Note: Descriptions are shown in the official language in which they were submitted.
CA 02590452 2009-11-09
SEAL SECTION FOR ELECTRICAL SUBMERSIBLE PUMP
Field of the Invention
This invention relates in general to electrical submersible well pumps and in
particular to a seal section that locates between the pump motor and the pump
for
equalizing lubricant pressure contained within the motor with hydrostatic
pressure on the
exterior.
Background of the Invention:
Electrical submersible pumps are often used for pumping a mixture of oil and
water from a well. Normally the pump assembly has an electrical motor and a
rotary
pump, which may be centrifugal or other types. The motor is filled with a
dielectric
lubricant, and a seal section between the motor and the pump serves to
equalize the
internal pressure of the lubricant with the hydrostatic pressure on the
exterior of the pump
assembly.
A typical seal section, also called a pressure equalizer, has a tubular
housing
through which a drive shaft extends for transmitting rotation of the motor to
the pump. A
thrust bearing assembly is often located in the seal section for absorbing
downthrust
created by the pump. The lubricant in the pump also lubricates the thrust
bearing.
Various means are employed to equalize lubricant pressure with the well fluid.
A
tubular elastomeric bladder may be mounted in the seal section, the bladder
having an
interior in fluid communication with the lubricant in the motor. A well fluid
passageway
allows well fluid to enter the seal section on the exterior of the bladder.
Labyrinth tubes
are also employed, either alone or in a separate chamber from the bladder. The
water of
the well fluid is normally denser than the oil. Generally, the labyrinth tubes
are mounted
with an upper inlet and a lower outlet, so that water flowing downward through
the tube
cannot flow back upward through the outlet in a manner so as to migrate into
the motor.
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The seal section also has features to accommodate expansion of the lubricant
in the
motor, which occurs as the motor gets hotter. A check valve may be employed to
expel
excess lubricant without allowing the entry of well fluid.
Most seal sections have multiple chambers, usually two to four, for housing
the
bladder and labyrinth tubes. Normally, each chamber is a cylindrical sleeve
secured at its
upper and lower ends by threads to adapters and shaft support members. The
additional
threaded sleeves add to the cost of a seal section.
Summary
The seal section of this invention has a number of desirable features. A
labyrinth
tube is located within the bladder for expelling air during filling. The
labyrinth tube has a
lower end that connects to a separate oil-filled chamber.
The seal section has upper and lower adapters for securing the seal section
between
a pump and motor. The housing is a single cylindrical sleeve connected between
the
upper and lower adapters. A thrust bearing assembly is located in the housing
above the
lower adapter. Lower and central radial bearing supports fit within the
housing for
radially supporting the shaft. Isolation tubes enclose the shaft and connect
between the
lower and central radial bearing supports and the central radial bearing
support and the
upper adapter. The lower and central radial bearing supports, the isolation
tubes, and the
bag can be assembled as a unit and inserted into one end of the housing.
Accordingly, in one aspect there is provided a seal section for a submersible
well
pump assembly, comprising:
a housing for connection between a pump and a motor of a submersible well pump
assembly;
a rotatable shaft extending through the housing for transmitting rotational
motion
from the motor to the pump;
a central radial bearing support that rotatably supports the shaft and which
defines
upper and lower chambers in the housing;
a well fluid passageway leading from an exterior portion of the housing to the
upper chamber;
upper and lower isolation tubes extending around the shaft within the upper
and
lower chambers, respectively, each of the isolation tubes having an inner
diameter larger
than the shaft, defiling an annular passage for fluid communication with
lubricant
contained in the motor;
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a bladder surrounding the upper isolation tube in the upper chamber for
separating
lubricant within the bladder from well fluid in the upper chamber on the
exterior of the
bladder; and
a labyrinth tube within the bladder and having an upper end in fluid
communication with a labyrinth port leading through near an upper end of the
upper
isolation tube to the annular passage, the labyrinth tube having a lower end
in fluid
communication with the lower chamber.
According to another aspect there is provided a seal section for a submersible
well
pump assembly, comprising:
upper and lower adapters for connection to a pump and to a motor,
respectively, of
a submersible well pump assembly;
a single continuous sleeve extending from the lower to the upper adapter;
a rotatable shaft extending through the upper and lower adapters and the
sleeve for
transmitting rotational motion from the motor to the pump;
a thrust bearing assembly mounted in the sleeve above the lower adapter for
adsorbing downthrust on the shaft;
a lower radial bearing support that rotatably supports the shaft above the
thrust
bearing assembly, the lower radial bearing support having a seal that seals to
an inner
diameter of the sleeve, the lower radial bearing support having a maximum
outer diameter
less than the inner diameter of the sleeve so that the entire lower radial
bearing support fits
within the sleeve;
a central radial bearing support that rotatably supports the shaft above the
lower
radial bearing support, the central radial bearing support having a seal that
seals to the
inner diameter of the sleeve, defining upper and lower chambers in the sleeve,
the central
radial bearing support having a maximum outer diameter less than the inner
diameter of
the sleeve so that the entire central radial bearing support fits within the
sleeve;
a well fluid passageway leading from an exterior portion of the sleeve to the
upper
chamber; and
upper and lower isolation tubes extending around the shaft within the upper
and
lower chambers, respectively, each of the isolation tubes having an inner
diameter larger
than the shaft, defining an annular passage for fluid communication with
lubricant
contained in the motor, the upper isolation tube being connected between the
central radial
bearing support and the upper adapter, the lower isolation tube being
connected between
the central radial bearing support and the lower radial bearing support.
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According to yet another aspect there is provided a seal section for a
submersible
well pump assembly, comprising:
a housing for connection between a pump and a motor of a submersible well pump
assembly;
a rotatable shaft extending through housing for transmitting rotational motion
from
the motor to the pump;
a central radial bearing support within the housing that rotatably supports
the shaft
and which defines upper and lower chambers in the housing;
upper and lower isolation tubes extending around the shaft within the upper
and
lower chambers, respectively, each of the isolation tubes having an inner
diameter larger
than the shaft, defining an annular passage for fluid communication with
lubricant
contained in the motor;
a bladder surrounding the upper isolation tube in the upper chamber;
a bladder communication port in a sidewall of the upper isolation tube within
the
bladder for communicating lubricant in the annular passage with the interior
of the
bladder; and
a labyrinth tube within the bladder and having an upper end in fluid
communication with a labyrinth port in the sidewall of the upper isolation
tube, the
labyrinth tube having a lower end in fluid communication with the lower
chamber.
Brief Description of the Drawings
Figures 1A and 1B comprise a vertical sectional view of a seal section for an
electrical submersible well pump assembly in accordance with this invention.
Figure 2 is an enlarged sectional view of an upper portion of the seal section
of
Figure 1.
Figure 3 is a schematic sectional view of an electrical submersible pump
assembly
in accordance with this invention.
Detailed Description of the Invention
Referring to Figure 3, an electrical submersible pump assembly 11 ("ESP") is
shown installed within casing 13 in a well. ESP 11 is suspended on a string of
tubing 15,
and in this embodiment, discharges well fluid up tubing 15. ESP 11 has a motor
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17, typically a three-phase AC motor. Motor 17 is connected to a seal section
19,
which in turn is connected to a pump 21. Motor 17 is filled with a lubricant,
and seal
section 19 equalizes the lubricant pressure with the hydrostatic pressure of
the well
fluid on the exterior. Pump 21 is a rotary pump, such as a centrifugal pump
having a
large number of stages, each stage having an impeller and a diffuser. Pump 21
has an
intake 23 on its lower end that draws well fluid in.
Referring to Figures 1A and 1B, seal section 19 has a lower adapter 25 for
securing to motor 17 (Figure 3). Lower adapter 25 typically has a flange 27
that
receives bolts that bolt to a mating flange of motor 17. An upper adapter 29
(Figure
1 A) connects seal section 19 to pump 21 (Figure 3). Upper adapter 29 has
threaded
holes 31 for receiving bolts from a lower adapter of pump 21. Seal section 19
has a
housing 33 that comprises a cylindrical sleeve secured to lower and upper
adapters 25,
29, preferably by threads. Housing 33 is preferably a single integral member.
A shaft 35 extends through seal section 19 for transmitting rotary motion from
motor 17 (Figure 3) to pump 21. Shaft 35 has an upper splined end 37 that
optionally
may have a latch member 39. Latch member 39 latches to the shaft (not shown)
of
pump 21 (Figure 3) so as to transmit tension. Shaft 35 has lower splined end
41 that
engages the shaft of motor 17 (not shown).
A conventional thrust bearing 42 is located in seal section 19, as illustrated
in
Figure 1 B. Thrust bearing 42 comprises a rotary thrust member or runner 43
that is
secured to shaft 35. Runner 43 rotatably engages a stationary downthrust
member or
base 45 that is mounted to the upper side of lower adapter 25. Runner 43 also
engages a stationary upthrust member 47 while in upthrust. Upthrust member 47
is
supported within housing 33 against upward movement by a retainer ring 48,
which
may be a snap ring.
A lower radial bearing support 49 is supported in housing 33 against
downward movement by retainer ring 48. Lower radial bearing support 49 has a
bushing 51 that is slidably engaged by shaft 35. Bushing 51 does not form a
seal on
shaft 35 and may have passages or channels through it to freely allow the
passage of
motor lubricant. Lower radial bearing support 49 has seals on its exterior
that
sealingly engage the inner diameter of housing 33. A lower isolation tube 53
extends
sealingly into a counterbore in lower radial bearing support 49 at the upper
end of
bushing 51. Lower isolation tube 53 has an inner diameter that is larger than
the outer
diameter of shaft 35, creating an annular passage for the flow of motor
lubricant.
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Motor lubricant is free to flow between the area surrounding thrust bearing 42
and the annular clearance within lower isolation tube 53.
The upper end of lower isolation tube 53 extends into sealing engagement with
a counterbore in a central radial bearing support 55. Central radial bearing
support 55
has seals on its exterior that seal against the inner diameter of housing 33.
Central
radial bearing support also has a bushing 57 that slidingly engages shaft 35
but does
not seal against the flow of lubricant. A lower chamber 59 is defined by the
annular
space between radial bearing supports 49 and 55 and surrounding lower
isolation tube
53. A passage 61 extends through central radial bearing support 55 from its
lower end
to its upper end.
Referring to Figures 1 A and 1 B, an upper isolation tube 63 has its lower end
sealingly engaged in a counterbore in central radial bearing support 55 above
bushing
57. The upper end of upper isolation tube 63 extends to upper adapter 29,
defining an
annular upper chamber 64 within housing 33. A tubular elastomeric bladder 65
is
located within upper chamber 64. Bladder 65 has a lower end 67 that fits
sealingly
around an upper neck portion of central radial bearing support 55. Bladder 65
has a
neck 69 on its upper end that is sealingly secured to a bladder retainer 71,
as shown in
Figure 2. Bladder retainer 71 is a tubular member that is secured by threads
to the
upper end of upper isolation tube 63. Bladder retainer 71 has an upper portion
that
sealingly engages a counterbore 70 formed in the lower end of upper adapter
29.
Referring again to Figures 1 A and 1 B, a port 72 is located in the sidewall
of
upper isolation tube 63 near its upper end. Port 72 communicates the annular
clearance within upper isolation tube 63 with the interior of bladder 65. In
addition, a
labyrinth tube 73 has its upper end secured to a port 75 located adjacent port
72. Port
75 is shown below port 72, but it could be located at the same level or even
above
port 72. Labyrinth tube 73 is a small diameter tube that extends from port 75
downward alongside upper isolation tube 63 sealingly into the upper end of
passage
61 (Figure IB) in central radial bearing support 55. Lubricant within lower
chamber
59 thus communicates with lubricant in the annular clearance around shaft 35
within
isolation tubes 53 and 63 via labyrinth tube 73.
Referring to Figure 2, a threaded plug receptacle 77 is located in upper
adapter
29. Plug receptacle 77 will normally contain a plug (not shown) during
operation, but
it is removed during the lubricant filling procedure. A radially extending
passage 79
joins an inner end of plug receptacle 77 and extends inward to an axial
passage 81
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through which shaft 35 extends. A bushing 83 is located within passage 81 for
slidingly engaging and radially supporting shaft 35. Bushing 83 does not
provide a
seal against the flow of lubricant. One or more check valves 85 are located
within a
vent port 87 in upper adapter 29. Vent port 87 extends upward from the lower
end of
upper adapter 29 into an intersection with radial passage 79 inward from plug
receptacle 77. Check valve 85 will allow downward flow of fluid into upper
chamber
64 but not allow upward flow. A well fluid port 89 extends from the lower end
of
upper adapter 29 to a cavity 91 formed in the upper end of upper adapter 29.
Cavity
91 is in fluid communication with well fluid on the exterior of seal section
19 via
intake 23 (Figure 3) of pump 21. Well fluid port 89 alternately could extend
through
an exterior side wall of upper adapter 29.
A mechanical seal assembly 92 is located at the upper end of shaft 35 for
sealing against the encroachment of well fluid from cavity 91 into motor 17
(Fig. 3)
In this embodiment, mechanical seal assembly 92 includes a rotary seal member
93
that rotates with shaft 35 and is biased by a coiled spring 95 against a
stationary seal
base 97. A secondary shaft seal 99 may optionally be located below seal base
97.
Lubricant seal 99 is shown to be a conventional shaft oil seal. Preferably a
lubricant
is located between oil seal 99 and seal assembly 92, and that lubricant may
differ from
the motor lubricant.
To assemble seal section 19, the internal components of sleeve or housing 33
are pre-assembled and pushed into housing 33 from one end. For example, the
user
may first install lower adapter 25, thrust bearing 42 and shaft 35 in housing
33. The
user then would preassemble upper and lower isolation tubes 63, 53 with radial
bearing support members 49 and 55 and bladder 65. The user then would push
this
subassembly over shaft 35 and into housing 33. The user then would secure
upper
adapter 29 to housing 33. Counterbore 70 slides sealingly over bladder
retainer 71 to
make up the engagement while the threads on upper adapter 29 engage the
threads
within housing 33.
Prior to operation, motor 17 and seal section 19 are filled with a motor
lubricant, and
various methods can be employed. In one technique, motor 17 is initially
filled with
lubricant at a manufacturing or service facility. At the well site, seal
section 19 is
secured to the upper end of motor 17, and the lubricant is pumped in from a
fill port
(not shown) at the upper end of motor 17. The plug for receptacle 77 (Fig. 2)
is
removed prior to pumping the lubricant into motor 17 (Fig. 3). The
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operator can pump lubricant from the fill port upward in seal section 19 until
lubricant
begins to flow out plug receptacle 77. Air in seal section 19 would be
displaced out
port 77 during that procedure.
During filling, lubricant flows upward through the spaces around thrust
bearing 42 (Fig. 1B) and the annular clearance around shaft 35 in lower
isolation tube
53. The lubricant flows up through the annular clearance in upper isolation
tube 63
and down into bladder 65 via port 72 (Figure 1A). Lubricant also flows into
lower
chamber 59 via labyrinth tube 73 and passage 61. Once lower chamber 59 and the
interior of bladder 65 are filled, the lubricant will flow up into the spaces
around shaft
35 in upper adapter 29, at least up to oil seal 99, if utilized.
After filling, a plug is installed in receptacle 77 and ESP 11 (Fig. 3) is
lowered
into the well. As ESP 11 is lowered into the well, well fluid enters upper
chamber 64
via cavity 91 and passage 89. The hydrostatic pressure of the well fluid is
exerted via
bladder 65 to the lubricant within bladder 65 and motor 17. When at the
desired
depth, the operator supplies power to motor 17, causing pump 21 to draw well
fluid in
through intake 23 and discharge the well fluid through tubing 15 to the
surface.
Motor 17 will begin to heat up, which causes the lubricant to expand. Due to
the expansion, excess lubricant may vent through ports 79, 87 and check valves
85
into upper chamber 64. The lubricant is normally less dense than the well
fluid,
which often contains a high percentage of salt water, thus the vented
lubricant in
upper chamber 64 will typically gravitate upward through passage 89 and into
cavity
91 where it would be pumped to the surface by pump 21 (Fig. 3).
Over time, some leakage of well fluid past mechanical seal 92 and oil seal 99
may occur. If so, this well fluid will gravitate downward past bushing 83 and
into the
annular clearance surrounding upper isolation tube 63. Some of the well fluid
will
flow out port 72 into bladder 65. Some of the well fluid will flow down
labyrinth
tube 73 into lower chamber 59. Any well fluid that enters bladder 65 will
collect at
the lower end and would not be able to reenter port 72 located near the upper
end of
bladder 65. Also, any well fluid that may collect in lower chamber 59 would
not be
able to flow upward into ports 72 or 75.
The invention has significant advantages. The single cylindrical sleeve of the
housing reduces cost over multiple sleeve housings. Because the lower and
central
radial bearing supports slide into the housing, the seal section can have more
volume
for oil expansion than a prior art seal section having the same overall
length. The
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labyrinth tube allows bleeding of trapped air and provides an additional
barrier for
well fluid in the event of leakage. The oil seal serves as backup seal to
reduce entry
of well fluid into contact with the lubricant. Filling and servicing are more
easily
performed.
While the invention has been shown in only one of its forms, it should be
apparent to those skilled in the art that it is not so limited but is
susceptible to various
changes without departing from the scope of the invention.
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