Downhole Apparatus Using Induction Motors with Magnetic Fluid in Rotor-Stator Gap
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.
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1. Field of the Disclosure
This disclosure relates generally to AC induction motors and to downhole apparatus that utilizes such motors, wherein a magnetic fluid is utilized between the rotor and stator to increase the efficiency of such motors.
2. Background of the Art
Wells (also referred to as “wellbores” or “boreholes”) are drilled in subsurface formations for the production of hydrocarbons (oil and gas). Wellbores often extend to depths of more than 5000 meters (over 15,000 ft.). Many such wellbores are deviated or horizontal. After a wellbore is formed, a casing is typically installed in the wellbore, which is perforated at hydrocarbon-bearing formation zones to allow the hydrocarbons to flow from the formation into the casing. A production string is typically installed inside the casing. The production string includes a variety of flow control devices and a production tubular that extends from the surface to each of the perforated zones. Some wellbores are not cased and in such cases the production string is installed in the open hole. Often, the pressure in the hydrocarbon-bearing subsurface formations is not sufficient to cause the hydrocarbons to flow from the formation to the surface via the production tubing. In such cases, one or more electrical submersible pumps (ESPs) are often deployed in production string to lift the hydrocarbons to the surface.
An ESP includes a pump driven by an AC induction motor. The rotor and stator of an AC Induction motor are separated by a gap that creates a magnetic field disconnect between the rotor and the stator, which generates a reluctance load within the motor and causes the stator to pull additional current. Additional current pulled by the stator makes the motor inefficient and also generates heat that increases the already high temperature of the motor in the wellbore, which temperature can exceed 300° F. In an AC induction motor, the highest reluctance and thus greatest loss of the magnetic field between the stator and the rotor is due to the gap between the rotor and stator because the medium in the gap (air in most AC induction motors with dielectric oil in most ESP AC induction motors) has low magnetic permeability. Therefore, increasing the magnetic permeability (i.e. reducing the reluctance) of the medium in the gap can improve the overall efficiency of an AC induction motor, reduce the heat generated by the motor and increase the overall efficiency and the operating life of the motor.
The disclosure herein provides apparatus and methods that in general improve the overall performance of AC induction motors, and particularly motors utilized in ESP pumps for downhole applications.
SUMMARYIn one aspect, an apparatus for use in a wellbore is disclosed that in one non-limiting embodiment includes an electric motor with a gap between a rotor and a stator and a magnetic fluid in the gap that contains an electrically nonconductive fluid and magnetic nanoparticles that increase the magnetic permeability of the gap.
In another aspect, a method of producing a fluid from a wellbore is disclosed that in one non-limiting embodiment may include: deploying a string in the wellbore that includes a pump driven by an electric motor that includes a magnetic fluid in a gap between a stator and rotor of the electric motor; and operating the pump with the electric motor to produce the fluid from the wellbore.
Examples of the more important features of the apparatus and methods of the disclosure have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features that will be described hereinafter and which will form the subject of the claims.
For a detailed understanding of the apparatus and methods disclosed herein, reference should be made to the accompanying drawings and the detailed description thereof, wherein like elements have generally been given like numerals and wherein:
In aspects, the magnetic fluid (270,
Referring to
The foregoing disclosure is directed to certain exemplary embodiments and methods. Various modifications will be apparent to those skilled in the art. It is intended that all such modifications within the scope of the appended claims be embraced by the foregoing disclosure. The words “comprising” and “comprises” as used in the claims are to be interpreted to mean “including but not limited to”. Also, the abstract is not to be used to limit the scope of the claims.
Claims
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 AB2O4, 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 AB2O4, 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 AB2O4, 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.
Type: Application
Filed: Dec 5, 2013
Publication Date: Jun 11, 2015
Applicant: BAKER HUGHES INCORPORATED (HOUSTON, TX)
Inventors: Carlos A. Prieto (Houston, TX), Deepak Kumar (Houston, TX), Bennett M. Richard (Kingwood, TX), Michael H. Johnson (Katy, TX)
Application Number: 14/097,992