Magnetic downhole tool and related subassemblies having mu-metallic shielding

Abstract

Systems and related methods are disclosed that involve the use of a magnetic downhole assembly or a magnetic downhole tool. The assembly and tool include a mu-metal sleeve that is operable to isolate a magnetic field and a permanent magnet disposed within the mu-metal sleeve. The assembly and tool also include an actuator that is operable to selectively extend and retract the sleeve to alternatingly expose and shield the permanent magnet. A conveyance is operable to deploy the magnetic downhole assembly and tool to a selected location within a wellbore and a controller is communicatively coupled to the actuator and operable to generate a control signal that causes the actuator to extend or retract the permanent magnet from the mu-metal sleeve.

We claim: 
     
         1 . A system of operating a magnetic downhole assembly comprising:
 a magnetic downhole assembly having a shielding sleeve operable to isolate a magnetic field, a permanent magnet disposed within the shielding sleeve, and an actuator, the actuator being operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet;   a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore; and   a controller communicatively coupled to the actuator and operable to generate a control signal.   
     
     
         2 . The system of  claim 1 , wherein the shielding sleeve comprises a mu-metal. 
     
     
         3 . The system of  claim 1 , wherein the actuator is selected from the group consisting of a hydraulic actuator, an electric actuator, and a mechanical actuator. 
     
     
         4 . The system of  claim 1 , further comprising:
 a tubing segment having a fluid flow path therethrough;   a reservoir coupled to the controller and having a magnetorheological fluid disposed therein, the reservoir being operable to disperse the magnetorheological fluid into the fluid flow path in response to the control signal.   
     
     
         5 . The system of  claim 4 , further comprising a pressure sensor coupled to the controller, wherein the magnetic downhole assembly is operable to extend the permanent magnet adjacent the fluid flow path to generate a magnetic field across the fluid flow path in response to the control signal, and wherein the controller is operable to generate the control signal in response to determining that a pressure at the pressure sensor is increasing at a rate that is greater than a predetermined rate. 
     
     
         6 . The system of  claim 1 , further comprising a tubing segment and a reservoir coupled to the controller, wherein the reservoir comprises a magnetorheological fluid disposed therein, and wherein the reservoir is operable to disperse the magnetorheological fluid adjacent the magnetic downhole assembly between an exterior surface of the tubing segment and a wellbore wall in response to the control signal. 
     
     
         7 . The system of  claim 6 , wherein the magnetic downhole assembly is operable to extend the permanent magnet to generate a magnetic field about the external exterior surface of the tubing segment in response to the control signal. 
     
     
         8 . A magnetic downhole tool comprising:
 a mu-metal sleeve operable to isolate a magnetic field;   a permanent magnet disposed within the mu-metal sleeve; and   an actuator, the actuator being operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet.   
     
     
         9 . The magnetic downhole tool of  claim 8 , wherein the mu-metal sleeve comprises a plurality of layers of mu-metal. 
     
     
         10 . The magnetic downhole tool of  claim 9 , wherein the layers of mu-metal are separated by at least one insulating layer. 
     
     
         11 . The magnetic downhole tool of claim  21 , wherein the actuator is selected from the group consisting of a hydraulic actuator, a solenoid, and a mechanical actuator. 
     
     
         12 . A method of operating a magnetic downhole tool, the method comprising:
 providing a magnetic downhole tool comprising a mu-metal sleeve operable to isolate a magnetic field, a permanent magnet disposed within the mu-metal sleeve, and an actuator, the actuator being operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet;   providing a controller, the controller being communicatively coupled to the actuator; and   generating a control signal to cause the actuator to extend or retract the metal sleeve.   
     
     
         13 . The method of  claim 12 , wherein the mu-metal comprises a nickel-iron alloy. 
     
     
         14 . The method of  claim 12 , wherein the step of generating the control signal is selected from the group consisting of generating a hydraulic control signal, generating an electric control signal, and generating a mechanical control signal. 
     
     
         15 . The method of  claim 12 , further comprising coupling the magnetic downhole tool to a conveyance and positioning the downhole tool at a selected location in a wellbore, wherein the conveyance is selected from the group consisting of a slickline, a wireline, and a tool string. 
     
     
         16 . The method of  claim 12 , further comprising exposing the permanent magnet to control the viscosity of a magnetorheological fluid. 
     
     
         17 . The method of  claim 12 , further comprising exposing the permanent magnet to remove a plug from a wellbore casing. 
     
     
         18 . The method of  claim 12 , further comprising exposing the permanent magnet and manipulating the magnetic downhole tool to adjust the position of a screen. 
     
     
         19 . The method of  claim 12 , further comprising exposing the permanent magnet and manipulating the magnetic downhole tool to adjust the position of a second downhole tool. 
     
     
         20 . The method of  claim 12 , further comprising exposing the permanent magnet to couple permanent magnet to a second downhole tool, delivering the second downhole tool to a selected location, and retracting the permanent magnet.