Downhole Apparatus Using Induction Motors with Magnetic Fluid in Rotor-Stator Gap

Abstract

In one aspect, an apparatus for use in a wellbore is disclosed that in one non-limiting embodiment includes an AC motor having a rotor and a stator with a gap between the rotor and the stator and a magnetic fluid in the gap that contains an electrically nonconductive fluid and magnetic nanoparticles.

1 . An apparatus for use in a wellbore, comprising:
 a motor having a rotor and a stator with a gap between the rotor and the stator; and   a magnetic fluid in the gap that contains an electrically nonconductive fluid and magnetic nanoparticles that increase magnetic permeability of the electrically nonconductive fluid.   
     
     
         2 . The apparatus of  claim 1  further comprising a pump driven by the motor. 
     
     
         3 . The apparatus of  claim 1 , wherein the magnetic nanoparticles are electrically nonconductive. 
     
     
         4 . The apparatus of  claim 1 , wherein the magnetic nanoparticles comprise a composition of AB 2 O 4 , wherein A is chosen from a group consisting of iron, manganese, cobalt, zinc, nickel and a combination thereof and B is iron. 
     
     
         5 . The apparatus of  claim 1 , wherein the magnetic nanoparticles include a core having an electrically-conductive magnetic material and a shell made from an electrically nonconductive material. 
     
     
         6 . The apparatus of  claim 5 , wherein the core includes a material selected from a group consisting of: a metal; nickel; iron; cobalt; and a combination thereof. 
     
     
         7 . The apparatus of  claim 1 , wherein the magnetic nanoparticles are suspended or substantially suspended in the electrically nonconductive fluid. 
     
     
         8 . The apparatus of  claim 1 , wherein size of the magnetic nanoparticles is selected from a group consisting of: less than 12 nm; and between 12 nm and 100 nm. 
     
     
         9 . The apparatus of  claim 1 , wherein amount of the magnetic nanoparticles in the magnetic fluid is selected to maintain an operating viscosity of the fluid in the gap between a desired range. 
     
     
         10 . The apparatus of  claim 1 , wherein the magnetic nanoparticles cause the magnetic fluid in the gap to move with magnetic field lines between the stator and the rotor to reduce friction loss caused by the electrically nonconductive fluid. 
     
     
         11 . The apparatus of  claim 1  further comprising:
 a reservoir that contains the magnetic fluid; and 
 a fluid circulation device that circulates the magnetic fluid in the motor. 
 
     
     
         12 . The apparatus of  claim 11 , wherein the circulation mechanism includes fins that cause the magnetic nanoparticles to mix with the electrically nonconductive fluid in the reservoir. 
     
     
         13 . A production system comprising:
 a production string in a wellbore including a tubing;   an electrical submersible pump that supplies a fluid from the wellbore to the tubing, wherein the electrical submersible pump includes:   a pump;   a motor having a gap between a stator and a rotor; and   a fluid in the gap that contains an electrically nonconductive fluid and magnetic nanoparticles that increase magnetic permeability of the nonmagnetic fluid.   
     
     
         14 . The apparatus of  claim 13 , wherein the magnetic nanoparticles are selected from a group consisting of: a material having composition of AB 2 O 4 , wherein A is selected from a group consisting of iron, manganese, zinc, cobalt, nickel and a combination thereof; and particles having an electrically-conductive core and an electrically nonconductive shell. 
     
     
         15 . A method of making an apparatus, comprising:
 providing a rotor inside a stator, with a gap between the rotor and the stator; and   filling the gap with a magnetic fluid.   
     
     
         16 . The method of  claim 15 , wherein the magnetic fluid includes an electrically nonconductive fluid and magnetic nanoparticles. 
     
     
         17 . A method of producing a fluid from a wellbore, the method comprising:
 deploying a string in the wellbore, the string including a pump driven by an motor, wherein the motor includes a rotor and a stator with a gap between the rotor and the stator and a magnetic fluid in the gap; and   operating the pump with the motor to produce the fluid from the wellbore.   
     
     
         18 . The method of  claim 17 , wherein the motor includes a fluid reservoir configured to circulate the magnetic fluid through the gap. 
     
     
         19 . The method of  claim 17 , wherein the magnetic nanoparticles are selected from a group consisting of: a material having composition of AB 2 O 4 , and particles having an electrically and magnetically-conductive core and an electrically nonconductive outer surface. 
     
     
         20 . The method of  claim 17 , wherein size of the magnetic nanoparticles is selected from a group consisting of: less than 12 nm; and between 12 nm and 100 nm.