Wells – Above ground apparatus – Moving tubing or cable into an existing well
Reexamination Certificate
2000-01-26
2001-04-17
Tsay, Frank (Department: 3672)
Wells
Above ground apparatus
Moving tubing or cable into an existing well
C166S085500, C166S385000
Reexamination Certificate
active
06216780
ABSTRACT:
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'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.
REFERENCES:
patent: 4655291 (1987-04-01), Cox
patent: 5553668 (1996-09-01), Council et al.
patent: 5566764 (1996-10-01), Elliston
patent: 5890534 (1999-04-01), Burge et al.
patent: 5918671 (1999-07-01), Bridges et al.
patent: 5975203 (1999-11-01), Payne et al.
patent: 6135202 (2000-10-01), Koshak
Goode John Edward
Graves Randall Scott
Steffenhagen Timothy Scott
Hubbard Marc A.
Hydra Rig, Inc.
Munsch Hardt Kopf & Harr P.C.
Tsay Frank
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