Note: Descriptions are shown in the official language in which they were submitted.
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ELECTRICAL SUBMERSIBLE PUMPING SYSTEMS HAVING STIRLING
COOLERS
BACKGROUND OF INVENTION
Field of the Invention
[0001] This invention relates generally to techniques for maintaining downhole
tools and
their components within a desired temperature range in high-temp environments,
and,
more specifically, to an electrical submersible pumping system having a
Stirling-Cycle
cooling system.
Background Art
[0002] Electrical submersible pumping systems (ESPs) are used for artificial
lifting of
fluid from a well or reservoir. An ESP typically comprises an electrical
submersible
motor, a seal section (sometimes referred to in the art as a protector), and a
pump having
one or more pump stages inside a housing. The seal section (or protector)
functions to
equalize the pressure between the inside of the system and the outside and
also acts as a
reservoir for compensating the internal oil expansion from the motor. The
protector may
be formed of metal, as in a bellows device, or an elastomer. An elastomer
protector is
sometimes referred to as a protector bag.
[0003] In addition to motors, pump sections, and seals, a typical submersible
pumping
system may further comprise a variety of additional components, such as a
connector
used to connect the submersible pumping system to a deployment system.
Conventional
deployment systems include production tubing, cable and coiled tubing.
Additionally,
power is supplied to the submersible electric motor via a power cable that
runs through or
along the deployment system.
[0004] ESPs often incorporate the use of a gauge having one or more sensors
and
associated electronics for measuring and monitoring parameters related to the
operation
of the ESP and the production of fluid from the well or reservoir. These
parameters may
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include, but are not limited to, motor temperature, well temperature, pump
intake
pressure, pump discharge pressure, and vibration. The gauge is typically
located below
the motor, from which it may draw electrical power. The sensors and associated
electronics included in the gauge are housed in protective chamber to isolate
them from
well fluids and well conditions, such as high temperature (up to 350 F) or
pressure (up to
30,000 psi) which may compromise their operation. The power cable used to
provide
power to the motor may also be used as a means for transmitting data from the
gauge to
the surface, where the data are interpreted and the operational parameters of
the ESP can
be adjusted to optimize the production of fluid from the well or reservoir.
[0005] Currently, ESPs are rated for use up to 550 F, but the electronics
controlling or
monitoring the pump fails at these high temperatures and is generally not
reliable above
300 F. These electronic components generally cannot function at high
temperature
without significant degradation of their lifetime or performance. These
components are
typically contained in a closed protective (insulating) chamber. The
accumulation or
transfer of heat into the chamber can raise the temperature inside the chamber
to a point
that exceeds the maximum operating temperature of the components. The heat
source
which raises the temperature inside the chamber may be the components
themselves (e.g.,
electrical losses) or high temperature well fluids external to the tool.
[0006] In addition, in certain high temperature thermal recovery production
methods,
such as Steam Assisted Gravity Drainage (SAGD), ESPs will be subject to well
temperatures exceeding the maximum operating temperature of the gauge (about
300 F).
These high temperatures may also destroy or weaken the seals, insulating
materials, and
other components of the submersible pumping system. Under these conditions,
the use of
a gauge for monitoring and optimizing production is compromised. This can have
a
substantial negative impact on the overall performance of a well and thus the
economics
of producing fluids from the well. As such, it is desirable to provide a means
for cooling
the gauge (or other components of a submersible pumping system) such that the
operational temperature of the gauge and components is maintained within an
acceptable
temperature range conducive to reliable operation of the gauge in harsh
operating
environments.
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DOCKET NO. 89.0512CIP
SUMMARY OF INVENTION
[0007] One aspect of the invention relates to submersible pumping systems. A
submersible pumping system in accordance with one embodiment of the invention
includes a submersible pump; a gauge disposed proximate the submersible pump;
a
Stirling cooler disposed proximate the gauge, wherein the Stirling cooler has
a cold end
configured to remove heat from the gauge and a hot end configured to dissipate
heat; and
an energy source configured to power the submersible pumping system.
[0008] One aspect of the invention relates to methods for constructing a
submersible
pumping system. A method in accordance with one embodiment of the invention
includes disposing a gauge proximate a submersible pump; and disposing a
Stirling
cooler proximate the gauge such that the Stirling cooler is configured to
remove heat
from the gauge.
[0009] One aspect of the invention relates to methods for methods for cooling
a gauge of
a submersible pumping system. A method in accordance with one embodiment of
the
invention includes providing a Stirling cooler proximate the gauge; and
energizing the
Stirling cooler such that heat is removed from the gauge.
[0010] Other aspects and advantages of the invention will be apparent from the
following
description and the appended claims.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 shows a submersible pumping system in accordance with one
embodiment
of the invention disposed in a borehole.
[0012] FIG. 2 shows an expanded section of the submersible pumping system of
FIG. 1.
[0013] FIG. 3 shows a schematic illustrating heat transfer using a Stirling
cooler in
accordance with one embodiment of the invention.
[0014] FIG. 4 shows a free-piston Stirling cooler in accordance with one
embodiment of
the invention.
[0015] FIG. 5 shows a diagram illustrating a Stirling cycle.
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[0016] FIG. 6 shows a schematic illustrating various states of the pistons in
the Stirling
cooler in a Stirling cycle.
[0017] FIG. 7 shows a schematic illustrating a Stirling cooler coupled to a
gauge of a
submersible pumping system in accordance with one embodiment of the invention.
[0018] FIG. 8 shows a schematic illustrating s Stirling cooler coupled to a
gauge of a
submersible pumping system in accordance with another embodiment of the
invention.
[0019] FIG. 9 illustrates a method for manufacturing an electrical submersible
pumping
system in accordance with one embodiment of the invention.
[0020] FIG. 10 illustrates a method for cooling a submersible pumping system
using a
Stirling cooler in accordance with one embodiment of the invention.
DETAILED DESCRIPTION
[0021] Embodiments of the invention relate to the use, construction and method
of using
a Stirling-cycle based cooling system to cool components (e.g., electrical
components and
sensors in a gauge) connected to an electrical submersible pumping (ESP)
system. As
noted above, ESPs are typically subject to extreme high temperatures that can
degrade the
performance of their electronic components or sensors. A thermal management
solution
using a Stirling cooler as a heat pump could keep the temperature of the
electronics
below the temperature of the well and within its rated operating temperature
range, thus
drastically improving the reliability of ESP's electronic module. Part of the
fluid pumped
by the ESP could be forced to circulate around the hot end of the Stirling
cooler to keep
the Stirling cooler reject temperature close to the well temperature
[0022] The Stirling-cycle cooling system functions efficiently in a closed
system,
requires no lubrication, and can function at relatively lower pressures as
compared to
prior art vapor compression cooling system. A Stirling cycle cooler is based
on the well
known Stirling thermodynamic cycle. A Stirling cooler uses mechanical energy
to
produce a temperature difference between the cold end and the hot end of the
cooler. This
temperature difference can be used to remove heat from an object to be cooled.
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DOCKET NO. 89.0512CIP
[0023] Various configurations of Stirling engines/coolers have been devised.
These can
be categorized into kinematic and free-piston types. Kinematic Stirling
engines use
pistons attached to drive mechanisms to convert linear motions of the pistons
to rotary
motions. Kinematic Stirling engines can be further classified as alpha type
(two pistons),
beta type (piston and displacer in one cylinder), and gamma type (piston and
displacer in
separate cylinders). Free-piston Stirling engines use harmonic motion
mechanics, which
may use planar springs or magnetic field oscillations to provide the harmonic
motion.
[0024] Due to daunting engineering challenges, Stirling cycle engines are
rarely used in
practical applications and Stirling cycle coolers have been limited to the
specialty field of
cryogenics and military use. The development of Stirling engines/coolers
involves such
practical considerations as efficiency, vibration, lifetime, and cost. Using
Stirling
engines/coolers on downhole tools presents additional difficulties because of
the limited
space available in a downhole tool (typically 3-6 inches in diameter) and the
harsh
downhole environments (e.g., temperatures up to 260 C and pressures up to
30,000 psi or
more). Stirling engines have been proposed for use as electricity generators
for downhole
tools (See U.S. Pat. No. 4,805,407 issued to Buchanan).
[0025] Embodiments of the present invention may use any Stirling cooler
designs. Some
embodiments use free-piston Stirling coolers. One free-piston Stirling cooler
embodiment
of the invention makes use of a moving magnet linear motor.
[0026] FIG. 1, shows a schematic of a submersible pumping system in accordance
with
one embodiment of the invention. As shown in FIG. 1, a submersible pumping
system
100 is disposed in a wellbore 11, which penetrates the formation 10, for
pumping
formation fluids to the surface via the production tubing 14. The submersible
pumping
system 100 comprises a pump section 110, a Stirling cooler 104, and a gauge
104. The
pump section 110 comprises a motor 101, seal section (protector) 102, and one
or more
pumps 103. Note that the order of the components shown here is for
illustration only.
One of ordinary skill in the art would appreciate that other arrangements are
also possible
without departing from the scope of the invention.
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[0027] Power may be supplied to the motor via a power cable 13 from a power
source 15
on the surface. Alternatively, power may be supplied by a battery or other
power source
downhole. A gauge 104, which contains one or more sensors 104a, is shown below
the
base of the motor 101. Note that the gauge 104 may also be disposed at other
locations,
e.g., above the pump 103. The gauge 104 consists of a housing that protects
the various
sensors and components 104a contained in the gauge 104. These components 104a
may
include electronics that need to be protected from high temperatures. The
components
are disposed in an insulating enclosure or chamber 104b and connected to a
Stirling
cooler 22. The Stirling cooler 22 is shown connected to the motor 101.
However, the
Stirling cooler 22 may also be arranged at other locations, and other power
sources may
be used. In the particular arrangement shown in this figure, the Stirling
cooler 22 is
conveniently arranged below the motor 101 such that the submersible pumping
system
motor 101 can be used to power both the Stirling cooler 22 and the gauge 104.
Further, a
means to remove heat from the hot end of the Stirling cooler can be
incorporated in this
arrangement to take advantage of the flow of well fluid passing by the motor
101 for
removal of heat by convective heat transfer.
[0028] FIG. 2 shows an expanded section of the pumping system shown in FIG. 1
for
better illustration. FIG. 2 shows the arrangement of the gauge 104, the
Stirling cooler 22,
and the pump section I 10. As shown, the Stirling cooler 22, which is in
direct contact
with the gauge 104 acts as a heat pump to remove heat from the gauge 104. The
heat
may be dissipated to the well fluid flowing past the motor. In this manner,
the heat
removed from the gauge is effectively "pumped" to the other end of the
Stirling cooler
and dissipated into the flow of well fluid passing the submersible motor.
[0029] The Stirling cooler may be in direct contact with the object to be
cooled (e.g.,
gauge), as shown in FIG. 2, or placed a some distance from the gauge and
cooled with a
heat transport mechanism disposed therebetween to transfer heat, as shown in
FIG. 3.
FIG. 3 schematically illustrates that a heat pipe 35 is disposed between the
Stirling cooler
22 and the gauge 104. As shown, heat can be conducted from the gauge 104 to
the
Stirling cooler 22 as illustrated by arrow Qc. The Stirling cooler 22 then
dissipates this
heat to the fluid flow, as illustrated by arrow Qh. Those skilled in the art
will appreciate
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that the heat transport mechanism may be any suitable heat transport device,
including
those implemented with circulating fluids. Therefore, the term "heat pipe" as
used herein
is intended to include any suitable heat transport mechanism, which may or may
not
comprise a "pipe." Embodiments of the invention may also be implemented with
heat
transport mechanisms on the cold side, or both the cold side and the hot side
(not shown).
[0030] Stirling coolers may have various configurations, using pistons and/or
displacers.
FIG. 4 shows a schematic of a free-piston type Stirling cooler that may be
used with
embodiments of the invention. As shown, the Stirling cooler 22 is attached to
an object
47 to be cooled. As noted above, in some embodiments, a heat pipe may be used
to
conduct heat between the object 47 and the Stirling cooler 22. The Stirling
cooler 22
includes two pistons 42, 44 disposed in cylinder 46. The cylinder 46 is filled
with a
working gas, typically air, helium or hydrogen at a pressure of several times
(e.g., 20
times) the atmospheric pressure. The piston 42 is coupled to a permanent
magnet 45 that
is in proximity to an electromagnet 48 fixed on the housing. When the
electromagnet 48
is energized, its magnetic field interacts with that of the permanent magnet
45 to cause
linear motion (in the left and right directions looking at the figure) of
piston 42. Thus,
the permanent magnet 45 and the electromagnet 48 form a moving magnet linear
motor.
The particular sizes and shapes of the magnets shown in FIG. 4 are for
illustration only
and are not intended to limit the scope of the invention. One of ordinary
skill in the art
would also appreciate that the locations of the electromagnet and the
permanent magnet
may be reversed, i.e., the electromagnet may be fixed to the piston and the
permanent
magnet fixed on the housing (not shown).
[0031] The electromagnet 48 and the permanent magnet 45 may be made of any
suitable
materials. The windings and lamination of the electromagnet are preferably
selected to
sustain high temperatures (e.g. up to 260 C). In some embodiments, the
permanent
magnets of the linear motors are made of a samarium-cobalt (Sm-Co) alloy to
provide
good performance at high temperatures. The electricity required for the
operation of the
electromagnet may be supplied from the surface, from batteries included in
downhole
tools, from generators downhole, or from any other means known in the art.
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[0032] The movement of piston 42 causes the gas volume of cylinder 46 to vary.
Piston
44 can move in cylinder 46 like a displacer in the kinematic type Stirling
engines. The
movement of piston 44 is triggered by a pressure differential across both
sides of piston
44. The pressure differential results from the movement of piston 42. The
movement of
piston 44 in cylinder 46 moves the working gas from the left of piston 44 to
the right of
piston 44, and vice versa. This movement of gas coupled with the compression
and
decompression processes results in the transfer of heat from object 47 to heat
dissipating
device 43. As a result, the temperature of the object 47 decreases. In some
embodiments, the Stirling cooler 22 may include a spring mass 41 to help
reduce
vibrations of the cooler resulting from the movements of the pistons and the
magnet
motor.
[0033] While FIG. 4 shows a Stirling cooler having a magnet motor that uses
electricity
to power the Stirling cooler, one skilled in the art would appreciate that
other energy
sources (or energizing mechanisms) may also be used. For example, operation of
the
Stirling cooler (e.g., the back and forth movements of piston 42 in FIG. 4)
may be
implemented by mechanical means, such as a fluid-powered system that uses the
energy
in the fluid flow coupled to a valve system and/or a spring (not shown). The
hydraulic
pressure of the fluid flow could be used to push the piston in one direction,
while the
spring is used to move the piston in the other direction. A conventional valve
system
may be used to control the flow of fluid to the Stirling piston in an
intermittent fashion.
Thus, the coordinated action of a hydraulic system, a spring, and a valve
system results in
a back and forth movement of the piston 42.
[0034] The movement of gas to the right and to the left of piston 44, coupled
with
compression and decompression of the gas in cylinder 46 by piston 42, creates
four
different states in a Stirling cycle. FIG. 5 depicts these four states and the
transitions
between these states in a pressure-volume diagram. FIG. 6 illustrates the four
states and
the direction of the movements of the pistons 42 and 44 in a Stirling cycle.
[0035] In process a (from state 1 to state 2), piston 44 moves from left to
right in FIG. 6,
while piston 42 remains stationary. Therefore, the volume in cylinder 46 (see
FIG. 4) is
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unchanged. The working gas in the cylinder is swept from one side of piston 44
to the
other side.
[0036] In the second process b (from state 2 to state 3), piston 42 moves to
the right,
increasing the volume in the cylinder (shown as 46 in FIG. 4). The magnet
motor, for
example, drives the movement of piston 42. Due to the increased volume in the
cylinder,
the gas expands and absorbs heat.
[0037] In process c (from state 3 to state 4), piston 44 moves to the left,
forcing the
working gas to move to its right. The volume of the gas remains unchanged.
[00381 In process d (from state 4 back to state 1), piston 42 moves to the
left, driven by
the magnet motor, for example. This compresses the working gas. The
compression
results in the release of heat from the working gas. The released heat is
dissipated from
the heat dissipater 43 into the heat sink or environment (e.g., the drilling
mud). This
completes the Stirling cycle. The net result is the transport of heat from one
end of the
device to the other. Thus, if the Stirling device is in thermal contact
(either directly or via
a heat pipe) with the object to be cooled (shown as 47 in FIG. 4), heat can be
removed
from the object. As a result, the temperature of the object is lowered or heat
generated at
the object can be removed.
[0039] To improve heat removal from the insulating chamber (e.g., the chamber
104b of
the gauge 104 in FIG. 2), auxiliary heat transfer/circulating mechanism may be
used in
conjunction with the Stirling coolers. For example, FIG. 7 shows a schematic
of a system
for heat removal using a Stirling cooler in accordance with another embodiment
of the
invention. As shown, a Stirling cooler 22 is coupled to an insulating
enclosure or
chamber 24. The chamber 24 is configured with an internal cavity 26 formed
therein and
adapted to provide an path over the component(s) to be cooled 23 housed
therein. The
cavity 26 may be formed using any conventional materials known in the art. A
fan 27 is
disposed within the chamber 24 to circulate air around the component 23 to be
cooled,
thereby actively transferring heat dissipating from the component(s) to the
cold side of
the Stirling cooler 22. The fan 27 may be powered by the electrical supply
feeding the
Stirling cooler or by an independent power network (e.g. separate battery) as
known in
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the art. This particular embodiment is equipped with a heat exchanger 28
disposed at one
end of the chamber 24 to increase cooling efficiency across the cooler/chamber
interface
and cool the recirculating air. The heat exchanger 28 may be a conventional
heat sink or
another suitable device as known in the art. Other embodiments may be
implemented
with multiple fans 27 to increase the cooling air flow.
[0040] FIG. 8 shows a schematic of another system for heat removal using a
Stirling
cooler in accordance with an embodiment of the invention. As shown, a Stirling
cooler 22
is coupled to an insulating enclosure or chamber 24. The chamber 24 is
configured with
an internal liquid-coolant system 29 disposed therein. The coolant system 29
is adapted
with a flow loop that allows a liquid to flow in a closed loop from the housed
component(s) 23 to a heat exchanger 28 attached to the cold side of the
Stirling cooler 22.
The coolant system 29 may be constructed using conventional materials known in
the art
(e.g., via multiple tubes). The heat exchanger 28 may be a conventional heat
sink or
another suitable device as known in the art. The coolant liquid, which may be
water or
any suitable alternative, is circulated in the flow loop via a pump 30 coupled
to the flow
lines and powered by the Stirling cooler 22 power network or using independent
power
means.
[0041] The Stirling cooler system of FIG. 8 is shown with the liquid-coolant
system 29
centrally disposed within the chamber 24, such that the component(s) 23 to be
cooled
surround the coolant system. Those skilled in the art will appreciate that
other
embodiments of the invention may be implemented with the liquid-coolant system
29 in
various configurations and lengths depending on space constraints. For
example,
embodiments of the invention may be implemented with the liquid-coolant system
configured within, or forming, the walls of the insulating chamber (not
shown). In such
embodiments the liquid-coolant system would not be centrally disposed within
the
chamber 24. Embodiments comprising the liquid-coolant system 29 render
increased
cooling efficiency as the liquid collects the heat dissipated in the component
23 chamber
and transfers it to the cold side of the Stirling 22 via the heat exchanger
28. In addition
the use of liquid coolant, and, if desired in some embodiments, insulated
coolant lines,
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allows a larger spatial separation between the Stirling cooler and the
component to be
cooled.
[0042] While the description related to FIGs. 4-6 uses a free-piston Stirling
cooler to
illustrate embodiments of the invention, one of ordinary skill in the art
would appreciate
that other types of Stirling coolers may also be used, including those based
on kinematic
mechanisms - e.g., double-piston Stirling coolers and piston-and-displacer
Stirling
coolers.
[0043] In accordance with embodiments of the invention, Stirling coolers are
used to
cool electronics, sensors or other heat sensitive parts that need to function
in the harsh
downhole environment. In these embodiments, the electronics are disposed in an
insulating chamber (e.g., a Dewar flask) and the cold end of the Stirling
cooler is coupled
to (either directly, via a heat pipe or another heat transport mechanism) one
side of the
chamber. It has been found that a substantial amount of heat (e.g., 150 W)
could be
removed with the cooler embodiments of the invention. Thus, it is possible to
maintain
an environment below 125 C for the electronics, even when the temperature in
the
borehole may be 175 C or higher. Model studies also indicate that the Stirling
cooler
embodiments of the invention are capable of removing heat at a rate of up to
400 W.
[0044] Some aspects of the invention relate to methods for producing a
downhole
electrical submersible pumping system having a Stirling cooling system. A
schematic of
a portion of a downhole electrical submersible pumping system including a
Stirling
cooler embodiment of the invention is illustrated in FIG. 1. A electrical
submersible
pumping system may be in oil and gas production.
[0045] FIG. 9 shows a process for producing an electrical submersible pumping
system
in accordance with one embodiment of the invention. As shown, the process 70
includes
disposing an insulating chamber in a downhole tool that includes a submersible
pump
(step 72). The insulating chamber forms the wall of a gauge (shown as 104 in
FIGs. 1
and 2) and may be a Dewar flask or a chamber made of an insulating material
suitable for
downhole use. In some embodiments, the insulating chamber may be formed by a
cutout
on the insulating tool body. Then, the gauge electronics or sensors that need
to function
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at relative low temperatures are placed into the insulating chamber (step 74).
Alternatively, the electronics or sensors may be placed in the insulating
chamber before
the latter is placed proximate the submersible pump. Then, a Stirling cooler
is disposed
proximate the gauge of the submersible pumping system (step 76). Note that the
relative
order of placement of the Stirling cooler and the insulating chamber is not
important, i.e.,
the Stirling cooler may be placed before the insulating chamber. Preferably,
the Stirling
cooler is placed proximate the insulating chamber. However, if space
limitations do not
permit placement of the Stirling cooler proximate the insulating chamber, the
Stirling
cooler may be placed at a distance from the insulating chamber (as shown in
FIG. 3) and
a heat pipe or other heat transport device may be used to conduct heat from
the insulating
chamber to the Stirling cooler.
[0046] FIG. 10 shows a process for cooling a sensor or electronics in a gauge
disposed in
an electrical submersible pumping system in accordance with one embodiment of
the
invention. The process 150 includes providing a Stirling cooler in the
submersible
pumping system proximate a gauge having the sensor or electronics (step 151);
and
energizing the Stirling cooler such that heat is removed from the sensor or
electronics in
the gauge (step 152).
[0047] Advantages of the present invention include improved
cooling/refrigeration
techniques for submersible pumping systems. A submersible pump with a Stirling
cycle
cooling system in accordance with embodiments of the invention can keep the
electrical
components and sensors (e.g., those associated with a gauge designed for used
with a
submersible pumping system) at significantly lower temperatures, enabling
these
components to render better performance and longer service lives in harsh
operating
conditions. This in turn allows for improved production optimization in wells
with harsh
operating conditions.
[0048] 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
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invention as disclosed herein. Accordingly, the scope of the invention should
be limited
only by the attached claims.
13
