Abstract:
An improved V-style gripper block to better accommodate a variable outer diameter material (e.g. cable, plastic, wire, or pipe). The gripper block comprises a block body being connectable to a gripper chain in an injector apparatus, a gripper plate having arcuate and/or angled gripping surfaces for engaging tubing of various outer diameters, and a flex layer disposed between the gripper plate and the block body to allow the gripping surface of the gripper plate to move relative to the block body to which it is attached. This relative movement allows the gripping surface of the gripper block to rapidly conform to changes in the outer diameter of coiled tubing. In various embodiments, the flex layer may be formed of elastomeric materials including natural or synthetic rubber; an encapsulated gel or liquid within a flexible membrane; or mechanical means such as springs.

Description:
BACKGROUND 
   The present invention relates to gripper blocks installed in coiled tubing injection equipment used in the oil and gas production industry. More specifically, the present invention relates to a gripper block designed to better accommodate lengths of coiled tubing with varying outside diameters. 
   Reeled or coiled tubing has been used for many years for performing certain downhole operations, including but not limited to completions, washing, circulating, production, production enhancement, cementing, inspecting, and logging. There are a number of patents issued on coiled tubing injectors and related equipment. Such injectors generally use a pair of opposed endless gripper chains mounted in a common plane. The gripper chains are normally made up of links, rollers, and gripper blocks. Opposed gripper blocks on the endless chains engage the tubing as to firmly grasp the tubing in such a way that the gripper blocks will force the tubing into or out of a wellbore when the gripper chains are driven. Upon setting the gripper chains into motion and upon each opposing pair of gripper blocks releasing their hold on the tubing, another pair of opposed gripper blocks grippingly engage the tubing and the cycle continues until a desired amount of tubing has been inserted into or withdrawn from the wellbore, or until the gripper chains are no longer driven. 
   Over the years, a variety of gripper blocks have been developed to improve the performance of coiled tubing injector units. Such improvements include designs directed to increasing the load carrying capability of gripper blocks, thus eliminating or limiting scarring and distortion of the tubing caused by gripper block engagement; providing the ability to accommodate differing tubing diameters without having to change gripper blocks; reducing the weight of gripper blocks; and reducing the manufacturing costs of gripper blocks. Such prior art gripper blocks are disclosed in U.S. Pat. No. 5,094,340 to Avakov, issued Mar. 10, 1992; U.S. Pat. No. 5,853,118 to Avakov, issued Dec. 29, 1998; and U.S. Pat. No. 6,230,955 B1 to Parks, issued May 15, 2001; each of these patents being assigned to the assignee of the present invention and the details of each of these patents being incorporated herein in its entirety by reference. 
   In the past, coiled tubing has had a constant cross section. However, maintaining a constant diameter for the tubing can present some problems under certain circumstances. For example, it may be desirable to reduce the weight of the string or to reduce the amount of drag in the wellbore by reducing the diameter of the tubing. Additionally, small diameter tubing is preferable if the size at the treatment area is particularly small or confined. However, it is also noted that smaller diameter tubing tends to buckle more readily than large diameter tubing and that smaller diameter tubing also presents significant pressure drop problems in longer tubing strings. It is notable that each of these problems with both large and small constant diameter tubing may beaddressed by allowing the use of larger outside diameter tubing at the top of the string and a smaller outside diameter tubing at the bottom of the string proximate to the treatment zone. One convenient way of linking or connecting coiled tubing having varying outside diameters utilizes one or more tapered connectors in the tubing string. Such a tapered connector generally comprises at least a first tubular portion having a first tubing outside diameter, a second tubular portion having a second tubing outside diameter which is different than the first, and a tapered portion disposed between the first and second tubing portions. One such tapered connector for a tubing string is disclosed in U.S. Pat. No. 6,367,557 B1 to Rosine et al., issued Apr. 9, 2002; this patent being assigned to the assignee of the present invention and the details of this patent being incorporated herein in its entirety by reference. 
   The tapered connector, according to Rosine et al., and the improved gripper block designs, according to Avakov and Parks, make it possible to insert coiled tubing into a well using a twin carriage coiled tubing injector apparatus as known in the art. One example of a twin carriage tubing injector apparatus is shown in U.S. Pat. No. 5,553,668 to Council et al., issued Sep. 10, 1996; this patent being assigned to the assignee of the present invention and the details of this patent being incorporated herein in its entirety by reference. Although it is possible to stop the injector apparatus to adjust the spacing between the moveable gripper chains to accommodate varying outer tube diameters, it would be desirable to have an improved gripper block to accommodate abrupt changes in the outer diameter of jointed tubulars and tapered strings without costly stoppages to make adjustments or modifications. Accordingly, there is a need for an improved gripper block capable of not only engaging the surfaces of tubing having changing outer diameters but to conform rapidly to these changing geometries and reduce the number of stoppages for adjustment or modification required in standard twin carriage tubing injector apparatus. 
   SUMMARY 
   The gripper block of the present invention will address these needs and provide other desirable properties by creating modified V-style gripper blocks that quickly conform to variable outer diameter elongated objects (e.g. cable, plastic, wire, or pipe). This may be accomplished by designing a V-style gripper block comprising a block body being connectable to a gripper chain in an injector apparatus, a gripper plate having arcuate and/or angled gripping surfaces for engaging tubing of various outer diameters, and a flex layer of elastomeric material disposed between the gripper plate and the block body to allow a gripping surface of the gripper block to move relative to the block body to which it is attached. This relative movement allows the gripping surface of the gripper block to rapidly conform to a changes in the outer diameter of coiled tubing. It is believed that a gripper block that rapidly conforms to changes in diameter will be less likely to bind, crimp, or damage the coiled tubing and will also be able to better accommodate fittings, including tapered connectors. 
   The elastomeric material located between the gripper plate and the block body is strategically placed within the gripper block to allow the gripping surface to move without damage to the tubular material. In one embodiment the elastomeric materials may be of various polymeric compounds or blends including natural or synthetic rubber. Moreover, it is also possible to encapsulate a gel or liquid within a flexible membrane to achieve the same function of the elastomeric material. In yet another embodiment, the function of the elastomeric material may be achieved through various mechanical means, such as springs which extend between the block body and the gripper plate and allow the gripper plate to move relative to the block body as the outer diameter of the flexible tubing changes. 
   It is believed that a gripper block constructed in accordance with the present invention will allow operators to run tubulars having changing outer diameters without interruption. Specifically, a gripper block constructed in accordance with the present invention will allow twin carriage tubing injectors as known in the art to accommodate abrupt changes in outer diameter, joint tubulars, and tapered strings without costly adjustments or modifications. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood in view of the detailed description in conjunction with the following drawings in which like reference numbers refer to like parts in each of the figures and in which: 
       FIG. 1  is an exploded perspective view of a first embodiment of a gripper block with a cushion flex layer constructed in accordance with the present invention; 
       FIG. 2  is an exploded cross-sectional view of the gripper block with a cushion flex layer as shown in  FIG. 1 ; 
       FIG. 3  is an assembled cross-sectional view of the gripper block with a cushion flex layer as shown in  FIG. 1 ; 
       FIG. 4  is an exploded perspective view of a second embodiment of a gripper block with a spring flex layer constructed in accordance with the present invention; 
       FIG. 5  is an exploded cross-sectional view of the gripper block with a spring flex layer as shown in  FIG. 4 ; and 
       FIG. 6  is an assembled cross-sectional view of the gripper block with a spring flex layer as shown in FIG.  4 . 
   

   DETAILED DESCRIPTION 
   Referring now to  FIGS. 1-3 , a first embodiment of a gripper block  10  constructed in accordance with the present invention is shown. As best seen in  FIG. 1 , viewed along the longitudinal axis, the upper portion of a gripper plate  100  features a generally V-shaped channel  110  adapted to receive, for example, elongated objects such as coiled tubing. The topmost portion of the gripper plate  100  has a gripping portion  120  for engaging elongated objects. The gripping portion  120  further comprises a pair of opposed gripping surfaces  130  extending perpendicularly from the longitudinal axis. The opposed gripping surfaces  130  are generally inclined or slanted inward toward each other and form an angle of not greater than about 120°. In one embodiment, the opposed gripping surfaces  130  may be inclined at about 90° to each other. The opposed gripping surfaces  130  further feature a series of ridges  140  formed by alternating crests and roots. The ridges  140  permit the opposed gripping surfaces  130  to better engage the surface of coiled tubing as it is moved into or out of a wellbore. Note that the generally V-shaped profile of the gripper plate  100  is well suited to accommodate coiled tubing and other elongated objects having varying outer diameters. 
   Still referring to  FIGS. 1-3 , it is also possible to incorporate a curved gripping surface  150  into the gripping portion  120  of the gripper plate  100 . The curved gripping surface  150  may further comprise ridges, not shown, formed by alternating crests and roots. In one embodiment, the curved gripping surface  150  has a particular radius of curvature designed to accommodate an elongated object having a predetermined minimum outer diameter. For objects exceeding this particular outer diameter, the opposed gripping surfaces  130  will come into play and allow the gripper plate  100  to engage the object. In most embodiments, the radius of curvature for the curved gripping surface  150  should sweep and angle of not more than about 150°. The use of both curved gripping surface  150  and opposed gripping surfaces  130  allow for the gripper plate  100  to achieve better fit and conformity with the elongated object. In yet another embodiment, the opposed gripping surfaces  130  may extend outwardly from the endpoints of the curved gripping surface  150  to form ridges having a rather unique V-shape with a rounded bottom. This particular ridge design for the gripping portion  120  of the gripper block  10  is set forth and described in greater detail in U.S. Pat. No. 6,230,955 B1 to Parks. 
   Referring now to  FIG. 2 , a cross-sectional view of the gripper plate  100  is shown. The gripper plate  100  is usually constructed by casting, forging, or machining a single metal ingot formed of steel, titanium, or other suitable metal alloys. Note that the gripper plate  100  is shown to have an upper portion  102  with a generally V-shaped profile when viewed along the longitudinal axis and a lower portion  104  which is generally more box-like in shape and adapted to fit into an opening or recess  220  in the upper portion of block body  200 . It is understood that, although a box-like lower portion  104  is shown as fitted into a rectangular recess  220 , a number of alternative shapes and geometries may be used such as fitting a hemispherical lower portion into a cup-like recess. Again, the ridges  140  formed of alternating crests and roots that comprise the opposed gripping surfaces  130  of the gripper plate  100  are clearly visible. 
   Referring still to  FIGS. 1-3 , one embodiment of the block body  200  adapted to support the gripper plate  100  will be set forth and described. As shown here, the block body  200  has a form of tongue and groove design which allows the gripper blocks  10  to be connected end-to-end. By linking a number of these gripper blocks  10  together in series, it is possible to form a caterpillar-like chain which may be used as a gripper chain in a device for moving elongated objects, including coiled tubing, suitable for use in oil and gas applications. Although it is to be understood that the block bodies  200  may have any number of embodiments and be connected together in a number of different ways, this particular design allows the block bodies  200  to be easily fitted together and held one to another by two pins, not shown. The pins are fitted through openings  210  which extend laterally or transversally across the block body  200  near leading edge  202  and trailing edge  204  of the block body  200 . As with the gripper plate  100 , the block body  200  is generally formed of a single metal ingot which is cast, forged, or machined of steel, titanium, or other suitable metal alloys. 
   Referring still to  FIGS. 2-3 , a cross-section of the block body  200  is shown. The cross-sectional views permit a better look at the details of the generally rectangular recess  220  located in the central top portion of the block body  200 . The recess  220 , as shown here, features three smaller recesses or slots  230  extending downward into the block body  200 . Of course, the number and geometry of the slots  230  may be varied to suit differing applications or to address particular needs. 
   In use, the gripper plate  100  may be fitted into the recess  220  on the block body  200  and multiple block bodies  200  may be linked together by fitting pins through the openings  210  to form a gripper chain. However, in accordance with the present invention, the gripper block  10  will further comprise a flex layer  250  disposed between the block body  200  and the gripper plate  100 . In one embodiment, the flex layer  250  may be a polymeric elastomer such as rubber or the like which is fitted into the recess  220  on the top of the block body  200  prior to attaching the gripper plate  100 . This layer of rubber or elastomer may be about 5 to about 20 millimeters thick and will usually allow the gripper plate  100  to flex or move relative to the block body  200  in use. Of course, the amount of relative movement between the gripper plate  100  and the block body  200  and the amount of force required to induce this movement may be varied by controlling the mechanical properties and the choice of material used to create the flex layer  250 . 
   Typically, it is desirable to facilitate a relative movement between the gripper plate  100  and the block body of up to about 10 millimeters in any one direction. Although the magnitude of this movement would appear to be quite small, it is believed that this should be sufficient to reduce crimping or damaging coiled tubing as it varies in diameter and also to better accommodate fittings such as tapered connectors. As best seen in  FIG. 3 , the slots  230  at the bottom of the recess  220  formed in the block body  200  serve to provide voids into which the flex layer  250  may be forced or guided as loads are applied to the gripper plate  100 . In  FIG. 3 , the gripper plate  100  is rocked or tilted away from its neutral or resting position to show deformation of the flex layer  250  and the movement of an elastomer or an encapsulated fluid into the slots  230 . 
   In one embodiment, the flex layer  250  may actually serve to attach the gripper plate  100  to the block body  200  by selecting a polymeric adhesive compound having the requisite elastomeric properties, such as a natural or synthetic rubber based compound. It is noted that in various alternative embodiments it is possible to create a flex layer  250  with the desired elastomeric properties using a compressible or incompressible fluid which has been properly encapsulated. This may be carried out by disposing a layer of fluid between the gripper plate  100  and the block body  200  and then sealing it in place with a flexible seal about the perimeter of the gripper plate  100  and the recess  220  of the block body  200 . 
   Another alternative embodiment would be to create a flex layer  250  by encapsulating a fluid that is substantially incompressible within a flexible polymer membrane to create a small flexible cushion. In use, as loading is applied to the gripper plate  100 , it will tend to force the fluid into the slots  230  of the block body  200  thereby allowing the gripper plate  100  to flex or move slightly in any direction relative to the block body  200 . As noted earlier, small movements of the gripper plate  100  permit the gripper block  10  to engage elongated objects such as coiled tubing and to adapt to changes in the diameter without damaging the elongated object as it is handled. In this particular embodiment, the gripper plate  100  essentially floats atop the encapsulated fluid cushion of the flex layer  250  and is allowed to rock slightly forward, backward, or side-to-side relative to the block body  200  to which it is attached. 
   Referring now to  FIGS. 4-6 , a gripper block  20  similar to that shown in  FIGS. 1-3  has been modified for use in an alternative gripper block design. The gripper plate  300  has a generally V-shaped channel  310  when viewed along the longitudinal axis and has a gripping portion  320  further comprising a pair of opposed gripping surfaces  330  along its top surface. The pair of opposed gripping surfaces  330  are provided with a number of ridges  340  formed by alternating crests and roots. As before, the opposed gripping surfaces  330  are sloped or inclined toward each other at an angle of not greater that about 120°. Also, as noted above in regard to  FIGS. 1-3 , it is possible to have a curved gripping surface  350  to better accommodate small diameter elongated objects. In most embodiments, the curved gripping surface  350  will have a radius of curvature that sweeps though an angle of not more than about 150°. 
   As best seen in  FIG. 5 , the gripper plate  300  has an upper portion  302  for engaging elongated objects and a lower portion  304  having a generally rectangular box-like design to be fitted into a recess  420  on block body  400 . However, in this particular embodiment, the gripper plate  300  has two cylindrical bores or openings  306  formed in its lower portion  304  and extend upward into the gripper plate  300 . The openings  306  are intended to accommodate a pair of mechanical springs. Although shown here as a pair of cylindrical bores  306  intended to accommodate a pair of generally cylindrical coil springs  450 , it is understood that a number of other mechanical solutions are possible involving various numbers and configurations of coil springs and the use of flat or leaf-type springs as well. 
   The block body  400  is similar to that shown in  FIGS. 1-3 , although the recess  420  in the block body  400  has been changed. The three slots or voids  230  which were previously intended to accommodate flowable liquids or movement of elastomeric materials have been removed and replaced by two cylindrical depressions or openings  430  extending downward into the block body  400 . The openings  430  may be used to accommodate the pair of springs  450 . The springs  450  serve to act as a functional equivalent to the flex layer  250  of various elastomeric materials or fluids described earlier in regard to the embodiments shown in  FIGS. 1-3 . The block body  400  has a form of tongue and groove design which allows the gripper blocks  20  to be connected end-to-end. By linking a number of these gripper blocks  20  together in series, it is possible to form a caterpillar-like chain which may be used as a gripper chain in a device for moving elongated objects, including coiled tubing, suitable for use in oil and gas applications. Although it is to be understood that the block bodies  400  may have any number of embodiments and be connected together in a number of different ways, this particular design allows the block bodies  400  to be easily fitted together and held one to another by two pins, not shown. The pins are fitted through openings  410  which extend laterally or transversally across the block body  400  near leading edge  402  and trailing edge  404  of the block body  400 . 
   Similarly, the materials used and the stiffness of the springs  450  as well as other physical characteristics may be selected to provide sufficient stiffness to hold the gripper plate  300  in place atop the block body  400  yet, under the application of applied loads, allow the gripper plate  300  to move or deflect up to about 10 millimeters in any one direction. Although this amount of deflection seems rather small in magnitude, it is sufficient to allow the gripper plate  300  to deflect quickly and accommodate changing outer diameters in coiled tubing better than unitary prior art gripper blocks. It is believed that by incorporating the springs  450  it is possible to reduce crimping and other damage to coiled tubing and also better accommodate fittings such as tapered connectors. Additionally, it is believed that gripper blocks having a separate gripper plate and block body with a flex layer placed therebetween will also result in less stoppages to adjust gripper chains and tubing injector apparatus settings when varying diameter coiled tubing is used in oil and gas operations. 
   While a number of preferred embodiments of the invention have been shown and described herein, modifications may be made by one skilled in the art without departing from the spirit and the teachings of the invention. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations, combinations, and modifications of the invention disclosed herein are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is defined by the claims which follow, that scope including all equivalents of the subject matter of the claims.