Not Applicable
Not Applicable
1. Field of the Invention
This application is in the field of devices used in the oil well drilling industry, for releasably connecting one tubular element to another tubular element or piece of downhole equipment.
2. Background Art
In the drilling, completion, production, servicing, and workover of oil and gas wells, it is often necessary to disconnect the work string from a downhole tool, or from a lower section of work string. The downhole tool might include a fluid production device, a drill motor, or a drill bit, or any other bottom hole assembly which might be lowered into the well bore on a work string. Regardless of the type of downhole tool, selective disconnection from the work string may become necessary.
For instance, the bottom hole assembly in use may become stuck in the well bore to such an extent that it is impossible to remove from the well bore. In that case, the operator usually must selectively part the work string from the bottom hole assembly, and remove the work string from the well. Then, other tools can be run into the well bore for removal of the stuck bottom hole assembly. These other tools might be devices for grappling and pulling on the bottom hole assembly, or for jarring the bottom hole assembly loose, or even for milling the bottom hole assembly away.
It is helpful to have a tubular disconnect device in the work string at the desired disconnect location, to allow a positive and predictable release of the bottom hole assembly from the work string. The disconnect device should be impervious to the stresses and strains generated by the bottom hole assembly, and it should not be subject to inadvertent separation or loosening. The well bore environment also often includes the presence of varying amounts of debris, which is usually borne by the fluid being pumped down through the work string or up through the annulus surrounding the work string. A disconnect device should operate reliably despite the presences of such debris.
Various tubular disconnect devices have been developed over the years to achieve this disconnection of the work string from a downhole tool. Some such tools use locking dogs to lock the work string and the downhole tool together. Others may use a grappling device. In either case, the locking dogs or the grappling device are often held in the lock position by a movable piston, with the piston being held in place by a shear pin. After a ball is dropped through the work string, the piston can be displaced by the buildup of working fluid pressure, shearing the shear pin, with the piston being subsequently moved to a position where the locking dogs or the grappling device are no longer held in the lock position. This allows release of the bottom hole tool from the work string, usually by pulling on the work string. Often, in these tools, the bottom hole tool may generate, or be subject to, significant vibrations. These vibrations are often transmitted through the tool into the shear pin, causing it to fail prematurely, thereby inadvertently releasing the downhole tool from the work string.
Another tool which has been used as a tubular disconnect device utilizes a collet finger, or a plurality of fingers, to hold the tool to the work string. An upper tool body is locked to a lower tool body by a sliding collet, with the collet finger being held in a locking groove on the lower tool body by a contour on a lower extension of the upper tool body. The work string is pulled upwardly, raising the upper tool body against the force of a spring between the upper tool body and the collet. When the upper tool body has raised sufficiently, the collet finger is allowed to spring free of the groove in the lower tool body, thereby releasing the lower tool body from the upper tool body. This tool can be released only when the downhole tool is held in place with sufficient force to allow the necessary overpulling of the upper tool body to compress the spring.
Another known tool has a first set of collet fingers which lock the upper tool body to the lower tool body, with the collet fingers being held in the locked position by the lower skirt of an inner piston. The inner piston is held in attachment to the upper tool body by a spring and a second set of collet fingers. After a ball is dropped through the work string, pressure builds up above the inner piston until an outer piston is displaced upwardly by the same fluid pressure to further compress the spring. Upward displacement of the outer piston allows the second set of collet fingers to release the inner piston from the upper tool body, after which the inner piston is driven downwardly by fluid pressure to release the first set of collet fingers, thereby releasing the lower tool body from the upper tool body. The construction of this tool is complicated and expensive, and its proper function depends upon the spring to withstand the jarring load, to prevent the outer piston from displacing sufficiently to inadvertently release the lower body.
Still another known tool has a main piston which holds a set of locking dogs in place, to lock the upper tool body to the lower tool body, with the main piston being held in place by a ball and detent mechanism. A pilot piston holds the ball in the detent, preventing movement of the main piston, with the pilot piston being held in place by shear pins. Dropping of a ball through the work string and application of fluid pressure above the pilot piston shears the shear pins, allowing the pilot piston to release the ball from the detent, resulting in downward movement of the main piston to release the locking dogs. The jarring and impact of high frequency devices on the work string can impart repetitive impact to the shear pins, ultimately resulting in failure of the shear pins and inadvertent release of the tool. Further, the locking dogs of this tool are positioned in cavities that are open to drilling fluids; the particulates carried by the drilling fluid can pack the locking dog cavities sufficiently to immobilize the locking dogs.
The present invention is a tubular disconnect device which has a collet held in place, relative to an upper body, by a set of outwardly biased collet fingers, or a shear pin and a set of collet fingers. The collet fingers are held in engagement with a groove by a movable piston, thereby preventing the application of any impact or force to the shear pin, where present. The collet holds a set of locking dogs in place, locking the upper body and a lower body together. The piston is biased upwardly away from the collet by a spring. Dropping of a ball through the work string allows application of fluid pressure above the piston, thereby compressing the spring. After sufficient compression of the spring and downward movement of the piston, the collet fingers are released, and the piston abuts the collet. Continued application of fluid pressure pulls the collet fingers out of their groove, and forces the collet downwardly, thereby freeing the locking dogs from engagement with the lower body, releasing the tool.
The collet can be sealed against the tool body to prevent contamination of the dog cavities with particulates in the drilling fluid. An adjustment sleeve can be provided to establish a rigid connection holding all the major body components in place, to prevent displacement during jarring operations. Where the shear pin is present, it maintains the collet in position after release of the collet fingers, until a higher fluid pressure shears the pin, giving the operator a positive indication that release of the tool has been achieved. However, the collet is actually held in place by the collet fingers, preventing application of impact to the shear pin. Since the collet fingers can not be released until the piston contacts the collet, the tool is highly resistant to inadvertent release.
The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which: