U.S. patent application number 10/710103 was filed with the patent office on 2005-05-12 for [downhole tools with a stirling cooler system].
This patent application is currently assigned to SCHLUMBERGER TECHNOLOGY CORPORATION. Invention is credited to Adolph, Robert A., Bernard, Larry J., Bonner, Stephen D., Gunawardana, Ruvinda, Hache, Jean-Michel, Revellat, Guillaume, Stoller, Christian, Zhou, Feng.
Application Number | 20050097911 10/710103 |
Document ID | / |
Family ID | 33519547 |
Filed Date | 2005-05-12 |
United States Patent
Application |
20050097911 |
Kind Code |
A1 |
Revellat, Guillaume ; et
al. |
May 12, 2005 |
[DOWNHOLE TOOLS WITH A STIRLING COOLER SYSTEM]
Abstract
A cooling system for a downhole tool includes an insulating
chamber disposed in the tool, wherein the chamber is adapted to
house an object to be cooled; a Stirling cooler is disposed in the
tool, the cooler has a cold end configured to remove heat from the
chamber and a hot end configured to dissipate heat; and an energy
source to power the Stirling cooler. A downhole tool includes: a
tool body, and a cooling system with an insulating chamber; wherein
the chamber is adapted to house an object to be cooled; a Stirling
cooler is disposed in the tool, the cooler has a cold end
configured to remove heat from the chamber and a hot end configured
to dissipate heat; and an energy source to power the Stirling
cooler.
Inventors: |
Revellat, Guillaume;
(Houston, TX) ; Stoller, Christian; (Kingwood,
TX) ; Adolph, Robert A.; (Pennington, NJ) ;
Bernard, Larry J.; (Missouri City, TX) ; Zhou,
Feng; (Missouri City, TX) ; Bonner, Stephen D.;
(Sugar Land, TX) ; Hache, Jean-Michel; (Houston,
TX) ; Gunawardana, Ruvinda; (Sugar Land, TX) |
Correspondence
Address: |
SCHLUMBERGER OILFIELD SERVICES
200 GILLINGHAM LANE
MD 200-9
SUGAR LAND
TX
77478
US
|
Assignee: |
SCHLUMBERGER TECHNOLOGY
CORPORATION
110 Schlumberger Drive
Sugar Land
TX
|
Family ID: |
33519547 |
Appl. No.: |
10/710103 |
Filed: |
June 18, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60517782 |
Nov 6, 2003 |
|
|
|
Current U.S.
Class: |
62/259.2 ;
62/6 |
Current CPC
Class: |
F25B 9/14 20130101; E21B
47/017 20200501 |
Class at
Publication: |
062/259.2 ;
062/006 |
International
Class: |
F25B 009/00; E21B
029/02; E21B 043/00; F25D 023/12 |
Claims
1. A cooling system for a downhole tool, comprising: an insulating
chamber disposed in the downhole tool, wherein the insulating
chamber is adapted to house an object to be cooled; a Stirling
cooler disposed in the downhole tool, wherein the Stirling cooler
has a cold end configured to remove heat from the insulating
chamber and a hot end configured to dissipate heat; and an energy
source to power the Stirling cooler.
2. The cooling system of claim 1, wherein the Stirling cooler is a
free-piston Stirling cooler.
3. The cooling system of claim 2, wherein the free-piston Stirling
cooler comprises a permanent magnet.
4. The cooling system of claim 1, wherein the energy source is one
selected from a surface electrical source, a downhole battery, a
hydraulic power source, and a downhole power generator.
5. The cooling system of claim 1, further comprising a heat
transport mechanism disposed between the cold end of the Stirling
cooler and the insulating chamber, wherein the heat transport
mechanism is adapted to conduct heat from the insulating chamber to
the cold end of the Stirling cooler.
6. The cooling system of claim 1, wherein the insulating chamber is
adapted to provide an airflow near the object to be cooled.
7. The cooling system of claim 1, wherein the insulating chamber is
adapted to provide a liquid fluid flow near the object to be
cooled.
8. A downhole tool, comprising: a tool body; and a cooling system
comprising: an insulating chamber disposed in the downhole tool and
adapted to house an object to be cooled; and a Stirling cooler
disposed in the downhole tool, wherein the Stirling cooler has a
cold end configured to remove heat from the insulating chamber and
a hot end configured to dissipate heat.
9. The downhole tool of claim 8, wherein the Stirling cooler is a
free-piston Stirling cooler.
10. The downhole tool of claim 9, wherein the free-piston Stirling
cooler comprises a permanent magnet.
11. The downhole tool of claim 8, further comprising an energy
source to power the Stirling Cooler, the source selected from one
of a surface electrical source, a downhole battery, a hydraulic
power source, and a downhole power generator.
12. The downhole tool of claim 8, further comprising a heat
transport mechanism disposed between the cold end of the Stirling
cooler and the insulating chamber, wherein the heat transport
mechanism is configured to conduct heat from the insulating chamber
to the cold end of the Stirling cooler.
13. The downhole tool of claim 8, wherein the insulating chamber is
adapted to provide an airflow near the object to be cooled.
14. The downhole tool of claim 8, wherein the insulating chamber is
adapted to provide a liquid fluid flow near the object to be
cooled.
15. A method for constructing a downhole tool, comprising:
disposing a sensor or electronics in an insulating chamber in the
downhole tool; and disposing a Stirling cooler in the downhole tool
proximate the insulating chamber such that the Stirling cooler is
configured to remove heat from the insulating chamber.
16. The method of claim 15, wherein the Stirling cooler is a
free-piston Stirling cooler.
17. The method of claim 16, wherein the free-piston Stirling cooler
comprises a permanent magnet.
18. The method of claim 15, wherein the insulating chamber is
adapted to provide an airflow near the sensor or electronics.
19. The method of claim 15, wherein the insulating chamber is
adapted to provide a liquid fluid flow near the sensor or
electronics.
20. A method for cooling a sensor or electronics disposed in a
downhole tool, comprising: providing a Stirling cooler in the
downhole tool proximate the sensor or electronics; and energizing
the Stirling cooler such that heat is removed from the sensor or
electronics.
21. The method of claim 20, wherein the Stirling cooler is a
free-piston Stirling cooler.
22. The method of claim 21, wherein the free-piston Stirling cooler
comprises a permanent magnet.
23. The method of claim 20, wherein the energizing is by supplying
electrical power from a source selected from one of a surface
electrical source, a downhole battery, a hydraulic power source,
and a downhole power generator.
24. The method of claim 20, wherein the sensor or electronics are
disposed in an insulating chamber in the downhole tool, the chamber
being adapted to provide an airflow or liquid fluid flow near the
sensor or electronics.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority, under 35 U.S.C. .sctn.119,
to Provisional Application Ser. No. 60/517,782, filed on Nov. 6,
2003, incorporated by reference in its entirety.
BACKGROUND OF INVENTION
[0002] 1. Field of the Invention
[0003] 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 a Stirling-Cycle cooling system for use with
downhole tools.
[0004] 2. Background Art
[0005] Various well logging and monitoring techniques are known in
the field of hydrocarbon and water exploration and production.
These techniques employ downhole tools or instruments equipped with
sources adapted to emit energy through a borehole traversing the
subsurface formation. The emitted energy passes through the
borehole fluid ("mud") and into the surrounding formations to
produce signals that are detected and measured by one or more
sensors, which typically are also disposed on the downhole tools.
By processing the detected signal data, a profile of the formation
properties is obtained.
[0006] A downhole tool, comprising a number of emitting sources and
sensors for measuring various parameters, may be lowered into a
borehole on the end of a cable, a wireline, or a drill string. The
cable/wireline, which is attached to some sort of mobile processing
center at the surface, provides the means by which data are sent up
to the surface. With this type of wireline logging, it becomes
possible to measure borehole and formation parameters as a function
of depth, i.e., while the tool is being pulled uphole.
[0007] An alternative to wireline logging techniques is the
collection of data on downhole conditions during the drilling
process. By collecting and processing such information during the
drilling process, the driller can modify or correct key steps of
the operation to optimize performance. Schemes for collecting data
of downhole conditions and movement of the drilling assembly during
the drilling operation are known as Measurement While Drilling
(MWD) techniques. Similar techniques focusing more on measurement
of formation parameters than on movement of the drilling assembly
are know as Logging While Drilling (LWD). Logging While Tripping
(LWT) is an alternative to LWD and MWD techniques. In LWT, a small
diameter "run-in" tool is sent downhole through the drill pipe, at
the end of a bit run, just before the drill pipe is pulled. The
run-in tool is used to measure the downhole physical quantities as
the drill string is extracted or tripped out of the hole. Measured
data is recorded into tool memory versus time during the trip out.
At the surface, a second set of equipment records bit depth versus
time for the trip out, and this allows the measurements to be
placed on depth. FIG. 1 shows a conventional logging tool 12
disposed in a borehole 11 that penetrates a subsurface formation
10. The logging tool 12 may be deployed on a wireline 13 via a
wireline control mechanism 14. In addition, the logging tool 12 may
be connected to surface equipment 15, which may include a computer
(not shown).
[0008] Downhole tools are exposed to extreme temperatures (up to
260.degree. C.) and pressures (up to 30,000 psi and possibly up to
40,000 psi in some instances). These tools are typically equipped
with sensitive components (e.g. electronics packages) that often
are not designed for such harsh environments. The trend among
manufacturers of electronic components is to address the
high-volume commercial market, making it difficult to find
components for downhole tools that function effectively at these
elevated temperatures. At the same time, the oilfield industry is
moving toward the exploration of deeper and hotter reservoirs. As a
result, there is an urgent need for methods or devices that permit
the sensitive electronic components to be operated at high
temperatures. Redesigning silicon chips to operate at high
temperatures (e.g., above 150.degree. C.) is costly and has a
significant impact on the development time and thus the time to
market. The alternative is to have systems to protect the
electronic components from the high temperature environments.
Conventional techniques include those that insulate the sensitive
components from the hot environments, such as putting them in Dewar
flasks. This technique protects the tool only for a certain amount
of time, and the nature of the flasks makes them intrinsically
fragile. A better approach is to use an active cooling system.
[0009] A cooling system capable of providing multi-watt
refrigeration for thermally protected electronic components in
downhole tools would enable the use of electronic and sensor
technologies that are otherwise not suitable for high temperature
applications. This would reduce the ever-increasing costs
associated with the development and implementation of
high-temperature electronics, and make it possible to introduce new
technologies to subsurface exploration and production.
[0010] A cooling system for use in a downhole tool needs to fit in
the limited space within the tool. Several miniature cooling
systems suitable for use in downhole tools have been proposed. See
e.g., Aaron Flores, "Active Cooling for Electronics in a Wireline
Oil-Exploration Tool," Ph.D. dissertation, MIT, 1996. This
technique was based on a once-through vapor compression cycle.
However, this approach requires very careful sealing and
lubrication due to high pressure in the condenser part.
[0011] Gloria Bennett proposed an active cooling system for
downhole tools based on a miniature thermoacoustic refrigerator,
"Active Cooling for Downhole Instrumentation: Miniature
Thermoacoustic refrigerator," 1991, University of New Mexico, Ph.D.
dissertation, UMI 1991.9215048. This approach is promising, but the
components used are relatively bulky, and the performance of a
miniature thermoacoustic refrigerator is uncertain.
[0012] Although cooling systems for use in downhole tools have been
proposed, a need remains for improved cooling/refrigeration
techniques for downhole tools.
SUMMARY OF INVENTION
[0013] One aspect of the invention relates to cooling systems for
downhole tools. A cooling system in accordance with one embodiment
of the invention includes an insulating chamber disposed in the
downhole tool, wherein the insulating chamber is adapted to house
an object to be cooled; a Stirling cooler disposed in the downhole
tool, wherein the Stirling cooler has a cold end configured to
remove heat from the insulating chamber and a hot end configured to
dissipate heat; and an energy source to power the Stirling
cooler.
[0014] One aspect of the invention relates to downhole tools. A
downhole tool in accordance with one embodiment of the invention
includes a tool body; and a cooling system comprising: an
insulating chamber disposed in the downhole tool, wherein the
insulating chamber is adapted to house an object to be cooled; a
Stirling cooler disposed in the downhole tool, wherein the Stirling
cooler has a cold end configured to remove heat from the insulating
chamber and a hot end configured to dissipate heat; and an energy
source to power the Stirling cooler.
[0015] One aspect of the invention relates to methods for
manufacturing downhole tools. A method in accordance with one
embodiment of the invention includes disposing a sensor or
electronics in an insulating chamber in the downhole tool; and
disposing a Stirling cooler in the downhole tool proximate the
insulating chamber such that the Stirling cooler is configured to
remove heat from the insulating chamber.
[0016] One aspect of the invention relates to methods for cooling a
sensor or electronics included in downhole tools. A method in
accordance with one embodiment of the invention includes providing
a Stirling cooler in the downhole tool proximate the sensor or
electronics; and energizing the Stirling cooler such that heat is
removed from the sensor or electronics.
[0017] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 shows a conventional downhole tool disposed in a
borehole.
[0019] FIG. 2 shows a downhole tool including a Stirling cooler in
accordance with one embodiment of the invention.
[0020] FIG. 3 shows a schematic illustrating heat transfer using a
Stirling cooler in accordance with one embodiment of the
invention.
[0021] FIG. 4 shows a free-piston Stirling cooler in accordance
with one embodiment of the invention.
[0022] FIG. 5 shows a diagram illustrating a Stirling cycle.
[0023] FIG. 6 shows a schematic illustrating various states of the
pistons in the Stirling cooler in a Stirling cycle.
[0024] FIG. 7 shows a schematic of an active air-flow cooling
system in accordance with an embodiment of the invention.
[0025] FIG. 8 shows a schematic of a liquid-fluid cooling system in
accordance with an embodiment of the invention.
[0026] FIG. 9 illustrates a method for manufacturing a downhole
tool in accordance with one embodiment of the invention.
[0027] FIG. 10 illustrates a method for cooling sensors or
electronics within downhole tools in accordance with the
invention.
DETAILED DESCRIPTION
[0028] Embodiments of the invention relate to cooling systems for
use in downhole tools. These cooling systems are based on Stirling
cycles that can function efficiently in a closed system, require no
lubrication, and can function at relatively lower pressures as
compared to a vapor compression system. A Stirling engine or cooler
is based on the Stirling (also referred to as "Sterling") cycle,
which is a well known thermodynamic cycle. A Stirling engine uses
heat (temperature difference) as the energy source to provide
mechanical work. A Stirling cooler operates in reverse; it uses
mechanical energy to produce a temperature difference e.g., as a
cooler or refrigerator.
[0029] 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 piston motions 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.
[0030] 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 [7.5-15 cm] in diameter) and the harsh
downhole environments (e.g., temperatures up to 260.degree. C.,
pressures up to 30,000 psi or more, and shock up to 250 g 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).
[0031] 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.
[0032] FIG. 2 shows a downhole tool (such as 12 in FIG. 1) in
accordance with one embodiment of the invention. As shown, a
downhole tool 20 includes an elongated housing 21 that protects
various components 23 of the instrument. These components 23 may
include electronics that need to be protected from high
temperatures. The components are disposed in an insulating
enclosure or chamber 24 and connected to a Stirling cooler 22.
Other components 25 of the downhole tool 20 may be included at the
other end of the Stirling cooler 22. The components 25 may include
other electronics for controlling the Stirling cooler 22 or
mechanisms to remove heat from the hot end of the Stirling cooler
22.
[0033] FIG. 3 shows a schematic of a system for heat removal using
a Stirling cooler in accordance with one embodiment of the
invention. As shown, a Stirling cooler 22 functions as a heat pump,
removing heat from the cold reservoir cartridge 33 to the mud flow
(hot reservoir) 31. In this manner, the heat removed from the
object to be cooled (the cold cartridge 33) is effectively "pumped"
to the other end (the hot end) of the Stirling cooler and
dissipated into the mud flow 31, for example. Note that the
Stirling cooler 22 may be in direct contact with the object to be
cooled. Alternatively, the Stirling cooler 22 may be placed at a
distance from the object to be cooled with a heat transport
mechanism 35 disposed therebetween to transfer the heat. Those
skilled in the art will appreciate that the heat transport
mechanism 35 may be any suitable heat transport device (e.g., a
heat pipe), including those implemented with circulating fluids.
Embodiments of the invention may also be implemented with heat
transport mechanisms on the cold side and the hot side (not
shown).
[0034] FIG. 4 shows a schematic of a free-piston Stirling cooler
that may be used with embodiments of the invention. As shown, the
Stirling cooler 40 is attached to an object 47 to be cooled. As
noted above, in some embodiments, a heat transport device may be
used to transport heat between the object 47 and the Stirling
cooler 40. The Stirling cooler 40 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 skilled in the art will 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).
[0035] 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.degree. 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 conventional batteries in the
downhole tool, from generators downhole, or from any other means
known in the art.
[0036] 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
40 may include a spring mass 41 to help reduce vibrations of the
cooler resulting from the movements of the pistons and the magnet
motor.
[0037] While FIG. 4 shows a Stirling cooler having a magnet motor
that uses electricity to power the Stirling cooler, one skilled in
the art will 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 mud flow coupled
to a valve system and/or a spring (not shown). The hydraulic
pressure of the mud 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 is used to control the flow
of mud 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.
[0038] 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.
[0039] 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 unchanged. The
working gas in the cylinder is swept from one side of piston 44 to
the other side.
[0040] 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 drives the movement of piston 42.
Due to the increased volume in the cylinder, the gas expands and
absorbs heat.
[0041] 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.
[0042] In process d (from state 4 back to state 1), piston 42 moves
to the left, driven by the magnet motor. 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
transport mechanism) 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.
[0043] 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) 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 the art. This particular
embodiment is further 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.
[0044] 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.
[0045] 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, allows a larger spatial separation between the
Stirling cooler and the component to be cooled.
[0046] While the above description uses a free-piston Stirling
cooler to illustrate embodiments of the invention, those skilled in
the art will 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.
[0047] In accordance with embodiments of the invention, Stirling
coolers are used to cool electronics, sources, sensors or other
heat sensitive parts that need to function in the harsh downhole
environment. In these embodiments, the component(s) to be cooled is
disposed in an insulating chamber (e.g., a Dewar flask) and the
cold end of the Stirling cooler is coupled to (either directly or
via a 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.degree. C. for the
housed component, even when the temperature in the borehole may be
175.degree. C. 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.
[0048] Some aspects of the invention relate to methods for
producing a downhole tool having a cooling system in accordance
with the invention. A schematic of a portion of a downhole tool
including a Stirling cooler embodiment of the invention is
illustrated in FIG. 2. It will be appreciated by those skilled in
the art that embodiments of the invention are not limited to any
particular type of downhole tool. Thus, the invention may be
implemented with any tool or instrument adapted for subsurface
disposal, including wireline tools, LWD/MWD/LWT tools, coiled
tubing tools, casing drilling tools, and with long-term/permanently
disposed tubulars used in reservoir monitoring.
[0049] FIG. 9 shows a process for producing a downhole tool in
accordance with one embodiment of the invention. As shown, the
process 70 includes disposing an insulating chamber in a downhole
tool (step 72). The insulating chamber 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 (not shown). Then, electronics
that need to function at relative low temperatures are placed into
the insulating chamber (step 74). Alternatively, the electronics,
sources, or sensors may be placed in the insulating chamber before
the latter is placed in the downhole tool. Then, a Stirling cooler
is disposed in the downhole tool (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
in the tool 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 and a heat transport
mechanism may interposed therebetween to conduct heat from the
chamber to the Stirling cooler.
[0050] FIG. 10 shows a process for cooling a sensor or electronics
disposed in a downhole tool in accordance with the invention. The
process 100 includes providing a Stirling cooler in the downhole
tool proximate the sensor or electronics (step 105); and energizing
the Stirling cooler such that heat is removed from the sensor or
electronics (step 110).
[0051] Advantages of the present invention include improved
cooling/refrigeration techniques for downhole tools. A cooling
system in accordance with embodiments of the invention can keep
downhole components at significantly lower temperatures, enabling
these components to render better performance and longer service
lives. Cooling systems in accord with embodiments of the invention
have closed systems, with minimal moving parts, ensuring smooth and
quiet operation as well as providing a major advantage in
qualifying the instruments for shock and vibration.
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