JP6389785B2 - Downhole compressor - Google Patents

Description

  The present invention relates to a downhole compressor, and more particularly to a downhole compressor suitable for ensuring reliability during high-speed rotation.

  A downhole compressor that is installed in a natural gas well and assists in the production of natural gas is installed in a well having a diameter of about several tens of centimeters. If the compressor is downsized, the cross-sectional area of the flow path is reduced, which may reduce the gas output. Furthermore, when a centrifugal compressor is used as a compressor type, the centrifugal force used for gas compression is reduced due to the reduction in the outer diameter of the impeller accompanying the downsizing, thereby reducing the pressure ratio and producing gas. There is a risk that sufficient pressure will not be obtained.

  In order to compensate for such a decrease in flow rate and pressure ratio due to the downsizing, downhole compressors are required to increase the rotor rotation speed. That is, the gas flow rate increases because the flow rate increases as the rotor speed increases. Further, since the centrifugal force increases due to the increase in speed, the pressure ratio increases. For example, the downhole compressor disclosed in (Patent Document 1) is operated at a high rotational speed of 20,000 rpm to 50,000 rpm.

  Oil-lubricated plain bearings and rolling bearings are widely used in general industrial turbomachines. However, in general high-speed rotating machines such as downhole compressors, the amount of heat generated by the bearings is excessive. Application is difficult. As a countermeasure against this, for example, in the above-mentioned known example, a static pressure gas bearing using a natural gas with a pressure increased is adopted. In gas bearings, the viscosity of the gas, which is a lubricant, is very small compared to liquids such as oil, so that the heat generation of the lubricant can be kept low, and the reliability of the bearing can be ensured.

U.S. Pat. No. 7,338,262

  The natural gas in the well may contain foreign substances such as liquids such as water and oil, and solids such as earth and sand. When natural gas is used as a lubricant for a gas bearing, the inclusion of such foreign matters may cause an increase in heat generation and physical damage, and may reduce the reliability of the bearing. Although the structure which reduces such a foreign material using a separator etc. is also considered, there exists a possibility that a foreign material cannot be removed completely, and there exists a possibility that the reliability of a bearing cannot fully be ensured.

  On the other hand, when a foreign substance is mixed into natural gas as a working fluid of a compressor, physical properties such as fluid density and viscosity change. For this reason, when the compressor is operated without taking into consideration the mixing of foreign matter, there are concerns such as a decrease in operating efficiency, generation of excessive fluid force, and occurrence of fluid instability due to changes in operating characteristics of the impeller. In a downhole compressor using a gas bearing, it is difficult to detect such a change in gas properties, and there is a possibility that the reliability of the apparatus cannot be sufficiently ensured.

  Further, there is a possibility that the thrust load acting on the impeller is increased due to the mixing of foreign substances into the natural gas. High-speed bearings such as gas bearings generally have a smaller load capacity than oil bearings and the like, making it difficult to design for a large thrust load due to contamination by foreign matter.

  Accordingly, an object of the present invention is to provide a downhole compressor that can ensure reliability during high-speed rotation even if the physical properties of natural gas change due to contamination of foreign substances.

  In order to achieve the above object, the present invention is a downhole compressor having a casing installed in a well, a rotor built in the casing, and an impeller disposed in the rotor, the casing having the casing. An electromagnetic control means for electromagnetically controlling the relative position of the rotor inside is provided.

  Furthermore, the present invention is a downhole compressor, characterized in that a bearingless motor is provided as the electromagnetic control means.

  Furthermore, the present invention is a downhole compressor, wherein the electromagnetic control means includes a magnetic bearing.

  Furthermore, the present invention is a downhole compressor, wherein a pressure adjustment chamber is provided in a rear portion of the impeller, and a shaft seal device is provided between the outlet portion of the impeller and the pressure adjustment chamber, and the pressure adjustment A communication means is provided between the chamber and the inlet of the impeller.

  Furthermore, the present invention is a downhole compressor comprising a displacement meter for measuring the axial displacement of the rotor, and the displacement meter is provided on the back surface of the impeller.

  Furthermore, the present invention is a downhole compressor, wherein the amount of leakage of the shaft seal device is reduced when the rotor is displaced upstream in the axial direction.

  Furthermore, the present invention is a downhole compressor, wherein the shaft sealing device has an axial gap, and the axial gap becomes smaller when the rotor is displaced upstream in the axial direction. is there.

  Furthermore, the present invention is a downhole compressor, wherein the control device of the electromagnetic control means is arranged on the ground.

  Furthermore, the present invention is a downhole compressor, wherein operating conditions are determined using a control signal of the electromagnetic control means.

  According to the present invention, since the rotor can be supported without using a lubricant such as natural gas by electromagnetically controlling the position of the rotor, it is possible to prevent a decrease in bearing reliability due to heat generated by the lubricant. In addition, the reliability of the apparatus can be stably secured because there is no influence of changes in the physical properties of natural gas on the shaft support characteristics.

It is principal part sectional drawing of the downhole compressor which concerns on 1st Example of this invention. It is sectional drawing showing the installation state of the downhole compressor which concerns on 1st Example of this invention. It is principal part sectional drawing of the downhole compressor which concerns on the 2nd Example of this invention. It is principal part sectional drawing of the downhole compressor which concerns on the 3rd Example of this invention. It is principal part sectional drawing of the downhole compressor which concerns on the 4th Example of this invention.

  EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is demonstrated using drawing.

  FIG. 1 is a sectional view of an essential part of a downhole compressor 1 according to a first embodiment of the present invention.

  An impeller 3 is installed at the end of the rotor 2, and the natural gas is pressurized as the rotor 2 rotates. A thrust load generated in the impeller 3 is supported by a thrust bearing (not shown). A bearingless motor 4 installed at the center of the rotor 2 generates a driving torque in the rotor 2 and generates an electromagnetic force so that a relative position between a casing (not shown) and the rotor 2 is substantially constant, thereby causing the rotor 2 to move. I support it. Since the position of the rotor 2 is electromagnetically controlled, the support characteristics of the rotor 2 do not change even if the physical properties of the natural gas change, and the rotor 2 can be supported stably.

  FIG. 2 is a cross-sectional view illustrating an installation state of the downhole compressor 1 according to the present embodiment. The downhole compressor 1 is installed in a natural gas well 5. The controller 6 of the bearingless motor 4 is installed on the ground 15, and the downhole compressor 1 and the controller 6 are connected by a cable 7. Since the controller 6 is installed on the ground 15, the control signal of the bearingless motor 4 can be easily taken out and can be used for setting the operating conditions of the downhole compressor 1.

  Since the electromagnetic control force for controlling the position of the rotor 2 in the casing of the downhole compressor 1 is proportional to the square of the control current, the dynamic fluid force acting on the rotor 2 can be grasped by monitoring the control current. it can. The physical properties of the natural gas and their unsteadiness can be estimated by collating the fluid force with the operating characteristics, driving torque, rotational speed, and the like of the impeller 3. By collating the estimated gas physical properties with the operating characteristics of the impeller 3, it is possible to appropriately set operating conditions such as rotational speed, and to prevent the occurrence of excessive fluid force and fluid instability phenomenon acting on the impeller 3. . For example, when the liquid content in the gas increases and the fluid force increases, the rotational force of the rotor 2 is reduced to reduce the fluid force, thereby ensuring the reliability of the apparatus.

  A second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a cross-sectional view of a main part of the downhole compressor 1 according to the present embodiment. In the configuration of the present embodiment, members having the same reference numerals as those of the first embodiment have the same configuration and effects, and therefore description thereof will be omitted, and only differences from the first embodiment will be described.

  In this embodiment, a motor 8 is arranged in place of the bearingless motor 4 as means for generating a driving torque in the rotor 2. Further, as the electromagnetic control means for the position of the rotor 2, a magnetic bearing 9 installed in a casing (not shown) is used instead of the bearingless motor 4. On both sides of the motor 8, radial magnetic bearings 9a for supporting a load in a direction perpendicular to the axis are arranged. A thrust collar 10 for transmitting a thrust load is disposed between the motor 8 and the impeller 3, and thrust magnetic bearings 9 b are disposed on both sides of the thrust collar 10. The magnetic bearing 9 incorporates a displacement sensor and an electromagnetic actuator, and the electromagnetic force is controlled so that the position of the rotor 2 in the casing is substantially constant. By using the magnetic bearing 9 independent from the motor 8, the load capacity can be increased and the reliability can be improved.

  Next, a third embodiment of the present invention will be described with reference to FIG.

    FIG. 4 is a cross-sectional view of a main part of the downhole compressor 1 according to the present embodiment. In the configuration of the present embodiment, members having the same reference numerals as those of the above-described embodiment have the same configuration and effects, and therefore description thereof is omitted, and only differences from the above-described embodiment will be described. In the second embodiment shown in FIG. 3, the pressure in the flow path portion of the impeller 3 increases from the inlet portion 3 b to the outlet portion 3 a, but the pressure in the back surface of the impeller 3 is in the outlet portion 3 a of the compressor 3. Since the pressure is almost equal to the pressure, a thrust load is generated on the impeller 3 from the back side toward the flow path side. Since the load capacity of the magnetic bearing 9 is smaller than that of a general oil-lubricated bearing, it is desirable to reduce the thrust load as much as possible when the magnetic bearing 9 is applied to the downhole compressor 1.

  In the third embodiment, a shaft seal device 12 is installed on the back surface of the impeller 3 to constitute a pressure adjustment chamber 11. Further, a communication means 13 is provided between the pressure adjustment chamber 11 and the inlet portion 3 b of the impeller 3 to reduce the pressure in the pressure adjustment chamber 11. For this reason, the pressure on the back surface of the impeller 3 can be reduced, the thrust load can be reduced, and the reliability of the thrust magnetic bearing 9b can be improved.

  In this embodiment, in order to stabilize the thrust load, it is desirable to keep the axial gap of the shaft seal device 12 constant. Therefore, in this embodiment, the position sensor 14 of the axial rotor 3 used for controlling the thrust magnetic bearing 9b is provided on the rear surface of the impeller 3, and the thrust magnetic bearing 9b is provided so as to keep the gap of the shaft seal device 12 constant. I have control.

  In this embodiment, an axial groove is provided on the fixed portion of the impeller 3 of the rotor 2 as the communication means 13. However, the axial groove may be provided on the impeller 3 side. A communication hole may be provided.

  Next, a fourth embodiment of the present invention will be described with reference to FIG.

  FIG. 5 is a cross-sectional view of a main part of the downhole compressor 1 according to the present embodiment. In the configuration of the present embodiment, members having the same reference numerals as those of the above-described embodiment have the same configuration and effects, and therefore description thereof is omitted, and only differences from the above-described embodiment will be described.

  In this embodiment, the shaft seal device 12 is installed on the outer diameter portion of the impeller 3. The shaft seal device 12 includes a so-called labyrinth seal 12a that opposes the outer periphery of the impeller 3 and an axial gap portion 12b that projects to the impeller 3 flow path side. When the leakage amount of the shaft seal device 12 increases, the back pressure of the impeller 3 increases, the thrust load increases, and the rotor 2 moves in the axial direction upstream. At this time, the axial gap 12b of the shaft seal device 12 is reduced and the leakage amount of the shaft seal device 12 is reduced, so that the thrust load is reduced and the rotor 2 is pushed back in the axial direction downstream side. As described above, since the thrust load is automatically adjusted according to the movement of the rotor 2, the thrust load acting on the thrust magnetic bearing 9b can be optimized, and the reliability of the apparatus can be improved.

Also in the fourth embodiment, the axial magnetic rotor 3 shown in the third embodiment may be provided with a position sensor 14 to control the thrust magnetic bearing 9b so as to keep the gap of the shaft seal device 12 constant. Is possible.

DESCRIPTION OF SYMBOLS 1 ... Downhole compressor 2 ... Rotor 3 ... Impeller 3a ... Outlet part 3b of impeller ... Inlet part 4 of impeller ... Bearing-less motor 5 ... Natural gas well 6 ... Controller 7 ... Cable 8 ... Motor 9 ... Magnetic bearing 9a ... Radial magnetic bearing 9b ... Thrust magnetic bearing 10 ... Thrust collar 11 ... Pressure adjustment chamber 12 ... Shaft seal device 13 ... Communication means 14 ... Axial rotor position sensor 15 ... Ground

Claims (6)

A casing installed in the well;
A rotor built into the casing;
A downhole compressor having an impeller disposed on the rotor,
A pressure adjustment chamber is provided on the back surface of the impeller,
A shaft seal device is provided between the outlet of the impeller and the pressure adjustment chamber,
A communication means is provided between the pressure regulation chamber and the inlet of the impeller,
And electromagnetic control means for electromagnetically controlling the relative position of the rotor in the casing,
A downhole compressor characterized in that a leakage amount of the shaft seal device decreases when the rotor is displaced upstream in the axial direction . The downhole compressor according to claim 1,
A downhole compressor comprising a bearingless motor as the electromagnetic control means. The downhole compressor according to claim 1,
The downhole compressor according to claim 1, wherein the electromagnetic control means includes a magnetic bearing. The downhole compressor according to claim 1,
A displacement meter for measuring the axial displacement of the rotor;
A downhole compressor comprising the displacement meter on a rear surface of the impeller. The downhole compressor according to claim 1,
The down-hole compressor according to claim 1, wherein the shaft seal device has an axial gap, and the axial gap becomes smaller when the rotor is displaced upstream in the axial direction. The downhole compressor according to any one of claims 1 to 5,
A downhole compressor characterized in that a controller for the electromagnetic control means is disposed on the ground.

Images