Patent Publication Number: US-10787870-B1

Title: Jointed pipe injector

Description:
TECHNICAL FIELD 
     This invention pertains to work-over related oil-field work, for example maintaining productions strings in pressurized oil wells. More specifically, the invention relates to a jointed pipe injector configured to support and move pipe and tubing, including jointed pipe, into and out of a well bore, which well bore may be pressurized or unpressurized. The injector of the current invention may operate either independently, or in conjunction with a conventional work-over and/or drill rig. 
     BACKGROUND 
     There are many known devices for injecting coiled tubing into a well bore. However, conventional coiled tubing injectors are not capable of handling jointed pipe. Injectors offer safety and speed advancements over the conventional methods of working with jointed pipe. A need therefore exists, for an injector capable of handling jointed pipe. 
     Further, conventional tubing injectors may use non-standard drive chains in which portions of the gripper block assemblies are integral parts of the chain itself. The use of non-standard drive chains may result in higher costs of acquisition, maintenance and/or operation. A need therefore exists, for an injector that uses standard roller chains to which the gripper block assemblies are removably attached. 
     SUMMARY 
     The present invention comprises a joined pipe injector apparatus that is capable of handling strings of jointed pipe in addition to other tubular goods including coiled tubing. A self-adjusting gripper block system allows for upset tubing joints to be passed through the unit without operator intervention. The gripper block assemblies can be interleaved, forming a continuous surface, to easily convey over the skate rollers during operation. The gripper blocks can bolt directly to standard chain, thus eliminating the need to build a custom chain to integrate the gripper blocks. A telescopic torque tube system can be used to mechanically time both drive chain systems. 
     In one aspect, a jointed pipe injector is provided that is capable of handling strings of jointed pipe that may or may not have upset joints resulting in localized variations in the diameter of the pipe along the string. The jointed pipe injector comprises a pair of endless drive chains, each drive chain configured in a loop and including a plurality of gripper blocks attached to the outward-facing side of the loop. The two drive chains are arranged with a portion of each loop running substantially parallel to the other and synchronized such that each gripper block on one chain faces a corresponding gripper block on the other chain. The opposing gripper blocks and piper inserts define a pipe passage therebetween. A self-adjusting gripper block system provides localized gripper compliance whereby the distance between opposing gripper blocks on the two drive chains in a first pair of gripper blocks can be different from the distance between opposing gripper blocks in a successive pair of gripper blocks. 
     In another aspect, a joined pipe injector is provided for injecting and withdrawing a length of pipe or tubing having a nominal diameter from a wellbore. The joined pipe injector comprises a pair of drive chains, each drive chain configured in an endless loop defining an outward-facing side and including a substantially straight portion, and wherein the outward-facing sides of the substantially straight portions are juxtaposed and spaced apart a first distance to define a pipe/tubing passage therebetween. A drive mechanism is provided for transporting the drive chains around the respective loops in synchronized fashion wherein both drive chains move along the pipe/tubing passage in a common direction defining a direction of travel and at a common speed. A plurality of gripper block assemblies are mounted on each drive chain, each gripper block assembly including a gripper block body connected to a respective one of the drive chains and extending from the outward-facing side thereof, at least one pipe insert slidingly mounted to an outward-facing side of the gripper block body for sliding movement between a maximum extension and a minimum extension perpendicular to the direction of travel of the respective drive chain, and at least one spring for each pipe insert. Each spring is operatively connected between the gripper block body and the respective pipe insert and biases the pipe insert outward toward the maximum extension. The first distance between the respective outward-facing sides of the drive chains along the pipe/tubing passage is selectively adjustable, whereby a length of pipe or tubing within the pipe/tubing passage is contacted at nominal portions of the pipe or tubing having a nominal diameter by a first set of the pipe inserts that move a nominal distance from the maximum extension against the bias of the respective springs. The pipe or tubing within the pipe/tubing passage is contacted and at secondary portions of the pipe or tubing having a secondary diameter, which is greater than the nominal diameter, by other sets of the pipe inserts that move a secondary distance, which is greater than the nominal distance, from the maximum extension against the bias of the respective springs of the other sets. 
     In one embodiment, the drive mechanism further comprises a pair of drive assemblies, each of the drive assemblies being slidably mounted on a common frame assembly and carrying one of the pair of drive chains. A timing mechanism extends between the pair of drive assemblies to synchronize the movement of the drive chains with one another. A plurality of traction cylinders are provided, the traction cylinders being operable to selectively move the drive assemblies relative to one another on the frame assembly to change the first distance across the pipe/tubing passage. 
     In another embodiment, the timing mechanism further comprises a telescoping torque-tube. 
     In yet another embodiment, the traction cylinders are connected between the pair of drive assemblies. 
     In a further embodiment, the joined pipe injector further comprises a skate assembly mounted on each drive assembly, wherein each skate assembly includes a skate body mounted inside the respective loop of drive chain along the substantially straight portion and a plurality of skate rollers rotatably mounted on the skate body in successive rows along the direction of travel to collectively form a substantially flat surface adjacent an inward side of the respective drive chain. 
     In a still further embodiment, each gripper block assembly further includes a slide plate connected to the gripper block body and disposed on the inward-facing side of the respective drive chain. The slide plate rolls over the skate rollers of the skate assembly along the substantially straight portion of the loop. 
     In another embodiment, the slide plate includes interleaved portions that simultaneously roll over at least two successive rows of the skate rollers and interfit with the interleaved portions of adjacent slide plates. 
     In yet another embodiment of the joined pipe injector, each drive assembly further comprises sprockets guiding the drive chain at each end of the pipe/tubing path, whereby motion of the gripper block assemblies attached to the drive chain transitions from curving motion to straight-line motion as the gripper block assemblies travel from the sprockets to the substantially straight portion. The injector further comprises an insert guide positioned between drive assemblies at the end of the pipe/tubing path to apply a pre-compression to the pipe inserts against the bias of the springs of the gripper block assemblies traveling in curving motion prior to those pipe inserts contacting the pipe/tubing and to release the pre-compression when the respective gripper block assemblies are moving in straight-line motion. 
     In a further embodiment, the insert guide has a double taper configuration including a first tapered portion forming a first angle with a centerline of the pipe/tubing passage, a second tapered portion forming a second angle with the centerline of the pipe/tubing passage, and a dwell portion disposed between the first and second tapered portions. 
     In a still further embodiment, the gripper block assemblies are removably attached by bolts to the drive chains. 
     In another embodiment, the springs of the gripper block assemblies attached to the drive chains comprise nitrogen gas springs. 
     In yet another aspect, a gripper block assembly is provided for a joined pipe injector having a drive chain including a plurality of interconnected links defining a direction of travel of the drive chain. The gripper block assembly comprises a gripper block body having an inward side and an outward side, the outward side being configured to define at least one insert channel having a channel axis and a slide plate having an outward side. The inward side of the gripper block body is mountable on a first side of at least one of a plurality of interconnected links of a drive chain and the outward side of the slide plate is mountable on a second side of the same at least one of the plurality of interconnected links. When so mounted, the gripper block body, the slide plate and the at least one of the plurality of interconnected links move as a unit and the insert channel axis is oriented perpendicular to a direction of travel of the drive chain. The gripper block assembly further comprises at least one pipe insert including an insert body portion and a gripper portion, wherein the insert body portion is slidingly mounted in the insert channel to be moveable between a maximum extension and a minimum extension along the insert channel axis and the gripper portion faces outward from the insert body portion. The gripper block assembly further comprises at least one spring corresponding, respectively, to each pipe insert, each spring having a fixed end portion and a moving end portion, wherein the moving end portion is biased away from the fixed end portion, and wherein the fixed end portion of each spring is operatively connected to the gripper block body and the moving end portion of the spring is operatively connected to the respective pipe insert to bias the respective pipe insert toward the maximum extension along the insert channel axis. 
     In one embodiment, at least one of the inward side of the gripper block body and the outward side of the slide plate is configured to interfit against the at least one of the plurality of interconnected links to transmit traction force from the drive chain to the gripper block assembly in the direction of travel when the gripper block body is connected to the slide plate across the at least one of the plurality of interconnected links. 
     In another embodiment, the gripper block body and the slide plate are configured for removable connection of the gripper block body to the slide plate on opposite sides of the at least one of the plurality of interconnected links using bolts. 
     In yet another embodiment, the inward side of the gripper block body and the outward side of the slide plate are configured to interfit against a single link of the drive chain. 
     In a further embodiment, the gripper block body defines at least two insert channels, and at least one pipe insert is slidingly mounted in each of the at least two insert channels. 
     In a still further embodiment, each of the at least one pipe inserts further comprises a multi-radius gripping surface having a plurality of curved portions including a first curved portion and second curved portion. The first curved portion curves with a first radius around a first center, and the second curved portion curves with a second radius around a second center. The second radius has a different length from the first radius, and the locations of the first and second centers are not coincident. 
     In another embodiment, each of the at least one pipe insert further comprises a pair of lateral arm portions extending away from the gripper portion in lateral directions substantially perpendicular to both the insert channel axis and the direction of travel. The at least one spring corresponding to each pipe insert further comprises at least one spring disposed between the gripper block body and each respective lateral arm portion of each respective pipe insert. Each lateral arm portion is biased independently of the other lateral arm portion by the respective at least one spring disposed under the respective lateral arm portion. 
     In yet another embodiment, the gripper block body defines two laterally extending insert channels configured parallel to one another. One pipe insert is slidingly mounted in each insert channel; the lateral arm portions each pipe insert extend laterally past each end of the respective insert channel, and one spring is disposed laterally adjacent to each end of each insert channel to bias the respective lateral arm portion toward the maximum extension. 
     In still another embodiment, the springs of the gripper block assembly comprise nitrogen gas springs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding, reference is now made to the following description taken in conjunction with the accompanying Drawings in which: 
         FIGS. 1 a , 1 b  and 1 c    are views of a joined pipe injector in accordance with one embodiment, wherein: 
         FIG. 1 a    is a front elevation view thereof; 
         FIG. 1 b    is a side elevation view thereof; and 
         FIG. 1 c    is a front perspective view thereof; 
         FIG. 2  is a front perspective view of the injector head assembly of the joined pipe injector of  FIGS. 1 a , 1 b    and  1   c;    
         FIGS. 3 a  and 3 b    are rear perspective views of the injector head assembly of  FIG. 2 , wherein: 
         FIG. 3 a    is a full view thereof; and 
         FIG. 3 b    is an enlarged partial view of the upper portion showing further details of a drive chain timing mechanism in accordance with another aspect; 
         FIGS. 4 a  and 4 b    show the injector head assembly of  FIG. 2  with the front cover plate removed showing the internal machinery spaces, sprockets, drive chains, and insert guides, wherein: 
         FIG. 4 a    is a front perspective view thereof; and 
         FIG. 4 b    is a front elevation view; 
         FIGS. 5 a -5 d    are partial views of a skate assembly, a drive chain and gripper block assemblies for a joined pipe injector in accordance with an additional aspects, wherein: 
         FIG. 5 a    is a front perspective view thereof with portions of the drive chain broken away for purposes of illustration; 
         FIG. 5 b    is a side elevation view thereof; 
         FIG. 5 c    is a rear perspective view thereof; and 
         FIG. 5 d    is a rear perspective view similar to  FIG. 5 c   , with the skate assembly removed for purposes of illustrating the underside of the drive chain and gripper block assemblies; 
         FIGS. 6 a , 6 b  and 6 c    are views of a gripper block assembly and a pipe insert for a joined pipe injector, wherein: 
         FIG. 6 a    is an exploded front perspective view of a gripper block assembly in accordance with another aspect; 
         FIG. 6 b    is a front perspective view of a pipe insert in accordance with yet another aspect; and 
         FIG. 6 c    is a front elevation side view of the pipe insert of  FIG. 6 b    along with the insert retainers; 
         FIG. 7  is a side elevation view of a guide block for an insert guide for a joined pipe injector in accordance with another aspect; 
         FIGS. 8 a , 8 b  and 8 c    are partial side elevation views of a joined pipe injector handling two sections of jointed pipe having an upset joint, wherein: 
         FIG. 8 a    is a partial side view of the injector head assembly of the injector showing the two drive assemblies gripping the sections of jointed pipe therebetween; and 
         FIG. 8 b    is an enlarged view of the portion of  FIG. 8 a    designated “ FIG. 8 b   ” showing the portions of the drive chains and gripper block assemblies directly adjacent to the upset joint of the jointed pipe where the two sections are connected; and 
         FIG. 8 c    is a partial side elevation view of the same portion of jointed pipe with the upset joint of  FIG. 8 b   , but removed from the injector for purposes of illustration with dashed lines indicating the horizontal alignment of the upset joint portion between  FIGS. 8 b    and  8   c.    
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, wherein like reference numbers are used herein to designate like elements throughout, the various views and embodiments of a joined pipe injector are illustrated and described, and other possible embodiments are described. The figures are not necessarily drawn to scale, and in some instances the drawings have been exaggerated and/or simplified in places for illustrative purposes only. One of ordinary skill in the art will appreciate the many possible applications and variations based on the following examples of possible embodiments. 
     Referring now to  FIGS. 1 a , 1 b  and 1 c   , there are shown, respectively, front, side and front perspective views of a joined pipe injector  100  in accordance with one embodiment. The injector  100  can support, inject and withdraw pipe (including jointed pipe) and tubing (including coiled tubing). For purposes of this application, unless otherwise specified, the term “inject” or “injection” refers to the operation of moving pipe or tubing into the wellbore of a well, and the term “withdraw” or “withdrawal” refers to the operation of moving pipe or tubing from the wellbore of a well. The wellbore may be pressurized or unpressurised during the injection and withdrawal of the pipe or tubing. Other than the drive assemblies and gripper block assemblies further described herein, the remaining portions of the injector  100  may be substantially conventional and therefore not illustrated, including, e.g., the power systems, hydraulic supply systems, tubing/pipe feeding systems etc. 
     The joined pipe injector  100  can include an injector head assembly  102  mounted on a frame assembly  104 . The frame assembly  104  can include an outer frame portion  104   a  and an inner frame portion  104   b . The outer frame portion  104   a  (or “crash frame”) can be configured with height, width and depth dimensions that exceed the respective dimensions of the injector head assembly  102  such that the injector head assembly can be entirely disposed within the confines of the crash frame and thereby substantially protected. The inner frame portion  104   b  (or “sub-frame”) can be configured to support the injector head assembly  102 . In the illustrated embodiment, the sub-frame  104   b  is pinned to the crash frame  104   a  for ease of assembly and removal; however other forms of connection, such as bolts or welding, can be used in other embodiments. In the illustrated embodiment, the inner frame portion  104   b  includes horizontal support members  104   c  configured to be received within drive support channels  204  (see  FIG. 2 ) on the injector head assembly  102 . This configuration allows the drive support channels  204  to slide along the horizontal support members  104   c , thereby allowing lateral movement of the respective halves of the injector head assembly  102  but resisting upward or downward movement of the injector head assembly caused by the weight of the assembly and/or forces produced during injection and withdrawal of the pipe or tubing. 
     The injector head assembly  102  includes a pair of drive assemblies  106  spaced apart from one another to define a pipe passage  108  therebetween for accommodating the pipe or tubing  110  to be moved by the injector. During normal use, the pipe passage  108  will be oriented in a direction substantially parallel to the well-bore angle at the surface (i.e., the surface of the ground). As further described below, each drive assembly  106  includes an endless drive chain  112  configured in a loop around two or more supporting sprockets. A plurality of gripper block assemblies  114  are attached to the outward-facing side of the drive chains  112 . Portions of the two drive chains  112  are disposed substantially parallel to one another between the drive assemblies  106  such that the gripper block assemblies  114  mounted on the respective drive chains extend towards one another along the pipe passage  108 . An insert guide  109  can be mounted between the drive assemblies  106  at one or both ends of the pipe passage  108  to control movement of the gripper assemblies  114  during initial engagement of the pipe or tubing  110  as further described herein. 
     The injector head assembly  102  can further include one or more traction cylinders  116 , one or more tension cylinders  118  and/or one or more drive motors  120 . The traction cylinders  116  can be connected between the two drive assemblies  106  and be operated to change the spacing between the drive assemblies (i.e., across the pipe passage  108 ). The traction cylinders  116  can move the two drive assemblies  106  towards one another to increase the tractive force of the gripper block assemblies  114  against the pipe  110  and can move the two drive assemblies away from one another to decrease the tractive force of the gripper block assemblies against the pipe. In the illustrated embodiment, three traction cylinders  116  are provided on each side of the injector head assembly  102 , however, a different number of traction cylinders may be used in other embodiments. In the illustrated embodiment, the traction cylinders  116  are hydraulic cylinder actuators, however, a different type of actuator may be used in other embodiments. 
     The tension cylinders  118  can be mounted on each drive assembly  106  and operated to change the position of a tension sprocket or roller  402  (see e.g.,  FIG. 4 a   ) disposed within the respective drive assembly so as to change the tension on the respective drive chain  112 . In the illustrated embodiment, two tension cylinders  118  are provided on each side of each drive assembly  106 , however, a different number of tension cylinders may be used in other embodiments. In the illustrated embodiment, the tension cylinders  118  are hydraulic cylinder actuators, however, a different type of actuator may be used in other embodiments. 
     The drive motors  120  can be mounted on each drive assembly  106  to rotate a drive sprocket  404  (see, e.g.,  FIG. 4 a   ) disposed within the respective drive assembly that drives the respective drive chain  112 . In the illustrated embodiment, one drive motor  120  is provided on each drive assembly  106 , however, a different number of drive motors may be used in other embodiments. In the illustrated embodiment, the drive motors  120  are hydraulic motors, however, electric motors, power take offs (PTOs) or other types of drives may be used in other embodiments. In some embodiments the drive motors  120  are synchronous motors, and in other embodiments the drive motors are non-synchronous motors. In the illustrated embodiment, each drive motor  120  drives the respective drive sprocket  404  through a planetary drive or transmission  122  mounted to the drive assembly  106 , however, in other embodiments the drive motors may be direct-drive motors or the transmissions may be located elsewhere. 
     Referring now to  FIG. 2 , the front side of the injector head assembly  102  and tubing  110  are illustrated without the frame assembly  104 . Each drive assembly  106  includes a front housing plate  202  connected to an inner frame structure  406  (see, e.g.,  FIG. 4 a   ). The drive support channels  204  (which receive the horizontal support members  104   c  of the frame assembly  104 ) are mounted to the front housing plates  202 . In the illustrated embodiment, the drive support channels  204  comprise spaced-apart upper and lower channel plates  206 ,  208  mounted to the front housing plates  202 . 
     Referring now to  FIGS. 3 a  and 3 b   , the rear side of the injector head assembly  102  and tubing  110  are illustrated without the frame assembly  104 . Each drive assembly  106  includes a rear housing plate  302  connected to the inner frame structure  406  (see, e.g.,  FIG. 4 a   ). Additional drive support channels  204  are mounted to the rear housing plates  302 . In the illustrated embodiment, the rear drive support channels  204  comprise spaced-apart upper and lower channel plates  206 ,  208  mounted to the rear housing plates  302 . 
     Referring now particularly to  FIG. 3 b   , there is illustrated a drive chain timing mechanism  303  for a pipe injector in accordance with another embodiment. The drive chain timing mechanism  303  can comprise a torque tube  304  operatively connected between the two drive assemblies  106  to maintain timing between the respective drive chains  112 . In some embodiments, the drive chain timing mechanism  303  can be operatively connected between the respective idler sprockets  408  of each drive assembly  106  to cause the idler sprockets to rotate in synchrony. In other embodiments, the drive chain timing mechanism  303  can be operatively connected between the respective drive sprockets  404  of each drive assembly  106  to cause the drive sprockets to rotate in synchrony. The synchronous rotation of the idler sprockets  408  and/or the drive sprockets  404  caused by the drive chain timing mechanism  303  ensures that the respective drive chains  112  move in synchrony even if non-synchronous drive motors  120  are used to power the respective drive chains. In the illustrated embodiment, the drive chain timing mechanism  303  is mounted to the respective rear housing plates  302  of the two drive assemblies  106  and comprises first bevel gears  306  mounted on the ends of the torque tube  304  that engage second bevel gears  308  connected to the idler sprockets  408 ; however, other forms of rotational connection may be used in other embodiments. The torque tube  304  can comprise two or more telescoping members that are slidingly engaged to transmit torque while allowing changes in overall length to accommodate relative movement between the two drive assemblies  106 . 
     Referring now to  FIGS. 4 a  and 4 b   , the injector head assembly  102  is illustrated with the front housing plates  202  removed to show the machinery space within the drive assemblies and the layout of the twin drive chains  112  and the self-adjusting gripper blocks  114  in accordance with additional aspects. Each drive chain  112  comprises an endless roller chain  410  having interconnected links  412  and outer plates  414  routed in a loop around the inner frame structure  406  of the respective drive assembly  106  to engage the respective drive sprocket  404 , tension sprocket or roller  402  and idler sprocket  408 . Preferably, the endless roller chain  410  is a standard roller chain, and in the illustrated embodiment, the roller chain is a standard quad roller chain. 
     In the illustrated embodiment, the idler sprockets  408  are disposed uppermost within the respective drive assemblies  106 , the drive sprockets  404  are disposed lowermost and the tension sprockets or rollers  402  are disposed therebetween. In other embodiments, the positions of the various sprocket and rollers may be rearranged; however, the respective functions will be substantially the same. For purposes of description, the section of drive chain  112  running between the uppermost sprocket and lowermost sprocket along the pipe passage  108  (i.e., near the mid-line of the injector head assembly  102 ) can be referred to as the “driving section” of the drive chain loop, and the remaining sections of drive chain running around the outer periphery away from the inner pipe passage can be referred to as the “return section” of the drive chain loop. During typical operation of the injector  100 , the driving section of the drive chain  112  has a direction of travel that is generally aligned with the well-bore angle at the surface (i.e., generally downward or slanting downward for injection and generally upward or slanting upward for withdrawal). 
     Referring now also to  FIGS. 5 a -5 d   , the gripper block assemblies  114  can be firmly attached to the drive chain  112  such that the gripper block assemblies are carried around the drive assembly  106  by the drive chain. Each gripper block assembly  114  can include a gripper block body  502  (or gripper block upper portion) and a slide plate  504  (or gripper block lower portion). Preferably, the gripper block body  502  can be removably attachable to the slide plate  504  to facilitate assembly and removal of the gripper block assemblies  114  from the drive chain  112 . In the illustrated embodiment, the underside of the gripper block body  502  and the upper side of the slide plate  504  are configured to “capture” a link  412  of the drive chain  112  therebetween for removably mounting the gripper block assembly  114  to the drive chain. Preferably the various components of the gripper block assemblies  114  do not act as tensile load-bearing components of the drive chain  112 ; for example, the tensile load-carrying capacity of the drive chain can be the same with our without the gripper block bodies  502  or slide blocks  504  being mounted thereon. 
     Referring now particularly to  FIG. 5 a   , the gripper block body  502  and/or slide plate  504  can be configured to connect to the links  412  of the drive chain  12 , and especially to the link rollers  413 , so as to transmit lateral force (i.e., traction force) in the direction of movement  500  from the drive chain to the pipe or tubing  110  (i.e., via the gripper block assemblies  114 ). In the illustrated embodiment, the gripper block bodies  502  includes one or more semi-circular force-transmitting surfaces  415  that cooperate with the rollers  413  of the link  412  to transmit traction force. 
     Referring still to  FIG. 5 a   , each drive assembly  106  can further comprise a skate assembly  416  having an elongated skate body  418  and a plurality of skate rollers  420 . For purposes of illustration,  FIG. 5 a    shows the skate assembly  416  and a portion of the drive chain  112  (including gripper block assemblies  114 ) removed from the drive assembly  106 . Each skate body  418  can be mounted to the internal structure  406  of the respective drive assembly  106  laterally adjacent to the driving section of the drive chain  112  with the elongated dimension of the skate body generally aligned with the direction of travel (denoted  500  in  FIG. 5 a   ) of the driving section. In some embodiments, the skate assemblies  416  are bolted to the internal structure  406  of the respective drive assemblies  106  to provide a rigid connection but allow ease of assembly and maintenance; however, other types of connection, such as welding, may be used in other embodiments. The skate rollers  420  can be rotatably mounted to the skate body  418  with the axes of rotation of each roller being oriented generally parallel to the (inner/rear) surface of adjacent drive chain  112  and generally perpendicular to the direction of travel  500  of the adjacent driving section, thereby collectively forming a rolling support surface. In the illustrated embodiment, the rolling support surface formed collectively by the rollers  420  is substantially planar, except at the ends where the skate body  418  includes a taper  422  to accommodate the curve of the drive chain  112  as it enters/exits the drive and idler sprockets  404 ,  408 . 
     As best seen in  FIG. 4 b   , as the two drive assemblies  106  move horizontally towards one another across the pipe passage  108  during operation of the injector  100 , the skate assemblies  416 , which are connected to the respective drive assemblies, likewise move towards one another (denoted in  FIG. 5 b    by arrow  506 ), thereby applying force against the undersides of the gripper assemblies  114 , and in this embodiment applying force from the rollers  420  against the undersides of the slide plates  504 , as the gripper assemblies are transported along the driving sections of the respective drive chains  112 . As further described herein, the inward force (in direction  506 ) provided by the skate assemblies  416  against the back of the gripper assemblies  114  can transmit tractive force from the drive chains  112  to the tubing  110  in the pipe passage  108 . 
     Referring now particularly to  FIGS. 5 d   , a rear view of the drive chain  112  and gripper block assemblies  114  is provided with the skate assembly  416  removed for purposes of illustration, thereby showing the underside surfaces  508  of the slide plates  504  of several successive gripper block assemblies, e.g., assemblies  114 ′ and  114 ″. The slide plates  508  can be configured to collectively form a substantially flat surface that rolls on the upper side surface of the skate rollers  420  of the skate bar assembly  416  during operation of the injector  100 . In the illustrated embodiment, the underside surface  508  of each slide plate  504  can be configured to define one or more fingers  510  and one or more slots  512  extending each way along the direction of travel  500 . The fingers  510  and the slots  512  on the slide block  504  can be dimensioned and configured such that the fingers  510  of one slide block  504 ′ are disposed at least partially within the slots  512  of an identical side block  504 ″ on a successive gripper block assembly  114 ″ in an interleaved arrangement. Because of this interleaving, each skate roller  420  can simultaneously contact fingers  510  from two adjacent slide plates  504  as the interleaved fingers pass over the roller. In this manner, the forces exerted by the rollers  420  may be smoothly transferred between successive slide plates  504 ′ and  504 ″, and hence between successive gripper assemblies  114 ′ and  114 ″. 
     Referring now to  FIG. 6 a   , each gripper block assembly  114  can include, in addition to the gripper block body  502  and slide plate  504 , one or more springs  602 , spring retainers  604 , pipe inserts  606  and insert retainers  608 . In the illustrated embodiment, each gripper block assembly  114  includes two pipe inserts  606  and two springs  602  per insert for a total of four springs; however, in other embodiments, the gripper block assembly can include a different number of pipe inserts, springs and/or springs per insert. For purposes of illustration, in  FIG. 6 a    the gripper block assembly  114  is shown in exploded view and the interconnecting links of the drive chain  112  are not shown. As previously described, each gripper block assembly  114  can be removably attached to a link  412  of the drive chain  112  by capturing the link between the gripper block body  502  and the slide plate  504 . In the illustrated embodiment, bolts  610  can pass through holes  612  in the slide plate  504 , between the rollers of the chain link  412 , and threadingly engage the underside of the gripper block housing  502 , thereby releasably capturing the chain link between the gripper block housing and the slide block. It will be appreciated that, in this configuration, neither the gripper block housing  502  nor slide plate  504  is an integral part of the chain  112 ; i.e., the tensile load-carrying capacity of the chain is the same with our without the gripper block housing or slide block attached thereto. 
     Referring now also to  FIGS. 6 b  and 6 c   , the pipe inserts  606  act as floating jaws. The pipe inserts  606  are the elements of the gripper block assembly  114  that actually contact the pipe or tubing  110  and transfer the traction force of the drive chain  112  to the tubing. The gripper block bodies  502  are mounted to the drive chain  112  but do not typically contact the tubing  110 . Each pipe insert  606  can be mounted in a cavity or channel  616  of its respective gripper block body  502  so that the insert is rigidly supported by the gripper block body in the machine direction (i.e., in the direction of travel  500  of the drive chain  112  around the sprockets) but is flexibly supported in the outward direction  514  ( FIG. 5 b   ) perpendicular to the machine direction. This allows the pipe inserts  606  to move in-and-out within the socket  616  as the pipe or tubing is contacted and released. The spring elements  602  (e.g., gas springs described below) bias the pipe inserts  606  to push outward from the socket  616  of the gripper block bodies  502  to provide gripping force when the insert contacts the tubing  110 . The pipe insert  606  is preferably independently supported by the spring elements  602  on each side of the drive chain centerline so that the insert can “float” as necessary to accommodate off-center forces. 
     As best seen in  FIG. 6 a   , the upper side of the gripper block body  502  can be configured to define one or more outward-facing spring cavities  614  and one or more outward-facing insert cavities or channels  616 . In this context, the outward direction  514  (also shown as direction  623  in  FIG. 6 a   ) is perpendicular from the localized direction of travel  500  of the drive chain  112  when the gripper block assembly  114  is mounted to the drive chain. The springs  602  can be mounted in the spring cavities  614  and secured in place with the spring retainers  604  such that a fixed portion  618  of the spring bears against the gripper block body  502  and outwardly biases a movable portion  620  of the spring. The pipe insert  606  can have a sliding portion of the body  622  that is configured to slide or “telescope” within the outward-facing insert channel  616  along a channel axis  623  (running essentially parallel to the outward direction  514 ). In the illustrated embodiment of  FIG. 6 a   , the insert channels  616  have a rectangular configuration, and the sliding portions of the insert bodies  622  have a compatible rectangular configuration; however, in other embodiments, the insert channels and insert bodies can have other compatible configurations, i.e., which allow the insert body to move within the insert channel along the channel axis  623  while substantially maintaining the orientation of the gripper portion  626  relative to the direction of travel  500 . 
     The pipe insert  606  can be operatively connected to the movable portion  620  of the spring  602  such that the pipe insert is upwardly biased by the spring away from the gripper block body  502 , however, upward movement of the pipe insert can be limited by the pipe insert retainer  608  such that at least a portion of the sliding portion the pipe insert is retained in the insert channel  616 . The pipe insert  606  can further be configured to have a gripper portion  626  dimensioned to accommodate the pipe or tubing to be handled by the injector  100 . In the illustrated embodiment, the gripper portion  626  includes a U-shaped curve having circumferential teeth or grooves  627  for gripping the pipe. To allow the injector  100  to handle different types of pipe or tubing, the pipe inserts  606  can be removed and replaced with alternative pipe inserts having a similar configuration (to fit in the same pipe insert cavities  616 ) except for a different configuration of the gripper portion  626 . Similarly, to allow the injector  100  to provide a different capacity of gripping force, the springs  602  can be removed and replaced with alternative springs having a similar configuration (to fit in the same spring cavities  614 ) except having different spring characteristics, e.g., spring rate, preload, usable stroke, etc. 
     As best seen in  FIGS. 6 b  and 6 c   , the pipe inserts  606  can have a center body portion  622  with a U-shaped, curved gripper portion  626  disposed on the outward-facing surface between a pair of lateral arms  624 . The gripper portion  626  can have circumferential slots or teeth  627  formed on the outer surface for better gripping the pipe. When the pipe insert  606  is mounted to the gripper block body  502 , the center portion  622  is typically disposed at least partially within the gripper block cavity or channel  616  with the curved gripper portion  626  remaining exposed. Each lateral arm  624  of the insert  606  is supported by a spring element  602  mounted in the gripper block body  502  behind (i.e., underneath) the lateral arm. The dimensions of the U-shaped central curve  626  of the gripper portion can be selected to engage the desired pipe size. 
     In some embodiments, the pipe insert  606  can have a gripper portion  626  configured with a U-shaped curved gripping surface having a single center point and single radius of curvature. In other embodiments, the pipe insert  606  can have a gripper portion  626  with a multi-radius gripping surface  638  configured to better grip pipe of different diameters or pipe having different diameters along the pipe-string. For example, a string of jointed pipe ( FIG. 8 c   ) has portions with two different diameters, a first nominal outer diameter (O.D.) along the majority of the pipe and a second, larger, O.D. at the collars/upsets/joints where the pipe sections join. The multi-radius gripping surface  638  has a plurality of curved portions  640 , wherein at least some of the curved portions have different center points and different radii of curvature. 
     In the embodiment illustrated in  FIGS. 6 b  and 6 c   , the gripper portion  626  of the pipe insert  606  has a multi-radius gripping surface  638  with a plurality of curved portions  640 , namely first curved portion  640 ′ and second curved portions  640 ″. The first curved portion  640 ′ curves with a first radius (denoted R 1 ) about a first center (denoted C 1 ) located at a first position, thus being well configured for gripping pipe P 1  (shown in broken line) having a first O.D.=(2×R 1 ). The second curved portions  640 ″ curves with a second radius (denoted R 2 ) about a second center (denoted C 2 ) located at a second position, thus being well configured for gripping pipe P 2  (shown in broken line) having a second O.D.=(2×R 2 ). For a string of jointed pipe, pipe P 1  can be the O.D. of the nominal sections and pipe P 2  can be the O.D. of the collars/upsets/joints. The gripping teeth or grooves  627  can be formed in some or all of the curved portions  640 ′,  640 ″ of a multi-radius gripping surface  638 . In the illustrated embodiment, the first curved portion  640 ′ of the smaller radius R 1  is disposed in the center of the multi-radius gripping surface  638 , with the second curved portions  640 ″ of the larger radius R 2  disposed on each side thereof, however in other embodiments, different numbers of the curved portions  640  of different radii can be provided and/or the curved portions of different radii can be arranged differently. 
     Referring again to  FIG. 6 a   , the springs  602  can be nitrogen gas springs. Nitrogen gas springs are preferred for the springs  602  in some embodiments where relatively high spring preload and relatively short overall spring length are required while still providing sufficient useable stroke after preload. In some embodiments, the springs  602  are nitrogen gas springs having a preload gas pressure of approximately 2700 psi. In some embodiments the springs  602  have a usable stroke of at least 1.25 inches from an overall length of not more than 4.0 inches, regardless of pre-load. In other embodiments, the springs  602  can be other types of gas springs or mechanical springs including, but not limited to, coil springs, belleville springs, leaf springs, elastomeric springs or pneumatic springs. 
     Referring still to  FIGS. 6 a , 6 b  and 6 c   , the pipe inserts  606  can have lateral arm portions  624  extending in a lateral direction  625  (i.e., perpendicular to both the channel axis  623  and the direction of travel  500 ) from the sliding portion  622  on each side of the gripper portion  626  and contacting the moving portions  620  of the springs  602 . The lateral arm portions  624  can be combined with lateral oversizing of the pipe insert channel  616  to provide the pipe insert  606  with a limited range of lateral movement (i.e., in direction  625  of  FIG. 6 a   ) during operation. In other embodiments, the springs  602  may be disposed partially or completely behind the pipe inserts  606 , e.g., within the sliding portion  622 . 
     For ease of assembly, repair and replacement, the pipe inserts  606  can be secured on the gripper block bodies  502  using insert retainers  608 . One or more insert retainer  608  can be used on the gripper block body  502  for each pipe insert  606 , for example two retainers can be used to hold in each pipe insert. The insert retainers  608  preferably merely hold the pipe inserts  606  in place on the gripper block bodies  502 ; the only force the insert retainers have to withstand is the weight of the pipe insert itself. The insert retainers  608  can be secured to the gripper block body using bolts  634  or other fasteners. In the illustrated embodiment, the same bolts  634  secure both the insert retainers  608  and the spring retainers  604 . The pipe inserts  606  and insert retainers  608  can have a quick-disconnect feature that allows the inserts to be removed from the gripper block bodies  502  by inserting a key  635  or tool into a keyway  632  to selectively move or change the shape of the retainer and release the insert from the gripper block. 
     As best seen in  FIGS. 6 a  and 6 c   , in the illustrated embodiment, the pipe insert retainers  608  include quick-disconnect features comprising spring clips  628  that angle downward and laterally inward from the interior lateral sides of the retainer into the insert cavities  616 . As the pipe insert  606  is inserted into the insert cavity  616  along axis  623 , the curved lower corners  631  of the sliding portion  622  push the spring clips  628  laterally outward (as shown in phantom in  FIG. 6 c   ), thus biasing the clips inward (i.e., back toward the center of the cavity). As the retaining shoulders  630  of the pipe insert  606  pass the ends of the spring clips  628 , the ends of the clips (urged by the bias) move back laterally inward above the retaining shoulders. Subsequent withdrawal of the pipe inserts  606  from the cavity  616  is prevented by interference between the shoulders  630  and the ends of the spring clips  628 . When thus secured by the spring clip  628 , the pipe insert  606  can still move up and down within the socket  616  (e.g., between maximum extension and minimum extension), but the insert cannot be removed from the gripper block body  502  without repositioning the spring clips. Each pipe insert  606  secured by the spring clip  628  of retainer  608  can be removed for maintenance or replacement by inserting a key  635  ( FIG. 6 a   ) into a keyway  632  formed through the upper surface of the pipe insert. The inserted key  635  pushes the respective spring clip  628  laterally out of the way of the retaining shoulder  630  (i.e., back to the position shown in phantom in  FIG. 6 c   ), such that the pipe insert  606  can be withdrawn from the gripper block body  502  while the keys remain in the keyways. The pipe insert  606 , or a replacement pipe insert, can be inserted into the cavity  616  and locked in place by the spring clips  628  without requiring the key. 
     Referring once again to  FIGS. 3 a -3 b , 4 a -4 b   , and also to  FIG. 7 , the insert guides  109  are structures located near the top and bottom ends of the pipe gap  108  between the drive assembly halves  106 . The insert guides  109  pre-compress the spring elements  602  to guide the pipe inserts  606  along a predetermined path during transition from circular motion to straight-line motion at the top and bottom of the pipe gap  108  prior to contacting the pipe or tubing  110 . Without the insert guides  109 , the pipe inserts  606  tend to slide on/against the pipe  110  during transition from circular motion to straight-line motion until purely straight-line motion is achieved. Damage to components of the injector  100  and/or to the pipe  110  can occur if a sliding pipe insert  606  contacts an upset joint  802  ( FIG. 8 c   ) of the pipe. The insert guide  109  pushes the pipe inserts  606  inward into the gripper block bodies  502  during curved motion, thereby delaying contact between the pipe insert and the pipe or upset joint until the insert is traveling with straight-line motion. As pipe insert  606  achieves straight-line motion, the insert guide  109  can gradually release the pipe insert to contact the pipe  110 . The insert guide  109  can be mounted to brackets and bolted to a center frame of the injector  100 . The insert guide  109  can be configured with a double taper profile ( FIG. 7 ) to first gradually compress the pipe insert  606  and then gradually contact the pipe  110  when correctly aligned. 
     Referring still to  FIGS. 3 a -3 b , 4 a -4 b   , and also to  FIG. 7 , in the illustrated embodiment the pipe insert  109  can be located at the top and bottom of the injector  100  at the ends of the driving section of the drive chain  112 . The insert guides  109  are configured to contact the pipe inserts  606  as the gripper block assemblies  114  move along a curving path to enter the pipe passage  108 . The insert guides  109  can move the pipe inserts  606  inward into the gripper block body  502  against the bias of the springs  602  to prevent the pipe inserts from contacting the pipe or tubing  110  where the drive chain is moving on a curving path (i.e., where the pipe inserts are not substantially parallel with the surface of the pipe or tubing). The insert guides  109  are further configured to release contact with the pipe inserts  606  as the gripper block assemblies  114  move fully into the driving section of the drive chain  112  and have substantially straight-line motion (i.e., where the inserts are perpendicular to the pipe surface). 
     Each insert guide  109  can include a pair of side plates  310  connected by a pair of spacer tubes  312  forming a pipe or tubing inlet/exit at the ends of the pipe passage  108 . A guide block  314  is mounted on the inner side of each side plate  310  such that the guide blocks contact each successive pipe insert  606  as the drive chain  114  moves around the sprocket  404  or  408  to enter the driving section. The guide blocks  314  are best seen in  FIG. 4 a   , wherein the front side plates  310  are removed for purposes of illustration, but the guide blocks are depicted in their operational positions. In the illustrated embodiment, the guide blocks  314  are configured to contact the lateral arm portions  624  of the pipe inserts  606  while remaining clear from the pipe or tubing  110  being handled by the injector  100 . As best seen in  FIG. 7 , the working surfaces of the guide blocks  314  of the insert guides  109  can be configured with a double linear taper configuration (i.e., on each side of the guide block) having an initial linear taper section  702  forming a first taper angle θ 1  from the pipe centerline  700 , a dwell section  704  substantially parallel to the pipe centerline, and a final linear taper section  706  forming a second taper angle θ 2  with the pipe centerline. In other embodiments, the working surfaces of the guide blocks  314  can have different configurations including a single linear taper configuration, a double curved taper configuration or a single curved taper configuration. 
     Referring now to  FIGS. 8 a  and 8 b   , when the injector  100  is in use, the drive assemblies  106  are oriented with the straight portions of the drive chain loops substantially aligned with the well-bore at the surface (i.e., parallel to the well-bore angle at the surface) and parallel to one another on either side of the pipe/tubing passage  108 . The drive assemblies  106  may be slidably mounted to a frame assembly  104  to allow the drive assemblies to move perpendicular to the well-bore angle while maintaining the substantially parallel orientation of the pipe/tubing passage. As previously described herein, as the drive assemblies  106  are pressed towards one another (i.e., towards the pipe/tubing passage  108 ), the skate bar assemblies  416  press against the underside surface  508  of the slide plates  504  carried by the drive chains  112 , thereby pressing the gripper blocks assemblies  114  with the outwardly-facing pipe inserts  606  against the pipe or tubing  110  positioned therebetween. The traction cylinders  116  can be operatively connected to the drive assemblies  106  to selectively move the assemblies together and apart and/or to exert greater or less force between the assemblies. In the illustrated embodiment, the traction cylinders  116  are connected between the drive assemblies  106 , and as the inward pull of the traction cylinders increases, the drive assemblies are pulled more strongly towards one another to increase the tractive force exerted by the pipe inserts  606  against the pipe, and as the inward pull of the traction cylinders is reduced, the drive assemblies are pulled less strongly towards one another to reduce the tractive force. The traction cylinders  116  may also push against the drive assemblies  106  to move the assemblies apart to change the spacing across the pipe/tubing passage  108 . Depending upon the value of the preload force of the springs  620  in the gripper block assemblies  114  compared to the selected tractive force desired from the gripper block assemblies against the pipe or tubing  110 , in some cases the pipe inserts  606  can be undeflected (i.e., at the maximum extension) while gripping the pipe or tubing, and in other cases the pipe inserts can be deflected (i.e., between the maximum extension and the minimum extension) while gripping the pipe or tubing. As further explained below, in yet other cases, the various pipe inserts  606  at different positions along the pipe or tubing  110  may have different values of deflection. 
     Still referring to  FIGS. 8 a  and 8 b   , and now also to  8   c , the injector  100  can have the capability to handle pipe or tubing  110  with a substantially constant (i.e., nominal) diameter D 1 , and can also have the capability to handle pipe or tubing having some portions with a nominal diameter D 1  and other portions with a secondary diameter D 2  that is larger than the nominal diameter. For example, jointed pipe  110 ′ can include so-called upset joint portions  802  where the pipe has an abrupt increase in dimension from a nominal diameter D 1  to a secondary, or upset, diameter D 2  to allow threaded connection to adjacent pipe sections. As best seen in  FIG. 8 c   , the nominal diameter D 1  of the jointed pipe  110 ′ increases significantly to the secondary/upset diameter D 2  at the upset joint section  802  compared to the standard/nominal diameter portions  804 . 
     In  FIGS. 8 a  and 8 b   , the joined pipe injector  100  is shown engaging sections of jointed pipe  110 ′. For purposes of illustration, the center portion of  FIG. 8 a    is enlarged in  FIG. 8 b    to better show the configuration of the injector  100  where gripping the upset joint portion  802  of the jointed pipe  110 ′, and  FIG. 8 c    shows the subject jointed pipe  110 ′ in isolation from the injector (but with the upset joint portion  802  disposed at the same horizontal location as in  FIG. 8 b    as indicated by the broken lines between  FIGS. 8 b  and 8 c   ). 
     As best seen in  FIG. 8 b   , because each of the pipe inserts  606  in each gripper block assembly  114  is independently spring-biased, the pipe inserts  606 ′ in the localized area adjacent to the upset joint  802  can deflect more (i.e., move further inward into the gripper block channel  616 ) when contacting the larger diameter D 2  of the upset joint, while the remaining pipe inserts  606 ″ can deflect less or have no deflection while remaining in contact against the standard diameter D 1  of the remaining (i.e., nominal) portions  804  of the jointed pipe  110 ′. This feature of localized differential deflection of the pipe inserts  606 ′,  606 ″ while all the pipe inserts continue maintaining an outward bias necessary for gripping is supplied by the independent bias of the springs  602  (i.e., including springs  602 ′ and  602 ″) in each gripper block assembly  114  acting between the respective gripper block bodies  502  and the pipe inserts  606 . In the illustrated embodiment, the springs  602 ′ and  602 ″ are nitrogen gas springs, however, other types of springs can used for the springs as previously described. 
     Although preferred embodiments have been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 
     It will be appreciated by those skilled in the art having the benefit of this disclosure that this jointed pipe injector provides a significant improvement over conventional injectors. It should be understood that the drawings and detailed description herein are to be regarded in an illustrative rather than a restrictive manner, and are not intended to be limiting to the particular forms and examples disclosed. On the contrary, included are any further modifications, changes, rearrangements, substitutions, alternatives, design choices, and embodiments apparent to those of ordinary skill in the art, without departing from the spirit and scope hereof, as defined by the following claims. Thus, it is intended that the following claims be interpreted to embrace all such further modifications, changes, rearrangements, substitutions, alternatives, design choices, and embodiments.