby reduce the yield loading on the tubing string upper sections. 
     It will be seen, therefore, that the tapered connector for a tubing string of the present invention is well adapted to carry out the ends and advantages mentioned as well as those inherent therein. While a presently preferred embodiment has been shown for the purposes of this disclosure, numerous changes in the arrangement and construction of parts may be made by those skilled in the art. All such changes are encompassed within the scope and spirit of the appended claims.