Controlling a subsea electric submersible pump based on sensing a rotor position

Abstract

The ESP assembly includes an electric motor having a stator, a rotor, a drive shaft, and an asymmetric magnet ring mounted to an end of the drive shaft. Power to drive the motor is provided from a surface power source and is delivered to the motor through a power cable inserted into the wellbore. The power cable lead is inserted into a star connection that is mounted around the end of the shaft having the ring and houses downhole sensors. During operation of the ESP assembly, the sensors track the rotor position by monitoring the ring rotation. Information about the rotor position is transmitted uphole along the power cable. A controller on the surface receives and processes the position information and issues control commands to the motor that are transmitted downhole along the power cable. The power cable is connected to the controller and the sensors through a current transformer.

Description

[0001] Inventor: Christopher Wrighton

[0002] Donald Jamison

[0003] Sacramenta Maharingan Technical Field

[0004] This disclosure relates to operating an ESP assembly based on sensing the position of the rotor in a downhole electric submersible pump ("ESP"), and more specifically, to an ESP assembly that uses existing multiphase power cables to sense the rotor position. Background Technology

[0005] In hydrocarbon production wells where the pressure is insufficient to lift the liquid from the well, an artificial lift is typically used. An ESP (Electrical Stirred Pump) is an artificial lift and includes an electric motor filled with dielectric fluid. A drive shaft connects the motor to a pump, which in turn excites the motor to rotate the shaft, thereby rotating the impeller in the pump. The pump is usually a centrifugal pump with multi-stage impellers and a diffuser for pressurizing the liquid. A seal is typically present between the motor and the pump to balance the pressure of the dielectric fluid within the motor with the hydrostatic pressure in the well.

[0006] ESP components typically use induction motors, which can operate in open-loop mode with long stepouts (over tens of kilometers) without feedback of rotor position to the variable frequency drive ("VFD") power supply. This power supply is becoming increasingly common due to the decreasing cost of the system. ESP components also employ permanent magnet motors ("PMMs"), which operate well in open-loop mode for up to approximately three kilometers. After that, the VFD needs the rotor position to properly excite each phase of the motor. Traditionally, this would require four wires of cable (three power cables and one rotor position cable), which is not attractive for ESP applications due to space constraints; three power cables are typically the standard in ESP applications. Synchronous reluctance motors ("SynRMs") are another motor topology gaining attention within the space constraints of induction motors. SynRMs are AC motors and require rotor position knowledge. These machines are very recyclable and therefore fall into the "sustainable" category. SyRMs require rotor position feedback, which means four wires of cable or additional devices are needed to transmit the rotor position. Summary of the Invention

[0007] This document discloses an example method for operating an ESP (Electronic Stability Program) assembly in a wellbore. The method includes: transmitting power from a variable speed drive via a power cable to operate a permanent magnet motor of the ESP assembly; monitoring the angular position of the drive shaft of the ESP assembly in the wellbore; transmitting information about the angular position to the power cable using a current transformer; receiving the information at ground level; and adjusting the amount of power transmitted to the motor based on the information received at ground level. In one embodiment, the angular position is monitored by sensing the presence of an asymmetric magnetic field extending radially from the end of the drive shaft. In this example, the magnetic field emanates from a loop coupled to and external to the end of the drive shaft. Optionally, the power cable comprises three power lines with different phase powers, and wherein a current transformer is connected to a first power line of the power lines. Furthermore, in this example, the current transformer is a first current transformer, and wherein information is received at ground level via a second current transformer connected to the first power line of the power lines. The example also includes powering instruments on a motor using power transmitted to the first power line via a third current transformer connected to the first power line in the power line, and optionally, the power is generated by a power source controlled by a processor communicating with information.

[0008] Also disclosed is an ESP assembly for use in a wellbore, comprising: a pump; a drive shaft coupled to a rotor, the drive shaft having an end connected to the pump and a non-drive end remote from the pump; a motor having a stator and a rotor, the rotor being rotatable within the stator and having a permanent magnet mounted on the drive shaft between the pump and the non-drive end; a ring having an asymmetric circumferential magnetic field and coupled to the outer periphery of the non-drive end; a star-shaped connection including a housing having axial holes for receiving the non-drive end of the drive shaft and the ring; a variable speed drive connected to the motor via a power cable including power lines communicating with the stator for carrying different phases of power; and a sensor selectively connected to the circumferential magnetic field and the variable speed drive. Alternatively, the rotating ring generates a pulsed magnetic field sensed by the sensor. The example also includes a processor communicating with the sensor and configured to estimate the angular position of the rotor based on the pulsed magnetic field sensed by the sensor. In the example, the variable speed drive responds to angular position information received from the processor. Optionally, the current transformer is mounted on the ground to a first power line in the power line, and the processor communicates with the sensor via the current transformer. In an alternative, the current transformer is a first current transformer, and the processor includes a first processor; in this alternative, the assembly also includes a second current transformer connected downhole to the first power line in the power line, and the second current transformer communicates with a second processor downhole that communicates with the sensor. Optionally, the sensor is disposed in a recess formed in the housing. In one example, the ring has a plurality of magnets spaced angularly apart from each other. In one embodiment, the power lines are interconnected within the housing, and the ring is alternatively disposed in an annular bushing that engages with the non-drive end of the drive shaft. An alternative also exists: an end cap is included, having an annular portion and a planar portion, the annular portion inserting into an axial bore inside the drive shaft, and the planar portion extending radially from the annular portion and interfering with the end of the bushing. Attached Figure Description

[0009] Some features and benefits of the invention have already been set forth, and other features and benefits will become apparent as the description is taken in conjunction with the accompanying drawings, wherein:

[0010] Figure 1 This is a side cross-sectional view of an example ESP component with a rotor position sensor.

[0011] Figure 1A yes Figure 1 A cross-sectional view of a portion of the ESP component.

[0012] Figure 2 yes Figure 1 A schematic example of a rotor position sensor.

[0013] Figure 3 yes Figure 2 A perspective view of an example connection in a rotor position sensor.

[0014] Figure 4 It has an asymmetric ring. Figure 3 A cross-sectional view of an example connection.

[0015] Figure 5 yes Figure 4 A perspective view of an example ring.

[0016] While the subject matter has been described in conjunction with the embodiments disclosed herein, it will be understood that the scope of this disclosure is not limited to any particular embodiment. Rather, it is intended to cover all alternatives, modifications, and equivalents thereof. Detailed Implementation

[0017] The methods and systems of this disclosure will now be described more fully below with reference to the accompanying drawings, which illustrate embodiments. The methods and systems of this disclosure may take many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and its scope will be fully conveyed to those skilled in the art. Similar reference numerals are used throughout to refer to similar elements. In embodiments, the term “about” includes + / - 5% of the referenced quantity. In embodiments, the term “substantially” includes + / - 5% of the referenced quantity, comparison, or description. In embodiments, the term “largely” includes + / - 10% of the referenced quantity.

[0018] It should also be understood that the scope of this disclosure is not limited to the exact details of the structures, operations, materials, or embodiments shown and described, as modifications and equivalents will be apparent to those skilled in the art. Illustrative embodiments have been disclosed in the drawings and specification, and although specific terminology has been used, it is used in a general and descriptive sense only and not for limiting purposes.

[0019] Figure 1The side cross-sectional view shows an example of an electric submersible pump ("ESP") assembly 10 arranged in a wellbore 12 and used to produce fluid F from within the wellbore 12. Fluid F is shown entering the wellbore 12 through a perforation 14 that protrudes radially outward from the sidewall of the wellbore 12 into the surrounding formation 16. Fluid F flows upward within the wellbore 12 and to an inlet 18 formed in a pump section 20 of the assembly 10. An impeller 22, shown in dashed outline in the pump section 20, is mounted on a pump shaft 24. A motor section 26 is shown located downhole relative to the pump section 20 in the ESP assembly 10. A seal 27 is provided between the pump section 20 and the motor section 26 such that the fluid pressure within the motor section 26 is equal to the ambient pressure. A motor shaft 28 is shown extending axially from the motor section 26 and coupled to the pump shaft 24. A housing 29 covers the pump section 20, the motor section 26, and the seal 27. In the arrangement shown, the pump 26 is activated to rotate the motor and pump shafts 26, 28, and impeller 22. The rotation of the impeller 22 drives the fluid F through the pump section 20 and into the diffuser (not shown) to pressurize the fluid F within the pump assembly 10.

[0020] A power cable 30 is shown inserted into the wellbore 12 and connected to the motor unit 26. Power from the variable speed drive ("VSD") 32 is supplied to the motor unit 26 via the cable 30. The cable 30 is routed through a channel in the wellhead assembly 34, which is shown mounted above the opening of the wellbore 12 and on the ground surface 36. The pressurized fluid F in the pump is discharged into a production conduit 38 shown at the discharge end of the pump unit 20. The conduit 38 is attached to the end of the pump unit 20 opposite to the inlet 18 (upstream end) and terminates within the wellhead assembly 34. The annular space between the conduit 38 and the sidewall of the wellbore 12 is blocked by a packer 40 to prevent the fluid F from flowing upstream and through the ESP assembly 10. Figure 1 It also includes: a sensor assembly 42 located inside the motor section 26 and shown in dashed outline; and a ground controller 44 connected to a cable 30 between the motor section 26 and the VSD 32 and located outside the wellbore 12.

[0021] Now for reference Figure 1A The figure shows the axial section view along... Figure 1A portion of the motor section 26 is shown as cut from line 1A-1A. In this example, the pump section 20 includes a rotor 45, which is shown mounted on and externally connected to the outer surface of the pump shaft 28. The rotor 45 includes magnetic poles 46 (i.e., north and south poles), which are made of permanent magnets and spaced apart from each other at an angular distance. Non-magnetic spacers 47 are provided in angled slots between adjacent magnetic poles 46. The stator 48 is shown located within the housing 29 and arranged radially outward relative to the outer surface of the rotor 46, allowing the rotor 46 to rotate relative to the stator 48. Coils 49 within the stator 48 are connected to a power cable 30, such that when energized, current is transmitted through the coils 49 to form an electric field synchronized with the opposite polarity of the magnetic poles 46, thereby causing the rotor 46 and the attached motor shaft 28 to rotate.

[0022] Figure 2 Schematic illustration of the flow from shaft 12 ( Figure 1 An example of a connection from the wellbore 12 to the surface 36. In this example, power cable 30 is shown with power lines 501-503, and sensor assembly 42 and surface controller 44 are both shown connected to line 501, wherein the connection between line 501 and surface controller 44 is on the surface 36, while the connection between line 501 and sensor assembly 42 is downhole in the wellbore 12. In this example, the connection between line 501 and sensor assembly 42 is achieved via connection 52, which provides electrical transmission from line 501 to power source 54. Power source 54 then delivers excitation power to modem 56 and processor 58, both of which are located downhole. As described in more detail below, sensor 60 is connected to processor 58 for detecting the rotor 46 in the wellbore 12 ( Figure 1 The angular orientation in the wellbore 12. In one embodiment, sensor 60 is a Hall effect sensor. Another connector 62, also in the wellbore 12, provides communication between modem 56 and line 501. Modem 56 modulates signal data received from processor 58, which is transmitted through connector 62 to line 501 and then along line 501 toward the surface. In the example, connectors 52 and 62 are both current transformer type connectors. In one example, the current transformer includes a secondary winding formed around the current in the primary conductor, and wherein the current in the secondary winding is proportional to the current in the primary conductor. An example of a current transformer is described in U.S. Patent No. 10,738,571, which is incorporated herein by reference in its entirety and for all purposes. Surface controller 44 is in communication with line 501 via connection 64, thereby providing the surface 36 ( Figure 1The modem 66 shown above provides signal communication. A controller 68, also on ground 36, is connected to the modem 66. The controller 68 is connected to the VSD 32 and also to the power supply 70. The power supply 70 is connected to line 501 via connection 72. In this embodiment, connections 64 and 72 are also current transformers.

[0023] Figure 3 A perspective view of the star-shaped connection 74 is shown, in which the downhole terminals of lines 501-503 are connected to each other. Figure 1 In the diagram, the connecting portion 74, outlined in dashed lines, is located in the portion of the motor portion 26 furthest from the sealing portion 27, and therefore in the bottom or lowest portion of the ESP assembly 10. See again. Figure 3 The connecting portion 74 is depicted as a generally cylindrical member having a housing 75 and a surface facing the wellbore for receiving the non-driven end of the motor shaft 28. Ring-shaped housings 761-763 are shown located on the surface facing the wellbore and radially spaced outward from the shaft 28. In the illustrated example, housings 761-763 extend axially upward from the surface facing the wellbore of the housing 75 and receive the ends of lines 501-503. An axial bore 78 is formed to axially pass through the connecting portion 74, and the lower end of the non-driven end of the motor shaft 28 is inserted into the axial bore 78. The annular bushing 80 is connected to the end of the shaft 28 inserted into the bore 78 by engaging a spline 81 on the shaft 28 with a complementary spline 82 on the inner surface of the bushing 80. The radial clearance between the bore 78 and the bushing 80 allows relative rotation of the bushing 80 (and the attached motor shaft 28) with respect to the bore 78.

[0024] See now Figure 4 The figure shows a partial cross-sectional view. Figure 3 Example of connection 74. A bore 82 extends through the shaft 28 and along axis Ax, and an annulus 84 is formed within the bushing 80. The axial length of the annulus 84 is greater than its radial thickness, and the annulus 84 extends substantially along the length of the bushing 80. An end cap 85 is mounted on the end of the shaft 28, the end cap 85 having an annular portion and a flat end, the annular portion being threaded into the bore 82, and the flat end projecting radially outward from the annular portion to provide an axial stop for the bushing 80. The end cap 85 has an opening through its axis to allow lubricating fluid to flow within the bore 82.

[0025] Figure 5 This is a perspective view of an example of ring 84, and shows sections 861-86. nIn this example, adjacent segments are spaced at an angle to each other. Furthermore, segments 861, 863, and 865 possess magnetic properties, for example, from a permanent magnet or electromagnet, to form corresponding electromagnetic fields 871, 873, and 875. When sensed radially outward from ring 84, a pulsed magnetic field is generated by rotating ring 84. In this example, segments 861-86... n The angular lengths are variable, thus allowing the characteristics of rotational orientation to be identified based on the measured lengths of the electromagnetic fields 871, 873, and 875 emanating from these magnetic segments. See again. Figure 4 The recess 88 is shown as being formed radially inward in the housing 75 of the connector 74, and the interior of the recess 88 is provided with electromagnetic fields 871, 873, 875 ( Figure 5 Sensor 60 responds to the signal. In the example, the bushing 80, ring 84, and recess 88 are sized such that when these segments 861, 863, 865 are angularly aligned with recess 88, sensor 60 detects electromagnetic fields 871, 873, 875 emanating from segments 861, 863, 865; and by not detecting the presence of an electromagnetic field, it also identifies when these segments 861, 863, 865 are angularly offset from recess 88. Embodiments exist where sensor 60 generates an output when magnetic fields 871, 873, 875 are detected, and another different output when no magnetic field is detected, or generates an output only when magnetic fields 871, 873, 875 are detected, and vice versa. In the example, the output(s) of sensor 60 include a signal, multiple signals, pulses, and / or sequences of signals or pulses. Alternatively, the force, energy, and / or magnitude of electromagnetic fields 871, 873, 875 may be the same or different from each other. In this example, the rotational orientation of ring 84 (and therefore shaft 28 and rotor 45) can be easily identified by monitoring the output of sensor(s) 60. The signal representing the sensing information is connected to processor 58 in one example. Figure 2 Line 92 is selectively transmitted.

[0026] In a non-limiting operational example, electricity is transmitted from ground 36 to motor 26, for example, via VSD 32. Figure 1 In an alternative embodiment, power from VSD 32 to ESP component 10 is supplied at a frequency ranging from approximately 50 Hz to approximately 60 Hz and at approximately 1 kV to approximately 6 kV. In this embodiment, VSD 32 is connected to a power source, such as a wire from a utility, generator, etc. In response to the transmission of power to motor section 26, motor 46 and winding 49 ( Figure 1A The electromagnetic interaction between the rotor and rotor 46 causes the motor shaft 28 to rotate. This, in turn, causes the ring 84 ( Figure 4The sensor rotates relative to the sensor 60, and the sensor 60 sends an output in response to the radiation of electromagnetic fields 871, 873, and 875. The output of the sensor 60 is transmitted to the processor 58. Figure 2 The data is transmitted to the controller 68 via connections 62 and 64. The controller 68 is configured to identify the rotational position of the rotor 46 based on the output of the sensor 60 and compare it with the expected rotational position, so that the power supplied to the winding 49 is in the appropriate phase and the motor 26 can operate continuously. Furthermore, in this example, the signal data transmitted via lines 501-503 is an AC signal with a voltage of approximately 10 volts to approximately 200 volts and a frequency of approximately 10 kHz to approximately 200 kHz. Conventional downhole measuring instruments use DC transmission, where each phase is offset by the same fixed DC voltage (10V-400V) and data is transmitted by modulating a small leakage current, similar to Morse code. The advantage of transmitting signal data in AC rather than DC is that any modulation of the current or voltage is transmitted at a higher frequency, providing an enhanced data transmission rate; this transmits the data to the surface 36 at a certain speed. Figure 1 It provides real-time rotational data, allowing for responsive corrective control of the ESP component 10 over a time span, thereby enabling continuous operation of the component 10. The data transmission speed along power cable 30 and inline 501 allows for the use of permanent magnet motors at well depths exceeding 10,000 feet.

[0027] Therefore, the invention described herein is well-suited for achieving the objectives of the invention and obtaining the mentioned effects and advantages, as well as other effects and advantages inherent therein. While presently preferred embodiments of the invention have been given for purposes of disclosure, many variations exist in the process details for achieving the desired results. These and other similar modifications will be apparent to those skilled in the art and are intended to be included within the spirit of the invention disclosed herein and the scope of the appended claims.

Claims

1. An ESP assembly for use in a wellbore, comprising: Pump; A drive shaft having an end connected to the pump and a non-drive end away from the pump; An electric motor, the electric motor including a stator and a rotor, the rotor being connected to the drive shaft and rotatable within the stator, the rotor including magnetic poles; A ring having segments including magnetic properties, providing an asymmetric circumferential magnetic field, and the ring being coupled to the outer periphery of the non-driving end; A star-shaped connection portion, the star-shaped connection portion including a housing having an axial hole for receiving the non-driving end of the drive shaft and the ring; A variable speed drive, the variable speed drive being connected to the motor via a power cable, the power cable including power lines connected to the stator for carrying different phases of power; as well as A sensor, which is selectively connected to the circumferential magnetic field and the variable speed drive.

2. The component according to claim 1, wherein, Rotating the ring generates a pulsed magnetic field sensed by the sensor.

3. The component of claim 2, further comprising a processor that communicates with the sensor and is configured to estimate the angular position of the rotor based on the pulsed magnetic field sensed by the sensor.

4. The component according to claim 3, wherein, The variable speed drive responds to angular position information received from the processor.

5. The component of claim 3, further comprising a current transformer mounted on the ground to a first power line in the power line, wherein, The processor communicates with the sensor via the current transformer.

6. The component according to claim 5, wherein, The current transformer includes a first current transformer, the processor includes a first processor, and the assembly further includes a second current transformer connected downhole to a first power line in the power line, wherein the second current transformer communicates with a second processor downhole that communicates with the sensor.

7. The component according to claim 1, wherein, The sensor is disposed in a recess formed on the housing.

8. The component according to claim 1, wherein, The ring includes a plurality of magnets spaced at an angle away from each other.

9. The component according to claim 1, wherein, The power lines are connected to each other within the housing.

10. The component of claim 1, wherein, The ring is disposed in an annular bushing, which is fitted into the non-driving end of the drive shaft.

11. The assembly of claim 10, further comprising an end cap including an annular portion and a planar portion, the annular portion being inserted into an axial bore inside the drive shaft, and the planar portion extending radially from the annular portion and interfering with an end of the bushing.

12. An ESP assembly for use in a wellbore, comprising: Pump; A drive shaft having an end connected to the pump and a non-drive end away from the pump; An electric motor, the electric motor comprising a stator and a rotor; A ring, connected to the outer periphery of the non-driving end and configured to provide an asymmetric circumferential magnetic field, the ring comprising segments extending along the axial length of the ring and a portion of the circumferential direction of the ring, the segments being angularly spaced from each other and having variable angular lengths; and A sensor, which is selectively connected to the circumferential magnetic field and the variable speed drive.

13. The component of claim 12, wherein, Electromagnetic fields are emitted from the section in question.

14. The component of claim 12, further comprising: A star-shaped connection portion, the star-shaped connection portion including a housing having an axial hole for receiving the non-driving end of the drive shaft and the ring.

15. The component of claim 12, further comprising: A variable speed drive, which is connected to the motor via a power cable, the power cable including power lines in communication with the stator for carrying different phases of power.

16. An ESP assembly for use in a wellbore, comprising: Pump; A drive shaft having an end connected to the pump and a non-drive end away from the pump; An electric motor, the electric motor comprising a stator and a rotor; A ring, connected to the outer periphery of the non-driving end and configured to provide an asymmetric circumferential magnetic field, the ring comprising segments spaced at an angle to each other and extending along the axial length of the ring and a portion of the circumferential direction of the ring, the segments being spaced at an angle to each other, and wherein an electromagnetic field is emitted from the segments; A sensor, which is selectively connected to the circumferential magnetic field and the variable speed drive; as well as A processor that communicates with the sensor and is configured to estimate the angular position of the rotor based on the pulsed magnetic field sensed by the sensor.

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