Patent Application
20080115929
The field of the invention is debris barriers for retrievable downhole tools and more particularly for mechanically set packers.
Packers are used downhole to isolate different zones. Some packers are made to be removed at a later time after being set in the well for what could be fairly long time periods. These packers are referred to as retrievable. They generally feature slips actuated by cones that are moved under the slips to move them out radially to support the packer. A sealing element assembly is between the upper and lower slips. In order to retrieve such packers the cone that wedges in a slip assembly has to be retracted from under the slip that it formerly wedged against a tubular. Usually, on mechanical set packers the mandrel is manipulated by tubing string rotation so that it pulls the cone out from under the upper slip assembly to allow the sealing element to relax as the packer extends so that it can then be pulled out.
Retrievable packers can be pressure set with applied pressure moving a piston that brings the cones of the slips together to move them out while compressing the sealing element. Mechanically set packers usually have drag blocks, which are spring energized members to give temporary support to the packer outer housing as a tubing string connected to the mandrel is manipulated by rotation. One style uses a j-slot so that the tubing can be turned and set down and the string weight applied to the mandrel sets the packer as the outer housing is supported on the drag blocks.
Pressure set retrievable packers, in the past, have recognized the need for a debris barrier above the upper slips. The solution offered in U.S. Pat. Nos. 6,302,217 and 6,112,811 involves a rubber ring on a slip ramp so that when a pressurized piston gets the packer parts moving, the upper slip riding on its respective ramp pushes out a rubber ring and wedges it into a gap against the surrounding tubular after it crests the slip ramp. In a variation, the debris barrier is initially held in a groove above and below a slip assembly and setting the slips with a pressurized piston forces the debris barrier ring out of its run in groove and up the slip ramp where it hopefully becomes wedged against the surrounding tubular.
While the design appears to address the problem on paper, it has many practical limitations. Directly forcing a ring to enlarge in diameter and move up an inclined ramp several issues are encountered. The ring as it enlarges in diameter can roll about its circumferential center line. If this happens it will move up the ramp unevenly leaving less than 360 protection and is also likely to rip before becoming wedged against the surrounding tubular. Another concern from this type of wedging action is that the debris barrier can be subjected to a wedging force that can be sufficient to extrude it, which can also result in a tear. If the ring is dependent of slip movement to ramp it out, any failure along the ramp can result in pieces of the ring acting as a brake on movement of the slip assembly up the ramp. As a result, a less than optimal grip is obtained and the set packer is exposed to the possibility of loss of grip.
While debris barriers have been offered in pressure set packers that rely on driving a setting piston to actuate the slips and sealing element, such barriers have not been available on mechanical set packers that are also designed to be retrievable. The present invention addresses this need in such packers with a design that can be simply retrofit on existing mechanical set retrievable packers. The design spaces the debris barrier from the slip assembly and keeps it energized while the packer is set. The barrier is retracted for run in and can be readily extended to bridge the gap to the surrounding tubular when the packer is set. These and other features of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings, recognizing that the full scope of the invention is indicated in the attached claims.
A debris barrier for a retrievable mechanical set packer is held retracted for run in. It is held spaced apart from upper slips and uses a spring bias that acts on the slips to keep them energized to also energize the barrier to the extended position to keep debris out of the upper slips when the packer is set. The debris barrier is preferably a sleeve that is axially compressed by the setting procedure to increase in diameter and span the gap between the packer mandrel and the set upper slips. Retrieving the packer is enabled by a retraction of the debris barrier as the upper slips are undermined with rotation and pickup force on the packer mandrel. The lack of a debris barrier could prevent retrieval of the packer in well bores where debris is present and has a tendency to settle around and more critically under the upper slips.
Those skilled in the art of mechanical set packers are presumed to be familiar with its major components and such components are depicted in the
In prior designs the spring 16 would bear on the top sub 12 on one end and on a slip assembly 18 shown in
The present invention modifies the existing mechanical set packer design by adding a ring 20 secured to top sub 12 at thread 22. A lower ring 24 has a bottom shoulder 26 on which spring 16 bears. For run in, the position of lower ring 24 is retained with respect to top sub 12 with a shear pin 28. The debris barrier 30 is preferably a sleeve that has captured ends 32 and 34 respectively by rings 20.and 24. Setting down weight on top sub 12 closes gap 36 as the shear pin 28 breaks. When that happens, the spring 16 that becomes more compressed as the setting of the packer proceeds pushes ring 24 uphole as ring 20 is moved downhole due to the setting down weight. The debris barrier 30 simply collapses as its ends 32 and 34 are brought toward each other and are biased toward each other by the action of spring 16. As shown in
The above description is illustrative of the preferred embodiment and various alternatives and is not intended to embody the broadest scope of the invention, which is determined from the claims appended below, and properly given their full scope literally and equivalently.
