Electric submersible pump motor stabilized by electromagnetics

An electric submersible pump (ESP) that has a motor section for driving the ESP. The motor section has a stator has an inner surface, winding channels disposed axially therein and windings disposed in the winding channels to generate an electromagnetic field when power is supplied to the ESP. The motor section also has a rotor rotatably disposed in the stator. The rotor has permanent magnets or induction windings disposed therein that are responsive to the electromagnetic field to facilitate rotation of the rotor relative to the stator. The motor section also includes a manipulated air gap disposed between the rotor and the stator that the electromagnetic field crosses. The manipulated air gap provides a desired constant radially directed load on the rotor to stabilize the rotor when instability of the motor section occurs. A method of designing and constructing the ESP disclosed herein. To design and construct the ESP, a desired constant radially directed load is determined for an electric submersible pump (ESP) to stabilize the ESP when instability of an electromagnetic field of the ESP occurs. The air gap is manipulated to achieve the desired constant radially directed load or the design of a stator of the ESP is manipulated to achieve the desired constant radially directed load. The ESP can then be constructed.

STABILIZED BY ELECTROMAGNETICS STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The present disclosure relates to an electrical submersible pump (ESP) using electromagnetics to stabilize portions of the ESP for increased reliability.

2. Description of the Related Art

ESPs are commonly used in the oil industry to provide artificial lift in wells where pressure is insufficient to produce oil to the surface. ESPs are supported by hydrodynamic bearings and can experience radial and axial loads during operation. Hydrodynamic bearings operate with a thin layer of lubricating oil between stationary and rotating sections of the bearings. The radial and axial loads can cause certain parts of the ESPs to become unstable under certain speeds and loads, which can cause the rotating parts of the bearings to come in contact with the stationary parts of the bearings. Rotating and stationary components of the bearing are separated by a layer of lubricating oil. The oil creates pressures through shear forces that separate the rotating “bearing sleeve” or “journal” from the stationary “bearing”. If the oil pressure that creates the separating force collapses or is overcome then the rotating and stationary parts make contact and damage each other.

A pre-load is a stationary force vector in the radial direction and aids in aligning the shear forces of the oil to yield stable pressures thus reducing the possibility of bearing contact. When the shaft is oriented horizontally, the force of gravity provides the stationary force vector for pre-load, but that force is negated when the motor orientation positions the shaft vertically. Accordingly, there is a need for an ESP that has a constant pre-load force to prevent bearing instability and increase the life of ESPs.

SUMMARY OF THE DISCLOSURE

The present disclosure is directed toward an electric submersible pump (ESP) that has a motor section for driving the ESP. The motor section has a stator has an inner surface, winding channels disposed axially therein and windings disposed in the winding channels to generate an electromagnetic field when power is supplied to the ESP. The motor section also has a rotor rotatably disposed in the stator. The rotor has permanent magnets or induction windings disposed therein that are responsive to the electromagnetic field to facilitate rotation of the rotor relative to the stator. The motor section also includes a manipulated air gap disposed between the rotor and the stator that the electromagnetic field crosses. The manipulated air gap provides a desired constant radially directed load on the rotor to stabilize the rotor when instability of the motor section occurs.

The present disclosure is also directed to a method of desiging and constructing the ESP disclosed herein. To design and construct the ESP, a desired constant radially directed load is determined for an electric submersible pump (ESP) to stabilize the ESP when instability of an electromagnetic field of the ESP occurs. The air gap is manipulated to achieve the desired constant radially directed load or the design of a stator of the ESP is manipulated to achieve the desired constant radially directed load. The ESP can then be constructed.

DETAILED DESCRIPTION OF THE DISCLOSURE

Referring now to the drawings,FIG.1and the present disclosure is directed to an electrical submersible pump (ESP)10that includes a centrifugal pump12driven by a motor section14that is stabilized using electromagnetics. The ESP10can also include a seal section16that separates the motor section14from centrifugal pump12to equalize internal pressure of lubricant within the motor section14to the pressure of the wellbore.

FIG.2shows the motor section14of the ESP10. The motor section14includes a stator18, at least one rotor20rotatably disposed within the stator18and a shaft22that extends at least partially through the rotor20(and motor section14) and the stator18. The shaft22also extends through the seal section16and at least partially into the centrifugal pump section12to operate various parts of the centrifugal pump section12. The shaft22is securely disposed to the rotor20so that when the rotor20turns in the stator18, the shaft22turns as well. The ESP10also includes bearing assemblies24that support the shaft22that extend out of the rotor20, or between rotors20if there are more than one, and through the bearing assemblies24. The rotors20, the stator18and the bearing assemblies can be disposed inside a housing26.

Referring now toFIGS.3A and3B, shown therein is an exemplary bearing assembly14. The bearing assembly24can include a bearing housing28with a bearing sleeve30disposed therein. The bearing sleeve30is designed such that the shaft22can extend therethrough and have a clearance volume disposed between the shaft22and the bearing sleeve30wherein a lubricant can be disposed between the bearing sleeve30and the shaft22and between the bearing sleeve30and the bearing housing28. The lubricant disposed between the bearing sleeve30and the shaft22creates a hydrodynamic bearing and facilitates the controlled rotation of the shaft22. The bearing sleeve30is allowed to rotate within the bearing housing28. The shaft22can also have a sleeve attached thereto that rotates within the bearing sleeve30. It should be understood and appreciated that any type of bearing used with ESPs can be implemented with the ESP10disclosed herein.

FIGS.4A-4Dshow a cross sectional views of a part of the stator18, the rotor20and the shaft22. An air gap32is shown disposed between an outside portion34of the rotor20and an inner surface36of the stator18. The rotors20, via permanent magnets and/or induction windings, and the stator18, via windings disposed therein, can be magnetized to create an electromagnetic field that crosses the air gap32. This electromagnetic field generates torque between the stator18and the rotor20, which causes the rotor20to rotate relative to the stator18.FIG.4Ashows a typical symmetrical air gap38, the electromagnetic forces between the rotor20and stator18are balanced radially about the rotor20and therefore there is no constant load dominate in any direction and permits damage to the bearing assemblies24when instability occurs in the oil film of the bearing which can be excited by imbalance loads during operation of the ESP10. The imbalanced load on the shaft22, via the rotor20, can cause the bearing sleeve30to be forced through the lubricant in the bearing assemblies24and make physical contact with the bearing housing28, which shortens the operable life of the bearing assemblies.

In various embodiments of the present disclosure, the rotor20and stator18of the ESP10are designed in such a way to create a magnetic field across the air gap32that generates a radial force on the rotor20that is stationary relative to the stator18while the ESP10is operational. The radial force on the rotor20that is stationary relative to the stator18is a constant load on the rotor20and thus the shaft22that is secured thereto. The constant load on the rotor20and shaft22prevents imbalanced loads caused by operation of the ESP10from causing as much damage to the bearing assemblies24as would occur without the constant load. The constant loads can be generated by manipulating the geometric shape of the air gap32. In one exemplary embodiment,FIG.4Bshows an eccentric air gap40, which is created by positioning the rotor20closer to one part the inner surface38of the stator18than others. Where the eccentric air gap40is narrower, a higher radial force is generated relative to the stator18. In this embodiment, the outer diameter of the rotor20and the inner diameter of the stator18are circular.

In another embodiment shown inFIG.4C, the ESP10has a flat-in air gap42wherein a portion of the inner surface36of the stator18has a flat section44that is closer to the rotor20than any other part of the inner surface36of the stator18. The flat section44can be along the entire length of the stator18, it can extend only a certain length of the stator18or there can be multiple flat sections44disposed on the inner surface36of the stator18. In one embodiment, if the inner surface36of the stator18has multiple flat sections44disposed thereon, the flat sections44would be in line in the axial direction on the inner surface36of the stator18.

In yet another embodiment shown inFIG.4D, the ESP10has a nodule-in air gap46wherein a portion of the inner surface36of the stator18has a nodule48disposed thereon. The nodule48is closer to the rotor20than any other part of the inner surface36of the stator18. The inner surface36of the stator can include a single nodule48or multiple nodules48. In one embodiment, if the inner surface36of the stator18has multiple nodules48disposed thereon, the nodules48would be in line in the axial direction on the inner surface36of the stator18. In a further embodiment, the multiple nodules48could be any size and distributed on the inner surface36of the stator18in any type of array to achieve the desired operational characteristics of the ESP10.

Referring now toFIGS.5A and5B, the stator18includes a body50with winding channels52that extend axially through the body50of the stator18. The body50of the stator18is part of the stator18that is between the inner surface36and an outer surface54of the stator18. The winding channels52allow for a place where windings56can be placed within the body50of the stator18to create the electromagnetic field across the air gap32.

In a further embodiment of the present disclosure shown in more detail inFIG.5A, another way to create the magnetic field across the air gap32that generates a radial force on the rotor20that is stationary relative to the stator18while the ESP10is operational is shown (i.e. constant load). To create the constant load, the size and shape of the winding channels52in the stator18are manipulated. The stator18can have many winding channels52disposed within its body50. The size and shape of the winding channels52in the stator18can be varied to generate the desired constant load described herein. In one exemplary embodiment, one of the winding channels52is bigger than all of the other winding channels52(i.e. can have larger radial cross-sectional shape—a cross section that is perpendicular to the length of the winding channels) and all of the other winding channels52are the same size. This imbalanced winding spacing creates the radial force on the rotor20that is stationary relative to the stator18(i.e. constant load). The number of windings56in the larger winding channel58can be more, less or the same as the number of windings56in the other winding channels52that have the uniform radial cross-sectional shape.

In yet another embodiment shown in more detail inFIG.5B, another way to create the constant load. To create the constant load, the number of windings56in the winding channels52can be varied. In an exemplary embodiment, the stator18can have a plurality of uniform radial cross-sectionally shaped winding channels52disposed in the body50of the stator18. A subset of the uniformly shaped winding channels52have less windings56disposed therein than the other uniformly shaped winding channels52. In this embodiment, the subset of the uniformly shaped winding channels can be two or more. The winding channels52not a part of the subset can all have the same number of windings56disposed therein. The number of windings56in each winding channel52of the subset can have any number of windings56disposed therein so long as there are less windings56than in each of the winding channels52not a part of the subset. In one embodiment, the number of windings56in each winding channel52of the subset is half the number of windings56disposed in each of the winding channels52not a part of the subset. In a further embodiment, the number of windings56in each winding channel52of the subset is less than 75% of the number of windings56disposed in each of the winding channels52not a part of the subset. In yet another embodiment, the number of windings56in each winding channel52of the subset is less than 50% of the number of windings56disposed in each of the winding channels52not a part of the subset.

The embodiments shown inFIGS.5A and5Bhave been described with the understanding that the air gap32is symmetrical, but it should be understood and appreciated that the air gap32can have any of the shapes and features described herein. Therefore, numerous ways are described herein for providing the constant load to the ESP10. It should be understood and appreciated that any of the embodiments described herein can be combined to generate the constant load.

The present disclosure is also directed toward a method of designing and constructing an ESP10that has a constant load as described herein. The extent of the desired constant load can be determined and a stator18and rotor20can be designed and constructed that can have any of the features described herein. The air gap32can be manipulated in any manner described herein to generate the desired constant load for the ESP10.

From the above description, it is clear that the present disclosure is well-adapted to carry out the objectives and to attain the advantages mentioned herein as well as those inherent in the disclosure. While presently preferred embodiments have been described herein, it will be understood that numerous changes may be made which will readily suggest themselves to those skilled in the art and which are accomplished within the spirit of the disclosure and claims.