Patent Publication Number: US-6216780-B1

Title: Coiled tubing injector with improved traction

Description:
FIELD OF THE INVENTION 
     The invention pertains generally to apparatus for running coiled tubing in and out of bores, particularly coiled tubing injectors. 
     BACKGROUND OF THE INVENTION 
     Continuous pipe, generally known within the oil and gas industry as coiled tubing because it is stored on a large reel, has been used for many years. It is much faster to run into and out of a well bore than conventional jointed straight pipe. There is no need to connect and disconnect short segments of straight pipe. 
     The only method by which a continuous length of tubing can be either forced against pressure into the well, or supported while hanging in the well bore or being lowered or raised, is by continuously gripping a length of the tubing just before it enters the well bore. This method is typically practiced by arranging two continuous chain loops with extended parallel sections on opposite sides of the tubing, in an opposing relationship. Each continuous chain carries a series of gripping elements. As each chain turns, the gripping elements come together on opposite sides of the tubing. A pair of skates, which include a long, straight and rigid beam that forces the grippers against the opposite sides of the tubing. The skates are pulled toward each other by hydraulic pistons or a similar mechanism to force the gripper elements against the tubing. Examples of coiled tubing injectors include those shown and described in U.S. Pat. No. 5,309,990, and U.S. applications Ser. Nos. 091070,592 and 09/070,593, all of which are incorporated herein by reference. 
     Coiled tubing has traditionally been used primarily for circulating fluids into the well and other work over operations, rather than drilling, because of its relatively small diameter and because it was not strong enough, especially for deep drilling. In recent years, however coiled tubing has been increasingly used to drill well bores. For drilling, a turbine motor is suspended at the end of the tubing and is driven by mud or drilling fluid pumped down the tubing. Coiled tubing has also been used as permanent tubing in production wells. These new uses of coiled tubing have been made possible by larger, stronger coiled tubing. 
     In order to handle larger, longer, and heavier tubing, the gripping force must be increased. Increased gripping force can be achieved by increasing the force pressing the gripper shoes against the tubing, the number of gripper shoes contacting the pipe, increasing the length of the chains, or the contact area of the gripper shoe. Increased gripping force can also be achieved through improving the gripping surfaces. 
     One problem with applying greater forces to the tubing is that dimensional variations of the components of the injector that are within manufacturing tolerances may nevertheless result in uneven gripping force applied to the tubing. For example, the position of a gripper element relative to the tubing may vary as the gripper elements moves on the injector&#39;s skate due to dimensional variations in the skate and rollers on which the gripper elements roll on the skate. Similarly, the position of the gripper element relative to the other gripper elements may also vary due to dimensional variations between the gripper elements, the elements of the chain and the elements used to attach the gripper element to the chain. The result of these dimensional variations is an uneven application of gripping force along the length of the tubing that is in the injector, resulting in less than maximum potential gripping force and less than satisfactory performance. The uneven application of force also results in excess stress placed on the tubing because all of the gripping force is being applied by certain grippers rather than distributed among all of the grippers. This excess force may cause undesirable deformation of the tubing. Excess stress and the strain associated with the deformation weakens the tubing and hastens its failure. 
     SUMMARY OF THE INVENTION 
     One objective of the invention is a coiled tubing injector that more evenly applies gripping force to tubing running through the injector, thereby overcoming the problems found in the prior art. Another object of the invention is a coiled tubing injector that is capable of applying a greater gripping force to tubing without damaging the tubing. 
     According to one aspect of the invention, dimensional variations in the elements of an injector that apply a gripping force to tubing are accommodated through a skate comprising a beam and a plurality of rollers mounted to the beam through a resilient pad. The beam applies a force to the rollers through the resilient pad, which in turn applies a force to gripper elements mounted to a rotating, continuous chain. The resilient material compresses to accommodate variations in the dimensions of the skate, rollers and gripper elements so that gripping surfaces of all gripper elements are better aligned with each other as they are pressed against the outside of the tubing, resulting in more even application of forces by each of the gripping elements against the tubing. 
     In one embodiment of the invention, a plurality of rollers are mounted to each of a plurality of carriers, and the carriers are retained on the beam, with resilient material between the carrier and the skate. Mounting a plurality of rollers on a carrier provides lateral stability while allowing close spacing between the rollers, as compared to a roller carrier with only one roller. The carriers and pad are slid into a slot formed along the length of the beam. This arrangement further permits limited twisting of the carrier against the resilient material in order to accommodate variations in the surface of the gripper element that rides on the rollers. The arrangement is also easy to install and maintain. 
     Another feature the invention solves a problem that arises when injectors are used to apply very large forces against tubing. A gripper element mounted on a chain in an injector must, as it moves past a sprocket on which the chain is mounted, turn to align with the tubing. At the point at which the gripper element rolls over a first roller of a skate, it is not aligned with the tubing. It must therefore pivot about the roller. Because the gripper element is rigid, its leading edge will extend into the path of the tubing as it is pivoting into alignment. The tubing will push against the gripper element, trying to force it to pivot into alignment. When applying large gripping forces to the chain, the tension in the chain is so high that the gripper element pinches the tubing, causing it to deform. The resulting strain will tend lead to premature failure of the tubing. 
     To solve this problem one embodiment of an injector in accordance with this aspect of the invention includes a skate, on which is mounted a plurality of rollers over which gripping elements roll. An end roller, rather than being mounted to the skate, is mounted on one end of a pivoting arm, which allows the roller to deflect away from the tubing. The arm is resiliently biased, such as by a spring, against the tension in the chain. However, it will deflect as the gripper element begins to pinch the tubing: the roller gives rather than the tubing. 
     These and other aspects and advantages of the invention will be apparent from the following detailed description of one or more embodiments of the invention, which are illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a coiled tubing injector. 
     FIG. 2 is a front, elevational view of the coiled tubing injector of FIG. 1, placed within a cage for transport but with a front panel of its case and other components removed to reveal certain internal structures. 
     FIG. 3 is a perspective view of a skate for the coiled tubing injector of FIGS. 1 and 2. 
     FIG. 4 is a side, elevational view of a portion of the coiled tubing injector of FIGS. 1 and 2 showing details of two gripper chains and skates, with several elements removed for clarity. 
     FIG. 5 is section through the skates and gripper chain of FIG. 4, taken along section line  5 — 5  in FIG.  4 . 
     FIG. 5A illustrates a portion of FIG. 5 on a larger scale. 
     FIG. 6 is a side view of a portion of the skate and gripper chain for the coiled tubing injector of FIGS. 1-4, with the gripper chain in a first position. 
     FIG. 7 is a side view of the gripper chain of FIG. 6 in a second, subsequent position. 
     FIG. 8 is a side view of the gripper chain of FIG. 6 in a third, subsequent position. 
     FIG. 9 is a perspective view of a pivoting roller assembly for the ends of the skates of the coiled tubing injector of FIGS.  1 - 8 . 
    
    
     DETAILED DESCRIPTION 
     In the following description, like numbers refer to like parts. 
     FIGS. 1 and 2 illustrate one embodiment of a coiled tubing injector  100 . FIG. 1, but not FIG. 2, includes a front panel  106   a  of a case generally designated as  106 . The front panel of the case has been removed in FIG. 2 for illustrating certain internal structures. Furthermore, in each figure, a gripper chain is not show in order to view other details of injector. The case also includes a front panel  106   a , a back panel  106   d , and side panels  106   b  and  102   c.    
     Mounted in the case are two sets of sprockets. Sprockets  108   a  and  108   b  support one continuous roller chain on which the gripper elements are mounted (sometimes referred to as a gripper chain which is not shown. Sprockets  110   a  and  110   b  support a second gripper chain, which is also not shown. Sprockets  108   a  and  108   b  are mounted on axle  112  for rotation. Sprockets  110   a  and  110   b  are mounted on a drive shaft that is not visible in FIG. 1 or shown in FIG.  2 . The drive shafts transmit power to the sprockets to turn the gripper chains. Each end of the axles on which sprockets  108   a  and  110   a  are mounted turn in bearings that are mounted in a sliding block  114 . Each of the blocks  114  is keyed to slide along the inside edges of openings  116 , which are formed in the front panel and back panels  106   a  and  106   d  of case  106 . The drive shafts, on which sprockets  108   b  and  110   b  are mounted, are supported on one end by bearings mounted in a fixed (as opposed to sliding) fashion to the front and back panels of the case  106 . Pocket  118 , on the front panel  106   a , carries one set of bearings for one end of the shaft for sprocket  108   b . A similar pocket on the back panel carries bearings for the opposite end of the shaft for sprocket  110   b . The other ends of the drive shafts are supported by another set of bearings that cannot be seen in these views. 
     Mounted on the same shafts as sprockets  108   b  and  110   b  are a set of timing gears  120   a  and  120   b . The timing gears ensure synchronous rotation of the sprockets. The axles of sprockets  108   b  and  110   b  are coupled through transmissions  122   a  and  122   b , respectively, to low speed, high torque, hydraulic motors that are not shown. Sprockets  108   a  and  110   a  are free to turn. 
     Between a top of each sliding block  114  and a top of each slot  116  is a hydraulic jack or cylinder  117 . The jacks are used to move the axles of sprockets  108   a  and  110   a  downwardly, thereby applying greater tension to a gripper chain mounted on the sprockets. 
     Referring now to FIGS. 1,  2  and  3 , inside case  106  are mounted two, opposing skates that are generally designated as  124   a  and  124   b . Each skate  124   a  and  124   b  includes a stiff beam  126   a  and  126   b , respectively. Behind each beam are a series of cross bars that extend from the front to the back of the case. Upper cross bars  128   a  and  128   b  and lower cross bars  132   a  and  132   b  are located at opposite ends of the beam. Cross bars  130   a  and  130   b  are further used to suspend or hang the skates within the case  106 . Each cross bar is connected to a flange that extends through opening in the front and back panels of the case  106 . Each flange is pivotally connected through a set of pins to one end of a hydraulic cylinder  136 . The hydraulic cylinders, which are seen in FIG. 1, pull together each pair of cross bars, thereby pulling together the skates. As the skates are pulled together, they will press gripper chains (not shown in these figures; see FIG. 4) against tubing that is between the skates. Flanges  134 , which are at the ends of the top and bottom cross bars  128   a  and  128   b , and  132   a  and  132   b , a free to move laterally within slots  138  to accommodate movement of the skates back and forth. Flanges  140 , which are at the ends of cross bars  130   a  and  130   b , includes a disk  142  that forms a journal for turning within block  144 . Block  144  slides along slots  146 , which are defined in the front and back panels of the case  106 . The journalled disk permits the skates to rotate slightly about their midpoints within the case. 
     On the side of each beam  126   a  and  126   b  that faces the other beam are mounted a plurality of rollers  148 . Referring now to FIGS. 3,  4 ,  5  and  5   a , the rollers are retained on the beam in a manner that permits them to float: that is, their movement is constrained with respect to the beam to a limited range of motion. In the illustrated embodiment, the plurality of rollers are mounted for rotation on a plurality of roller carriers  150 , which in turn are retained on the beam in a manner that permits limited lateral movement and rotation. As seen best in FIG. 5 a , each roller  148  turns on an axle  152 . Each axle  152  is mounted through openings in parallel flanges  154  of one of the roller carriers  150 . 
     Each carrier  150  includes a pair of flanges  156 . To retain the roller carriers, each beam has an elongated, vertical slot  157  in which the carriers are stacked. Also formed along the beam is a set of vertical grooves  158 , which face inwardly, toward each other, to receive outwardly extending flanges  156  of the carriers  150 . The slot and grooves are open at one end of each beam so that the carriers can be dropped into the slot for easy installation and removal. The thickness of the flanges  156  are less than the widths of the grooves  158 , thereby allowing the carrier to move laterally a limited distance and to rotate slightly with respect to the beam. Alternately, the roller carriers may have, for example, inwardly facing flanges that engage outwardly facing grooves on the beam or that wrap behind the beam. As a further alternative, the grooves on each of the beams can, in effect, be inverted and replaced with a ridge or similar raised element that mates with a complementary groove or recessed element formed on the roller carrier. 
     Referring now only to FIGS. 4,  5  and  5   a , a pad  160  comprised of a resilient material is located between each beam and the carriers  150  mounted on the beam. The pad can be slid into slot  157  for easy installation and removal. The resilient pad, which runs the length of beam behind the roller carriers, permits the roller carriers to be displaced laterally toward the beam against a spring force. The resilient pad generates a large spring force when compressed. The manner in which the roller carriers are mounted to the beam pad also permits the carriers to rock, such that one roller can be displaced more than the other roller on the same carrier. 
     Gripper chains  162   a  and  162   b  each include a plurality of gripper elements  164  mounted on a roller chain. The gripper elements are shaped to grip tubing  166  as it passes between the skates  124   a  and  124   b . Each roller chain is formed by plurality of pin link plates  170 , link plates  172 , and rollers  174 . Each pin link plate includes two integrated pins  170   a  and a link plate  170   b . Rollers  174  are mounted on each end of each pin  170   a , between a set of link plates. The pin also acts to retain the gripper element  164  on the chain by passing through the gripper element. 
     A back side of the gripper elements  164  roll on rollers  148  as they move across the skates. Small variations in the dimensions of each gripper element  164 , roller carrier  150 , and rollers  148 , as well as variations in the dimension of the beams  126   a  and  126   b  along their respective lengths may result in a disproportionate application of force to tubing  166 . Even though each element may be made to within acceptable manufacturing tolerances, the sum of the variations may result for a given gripper element at any given location along the skate in it a gripper element sticking out further toward the pipe than other gripper elements, thereby making it difficult to apply force to other gripping elements. At very high gripping pressures, the tubing may be deformed because of the unequal distribution of the load of the gripping forces. The strain of deformation will tend to lead to premature failure of the tubing, and may even damage the tubing. However, the resilient pad  160  between each of the beams  126   a  and  126   b  and the roller carriers  150  mounted on the respective beams will instead resiliently deform to the extent necessary. More gripper elements will therefore contact the tubing with the desired pressure, resulting in improved gripping of the tubing. 
     Although each roller carrier is shown with two rollers, one or more than two rollers could be used. Two carriers provides a wide base but allows for close spacing of the rollers and relatively fine accommodation of dimensional variations in the gripper chain along the length of the skate. Carriers with only a single roller can be used, but with a smaller base or wide spacing. Carriers with more than two rollers become long and are less able to accommodate dimensional variations that may be present between adjacent gripper elements. 
     Referring now to FIGS. 2,  3 ,  4 , and  6  through  9 , at each end of skates  124   a  and  124  is mounted a pivoting roller assembly  176 . The pivoting roller assembly includes a roller  178 . The roller and a bracket  179  are mounted to one end of swing arm  180 . The swing arm pivots about the end of fixed arm  182 . Fixed arm  182  is attached to mounting  184 . Extending from the bracket  179  are pins  186 , on which are stacked spring washers  188 . The stacked spring washers act as a spring to bias the roller away from the beam. The purpose and function of the pivoting roller element is to allow the first and last rollers on the skate to deflect away from pipe as each gripper element  164  engages and disengages tubing. When each gripper element turns into, or out of, alignment with the plane of the skate, it pivots on the last roller of the skate, namely roller  178 . During pivoting an edge of the gripper element it will tend move toward the axis of the tubing as the gripper element pivots on the roller. Without a deflection of the pivoting roller element, this pivoting of the gripper element would tend to cause the edge of the gripper element to dig into the tubing, momentarily deforming it. However, with the pivoting roller assembly, the tubing pushes back the roller  178 , against the force of the spring washers  188 , as the gripper element pivots. The stack of spring washers are compressed the distance necessary to allow a gripper element to pivot into alignment under a force that does not place undue or excess strain on the tubing. Because the spring washers will already be compressed under the load imposed by the tension in the chain, the spring constant of the stack of spring washers with this load should allow further compression to provide the clearance of the gripper elements under a force that avoids or reduces placing undue strain on the tubing. 
     The forgoing description is made in reference to exemplary embodiments of the invention. However, an embodiment may be modified or altered without departing from the scope of the invention, which scope is defined and limited solely by the appended claims.