Abstract:
A coiled tubing injector apparatus for use in inserting coiled tubing into a well, temporarily suspending the coiled tubing, and removing the coiled tubing from the well is described. The apparatus includes a base with a pair of spaced carriages extending upwardly therefrom. The base is attached to a superstructure. The carriages each have a gripper chain drive system rotatably mounted thereon and movable therewith. An actuation and linkage system allows the carriages to move toward and away from one another in a lateral or transverse direction with respect to the superstructure and the base. Thus, the gripper chain systems can be engaged or disengaged from tubing extending through the apparatus. Each of the carriages are pivotally attached to the base with a load pin which extends through lugs attached to the base and corresponding lugs extending down from the carriage.

Description:
BACKGROUND OF THE INVENTION 
     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 that is inserted into the well is normally inserted through a lubricator mechanism which provides a seal about the O.D. of the tubing for the retention of any pressure that may be present at or near the surface of the well. The tubing is inserted by a coiled tubing injector apparatus which generally incorporates a multitude of gripper blocks for handling the tubing as it passes through the injector. The tubing is 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. 
     The coiled tubing injector apparatus utilizes a pair of opposed endless drive chains which are arranged in a common plane. These opposed endless drive chains are often referred to as gripper chains because each chain has a multitude of gripper blocks attached therealong. The gripper chains are driven by respective drive sprockets which are in turn powered by a reversible hydraulic motor. Each gripper chain is also provided with a respective idler sprocket to maintain each gripper chain within the common plane. Both the drive sprockets and idler sprockets are mounted on a common frame wherein the distance between centers of all the sprockets are essentially of a constant distance from each other. That is, the drive sprockets are free to rotate but are not free to move either vertically or laterally with respect to each other. The idler sprockets are not free to move laterally with respect to each other, but are vertically adjustable within a limited amount in order to set the amount of play in each gripper chain. Such vertical adjustment is done by either a mechanical adjusting means or a hydraulic adjusting means. Typically, for injectors having mechanical adjustment means, the adjustment is made when the injector is not in operation. 
     The opposed gripper chains, preferably via the gripper blocks, sequentially grasp the coiled tubing that is positioned between the opposed gripper chains. When the gripper chains are in motion, each chain has a gripper block that is coming into 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. Preferably, gripper blocks such as those set forth in U.S. Pat. No. 5,094,340, issued Mar. 10, 1992, to Avakov, which is incorporated herein, are used. 
     Because the gripper chain drive sprockets and idler sprockets are essentially in a fixed relationship with each other, the gripper chain is provided with a predetermined amount of slack which allows the gripper chain to be biased against the coiled tubing to inject the tubing into and out of the wellbore. This biasing is accomplished with an endless roller chain disposed inside each gripper chain. Each roller chain engages sprockets rotatably mounted on a respective linear bearing beam. A linkage and hydraulic cylinder mechanism allows the linear bearing beams to be moved toward one another so that each roller chain is moved against its corresponding gripper chain such that the tubing facing portion of gripper chain is moved toward the tubing so that the gripper blocks can engage the tubing and move it through the apparatus. The gripper blocks will engage the tubing along a working length of the linear beam. 
     Each chain has a gripper block that contacts the tubing at the top of the working length as a gripper block on the same chain is breaking contact at a bottom of the working length of the linear beam. 
     The fixed distance between each set of gripper chain drives and idler sprockets requires some significant lateral movement in the gripper chain when engaged by the roller chain on the corresponding linear beam in order to allow the gripper chains to engage the tubing by way of the gripper blocks. The reason for having the requisite amount of lateral play in the gripper chains is to provide a limited amount of clearance between the gripper chains, upon moving the respective roller chains away from the vertical center line of the injector, to allow the passage of tubing and tools having larger outside diameters or dimensions. An inherent shortcoming in this design is that the required slack can often cause misalignment problems and even binding problems with the chains due to having to accommodate ever increasing outside nominal dimensions of downhole tools and wellhead equipment. Another troublesome characteristic manifests itself in the large approach and departure angles defined by the region where the respective paths of the gripper chains converge upon, and diverge away from, the working center line of the injector wherein the coiled tubing is preferably positioned for being injected or extracted into or out of the well. The large approach and departure angles reduce the overall efficiency of the injector due to the necessity of supporting and contending with the reactive forces generated by the chains when the injector is in operation. 
     A further, if not more predominate reason why large gripper chain approach and departure angles are not desired, is that large angles tend to increase the likelihood of the chain-mounted gripper blocks to mark, or gouge, the tubing as the blocks come into contact with the tubing. Such marks, or gouges, create stress risers within the wall of the tubing which can lead to premature structural failure of the tubing. A tubing injector apparatus not having large gripper chain approach or departure angles, yet being able to accommodate large diameter tubing and wellhead equipment would advance the art considerably. 
     Therefore, there is a need within the art to provide an injector that, while the injector remains installed about the wellhead, can accommodate large nominal diameter tools and surface equipment, yet can provide efficient and reliable chain operation to generate the high forces needed for injecting and extracting tubing of long lengths and large diameters into and out of the wellbore. 
     Another need within the art is for an injector having the ability to accommodate a wide range of tubing diameters while in operation. Such an injector would allow for improving operations wherein coiled tubing having differing diameters that have been connected to each other to form a single string of tubing are being used in the servicing of the well. 
     Another need within the art is for an injector that can accommodate the ever-increasing nominal outside diameters of tubing while avoiding: chain misalignment, chain binding tendencies, improper chain tension, gripper block marking or gouging, and other inherent design problems of prior injectors which manifest themselves when working with tubing, tools, and surface equipment having large nominal outside diameters. 
     One coiled tubing injector apparatus which resolves the foregoing problems is the apparatus described in patent application Ser. No. 08/508,411 entitled TWIN CARRIAGE TUBING INJECTOR APPARATUS, assigned to the assignee of the present invention, the details of which are incorporated herein by reference. However, the apparatus described therein, along with prior injectors, do not address other difficulties associated with injecting, suspending and extracting coiled tubing from a wellbore. 
     Generally, as provided herein, the wellbore in which the tubing is injected will be pressurized, so that as the tubing is initially inserted through the injector and into the wellbore, the pressure will tend to resist injection of the tubing. In other words, when the length of tubing in the well is such that it is insufficient to overcome the pressure in the wellbore, the pressure will tend to resist injection and will act to force the tubing upward. At some point, the weight of the tubing will overcome the pressure in the wellbore. The weight of the tubing will then apply a downward vertical load to the gripper blocks that engage the tubing. The downward load is typically called a “hoisting” load. 
     When the gripper chains are in motion, the gripper blocks along the working length of the linear beam engage the tubing. The lateral load applied to the tubing by the opposed gripper chains will generally be uniform along the working length of the linear beam. The vertical hoisting load is carried by linking pins which connect the gripper blocks together to form the endless gripper chains. Because the lateral load applied to the tubing is substantially uniform, the vertical load applied to the gripper chain by the tubing will be carried primarily by the linking pins which connect the gripper blocks at the lower or bottom end of the working length of the linear beam. The linking pins connecting the remainder of the blocks carry little or no vertical load. Because the vertical load during hoisting is concentrated on the lower linking pins, the life of the chain is reduced. 
     Thus, there is a need for a coiled tubing injector apparatus which will accommodate large nominal diameter tools and tools of differing diameters while in operation, and at the same time redistribute the vertical load created by the tubing from the linking pins at the bottom of the working length to all of the pins along the working length of the linear beam and the corresponding working length of the gripper chain. 
     SUMMARY OF THE INVENTION 
     The present invention is a coiled tubing injector apparatus for use in inserting coiled tubing into a well, temporarily suspending the tubing in the well, and for extracting coiled tubing from the well. The apparatus generally comprises a base, a carriage extending upward from the base, and a gripper chain drive system mounted in the carriage. The base is connected to a superstructure which is mounted above a wellhead. 
     The carriage is pivotally attached to the base, and is preferably laterally movable with respect to the base. The gripper chain drive system is movable with the carriage, and is adapted to engage tubing extending through the superstructure. The carriage is preferably one of a pair of spaced carriages which are pivotally attached to and laterally movable with respect to the base. The tubing will pass between the spaced carriages and through the base along a pre-selected center line, so that the tubing will pass between and be engaged by the gripper chain drive systems when the carriages are moved toward one another. 
     The base has a pair of attachment lugs extending upwardly therefrom. The attachment lugs will mate with corresponding carriage lugs located at a lower end of the carriages. The carriages are attached to the base with a load pin extending through the attachment lugs and corresponding carriage lugs. The attachment lugs are slidably connected to the base, so that the carriages are laterally movable with respect to the base and each other. 
     The gripper chain drive system comprises a drive shaft mounted on the carriage, drive sprockets mounted on the drive shaft, an idler shaft mounted on the carriage and idler sprockets mounted on the idler shaft. A gripper chain which includes a plurality of gripper blocks attached thereto engages the drive and idler sprockets. 
     A roller chain system for supporting the gripper chain when it engages the tubing is also included. The roller chain system is mounted on a pressure, or linear beam that is rigidly positioned in the carriage. The roller chain system includes an upper mounting shaft mounted on the linear beam, an upper roller sprocket mounted on the upper mounting shaft, a lower mounting shaft mounted on the linear beam, a lower roller sprocket located on the lower mounting shaft, and a roller chain engaged with the upper and lower roller sprockets. Each linear beam has a working length defined thereon to support the gripper chain. When the carriages are moved so that the gripper chains engage the coiled tubing, the chain will engage the tubing along the working length of the linear beam, and a corresponding working length of the gripper chain. 
     The apparatus includes a means for moving the carriages laterally, which may comprise a plurality of hydraulically actuated gripper cylinders. When the gripper cylinders are actuated to move the carriages toward one another so that the gripper chain will engage the tubing, a lateral, or transverse load is applied to the tubing by the gripper chains. The lateral load applied by the gripper cylinders is typically distributed uniformly along the working length of the linear beam. When the weight of the tubing in the wellbore causes a downward load to be applied to the gripper chain, a moment around the load pins is created. That moment is reacted by a lateral force between the tubing and the gripper chains. The moment is reacted so that the total lateral load at the top of the working length, which is comprised of the load applied by the gripper cylinder and the reaction load caused by the moment around the load pin, is higher than the lateral load at the bottom of the working length. The lateral load gradually decreases from its highest magnitude at the top to its lowest magnitude at the bottom of the working length of the linear beam. Because the lateral load is higher at the top of the working length, the vertical load caused by the tubing in the wellbore will be more evenly distributed along the working length of the gripper chain than it would be if the lateral load were uniform. The vertical, or hoisting load will therefore be carried by the linking pins which connect the links of the gripper chain along the entire working length of the linear beam. The apparatus thus equalizes the hoist load so that it is carried by all of gripper blocks along the working length of the gripper chain. With prior art injectors, the hoisting load was carried primarily by the gripper blocks, and thus by the linking pins connecting the gripper blocks, at the lower end of the working length. 
     Numerous objects and advantages will become apparent as the detailed description of the preferred embodiment is read in conjunction with the drawings which illustrate such embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically shows the load equalizing coiled tubing injector apparatus of the present invention in position for inserting coiled tubing into an adjacent wellhead. 
     FIG. 2 shows a front view of the apparatus of the present invention. 
     FIG. 3 shows a side view of the apparatus of the present invention. 
     FIG. 4 shows a partial front view and a partial cross section of the carriages with a portion of the outer plate removed. 
     FIG. 5 shows a partial schematic looking at the inner side of a carriage from the center of the apparatus with the gripper and roller chains removed. 
     FIG. 6 shows a view from line  6 — 6  in FIG.  3 . 
     FIG. 7 shows a view of the linear beam. 
     FIG. 8 shows the working face of the linear beam without the roller chain. 
     FIG. 9 shows a view taken from line  9 — 9  on FIG.  6 . 
     FIG. 10 shows a view taken from line  10 — 10  on FIG.  6 . 
     FIGS. 11 and 12 show section views taken from lines  11 — 11  and  12 — 12 , respectively, on FIG.  2 . 
     FIG. 13 schematically shows the base of the present invention. 
     FIG. 14 shows a view taken from line  14 — 14  of FIG.  13 . 
     FIGS. 15 and 16 show detailed views of the carriage lug of the present invention. 
     FIGS. 17 and 17A show perspective views of a portion of the chain of the present invention. 
     FIG. 18 schematically shows the loads applied when the present invention is in use. 
     FIG. 19 schematically shows the top view of the gripper blocks and tubing when engaged. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and more particularly to FIG. 1, the coiled tubing injector apparatus of the present invention is shown and generally designated by the numeral  10 . Injector  10  is shown positioned above a wellhead  12  at a ground surface or subsea floor  14 . A lubricator or stuffing box  16  is connected to the upper end of wellhead  12 . 
     Tubing  18 , having a longitudinal central axis  17  and an outer diameter or outer surface  19  is supplied on a large drum or reel  20  and is typically several thousand feet in length. Tubing of sufficient length, such as 10,000 feet or greater, may be inserted into the well either as single tubing, or as tubing spliced by connectors or by welding. The outer diameters of the tubing can range from approximately one inch (2.5 cm) to approximately five inches (12.5 cm). However, the disclosed injector apparatus is readily adaptable to even larger diameters. Typically, tubing  18  is in a relaxed but coiled state when supplied from drum  20 . It is spooled from the drum typically supported on a truck (not shown) for mobile operations. 
     Injector apparatus  10  is mounted above wellhead  12  on a superstructure  22 . Extending upwardly from superstructure  22  is a guide framework  24  having a plurality of pairs of guide rollers  26  and  28  rotatably mounted thereon. 
     Tubing  18  is supplied from drum  20  and is run between rollers  26  and  28 . As tubing  18  is unspooled from drum  20 , generally it will pass adjacent to a measuring device, such as wheel  30 . Alternatively, the measuring device may be incorporated in apparatus  10 , such as described in U.S. Pat. No. 5,234,053, issued Aug. 10, 1993, to Connell. 
     Rollers  26  and  28  define a pathway for tubing  18  so that the curvature in the tubing is slowly straightened as it enters apparatus  10 . As will be understood, tubing  18  is preferably formed of a material which is sufficiently flexible and ductile that it can be curved for storage on drum  20  and also 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 suffer from premature fatigue failure should the curvature be severe. Rollers  26  and  28  are spaced such that straightening of the tubing is accomplished wherein the tubing is inserted into the well without kinks or undue bending on the tubing. However, the disclosed injector can be used for injecting, suspending, or extracting any generally elongated body. All of this is done in a manner known in the art. 
     Referring now to FIGS. 2-18, the details of coiled tubing injector apparatus  10  will be discussed. The apparatus generally comprises a base  32  and a pair of substantially similar carriages  35  extending upward therefrom. Each carriage  35  includes a pair of spaced outer plates and a back plate. Each carriage has a carriage lug  50  extending downward from a lower end thereof. The carriage lugs  50  mate with a pair of attachment lugs  55  which extend upwardly from base  32  and which are slidable relative thereto as explained more fully herein. Attachment lugs  55  may include a lug base  56  having upper and lower surfaces  57  and  58 , respectively, and an attachment portion  59  extending upward therefrom. A load pin  52 , having a center or longitudinal central axis  53 , extends through each carriage lug and the corresponding attachment lug, so that the carriages are pivotally attached to the base  32 . The apparatus also includes a means  60  for moving the carriages laterally with respect to one another and with respect to the base  32 . The apparatus  10  has a front, or forward side  62 , and a back, or rear side  64 . 
     The spaced carriages  35  comprise a first or right side carriage  66  and a second or left side carriage  68 . Carriages  66  and  68  will move towards and away from each other when actuating means, or means for moving  60  is actuated. The carriages are substantially similar in that, as seen in FIG. 2, the carriages are mirror images of one another. Right side carriage  66  comprises first outer plate  70  and second outer plate  72 . Plates  70  and  72  are mirror images of one another. First outer plate  70  may include rectangular cutout  74  at a lower end  76  thereof. A pair of bosses  78  extend downward from the top  82  of rectangular cutout  74 . First outer plate  70  also includes horizontal and vertical access slots  84  and  86 , respectively. The first outer plate  70  also has a stepped mounting boss  88  at an upper end  90  thereof. 
     Mounting boss  88  has steps  87  and  89  defined thereon. Second outer plate  72 , being a mirror image of plate  70  likewise includes a rectangular opening  92  at a lower end  91  thereof, a pair of bosses extending downwardly from a top  96  of opening  92 , horizontal and vertical access openings  98  and  100 , respectively. Outer plate  72  has an upper mounting boss  102  having steps  99  and  101  at an upper end  103  thereof. First outer plate  70  is the forward outer plate of right side carraige  66  and second outer plate  72  is the rear outer plate. Because plates  70  and  72  are mirror images, and because right and left side carriages  66  and  68  are mirror images, the forward outer plate of left side carriage  68  is substantially identical to, and may be comprised of second outer plate  72 , which is the rear outer plate on the right side carriage. Likewise, the rear outer plate on carriage  68  is substantially identical to and may be comprised of first outer plate  70 . A back plate  45  is connected to outer plates  70  and  72 . Right and left side carriages may also include upper caps  105  and  107  respectively disposed between the upper ends of the outer plates. Back plate  45  may be connected using bolts or other means known in the art. For instance, as shown in FIG. 2, the back plate may have lugs  104  extending inwardly therefrom so that bolts extending through the side plates may be attached thereto. 
     Each carriage also includes a gripper chain drive system  106  and a roller chain drive system  108 . Referring to FIGS. 4 and 5, the gripper chain drive system includes a pair of spaced pair gripper chain drive sprockets  110  rotatably disposed in the carriage. Sprockets  110  are mounted on a shaft  112  having a center, or longitudinal central axis  113 . As better seen in FIG. 12 shaft  112  extends through the upper mounting boss on the forward side of the apparatus and into to a flanged bearing  114 . A bearing adapter  116  is also included and is attached to the upper mounting boss. The gripper chain drive sprockets are driven by a reversible hydraulic motor  118  attached to each carriage on the back side  64  of the apparatus. The motor is of a type known in the art and is driven by a planetary gear and has an integral brake. Thus, the hydraulic motor can inject, retract or suspend tubing  18  in a well. 
     The gripper chain drive system also includes a pair of spaced gripper chain idler sprockets  120  which are rotatably disposed in the lower end of the carriage. The idler sprockets are mounted on a shaft  122  having a center, or longitudinal central axis  119 . As best seen in FIG. 11, gripper chain tensioners  124  are connected to the opposite ends of shaft  122 . Tensioners  124  are mounted on bosses  78  of first outer plate  70  and bosses  94  of second outer plate  72 . Tensioners  124  are mounted so that they can be vertically adjusted within rectangular openings  74  and  92  of the outer plates, respectively. A gripper chain  126  is engaged with gripper chain drive sprockets  110  and the gripper chain idler sprockets  120  in each carriage. Gripper chain  126  is of a kind known in the art and has a plurality of outwardly facing gripper blocks  128  disposed thereon. 
     Gripper blocks  128  are adapted for engaging coiled tubing  18  and moving it through apparatus  10 . Preferably gripper blocks  128  are such as those set forth in U.S. Pat. No. 5,094,340 issued Mar. 10, 1992, to Avakov. When actuating means  60  is actuated to move the carriage together, a gripping force is applied to the tubing by the gripper blocks. 
     As schematically shown in FIG. 17A, gripper blocks  128  have an inner face  129 . The gripper blocks will contact outer diameter  19  of tubing  18  on both sides of center line  17 . When gripper blocks having a V-shaped groove are used, such as those described in U.S. Pat. 5,094,340 to Avakov, the gripping forces are applied at contact points  121 ,  121   a,    123  and  123   a  as seen in FIGS. 18 and 19. As shown therein, points  121  and  121   a  rest on the plane defined by line  125  in FIG.  18  and line  125   a  in FIG.  19 . Likewise, points  123  and  123   a  rest on the plane defined by line  127  in FIG.  18  and line  127   a  in FIG.  19 . 
     As set forth herein, a carriage lug  50  is rigidly mounted to and extends downwardly from the lower end of each carriage. As shown in FIGS. 15 and 16, each carriage lug has a pair of ears  130  extending outwardly therefrom. Ears  130  have openings  131  defined therein. Carriage lug  50  also includes a pair of spaced carriage mounting lugs  132 . 
     Gripper chain tensioners  124  are vertically adjustable within the lower rectangular openings of the outer plates so that the proper tension on gripper chain  126  may be maintained. Tensioner  124  includes a bearing portion  134  and has a tensioning shaft  136  mounted to and extending downwardly from bearing portion  134 . Idler shafts  122  are mounted in bearing portion  134 . Tensioning shafts  136  extend through openings  131  in the pair of ears  130  on carriage lug  50 . A spring  140  is disposed around the shaft  138 . The tension in gripper chain  126  can be adjusted simply by rotating a nut  142  on the threaded end of shaft  136 . 
     The roller chain drive system  108  is rigidly positioned in each carriage between the outer plates. Roller chain drive system  108  includes a linear or pressure beam  150  rigidly fixed to the outer plates of the carriage. The linear beam is shown in FIGS. 7 and 8. Linear beam  150  may be comprised of a linear beam frame  152  with a bearing plate  154  attached thereto. Linear beam frame  152  has side webs  156  which will nest between the outer plates of the carriages. The linear beam may be rigidly attached to the carriage with bolts extending through outer plates  70  and  72  and side webs  156 . A working length  158  is defined on the linear beam. Working length  158  has upper and lower ends  157  and  159 , respectively. The working length  158  corresponds to the flat portion of bearing plate  154 . The linear beam has upper and lower ends  164  and  166  respectively. A pair of spaced upper, or first roller chain sprockets  168  are rotatably disposed on upper end  164  of linear beam  150 . A pair of spaced lower, or second roller chain sprockets  170  are rotatably disposed on lower end  166  of the linear beam. A roller chain  172  engages upper and lower roller chain sprockets  168  and  170 , respectively. Roller chain  172  has an outer side  173  which will engage an inner side  175  of gripper chain  126  along a line generally indicated by the numeral  177 . The upper and lower sprockets may be mounted on bearings  174  supported by shafts  176 . Lower sprockets  170  incorporate a tensioner (not shown), of a type known in the art to keep the proper tension on roller chain  172 . 
     The carriages are attached to base  32  with load pins  52  which extend through carriage lugs  50  and corresponding attachment lugs  55  which extend upward from the base. As shown in FIGS. 13 and 14 attachment lugs  55  are slidably mounted to base  32 . Base  32  is mounted to superstructure  22 , and has an opening  181  defined therein for tubing  18  to pass therethrough. Base  56  of lugs  55  are slidably received in tracks  186 , which are rigidly attached to base  32 . The carriages are thus slidable toward and away from each other to accommodate various tubing sizes. 
     As better seen in FIG. 2, lines designated by the numerals  180  and  182  depict lines which run through the centers  113  and  119  of the gripper chain drive and idler sprockets. The apparatus  10  has a longitudinal central axis  184 . Longitudinal central axis  184  is colinear with longitudinal central axis  17  of tubing  18  as it passes downward through the apparatus. Centers  53  of loading pins  52  preferably are positioned to the outside of the center lines  180  and  182 . 
     The means for moving  60  comprises a plurality of, and preferably four, hydraulic actuator cylinders  183 . The invention may include upper cylinders  185  having a longitudinal central axis  187 , and lower cylinders  188  having longitudinal central axis  189 . Actuator mounting plates  190  and  192  having clevis lugs  191  and  193  respectively extending therefrom are rigidly mounted to the outer plates of the carriages. The ends of cylinders  188  are attached to lugs  191  and  193 . Mounting plates  190  and  192  may be attached utilizing eight bolts  196  which extend through the mounting plates  190  and  192  and the outer plates of the carriage. The four innermost bolts, generally designated by the numeral  197 , which attach the actuator mounting plates may also extend through side webs  156  of the linear beam to rigidly attach the linear beam to the outer plates. 
     The apparatus also includes upper and lower equalizer linkages  200  and  202 . Linkage  200  includes a central link  204 , an upper outer link  206  and a lower outer link  208 . Center link  204  is pivotally mounted to a laterally extending guide plate  210  which is rigidly attached at its ends to superstructure  22 . The outer ends of the upper and lower outer links  206  and  208  are mounted to slider plate assemblies  212  and  214  as better seen in FIGS. 6,  9  and  10 . Slider plate assembly  212  includes an upper slider plate  216  and a lower slider plate  218 . Upper and lower slider plates  216  and  218  are mounted to the carriage utilizing fasteners  220 . Bearings  222  are mounted on fasteners  220  between upper and lower slider plates  216  and  218  and engage an inner side  224  of guide plate  210 . Slider plate assembly  212  also includes bearings  226  which are mounted between upper and lower slider plates  216  and  218  using fasteners  228 . Bearings  226  engage an outer edge  230  of guide plate  210 . 
     Slider assembly  214  is arranged similar to slider plate assembly  212  and thus includes upper and lower slider plates  232  and  234 , respectively. Upper and lower slider plates  232  and  234  are mounted to the carriage utilizing fasteners  236 . Bearings  238  are mounted on fasteners  236  between upper and lower slider plates  232  and  234  and engage the inner side  224  of guide plate  210 . Slider plate assembly  214  also includes bearings  240  mounted between upper and lower slider plates  232  and  234  using fasteners  242 . Bearings  240  engage outer edge  230  of guide plate  210 . The height of bearings  222 ,  226 ,  238  and  240  are substantially identical and is such that there is clearance between the slider plates and guide plates  210 . Each of the bearings engage the sides of the guide plates so that when the actuators move the carriages laterally, the carriages are supported by and slide along guide plates  210 . Lower equalizer linkage  202  is substantially identical to upper equalizer linkage  200  and includes the components set forth above. 
     As shown in FIGS. 9 and 10, outer link  206  of each linkage is connected to upper slider plate  232 . Outer link  206  is connected utilizing a pair of fasteners  244  and a pin  246  extending therebetween. The pin  246  extends through an opening in the end of upper outer link  206 . In like manner, lower outer link  208  is connected utilizing a pair of fasteners  248  with a pin  250  extending therebetween through an opening in the end of lower outer link  208 . Center link  204  is connected at center line  184  of the apparatus so that when the hydraulic actuators are actuated, each carriage will move an equal distance away or toward the center line. 
     In operation, when it is desired that tubing be lowered, raised or suspended in a well, the hydraulic actuators will be actuated until the gripper blocks  128  engage the sides of tubing  18 . The gripper chains will engage the tubing along working length  158  of the linear beams of each carriage, and a corresponding working length  252  of the chain. Thus, gripper chain  126  will first contact the tubing at upper end  157  of the working length of the linear beam, and the contact between the tubing and gripper chains  126  will break as the tubing passes lower end  159  of the working length. As set forth previously, a gripper chain utilizing blocks of the type shown in U.S. Pat. No. 5,094,340 to Avakov is preferably included. Referring to FIGS. 17 and 17A, the gripper chains may thus be comprised of outer links  300  and gripper blocks  128 . The outer links and the gripper blocks are connected to form an endless chain utilizing linking pins  302  which extend through the outer links and the gripper blocks. 
     When the tubing is engaged by the gripper blocks, the hydraulic actuators will cause the chains to apply a uniform lateral load to the tubing. The load will be applied along the working length  158  of the pressure beam, and the corresponding working length  252  of the gripper chain, where the gripper chain engages the tubing. As the tubing is lowered into a pressurized wellbore, pressure in the well will tend to try to force the tubing upward. At some point, the weight of the tubing will overcome the load applied by the pressure in the wellbore. At that point, the tubing will apply a downward vertical, or hoisting load  254  to the gripper blocks. The vertical load  254  is applied to the chains of both carriages, so that one-half of the total vertical load is applied to each gripper chain. As shown in the schematic shown in FIG. 18, the load applied to each chain is designated by the numeral  255 , and, in the embodiment shown would be applied at contact points  121 ,  121   a,    123  and  123   a.    
     In a typical prior art coiled tubing injector apparatus, the vertical load applied to each chain is reacted primarily by the gripper blocks  128  located at and toward the lower end  159  of the working length. The load is thus concentrated in the linking pins  302  which connect the gripper blocks at the lower end of the working length. The reason for this is that the lateral load applied by the hydraulic actuators is uniformly distributed along the working length during injecting, retracting and suspending operations. The uniform lateral load is schematically shown in FIG.  18  and is generally designated by the numeral  320 . However, with the present invention, the lateral load applied to the tubing does not stay uniform once the weight of the tubing overcomes the load created by the pressure in the well. As shown in FIG.  18 , the centers  53  of load pins  52  are offset from lines  125  and  127  which are drawn through contact points  121  and  121   a,  and contact points  123  and  123   a  respectively. The offset between lines  125  and  127  and the corresponding centers  53  of load pins  52  is generally designated by the numeral  260 . Thus, contact points  121  and  121   a  are offset a distance  260  from the center  53  of the load pin  52  of the corresponding carriage. Likewise, contact points  123  and  123   a  are offset a distance  260  from the center  53  of the load pin  52  of the corresponding carriage. As set forth previously, the load  255  applied to each gripper chain is applied at the contact points on the gripper blocks. The load is thus applied to each chain at a distance equivalent to offset  260  from the centers  53  of the load pins. Because each carriage has its own independent load pin, and because the load pin is offset from the contact points where the vertical load  255  is applied, the vertical load applied by the tubing to the gripper blocks causes a moment around each load pin  52 . That moment causes an increased lateral load along the working length of each gripper chain. The moment is reacted so that the lateral load along the working length of the gripper chain is no longer uniform, but is higher at the top than at the bottom. The lateral load will gradually decrease until it reaches its lowest magnitude at the bottom of the working length of the chain as schematically shown in FIG.  18  and generally designated by the numeral  322 . 
     Because the lateral load is increased at the top of the working length, the vertical load  255  applied by the tubing to each chain will be distributed upward along the working length of the gripper chain and will be carried by all of the gripper blocks  128  and linking pins  302  between the upper and lower ends  157  and  159  of the working length  158  rather than being carried primarily by the linking pins at the lower end of the working length. Thus, by providing for lateral offset  260  between the load pin of each independent carriage and the point of load application to the chain, the hoisting load can be distributed among the gripper blocks  128  and the corresponding linking pins  302  located along the operating or working length of the linear beam. This reduces the load on the linking pins at the lower end of the working length and increases the chain life. 
     The offset  260  should not exceed “a” which can be defined using the equation set forth below        a   ≺     2        (     e   +     2      c     +     (     bxf   2     )       )                              
     In the equation, a is the offset  260 , e is a distance  262  between the centers  185  and  189  of the upper and lower hydraulic gripper cylinders which apply the gripping force, c is the distance  264  from the center  185  of the upper gripper cylinder to the upper end  157  of the working length of the linear beam which is the point at which the chains first engage the tubing, and b is the distance  266  from lower surface  58  of the base of attachment lug  55  to upper end  157  of the working length. “f” in the equation is the friction coefficient between the base  56  of attachment lug  55  and track  186 . When a steel material is used for both the lug  55  and the track, f will typically be about 0.10, assuming proper lubrication. 
     As will be recognized by those in the art, the contact point between the tubing and the gripper block will vary depending on the size of the tubing, and the type of gripper block used. Thus, the actual offset  260  or distance a is not fixed. 
     To insure that the offset  260  does not exceed the desired magnitude, an offset  261  from the face  129  of a gripper block  128  to the center  53  of the corresponding load pin should not exceed a 1  which is defined using the equation          a   1     ≺     2        (     e   +     2      c     +     (     bxf   2     )       )                              
     where e, c, b and f are as defined above. The face  129  of the gripper blocks represents the farthest point from the centers of the load pins that the load could possibly be applied by the tubing to the chain  126 . Thus, by using the outer surface  129  of the gripper block to define the offset, it can be insured that the distance a, or actual offset  260 , will never exceed the maximum allowable. 
     In sum by positioning the load pins at a location which is offset from the point at which the load is applied to the chain on each carriage, and by insuring that that offset does not exceed the maximum as defined herein, a moment will be created by the hoisting load and will be reacted in such a way as to increase the lateral load applied by each carriage at the top of the working length of the linear beam. The result is that the vertical load is distributed and reacted by all of the gripper blocks along the working length thereof as opposed to being reacted only by the gripper blocks at a lower end of the working length. 
     It has been shown that the improved coiled tubing injector apparatus of this invention fulfills all objects forth hereinabove and provides distinct advantages over the known prior art. It is understood that the foregoing description of the invention and illustrative drawings which accompany the same are presented by way of explanation only and that changes may be had for those skilled in the art without departing from the true spirit of this invention.