Abstract:
The gripping element of a coiled tubing injector has a carrier and a removable gripping shoe mounted to the carrier. The removable shoe slides onto slots formed on the carrier and is floated on the carrier by inserting an elastomeric pad sandwiched between the carrier and shoe. A manually depressible spring along ones side of the carrier prevents the shoe from sliding out of the slots during operation of the injector.

Description:
This application is a continuation reissue application of reissue application Ser. No. 10/345,836, filed Jan. 16, 2003 now U.S. Pat. No. Re.43,410 and is a reissue of U.S. Pat. No. 6,173,769, which claims the benefit of provisional application No. 60/045,365, filed May 2, 1997. 
     This application claims the benefit of U.S. provisional application no. 60/045,365, filed May 2, 1997, which application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to coiled tubing injectors for handling a continuous length of tubing or pipe for insertion into or removal from a well bore, and for drilling well bores. More particularly, it concerns gripping elements used by such injectors. 
     BACKGROUND OF THE INVENTION 
     Continuous, reeled pipe is generally known within the industry as coiled tubing and has been used for many years. It is much faster to run into and out of a well bore than conventional jointed, straight pipe. 
     Coiled tubing is run into and out of well bores using what are known in the industry as coiled tubing injectors. The name derives from the fact that, in preexisting well bores, the tubing must be literally forced or “injected” into the well through a sliding seal to overcome the well pressure until the weight of the tubing exceeds the force produced by the pressure acting against the cross-sectional area of the tubing. However, once the weight of the tubing overcomes the pressure, it must be supported by the injector. The process is reversed as the tubing is removed from the well. 
     The only method by which a continuous length of tubing can be either forced against pressure into the well, or supported while hanging in the well bore or being lowered or raised is by continuously gripping a length of the tubing just before it enters the well bore. This is achieved by arranging continuous chain loops on opposite sides of the tubing. The continuous chains carry a series of grippers which are pressed against opposite sides of the tubing and grip the tubing. 
     Coiled tubing has traditionally been used primarily for circulating fluids into the well and other work over operations, rather than drilling, because of its relatively small diameter and because it was not strong enough, especially for deep drilling. However, in recent years, coiled tubing has been increasingly used to drill well bores. For drilling, a turbine motor suspended at the end of the tubing and is driven by mud or drilling fluid pumped down the tubing. Coiled tubing has also been used as permanent tubing in production wells. These new uses of coiled tubing have been made possible by larger, stronger coiled tubing. 
     SUMMARY OF THE INVENTION 
     A coiled tubing injector according to the present invention includes a quick-release carrier for mounting gripping shoes to chains of the injector. The carrier enables removal and replacement of grippers in the field without tools, even when the injector is operating. An injector thus may be quickly adapted to run coiled tubing within a wide range of diameters, for purposes of a well work over to drilling. Furthermore, an injector having grippers according to the present invention may be used to run conventional jointed, straight pipe, or a tool string on the end of coiled tubing. The diameter of joints are larger than the diameter of the pipe. Tool strings have various diameters. The quick-release carrier enables gripping shoes to be easily removed to accommodate a joint or a tool as it passes through the injector during operations. Gripping shoes can be easily replaced with gripping shoes that have the appropriate size and shape for gripping the tool. All shoes are sized so that, when attached to the injector, they have same centerline or axis as the other shoes. Thus, gripping shoes of differing sizes can be used on the injector to grip a downhole tool or irregularly sized object in the pipe string as it is passing through the injector. 
     These and other aspects and advantages of the invention are discussed below in connection with a preferred embodiment illustrated by the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of a coiled tubing injector intended to be representative of coiled tubing injectors generally, but with grippers according to the present invention. 
         FIG. 2  is a front elevational view of the coiled tubing injector shown in  FIG. 1 . 
         FIG. 3  is a left side elevational view of the coiled tubing injector shown in  FIGS. 1 and 2 . 
         FIG. 4  is an plan view of a drive chain of a coiled tubing injector having gripper carriers according to the present invention. 
         FIG. 5  is a side, elevational view, partially sectioned, of a gripper with a first shoe type mounted on one of the gripper carriers on the drive chain of  FIG. 4 . 
         FIG. 6  is a side, elevational view, partially sectioned, of a gripper with a second shoe type mounted on one of the gripper carriers on the drive chain of  FIG. 4 . 
         FIG. 7  is a side, elevational view, partially sectioned, of a gripper with a third shoe type mounted on one of the gripper carriers on the drive chain of  FIG. 4 . 
         FIG. 8  is a perspective view of the gripper carrier and the gripper shoe of  FIG. 6  before as one is being mounted to the other. 
         FIG. 9  is a side, elevational view of the gripper shoe mounted on the gripper carrier of  FIG. 8 . 
         FIG. 10  is a top, plan view of the gripper shoe of  FIG. 6 . 
         FIG. 11  is a partially sectioned, end view of the gripper shoe of  FIG. 10 . 
         FIG. 12  is a partially sectioned, side view of the gripper shoe of  FIG. 10 . 
         FIG. 13  is a bottom, plan view of the gripper shoe of  FIG. 10 . 
         FIG. 14 . is a top, plan view of the gripper carrier shown in  FIGS. 4-9 . 
         FIG. 15  is a side view of the gripper carrier of  FIG. 14 . 
         FIG. 16  is a cross-section of the gripper carrier taken along section line  16 - 16  in  FIG. 15 . 
         FIG. 17  illustrates flexing of a leaf spring of the gripper carrier. 
     
    
    
     DESCRIPTION 
     In the following description, like numbers refer to like elements. 
       FIGS. 1, 2 and 3  illustrate an example of a coiled tubing injector  101 . It is intended to be representative of coiled tubing injectors generally for purposes of describing the invention, even though it may differ from other prior art coiled tubing injectors in several important aspects. 
     Referring first to  FIG. 1 , coiled tubing is transported into the top of coiled tubing injector  101  from a reel (not shown) on a “goose-neck” support  103 . The goose-neck support includes a frame  105  supporting a plurality of rollers  107 . Bracing  108  extending from cage  109  positions the goose-neck support  103  in proper relation to the injector  101 . The cage also supports the injector  101  for transportation. Legs (not shown) may also be attached to the corners of the bottom of the cage  101  to stand the injector above a well head (not shown). 
     Referring now to  FIGS. 1, 2 and 3  together, injector  101  includes two, continuous loop drive chains generally designated by reference numbers  111  and  113 . The drive chains revolve generally within a common plane defined by axes  114  and  116 , which plane is normal to axis  118 . Connected to each drive chain is a plurality of grippers  115 . The drive chains  111  and  113  are arranged in a conventional, opposing relationship. Each drive chain  111  and  113  is mounted on an upper drive sprocket (not shown) and a lower drive sprocket  119  and  121 , respectively. The upper drive sprockets are mounted within drive housing  117  and are not visible in these views. One set of bearings for the shafts of upper drive sprockets are mounted within bearing housings  118  and  120 , respectively. The other set of bearings on which the shafts of upper drive sprockets are journalled are mounted to the opposite side of the drive housing  117 . 
     A box-shaped frame is formed from two, parallel front plates  123  and  125 , separated by side plate  127  and a second side plate parallel to side plate  127  but not visible in these views. This frame supports the drive housing  117  and transmission gear box  131  at its upper end, and the lower drive sprockets at its lower end. 
     The lower drive sprockets  119  and  121  are connected to shafts  133  and  135 , respectively. The ends of each shaft is journalled on opposite sides of the injector frame within a movable carrier  137 . Each carrier is mounted so that it may slide vertically within an elongated slot  139  defined in either the front plate  123  or rear plate  125 . A hydraulic cylinder  141  is inserted between the top of each carrier  137  and a block  143  connected to the frame at the top of each elongated slot  139 . Each cylinder  141  applies a spreading force between the stationary block and the moving carrier  137  to push down on the lower drive sprockets  119  and  121  and thus tension the drive chains. 
     Although not visible, coiled tubing injector  101  includes two skates, one for each drive chain, for forcing the grippers  115  toward each other as they enter the area between the two drive chains through which the coiled tubing passes. Examples of such skates are shown in U.S. Pat. No. 5,309,990 and are well known in the art. A plurality of hydraulic cylinders  145  are used to pull together the skates and maintain uniform gripping pressure against coiled tubing (not shown) along the length of the skates. Each cylinder  145  is connected at each end through a clevis and pin to an eyelet  147  of a bar extending behind one of the skate and terminating in another eyelet connected to another piston on the opposite side of the injector. 
     At the bottom of the injector, a stripper  149  carried by a stripper adapter  151 , connects the injector to a well head. Power for driving the injector is provided by a high speed, low torque hydraulic motor  153  coupled with the transmission gear box  131  through brake  155 . The hydraulic motor is supplied with a pressurized hydraulic fluid in a conventional manner. 
     Referring now to  FIGS. 4-7 , drive chain  111  includes a roller chain having two strands,  157  and  159 , on either side of the row of grippers  115 . (Note that in  FIG. 4 , the grippers have their shoes removed, revealing gripper carriers  161 .) The roller chain is of well-known construction. Rollers  163  are mounted on pins  165  which extend from an exterior side of strand  157 , through gripper carrier  161 , to the exterior side of strand  159 . Roller links  167  are disposed on opposite sides of each pair of rollers  163 . Pin link plates  169  are outboard of each roller plate and connect pairs of pins. 
     Mounted to an underside of gripper carriers  161  are a pair of roller bearings  171  and  173  which ride upon the skates of the injector. The roller bearings are rotatably mounted on pin  175 . 
     As illustrated by  FIGS. 5, 6 and 7 , a plurality of different shoes of unitary construction may be attached to the same gripper carrier  161 . For example, in  FIG. 5 , “V”-shaped gripper shoe  179  can support large diameter tubing or pipe, the outer diameter of which is indicated in phantom by dashed circle  181 . In  FIG. 6 , it is round-shaped gripper shoe adaptor  183  which may hold various sizes of rounded gripper shoes disposed therein (not shown) for gripping smaller diameter pipes and tubing. In  FIG. 7 , a comparatively small gripper shoe  185  is shown mounted to gripper carrier  161 . When installed in an injector, the position of the center line of the pipe to be gripped by gripper shoe  185  will be the same as the center line of the larger diameter pipe to be gripped by gripper shoe  179 . This allows different shoes to be installed on the same injector in order to accommodate gripping of irregularly shaped tools or joints being passed through the injector without changing the relative position of the skates on which the gripper carriers roll. 
     Each of the gripper shoes may be quickly inserted and removed from the gripper carrier  161  without the use of tools. This is especially useful when running conventional, jointed pipe rather than coiled tubing, or when running a tool string corrected to one end of the coiled tubing. One or more gripper shoes are removed from each drive chain to pass the pipe joint or tool. In  FIG. 5 , for example, the diameter of a joint is illustrated by dashed circle  187  and the outer diameter of the pipe by dashed circle  181 . 
     Referring now to  FIGS. 8-17 , to mount a gripper shoe to the carrier  161 , a universal base  189  is integrally formed on the bottom of the gripper shoe. The base mounts to the gripper shoe carrier using a tongue and groove type of mounting that allows the gripper shoe to be slid onto and out of the mounting in directions that, when the injector is in an operational position, are generally parallel to the ground, which directions are generally oriented along axis  118 , and perpendicular to the directions in which the chain moves, which directions are generally oriented along axis  114 . Thus, forces exerted by the pipe string on the gripping elements, which forces are primarily along axis  114 , tend to act in a direction along axis  114 . along which the grippers shoe is slid into and out of the gripper shoe carriers. For purposes of explanation only, the gripper shoe adaptor  183  is chosen to illustrate this base. The same base is found on each of the gripper shoes  179  and  185 . The universal base  189  includes four mounting lugs,  191 a,  191 b,  191 c and  191 d which function as tongues that slide into grooves in the form of slots defined by ledges  195  and rails  197  around the periphery of the carrier. When the gripper shoe is lowered toward the carrier, lug  191 a fits into slot  193 a defined between ledges  195 a and  195 c extending from left side rail  197 a. Lug  191 b fits in slot  193 b defined between ledges  195 b and  195 c extending from right side rail  197 b. Lugs  191 c and  191 d fit over the end of the side rails  197 a and  197 b, respectively. The base of the gripper shoe presses against a flat, metal leaf spring  199 , forcing it down to allow the gripper shoe base  189  to be slid into the base, toward end rail  201 . When base is pushed back to the end rail, the lugs  191 a- 191 d pass under ledges  195 a- 195 d, respectively and cooperate with the ledges to retain the gripper shoe on the carrier. Leaf spring  199  then pops up, as best shown in  FIG. 9 , and retain the gripper show on the carrier. During normal operation of the injector, lateral forces which would push the gripping shoe against the leaf spring are not substantial. Nevertheless, the leaf spring does possess substantial lateral strength. To reduce the effect of forces acting as the gripper shoes in lateral direction, the orientation of the carriers may be alternated on the chain, thus preventing the springs from carrying the lateral load. 
     The flat, metal leaf spring  199  is formed of an arched body section  199 a and feet  199 b and  199 c. The feet of the spring are trapped within open-ended slots  203 a and  203 b formed in the carrier  161 . Depressing the leaf spring flattens it and causes the feet to slide outward, as illustrated in phantom by  FIG. 17 . When the feet slide outward, any dirt or other debris which may have accumulated in the slots  203 a and  203 b is pushed out through their open ends. The spring force of the spring is such that it may easily be manually depressed to release the gripper shoe, or pulled to remove the spring to clean a shallow channel  205  formed in the carrier between the open slots  203 a and  203 b for accommodating the body of the leaf when it is depressed. 
     Sandwiched between the gripper shoe base  189  and the carrier  161  is an elastomeric pad  206  of high spring rate which allows the gripper shoe to float on the carrier  161 . Slightly floating the gripper shoe allows the gripper shoe to automatically make small adjustments in its alignment with the coil tubing or pipe as it engages the tubing or pipe, thus providing a more even distribution of gripping forces across the shoe. The elastomeric pad also accommodates manufacturing tolerances that result in slight variations in the distances between the skate on which the roller bearings of the gripper carriers ride and the centerline of the pipe or other object being gripped. Thus, more of the gripping shoes will make good gripping contact with the pipe, improving overall grip. Preferably, only gripping shoes are used that have fixed shapes conforming to the normal shape of the pipe, and that surround substantially half of the circumference of the pipe. The fixed shape shoes cause the pipe to maintain its normal shape as strong forces are applied to the pipe, thus preventing deformation. By forcing the pipe to retain its normal shape and floating the gripper shoe for better alignment of the shoe with the pipe, contact area between the gripping shoe and pipe is increased. Furthermore, greater force may be applied to the pipe without concern of deformation. Thus, with greater contact area and force, gripping is improved. 
     Each shoe carrier  161  is mounted to one of the two drive chains by inserting one of the chain pins  165  ( FIG. 5 ) through each of the bores  207 a and  207 b. Rollers  171  and  173  ( FIGS. 5-7 ) are mounted between flanges  209 a,  209 b and  209 c. Roller  175  extends though openings  211 a and  211 b in flanges  209 a and  209 b, and in a similar opening in flange  209 c which is not visible in these views. 
     Gripping shoe adaptor  183  includes rims  213 a and  213 b located at opposite ends for retaining removable gripping elements (not shown). Gripping elements may thus be replaced when worn or changed in size or shape, or to accommodate passing of downhole tools or other downhole assemblies having different diameters than the pipe. 
     The forgoing embodiments are but examples of the invention. Modifications, omissions, substitutions and rearrangements may be made to the forgoing embodiments without departing from the invention as set forth in the appended claims.