1. Field of the Invention
The invention relates generally to wellbore packer assemblies and, in particular aspects, to packer devices that are set within a wellbore by radial expansion.
2. Description of the Related Art
Traditional packers are comprised of an elastomeric sealing element and at least one mechanically set slip. Typically, a setting tool is run in with the packer to set it. The setting can be accomplished hydraulically due to relative movement created by the setting tool when subjected to applied pressure. This relative movement causes the slips to ride up on cones and extend into biting engagement with the surrounding tubular. At the same time, the sealing element is compressed into sealing contact with the surrounding tubular. The set can be held by a body lock ring, which would prevent the reversal of the relative movement that caused the packer to be set in the first instance.
As an alternative to applying pressure through the tubing to the setting tool to cause the packer to set, another alternative was to run the packer in on wire line with a known electrically-operated setting tool, such as an “E-4”-style setting tool that is available commercially from Baker Oil Tools of Houston, Tex. In setting the packer device, a signal fires the E-4 causing the requisite relative movement for setting. If the packer device is of a retrievable type, a retrieving tool could later be run into the set packer and release the grip of the lock ring and allow movement of the slips back down their respective cones and a stretching out of the sealing element so that the packer device can be removed from the well.
One problem with conventional packer devices arises from the use of elastomeric sealing elements in packer devices. Nitrile rubber and other elastomers tend to extrude from the packer device over time, particularly in high temperatures, thereby compromising their ability to maintain a fluid seal. Additionally, elastomers may react chemically with other chemicals present in the wellbore, thereby degrading their effectiveness. Certain thermoplastic polymers, such as TEFLON® and PEEK, are chemically inert and resistant to high temperatures, which would make them appear to be good candidates for use in creating fluid seals within a wellbore. However, these compounds are also substantially non-pliable, making it difficult to cause them to remain in an outwardly set position against the wall of a surrounding tubular.
A further problem with conventional packer designs is that the presence of ramps on the outer surface of a packer mandrel for setting the slips necessitates a reduction in the available interior bore diameter. As a result, some packer designs seek to create an engagement of packer element slips or wickers by direct radial expansion of the slips or wickers. Examples of such expandable packer designs are found in a parent application to this one, U.S. Patent Publication No. US 2005/0028989 A1. This Publication describes packer devices that are set by radially expanding an outer expansion mandrel in response to fluid pressure from the flowbore.
The inventors have recognized that there are difficulties inherent in mounting a separate slip component to the outside of the expansion mandrel. Merely placing the slip component to radially surround the expansion mandrel can lead to the slip component undesirably shifting with respect to the expansion mandrel during running-in. As a result, the slip component may not be properly seated upon the expansion mandrel during setting, and the wickers of the slips could become poorly anchored. Further, any abrupt change in the geometry of the outer surface of the expansion mandrel, such as sharp grooves or holes, creates a risk that the expansion mandrel could burst or otherwise fail during expansion. Thus, securing an outer slip component directly to the expansion mandrel using, for instance, screws that penetrate the expansion mandrel, would not be desirable.
The present invention addresses the problems of the prior art.