Abstract:
A means and method for improving the injection of coiled tubing into and from a well by providing a secondary injection device for supplementing the thrust forces of the primary injector means. Use of the secondary injection device coacting in tandem with the coiled tubing injector permits developing significantly higher axial forces in the tubing than can be provided by the primary injector alone. The selectably operable thrust enhancement device of this invention provides a short, repeatable stroke in either direction. The thrust enhancement device operates by selectably gripping the tubing with a reciprocably moveable means in a first position, shifting the moveable means to a second position thereby moving the tubing, gripping the tubing with a static means at its new position, releasing the tubing from the moveable means, and returning the moveable means to its first position. When the thrust enhancement device is not needed for the injection operation, its gripping means are disengaged from the tubing.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus for increasing the thrust applied to coiled tubing over that applied by its injector alone during its injection into and withdrawal from a well bore. The apparatus of the invention is mounted in series with an injector and is used in situations where additional thrusting force is required to cause the tubing in the well bore to overcome high resisting forces due to obstructions, the annulus being sanded up, or the like. The apparatus provides a short, repeatable reciprocating stroke in either direction. 
     BACKGROUND OF THE INVENTION 
     Devices and methods for injecting coiled tubing into and retrieving it from wells are well known. Prior art injection systems include U.S. Pat. Nos. 6,142,406; 5,842,530; 5,839,514; 5,553,668; 5,309,990; 5,244,046; 5,234,053; 5,188,174; 5,094,340; 4,899,823; 4,673,035; 4,655,291; 4,585,061; and many other similar disclosures. In the prior art an injector at the wellhead is used to grip and control the injection and withdrawal of the tubing. 
     Conventional track injectors utilize gripper blocks mounted on two continuous parallel and opposed conveyor chains which are urged or pushed against the outer surface of the tubing. The interface forces between the gripper blocks and the tubing permit developing frictional forces which are used to transfer tangential loads from the conveyor chains to the tubing and vice versa. If insufficient interface force is applied to the tubing by the gripper blocks, slippage with attendant loss of control and wear occurs between the blocks and tubing. If excessive interface force is applied to the tubing by the gripper blocks, the tubing wall may be distorted and damaged or the injector may be damaged. A problem with such tracks results when the track is rotated into or out of engagement with the tubing from the sprockets at the ends of the track mounting assembly. This rotation can cause differential movement between the track and the tubing in the direction of the tubing axis so that rubbing occurs. This rubbing will cause undesirable wear of both the tubing and the gripper blocks. 
     Historically, the approach used to increase the injection forces with conventional track injectors has been to lengthen the injector while maintaining a sufficiently safe interface force between the individual gripper blocks and the tubing. U.S. Pat. No. 5,842,530 for example shows provision of substantially more gripper blocks along the length of its injector. 
     Other injectors utilizing two continuous, parallel, and opposing track injectors having grooved shoes or blocks mounted thereon are known in the art. These opposing track units have facing portions where the multiplicity of gripping blocks run parallel for gripping the tubing therebetween and are typically positioned in line, directly adjacent and above the wellhead. 
     Another approach has been to utilize a large diameter driven wheel with an annularly is grooved outer diameter to conform to and support the tubing. Relatively small-diameter hold-down idler rollers radially press the tubing against the wheel to provide extra interface force between the tubing and the wheel so that high tangential frictional forces can be imparted to the tubing by the wheel without maintaining large back tensions. These hold-down rollers have arcuate faces to match the tubing. One such wheel type injector is disclosed in U.S. Pat. No. 5,839,514. 
     A more recent injector system known in the art is a linear injector, which pulls on only one side of the tubing. For this type of device, coiled tubing is driven along a single linear section of an endless chain conveyor with normal forces being applied by an opposing linear array of small-diameter arcuate face hold-down idler rollers. These hold-down rollers are sized to conform to the tubing. Such a linear or one-track injector eliminates the necessity of synchronizing the two opposed sides of a conventional track type injector and is less damaging to the surface of the coiled tubing, but it requires a much longer unit, which of necessity extends much higher and requires additional overhead clearance. Additionally, such an injector is more expensive because it requires a considerable number of gripper blocks and rollers and a longer support track. 
     Copending U.S. Provisional Patent Application “Coiled Tubing Injector Utilizing Opposed Drive Modules and Having an Integral Bender”, Ser. No. 60/304,681, filed Jul. 11, 2001, utilizes a novel approach to imparting tangential injection forces to the tubing. That invention provides support over a larger portion of the tubing circumference by positioning the driving means around the circumference of the tubing. By using a plurality of sets of opposed individually driven annularly grooved rollers which closely conform to the tubing and alternating the orientations of adjacent roller sets so that they are 90° apart about the through axis of the injector, excellent tubing support is provided. That invention is economical and efficient, as well as being lightweight, compact, easy to service and adapt for different tubing sizes. 
     A major problem with tubing injectors of all types is providing sufficient injection force on the tubing so that not only normal, smoothly operating injection loads are provided, but also sufficient injection force is available to overcome temporary, abnormally high resistances to tubing movement. Such abnormally high loads normally would be the result of a buildup of sand around the tubing, hanging up on a shoulder within the well, or other similar unexpected problems. Generally, such abnormally high loads only occur over a short section of a given well bore, if at all. The conventional means for overcoming such abnormally high injection forces is to use an injector which is able to provide the maximum push/pull required. Generally, the result of such an approach is that the injector is oversized for conventional non-problematic operation. Resulting in an injector that is larger, heavier, and more expensive to build and operate than is necessary for routine operations. 
     There exist a need for a simple and efficient method to provide an injection force in excess of that required for routine, non-problematic operation without having to provide an injector built to supply the maximum force predicted to be needed in the field. 
     SUMMARY OF THE INVENTION 
     The present invention utilizes a novel means and method for improving the system of injecting of coiled tubing into and from a well by providing a secondary injection device for supplementing the primary injector means. The secondary injection device is used to increase the axial forces in the tubing over the force provided by the primary injector alone. The selectably operable thrust enhancement device of this invention provides a short, repeatable stroke in either direction. The thrust enhancement device operates by gripping the tubing with a reciprocably moveable means in a first position, moving the moveable means to a second position thereby moving the tubing, then gripping the tubing with a static means at its new position, releasing the tubing from the moveable means, and returning the moveable means to its first position. When the thrust enhancement device is not needed for the injection operation, it is disengaged from the tubing. 
     One aspect of the invention is a coiled tubing injection system for moving coiled tubing into or out of a wellbore comprising a coiled tubing injector; a static tubing gripper having a closed and an open position; and a moveable tubing gripper having a closed and an open position, said movable tubing gripper being coaxially reciprocable between a first and a second position; wherein the coiled tubing injector, the static tubing gripper and the moveable tubing gripper are positioned coaxially along a length of coiled tubing and are independently selectively operable. 
     Another aspect of the invention is a coiled tubing injection system for moving coiled tubing into or out of a wellbore comprising a coiled tubing injector; a tubular body having a static transverse deck and a moveable transverse deck with the moveable transverse deck is coaxially reciprocable between a first and a second position; a first tubing gripper attached to the static transverse deck and a second tubing gripper attached to the moveable transverse deck. The first tubing gripper has a first and a second side, each having a back end, a central portion and a front end. The first and second sides are connected at the back ends and have a circularly arcuate groove in the central portion, where the interior surface of the groove serves as a tubing gripping surface when the first tubing gripper is in a closed position. When the first tubing gripper is in an open position the front ends of the first and second sides are separated and when it is in a closed position the front ends of the first and second sides are urged together. Similarly, the second tubing gripper has a first and a second side, each side having a back end, a central portion and a front end. The first and second sides are connected together on the back ends and have a circularly arcuate groove in the central portion, where an interior surface of the groove serves as a tubing gripping surface when the second tubing gripper is in a closed position. The second tubing gripper is in an open position when the front ends of the first and second sides are separated and in a closed position when the front ends of the first and second sides are urged together. The second tubing gripper reciprocates between a first location and a second location in tandem with the reciprocation of said moveable transverse deck between the first position and second position. The coiled tubing injector, the opening and closing of the first tubing gripper, the opening and closing of the second tubing gripper and the reciprocation of the moveable transverse deck are independently selectively operable. 
     Yet another aspect of the invention is a method for moving coiled tubing into or out of a wellbore using a coiled tubing injector and a thrust enhancer where the thrust enhancer comprises: (i) a tubular body having a static transverse deck and a moveable transverse deck, with the moveable transverse deck coaxially reciprocable between a first and a second position within the tubular body; (ii) a first tubing gripper attached to the static transverse deck, the first tubing gripper having a closed and an open position and an interior surface that serves as a tubing gripping surface when the first tubing gripper is in a closed position; and (iii) a second tubing gripper attached to the moveable transverse deck and reciprocating in tandem with the moveable transverse deck, where the second tubing gripper has a closed and an open position and an interior surface that serves as a tubing gripping surface when the second tubing gripper is in a closed position. The method comprising the steps of: (1) coaxially attaching the thrust enhancer to the coiled tubing injector, (b) feeding a coiled tubing through the functional path of the coiled tubing injector and the first and second tubing grippers; (c) engaging the coiled tubing injector to move tubing into or out of a wellbore; (d) closing the second tubing gripper so that its interior surface will grasp the surface of the coiled tubing; (e) moving the moveable transverse deck from the first position to the second position; (f) closing the first tubing gripper such that it grasps the surface of the coiled tubing; (g) disengaging the second tubing gripper; and (h) moving the moveable transverse deck from the second position back to its first position. Thus, the thrust applied to the coiled tubing is greater than the thrust applied by the coiled tubing injector or the thrust enhancer alone. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features which are believed to be characteristic of the invention, both as to its organization and methods of operation, together with the objects and advantages thereof, will be better understood from the following description taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is an oblique view of an opened manually operated tubing clamp; 
     FIG. 2 is an oblique view of the clamp of FIG. 1 shown mounted to a support surface and gripping a section of tubing; 
     FIG. 3 is a plan view of the clamp of FIG. 1 showing the clamp in open position, but with a section of tubing within its throat; 
     FIG. 4 is a plan view corresponding to that of FIG. 3, but with the clamp closed and gripping the tubing; 
     FIG. 5 is an oblique view of a hydraulically operated powered tubing clamp mounted to a support surface, and having a closing latch wedge shifted downwardly along its axis of travel; 
     FIG. 6 is a bottom view of the hydraulically operated powered tubing clamp of FIG. 5 clamped on a section of tubing within its throat; 
     FIG. 7 is a longitudinal vertical sectional view of the closed hydraulically operated powered tubing clamp of FIG. 5; 
     FIG. 8 is a transverse vertical sectional view of the wedging mechanism of the closed hydraulic clamp of FIG. 7; 
     FIG. 9 is an oblique view showing the wedging closure block used with the hydraulic clamp of FIG. 5; 
     FIG. 10 is an oblique view of one embodiment of the thrust enhancement device of this invention, which utilizes the hydraulic clamp of FIG. 5; 
     FIG. 11 is a vertical longitudinal partially sectioned view of the thrust enhancement device of FIG. 10, in a first operational position; 
     FIG. 12 is a vertical transverse partially sectioned view of the thrust enhancement device of FIG. 11 in its first operational position; 
     FIG. 13 is a vertical transverse partially sectioned view of the thrust enhancement device corresponding to the view shown in FIG. 12, but with the device in a second operational position; 
     FIG. 14 is a vertical transverse partially sectioned view of another embodiment of the thrust enhancement device, which utilizes the manual clamp of FIG. 1, in a first operational position; 
     FIG. 15 is a vertical transverse partially sectioned view of the embodiment of the thrust enhancement device corresponding to that of FIG. 14, but with the device in its second operational position; 
     FIG. 16 is an exploded oblique view of the gripping elements of the hydraulically operated powered tubing clamp of FIG. 5; and 
     FIG. 17 is a side profile view of the thrust enhancement device of this invention showing its relationship with the other elements of a coiled tubing injection system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings and initially to FIG. 1, it is pointed out that like reference characters designate like or similar parts throughout the drawings. The Figures, or drawings, are not intended to be to scale. For example, purely for the sake of greater clarity in the drawings, wall thickness and spacing are not dimensioned as they actually exist in the assembled embodiment. The materials of construction can be varied, but are preferably either mild or high-strength low-alloy steel. 
     Referring to FIGS. 1 through 4, the manual tubing clamp  170  used in a manually operated embodiment of this invention is shown in both an exploded and an assembled, closed oblique view and also assembled in both open and closed views down the tubing axis. Manual tubing clamp  170  consists of right-hand gripper  171 , left-hand gripper  181 , a hinge shaft  188  with hinge nuts  189 , and a pair of clamp bolts  192  with associated clamp nuts  193 . Right-hand gripper  171  has a flat vertical interior face with a vertical axis circularly arcuate groove, which serves as a tubing gripping, face  172  positioned in the middle portion of the vertical interior face. The axis of the arcuate groove is spaced slightly away from and outside the vertical interior face so that the arc of the vertical arcuate groove is less than 180°, and the diameter of the gripping face  172  corresponds to that of the tubing with which the gripper will be used. At one side of the vertical interior face two spaced apart hinge eyes  173   a,b  are formed, with eye  173   a  at the top and eye  173   b  just below midheight. Hinge eyes  173   a,b  are short cylindrical elements with coaxial vertical axes which are spaced slightly away from and outside the flat vertical interior face. The outer cylindrical faces of hinge eyes  173   a,b  are tangent to the exterior vertical face of right-hand gripper  171 . The wall thickness of right-hand gripper  171  is thickened adjacent tubing gripping face  172  to support high bending stresses in that region. Vertical hinge bolt hole  174  is bored coaxially with the hinge eyes  173   a,b  and passes through both those eyes. Clamping ear  175  is formed on the opposite side of right-hand gripper  171  from the hinge eyes  173   a,b  and has its outer face parallel to the vertical interior face. The horizontal top and bottom surfaces and the outer transverse side of clamping ear  175  are flat. Through clamping bolt holes  176  are located in clamping ear  175  normal to the vertical interior face and symmetrically spaced about the horizontal midplane of right-hand gripper  171 . 
     Left-hand gripper  181  is substantially identical to right-band gripper  171 , except for the provision of an antirotation pocket for boltheads on its outer face. Left-hand gripper  181  has a flat vertical interior face with a vertical axis circularly arcuate groove, which serves as a tubing gripping, face  182  positioned in the middle portion of its vertical interior face. The axis of the arcuate groove is spaced slightly away from and outside the vertical interior face so that the arc of the vertical arcuate groove is less than 180°, and the diameter of the gripping face  182  corresponds to that of the tubing with which the gripper will be used. At one side of the vertical interior face two spaced apart hinge eyes  183   a,b  are formed, with eye  183   b  at the bottom and eye  183   b  just below midheight. Hinge eyes  183   a,b  are short cylindrical elements with coaxial vertical axes which are spaced slightly away from and outside the flat vertical interior face. The outer cylindrical faces of hinge eyes  183   a,b  are tangent to the exterior vertical face of left-hand gripper  181 . The wall thickness of left-hand gripper  181  is thickened adjacent tubing gripping face  182  to support high bending stresses in that region. Vertical hinge bolt hole  174  is bored coaxially with the hinge eyes  183   a,b  and passes through both those eyes. Clamping ear  185  is formed on the opposite side of left-hand gripper  181  from the hinge eyes  183   a,b  and has its outer face parallel to the vertical interior face. The horizontal top and bottom surfaces and the outer transverse side of clamping ear  185  are flat. Through clamping bolt holes  186  are located in clamping ear  185  normal to the vertical interior face and symmetrically spaced about the horizontal midplane of left-hand gripper  181 . Identical extensions of the exterior flat external face of clamping ear  185  extend into the thickened wall of left-hand gripper to accommodate the enlarged heads of clamp bolts  192 . These extensions have inboard vertical edges normal to the exterior flat external face of clamping ear  185  which are offset laterally from the centerline of clamping bolt holes  186  by a distance equal to or slightly more than the eccentricity of the bolt head flats from the clamp bolt axis. 
     Left-hand gripper  181  has its hinge eyes  183   a,b  coaxial with the hinge eyes  173   a,b  of right-hand gripper  171  and is mounted inverted relative to the right-hand gripper. The length and position of hinge eyes  173   a,b  and  183   a,b  are such that they intermesh closely when right-band gripper  171  and left-hand gripper  181  are positioned together. Hinge shaft  188  is a long cylindrical round shaft with male threads at both ends. Hinge shaft  188  has a close sliding fit into the hinge bolt hole  174  and serves as a pivot and mounting shaft for the right-hand and left-hand grippers. Hinge shaft  188  is made sufficiently long so that it can be inserted through a supporting base for the manual tubing clamp  170  and thereby support the clamp. Internally threaded clamp nuts  189  are mounted on the top and bottom threaded portions of hinge shaft  188  to cause the components of the clamp assembly to fit closely to themselves and to their mounting base. In particular, the hinge eyes  173   a,b  and  183   a,b  interleave with a close fit to minimize axial play of the grippers on hinge shaft  188 . Clamp bolts  192  are inserted through clamping bolt holes  186  and  176  of, respectively, the left-hand gripper  181  and the right-band gripper  171  so that a flat on the head of each of the clamp bolts will abut the vertical transverse face of the exterior flat face extensions when the bolts are torqued. A clamp nut  193  is threaded onto the end of each of clamp bolt  192 . Approximately round coiled tubing  198  may be deployed within the arcuate tubing gripping faces  172  and  182  as shown in FIG.  2 . 
     Powered tubing clamp  40 , shown in FIGS.  5 , 6 , 7 , and  8 , is similar in many respects to manual tubing clamp  170 , but uses a selectably operable hydraulically driven wedge tightening system instead of clamp bolts. Power tubing clamp  40  consists of right-hand gripper  41 , left-hand gripper  51 , a hinge shaft  58  with hinge nuts  60 , two Belleville spring washers  61 , an operator cylinder support  64 , an operator cylinder assembly  69 , and wedge block  80 . 
     Right-hand gripper  41  has a flat vertical interior face with a vertical axis circularly arcuate groove, which serves as a tubing gripping, face  42  positioned in the central portion of the vertical interior face. The axis of the arcuate groove is spaced slightly away from and outside the vertical interior face so that the arc of the vertical arcuate groove is less than 180°, and the diameter of the gripping face  42  corresponds to that of the tubing  90  with which the gripper will be used. At one side of the vertical interior face two spaced apart hinge eyes  43   a,b  are formed, with eye  43   a  at the top and eye  43   b  just below midheight. Hinge eyes  43   a,b  are short cylindrical elements with coaxial vertical axes which are spaced slightly away from and outside the flat vertical interior face. The outer cylindrical faces of hinge eyes  43   a,b  are tangent to the exterior vertical face of right-hand gripper  41 . The wall thickness of right-hand gripper  41  is thickened adjacent tubing gripping face  42  to support high bending stresses in that region. Vertical hinge bolt hole  44  is bored coaxially with the hinge eyes  43   a,b  and passes through both those eyes. Clamping ear  45  is formed on the opposite side of right-hand gripper  41  from the hinge eyes  43   a,b . The horizontal top and bottom surfaces and the outer transverse side of clamping ear  45  are flat. The wedging outer surface  46  of clamping ear  45  is obverse to the vertical interior face and is flat and inclined from the vertical by an angle of approximately 6.5° so that the thickness of clamping ear  45  decreases downwardly. The taper angle of wedging outer surface  46  is chosen to be a “non-slipping angle”. A wedge with such an angle has the property that due to friction it will not slip when the wedge is under transverse load without the application of sufficient external force substantially parallel to the wedging surfaces. Located on wedging outer surface  46  parallel to and spaced away from the outer transverse side of clamping ear  45  is a rectangular guide groove of constant cross-section. 
     Left-hand gripper  51  is in several respects similar to right-hand gripper  41 . Left-hand gripper  51  has a flat vertical interior face with a vertical axis circularly arcuate groove, which serves as a tubing gripping, face  52  positioned in the central portion of its vertical interior face. The axis of the arcuate groove  52  is spaced slightly away from and outside the vertical interior face so that the arc of the vertical arcuate groove is less than 180°, and the diameter of the gripping face  52  corresponds to that of the tubing with which the gripper will be used. At one side of the vertical interior face two spaced apart hinge eyes  53   a,b  are formed, with eye  53   b  at the bottom and eye  53   b  just below midheight. Hinge eyes  53   a,b  are short cylindrical elements with coaxial vertical axes which arc spaced slightly away from and outside the flat vertical interior face. The outer cylindrical faces of hinge eyes  53   a,b  are tangent to the exterior vertical face of left-hand gripper  51 . The wall thickness of left-hand gripper  51  is thickened adjacent tubing gripping face  52  to support high bending stresses in that region. Vertical hinge bolt hole  44  is bored coaxially with the hinge eyes  53   a,b  and passes through both those eyes. Clamping ear  55  is formed on the opposite side of left-hand gripper  51  from the hinge eyes  53   a,b  and has its outer face parallel to the vertical interior face. The horizontal top and bottom surfaces and the outer transverse side of clamping ear  55  are flat. The wedging outer surface  56  of clamping ear  55  is obverse to the vertical interior face and is flat and inclined from the vertical by the same angle as that of wedging outer surface  46  of right-hand gripper  41  so that the thickness of clamping ear  55  decreases downwardly. Located on wedging outer surface  56  parallel to and spaced away from the outer transverse side of clamping ear  55  is a rectangular guide groove of constant cross-section. Two shallow, flat-bottomed circular spring pockets  57  are located symmetrically about the horizontal midplane of left-hand gripper  51  on the vertical interior face of clamping ear  55 . 
     Left-band gripper  51  has its hinge eyes  53   a,b  coaxial with the hinge eyes  43   a,b  of right-hand gripper  41  and is mounted so that the wedging outer surfaces  46  and  56  of the grippers both taper downwardly. The length and position of hinge eyes  43   a,b  and  53   a,b  are such that they intermesh closely when right-hand gripper  41  and left-hand gripper  51  are positioned together. Hinge shaft  58  is a long cylindrical round shaft with male threads at both ends and a coaxial cylindrical intermediate shaft upset section  59  with transverse upper and lower sides located nearly at the upper end of the shaft. Hinge shaft  58  has a close sliding fit into the hinge bolt hole  44  and serves as a pivot and mounting shaft for the right-hand and left-hand grippers. The lower transverse side of intermediate shaft upset  59  bears on the upper transverse face of hinge eye  43   a . Hinge shaft  58  is made sufficiently long so that it can be inserted through a supporting base for the power tubing clamp  40  and thereby support the clamp. Internally threaded clamp nuts  60  are mounted on the top and bottom threaded portions of hinge shaft  58  to cause the components of the clamp assembly to fit closely to themselves and to their mounting base. In particular, the hinge eyes  43   a,b  and  53   a,b  interleave with a close fit to minimize axial play of the grippers on hinge shaft  58 . A Belleville spring washer  61  is fined within each of the spring pockets  57  of clamp ear  55  so that it protrudes beyond the vertical interior face of left-hand gripper when uncompressed. The Belleville spring protrusion beyond the vertical interior face is such that the spring exerts substantial force on clamping car  45  of right-hand gripper  41  when the tubing is tightly gripped by power tubing clamp  40 . 
     Operator cylinder support  64  is a steel plate approximately two inches thick and having a lozenge shape with rounded corners. Threaded cylinder mount hole  65  is located at the first end of operator cylinder support  64 , tubing clearance hole  66  is located in the middle, and hinge shaft hole  67  is at the second end. Tubing clearance hole  66  is fairly large to provide ample clearance for passage of tubing through the power tubing clamp  40 . Hinge shaft hole  67  is a close fit to hinge shaft  58 . Operator cylinder support  64  is positioned horizontally with the upper end of hinge shaft  58  through hinge shaft hole  67  and the lower face of support  64  bearing on the upper transverse shoulder of intermediate shaft upset  59  of hinge shaft  58 . A hinge shaft nut  60  is torqued down onto the upper threads of hinge shaft  58  on the upper side of operator cylinder support  64  to firmly clamp the support to the hinge shaft  58 . 
     Double-acting operator hydraulic cylinder assembly  69  consists of cylinder body  70 , piston  71 , and rod  72 , along with associated elbow fittings  73  and hydraulic tubing  74 . Cylinder body  70  is of conventional tubular construction with a cylindrical male threaded front nose mount, an elastomeric rod seal in the front nose, and both a rod extension and a rod retraction port at opposed ends of the cylinder interior. Piston  71  is a short circular cylindrical disk with an annular elastomeric seal in its annular groove and integral cylindrical rod  72  attached to its lower side. The lower end of rod  72  is provided with a conventional wrench flat and male threads. The threaded front nose of the cylinder assembly  69  is screwed into the threaded cylinder mount hole  65  of operator cylinder support  64 . A hydraulic elbow fitting  73  is screwed into each of the ports of cylinder assembly  69 , and hydraulic tubing  74  is sealingly attached to the elbow fitting by the conventional compression nut of the fitting. Hydraulic pressure from a conventional hydraulic power system is applied by means of a selectably controlled hydraulic valve to one or the other hydraulic tubing  74  and thence to the operator hydraulic cylinder assembly  69 . This hydraulic power system is not shown herein, but is well understood by those skilled in the art. 
     Wedge block  80  is a rectangular block approximately 12 inches high by 7 inches wide and 3 inches thick. Wedge cavity  81 , located on one of the largest faces of wedge block  80 , has a constant depth trapezoidal shape symmetrical about the vertical perpendicular midplane of that face of the block. Wedge cavity  81  decreases in width downwardly with side tapers matching those of the wedging outer surfaces  46  and  56  of, respectively, right-hand gripper  41  and left-hand gripper  51 . On each tapered side of wedge cavity  81  is rectangular cross-section retainer land  82  parallel to and spaced apart from the face of wedge block  80  which contains wedge cavity  81 . Retainer lands  82  of wedge block  80  comate and interact with the rectangular guide grooves in the clamping outer faces  46  and  56  of, respectively, right-hand gripper  41  and left-hand gripper  51  when these elements are assembled so that the clamping ears  45  and  55  of the grippers are positioned in wedge cavity  81 . Retainer lands  82  thus retain and provide guidance to wedge block  80 . In the middle of the upper transverse face of wedge block  80  is a female threaded blind hole which has threads which are comated with the rod end threads of the rod  72  of operator cylinder assembly  69  so that wedge block  80  can be reciprocated vertically. Approximately round coiled tubing  90  may be deployed within the arcuate tubing gripping faces  42  and  52 . 
     Another embodiment of the thrust enhancement device for coiled tubing injectors, shown in FIGS. 10 through 13, is based upon the powered tubing clamp  40 , shown in FIGS. 5-9 and  16 . Remotely controlled thrust enhancement device  1  consists of a structural tube body  2 , multiple hydraulic thrust cylinders  20 , a moveable transverse deck  30 , and two powered tubing clamps  40 . Square structural tube body  2  is a commercially available steel section which is approximately 18 inches by 18 inches square and with 0.625 inch wall thickness by 61.25 inches long. The corners of the tube are radiused due to its manner of fabrication. Identical bottom  3  and top transverse flanges  4  are made of plate steel cut into a hollow square pattern and welded to the tubular body  2 . Transverse through mounting holes are provided on the outer corners of each of the flanges  3  and  4  to facilitate mounting the thrust enhancement device to the blowout preventers of the coiled tubing rig and/or the separate conventional coiled tubing injector system. Rectangular windows with rounded corners to provide reductions of stress concentrations are cut into each of the side walls of tubular body  2  to provide access and visibility for the tubing and the other hardware mounted therein. The four upper windows  8  are identical, approximately square cutouts with each positioned symmetrically about the centerline of its respective face of body  2  close to the top transverse flange  4 . The four lower windows  9  are identical and higher than they are wide. The lower windows are each positioned symmetrically about the centerline of their respective faces of body  2  close to the bottom transverse flange  3 . 
     Static transverse deck  12  is a horizontal square piece of plate approximately 2 inches thick with radiused corners on the vertical corners of the square to closely fit inside tubular body  2 . Static transverse deck  12  is welded into place inside tubular body  2  normal to the through axis of the body between the upper windows  8  and the lower windows  9 . A round through hole for powered tubing clamp mounting  13  is positioned on a first vertical midplane but offset to one side of the second, transverse vertical midplane of static transverse deck  12 . The through hole for powered tubing clamp mounting  13  provides a snug fit to the lower end of clamp hinge shaft  58 , which is mounted in the hole and retained by a hinge shaft nut  60  on the lower side of static transverse deck  12 . The offset of through hole  13  from the second vertical midplane is chosen so that the tubing  90  will be on the vertical centerline axis of body  2  when held by a powered tubing clamp  40  mounted by means of hole  13 . A rectangular through hole for tubing clearance  14  with rounded corners is symmetrical about the first vertical midplane but offset to the opposite side of the other, second transverse vertical midplane of static transverse deck  12  from through hole  13  for powered tubing clamp mounting. The through hole for tubing clearance  14  permits the tubing to pass through thrust enhancement device  1  on the vertical centerline of body  2 . Tubing clearance hole  14  is oversized to also permit ample clearance for downward unlatching movement of the wedge block  80  of powered tubing clamp  40 . Additionally, static transverse deck  12  also has a doubly symmetric pattern of four female threaded blind holes  15  on its lower side for attachment of the rod ends of hydraulic thrust cylinders  20 . 
     Hydraulic thrust cylinder  20  is a conventional double-acting cylinder with a single rod and a coaxial rear bolt mounting. Although the individual parts of the hydraulic thrust cylinder are not shown, it has a conventional construction and is well known in the art. Cylinder body has a rod gland with an elastomeric rod seal on its upper end with a coaxial female threaded mounting hole on the lower transverse blind end of the cylinder. Cylinder body has a radial rod return port near its upper end and a radial rod extend port near its lower end. Cylinder piston is a short circular cylindrical disk with an annular elastomeric seal in its annular groove and integral cylindrical cylinder rod  25  attached to its upper side. The upper end of rod  25  is provided with a conventional wrench flat and male threads which are comated with the female threads of the threaded blind holes for cylinder rod attachment  15  located on the bottom side of static transverse deck  12  of body  2 . Hex-headed cylinder mounting screw  28  comates with the female thread on the bottom side of cylinder body to mount the cylinder  20  to moveable transverse deck  30 . An elbow hydraulic fitting is screwed into each of the ports of the thrust cylinder, and hydraulic tubing is sealingly attached to the elbow fitting by the conventional compression nut of the fitting. Hydraulic pressure from a conventional hydraulic power system is applied by means of a selectably controlled hydraulic valve to one or the other hydraulic tubing and thence to the hydraulic thrust cylinder. This hydraulic power system is not shown herein, but is well understood by those skilled in the art. Four identical hydraulic thrust cylinders  20  are used in a doubly symmetrical mounting pattern when viewed in plan view to provide direct thrust loading without attendant bending to the tubing. 
     Moveable transverse deck  30  is a horizontal square piece of plate approximately 3 inches thick having large chamfers on the vertical corners of the square for clearance to fit inside tubular body  2 . Moveable transverse deck  30  is sized to be a close slip fit within tubular body  2  when it is reciprocated along the axis of the body. Moveable transverse deck  30  has the same pattern for its four through holes for cylinder mounting  33  as is used for the threaded blind holes for cylinder rod attachments  15  on the static transverse deck  12  of tubular body  2 . Likewise, the pattern for its through hole for powered tubing clamp mounting  32  and its through hole for tubing clearance  33  are the same as the corresponding holes  13  and  14  of static transverse deck  12  of tubular body  2 . Moveable transverse deck  30  is installed below static transverse deck  12  with its clamp mounting hole  32  coaxial with that of clamp mounting hole  13  of static transverse deck  12 . The bottom end of each of the four cylinders  20  is clamped to the top surface of moveable transverse deck  30  by means of cylinder mounting screws  28  engaged in through holes for cylinder mounting bolts  34  and the female threaded holes on the bottom end of cylinders  20 . 
     One powered tubing clamp  40  (described previously) is mounted on the upper surface of static transverse deck  12  by means of its hinge shaft  58  and a hinge shaft nut  60  coaxial with through hole  13  in the static transverse deck of body  2 . The vertical plane of symmetry of tubing clamp  40  is coplanar with the aforementioned first vertical plane of symmetry of the static transverse deck  12  of body  2 . A second powered tubing clamp  40  is mounted on the upper surface of moveable transverse deck  30  by means of its hinge shaft  58  and a hinge shaft nut  60  coaxial with through hole  32  in the moveable transverse deck  30 . The vertical plane of symmetry of tubing clamp  40  is coplanar with the aforementioned first vertical plane of symmetry of the moveable transverse deck  30 . 
     Another embodiment of the thrust enhancement device for coiled tubing injectors, shown in FIGS. 14 and 15, is based upon the manual tubing clamp  170 , shown in FIGS. 1-4. Manually controlled thrust enhancement device  101  consists of a structural tube body  102 , multiple hydraulic thrust cylinders  120 , a moveable transverse deck  130 , and two manual tubing clamps  170 . With the exception of the types of tubing clamps used, the manually controlled  101  and remotely controlled  1  thrust enhancement devices are identical. The part numbers  2  through  34  of thrust enhancer device  1  correspond to part numbers  101 - 134  of thrust enhancement device  101  and arc not necessarily discussed individually herein. 
     Square structural tube body  102  is a commercially available steel section which is approximately 18 inches by 18 inches square and with 0.625 inch wall thickness by 61.25 inches long. The corners of the tube are radiused due to its manner of fabrication. Identical bottom  103  and top transverse flanges  104  are made of plate steel cut into a hollow square pattern and welded to the tubular body  102 . Transverse through mounting holes are provided on the outer corners of each of the flanges  103  and  104  to facilitate mounting the thrust enhancement device to the blowout preventers of the coiled tubing rig and/or the separate conventional coiled tubing injector system. Rectangular windows with rounded corners to provide reductions of stress concentrations are cut into each of the side walls of tubular body  102  to provide access and visibility for the tubing and the other hardware mounted therein. The four upper windows  108  are identical, approximately square cutouts with each positioned symmetrically about the centerline of its respective face of body  102  close to the top transverse flange  104 . The four lower windows  109  are identical and higher than they are wide. The lower windows are each positioned symmetrically about the centerline of their respective faces of body  102  close to the bottom transverse flange  103 . 
     Static transverse deck  112  is a horizontal square piece of plate approximately 2 inches thick with radiused corners on the vertical corners of the square to closely fit inside tubular body  102 . Static transverse deck  112  is welded into place inside tubular body  102  normal to the through axis of the body between the upper windows  108  and the lower windows  109 . A round through hole for manual tubing clamp mounting  113  is positioned on a first vertical midplane but offset to one side of the second, transverse vertical midplane of static transverse deck  112 . The through hole for powered tubing clamp mounting  113  provides a snug fit to the lower end of clamp hinge shaft  188 , which is mounted in the hole and retained by a hinge shaft nut  189  on the lower side of static transverse deck  112 . The offset of through hole  113  from the second vertical midplane is chosen so that the tubing  198  will be on the vertical centerline axis of body  102  when held by a manual tubing clamp  170  mounted by means of hole  113 . A rectangular through hole for tubing clearance  114  with rounded corners is symmetrical about the first vertical midplane but offset to the opposite side of the other, second transverse vertical midplane of static transverse deck  112  from through hole  113  for manual tubing clamp mounting. The through hole for tubing clearance  114  permits the tubing  198  to pass through thrust enhancement device  101  on the vertical centerline of body  102 . Additionally, static transverse deck  112  also has a doubly symmetric pattern of four female threaded blind holes  115  on its lower side for attachment of the rod ends of hydraulic thrust cylinders  120 . 
     Hydraulic thrust cylinder  120  is a conventional double-acting cylinder with a single rod and a coaxial rear bolt mounting. Cylinder body  121  has a rod gland with an elastomeric rod seal on its upper end with a coaxial female threaded mounting hole on the lower transverse blind end of the cylinder. Cylinder body  121  has a radial rod return port  122  near its upper end and a radial rod extend port  123  near its lower end. Cylinder piston  124 , which is not shown but is of conventional construction, is a short circular cylindrical disk with an annular elastomeric seal in its annular groove and integral cylindrical cylinder rod  125  attached to its upper side. The upper end of rod  125  is provided with a conventional wrench flat and male threads which are comated with the female threads of the threaded blind holes for cylinder rod attachment  115  located on the bottom side of static transverse deck  112  of body  102 . Hex-headed cylinder mounting screw  128  comates with the female thread on the bottom side of cylinder body  121  to mount the cylinder  120  to moveable transverse deck  130 . An elbow hydraulic fitting  126  is screwed into each of the ports  122  and  123  of thrust cylinder  120 , and hydraulic tubing  127  is sealingly attached to the elbow fitting by the conventional compression nut of the fitting. Hydraulic pressure from a conventional hydraulic power system is applied by means of a selectably controlled hydraulic valve to one or the other hydraulic tubing  127  and thence to the hydraulic thrust cylinder  120 . This hydraulic power system is not shown herein, but is well understood by those skilled in the art. Four identical hydraulic thrust cylinders  120  are used in a doubly symmetrical mounting pattern when viewed in plan view to provide direct thrust loading without attendant bending to the tubing. 
     Moveable transverse deck  130  is a horizontal square piece of plate approximately 3 inches thick having large chamfers on the vertical corners of the square for clearance to fit inside tubular body  12 . Moveable transverse deck  130  is sized to be a close slip fit within tubular body  102  when it is reciprocated along the axis of die body. Moveable transverse deck  130  has the same pattern for its four through holes for cylinder mounting  133  as is used for the threaded blind holes for cylinder rod attachments  115  on the static transverse deck  112  of tubular body  102 . Likewise, the pattern for its through hole for powered tubing clamp mounting  132  and its through hole for tubing clearance  133  are the same as the corresponding holes  113  and  114  of static transverse deck  112  of tubular body  102 . Moveable transverse deck  130  is installed below static transverse deck  112  with its clamp mounting hole  132  coaxial with that of clamp mounting hole  113  of static transverse deck  112 . The bottom end of each of the four cylinders  120  is clamped to the top surface of moveable transverse deck  130  by means of cylinder mounting screws  128  engaged in through holes for cylinder mounting bolts  134  and the female threaded holes on the bottom end of cylinders  120 . 
     One manual tubing clamp  170  (described previously) is mounted on the upper surface of static transverse deck  112  by means of its hinge shaft  188  and a hinge shaft nut  189  coaxial with through hole  113  in the static transverse deck of body  102 . The vertical plane of symmetry of tubing clamp  170  is coplanar with the aforementioned first vertical plane of symmetry of the static transverse deck  112  of body  102 . A second manual tubing clamp  170  is mounted on the upper surface of moveable transverse deck  130  by means of its hinge shaft  188  and a hinge shaft nut  189  coaxial with through hole  132  in the moveable transverse deck  130 . The vertical plane of symmetry of tubing clamp  170  is coplanar with the aforementioned first vertical plane of symmetry of the moveable transverse deck  130 . 
     FIG. 17 shows the relationship of the thrust enhancement device of this invention to the other components of a coiled tubing injection system and a typical onshore wellhead of a well used for the production of petroleum products. The rigged up coiled tubing rig  200  on the wellhead  201  consists of the blowout preventors  202 , the thrust enhancement device  1  or  101 , the coiled tubing injector  203 , the gooseneck  204 , the storage reel  205 , and the coiled tubing  206 . Wellhead  201  is attached to the top end of the outer, initial casing of a well and provides physical support and flow isolation for the other various casing strings and tubing of the well, as well as valving and fluid connections for hooking the well up to the surface facilities for the well. The blowout preventors  202  for the coiled tubing rig are a modular assembly which can either seal on the exterior of the coiled tubing  206  or shear it and then seal across the upward looking end of the sheared coiled tubing. The blowout preventors  202  arc attached to the flange on the top of the wellhead by a similar, comating flange on the bottom of the blowout preventor assembly. A flange at the top of the blowout preventor assembly is attached to either the bottom flange  3  of the remotely controlled thrust enhancement device  1  or the bottom flange  103  of the manually controlled thrust enhancement device  101 , depending on which embodiment of the invention is used. A coiled tubing injector  203  is attached to either the top flange  4  of thrust enhancement device  1  or the top flange  104  of thrust enhancement device  101 , as appropriate. The coiled tubing injector  203  could be any one of a variety of designs, including that shown in copending U.S. Provisional Patent Application “Coiled Tubing Injector Utilizing Opposed Drive Modules and Having an Integral Bender”, filed Jul. 11, 2001, a conventional opposed track type, or a single-side track type with hold-down rollers. A gooseneck  204  of conventional construction is mounted on the top of injector  203 . The tubing  206  is stored on reel  205  and passes from the reel, over the gooseneck  204 , through the injector  203 , through the thrust enhancement device ( 1  or  101 ), and into the wellhead  201  and, thence, the well. These coiled tubing rig components are standard equipment items well known in the oilfield industry. 
     Operation of the Invention 
     The operation of both of the clamps  40  and  170  and of the thrust enhancement device embodiments  1  and  101  described herein is simple and straightforward. The thrust enhancement device embodiments are used in conjunction with the other hardware of a typical coiled tubing rig as shown in FIG.  17 . As may understood by those familiar with this equipment the thrust enhancement device could be positioned between the injector and the gooseneck, rather than as shown in FIG.  17 . Likewise, the thrust enhancement device could be used with a wheel type injector, rather than a single or double tracked injector or the device of the aforementioned copending injector. 
     The operation of manual tubing clamp  170  is best understood from referring to FIGS. 3 and 4. In FIG. 3, manual tubing clamp  170  is shown with the right-hand gripper  171  and the left-hand gripper  181  pivoted relative to each other about hinge shaft  188  to the open position of the clamp. This opening is possible because a manually operated wrench (not shown) has been used to loosen clamp nuts  193  so the clamp halves can separate and normally will not grip the tubing tightly. The position of the clamp  170  corresponds to the position, which is required for initially passing the tubing through the axis of the manually controlled thrust enhancement device  101 . This same position is used for both manual clamps in a manually controlled thrust enhancement device. In the event that the tubing binds in the grooves  172  and  182  of the grippers  171  and  181 , a prying device can be used to separate the grippers and a hammer or other suitable device can be used to separate a binding gripper from the tubing. This operation is not problematic, since generally only very short axial travels of the tubing equivalent to a very small number of thrust enhancement device strokes are required to overcome and excessive resistance to tubing injection which might necessitate use of the devices of this invention. The manual tubing clamp  170  is caused to grip the tubing by tightening the clamp nuts  193  manually with a wrench until the torque applied is sufficient to cause the gripper  171  and  181  to tightly hold the tubing  198 . The heads of clamp bolts  192  are restrained from rotating during the torqueing of clamp nuts  193  by the inboard vertical edges of the extensions of the external flat transverse face of clamping ear  185 . 
     The operation of powered tubing clamp  40  is best understood from FIGS. 6,  7 , and  8 . When wedge block  80  is caused to move downwardly by selectably applying hydraulic pressure to the rod extend port of the operator hydraulic cylinder assembly  69 , the wedging faces of wedge cavity  81  are caused to tend to separate from the wedging outer surfaces  46  and  56  of the right-hand and left-hand grippers  41  and  51 , respectively. When the wedging action is thus released by the downward shifting of wedge block  80 , the Belleville spring washers  61  force the interior faces of the grippers apart through rotation about hinge shaft  58 , thereby opening the clamp and causing the tubing  90  to be released by the clamp  40 . The open position of the clamp  40  is also the position of the clamp during initial loading of the clamp or when the thrust enhancement device is inactive. In order to close the clamp  40  so that it will grip the tubing  90 , hydraulic pressure is selectably applied to the rod return port of operator cylinder assembly  69  so that the rod  72  retracts, thereby raising wedge block  80  so that the wedging surfaces of wedge cavity  81  forcibly urge the grippers  41  and  51  to rotate together about hinge shaft  58  due to pressure on the wedging outer surfaces  46  and  56  of the clamping ears  45  and  55 . When the grippers  41  and  51  have moved sufficiently together, then the tubing  90  will be tightly gripped in grooves  42  and  52 . 
     The operation of the remotely controlled thrust enhancement device  1  proceeds as follows. Here it is assumed that the thrust enhancement device  1  is aiding in withdrawing the tubing  90  from the well. Hydraulic pressure is applied to the rod extend ports of selectably operable hydraulic thrust cylinders  20  so that moveable transverse deck  30  is caused to shift to its lowest position. During this initial downward reciprocation of the device  1 , both the upper and lower tubing clamps  40  are open. After moveable transverse deck  30  has reached its lowest position, the lower clamp  40  is selectably engaged to grip the tubing  90 . Hydraulic pressure is then applied to the retract the rods of thrust cylinders  20 , thereby both raising the moveable transverse deck  30  and pulling the tubing  90  upwardly. When moveable transverse deck  30  reaches its upper position, upper clamp  40  is engaged and then lower clamp  40  is released from the tubing  90 . Upper clamp  40  serves to hold the tubing  90  against moving downwardly back into the well. At this point, moveable transverse deck  30  is again selectable stroked downwardly for another stroke, if required. The next upward reciprocation stroke can begin when the lower clamp grips the tubing and the upper clamp then releases the tubing. When the pulling of the tubing from the well by means of reciprocating the thrust enhancement device  1  is complete, both clamps  40  are then released from the tubing. However, if the tubing must be held, then both clamps  40  can be used to grip the tubing tightly and the thrust cylinders  20  hydraulically locked in position to prevent movement. In order to force tubing into the well, the lower tubing clamp  40  on the moveable transverse deck  30  first grips the tubing at the upper position of the moveable deck  30 , the grip of the upper clamp  40  is released, and the moveable is stroked downwardly. At the end of the downward reciprocation, the upper clamp  40  grips the tubing and the lower clamp releases the tubing to permit reciprocating the moveable deck upwardly for another downstroke, similarly to the procedures used for the withdrawal of tubing from the well. 
     The operation of the manually controlled thrust enhancement device is identical in all respects to that of the remotely controlled thrust enhancement device, with the exception of the need to manually open and close the upper and lower tubing clamps  170 . The operation of the manually controlled thrust enhancement device  101  proceeds as follows. Here it is assumed that the thrust enhancement device  101  is aiding in withdrawing the tubing  198  from the well. Hydraulic pressure is applied to the rod extend ports  123  of selectably operable hydraulic thrust cylinders  120  so that moveable transverse deck  130  is caused to shift to its lowest position. During this initial downward reciprocation of the device  101 , both the upper and lower tubing clamps  170  are open. After moveable transverse deck  130  has reached its lowest position, the lower clamp  170  is selectably engaged to grip the tubing  198 . Hydraulic pressure is then applied to the retract the rods of thrust cylinders  120 , thereby both raising the moveable transverse deck  130  and pulling the tubing  198  upwardly. When moveable transverse deck  130  reaches its upper position, upper clamp  170  is engaged and then lower clamp  170  is released from the tubing  198 . Upper clamp  170  serves to hold the tubing  198  against moving downwardly back into the well. At this point, moveable transverse deck  130  is again selectable stroked downwardly for another stroke, if required. The next upward reciprocation stroke can begin when the lower clamp grips the tubing and the upper clamp then releases the tubing. When the pulling of the tubing from the well by means of reciprocating the thrust enhancement device  101  is complete, both clamps  170  are then released from the tubing. However, if the tubing must be held, then both clamps  170  can be used to grip the tubing tightly and the thrust cylinders  120  hydraulically locked in position to prevent movement. In order to force tubing into the well, the lower tubing clamp  170  on the moveable transverse deck  130  first grips the tubing at the upper position of the moveable deck  130 , the grip of the upper clamp  170  is released, and the moveable deck  130  is stroked downwardly, forcing the tubing downwardly. At the end of the downward reciprocation of moveable deck  130 , the upper clamp  170  grips the tubing and the lower clamp releases the tubing to permit reciprocating the moveable deck upwardly for another downstroke, similarly to the procedures used for withdrawing tubing from the well. 
     Advantages of the Invention 
     The novel thrust enhancement device for use with conventional coiled tubing injectors based on using the mechanisms of this invention offers several important advantages over using a conventional coiled tubing injector alone. Coiled tubing injectors are normally sized for a maximum service thrust based upon a certain tubing weight and well pressure plus a substantial extra allowance for the tubing motion in the well being obstructed by a shoulder, being sanded in, or the like. When the novel thrust enhancement device of this invention is used to provide the extra allowance for overcoming the obstructions to tubing motion, then the injector can be sized based its routine service requirements only. This permits the very significant advantage of using a more economical injector of smaller size and weight. The weight and cost of the thrust enhancement device of this invention are relatively small compared to the thrust delivered, so that the combination of the thrust enhancement device with a smaller injector is lighter and less expensive when compared to a large injector of equivalent thrust. This reduction in system weight is important for areas where significant weight limits are placed on transportation vehicles. 
     The thrust enhancement device of this invention can be used very effectively in either insertion or withdrawal of the coiled tubing in the well. Thrust capability is directly related to the piston areas of the thrust cylinders. Since use of larger thrust cylinders adds system cost and weight at a rate much less than proportional to the thrust increase ratio, a higher margin of safety can be obtained very economically for ensuring that the tubing can be withdrawn from the well. Additionally, the tubing clamping means of either of the embodiments of this invention can passively grip and hold the tubing against movement in either direction when the coiled tubing injector is not being operated, even with a leaky hydraulic system. 
     These and other advantages will be obvious to those skilled in the art. It may be understood readily that certain detail changes from the design herein arc still within the scope of this invention. For instance, another type of spring could be substituted for the Belleville springs used to passively release the powered tubing clamp. The wedging angles used in the powered tubing clamp could also be modified from those shown. Similarly, several variations can be made in the supporting body construction or the means for mounting the hydraulic cylinders without changing the basic principles of this invention. Likewise, power screws could be used to cause reciprocation of the moveable transverse deck holding the lower tubing clamp for the system without departing from the spirit of this invention.