BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] 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.
2. Description of the Related Art
[0002] 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.
[0003] 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
US Patent No. 7,338,262, is operated at a high rotational speed of 20,000 rpm to 50,000 rpm.
[0004] 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
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] Further, the present invention is the downhole compressor characterized in including
a bearingless motor as an electromagnetic control unit.
[0011] Furthermore, the present invention is the downhole compressor characterized in that
the electromagnetic control unit includes a magnetic bearing.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] Furthermore, the present invention is the downhole compressor characterized in that
a control device for the electromagnetic control unit is disposed on the ground.
[0017] 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.
[0018] 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
[0019]
Fig. 1 is a cross-sectional view illustrating a main portion of a downhole compressor
according to a first embodiment of the present invention;
Fig. 2 is a cross-sectional view illustrating an installation state of the downhole
compressor according to the first embodiment of the present invention;
Fig. 3 is a cross-sectional view illustrating a main portion of a downhole compressor
according to a second embodiment of the present invention;
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
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
[0020] Embodiments to implement the present invention will be described below using the
drawings.
First embodiment
[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] 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.
[0023] 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.
[0024] 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
[0025] 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.
[0026] 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
[0027] Next, a third embodiment of the present invention will be described using Fig. 4.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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
[0032] Next, a fourth embodiment of the present invention will be described using Fig. 5.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] Features, components and specific details of the structures of the above-described
embodiments may be exchanged or combined to form further embodiments optimized for
the respective application. As far as those modifications are readily apparent for
an expert skilled in the art they shall be disclosed implicitly by the above description
without specifying explicitly every possible combination, for the sake of conciseness
of the present description.
1. A downhole compressor (1), comprising:
a casing disposed inside a well;
a rotor (2) built inside the casing; and
an impeller (3) disposed at the rotor (2), characterised in that an electromagnetic control unit is configured to electromagnetically control a relative
position of the rotor (2) inside the casing is provided.
2. The downhole compressor (1) according to claim 1, wherein a bearingless motor (4)
is provided as the electromagnetic control unit.
3. The downhole compressor (1) according to claim 1, wherein a magnetic bearing is provided
as the electromagnetic control unit.
4. The downhole compressor (1) according to claim 1, wherein
a pressure regulating chamber is provided at a back surface portion of the impeller
(3),
a shaft sealing device is provided between an outlet portion of the impeller (3) and
the pressure regulating chamber, and
a communication unit is provided between the pressure regulating chamber and an inlet
portion of the impeller (3).
5. The downhole compressor (1) according to claim 1 or 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 (3).
6. The downhole compressor (1) according to claim 4, wherein a leakage amount at the
shaft sealing device is reduced when the rotor (2) is displaced to an axial upstream
side.
7. The downhole compressor (1) according to claim 6, wherein the shaft sealing device
includes axial clearance, and the axial clearance is reduced when the rotor (2) is
displaced to the axial upstream side.
8. The downhole compressor (1) according to claim 1, wherein a control device for the
electromagnetic control unit is disposed on the ground.
9. The downhole compressor (1) according to claim 1 or 8, wherein an operating condition
is determined by using a control signal of the electromagnetic control unit.
1. Bohrlochverdichter (1), der Folgendes umfasst:
ein Gehäuse, das in einem Schacht angeordnet ist;
einen Rotor (2), der in dem Gehäuse eingebaut ist; und
ein Laufrad (3), das an dem Rotor (2) angeordnet ist, dadurch gekennzeichnet, dass eine elektromagnetische Steuereinheit, die konfiguriert ist, eine Relativposition
des Rotors (2) in dem Gehäuse zu steuern, vorgesehen ist.
2. Bohrlochverdichter (1) nach Anspruch 1, wobei ein lagerloser Motor (4) als die elektromagnetische
Steuereinheit vorgesehen ist.
3. Bohrlochverdichter (1) nach Anspruch 1, wobei ein Magnetlager als die elektromagnetische
Steuereinheit vorgesehen ist.
4. Bohrlochverdichter (1) nach Anspruch 1, wobei
eine druckregulierende Kammer an einem Rückflächenabschnitt des Laufrads (3) angeordnet
ist,
eine Wellendichtungsvorrichtung zwischen einem Auslassabschnitt des Laufrads (3) und
der druckregulierenden Kammer vorgesehen ist, und
eine Kommunikationseinheit zwischen der druckregulierenden Kammer und einem Einlassabschnitt
des Laufrads (3) vorgesehen ist.
5. Bohrlochverdichter (1) nach Anspruch 1 oder 4, wobei
einen Verschiebungsmesser vorgesehen ist, der konfiguriert ist, eine axiale Verschiebung
zu messen, und
der Verschiebungsmesser an einem Rückflächenabschnitt des Laufrads (3) angeordnet
ist.
6. Bohrlochverdichter (1) nach Anspruch 4, wobei eine Leckmenge an der Wellendichtungsvorrichtung
verringert wird, wenn der Rotor (2) auf eine axial stromaufwärts gelegene Seite verschoben
wird.
7. Bohrlochverdichter (1) nach Anspruch 6, wobei die Wellendichtungsvorrichtung ein axiales
Spiel aufweist und das axiale Spiel verringert wird, wenn der Rotor (2) auf eine axial
stromaufwärts gelegene Seite verschoben wird.
8. Bohrlochverdichter (1) nach Anspruch 1, wobei eine Steuervorrichtung für die elektromagnetische
Steuereinheit auf dem Boden angeordnet ist.
9. Bohrlochverdichter (1) nach Anspruch 1 oder 8, wobei ein Betriebszustand durch Verwenden
eines Steuersignals der elektromagnetischen Steuereinheit bestimmt wird.
1. Compresseur de fond de trou (1), comprenant :
un carter disposé à l'intérieur d'un puits ;
un rotor (2) assemblé à l'intérieur du carter ; et
une hélice (3) disposée sur le rotor (2),
caractérisé en ce qu'il est prévu une unité de commande électromagnétique qui est configurée pour commander
par voie électromagnétique une position relative du rotor (2) à l'intérieur du carter.
2. Compresseur de fond de trou (1) selon la revendication 1, dans lequel un moteur sans
palier (4) est prévu à titre d'unité de commande électromagnétique.
3. Compresseur de fond de trou (1) selon la revendication, dans lequel un palier magnétique
est prévu à titre d'unité de commande électromagnétique.
4. Compresseur de fond de trou (1) selon la revendication 1, dans lequel une chambre
de régulation de pression est prévue au niveau d'une portion de surface arrière de
l'hélice (3),
un dispositif d'étanchement d'arbre est prévu entre une portion de sortie de l'hélice
et la chambre de régulation de pression, et
il est prévu une unité de communication entre la chambre de régulation de pression
et une portion d'entrée de l'hélice (3).
5. Compresseur de fond de trou (1) selon la revendication 1 ou 4, dans lequel il est
prévu un dispositif de mesure de déplacement configuré pour mesurer un déplacement
axial, et
le dispositif de mesure de déplacement est disposé à une portion de surface arrière
de l'hélice (3).
6. Compresseur de fond de trou (1) selon la revendication 4, dans lequel une fuite quantitative
au niveau du dispositif d'étanchement d'arbre est réduite quand le rotor (2) est déplacé
vers un côté amont axial.
7. Compresseur de fond de trou (1) selon la revendication 6, dans lequel le dispositif
d'étanchement d'arbre inclut un jeu axial et le jeu axial est réduit quand le rotor
(2) est déplacé vers le côté amont axial.
8. Compresseur de fond de trou (1) selon la revendication 1, dans lequel un dispositif
de commande pour l'unité de commande électromagnétique est disposé sur le fond.
9. Compresseur de fond de trou (1) selon la revendication 1 ou 8, dans lequel une condition
de fonctionnement est déterminée en utilisant un signal de commande de l'unité de
commande électromagnétique.