U.S. patent application number 10/804792 was filed with the patent office on 2004-09-30 for submersible pump deployment and retrieval system.
Invention is credited to Traylor, Leland B..
Application Number | 20040188096 10/804792 |
Document ID | / |
Family ID | 32994994 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040188096 |
Kind Code |
A1 |
Traylor, Leland B. |
September 30, 2004 |
Submersible pump deployment and retrieval system
Abstract
The present invention relates to a system for deployment and
retrieval of a submersible pump in a well. The submersible pump is
deployed and retrieved by using a power conduit that conveys power
to the submersible pump. More specifically, the power conduit has a
substantially neutral buoyancy when submersed in the well fluid.
The buoyancy reduces the mechanical loading of the power conduit
when submerged in the well fluid.
Inventors: |
Traylor, Leland B.; (Draper,
UT) |
Correspondence
Address: |
OSHA NOVAK & MAY L.L.P.
Suite 2800
1221 McKinney Street
Houston
TX
77010
US
|
Family ID: |
32994994 |
Appl. No.: |
10/804792 |
Filed: |
March 19, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60458860 |
Mar 28, 2003 |
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Current U.S.
Class: |
166/369 ;
166/108 |
Current CPC
Class: |
E21B 43/128 20130101;
E21B 43/121 20130101 |
Class at
Publication: |
166/369 ;
166/108 |
International
Class: |
E21B 027/00 |
Claims
What is claimed is:
1. A system for pumping a fluid from a well, comprising: a
submersible pump; a power conduit disposed in the fluid and
operatively connected to the submersible pump, wherein the power
conduit has a density similar to the density of the fluid within
the well; and a sealing device operatively connected to the
submersible pump, wherein the sealing device supports a pressure
differential created by the submersible pump.
2. The system of claim 1, wherein the power conduit comprises a
hollow section.
3. The system of claim 2, wherein the submersible pump is operated
by pressure conveyed through the hollow section.
4. The system of claim 1, wherein the power conduit comprises at
least one conductor and an insulating material.
5. The system of claim 4, wherein the submersible pump is operated
by electrical power conveyed through the conductor.
6. The system of claim 1, wherein the sealing device is disposed in
a well casing.
7. The system of claim 1, wherein the submersible pump is disposed
in a liner.
8. The system of claim 7, wherein the sealing device is disposed in
the liner.
9. The system of claim 1, wherein the sealing device comprises a
packer.
10. The system of claim 9, wherein the packer has a release
mechanism operated by tension in the power conduit.
11. The system of claim 9, wherein the packer equalizes the
pressure above and below the packer when the submersible pump is
deactivated.
12. The system of claim 9, wherein the packer is disposed above the
submersible pump.
13. The system of claim 9, wherein the packer is disposed below the
submersible pump.
14. The system of claim 1, wherein the sealing device comprises a
shoe.
15. The system of claim 14, wherein the shoe is disposed in a well
casing.
16. The system of claim 14, wherein the shoe is disposed in a
liner.
17. The system of claim 1, wherein the submersible pump comprises a
buoyant material to decrease the weight of the submersible pump
when submerged in the well.
18. The system of claim 1, further comprising a backflow preventer
disposed below the submersible pump.
19. A system for pumping fluids from a well, comprising: an
electric submersible pump; a power conduit operatively connected to
the electric submersible pump, wherein the power conduit has a
density near the density of a fluid within the well; and a sealing
device operatively connected to the electric submersible pump,
wherein the sealing device supports a pressure differential created
by the electric submersible pump.
20. The system of claim 19, wherein the power conduit comprises a
conductor and an insulating material.
21. The system of claim 20, wherein the submersible pump is
operated by electrical power conveyed through the conductor.
22. A system for pumping fluids from a well, comprising: a
hydraulically driven submersible pump; a power conduit operatively
connected to the hydraulically driven submersible pump, wherein the
power conduit has a density near the density of a fluid within the
well; and a sealing device operatively connected to the
hydraulically driven submersible pump, wherein the sealing device
supports a pressure differential created by the submersible
pump.
23. The system of claim 22, wherein the power conduit comprises a
hollow section.
24. The system of claim 23, wherein the submersible pump is
operated by pressure conveyed through the hollow section.
25. A method for deploying a submersible pump in a well, the method
comprising: operatively connecting a power conduit to the
submersible pump, wherein the power conduit has a density near the
density of a fluid in the well; lowering the submersible pump into
the well, wherein the submersible pump is supported by the power
conduit and the well is substantially full of the fluid; sealing
between a submersible pump outlet and a submersible pump inlet; and
conveying power to the submersible pump through the power
conduit.
26. The method of claim 25, wherein the power conveyed through the
power conduit is electrical.
27. The method of claim 25, wherein the power conveyed through the
power conduit is hydraulic.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit, pursuant to 35 U.S.C.
.sctn.119(e), of U.S. Provisional Application No. 60/458,860,
entitled, "Submersible Pump Deployment and Retrieval System," filed
on Mar. 28, 2003. That application is incorporated by reference in
its entirety.
BACKGROUND ART
[0002] The invention of the electrically actuated submersible pumps
by Armais Arutunoff in 1933 started an era where electrical power
replaced mechanical force as the method used to transmit the
necessary power to downhole pumps for the extraction of various
materials. Since the Arutunoff invention, methods have been
improved to take advantage of the unique characteristics of the
pump and power source. The most significant improvement was the
dramatic reduction in the mass and size of the elements used to
transmit the power and to react the resulting forces. For example,
steel rods were replaced with much lighter electrical cable and
heavy production tubing once required to react mechanical actuation
was replaced with much lighter production tubing.
[0003] The successful installation of an electrical submersible
pump in a well usually requires that several steps and functions
take place. The first step is the suspension of the mass of the
production string either from the wellhead or the casing. As that
term is typically used, the production string includes everything
inside the casing below the wellhead, and typically includes the
production tubing, the fluid inside the production tubing and the
electrical cable. Secondly, there must be proper conveyance of the
pumped fluid from the pump to the surface, typically through a
closed tube. Finally, electrical power must be conveyed from the
surface to the pump. For example, modern electrical submersible
pumps are installed in drilled wells that may have been cased with
steel pipe, and have installed inside the casing production tubing
that consists of 30 foot sections of 2 inch production tubing that
are screwed together to form a continuous pipe. Attached to the
production tubing is a multi-conductor electrical cable used to
provide power to the pump. The electrical cable is typically banded
to the production tubing every 10 feet, and is installed outside
the production tubing. Two of the required functions are
accomplished by the production tubing, namely suspension of the
mass and conveyance of the pumped fluid. The third function,
conveyance of electrical power, is accomplished by the electrical
cable banded to the production tubing.
[0004] Numerous attempts have been made to improve conventional
practice by combining two or three of these functions into a single
structure that can be spooled on a reel and deployed continuously
into the well. Lighter (hence cheaper) structures can be obtained
by this combination, and easier installation is the result of a
continuous structure that can be conveniently transported and
deployed into the well from a reel. Another significant advantage
is the ability to quickly and easily remove the pump for
maintenance. As early as 1968, U.S. Pat. No. 3,411,454 proposed a
flexible cable that consisted of strong steel fibers interwoven
with electrical conductors to form a cable that provides electrical
power and load suspension. An additional structure, a liner, was
used to convey fluids from the pump to the surface. Because the
pump was located inside the liner, the pump could be installed and
replaced without removing the liner, thus providing most of the
advantages of combination.
[0005] Variations of this theme, commonly referred to as cable
suspended pumping systems or CSPS, were pursued for the next 20
years. One problem with such systems is the tendency of the
electrical cable and the mechanical cable to be incompatible under
mechanical load. One solution to this problem was suggested in U.S.
Pat. No. 4,681,169, which separated the mechanical cable from the
electrical cable and loosely attached the cables. This type of
system allowed load to be transferred from the electrical cable to
the steel cable, but did not tightly tie the two together. However,
this approach did not address the conveyance of fluids from the
pump to the surface. With the introduction of coiled production
tubing, the load suspension element was changed from wire rope to
coiled production tubing, and many variations of combinations of
coiled production tubing and electrical cable were patented.
[0006] One example of a cable suspended pumping system is
illustrated in U.S. Publication No. 20020108757. The method is
intended to solve the issues of incompatibility between the power
conduit, suspension cable, and the coiled production tubing by
providing a means for the cables to lengthen different amounts when
loaded. In this example, the power conduit, suspension cable, and
the coiled production tubing are combined at the surface using
removable clamps as the pump is lowered into the well. The clamps
are spaced relatively far apart to allow the three elements to
expand or contract between the clamps without damage.
[0007] U.S. Pat. No. 5,906,242 issued to Bruewer illustrates
another typical system, wherein the coiled or jointed tubing bears
the weight of the pump and the electrical cable. The coiled or
jointed tubing is filled with a fluid having sufficient density to
float the particular electrical cable being used. Both the coiled
or jointed tubing and flexible steel cable combined with electrical
cable accomplished the suspension and electrical power conveyance,
but required that an additional function, namely fluid conveyance
to the surface, be accomplished by another structure. This would
typically be accomplished by a liner or the well casing.
[0008] An alternative approach is expressed in U.S. Pat. No.
3,411,454, which proposed a flexible cable that consisted of strong
steel fibers interwoven with electrical conductors to form a cable
that provides electrical power and load suspension. However, high
axial loads on the cable may cause cable failures.
[0009] What is still needed, therefore, is a system for suspending
a submersible pump in a well wherein a single component
accomplishes both the power conveyance and the load suspension.
SUMMARY OF INVENTION
[0010] In one aspect, the present invention relates to a system for
pumping fluids out of a well. The system comprises a power conduit
operatively connected to a submersible pump.
[0011] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0012] FIG. 1 is a schematic side view of an installed submersible
pump in accordance with one embodiment of the invention.
[0013] FIG. 2 is a schematic side section view of an adaptor with
an inflatable packer in accordance with one embodiment of the
present invention.
[0014] FIG. 3 is a side section view of an installed submersible
pump in accordance with one embodiment of the invention.
[0015] FIG. 4 is a side section view of an installed submersible
pump in accordance with one embodiment of the invention.
[0016] FIG. 5 is a side section view of an installed submersible
pump in accordance with one embodiment of the invention.
[0017] FIG. 6 is a flowchart of a method in accordance with one
embodiment of the invention.
DETAILED DESCRIPTION
[0018] In one or more embodiments, the present invention relates to
suspending a submersible pump in a well by using a power conduit
that also provides the suspension of the pump. More specifically,
the power conduit has a substantially neutral buoyancy when
submersed in the well fluid. The buoyancy reduces the mechanical
loading of the power conduit that is attributed to the weight of
the power conduit.
[0019] FIG. 1 illustrates a system in accordance with one
embodiment of the present invention. In FIG. 1, a liner 5 is
installed inside of a well casing 7. A backflow preventer is
located proximal to the distal end (i.e., the end closest to the
well bottom) of the liner 5. In one embodiment, the backflow
preventer comprises a check valve 8. In a typical embodiment, the
liner 5 is then filled with a fluid 4. The fluid 4 may be provided
from the well or pumped into the well from an outside source.
Typically, the fluid 4 is water based. The check valve 8 is adapted
such that the fluid 4 is allowed to flow through the check valve 8
from below, but fluid is prevented from flowing from above. This
function allows the liner 5 to stay filled with the fluid 4. While
the backflow preventer is shown as a check valve 8, one of ordinary
skill in the art will appreciate that other mechanisms could
provide a similar function without departing from the scope of the
present invention. Other backflow preventer options could include
valves operated by electrical power conveyed through the power
conduit. The backflow preventer could also be integrated into the
submersible pump such that flow is only allowed to flow in one
direction. In some instances, if the formation has a high enough
pressure, a sufficient column of fluid can be supported without a
backflow preventer.
[0020] After the liner 5 is sufficiently filled with the fluid 4, a
submersible pump 1 is lowered into the well and supported by a
power conduit 2. The power conduit 2 and the fluid 4 have similar
densities. Whether the liner 5 is "sufficiently filled" is
determined by the strength of the power conduit 2 and the ability
to support the free hanging weight of the power conduit 2 and the
submersible pump 1. The portion of the power conduit 2 that is
submerged in the fluid 4 is supported by the buoyancy of the power
conduit 2. This reduces the loading on the power conduit 2 caused
by the weight of the power conduit 2.
[0021] In the pictured embodiment, a packer 3 is located above the
submersible pump 1. The power conduit 2 passes through a
feedthrough 11 and is connected to the submersible pump 1. In other
embodiments, the packer 3 may be disposed below the submersible
pump 1, which would allow the power conduit 2 to be directly
connected to the submersible pump 1. After reaching the appropriate
location in the well, the packer 3 is activated to seal between the
liner 5 and the submersible pump 1. Once the packer 3 is activated,
the weight of the submersible pump 1 may be fully supported by the
packer 3.
[0022] After being fully installed, the submersible pump 1 may be
turned on from the surface by power conveyed through the power
conduit 2. Typically, power is supplied by hydraulic pressure or
electricity. The submersible pump 1 may accordingly be operated by
hydraulic pressure or electricity conveyed through the power
conduit 2. When the submersible pump 1 is operating, fluid 4 flows
from perforations 10 into the well casing. Then, the fluid 4 flows
through the check valve 8 into the liner 5. The fluid 4 is taken
into the pump inlet 9, through the submersible pump 1, and out into
the liner 5 after exiting through the pump outlet 6. Fluid 4 flows
from that point up towards the surface. The fluid flow is indicated
in FIG. 1 by arrows.
[0023] Submersible pumps wear out over time depending on the
particular submersible pump and the conditions in the well. The
well ceases to produce once the submersible pump fails. After a
submersible pump failure, the submersible pump is brought to the
surface and replaced. Typically, retrieval of the submersible pump
is accomplished using the system that was used for deploying of the
submersible pump. Replacing the submersible pump requires releasing
the sealing device so that the submersible pump can be pulled to
the surface by the power conduit.
[0024] FIG. 2 illustrates a release mechanism in accordance with
one embodiment of the present invention. One suitable release
mechanism known in the art is an inflatable packer 203. The
inflatable packer 203 is activated by differential pressure
experienced in the well. In this example, the inflatable packer 203
is installed above the submersible pump, not shown. The power
conduit 2 passes through a feedthrough 11 to connect to the
submersible pump. In order to release this particular inflatable
packer 203, there is a packer release mechanism 201, which deflates
the inflatable packer 203 when tension is applied by the power
conduit 2. There are many sealing device options with various
release mechanisms that may be suitable for the present invention.
For example, an inflatable packer may have a small orifice that
leaks pressure gradually. When the submersible pump deactivates,
the small orifice deflates the inflatable packer by equalizing the
pressure above and below the inflatable packer. One of ordinary
skill in the art will appreciate that the sealing device and
release mechanism may vary without departing from the scope of the
invention.
[0025] Turning to FIG. 3, another embodiment of the present
invention is shown. In this embodiment, a packer 301 is shown
installed directly into the well casing 7. The packer 301 has a
profile on top that enables a shoe 302 to seal using a shoe seal
303. The packer 301 may be installed using any means known in the
art, such as a wire line. A shoe 302 can then be run into the well
and seal against the packer 301 using the shoe seal 303. Typically,
the shoe 302 would be run into the well using wire line that is
attached to the shoe 302 by the wire line connection groove 304. A
check valve 8 is installed inside of the shoe 302 to maintain fluid
in the casing above the packer 301. After the above items have been
installed, fluid 4 would fill the casing as discussed with respect
to FIG. 1.
[0026] Continuing with FIG. 3, a submersible pump 1 is run into the
well while attached to the power conduit 2, which has a density
substantially equal to the fluid 4. The submersible pump 1 includes
a pump seal 306, which seals against the shoe 302. The weight of
the submersible pump 1 would then be supported by the shoe 302 and
the packer 301. Once the submersible pump 1 seals against the shoe
302, the submersible pump 1 can be powered by power conveyed
through the power conduit 2. At that point, the submersible pump 1
would pump fluid 4 from below the packer 301 to the surface. The
fluid 4 would be conveyed to the surface through the casing 7.
[0027] As discussed with respect to FIGS. 1 and 2, the submersible
pump 1 will eventually require replacement. In the embodiment
illustrated in FIG. 3, the packer 301, check valve 8, and the shoe
302 may be permanently installed into the well. When the
submersible pump 1 is turned off, the submersible pump 1 may be
pulled to the surface by the power conduit 2. In this
configuration, a release valve 305 is included above the
submersible pump 1. The release valve 305 would relieve the
pressure difference above and below the submersible pump 1 allowing
the power conduit 2 to retrieve the submersible pump 1 with minimal
force. The release valve 305 may operate by tension in the power
conduit 2, a small orifice that relieves pressure when the
submersible pump 1 is turned off, or any other means known in the
art. One of ordinary skill in the art will appreciate that other
devices could be used to aid the release of the submersible pump
without departing from the scope of the invention. If no release
mechanism is used, then the power conduit 2 would provide the force
required to overcome the pressure differential that exists above
and below the pump. A release mechanism would reduce this force
requirement.
[0028] FIG. 4 illustrates another embodiment in accordance with the
present invention. A liner 5 is shown in the well. A seating nipple
402 is disposed on the end of the liner 5. A shoe 302 is installed
inside the liner 5 and includes a seal 401 that is adapted to seal
against the seating nipple 402. A check valve 8 is installed inside
of the shoe 302. After installation of these components, a
submersible pump would be installed as discussed with the previous
embodiments. Fluid would be conveyed to the surface through the
liner 5. One of ordinary skill in the art will appreciate that the
liner could be any other tubing, such as jointed pipe or coiled
tubing, without departing from the scope of the present
invention.
[0029] Turning to FIG. 5, a pumping system in accordance with an
embodiment of the present invention is shown. The embodiment shown
in FIG. 5 is similar to that of FIG. 4. The submersible pump is a
hydraulically driven submersible pump 502. Pressure is conveyed
through the power conduit to power the hydraulically driven
submersible pump 502. In this embodiment, the power conduit
comprises twin floating hydraulic tubing 501. The twin floating
hydraulic tubing 501 would have a density substantially equal to
the fluid 4.
[0030] Several methods are available to create power conduit that
has substantially neutral buoyancy. The term "neutral buoyancy,"
when applied to the power conduit, refers to the power conduit
having a density near the density of the fluid in the well. When
the power conduit has neutral buoyancy, the power conduit does not
experience increased loading from the weight of the power conduit.
The weight of the power conduit is fully supported in that case. If
the power conduit is too buoyant, it may be unable to lower the
submersible pump into the well because the power conduit will float
and lift the submersible pump. Excess buoyancy will also create
tension in the power conduit. Whether the power conduit is "too
buoyant" will depend on the weight of the submersible pump and the
tensile strength of the power conduit. Alternatively, if the power
conduit has less than neutral buoyancy, the tension in the cable
will increase with length. The negative buoyancy that can be
allowed will vary based on the weight of the submersible pump and
the tensile strength of the power conduit.
[0031] In some embodiments of the present invention which employ
electrical submersible pumps, the power conduit is constructed of
at least two types of materials. For example, in one embodiment, a
power conduit comprises an electrical conductor, which conveys
electricity to the pump, and an insulating material. In an
alternative embodiment, multiple power conduits are combined by
extruding a sleeve over the power conduits to form a single
structure. The conducting material may be formed of a metal, copper
or aluminum, for example. These materials have a density greater
than 1.0 g/cc. The insulating material may be formed from a plastic
material having a density of less than 1.0 g/cc. By adjusting the
relative amounts of these two materials, an overall density of the
cable of 1.0 g/cc can be achieved, which is equal to the density of
water. The overall density of the cable may be adjusted if the
fluid in the well has a different density.
[0032] As an example of a power conduit design in accordance with
an embodiment of the invention, a number 10 copper conductor with a
diameter of 0.102 inches is used. The area of the conductor is
0.00817 square inches. The density of the copper conductor is 8.93
g/cc. If a low density polyethylene, or polypropylene insulator is
used, the specific gravity of the sleeve will be about 0.90 g/cc.
If copper conductor is round, and the inside diameter of the
insulating layer is the outside diameter of the copper, then
neutral buoyancy can be obtained by adjusting the outside diameter
to achieve an average specific gravity of 1.00. The equation for
the cable to have a specific gravity of 1.00 is: Area of the
conductor X specific gravity of the conductor equals Area of the
insulator X specific gravity of the insulator. Assuming copper and
polyethelene, and a number 10 conductor, solving for the outside
diameter of the insulator gives an outside diameter of about 0.34
inches. To power some submersible pumps, three of these cables
would be twisted together. The combination of the three cables
results in a diameter of about 0.75 inches.
[0033] In some applications, a diameter of 0.75 inches may be too
large. To decrease the diameter of the power conduit, a lower
density material can be created by using lower density
polyethylene, foaming polyethylene, or by filling the polyethylene
with a low density filler such as glass microballons, or low
molecular weight filler material such as polywax 500 available from
Baker-Hughes Petrolite division. At great depths, the glass
microballons may be preferred due to the tendency of foamed
materials to collapse under extreme pressures.
[0034] In addition to the filler, a strength member such as a
polyamide (Kevlar) rope may be added to reduce density and add
strength. Another method to reduce the bulk of the neutral density
cable is to use aluminum conductors in place of copper. This will
reduce the weight of the conductors for the same current carrying
capabilities, further reducing the bulk of the low density
component of the cable. Aluminum does have the disadvantage of
being reactive in some environments, so care must be taken to
protect the conductors, especially in areas where well fluids may
enter. Examples of methods to protect an aluminum conductor include
coatings or jackets made of non-reactive materials.
[0035] The buoyancy of the power conduit may be adjusted by the
attachment of weights and floats at various locations along the
length of the power conduit. This additional adjustment allows the
power conduit to be adapted to a particular well fluid after the
power conduit has been manufactured. In some cases, the well fluid
may be water with dissolved salt such that the overall density of
the well fluid is 1.1 g/cc. This well fluid would cause a power
conduit having an average density of 1.0 g/cc to have positive
buoyancy. The power conduit could be weighted at locations along
the length so that the average density is 1.1 g/cc to match the
well fluid. In a scenario where the power conduit is denser than
the well fluid, floats could be attached at locations along the
length to make the power conduit more buoyant.
[0036] The various materials of the power conduit can be utilized
in varying ratios to suit particular applications. The required
electrical power, liner or casing size, fluids in the well, depth,
and required strength each factor into the design of the power
conduit. One of ordinary skill in the art will appreciate that the
selected materials, ratios of the materials, and overall size of
the cable may vary without departing from the scope of the
invention.
[0037] In FIG. 6, a method in accordance with an embodiment of the
invention is shown. In step 610, a check valve, or other backflow
preventer, is installed in the distal end of a liner. In other
embodiments, the check valve may be installed at another location
in the liner that is below the intended location for the
submersible pump. Additionally, the check valve may be installed in
a casing in the well. In step 620, the liner is filled with a
fluid. If the check valve is installed in the casing, the casing
would be filled with fluid. Typically, the fluid would comprise
water provided from the well or other outside source. In step 630,
a submersible pump is deployed using a power conduit having a
density similar to the density of the fluid. Then, in step 640, a
seal is formed between the inlet and outlet of the submersible
pump. In step 650, power is conveyed to the submersible pump
through the power conduit.
[0038] While the above discussion was focused on the design to make
power conduit for conveying electricity neutrally buoyant, similar
principles can be used to design power conduits for conveying
hydraulic pressure. To convey hydraulic pressure, the power conduit
would typically include a hollow passageway. The hydraulic pressure
could be conveyed by a fluid disposed in the hollow passageway. The
fluid could be air, oil, or any other suitable fluid. A metal, such
as steel, could wrap the power conduit for tensile and pressure
capability. The balance and selection of materials for a power
conduit to convey hydraulic pressure will vary according to the
specific application.
[0039] One factor in the strength requirement of the cable is the
weight of the submersible pump when submerged in the well. The
weight of the submersible pump will vary according its size and
capacity. For example, a submersible pump having a diameter of 21/2
inches might weigh 80 pounds when submerged in water. A submersible
pump having a diameter of about 4 inches might weigh 160 pounds
when submerged in water. One option to reduce the weight of the
submersible pump in the well, and the strength requirement of the
cable, is to attach buoyant material to the submersible pump. The 4
inch submersible pump could have enough buoyant material attached
so that the weight of the pump decreased to 80 pounds when
submerged in the well. Some negative buoyancy is required so that
the submersible pump can be lowered into the well. The required
negative buoyancy will vary depending on the well geometry and the
sealing devices. For example, a shoe typically requires a load to
form a seal with the submersible pump.
[0040] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
* * * * *