1. Field of the Invention
The present invention relates generally to actuators used in subterranean wellbores, and specifically to actuators for use with subterranean wellbore tools which are operable in a plurality for operating modes and switchable between selected operating modes by application of axial force.
2. Description of the Prior Art
A variety of conventional wellbore tools which seal, pack, hang, and connect with or between concentrically nested wellbore tubular members are set into position by application of axial forces to the tool, such as, for example, by either lifting up on a tubular string to lessen the load on a tool, or by applying a selected amount of set down weight to the tubular string, to cause selected components to move relative to one another. For example, liner hangers frequently include slip and cone assemblies which are loaded to cause a portion of the assembly to come into gripping engagement with a selected wellbore surface. For alternative example, packers frequently include elastomeric sleeves which are compressed and energized to urge the sleeve into sealing engagement with a selected wellbore surface.
Of course, these types of wellbore tools require that operations usually performed at the surface cause an intended effect at a remote location deep within the wellbore, and in particular require that axial force be transferred effectively over great distances, even in difficult wellbores, such as deviated or spiral-shaped wellbores. Those knowledgeable about wellbore completion operations will appreciate that a force-transmitting tubular string may contact other wellbore tubulars or wellbore surfaces at a number of locations, dissipating the axial setting force which is intended for application at another location, and frustrating completion operations.
Another related problem with the prior art devices is that the wellbore tool may be unintentionally subjected to axial, or other, loads during running of the tool into the wellbore, which may cause unintentional setting of the tool in an undesirable or unintended location. Since many wellbore tools, such as liner hangers or packers, are designed to permanently lock in a set position, such as accidental setting can result in extremely expensive and time-consuming retrieval operations.
In prior art devices, the interconnected components which are intended, and engineered, to provide a permanent lock may, themselves, present operating problems, once the tool is disposed at a desired location within the wellbore, since they may either fail to operate properly during setting procedures, or to operate for the duration of the intended "life" of the tool. Failures can occur for a number of reasons, most of which are attributable to the harsh wellbore environments frequently encountered. The unsetting of wellbore tools which are intended for permanent placement can have disastrous financial and engineering consequences.