Actuation system with locking feature

Abstract

A technique facilitates use of an actuator with a locking feature enabling selective locking of the actuator in a desired operational position. For example, the actuator may comprise a mandrel which can be used to shift a tool between operational positions. The mandrel is surrounded by a housing which creates a cavity. A magneto rheological fluid is disposed within the cavity and operates in cooperation with the mandrel to enable selective locking of the mandrel at a desired operational position or positions. Magnetic field can be generated via an electromagnetic coil or a permanent magnet to selectively increase the viscosity of the magneto rheological fluid to lock the mandrel at the appropriate operational position.

What is claimed is: 
     
         1 . A system for controlling actuation, comprising:
 a tool string deployed in a wellbore, the tool string comprising:
 a shiftable device; and 
 an actuator having a mandrel slidably positioned through a housing and coupled with the shiftable device, the housing containing magneto rheological fluid in a manner such that shifting the mandrel with respect to housing causes movement of the magneto rheological fluid, the actuator further comprising a device for selectively establishing a magnetic field to change the viscosity of the magneto rheological fluid to resist movement of the mandrel relative to the housing. 
   
     
     
         2 . The system as recited in  claim 1 , wherein the shiftable device comprises a valve. 
     
     
         3 . The system as recited in  claim 1 , wherein the shiftable device is part of a multi-cycle circulation valve and wherein the tool string further comprises a milling tool. 
     
     
         4 . The system as recited in  claim 1 , wherein the actuator further comprises a spring member acting against the mandrel to bias the mandrel in a given direction. 
     
     
         5 . The system as recited in  claim 1 , wherein the mandrel comprises an orifice through which the magneto rheological fluid passes during shifting of the mandrel with respect to the housing. 
     
     
         6 . The system as recited in  claim 4 , wherein the device for selectively establishing a magnetic field comprises an electromagnetic coil or an electromagnetic coil and a permanent magnet. 
     
     
         7 . The system as recited in  claim 6 , wherein the mandrel is shifted against the bias of the spring member by establishing a sufficient fluid pressure at an opposite end of the mandrel. 
     
     
         8 . The system as recited in  claim 7 , wherein the shiftable device comprises a valve and the valve is opened and closed via shifting of the mandrel under the influence of either the sufficient fluid pressure or the force exerted by the spring member, the shifting being enabled while the coil is not energized and the magneto rheological fluid is in a lower viscosity state. 
     
     
         9 . The system as recited in  claim 8 , wherein the coil is energized to establish the magnetic field, thus locking the mandrel and the valve in an open state or a closed state via the increased viscosity of the magneto rheological fluid. 
     
     
         10 . A method for controlling actuation, comprising:
 providing an actuator with a shiftable mandrel;   operatively coupling the shiftable mandrel with a volume of magneto rheological fluid such that movement of the shiftable mandrel forces the magneto rheological fluid through an orifice;   connecting the mandrel to a well device which controls flow of fluid in a wellbore; and   selectively changing the properties of a magnetic field to change the viscosity of the magneto rheological fluid to and change a resistive force applied by the magneto rheological fluid to the mandrel.   
     
     
         11 . The method as recited in  claim 10 , further comprising applying the actuator and the well device downhole via a tool string. 
     
     
         12 . The method as recited in  claim 11 , further comprising using the tool string to perform a milling operation. 
     
     
         13 . The method as recited in  claim 12 , further comprising using the actuator to selectively actuate the well device between a milling mode and a circulation mode. 
     
     
         14 . The method as recited in  claim 13 , wherein selectively changing comprises using an electromagnetic coil, or using an electromagnetic coil and a permanent magnet to temporarily lock the mandrel and thus the well device in at least one of the milling mode or the circulation mode. 
     
     
         15 . The method as recited in  claim 10 , wherein operatively coupling comprises moving the shiftable mandrel through a cavity containing the magneto rheological fluid. 
     
     
         16 . The method as recited in  claim 15 , further comprising sealing the magneto rheological fluid within the cavity via a surrounding housing and a plurality of seals. 
     
     
         17 . The method as recited in  claim 14 , further comprising mounting the electromagnetic coil or the permanent magnet for movement with the shiftable mandrel. 
     
     
         18 . A system, comprising:
 an actuator having:
 a mandrel comprising an orifice; 
 a housing surrounding the mandrel to create a cavity; 
 a magneto rheological fluid disposed in the cavity such that movement of the mandrel relative to the housing forces the magneto rheological fluid through the orifice; and 
 an electromagnetic device selectively energized to increase the viscosity of the magneto rheological fluid in the cavity so as to resist movement of the mandrel relative to the housing. 
   
     
     
         19 . The system as recited in  claim 18 , further comprising a well device coupled to the mandrel and adjustable between operational positions via movement of the mandrel. 
     
     
         20 . The system as recited in  claim 19 , wherein the well device controls fluid flow in a downhole milling operation.