U.S. patent application number 15/053274 was filed with the patent office on 2016-09-22 for downhole compressor.
The applicant listed for this patent is Hitachi, Ltd.. Invention is credited to Yohei MAGARA, Kazuyuki YAMAGUCHI, Toyomi YOSHIDA.
Application Number | 20160273324 15/053274 |
Document ID | / |
Family ID | 55640526 |
Filed Date | 2016-09-22 |
United States Patent
Application |
20160273324 |
Kind Code |
A1 |
YAMAGUCHI; Kazuyuki ; et
al. |
September 22, 2016 |
Downhole Compressor
Abstract
A downhole compressor includes: a casing disposed inside a gas
well; a rotor built inside the casing; and an impeller disposed at
the rotor, and an electromagnetic control unit that
electromagnetically controls a relative position of the rotor
inside the casing is provided.
Inventors: |
YAMAGUCHI; Kazuyuki; (Tokyo,
JP) ; MAGARA; Yohei; (Tokyo, JP) ; YOSHIDA;
Toyomi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hitachi, Ltd. |
Tokyo |
|
JP |
|
|
Family ID: |
55640526 |
Appl. No.: |
15/053274 |
Filed: |
February 25, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04D 29/0516 20130101;
F04D 25/0606 20130101; E21B 43/129 20130101; E21B 43/128 20130101;
F04D 29/058 20130101 |
International
Class: |
E21B 43/12 20060101
E21B043/12 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 2015 |
JP |
2015-054152 |
Claims
1. A downhole compressor, comprising: a casing disposed inside a
well; a rotor built inside the casing; and an impeller disposed at
the rotor, wherein an electromagnetic control unit configured to
electromagnetically control a relative position of the rotor inside
the casing is provided.
2. The downhole compressor according to claim 1, wherein a
bearingless motor is provided as the electromagnetic control
unit.
3. The downhole compressor according to claim 1, wherein a magnetic
bearing is provided as the electromagnetic control unit.
4. The downhole compressor according to claim 1, wherein a pressure
regulating chamber is provided at a back surface portion of the
impeller, a shaft sealing device is provided between an outlet
portion of the impeller and the pressure regulating chamber, and a
communication unit is provided between the pressure regulating
chamber and an inlet portion of the impeller.
5. The downhole compressor according to claim 4, wherein a
displacement meter configured to measure axial displacement is
provided, and the displacement meter is disposed at a back surface
portion of the impeller.
6. The downhole compressor according to claim 4, wherein a leakage
amount at the shaft sealing device is reduced when the rotor is
displaced to an axial upstream side.
7. The downhole compressor according to claim 6, wherein the shaft
sealing device includes axial clearance, and the axial clearance is
reduced when the rotor is displaced to the axial upstream side.
8. The downhole compressor according to claim 1, wherein a control
device for the electromagnetic control unit is disposed on the
ground.
9. The downhole compressor according to claim 8, wherein an
operating condition is determined by using a control signal of the
electromagnetic control unit.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a downhole compressor, and
particularly relates to a downhole compressor suitable for securing
reliability at the time of high-speed rotation.
[0003] 2. Description of the Related Art
[0004] Since a downhole compressor installed inside a natural gas
well and adapted to assist production of natural gas is installed
inside a borehole having a diameter of approximately several
centimeters, size reduction of the device is needed. When the size
of the compressor is reduced, a gas production amount may be
reduced because a flow passage cross-sectional area is reduced.
Further, in the case of adopting a centrifugal compressor as a form
of the compressor, centrifugal force used for gas compression is
reduced due to reduction of an outer diameter size of an impeller
due to size reduction of the compressor. Therefore, there may be
possibility that a pressure ratio is reduced and sufficient
pressure cannot be obtained for gas production.
[0005] A rotational speed of a rotor is required to be accelerated
in the downhole compressor in order to compensate such a reduced
flow rate and reduced pressure ratio caused by size reduction. In
other words, a gas flow rate is increased because a flow speed is
increased by accelerating rotation of the rotor. Further, the
pressure ratio is increased because the centrifugal force is
increased by acceleration. For instance, a downhole compressor
disclosed in U.S. Pat. No. 7,338,262, is operated at a high
rotational speed of 20,000 rpm to 50,000 rpm.
[0006] In a general industrial turbo machine, an oil lubrication
sliding bearing and a rolling bearing are widely used. However, in
a high-speed rotary machine such as a downhole compressor, these
general bearings are hardly applied because an amount of heat
generation at the bearings is excessively large. As a
countermeasure to such a phenomenon, the above-described known art
adopts, for example, a static pressure gas bearing in which natural
gas is pressurized and then used. In the gas bearing, heat
generation of the lubricant can be kept low because viscosity of
the gas that is the lubricant is extremely low compared to
viscosity of liquid such as oil, and it can be considered that
reliability of the bearing can be secured.
SUMMARY OF THE INVENTION
[0007] In natural gas inside a borehole, foreign matters such as
liquid like water and oil and solids like earth and sand may be
mixed some times. In the case of using the natural gas as
lubricant, such mixture of the foreign matters causes increase of
heat generation and physical damages, and reliability of the
bearing may be degraded. Such foreign matters may be reduced by a
structure using a separator or the like, but there may be
possibility that the foreign matters cannot be completely removed
and reliability of the bearing may not be sufficiently secured.
[0008] On the other hand, when the foreign matters are mixed inside
the natural gas used as working fluid of the compressor, properties
such as density and viscosity of the fluid are changed. Therefore,
when the compressor is operated without considering such mixture of
the foreign matters, there is concern that deterioration of
operation efficiency, generation of excessive fluid force,
occurrence of unstable phenomena in the fluid, and the like may be
caused by change of operating characteristics of an impeller. In
the downhole compressor using the gas bearing, such change of the
gas properties can be hardly detected, and there may be possibility
that sufficient reliability of a device cannot be secured.
[0009] Further, a thrust load acting on the impeller may be
increased due to mixture of the foreign matters inside the natural
gas. In a high-speed bearing such as the gas bearing, load capacity
is generally small compared to an oil bearing and the like.
Therefore, it is difficult to design a bearing that can handle a
large thrust load caused by mixture of the foreign matters.
[0010] In view of the above-described situations, the present
invention is directed to providing a downhole compressor in which
reliability can be secured at the time of high-speed rotation even
when natural gas properties are changed due to mixture of foreign
matters and the like.
[0011] To achieve the above-described object, the present invention
provides a downhole compressor, including: a casing disposed inside
a well; a rotor built inside the casing; and an impeller disposed
at the rotor, wherein an electromagnetic control unit configured to
electromagnetically control a relative position of the rotor inside
the casing is provided.
[0012] Further, the present invention is the downhole compressor
characterized in including a bearingless motor as an
electromagnetic control unit.
[0013] Furthermore, the present invention is the downhole
compressor characterized in that the electromagnetic control unit
includes a magnetic bearing.
[0014] Furthermore, the present invention is the downhole
compressor characterized in that a pressure regulating chamber is
provided at a back surface portion of the impeller, a shaft sealing
device is provided between an outlet portion of the impeller and
the pressure regulating chamber, and a communication unit is
provided between the pressure regulating chamber and an inlet
portion of the impeller.
[0015] Furthermore, the present invention is the downhole
compressor characterized in that a displacement meter to measure
axial displacement of the rotor is provided, and the displacement
meter is disposed at the back surface portion of the impeller.
[0016] Furthermore, the present invention is the downhole
compressor characterized in that a leakage amount at the shaft
sealing device is reduced when the rotor is displaced to an axial
upstream side.
[0017] Furthermore, the present invention is the downhole
compressor characterized in that the shaft sealing device includes
axial clearance, and the axial clearance is reduced when the rotor
is displaced to the axial upstream side.
[0018] Furthermore, the present invention is the downhole
compressor characterized in that a control device for the
electromagnetic control unit is disposed on the ground.
[0019] Furthermore, the present invention is the downhole
compressor characterized in that an operating condition is
determined by using a control signal of the electromagnetic control
unit.
[0020] According to the present invention, the rotor can be
supported by electromagnetically controlling a position of the
rotor without using lubricant such as natural gas. Therefore,
deterioration of reliability of the bearing caused by heat
generation of the lubricant can be prevented. Further, reliability
of the device can be stably secured because there is no effect on
supporting characteristics from change of the natural gas
properties.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a cross-sectional view illustrating a main portion
of a downhole compressor according to a first embodiment of the
present invention;
[0022] FIG. 2 is a cross-sectional view illustrating an
installation state of the downhole compressor according to the
first embodiment of the present invention;
[0023] FIG. 3 is a cross-sectional view illustrating a main portion
of a downhole compressor according to a second embodiment of the
present invention;
[0024] FIG. 4 is a cross-sectional view illustrating a main portion
of a downhole compressor according to a third embodiment of the
present invention; and
[0025] FIG. 5 is a cross-sectional view illustrating a main portion
of a downhole compressor according to a fourth embodiment of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] Embodiments to implement the present invention will be
described below using the drawings.
First Embodiment
[0027] FIG. 1 is a cross-sectional view illustrating a main portion
of a downhole compressor according to a first embodiment of the
present invention.
[0028] An impeller 3 is disposed at an end portion of a rotor 2,
and natural gas is pressurized by rotation of the rotor 2. A thrust
load generated at the impeller 3 is supported by a thrust bearing
not illustrated. A bearingless motor 4 disposed at center of the
rotor 2 generates drive torque at the rotor 2 and simultaneously
supports the rotor 2 by generating electromagnetic force such that
relative positions between the rotor 2 and a casing not illustrated
is kept substantially constant. Since the position of the rotor 2
is electromagnetically controlled, supporting characteristics of
the rotor 2 do not change even when the natural gas properties are
changed, and the rotor 2 can be stably supported.
[0029] 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 inside a
natural gas well 5. A controller 6 of the bearingless motor 4 is
disposed on the ground 15, and the downhole compressor 1 and the
controller 6 are connected via a cable 7. Since the controller 6 is
disposed on the ground 15, a control signal of the bearingless
motor 4 can be easily extracted and used for setting an operating
condition of the downhole compressor 1.
[0030] Electromagnetic control force to control the position of the
rotor 2 inside the casing of the downhole compressor 1 is
proportional to the square of control current. Therefore, dynamic
fluid force that acts on the rotor 2 can be grasped by monitoring
the control current. The natural gas properties and unsteadiness
thereof can be estimated by collating the fluid force, operating
characteristics of the impeller 3, drive torque, rotational speed,
and so on. An operating condition such as the rotational speed can
be appropriately set by collating the estimated gas properties and
operating characteristics of the impeller 3, and excessive fluid
force that may act on the impeller 3 and unstable phenomena of the
fluid can be prevented. For example, in the case where the fluid
force is increased by increased liquid content inside the gas, the
fluid force can be decreased by reducing the rotational speed of
the rotor 2, and reliability of the device can be secured.
Second Embodiment
[0031] A second embodiment of the present invention will be
described using FIG. 3. FIG. 3 is a cross-sectional view
illustrating a main portion of a downhole compressor 1 according to
the present embodiment. In a structure of the present embodiment, a
component denoted by a reference sign same as a first embodiment
has the same structure and effects. Therefore, a description
therefor will be omitted and only a different point from the
above-described first embodiment will be described.
[0032] In the present embodiment, a motor 8 is disposed as a unit
to generate drive torque at a rotor 2 instead of a bearingless
motor 4. Further, as an electromagnetic control unit for a position
of the rotor 2, a magnetic bearing 9 disposed at a casing not
illustrated is used instead of the bearingless motor 4. On both
sides of the motor 8, radial magnetic bearings 9a to support a load
in an axial orthogonal direction are disposed. Further, a thrust
collar 10 to transmit a thrust load is disposed between the motor 8
and the impeller 3, and thrust magnetic bearings 9b are disposed on
both sides of the thrust collar 10. A displacement sensor and an
electromagnetic actuator are built inside the magnetic bearing 9,
and electromagnetic force is controlled such the position of the
rotor 2 inside the casing is kept substantially constant. Load
capacity can be increased by using the magnetic bearing 9
independent from the motor 8, and reliability can be improved.
Third Embodiment
[0033] Next, a third embodiment of the present invention will be
described using FIG. 4.
[0034] FIG. 4 is a cross-sectional view illustrating a main portion
of a downhole compressor 1 according to the present embodiment. In
a structure of the present embodiment, a component denoted by a
reference sign same as above-described embodiments has the same
structure and effects. Therefore, a description therefor will be
omitted and only a different point from the above-described
embodiments will be described. According to the second embodiment
illustrated in FIG. 3, pressure in a flow passage portion of an
impeller 3 is increased from an inlet portion 3b to an outlet
portion 3a, but pressure on a back surface of the impeller 3 is
substantially equal to the pressure at the outlet portion 3a of the
impeller 3. Therefore, a thrust load is generated at the impeller 3
in a direction from the back surface side to a flow passage side.
Load capacity of a magnetic bearing 9 is small compared with a
general oil lubrication bearing. Therefore, in the case of applying
the magnetic bearing 9 in the downhole compressor 1, the thrust
load is preferably reduced as much as possible.
[0035] According to the third embodiment, a shaft sealing device 12
is disposed at a back surface portion of the impeller 3 and forms a
pressure regulating chamber 11. Further, a communication unit 13 is
provided between the pressure regulating chamber 11 and the inlet
portion 3b of the impeller 3 and decreases pressure at the pressure
regulating chamber 11. As a result, the thrust load can be reduced
by decreasing the pressure at the back surface of the impeller 3,
and reliability of a thrust magnetic bearing 9b can be
improved.
[0036] Further, in order to stabilize the thrust load in the
present embodiment, axial clearance of the shaft sealing device 12
is preferably kept constant. Therefore, a position sensor 14 for an
axial rotor 2 used to control the thrust magnetic bearing 9b is
provided at the back surface portion of the impeller 3, and the
thrust magnetic bearing 9b is controlled so as to keep the
clearance of shaft sealing device 12 constant.
[0037] Additionally, according to the present embodiment, an axial
groove is provided as the communication unit 13 at a fixing portion
of the impeller 3 of the rotor 2. The axial groove may also be
provided on the impeller 3 side and a communication hole may be
provided at the rotor 2 and the impeller 3.
Fourth Embodiment
[0038] Next, a fourth embodiment of the present invention will be
described using FIG. 5.
[0039] FIG. 5 is a cross-sectional view illustrating a main portion
of a downhole compressor 1 according to the present embodiment. In
a structure of the present embodiment, a component denoted by a
reference sign same as above-described embodiments has the same
structure and effects. Therefore, a description therefor will be
omitted and only a different point from the above-described
embodiments will be described.
[0040] According to the present embodiment, a shaft sealing device
12 is disposed at an outer diameter portion of an impeller 3. The
shaft sealing device 12 includes a so-called labyrinth seal 12a
opposing to an outer periphery of the impeller 3 and an axial
clearance 12b projecting to a flow passage side of the impeller 3.
When a leakage amount at the shaft sealing device 12 is increased,
back pressure of the impeller 3 is increased and a thrust load is
increased, thereby moving a rotor 2 to an axial upstream side. At
this point, the axial clearance 12b at the shaft sealing device 12
becomes small, and the leakage amount is reduced at the shaft
sealing device 12. Therefore, the thrust load is reduced and the
rotor 2 is pushed back to an axial downstream side. Since the
thrust load is thus automatically adjusted in accordance with
movement of the rotor 2, the thrust load that acts on a thrust
magnetic bearing 9b can be properly adjusted and reliability of the
device can be improved.
[0041] Meanwhile, in the fourth embodiment also, the thrust
magnetic bearing 9b can be controlled so as to keep the clearance
at the shaft sealing device 12 constant by providing a position
sensor 14 at an axial rotor 2 illustrated in the third
embodiment.
* * * * *