Patent Application
20160369585
The field of the invention is retrievable packers or plugs and more particularly where the seal assembly can be unset before the slips are released to facilitate retrieval of the packer or plug.
Retrievable packers or plugs typically have a multi-element sealing system between upper and lower slips. When set mechanically with a known setting tool relative movement is created when the outer assembly of slips and the sealing system are pushed on while the setting tool pulls on the mandrel at the same time. Generally, the result is that the upper slips set and then the seal is axially compressed followed by the extension of the lower slips. The outer assembly features a lock ring that can hold the outer assembly is the compressed and set position. The release occurs when the lock ring that fixates the outer assembly with respect to the mandrel is defeated. Defeating the locking mechanism can occur with a mandrel pull that shears a retainer or with cutting the mandrel to allow the outer assembly to relax or by running a tool into the mandrel to forcibly defeat a shear device that holds the set of the outer assembly.
One potential problem with releasing the outer assembly components at the same time is the potential for binding the slips with the released rubber pressure in the sealing element assembly causing one of the slip assemblies to bind. One way to alleviate this problem is to provide a mechanism that is designed to relieve runner pressure on the seal assembly before releasing the slips. While that is the intention of the device shown in U.S. Pat. No. 8,291,989 FIG. 2B using engaged threads 75 and 76 and selectively raising a mandrel slot 78 into alignment with threads 75 to let fingers 73 flex toward the mandrel with the hope that a separation will occur, the reality is that the force holding threads 75 and 76 in the set position can be so strong such that aligning the slot 78 will still not result in a release of the pressure in the seal assembly 42. What is needed and provided by the present invention is a rubber pressure release system where mandrel movement takes with it initially a part of the outer assembly that underpins a lock for the set of the sealing system and provides a large space outside the mandrel for the force of the retained rubber pressure to forcibly push the locking member to retract in a radial direction by including a radial component of the release force toward the mandrel to promote lock retraction. The lock has a wedge pulled out from under it to allow it to flex toward the mandrel outer surface and to be pushed by the force of the relaxing seal assembly. These and other aspects 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 while understanding that the full scope of the invention is to be determined from the appended claims.
A retrievable packer has its sealing system unloaded before the slip system is relaxed by separation of slip cones from slips that flank the seal assembly. The mandrel is cut so that the portion above the cut can be raised to take a cone up and away from collet heads which previously were trapped by the cone. The collet heads are disposed between opposed sloping surfaces so that the retraction of the cone from under the heads allows the residual rubber pressure to force the heads toward the mandrel into the space created by relative movement of the mandrel that took the wedge cone uphole. The heads are at ends of fingers having a radially inward bias to further assist retraction of the heads toward the mandrel. With the heads retracted the sealing element stretches out before slip cones are moved relative to the slips.
Referring to
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The differences from the design in U.S. Pat. No. 8,291,989 are notable. The release movement occurs outside the mandrel 32 rather than a notch in the outer surface of the mandrel. The release comprises movement into a created space that is urged by the stored potential energy in the collet heads from fingers 46 and from the interaction of tapered surfaces on the heads 48 on opposed sides with adjacent surfaces to create a radial force toward the mandrel 32 due to the tapered surfaces abutting and the pushing form the seal assembly 12 relaxing. In essence the opposed tapers on the heads and the abutting surfaces take the axial force from the relaxation of the sealing assembly 12 and create a radial component of force toward the mandrel 32 as the heads retract into the newly formed space as ramp 62 is pulled away from ramp 70 to put all the above described parts into motion as explained above. These feature assure the release of the pressure in the sealing assembly 12 before further mandrel movement allows the slip assemblies 28 and 30 to retract. It is also notable that unlike the design in U.S. Pat. No. 8,291,989 the release of the seal assembly 12 does not entail relative axial motion of formerly meshing thread patterns. The setting force is held through heads 48 rather than the structurally weaker mating thread patterns in U.S. Pat. No. 8,291,989. Additionally, the heads 48 are far better isolated from debris in the borehole than in U.S. Pat. No. 8,291,989. The cavity into which the c-ring 75 in U.S. Pat. No. 8,291,989 is pushed has to be open to well fluid to avoid liquid lock as sleeve 72 moves up. Also item 75 in this patent is a split c-ring that can let in debris in the gap in the set position. This exposes the annular space within item 12 in FIG. B to debris buildup that can prevent release. The heads 48 move into a newly created space upon movement of mandrel 32 so that debris is effectively kept out of the location where the heads 48 need to move. The overlying sleeve 72 also keeps debris away from heads 48 insuring that they will operate to release the plug or packer 10 when needed.
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below:
