Abstract:
An apparatus and method for moving a tubing along a path, according to which the tubing is engaged by an outer chain which is driven to advance the tubing. The chain is adapted to be deflected radially in response to an increase in the diameter of the tubing, and a plate is compressed in response to the deflection of the chain to accommodate the variation in diameter.

Description:
BACKGROUND 
   The present invention relates to an injector for injecting coiled tubing into an oil or gas well. 
   Coiled tubing injectors are often used to inject coiled tubing into an oil or gas well to facilitate the servicing of the well. For some well-servicing applications, the diameter of the tubing must be increased in the upper sections of the tubing for reasons related to the well-servicing process. 
   One technique for accommodating an increase in diameter is to dispose a tapered connector between a relative small-diameter section and a relatively large diameter section. However, a problem arises in connection with this technique especially when the tubing passes through an injector for injecting it into the well. In particular, due to the rigidity of the injector structure, substantially all of the loading on the tubing provided by the injector is applied to the area of the connector having the relatively larger diameter. This results in a relatively small percentage of the exterior surface of the connector bearing substantially all of the loading, creating high stress areas at the points of contact with the injector, and possibly causing failure in the connector and/or the tubing. 
   Therefore, what is needed is an injector for passing coiled tubing through an injector that overcomes this problem. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partial elevational/partial sectional view, not necessarily to scale, depicting a coiled tubing injector according to an embodiment of the invention. 
       FIG. 2  is an enlarged view of a portion of the injector of  FIG. 1 . 
       FIG. 3  is an enlarged front elevational view depicting a portion of one of the carriages of  FIG. 2 . 
       FIG. 4  is a cross-sectional view, taken along the line  4 — 4  of  FIG. 3   
       FIG. 5  is a cross-sectional view similar to that of  FIG. 4 , but depicting additional structure. 
       FIG. 6  is an vertical cross-sectional view of a tapered connector for the coiled tubing of  FIG. 1 . 
       FIG. 7  is an enlarged, partial, elevational view depicting the tapered connector of  FIG. 6  disposed between the carriages of  FIG. 2  during an injection operation. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , the reference numeral  10  refers, in general, to a coiled tubing injector  10  positioned directly above a well  12 . A well-head  14  extends above the well, and a lubricator, or stuffing box  16  extends above the well-head. 
   A spool of coiled tubing  18  is positioned at a predetermined location away from the injector  10 . Unspooled tubing  20  passes from the spool and under a measuring device, such as a wheel  22 , and between several (seven in the example of  FIG. 1 ) pairs of opposed rollers  24  rotatably mounted to an arcuate support platform  26 . The tubing  20  then passes from the last pair of rollers into the injector  10 . 
   The injector  10  includes a frame  28  having a base  28   a , and a pair of substantially similar carriages  30   a  and  30   b  mounted on the base via a pair of carrier lugs  31   a  and  31   b . The carriages  30   a  and  30   b  drive the tubing  20  into the stuffing box  16  for passage through the well-head  14  and into the well  12 . 
   The carriages  30   a  and  30   b  are depicted in greater detail in  FIG. 2 , with the remaining structure of the injector  10  and the tubing  20  being removed from view in the interest of clarity. Two hydraulic actuated cylinders  32   a  and  32   b  extend between the carriages  30   a  and  30   b  and are connected to the carriages in any conventional manner. The cylinders  32   a  and  32   b  are connected to the carriage  30   b  by two mounting brackets  33   a  and  33   b , respectively, and each cylinder  32   a  and  32   b  includes a piston (not shown) that reciprocates in a cylinder housing in response to hydraulic fluid being introduced into, and discharged from, the housing, in a conventional manner. 
   Two rods  34   a  and  34   b  extend out from the cylinders  32   a  and  32   b , respectively, with one end of each rod being connected to its corresponding piston and the other end connected to the carriage  30   a  by two mounting brackets  35   a  and  35   b , respectively. It is understood that the cylinders  32   a  and  32   b  are connected in a hydraulic circuit (not shown) so that fluid is selectively introduced and discharged from the cylinders to cause corresponding contraction and extension of the cylinders. An example of the hydraulic circuit that may be used is disclosed in co-pending patent application Ser. No. 10/840,787 the disclosure of which is incorporated herein by reference in its entirety. This contraction and extension of the cylinders  32   a  and  32   b  causes corresponding movement of the carriages  30   a  and  30   b  towards each other to grip the tubing  20 , and away from each other to release the tubing. It is understood that two other cylinders (not shown), identical to the cylinders  32   a  and  32   b , are connected to the carriages  30   a  and  30   b  on the other sides of the carriages. 
   The carriage  30   a  includes a gripping chain  36  extending between, and engaged with, two spaced sprockets  37  (one of which is shown in  FIG. 2 ). A plurality of gripping elements  38  are mounted to the outer surface of the chain  36  and are adapted to engage and grip the tubing  20  in a conventional manner. A roller chain  40  is also provided that extends within the gripping chain  36  and engages two spaced sprockets  42  (one of which is shown in  FIG. 2 ). Both the roller chain  40  and the gripping chain  36  are disposed around a linear beam  44 , shown partially in  FIG. 2 , and the gripping elements  38  of the gripping chain  36  engage the tubing  20  along substantially the entire length of the beam  44 . 
   The outer surface of the chain  40  is in engagement with the inner surface of the chain  36  and is free wheeling about its sprockets  42 . It is understood that a motor (not shown) is provided to drive at least one of the sprockets  37 , and therefore the chain  36 . The engagement between the chains  36  and  40  is such that the chain  36  drives the chain  40  which functions to support the chain  36 . 
   Since the carriage  30   b  is identical to the carriage  30   a  the above components of the carriage  30   a  will be referred to by the same reference numerals in connection with the carriage  30   b.    
   During the general operation, and referring to  FIGS. 1 and 2 , the tubing  20  is unspooled from the spool  18  and passes through the rollers  24  where it is straightened before it enters the injector  10 . The cylinders  32   a  and  32   b  are normally in their extended positions and are actuated via the above-mentioned hydraulic circuit to force them to their retracted position and therefore drive the carriages  30   a  and  30   b  towards each other until the gripping elements  38  on the gripping chain  36  engage the tubing  20  at a predetermined loading. The above-mentioned motors are then activated to drive the sprocket  37  and the gripping chain  36 , which, in turn drives the roller chain  40 . It is understood that the carriage  30   b  functions in the same manner as the carriage  30   a  so that the gripping chain  36  on the carriage  30   b  engages the tubing  20  from a diametrically opposite direction with a predetermined load, or force. As a result, the tubing  20  is driven into the well  12 . 
   The beam  44  associated with the carriage  30   a  is shown in detail in  FIGS. 3–5 , and includes a pair of spaced, parallel plates  44   a  and  44   b  connected by two spaced, parallel webs  44   c  and  44   d  that extend perpendicular to the plates  44   a  and  44   b  and are connected, at their respective ends, to the corresponding inner surfaces of the plates in any known manner. The beam  44  extends for a length that is substantially the same as the distance between the sprockets  42  for the roller chain  40  and is positioned so that the beam plate  44   b  faces the carriage  30   b.    
   As better shown in  FIGS. 4 and 5 , an elastomer plate  50  extends along the outer surface of the beam plate  44   b  for the length of the beam  44 . The plate  50  is sandwiched between the beam plate  44   b  and a rigid support plate  52  having an outer surface that is engaged by the corresponding inner surface of the chain  40 . The plates  50  and  52  can be fastened to the beam plate  44   b  in any conventional manner such as by shoulder bolts, or the like (not shown), preferably near the respective ends of the plates, with the fastening being such that the plates can deflect in the radial direction in a manner to be described. It is noted that  FIG. 5  depicts a portion of the arrangement of  FIG. 4  in addition to the gripping chain  36  and the gripping elements  38 , with the latter chain extending around, and in engagement with, the chain  40 . 
   As shown in  FIG. 2 , the carriage  30   b , including its beam  44 , is identical to the carriage  30   b  and is positioned with the inner portion of its gripping chain  36  facing the inner portion of the gripping chain  36  of the carriage  30   a.    
   Although the tubing  20  is depicted in  FIGS. 1 and 2  as having a constant diameter, it is understood that the diameter of the tubing can vary along its length. For example, and referring to  FIG. 6 , a section  20   a  of the tubing  20  has a relatively small diameter D 1  and another section  20   b  of the tubing  20  has a relatively large diameter D 2 . In order for the injector  10  to accommodate this diameter variance, a frustoconical connector  56  is fastened between the sections  20   a  and  20   b , with the smaller diameter of the connector  56  corresponding to, and being connected to, the relatively small-diameter tubing section  20   a , and the larger diameter of the connector corresponding to, and being connected to, the relatively large diameter tubing section  20   b . These connections can be provided in any conventional manner, such as by providing external threaded nipples (not shown) on the respective ends of the connector  56  and threading the nipples into an internal threaded end portion of each of the sections  20   a  and  20   b . As a result, the diameter of the tubing  20  gradually increases as the sections  20   a  and  20   b  pass through the injector  10 . 
   In operation, the tubing  20 , including one or more tubing sections  20   a  and  20   b  joined by a connector  56 , is unspooled through a pathway defined by the rollers  24  and is straightened as it passes through the rollers and enters the injector  10 . In this context, it is understood that the connector  56  and the relatively large-diameter tubing section  20   b  follow a relatively small section  20   a  as the tubing is unspooled and that the rollers  24  are adapted to pivot, retract, or the like, in a conventional manner to accommodate the connector  56  and the relatively large section  20   b.    
   The cylinders  32   a  and  32   b  (as well as the two cylinders located on the back sides of the carriages  30   a  and  30   b ) are actuated via the above-mentioned hydraulic circuit to draw the carriages  30   a  and  30   b  towards each other in the manner described above until the gripper elements  38  on the gripping chains  36  engage the tubing  20  at a predetermined loading. The above-mentioned motors are then activated to drive the sprockets  37  and the gripping chain  36  of each carriage  30   a  and  30   b , thereby gripping and lowering the tubing  20  into the well  12 . Each gripping chain  36  also drives its corresponding roller chain  40  about the sprockets  42 , with the roller chains providing support for their respective gripping chains. 
   During the passage of the tubing  20  through the injector  10  in the above manner, when a connector  56  enters the region of the injector  10  between the gripping chains  36  of the carriages  30   a  and  30   b , the variable increasing diameter of the connector  56  creates a radially directed force that gradually increases along the length of the tubing. This force is applied directly to the chains  36  and  40  and deflects the chains radially outwardly causing a corresponding deflection of the plates  52  against their corresponding elastomer plates  50 . As a result, the plates  50  are compressed against their corresponding beam plates  44   b  to accommodate this increase in diameter of the tubing  20 . 
   Each elastomer plate  50  will continue to compress further as the diameter of the connector  56  gradually increases as it passes through the path defined between the carriages  30   a  and  30   b . Thus compression of the plates  50  will increase along their respective lengths so that the respective inner surfaces of the plates will take a tapered shape corresponding to the shape of the outer surface of the connector, as shown in  FIG. 7 . 
   Since the lengths of the plates  50  and  52  extend for substantially the length of the carriages  30   a  and  30   b , a substantial number of gripper elements  38  of each of the chains  36  will contact the connector  56  during this gradual diameter increase of the tubing  20 . Therefore, a uniform force distribution will be maintained along the length of the connector  56  which prevents the creation of isolated high stress areas. 
   It is understood that the above technique is the same when the tubing  20  is withdrawn from the well  12  and spooled back on the spool  18 , with the direction of movement being opposite that discussed above. 
   It is understood that variations may be made in the foregoing without departing from the scope of the invention. For example, the invention may be used without the connector  56 , such as with a spool of coiled tubing having a gradually increasing diameter along its entire length or with a spool of coiled tubing having a substantially constant diameter. Also, the plates  50  and/or  52  can be fastened to the beam plate  44   b  via fasteners other than shoulder bolts, such as with studs rigidly connected to and extending from the beam plate  44   b . Further, the quantity of cylinders  32   a  and  32   b  may vary as long as an evenly distributed load is applied to the tubing  20  via the gripper elements  38 . Moreover, any type of hydraulic circuit may be utilized to extend and retract the cylinders. 
   Any foregoing spatial references, such as “upper,” “between,” “front,” “right side,” “side,” “above,” etc., are for the purpose of illustration only and do not limit the specific spatial orientation of the structure described above. 
   The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.