U.S. patent application number 11/383932 was filed with the patent office on 2007-08-09 for field application of polymer-based electrical insulation.
This patent application is currently assigned to Composite Technology Development, Inc.. Invention is credited to Craig Hazelton, Michael L. Tupper.
Application Number | 20070181306 11/383932 |
Document ID | / |
Family ID | 38332822 |
Filed Date | 2007-08-09 |
United States Patent
Application |
20070181306 |
Kind Code |
A1 |
Tupper; Michael L. ; et
al. |
August 9, 2007 |
FIELD APPLICATION OF POLYMER-BASED ELECTRICAL INSULATION
Abstract
Methods are disclosed for producing an insulated electrical
conductor. Electrically uninsulated portions of respective
electrical conductors are connected. A joint between the
electrically uninsulated portions is coated with a preceramic
resin, which is heated to cure the preceramic resin into a
green-state insulator that substantially covers the joint.
Inventors: |
Tupper; Michael L.;
(Lafayette, CO) ; Hazelton; Craig; (Lafayette,
CO) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Composite Technology Development,
Inc.
Lafayette
CO
|
Family ID: |
38332822 |
Appl. No.: |
11/383932 |
Filed: |
May 17, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11351654 |
Feb 9, 2006 |
|
|
|
11383932 |
May 17, 2006 |
|
|
|
Current U.S.
Class: |
166/302 ;
166/57 |
Current CPC
Class: |
E21B 36/04 20130101;
C23C 18/1208 20130101; E21B 43/2401 20130101 |
Class at
Publication: |
166/302 ;
166/057 |
International
Class: |
E21B 36/00 20060101
E21B036/00 |
Claims
1. A method of producing an insulated electrical conductor, the
method comprising: connecting a first electrically uninsulated
portion of a first electrical conductor with a second electrically
uninsulated portion of a second electrical conductor; coating a
joint between the first and second electrically uninsulated
portions with a preceramic resin; and heating the preceramic resin
to cure the preceramic resin into a green-state insulator that
substantially covers the joint.
2. The method recited in claim 1 further comprising applying a
compressive force to the preceramic resin while curing the
preceramic resin into the green-state insulator to consolidate the
preceramic resin.
3. The method recited in claim 2 wherein applying the compressive
force comprises disposing a sleeve around the preceramic resin, the
sleeve being made of a material having a volumetric
thermal-expansion coefficient between about 10.sup.-4 and 10-2
K.sup.-1 and a Young's modulus between about 10.sup.5 and 10.sup.8
N/m.sup.2.
4. The method recited in claim 3 wherein the material comprises
silicone rubber.
5. The method recited in claim 2 wherein applying the compressive
force comprises applying pressure to the preceramic resin with a
pressurized containment system.
6. The method recited in claim 2 wherein applying the compressive
force to the preceramic resin comprises: applying a resin
containment film to the preceramic resin; and disposing a sleeve
around the resin containment film, the method further comprising
removing the sleeve and the resin containment film.
7. The method recited in claim 1 wherein each of the first and
second electrical conductors comprises an electrically insulated
portion.
8. The method recited in claim 1 wherein each of the first and
second electrical conductors comprises a solid electrically
conductive rod.
9. The method recited in claim 1 wherein each of the first and
second electrical conductors comprises a stranded electrical
conductor.
10. The method recited in claim 1 wherein curing the preceramic
resin into the green-state insulator comprises passing an
electrical current through the first and second electrical
conductors.
11. The method recited in claim 1 wherein curing the preceramic
resin comprises curing the preceramic resin in a field location
with locally mounted heaters.
12. A method of assisting an oil-recovery process, the method
comprising: deploying a first electrical conductor into an
oil-recovery environment, the first electrical conductor comprising
a first electrically uninsulated portion; connecting the first
electrically uninsulated portion with a second electrically
uninsulated portion of a second electrical conductor; coating a
first joint between the first and second electrically uninsulated
portions with a preceramic resin; curing the preceramic resin to
convert the preceramic resin into a green-state insulator that
substantially covers the first joint to form a continuous
conductor; applying a compressive force to the preceramic resin
while curing the preceramic resin to consolidate the preceramic
resin; and deploying at least a portion of the continuous conductor
corresponding to the second electrical conductor into the
oil-recovery environment.
13. The method recited in claim 12 further comprising: coating a
portion of the first electrical conductor with the preceramic resin
before deploying the first electrical conductor into the
oil-recovery environment; and pyrolyzing the preceramic resin of
the coated portion to convert the preceramic resin of the coated
portion into a ceramic insulator that electrically insulates the
portion, wherein pyrolyzing the preceramic resin of the coated
portion is performed before connecting the first electrically
uninsulated portion with the second electrically uninsulated
portion.
14. The method recited in claim 12 further comprising: connecting a
third electrically uninsulated portion of the second electrical
conductor with a fourth electrically uninsulated portion of a third
electrical conductor; coating a second joint between the third and
fourth electrically uninsulated portions with the preceramic resin;
curing the preceramic resin coating the second joint to convert the
preceramic resin into a green-state insulator that substantially
covers the second joint to form the continuous conductor; applying
a second compressive force to the preceramic resin coating the
second joint while curing the preceramic resin coating the second
joint to consolidate the preceramic resin; and deploying a portion
of the continuous conductor corresponding to the third electrical
conductor into the oil-recovery environment.
15. The method recited in claim 12 wherein applying the compressive
force comprises disposing a sleeve around the preceramic resin, the
sleeve being made of a material having a volumetric
thermal-expansion coefficient between about 10.sup.-4 and 10.sup.-2
K.sup.-1 and a Young's modulus between about 10.sup.5 and 10.sup.8
N/m.sup.2.
16. The method recited in claim 15 wherein the material comprises
silicone rubber.
17. The method recited in claim 15 wherein applying the compressive
force comprises applying pressure to the preceramic resin with a
pressurized containment system.
18. The method recited in claim 15 wherein applying the compressive
force to the preceramic resin comprises: applying a resin
containment film to the preceramic resin; and disposing a sleeve
around the resin containment film, the method further comprising
removing the sleeve and the resin containment film.
19. The method recited in claim 12 wherein pyrolyzing the
preceramic resin comprises passing an electrical current through
the first and second electrical conductors.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 11/351,654, entitled "IN SITU PROCESSING OF
HIGH-TEMPERATURE ELECTRICAL INSULATION," filed Feb. 9, 2006 by
Matthew W. Hooker et al., the entire disclosure of which is
incorporated herein by reference for all purposes.
BACKGROUND OF THE INVENTION
[0002] This application relates generally to high-temperature
electrical insulation. More specifically, this application relates
to in situ processing of high-temperature electrical insulation.
Certain examples described in detail relate to oil-recovery
applications.
[0003] In recent years, concerns regarding the availability of
sufficient oil to meet demands have been increasing. This is due in
part to the fact that global demand for petroleum has been
increasing and continues to increase, particularly as developing
nations evolve more mature petroleum-consumption patterns that
parallel those of developed nations. No near-term curtailment of
this pattern of increasing demand is foreseen, and it is estimated
that the oil industry will need to add on the order of 100,000,000
barrels/day in production to meet the projected rate of consumption
by 2015. This pattern may be problematic by itself. But coupled
with these increases in demand is also a growing recognition that
oil recovery itself is likely to become more difficult over time.
Very few new oil-field discoveries have been made since the 1970's,
contributing to a general view that such discoveries are likely to
be ever more infrequent.
[0004] The combination of increasing demand and increasing
difficulty in production has resulted in a wide acknowledgment that
there will be a production shortfall sooner than had previously
been anticipated. There is accordingly an acute need in the art for
improved methods for oil recovery. Associated with this increase in
demand and production difficulties is an increase in the cost of
oil which provides impetus and capital for the development of new
sources of oil and the associated new production and recovery
technology.
BRIEF SUMMARY OF THE INVENTION
[0005] Embodiments of the invention provide methods for assisting
oil-recovery processes that have thermal aspects. This may be done
with a heater cable having a structure that is modified after
installation. In particular, the heater cable includes a preceramic
resin based composite that is pyrolyzed after deployment to form a
ceramic insulator. While the ceramic insulator has material
properties that are effective during use of the heater cable,
fabrication, transportation, and installation of the heater cable
may be simplified significantly when the preceramic resin, which is
cured into its green state, is present instead of the ceramic
insulator.
[0006] A first set of embodiments of the invention is accordingly
directed to methods of producing a heater cable. An electrical
conductor is coated with a preceramic resin. At least a portion of
the coated electrical conductor is deployed into an operational
location. The green-state preceramic resin is pyrolyzed while the
at least a portion of the electrical conductor is in the
operational location to convert the preceramic resin into a ceramic
insulator disposed to electrically insulate the electrical
conductor.
[0007] The coated electrical conductor may sometimes be sheathed
within a sheath, with the at least a portion of the coated
electrical conductor being deployed into the operational location
by deploying at least a portion of the sheathed electrical
conductor into the operational location. The ceramic insulator then
electrically insulates the electrical conductor from the sheath. In
one such embodiment, the preceramic resin is pyrolyzed by applying
a direct-current voltage to the electrical conductor. In one
embodiment, the coated electrical conductor is sheathed by welding
the sheath to the coated electrical conductor. The coated
electrical conductor may have a length between 1 and 5000 meters,
in some instances being continuous without a splice or joint.
[0008] In other instances, the electrical conductor comprises a
plurality of electrical conductors that are coated with the
preceramic resin, with the at least a portion of the coated
electrical conductor being deployed into the operational location
by deploying each of the plurality of coated electrical conductors
into the operational location. The plurality of electrical
conductors are then electrically insulated from each other with the
preceramic resin as well as after pyrolyzing the preceramic resin.
In one such embodiment, the preceramic resin is pyrolyzed by
applying an alternating-current voltage to the plurality of
electrical conductors. In different embodiments, each of the
plurality of coated electrical conductors may be sheathed with a
sheath or the plurality of electrical conductors may collectively
be sheathed with a sheath.
[0009] A variety of different specific compositions may be used in
different embodiments. For example, the electrical conductor may
comprise a solid copper rod. Examples of preceramic resins that may
be used include inorganic preceramic polymers.
[0010] There are also a variety of ways in which the electrical
conductor may be coated with the preceramic resin. In one
embodiment, material pre-impregnated with the preceramic resin is
wound around the electrical conductor. Material may be impregnated
with a vacuum-pressure-impregnation or vacuum-assisted
resin-transfer-molding process.
[0011] The preceramic resin may be cured into a green state before
deploying the at least a portion of the sheathed rod into the
operational location by heating the preceramic resin to a
temperature between 15 and 250.degree. C. In one embodiment, the
temperature is between 125 and 200.degree. C. The preceramic resin
may be pyrolyzed by heating the preceramic resin to a temperature
between 400 and 1500.degree. C. In one embodiment, the temperature
is between 750 and 1000.degree. C. In some instances, the
preceramic resin is pyrolyzed with a ramp-and-soak process: a
temperature of the preceramic resin is increased monotonically for
a first period of time and, thereafter, the temperature of the
preceramic resin is maintained at an elevated temperature for a
second period of time.
[0012] In a second set of embodiments, methods are provided for
assisting an oil-recovery process. A heater cable is deployed into
an oil-recovery environment. The heater cable comprises an
electrical conductor coated with a preceramic resin. The preceramic
resin is pyrolyzed while the heater cable is deployed in the
oil-recovery environment to form a ceramic insulator by converting
the preceramic resin, with the ceramic insulator electrically
insulating the electrical conductor. In some embodiments, a
temperature of the heater cable is increased to greater than
500.degree. C. after pyrolyzing the preceramic resin to assist the
oil-recovery process.
[0013] In some such embodiments, the heater cable further comprises
a sheath within which the coated electrical conductor is disposed.
The ceramic insulator electrically insulates the electrical
conductor from the sheath. In such embodiments, the preceramic
resin may be pyrolyzed by applying a direct-current voltage to the
electrical conductor. In other embodiments, the electrical
conductor comprises a plurality of electrical conductors coated
with the preceramic resin. In some of those embodiments, the
preceramic resin may be pyrolyzed by applying an
alternating-current voltage to the plurality of electrical
conductors. In those embodiments, the heater cable may comprise a
sheath within which the plurality of coated electrical conductors
are disposed
[0014] These embodiments find utility in different oil-recovery
processes. For instance, in one embodiment, the oil-recovery
process comprises a shale oil-recovery process. The heater cable is
accordingly deployed into a shale deposit. Increasing the
temperature of the heater cable causes kerogen present in the shale
deposit to be converted to oil and/or gas. The oil and/or gas is
accordingly available to be recovered from the shale deposit. In
another embodiment, the oil-recovery process comprises a tertiary
oil-recovery process or enhanced oil-recovery process. In such an
embodiment, the heater cable is deployed into an oil field.
Increasing the temperature of the heater cable causes a viscosity
of the oil present in the oil field to be reduced. This oil may
then be recovered from the oil field. In yet another embodiment,
the oil-recovery process comprises an oil-sands oil-recovery
process in which the heater cable is deployed on or near a ground
surface of an oil-sands environment.
[0015] In various of these embodiments, the electrical conductor
may comprise a solid copper rod and/or the preceramic resin may
comprise an inorganic preceramic polymer. The preceramic resin may
be pyrolyzed in the various manners described above. While the
above summary has noted certain oil-recovery applications, these
are intended only for purposes of illustration since the scope of
the invention contemplates other applications also.
[0016] In still another set of embodiments, methods are provided of
producing an insulated electrical conductor. A first electrically
uninsulated portion of a first electrical conductor is connected
with a second electrically uninsulated portion of a second
electrical conductor. A joint between the first and second
electrically uninsulated portions is coated with a preceramic
resin. The preceramic resin is heated to cure the preceramic resin
into a green-state insulator that substantially covers the
joint.
[0017] In some of these embodiments, a compressive force may be
applied to the preceramic resin while curing the preceramic resin
into the green-state insulator to consolidate the preceramic resin.
The compressive force may be applied by disposing a sleeve around
the preceramic resin. The sleeve is made of a material having a
volumetric thermal-expansion coefficient between about 10.sup.-4
and 10.sup.-2 K.sup.-1 and a Young's modulus between about 10.sup.5
and 10.sup.8 N/m.sup.2. One example of such a material comprises
silicone rubber. Alternatively, the compressive force may be
applied by applying pressure to the preceramic resin with a
pressurized containment system. In some instances, applying the
compressive force comprises applying a resin containment film to
the preceramic resin and disposing a sleeve around the resin
containment film, with the sleeve and resin containment film
subsequently being removed.
[0018] In certain instances, each of the first and second
electrical conductors comprises an electrically insulated portion.
Examples of electrical conductors that may be used in different
embodiments include both solid electrically conductive rods and
stranded electrical conductors.
[0019] Different methods may be used to cure the preceramic resin.
For example, in one embodiment, the preceramic resin is cured by
passing an electrical current through the first and second
electrical conductors. In another embodiment, the preceramic resin
is cured in a field location with locally mounted heaters. Both
methods can be conducted in the field or in a manufacturing
facility.
[0020] The methods of this set of embodiments may be incorporated
into methods of assisting an oil recovery process. For example, the
first conductor may be deployed into an oil-recovery environment,
with curing of the preceramic resin converting the preceramic resin
into a ceramic insulator that substantially covers the joint to
form a continuous conductor. A portion of the continuous conductor
corresponding to the second electrical conductor may then also be
deployed into the oil-recovery environment. The process may be
repeated with a third conductor to increase the overall length of
the continuous conductor. Once the full length of the insulated
conductor is assembled and the preceramic resin is cured to the
green state, all the green-state insulation covering the first,
second, and third conductors, as well as the regions where the
first, second, and third conductors are joined can be pyrolyzed
into a ceramic insulation in situ.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] A further understanding of the nature and advantages of the
present invention may be realized by reference to the remaining
portions of the specification and the drawings wherein like
reference numerals are used throughout the several drawings to
refer to similar components.
[0022] FIG. 1 provides a schematic illustration of an in situ
retorting process for recovering oil;
[0023] FIGS. 2A-2C are cross-sectional views of heater cables used
in various embodiments of the invention;
[0024] FIGS. 3A and 3B are flow diagrams summarizing certain
methods for field application of polymer-based electrical
insulation in accordance with embodiments of the invention;
[0025] FIG. 4A is a flow diagram summarizing methods for oil
recovery that may be performed in accordance with embodiments of
the invention;
[0026] FIG. 4B is a graph illustrating a temperature profile that
may be used for pyrolysis of an insulator in the heater cable of
FIG. 2 according to some embodiments of the invention;
[0027] FIG. 5 is a flow diagram summarizing methods of using in
situ pyrolysis of heater-cable insulation in a shale oil-recovery
process;
[0028] FIG. 6 is a flow diagram summarizing methods of using in
situ pyrolysis of heater-cable insulation in a thermal tertiary
oil-recovery process;
[0029] FIG. 7 is a flow diagram summarizing methods for oil
recovery that use field application of polymer-based electrical
insulation on conductor joints; and
[0030] FIGS. 8A-8D are schematic illustrations of stages in
executing the methods of FIG. 7.
DETAILED DESCRIPTION OF THE INVENTION
[0031] Embodiments of the invention are directed generally at in
situ processing of high-temperature electrical insulation. While
much of the discussion that follows illustrates such processing
with deployment of heater cables in certain oil-recovery
environments, such illustrations are intended to be exemplary
rather than limiting. As is noted below, embodiments of the
invention find utility in a wide range of applications outside of
oil-recovery techniques.
[0032] Those embodiments where the in situ processing is used to
aid oil-recovery processes generally make use of certain thermal
processes. In particular, these thermal processes rely on the
deployment of heater cables that provide the thermal energy used in
oil recovery. Such heater cables have a structure in which an
electrical conductor is sheathed, with an electrical insulator
being disposed to insulate the conductor from the sheath.
Embodiments of the invention permit the heater cables to be
deployed with a precursor to the electrical insulation in a
green-state that is physically flexible but still electrically
insulating. After deployment, pyrolysis of the green-state
insulation forms a ceramic insulator that functions actively during
the oil-recovery processes. The ability to deploy the heater cables
with the flexible precursor permits the cable to be bent through
curves and otherwise manipulated during deployment to a much higher
degree than would be possible with the more brittle ceramic
insulator. Not only does this make the thermal oil-recovery
processes more efficient by reducing the risk of damage to the
heater cables, it increases the variety of different environments
in which deployment is possible.
1. Oil Recovery
[0033] There are a variety of different kinds of techniques used
for oil recovery, with the specific nature of individual techniques
often depending on geophysical properties of the region being
explored. Techniques used in the development of oil fields are
often categorized into three distinct phases of oil recovery:
primary, secondary, and tertiary; tertiary recovery is also
sometimes referred to in the art as "enhanced recovery." As used
herein, the term "oil field" refers to a terrestrial reservoir
having a shape that traps hydrocarbons and that is covered by
sealing rock.
[0034] Primary recovery uses the natural pressure of a reservoir as
the driving force to push oil to the surface through a wellbore.
During this recovery phase, wells may be stimulated through the
injection of fluids, which fracture hydrocarbon-bearing formations
to improve the flow from the reservoir to the wellhead. Pumping and
gas lift may also sometimes be used during this phase to help
production when the reservoir pressure dissipates. Currently, such
primary-phase methods recover only about 10-30% of a reservoir's
original oil.
[0035] Secondary recovery uses other mechanisms to produce residual
oil remaining after the primary recovery. Examples of these
secondary-recovery mechanisms include injection of natural gas to
maintain reservoir pressure and water flooding to displace oil and
drive it to a production wellbore. These techniques were developed
shortly after World War II to extend the productive period of U.S.
oil fields, and permit an additional 20-40% of the original oil
reserve to be recovered. While these types of methods have
successfully increased the quantity of oil that may be recovered
from a field, still less than half the oil in place is typically
recovered.
[0036] This has led to the more recent development of several
tertiary oil-recovery techniques that offer prospects of ultimately
producing 30-90% (or perhaps even more) of a reservoir's original
oil. There are at least three major categories of tertiary recovery
that have been found to be commercially successful to varying
degrees. Techniques are employed to increase the mobility of the
oil, which comprises reducing the oil's resistance to flow, and
increasing the efficiency of the fluid or gas pushing the oil. Gas
injection uses gases that expand in a reservoir to push oil towards
a wellbore. Gases that have such properties include steam, natural
gas, nitrogen, and carbon dioxide. In some other gas-injection
forms of tertiary recovery, gases that dissolve in the oil and
lower its viscosity have been investigated. Chemical injection uses
surfactants to reduce the surface tension of the oil to enable it
to travel through a reservoir to the wellbore. Thermal recovery
uses a temperature increase to lower the viscosity of the oil and
thereby improve its ability to flow through the reservoir. In some
instances, this temperature increase is affected by introducing
steam into the well. Thermal techniques account for more than 50%
of U.S. tertiary recovery production, with gas injection making up
the bulk of the remainder; chemical techniques currently account
for less than 1% of tertiary recovery techniques in the United
States.
[0037] Thermal techniques are also used in the recovery of oil from
shale. Such a process extracts oil from the shale with the use of
underground heaters to separate kerogen, the organic material from
which oil is derived, from the shale in situ. This process is
illustrated schematically with FIG. 1, which shows a shale deposit
104. As used herein, "shale" refers to detrital sedimentary rock
formed by consolidation of clay into thin layers. Oil shale is
found on all of the inhabited continents of the Earth, but many
deposits are thin and irregular, yielding little oil. Unusually
thick oil shale deposits are found in the western United States,
providing roughly 75% of the world's estimated supply of
recoverable oil shale resources. Although the exploration costs for
oil shale are relatively low when compared with exploration for
conventional crude oil, the recovery costs are notably higher.
Kerogen does not flow as conventional crude oil does, and crushing
does not free it from the host rock. Heat is accordingly used to
remove kerogen from rock.
[0038] There are two principal methods that may use heat to extract
oil from oil shale. In one method, known in the art as "retorting,"
the oil shale is mined and the kerogen-containing rocks are heated
to elevated temperatures. This process is economically inefficient
because of the high cost of mining the oil shale and its relatively
low yield. In one long-term project from 1980-1991, this technique
extracted only 34 gallons of oil per ton of rock. Embodiments of
the invention are instead directed to "in situ retorting," in which
holes are bored into underground shale deposits and heaters placed
into the holes. The holes may be up to about 2500 feet deep in some
embodiments, although the invention is not restricted to any
particular hole depth. This process is illustrated in FIG. 1, with
the heaters being identified with reference numbers 108. Activation
of the heaters 108 produces heat 112 in the shale, raising its
temperature sufficiently to convert the kerogen to oil in place. As
used herein in discussions of kerogen conversion, "oil" refers to
the conversion products. This process eliminates the shale mining
costs and permits the newly formed oil to be pumped to the surface
through a producer well 116. Temperatures greater than about
500.degree. C. are sufficient to convert the kerogen into oil, and
some heavier compounds may also be partially converted in lighter
end products such as light oil and methane. The process is not only
more cost effective than conventional retorting, but is also more
environmentally benign because it eliminates the need to dispose of
the mined shale once the oil has been extracted.
[0039] It is noted that the general structure of FIG. 1 also
illustrates processes used for thermal tertiary oil recovery, with
the deployed heaters 108 acting as a source of thermal energy 112
to lower oil viscosity and improve flow. In such instances, the
heated oil may also be pumped to the surface through a producer
well 116.
2. Heater Cables
[0040] Embodiments of the invention broadly encompass aspects
related to the use of heater cables in thermal oil recovery
techniques. The inventors have recognized that a process similar to
that used for shale oil recovery may also be applied to other oil
recovery processes, examples of which include tertiary recovery and
recovery of oil from oil sands. In such embodiments, the heat used
to lower the viscosity of the oil is supplied by heater cables
deployed in an oil reservoir and heated to a temperature greater
than 500.degree. C. Heater cables like those described below may
accordingly be used in a variety of different thermal oil-recovery
techniques, of which tertiary recovery and shale recovery are used
as examples for specific illustrations below.
[0041] One challenge presented by the use of electrical heaters for
oil-recovery applications is the need to develop heater cables
suitable for long-term high-temperature operation in downhole
environments. To accommodate the geometry of the recovery
environments, such heater cables are typically of long length, and
may be of long lengths without splices or joints. For instance, in
certain embodiments, the cable lengths may range from less than 1
meter to more than 5000 meters; in other embodiments, the cable
lengths may be between 100 and 1500 meters. To function effectively
in such applications, the heater cables need to provide
sufficiently high power, preferably at high voltages, to maintain
the desired temperatures. As noted above, it is when cables are
heated to these temperatures that heat transferred to oil
sufficiently lowers its viscosity that its flow characteristics
permit it to be extracted during tertiary recovery processes. It is
also at these temperatures that sufficient heat is transferred to
kerogen to permit its conversion to oil in shale recovery
processes. In some embodiments, it is preferable for the heater
cables to have a similar durability while providing even higher
temperature increases to the downhole environments. The additional
heat transferred to oil at these higher temperatures in such
applications as thermal tertiary recovery processes may result in
even greater viscosity reductions to provide even better flow
characteristics for the oil. One method to attain these higher
heater temperatures applies higher voltages to the conductor,
further electrically stressing the insulation. Voltages can range
from 100 volts or less to 5000 volts or more, with both direct
current and alternating current. Similarly, the conversion of
kerogen to oil in shale recovery processes may be more efficient
when the heater cables operate at higher temperatures and higher
voltages. In some embodiments, the temperatures maintained by the
heater cables exceed 700.degree. C. and in still other embodiments,
the temperatures maintained by the heater cables exceed 900.degree.
C.
[0042] Structures for heater cables used in embodiments of the
invention are shown with the cross-sectional views of FIGS. 2A-2C.
FIG. 2A illustrates a structure suitable for embodiments where
direct current is to be used, while FIGS. 2B and 2C illustrate
structures suitable for embodiments where alternating current is
used. In the embodiment of FIG. 2A where direct current is to be
used, each cable 200 comprises a central electrical conductor 204,
surrounded by an electrical insulator 208, with the structure being
embodied within a sheath 212. Merely by way of example, the central
electrical conductor 204 may comprise copper or some other metal or
metallic alloy and the sheath 212 may comprise a metal such as
stainless steel. The insulator 208 electrically isolates the
central conductor 204 from the sheath 212. The cables 200 typically
have a length of 1-5000 meters, and may or may not contain joints
or splices over this length, but the invention is not limited to
any specific cable length. The outside diameter of the sheath 212
may be on the order of 1-10 cm in some embodiments, although the
invention is not limited to any particular sheath diameter.
[0043] In the embodiments of FIGS. 2B and 2C where alternating
current is to be used, each cable 240 or 240' comprises a plurality
of electrical conductors 220 surrounded by electrical insulation
224 that electrically isolates each conductor 220 from each other
as well as from the surroundings. A sheath 232 or 232' may be
applied to the exterior of such a multiconductor structure to
protect the cable 240 or 240' during installation. In some
instances, additional interior sheaths 228 may be provided for
robustness and protection--for purposes of illustration, such
interior sheaths 228 are shown in FIG. 2B, but could be omitted in
the configuration of FIG. 2B or additionally included in the
configuration of FIG. 2C. Similar to the direct-current
configurations, the electrical conductors 204 may comprise copper
or some other metal or metallic alloy, and the sheaths 228, 240,
and 240' may comprise a metal such as stainless steel. The cables
240 and 240' again typically have a length of 1-5000 meters, and
may or may not contain joints or splices over this length. The
outside diameter of the multiconductor heater cables 240 or 240'
may be on the order of 1-20 cm, but the invention is not limited to
any specific cable length nor to any particular cable diameter.
[0044] In certain embodiments, the insulator 208 comprises a
ceramic material formed as a result of pyrolysis of a preceramic
polymeric resin. Examples of suitable preceramic resins include
polymer resins like those described in detail in commonly assigned
U.S. Pat. No. 6,407,339, entitled "CERAMIC ELECTRICAL INSULATION
FOR ELECTRICAL COILS, TRANSFORMERS, AND MAGNETS," filed Sep. 3,
1999 by John A. Rice et al. ("the '339 patent"), the entire
disclosure of which is incorporated herein by reference for all
purposes. The '339 patent claims the benefit of the filing date of
U.S. Prov. Pat. Appl. No. 60/099,130, filed Sep. 4, 1998, the
entire disclosure of which is also incorporated herein by reference
for all purposes. Preceramic polymers that may be used as
precursors for the insulator 208 include monomers or polymers that
are liquid at an application temperature and that will polymerize
to form a solid compound, and which can be pyrolyzed at elevated
temperatures to form a ceramic material. The polymer structure
comprises inorganic molecules that link together to form chains.
The ceramic material resulting after pyrolysis may comprise silica,
silicon oxynitride, silicon carbide, silicon oxycarbide, a metal
silicate, a metal nitride, a metal carbide, a metal oxycarbide, an
alumina silicate, or other ceramic phases or mixtures thereof.
While many preceramic polymers are based on silicon, the invention
is not limited to such preceramic polymers and preceramics based on
or containing other materials such alumina, magnesia, or zirconia
are also within the scope of the invention. Other examples of
preceramic polymers that may be used include polyureasilazane,
hydridosiloxane, polysiloxane, polycarbosilazane, polysilazane,
perhydropolysilazane, other organosilazane polymers, cyclosiloxane
monomer, silicate esters, and blends thereof.
[0045] As noted in the '339 patent, different types of fillers or
reinforcements may be used to modify the mechanical and/or
electrical properties of the insulator 208, such as by addition of
glass or ceramic powders to improve the compression strength and
modulus of the insulator 208. A variety of glass or ceramic
whiskers or fibers may be added to improve the shear and tensile
strength of the insulator 208. In one embodiment, fibers having a
composition of about 70% aluminum oxide, 28% silicone dioxide, and
2% boron oxide are used for fiber reinforcement.
3. Insulation Application
[0046] The deployment of heater cables described in detail below is
an example of a more general process by which insulation may be
applied to conductors in accordance with embodiments of the
invention. Aspects of these general methods are summarized with the
flow diagrams of FIGS. 3A and 3B. The application of insulation
illustrated in FIG. 3A begins at block 304 by coating an electrical
conductor with preceramic resin. The electrical conductor may take
a number of different forms in specific embodiments. Merely by way
of example, the electrical conductor may comprise an electrically
conductive rod in the form of a solid or stranded electric
conductor, may comprise mineral insulated cable, or the like.
[0047] The coating may be performed in a number of different ways.
In one embodiment, a prepreg that includes the resin is wound
around the electrical conductor. As used herein, a "prepreg" refers
to material preimpregnated with resin; the material may be in the
form of a mat, fabric, nonwoven material, roving, or the like.
Merely by way of example, a vacuum-pressure impregnation ("VPI")
process or a vacuum-assisted resin-transfer-molding ("VARTM")
process may be used to impregnate material with the resin for
winding around the electrical conductor. As will be known to those
of skill in the art, VPI processes impregnate material under vacuum
and pressure. In a further embodiment, the electrical conductor may
be wrapped with a dry material and passed through a resin bath.
Still other application methods may be used in different
embodiments, including braiding and the like. In some instances,
the entirety of the electrical conductor is coated with the
preceramic resin, in which case the ceramic formed after curing may
insulate the entirety of the electrical conductor. In other
instances, a portion of the electrical conductor is coated with the
preceramic resin so that other portions of the electrical conductor
remain uninsulated after curing the preceramic resin.
[0048] The preceramic resin may be provided as a liquid,
semiliquid, putty, paste, b-staged condition, or the like in
different embodiments. In some instances, the preceramic resin
includes inorganic binders, which may be particulate-reinforced or
may contain nanoparticulate reinforcement. In other instances, no
reinforcement is provided in the preceramic resin, in which case it
is sometimes referred to as "neat resin." As indicated at block
308, resin containment and release film may sometimes be applied
over the preceramic resin in some embodiments.
[0049] At block 312, the resin is subjected to a compressive force
that acts to consolidate the resin. In some embodiments, the
compressive force is provided by installing a sleeve over the
conductor/resin assembly, the sleeve having suitable
thermal-expansion and stiffness characteristics to provide the
desired consolidation while the temperature of the assembly is
increased to a resin curing temperature. One suitable material
comprises silicone rubber, which has a volumetric thermal-expansion
coefficient of about 7.times.10.sup.-4 K.sup.-1 and a Young's
modulus of about 4.times.10.sup.6 N/m.sup.2. Suitable materials may
include those that have a volumetric thermal-expansion coefficient
between 10.sup.-4 and 10.sup.-2 K.sup.-1 and a Young's modulus
between 10.sup.5 and 10.sup.8 N/m.sup.2. Other examples of
materials that may be used for the sleeve include various rubbers
or heat-activated shrink polymers, which may be provided in the
form of tape, tubing, or the like. Alternative structures such as
pressurized bladders or clamping molds may be used in other cases
to provide the compressive force. Some other source of external
pressure such as may be provided with a pressurized containment
system may also be used to provide the compressive force in other
embodiments.
[0050] The resin is cured thermally to the green-state at block 316
by raising the temperature of the preceramic resin to a curing
temperature, with the compressive force active to provide
consolidation pressure to accommodate the natural expansion of the
resin during the temperature change. A variety of different
techniques may be used to cure the resin, including the use of
direct heat by placing the assembly in an over or furnace or
through the use of locally mounted heaters. In other embodiments,
the resin is heated resistively by passing a current through the
conductor. It will be appreciated that the availability of the
various types of curing and consolidation techniques permit
installation to be accomplished in a variety of different venues,
including in the field, in a remote location, in a manufacturing
facility, or the like. Assembly in the field or in a remote
location may advantageously avoid the use of a large, permanently
mounted oven or furnace.
[0051] After the green-state insulation has been formed by curing
the resin, the compressive force may be removed as indicated at
block 320. Depending on how the compressive force was applied, such
removal may comprise removing a sleeve from the assembly, removing
the assembly from a pressurized containment system, or the like. If
the method included the use of a resin containment and release
film, that material may also be removed at block 320.
[0052] The flow diagram of FIG. 3B summarizes methods for applying
insulation that accommodates joints in the conductor. Partially
insulated electrical conductors are provided at block 324. The
insulation on these conductors may have been formed using a method
like that described in connection with FIG. 3A or may have been
formed with other techniques. The exposed portions of the
conductors are generally at one or both ends of the conductors when
the conductors are provided with a generally linear shape, but may
be in other positions, particular with conductor structures having
different shapes.
[0053] The uninsulated portions of different conductors are
connected at block 328 to form a joint. The joint connection may be
made by any suitable technique known to those of skill in the art,
including through the use of welding, the use of mechanical links,
the use of threaded joints, and the like. Insulation of the joint
subsequently begins by coating the joint with preceramic resin at
block 332. Generally, the preceramic resin coats the joint
structure itself as well as other uninsulated portions of the
conductors proximate the joint. Application of a compressive force
at block 336 to consolidate the resin during temperature changes to
cure the resin thermally at block 340 produce green-state ceramic
that insulates the joint. The application of compressive force may
be performed using any of the methods described in connection with
FIG. 3A, including the placing of a constrained-expansion sleeve
around the assembly, placing the assembly in a pressurized
containment system, or the like. Similarly, any of the methods
described in connection with FIG. 3A may be used to cure the resin
thermally, including the use of ovens or furnaces, the use of
locally mounted heaters, or the use of resistive heating that
results from passing an electrical current through the joined
conductors. After curing, the compressive force is removed at block
344.
[0054] These methods allow joints to be made and locally
electrically insulated between partially insulated conductors in
the field or in remote locations, thus enabling arbitrarily long
lengths of continuous insulated conductor to be fabricated in the
field. In some applications, the length of conductor that may be
provided to the field is limited by the stiffness of the conductor
and/or the brittleness of the insulation material, which prevent
the material from being coiled to a sufficiently small diameter for
practical transport to the point of use or installation. This
restriction may be accommodated through use of the joint-insulating
technique by enabling shorter, transportable lengths of conductor
to be provided to the field, where they are joined and insulated to
form whatever length is desired for a specific use. Since one
factor in the ability to coil the conductor is its thickness,
methods of the invention enable field use of conductors having
larger thickness, ranging from fractions of an inch to several
inches in diameter or greater. These methods also enable certain
other specific applications in various embodiments. For instance,
other types of insulated conductor that are not otherwise easily
joined together may be joined, such as by using the polymer-based
insulation to join sections of hermetically sealed mineral
insulated cable. In other applications, in-field repair of
conductor structures that have been damaged, such as during
transportation, handling, or installation procedures. Generally,
the methods enable complete fabrication of structures in the field
provided that uncured resin can be provided to the field
location.
4. In Situ Deployment of Heater Cables
[0055] Methods of oil recovery are aided in embodiments of the
invention by deploying heater cables into an oil recovery
environment with the preceramic resin in a green-state. After
deployment, the resin is heated to convert it to form the ceramic
insulator, enabling the deployed cables thereafter to be used for
thermal oil-recovery processes. The insulation material provides
electrical insulating capabilities while in the green-state, during
the process of conversion to a ceramic, as well as after it is
converted to a ceramic. This enables the heater to aid in the
oil-recovery process immediately after installation, as well as
prior to and during the conversion process of the preceramic
polymer to a ceramic.
[0056] An overview of such embodiments is provided with the flow
diagram of FIG. 4A. At block 404, the method begins by coating an
electrically conductive rod with a preceramic resin, using any of
the methods described in connection with FIG. 3A. As indicated at
block 408, the resin is cured into a green state, usually through
the application of heat at a temperature between 15 and 250.degree.
C. In some embodiments, green-staging of the resin is performed at
a temperature between 125 and 200.degree. C., being performed at
approximately 150.degree. C. in a specific embodiment. In some
embodiments, the heater cable is produced by sheathing the rod at
block 412. This may be performed by welding the sheath to the
insulated rod. In the resulting state, the heater cable may then be
deployed into an oil-recovery environment at block 416. Usually
such deployment occurs through a well bore or drilled penetration
into the oil reservoir or oil shale deposit, or on the surface or
near the surface for oil sands applications, although other types
of deployment may also be performed depending on the specific
configuration of the oil-recovery site.
[0057] The green-state resin is pyrolyzed into a ceramic in situ
after its deployment in the oil-recovery environment, as indicated
at block 420. Such pyrolysis is performed by applying an electric
current to the electrical conductor and thereby raising the
temperature of the heater cable. Pyrolysis is typically performed
at temperatures between 400 and 1500.degree. C., and may be
performed at between 750 and 1000.degree. C. in some embodiments.
In some instances, the pyrolysis may be performed by application of
a ramp-and-soak profile like the one shown for illustrative
purposes in FIG. 4B. With such a ramp-and-soak profile, the
temperature is increased substantially monotonically for a first
period of time and then held at a substantially constant
temperature for a second period of time. The profile shown in FIG.
4B includes two stages of ramping and soaking, with the ramping
being performed substantially linearly in time. The first stage
applies heat at a temperature of about 300.degree. C. for about
five hours after a five-hour ramp, and the second stage applies
heat at a temperature of about 900.degree. C. for about five hours
after a ten-hour ramp. In some cases, multiple ramp and soak stages
may be used to completely pyrolyze the preceramic polymer and to
provide suitable mechanical and electrical properties in the
insulation material. Higher temperatures and faster heating rates
can be achieved by applying higher voltages to the conductor within
the heater cable, thus further electrically stressing the
insulation.
[0058] Once the resin has been pyrolyzed at block 420 to form the
ceramic insulator, the heater cable may be used in thermal
oil-recovery processes as indicated at block 424. Pyrolysis of the
resin in situ after deployment in an oil-recovery environment
advantageously permits the heater cable to be handled with
considerably more versatility before deployment. In particular,
when the resin is still in a green-state, the heater cable may be
wrapped onto a smaller-diameter spool for packaging and storage
when compared with the requirements imposed for a heater cable
having a ceramic insulator. This results in a smaller package for
transport and may permit a longer length of heater cable to be
packaged onto a single spool. In addition, the heater cable with
green-state resin is more damage tolerant during deployment,
particularly during run-in processes to deploy it downhole,
significantly reducing the risk of damage to the insulation during
deployment. This technique also enables a wider range of material
properties of the ceramic insulator to be used. In particular, the
focus for selection of ceramic insulation materials may be on the
electrical and mechanical properties most suitable for particular
operations in an oil-recovery environment. These considerations
need not additionally be constrained by the need to provide high
strain tolerance and toughness for efficient transport and
deployment of the cables downhole. While the imposition of such
constraints on heater cables that include the ceramic insulator may
be quite limiting, the desired strain tolerance is much more easily
achieved with the green-state resin.
5. Applications
[0059] As previously noted, there are numerous applications to the
in situ pyrolysis described in detail in connection with FIG. 4A.
This includes, in particular, thermal processes used for oil
recovery. FIGS. 5 and 6 are flow diagrams that illustrate the
integration of in situ pyrolysis with specific exemplary
oil-recovery processes. In the case of FIG. 5, this is illustrated
for a shale oil-recovery process, while FIG. 6 provides a similar
illustration for a thermal tertiary oil-recovery process. The
processes are generally similar, demonstrating the ability for
embodiments of the invention to apply to a variety of different
thermal oil-recovery methods.
[0060] The shale oil-recovery process of FIG. 5 begins at block 504
with heater cables being produced with green-state preceramic
resin, as described in more detail in connection with FIG. 3. Holes
are bored into the shale deposit at block 508, permitting the
heater cables produced at block 504 to be deployed into the holes
at block 512. A flow of electrical current through the central
conductor of the heater cable is used at block 516 to pyrolyze the
resin in situ and thereby form a ceramic insulator. The heater
cable is then ready for use at block 520 as part of the
oil-recovery process by maintaining or increasing its temperature
to provide heat in the oil-recovery environment that converts
kerogen in the shale to oil. Use of the heater cable in such
applications is generally expected to be through the application of
a DC voltage to the heater cable, but the invention is not limited
to such a usage. Once the kerogen has been converted to oil at
block 520, the oil may be pumped to the surface at block 524.
[0061] The oil-recovery process illustrated in FIG. 6 may be
performed on an oil field and may use multiple extraction
techniques to recover as much oil as possible. This is noted at
blocks 604 and 608, which respectively identify the performance of
primary and secondary oil-recovery processes as discussed above. A
thermal tertiary oil-recovery process may use heater cables
produced at block 612 with green-state preceramic resin. Holes are
bored into the oil field at block 616. In some embodiments, these
holes may be bored specifically for use with the thermal tertiary
oil-recovery process, but in other instances may be bored earlier
in the oil-recovery effort as part of the primary or secondary
oil-recovery processes. Irrespective of precisely at which point in
the recovery effort the holes are bored, they may be used at block
620 for deployment of the heater cables. In situ pyrolysis of the
resin of the heater blocks at block 624 produces a ceramic
insulator, thereby creating a heater cable having the desired
characteristics for use at block 628. This use may be affected by
applying a voltage to the heater cable to generate heat that
increases the temperature of oil in the oil field. Use of the
heater cable in these applications is generally expected to be
through the application of an AC voltage, but the invention is not
limited in such a respect. The increase in temperature imparted to
the oil in the oil field lowers its viscosity, making it more
amenable to pumping to the surface at block 632.
[0062] The oil recovered with the embodiments of either FIG. 5 or
FIG. 6, or with other thermal methods that use in situ curing of
preceramic resin, may subsequently be used for any suitable
applications. The in situ processing of the high-temperature
insulation described herein can be used for numerous other
applications in addition to use in oil recovery. Merely by way of
example, this insulation can accordingly be used on heaters,
sensors, and other devices that operate at elevated temperature.
Installation of the device, with the insulation in the green-state,
enables the device or cable to withstand high levels of strain, in
bending, tension, or compression, up to and in excess of 2%. This
in turn enables compact packaging of long lengths of cable for
transport or other uses, or installation of the device through a
tortuous path, or reconfiguring the shape of the cable by bending
the cable or device into complex or curved shapes within or around
a component to be heated. Pyrolysis of the green-state insulation
into a ceramic material can be affected by applying a voltage to
the conductor contained within the insulation, or by another
mechanism of increasing the temperature to an appropriate level to
pyrolyze the preceramic insulation. This pyrolysis can be affected
during initial and normal operation of the component to be heated
or through a special thermal cycle designed to pyrolyze the
green-state insulation. Furthermore, the green-state material
provides suitable insulation properties to enable the normal
operation of the devices while the insulation is in the
green-state, while the insulation is undergoing the pyrolysis
process, as well as when it is converted into a ceramic.
Applications for this insulation material may include, but are not
limited to, heaters for industrial ovens and furnaces, pipelines,
sub-sea pipelines, heat-treating equipment, vacuum chambers, and
many more.
[0063] An illustration of field applications that make use of the
joint-insulating methods described in connection with FIG. 3B are
provided with the flow diagram of FIG. 7 and the corresponding
schematic diagrams of FIGS. 8A-8D. The schematic diagrams of FIGS.
8A-8D illustrate configurations during different deployment stages
of a heater cable corresponding to different stages in the method
of FIG. 7.
[0064] The method begins at block 704 by deploying a partially
insulated conductor into an oil-recovery environment such as an oil
field, oil sands, shale deposit or the like. Any method may have
been used to provide partial insulation of the conductor, including
use of the methods described above. Deployment of the partially
insulated conductor is illustrated in FIG. 8A, which shows an
oil-recovery environment 804 that includes a deployment hole within
which the partially insulated conductor 808-1 is deployed. In this
illustration, the uninsulated portion 812 of the conductor 808-1 is
disposed at an end of the conductor 808-1.
[0065] As indicated at block 708 and illustrated in FIG. 8B, the
exposed portion 812 of the conductor 808-1 is connected with the
exposed portion of another partially insulated conductor 808-2.
Such connection may be made by any suitable technique, examples of
which include the use of welding, the use of mechanical links, the
use of threaded joints, and the like. The resulting conductor
connection 816 is coated with preceramic resin 820 at block 712, as
illustrated in FIG. 8C. The preceramic resin is cured in the field
at block 716 to form green-state insulation around the joint and
thereby produce a continuous conductor 824 from the two pieces.
This continuous conductor 824 may be completely or partially
insulated. Examples of circumstances where the continuous conductor
824 is partially uninsulated include those where still further
joints are to be made. For instance, the second conductor 808-2
could be uninsulated at both its ends so that it remains
uninsulated at one end even after the connection 816 is
insulated.
[0066] The curing of the joint may include some of the steps
described in connection with FIGS. 3A and 3B above. For example, a
compressive force may be applied to consolidate the preceramic
resin, particularly as the resin expands as the temperature is
changed in curing the resin. This may be preceded by application of
a resin containment and release film to the conductor, which may be
removed after the thermal curing at block 716. The compressive
force may be applied by use of a sleeve, by use of pressurized
containment system, use of a clamping mold, or the like. The curing
itself may be accomplished by passing an electrical current through
the conductor connection 816, by using locally mounted heaters, or
the like.
[0067] After production of the continuous conductor 824 in this
way, the portion that corresponds to the additional conductor 808-2
is deployed into the oil-recovery environment at block 720 and as
illustrated in FIG. 8D. This process may be repeated with
arbitrarily many additional conductors by progressively returning
to block 708 to increase the length of the continuous conductor to
the desired length for deployment in the oil field. Once deployment
has been completed, the continuous conductor 824 may be used for
oil recovery at block 724.
[0068] In addition to being used in conjunction with initial
deployment in an oil-recovery environment, these methods may also
be used for the repair, reinforcement, and/or strengthening of
conductors used in oil-recovery environments. The methods may be
applied to fiber matrix insulation, mineral insulated insulation,
or connectors and conductors of insulation.
[0069] Thus, having described several embodiments, it will be
recognized by those of skill in the art that various modifications,
alternative constructions, and equivalents may be used without
departing from the spirit of the invention. For example, the
methods described herein for insulating conductors and making
insulated joints can be used for numerous applications in addition
to their use in oil recovery. For instance, these techniques may be
used on heaters, sensors, and other devices that can be insulated
using polymer-based insulation systems. Applications for this type
of insulation include heaters for industrial ovens and furnaces,
pipelines, sub-sea pipelines, heat-treating equipment, vacuum
chambers, and many more. Accordingly, the above description should
not be taken as limiting the scope of the invention, which is
defined in the following claims.
* * * * *