Note: Descriptions are shown in the official language in which they were submitted.
Atty Ref: ET-031CA1 / 4336-6
Augmented generation of hydrogen in deviated or horizontal wells
Technical Field
[0ow] This disclosure relates to the production of hydrogen and hydrogen-rich
fluids through
serpentinization of ferrous iron sources in underground reservoirs.
Technical Background
[0002] Hydrogen gas has been recognized as a promising alternative fuel. Since
pure hydrogen
produces only water when combusted, it is generally referred to as a "clean"
fuel. Hydrogen occurs
naturally in the Earth's crust, in mid-ocean ridges and Precambrian
crystalline shields, as well as in
celestial bodies. Natural hydrogen gas reserves, such as the extensive
hydrogen field at Bourakebougou
in Mali, are currently being exploited.
[0003] Aside from the harvesting of naturally occurring hydrogen gas, efforts
to produce hydrogen have
concentrated on several known methods, such as electrolysis (i.e.,
hydrolysis), natural gas reforming,
biomass gasification, and natural gas or fossil fuel combustion. The resultant
hydrogen may be
considered "gray", "blue" or "green" depending on the level of carbon
emissions associated with
powering the hydrogen generating reaction and the products of the reaction
itself. For example,
hydrogen produced from combustion is generally considered gray hydrogen,
associated with high
carbon emissions. Hydrogen produced in this manner may be considered blue if
accompanied by carbon
capture, utilization and storage, which lowers the net level of carbon
emissions. Hydrogen produced via
hydrolysis, when powered by a low-carbon source, is considered green since
hydrolysis produces only
hydrogen and oxygen.
[0004] Currently, using known methods, blue hydrogen is more cost effective to
produce than green
hydrogen; but even so, blue hydrogen still requires additional measures to
mitigate carbon emissions.
For example, methane reforming can be used to produce hydrogen at an
industrial scale, but ultimately
produces carbon dioxide that must be sequestered or otherwise disposed of.
Accordingly, it is desirable
to develop alternative means of hydrogen production that minimizes the
production of carbon
emissions.
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Summary
[0005] Hydrogen is produced in underground reservoirs through artificial
inducement and/or
augmentation of a serpentinization reaction between water and a ferrous iron
source.
[0006] In some implementations, a suitable reservoir is seeded via an
injection well with particles
containing ferrous iron, such as ferrous iron nanoparticles. In other
implementations, the reservoir
already includes host rock containing a suitable ferrous iron source, such as
fayalite, but may lack
sufficient water or heat to spontaneously react. The serpentinization reaction
is artificially triggered or
augmented through the application of well stimulation techniques
conventionally associated with
hydrocarbon production, such as hydraulic fracturing (fracking) to enhance the
permeability of the
reservoir, or thermal stimulation through water or steam injection. The
resultant serpentinization
reaction produces molecular hydrogen, which is recovered via a production
well. The pH of injected or
existing water can be altered to improve the reaction rate. Carbon-containing
material present in the
reservoir or injected into the reservoir can result in production of a
hydrogen-rich fluid such as methane
instead of, or in addition to, molecular hydrogen. Thus, spent hydrocarbon
wells may be adapted for
hydrogen production without requiring the installation of natural gas
reforming equipment necessary
for production of grey or blue hydrogen.
[0007] Where the reservoir already contains host rock providing a sufficient
ferrous iron source to
sustain production of hydrogen, any hydrogen produced by naturally occurring
serpentinization
reactions can be extracted via production wells. Once the naturally occurring
hydrogen has been
depleted, or if a naturally occurring serpentinization reaction is not
detectable in the reservoir, the
serpentinization reaction can then be artificially triggered or augmented.
[0008] Since there is no combustion contemplated in this process, there are no
waste combustion
products to be sequestered. This may be contrasted to techniques such as in
situ combustion of
underground hydrocarbon reserves which does generate pollutants such as carbon
monoxide and
carbon dioxide that must then be sequestered within the reservoir.
[0009] Thus, in some implementations, a method for underground production of
hydrogen includes
injecting particles comprising ferrous iron into an underground reservoir via
an injection well, to thereby
cause a serpentinization reaction with water in the reservoir, and extracting
hydrogen or a hydrogen-
rich fluid produced in the underground reservoir via a production well. In
other implementations, the
method includes locating at least one injection well at an underground
reservoir, the underground
reservoir comprising host rock comprising ferrous iron silicate material,
locating at least one horizontal
or deviated production well at the underground reservoir, performing at least
one stimulation action to
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stimulate a serpentinization reaction in the underground reservoir, and
extracting hydrogen or a
hydrogen-rich fluid using the at least one production well.
[0010] In all implementations, the serpentinization reaction can be stimulated
by increasing a
temperature of the underground reservoir, increasing the temperature by water,
increasing the
temperature by steam injection, and/or hydraulic fracturing, including a
combination of two or more of
these techniques. At least some water for the serpentinization reaction may be
supplied by connate
water. In some implementations, the proppant employed in hydraulic fracturing
comprises ferrous iron.
Also, in some implementations, the serpentinization reaction is stimulated or
produced by injecting the
particles of ferrous iron, where the average particle size is smaller than an
average pore throat size of
the reservoir, 50% or less than the average pore throat size of the reservoir,
or nanoparticles. In some
implementations, the particles of ferrous iron are fayalite. In some
implementations, the stimulation
action raises an average temperature of the underground reservoir to at least
200 degrees Celsius.
[0011] In these implementations, the injection and production wells can be
drilled at a site of a
reservoir comprising host rock with iron silicate material, or previously-
drilled wells can be employed for
producing hydrogen. The injection and production wells can be horizontal or
deviated.
Brief Description of the Drawings
[0012] FIG. 1 is a flowchart illustrating, at a high level, a method for
production of hydrogen using
artificial induction or augmentation.
[0013] FIG. 2 is a flow chart illustrating, at a high level, a further method
for production of hydrogen
using artificial induction or augmentation.
[0014] FIG. 3 is a schematic diagram illustrating an example hydrogen
production system with a first
arrangement of injection and production wells.
[0015] FIG. 4 is a schematic diagram illustrating a further arrangement of
injection and production
wells.
[0016] FIG. 5 is a schematic diagram illustrating another arrangement of
injection and production wells.
[0017] FIG. 6 is a schematic diagram illustrating a further arrangement of a
substantially vertical
injection well and a plurality of production wells.
Detailed Description
[0018] The generation of naturally occurring subsurface hydrogen has been well
documented.
Subsurface hydrogen is naturally created by radiolysis, the disassociation of
water due to irradiation by
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radioactive ores, or by serpentinization of iron-containing rocks. Hydrogen
production by
serpentinization in mid-ocean ridges and basins has been documented or
modelled. Serpentinization is
used to describe the metamorphic hydration and oxidation of ultramafic rock to
serpentinite. Typically,
the source rock is low in silica, and can include iron-bearing species such as
olivine and pyroxenes.
[0019] Olivine, in particular, is a magnesium iron silicate, where the ratio
of magnesium to iron varies.
Olivine thus has endmembers consisting of only magnesium silicate (forsterite,
Mg2SiO4) and iron silicate
(fayalite, Fe2SiO4). Iron-containing silicate forms contain ferrous iron
(iron(II)) and can react with water
to produce hydrogen.
[0020] In particular, water reacts with fayalite to oxidize the iron(II) and
produce magnetite, silicon
dioxide (quartz), and hydrogen:
3Fe2SiO4 + 2H20 4 2Fe304 + 3Si02 + 2H2
[0021] This reaction can involve the intermediate production of ferroan
brucite or iron(II) hydroxide,
MgxFei,(OH)2 or Fe(OH)2; the iron(II) hydroxide can then be converted to
magnetite, hydrogen, and
water as described by the Schikorr reaction, which may be expressed as:
3Fe(OH)2 4 Fe304 + H2 + 2H20
[0022] When a carbon source is present, some hydrocarbon gases may also be
produced from olivine,
for example when reacted with carbon dioxide:
18Mg2SiO4 + 6Fe2SiO4 + 26H20 + CO2 4 12Mg3Si205(OH)4 + 4Fe304 + CH4
[0023] A "serpentinization" reaction, as used herein, refers to a reaction of
ferrous iron-containing
material with water that produces hydrogen, whether in the form of molecular
hydrogen or a hydrogen-
rich fluid such as methane. Some impurities may be comprised in the hydrogen
product depending on
the constituents of the reaction components or trace gases present in the
reservoir where the reaction
occurs.
[0024] While the serpentinization reaction will naturally occur with the
fortuitous concomitance of
fresh (unreacted) ultramafic rock, water, and suitable temperature, the
development of a naturally-
occurring hydrogen field also depends on a suitable geologic structure that
traps the produced hydrogen
and avoids or reduces migration or leakage. In the case of the Bourakebougou
field, for example, layers
of dolerite shields and aquifers likely confined the naturally produced
hydrogen until its discovery.
However, as discussed below, underground reservoirs that do not currently
produce a detectable or
viable amount of hydrogen¨or that do not produce any hydrogen at all¨can be
used for the
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production of hydrogen by artificially induced or augmented serpentinization
reactions, using
stimulation techniques previously associated with hydrocarbon production such
as hydraulic fracturing
and thermal stimulation. This adaptation can be applied to pre-existing,
abandoned or to-be-abandoned
wells, or to newly drilled wells, whether or not the reservoir contains
sufficient ferrous iron-containing
rock.
[0025] An example production method is generally illustrated by the flowchart
of FIG. 1. Briefly, at 100,
injection and production wells are located at a suitable site for hydrogen
production. In this example,
the site is an underground reservoir with host rock having sufficient ferrous
iron silicate material, such
as unreacted fayalite or iron-containing olivine, to support sufficient
serpentinization reactions to
generate viable hydrogen, that is to say, hydrogen in sufficient quantities
for production purposes. It is
also presumed that the geologic makeup of the reservoir, including the
availability of ferrous iron silicate
material and the permeability of the host rock, has already been determined,
either from previous
production activity at the site (e.g., in the case where pre-existing
injection or production wells used for
hydrocarbon production are available) or as part of an exploratory phase. If
the injection and production
wells are not already present at the site, locating the injection and
production wells can include some or
all of the typical drilling and completion steps. At 105, optionally any
naturally occurring hydrogen is
extracted prior to engaging in artificial inducement or augmentation of a
serpentinization reaction, but
this step may be bypassed; if there is naturally occurring hydrogen it may be
collected along with the
product of the artificially induced or augmented serpentinization reaction. At
110, the basic conditions
for a serpentinization reaction in the reservoir are determined, such as
availability of sufficient water
and the temperature of the reservoir; however, these may be already known from
previous production
or exploratory activity. This can include measurement of the pH of available
water and the presence of
other constituents in the reservoir.
[0026] Based on the geologic makeup and reaction conditions, one or more
artificial inducement or
augmentation actions are performed at 115. As those skilled in the art will
appreciate, typical limiting
factors of a reaction rate, such as the serpentinization reaction rate, are
temperature, availability of
source materials (reactants and reagents), and surface contact between source
materials. Connate
water may supply the serpentinization reaction, but if insufficient water is
present, then water is
injected 120 and enters the reservoir through perforations in the injection
well (assuming the injection
well is lined at the reservoir). A serpentinization reaction can occur at
about 200 C, or even lower; thus,
depending on the depth of the reservoir and a target rate of reaction, heating
of the water will generally
be required. Thus water heated at the surface (e.g., to 200 C, in the form of
wet or dry steam) is injected
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into the reservoir 125, for example using techniques and equipment known in
hydrocarbon production,
such as conventional heaters or boilers. Once condensed in the reservoir, this
also provides a water
source for the serpentinization reaction. Use of low-carbon energy sources for
heating the water will
minimize the environmental impact of this step.
[0027] Other sources of heat energy (not illustrated in the drawings) may be
used to raise the water
temperature in the reservoir or prior to reaching the reservoir. Geothermal
energy can be used to raise
the temperature of water in the reservoir. Alternatively, heated water can be
sourced from existing
deeper aquifers; or, if the reservoir is located under existing thermal oil or
in situ oilsands operations,
the remaining hot water in those oil formations can be circulated into the
reservoir. Injection of heated
water thus includes circulating the heated water from an underground source
rather than from surface.
[0028] Additives may be used to modify the pH of the water 130 in the
reservoir. It has been found that
the rate of hydrogen production by serpentinization increases with higher pH;
thus, additives such as
sodium hydroxide or potassium hydroxide can be useful to accelerate
production.
[0029] The rate of a reaction can also be limited by the surface contact with
reactants. In the reservoir,
relatively low permeability of the rock containing ferrous iron may retard the
serpentinization reaction
rate. Thus, hydraulic fracturing techniques, as known in hydrocarbon
production, can be applied 135 to
induce fractures and improve permeability in the reservoir. A wide variety of
fracking fluid formulations
is available; in view of the possibility of enhancing the reaction rate by
increasing pH, alkaline fracking
fluid additives such as NaOH and KOH, as noted above, can be useful. Carbon-
containing additives such
as cellulose may result in the generation of some hydrocarbons, as noted
above. Conventional
proppants can be used as well. However, in place of conventional frac sand
(quartz sand), other
substances can be used as proppants while augmenting the serpentinization
reaction. For instance,
since fayalite has a similar hardness to quartz, sand comprising or consisting
of fayalite can serve as a
suitable proppant while providing additional ferrous iron for further
serpentinization reactions.
[0030] As a result of these one or more inducement or augmentation techniques,
serpentinization
reactions in the reservoir generate hydrogen in a gas stream which is
extracted via a production well
140. If the resultant gas stream includes contaminants or other gases (e.g.,
nitrogen or methane), a
recovery method 145, such as membrane diffusion, can be employed to capture
the hydrogen and
remove other gases. This can be carried out at surface, or alternatively
subsurface in the production
well. The hydrogen is brought to surface for storage, transport and use.
[0031] In the production method discussed above, the reservoir included
sufficient ferrous iron source
material to support a serpentinization reaction and viable hydrogen
production. However, suitable
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injection and production wells can be located at other sites that by
themselves do not provide viable
hydrogen quantities, or indeed any at all. This may be the case where an
abandoned or to-be-
abandoned well providing adequate reservoir pressure and temperature is
converted for hydrogen
production, or where a reservoir site is chosen based on proximity to a
subsurface aquifer or thermal oil
operations providing a heated water source, as suggested above. In that case,
a similar production
method as that described above can be employed, but with the injection of
ferrous iron particulate
matter to seed the reservoir with a reactant to induce the serpentinization
reaction.
[0032] FIG. 2 provides a flowchart illustrating an example of this production
method. Similar to the
process of FIG. 1, at 200 injection and production wells are located at the
desired site. Again, it is
presumed that the geologic makeup of the reservoir was previously determined
in the course of
previous production or exploratory activity. Locating the wells, again, can
include some or all of the
conventional drilling and completion steps if the wells are not already
available. Optionally, any existing
hydrogen is extracted (not shown in FIG. 2) prior to artificially inducing
generation, although in this
implementation this step is not expected. At 205, the basic conditions for a
serpentinization reaction are
determined. At 210, particles providing ferrous iron are injected into the
reservoir to provide source
material for the serpentinization reaction. These particles can be fayalite
particles, although other
materials providing a ferrous iron source can be used instead, and can be
transported as an aqueous
dispersion, which can also supply some of the water required for the
serpentinization reaction. To
mitigate the risk of plugging the reservoir, the particles are smaller than
the average pore throat size of
the rock forming the reservoir (which would have been determined at an earlier
stage), e.g., 50% or less
than the average pore throat size. Nanoparticles containing ferrous iron, such
as fayalite nanoparticles,
would ensure passage through most macroporous and some mesoporous rock; in
addition, the small
size of the particles favours the serpentinization reaction rate since it
increases the available reactant
surface area available to water.
[0033] At 215 one or more stimulation actions are performed as described
above, based on the
conditions in the reservoir. If insufficient water is present and not provided
with the injection of the
ferrous iron-containing particles, then water is injected 220. If heat is
required to trigger or accelerate
the reaction, this can be supplied in the form of heated water or steam
injection 225, whether from
surface or from a subsurface source as described above. Additives can be
provided to modify the pH 230
to enhance the serpentinization reaction, for example to increase alkalinity
as discussed above. Fracking
235 may again be carried out, as described above, to improve permeability in
the reservoir. Since some
particles may rest in the injection well 310, the serpentinization reaction
can thus occur within the
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injection well instead of, or as well as, in the surrounding reservoir. The
resultant hydrogen then escapes
the injection well through perforations and travels through the reservoir to
the production well, where
it is extracted 240. Again, if the resultant gas stream includes other gases
or contaminants, a recovery
method 245 is used to capture the hydrogen, which is then stored, transported,
and used.
[0034] The technique of injecting particles can be combined with the
production method described
with reference to FIG. 1 above to further augment the serpentinization
reaction with additional
reactant. Moreover, the order of steps depicted in FIGS. 1 and 2 can be
altered. For instance,
determination of the basic conditions for the serpentinization reaction at 110
or 205 can be determined
during an exploratory phase prior to locating the injection and production
wells at 100, as noted above,
or during the extraction of naturally occurring hydrogen 105. Hydraulic
fracturing can occur at an earlier
stage, for example prior to introduction of additional water 120 or 220, or
prior to introduction of
ferrous iron-containing particles if this step is undertaken. Stimulation
actions undertaken in the method
of FIG. 2 may occur concurrently with the injection of particles at 210. The
selection of various
stimulation techniques, and variations in the steps of the processes shown in
FIGS. land 2, are within
the skill of the person of ordinary skill in the art.
[0035] Turning to FIG. 3, a schematic depicting main components of a hydrogen
production system 300
for implementing the methods described above is shown. One or more injection
wells 310 and one or
more production wells 350 are located at an appropriate site. The site can be
selected based on the
presence of one or more of host rock containing a suitable ferrous iron source
to support a
serpentinization reaction, host rock providing suitable permeability and
porosity to accommodate a
serpentinization reaction with injected ferrous iron source material, pre-
existing wells and/or host rock
that may be adapted for hydrogen production, and/or underground heated water
sources, as discussed
above. For simplicity, FIGS. 3-5 depict only a single injection well 310 and a
single production well 350
and FIG. 6 depicts only a single injection well 310 and multiple production
wells 350, but more than one
injection and production well can be employed. In particular, when particles
are injected to supply a
ferrous iron source for the serpentinization reaction, the use of multiple
injection wells can be useful to
increase the rate of introduction of the ferrous iron.
[0036] The injection 310 and production 350 wells can be horizontal or
deviated wells, although as can
be seen in the example of FIG. 6 the injection well 110 is vertical or
substantially vertical. As shown in
FIG. 3, the injection well 310 is equipped with an injection system 312 and
string 313. This injection
system 312 is used to introduce water as a reagent for the serpentinization
reaction, and/or heated
water or steam to provide thermal stimulation to augment the reaction, with or
without additives to
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alter the pH of the water. The injection system 312 can also be employed to
inject ferrous iron-
containing particles to induce or augment the serpentinization reaction. Thus,
the injection system 312
will include a number of components for one or more of these purposes, such as
water storage tanks, a
heater or boiler, storage and hoppers/feeders for ferrous iron particulates,
additives for injected water
or steam, pumps and a mixer (e.g., a shear unit). If hydraulic fracturing is
employed, the system 300 will
also include a hydraulic fracturing system 320 including components such as
storage and
hoppers/feeders and a slurry blender for mixing the fracturing fluid and
proppants, if used. In this
example, a water-based fracturing fluid would supply hydration for the
serpentinization reaction; thus
the hydraulic fracturing system 320 could be combined or share components with
the injection system
312.
[0037] The injection well 310 extends into or through the reservoir 370,
generally a lower part of the
reservoir 370. The injection well 310 can also include well monitoring devices
such as a fluid analyzer
340 and a temperature sensor 342 proximate to the reservoir 370. The fluid
analyzer 340 can be
operable to detect the presence of water and gases (e.g., naturally occurring
hydrogen) and the pH of
water in the reservoir. Readings from the fluid analyzer 340 and temperature
sensor 342 are received by
a control system 380 at surface, which can be programmed to automatically
control the injection system
312, e.g., when injecting water or steam.
[0038] The production well 350 includes production tubing 352 for extracting
the hydrogen, connected
to storage tanks and associated equipment (e.g., compressors) 354 for storing
the produced hydrogen.
As mentioned above this can include hydrogen recovery equipment, if required
(not illustrated).
[0039] The production well 350 is located above the injection well 310, and
possibly separated from the
reservoir 370 by caprock, although in the illustrated examples, at least one
region of the production well
350 extends into the reservoir 370 as well. A flow path to the production well
350 is defined. In the
example of FIG. 3, the injection well 310 is horizontal and the production
well 350 is deviated, and the
toe 355 of the production well is positioned a short vertical distance above
the toe 315 of the injection
well; thus the flow path can be located where the distance between the
production and injection wells
is shortest. In this example, the closest vertical distance between the toes
315, 355 may be at least
about 2m, but less than about 10m.
[0040] As the reaction occurs in the reservoir 370, the generated gas
(molecular hydrogen or possibly
hydrogen-rich fluids, depending on the reactants in the reservoir) rises in
the reservoir 370 to the
production well 350, where it can then be extracted. The production well 350
can be perforated at or
near this point of greatest proximity to permit hydrogen flow to the tubing
352. If the flow path extends
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through caprock, hydraulic fracturing may be employed to increase permeability
to permit gas flow
upward. As production progresses, further stimulation can occur through
perforations along the
injection well, for example in the direction of the arrow indicated in FIG. 3.
Additional flow paths can be
established between the reservoir 370 and the production well 350. This can
occur naturally as the
serpentinization reaction continues.
[0041] FIGS. 4 and 5 illustrate other possible arrangements with a horizontal
injection well 310 and
deviated production well 350. In these examples, the flow path can again be
defined at the region of
closest proximity, between a portion of the foot 317 of the injection well and
the heel 357 of the
production well. Since the drawings depict side views of the reservoir, the
lateral spread of the injection
and production wells is not illustrated, but the production well 350 need not
be positioned directly
above the injection well 310 for its full length. That is to say, the
injection well is positioned at a greater
vertical depth than the production well, but the injection and production
wells need not be aligned in
the same vertical plane.
[0042] FIG. 6 illustrates a further possible arrangement with a vertical, or
substantially vertical,
injection well 310 and one or more deviated production wells 350. As the
serpentinization reaction
progresses, the reservoir 370 can extend upwards towards the surface and
additional flow paths can be
defined upwards along the length of the wells. This configuration can be
useful in pinnacle reef
formations, which often have good permeability and porosity characteristics
thereby reducing the need
for fracking.
[0043] In all cases, the specific well geometry will be determined by the
characteristics of the host rock.
In some implementations, both the injection and production wells 310, 350 are
horizontal, for example
in the case where a steam assisted gravity drainage (SAGD) steam chamber is
repurposed for hydrogen
production. Alternatively, the injection well 310 may be deviated while the
production well 350 is
deviated or horizontal. In some implementations, an operating SAGD well pair
can be employed.
Conventionally in a SAGD operation, an injection well is positioned above a
production well. An
additional production well for hydrogen can be positioned above the injection
well, arranged relative to
the injection well similar to the arrangements described above. If the SAGD
reservoir already includes a
ferrous iron source, steam introduced by the injection well can be directed to
the ferrous iron source as
well to stimulate a serpentinization reaction for collection by the hydrogen
production well. Optionally
ferrous iron can be injected as described above.
[0044] While example implementations have been shown and described,
modifications can be made by
those of ordinary skill in the art without departing from the scope or
teaching herein. Options or
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variations described in connection with one implementation may be combined
with other options or
variations of other implementations. Use of any particular term should not be
construed as limiting the
scope or requiring undue experimentation to implement the claimed subject
matter or embodiments
described herein. While this disclosure may have articulated specific
technical problems or advantages
that are addressed or provided by the implementations described above, this
disclosure is not intended
to be limiting in this regard; the person of ordinary skill in the art will
readily recognize other technical
problems addressed or advantages provided by the embodiments discussed above.
Accordingly, the
scope of protection is not limited to the embodiments described herein, but is
only limited by the claims
that follow, the scope of which shall include all equivalents of the subject
matter of the claims.
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