Note: Descriptions are shown in the official language in which they were submitted.
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MULTICOMPONENT DEGRADABLE MATERIALS AND USE
BACKGROUND
[0001] Degradable
materials have many uses in our society, ranging from making
degradable plastic bags, diapers, and water bottles, to making degradable
excipients
for drug delivery and degradable implants for surgical use, to a wide variety
of
industrial uses, such as in remediation, agriculture, and oil and gas
production.
[0002] For example,
degradable materials have been used for fluid loss control, for
diversion, and as temporary plugs in downhole applications of oil and gas
production.
Examples of degradable materials used in such ways include rock salt, graded
rock
salt, benzoic acid flakes, wax beads, wax buttons, oil-soluble resin material,
etc. In
addition to filling and blocking fractures and permeable zones right in the
reservoir,
degradable materials have also been used to form consolidated plugs in
wellbores that
will degrade after use, eliminating the need for retrieval.
[0003] New
materials that can be used in such applications are always needed, however,
and in particular materials that degrade under downhole conditions are
particularly
needed.
SUMMARY
[0004] In general,
the current disclosure relates to multicomponent fibers that have
accelerated degradation in water in low temperature conditions, and their
various
industrial, medical and consumer product uses. Such materials are especially
useful
for uses in subterranean wells in oil and gas production. In some embodiments,
the
compositions of materials have accelerated degradation even at Ultra Low
Temperature ("ULT") (< 60 C) in subterranean formations.
[0005] In some
cases, the multicomponent fibers comprise components that degrade at
different rates in water, or water soluble components in combination with
water
degradable components, or hydrocarbon soluble components in combination with
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water degradable components. Some of the multicomponent fibers described
herein
lost more than 60% weight at temperatures below 60 C in water within a week.
[0006] The
degradable materials described herein, especially the non-toxic materials,
have a variety of uses, e.g., to make consumer products such as plastic
grocery bags
and diaper liners, and also medical uses as implants, bandages, sutures, or
drug
delivery materials. However, our main interest for such material lies in oil
and gas
production, and other geological, mining, agriculture or remediation uses.
[0007] Embodiments
of the current application can be used in various operations
servicing subterranean wells. For example, materials of the current
application can be
applied to proppant flowback control, transportation of proppant, diversion in
hydraulic fracturing, carbonate acidizing, and flow channeling in proppant
pack.
[0008] Materials of
the current application can also be added to drilling fluids to help
minimize lost circulation, and added to cement to improve the flexural
strength of the
set cement. In some of the applications, such as diversion and carbonate
acidizing,
materials of the current application (such as fibers) may form a temporary
plug in a
fracture, a perforation, a wellbore or more than one of the locations in a
well to allow
some downhole operations, and the plug then degrades or dissolves after a
selected
time, such that the plug disappears. The materials can even be formed into
solid plugs
for temporary uses to plug wellbore equipment.
[0009] The time
frame for the fiber to degrade to remove the fiber plugs is dependent on
the choice of fibers (polymers) and on wellbore temperatures. However, the
materials
of the invention degrade in water at 60 C in less than a month. Degradation
can be
accelerated with additives, with reactive fillers or with acids or bases in
the injection
fluid.
[0010] According to
certain embodiments of the current application, there are provided
multicomponent composite fibers having components that degrade at different
rates in
water, or having water soluble components (sheath or core, sea or one side) in
combination with water degradable components, or having hydrocarbon soluble
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component (core, island or one side) in combination with water degradable
components.
[0011] In addition,
such multicomponent fibers may be processable, have comparable
strength and stiffness to mono-component PLA fibers, and contain locally
concentrated reactive fillers and other additives that promote fast
degradation in water
at low temperatures (T < 60 C) in subterranean wells.
[0012] Materials
that are suitable for the current application include, but are not limited
to, polymers that are capable of being degraded (break down to oligomers or
monomers) in aqueous environment. The polymer degradation in water is
measurable
by the decrease of molecular weight of the polymer (measured by drying and
weighing, or by gel permeation chromatography), and the weight loss of the
solid
polymers over a period of time from a few hours, to a few days, weeks and
months
depending on the temperatures, the pH of the water, the nature of the polymers
and
whether the presence of a catalyst. For a downhole application, degradation
can also
be assessed by permeability, such that the polymer degrades or solubilizes
enough to
allow fluid flow.
[0013] Examples of
the suitable, degradable polymers for the degradable composites
include, but are not limited to, aliphatic polyesters, poly(lactic acid),
poly(E-
caprolactone), poly(glycolic acid) (PGA), poly(lactic-co-glycolic acid)
(PLGA),
poly(hydroxyl ester ether), poly(hydroxybutyrate), poly(anhydride),
polycarbonate,
poly(amino acid), poly(ethylene oxide), poly(phosphazene), polyether ester,
polyester
amide, polyamides, sulfonated polyesters, poly(ethylene adipate) (PEA),
polyhydroxyalkanoate (PHA), poly(ethylene terephtalate) (PET), poly(butylene
terephthalate) (PBT), Poly(trimethylene terephthalate) (PTT), poly(ethylene
napfithalate) (PEN) and copolymers, blends, derivatives or combination of any
of
these degradable polymers.
[0014] In some
cases, the degradable polymers are poly(lactic acids), poly(E-
caprolactones), poly(glycolic acids) (PGA), and poly(lactic-co-glycolic acids)
(PLGA). Poly(lactic acids) can be produced either by direct condensation of
lactic
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acids or by catalytic ring-opening polymerization of cyclic lactides, or can
be
commercially provided.
[0015] Lactic acid,
often produced commercially through bacterial fermentation, is a
chiral molecule and has two optical active isomers: the D isomer and the L
isomer.
The D isomer content in the PLA determines the crystallinity of the PLA
polymer.
Fully amorphous PLA incudes relatively high D content (>20%) where highly
crystalline PLA contains less than 2% D isomer.
[0016] Examples of
the amorphous PLA resins include 6060D, 6302D, or 4060D resins
from Naturcworks. Examples of crystalline PLA resins include 6201D or 6202D
resins from Natureworks. The matrix polymer in the degradable composites may
comprise only the amorphous, only the crystalline PLA, or the blend of
amorphous
and crystalline PLA. A PLA polymer blend can be a simple mechanical mixture of
molten amorphous and crystalline PLA polymers.
[0017] In some
embodiments, a reactive filler, such as a base, metal oxide, or other
catalysts can be included inside the fibers to accelerate degradation through
fast water
diffusion and fast kinetics. Besides basic properties, the additives can
provide metal
ions (Zn2', Mg2', etc.) that may act as Lewis acids and enhance ester bond
cleavage
as well. Thus, such additives can assist in controlling the rate of
degradation.
[0018] The reactive
fillers may include, but are not limited to, bases or base precursors
that generate hydroxide ions or other strong nucleophiles when in contact with
water.
The reactive fillers improve both the rate of water penetration into the
fibers and the
rate of ester hydrolysis through the catalytic effect of nucleophiles.
[0019] Examples of
reactive fillers include, but are not limited to, Ca(OH)2, Mg(OH)2,
CaCO3, Borax, MgO, CaO, ZnO, NiO, CuO, A1203, and other bases or compounds
that can convert to bases when in contact with water.
[0020] Taking
advantage of this multicomponent fiber technology and carefully designed
multicomponent composite fibers that allow reactive fillers to concentrate in
certain
part of the fibers may result in rapid degradation of the polymers surrounding
the
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filler particles, and cause the fiber to deteriorate into small particles
(particle size <20
um) within one or two weeks at ultra low temperatures (<60 C).
[0021] If needed,
the reactive fillers in the multicomponent fibers can be surrounded by
another component of polymer. Thus, the fibers can be used in applications in
both
neutral and acid solution without undesired interference from the reactive
fillers. In
other embodiments, the fillers are contained on the outside and e.g., acid is
used to
accelerate degradation. In some embodiments, the reactive fillers are
dispersed
uniformly in at least one of the polymer components.
[0022] The
concentration of the reactive fillers, defined as weight% of filler in one
polymer component, may be the same (evenly distributed reactive fillers in the
fibers)
or may be different in each polymer component so that the reactive fillers are
locally
concentrated in certain parts of the fibers.
[0023] The
materials of the current application may be in the shape of rods, particles,
beads, films and fibers. Alternative, a solid plug or other shape can be
formed, for
example by pressing. Fabrics and woven mats can also be made with the fibers.
[0024] In some
embodiments, multicomponent fibers are made from extruding two or
more polymers from the same spinneret with both polymers contained within the
same filament. By this technique, polymers with different properties can be
tailored
into the same filament with any desired cross sectional shapes or geometries.
In the
multicomponent fibers, two or more polymer components can be joined, combined,
united or bonded to form a unitary fiber body.
[0025]
Multicomponent fibers can be classified by their fiber cross-section
structures as
side-by-side, sheath-core, islands-in-the-sea and citrus fibers or segmented-
pie cross-
section types, and various combinations thereof FIG. 1 and 2 show the examples
of
cross sections of multicomponent fibers.
[0026] Polymer
resins with different morphology, melting temperatures, dissolution and
degradation kinetics may also be designed into multicomponent fibers to
achieve the
81780411
optimum degradation, tensile strength and dimension stability (minimum
shrinkage) at
given temperatures in water.
[0027] Fibers can also include other types of additives in addition to
reactive fillers, for
example to impart color, flexibility, or other desirable properties. The
particle sizes of the
various additives may be in the range of 10 nm to several hundred nanometers.
Reactive
fillers with larger total surface area may result in faster degradation at the
given
temperatures compared to bigger fillers with smaller total surface area.
[0028] The loading of the various fillers as a weight percentage of the
total composite can be
in the range of 0-10% or 0.2% to 4% in fibers, depending on the choice of
fillers, their
molecular weight and the process condition. Each filler can be used alone or
combined
with other fillers and additives. The most preferred fillers for developing
degradable/soluble bicomponent fibers are ZnO and the combination of ZnO with
a small
amount of other fillers, such as MgO, salts, waxes, plasticizers, and
hydrophilic polymers
such as ethylene vinyl alcohol (EVOH) or polyvinyl alcohol (PVOH).
[0028a] Thus, in one aspect there is provided a degradable multicomponent
fiber, comprising:
a) a degradable polymer selected from the group consisting of polylactic acid
(PLA),
polycarprolactone, polyglycolic acid, polylactic-co-polyglcolic acid, and
mixtures thereof;
b) a water soluble polymer or a hydrocarbon soluble polymer; and c) a reactive
filler
mixed with the degradable polymer, that shortens a degradation time of said
degradable
polymer when mixed therewith, the reactive filler being selected from the
group consisting
of Ca(OH)2, Mg(OH)2, Borax, MgO, CaO, ZnO, NiO, CuO, 4-Dimethylaminopyridine
and
A1203; d) wherein the degradable polymer is different from the water soluble
polymer and
the hydrocarbon soluble polymer; and e) said multicomponent fiber having a
diameter of
less than 100 micrometers, said fiber being degradable in 30 days or less at
60 C in a
subterranean formation.
[0028b] In a further aspect, there is provided a degradable multicomponent
fiber, comprising:
a) a degradable polyester; b) a water soluble polymer or a hydrocarbon soluble
polymer;
and c) a reactive filler mixed with the degradable polyester that shortens a
degradation time
of the degradable polyester, said reactive filler being selected from the
group consisting of
Ca(OH)2, Mg(OH)2, Borax, MgO, CaO, ZnO, NiO, CuO, 4-Dimethylaminopyridine
(DMAP), and A1203; d) wherein the degradable polyester differs from the water
soluble
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polymer and the hydrocarbon soluble polymer, and wherein the degradable
polyester and the
water soluble polymer or the hydrocarbon soluble polymer are adjacent to each
other in said
fiber, and wherein said fiber degrades in <30 days at 60 C in a subterranean
formation.
[0028c] In a further aspect, there is provided a multicomponent fiber
comprising a first
degradable polymer adjacent a second hydrocarbon soluble polymer, wherein said
fiber
degrades in 30 days or less at 60 C in a subterranean formation, wherein the
first
degradable polymer is selected from the group consisting of polyester,
polylactic acid
(PLA), polycarprolactone, polyglycolic acid, polylactic-co-polyglcolic acid
and mixtures
thereof, the second hydrocarbon soluble polymer is selected from the group
consisting of
ethylene vinyl acetate, olefin, propylene, ethylene and combinations thereof,
and a reactive
filler is mixed with the first degradable polymer, the reactive filler being
selected from the
group consisting of Ca(OH)2, Mg(OH)2, Borax, MgO, CaO, ZnO, NiO, CuO, Al2O3,
DMAP, and mixtures thereof, wherein the reactive filler shortens a degradation
time of the
first degradable polymer.
[0028d] In a further aspect, there is provided a multicomponent fiber,
comprising: an
amorphous polymer selected from the group consisting of amorphous PLA and
amorphous
PLA intimately admixed with ZnO, adjacent to a crystalline polymer selected
from the
group consisting of crystalline PLA and crystalline PLA intimately admixed
with ZnO,
said fiber having a diameter of less than 1001.1M and being degradable in
water at 60 C in
30 days or less in a subterranean formation.
100291 The use of the word -a" or "an" when used in conjunction with the
term "comprising"
in the claims or the specification means one or more than one, unless the
context dictates
otherwise.
[0030] The term "about" means the stated value plus or minus the margin of
error of
measurement or plus or minus 10% if no method of measurement is indicated.
[0031] The use of the term "or" in the claims is used to mean "and/or"
unless explicitly
indicated to refer to alternatives only or if the alternatives are mutually
exclusive.
[0032] The terms "comprise", "have", "include" and "contain" (and their
variants) arc opcn-
ended linking verbs and allow the addition of other elements when used in a
claim.
[0033] The phrase "consisting of' is closed, and excludes all additional
elements.
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[0034] The phrase "consisting essentially of" excludes additional material
elements, but
allows the inclusions of non-material elements that do not substantially
change the
nature of the invention.
[0035] By "multicomponent fibers" what is meant is that a fiber has at
least two different
components therein, and such components are at least partially adjacent each
other,
although many configurations thereof are possible. The term does not include
fibers
where the components are intimately admixed or blended, however.
[0036] By "bicomponent fibers" what is meant is that a fiber has two
different
components therein that are adjacent.
[0037] By "degradable polymer" what is meant is a polymer that can be
degraded in
water at 60 C in 30 days or less, preferably in two weeks, or a week or less.
[0038] By "degraded" what is meant is at least a 50% reduction in dry
weight or if
assessed downhole by flowthrough at least a 50% increase in flow.
[0039] By "hydrocarbon soluble polymer" what is meant is a polymer that is
soluble in
petroleum hydrocarbons in 30 days or less, preferably in two weeks or in a
week or
less.
[0040] By "water soluble polymer" what is meant is a polymer that dissolves
in water in
30 days or less, preferably in two weeks or in a week or less.
[0041] The following abbreviations are used herein:
ABBREVIATION TERM
DI Deionized water
DMAP 4-Dimethylaminopyridine
G-PVOH Nichigo G-polymerTM
PLA Polylactic acid
SEM Scanning electron microscope
ULT Ultra low temperatures
DESCRIPTION OF FIGURES
[0042] FIG. 1: Examples of sheath-core (1 and 2), islands-in-the-sea (3 and
4) and
segmented-pie (5 and 6) cross-section types.
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[0043] FIG. 2: Cross-section of various side-by-side multicomponent fibers.
[0044] FIG. 3. Schematic view of Fibers 1 in Table 1.
[0045] FIG. 4A-D. Schematic views of bicomponent fibers consisting of
degradable
polymer and water soluble polymer.
[0046] FIG. 5A-B. Schematic views of bicomponent fibers consisting of
degradable
polymer and oil soluble polymer.
[0047] FIG. 6A-B. The optical images of the bicomponent fibers. A: Bi-
505/50C-Zn0;
B: Bi-755/25C.
[0048] FIG. 7. The degradation of the bicomponent fibers, Bi-50S/50C
(vertical hatching)
and Bi-75S/25C (horizontal hatching) having different rations of core versus
sheath
material, at 60 C in water over 14 or 21 days.
[0049] FIG. 8. The degradation profiles of the bicomponent fibers, Bi-
50S/50C (star) and
Bi-50S/50C-ZnO (4%) (circle), at 60 C in water versus time in days.
[0050] FIG. 9. Influence of additives on the degradation rate of PLA fibers
at 60 C for 48
hours. The PLA fibers were provided by NatureWorks.
100511 FIG. 10A-B. A: SEM image of as-spun PLA/G-PVOH (8042p) bicomponent
fiber
with a sheath:core ratio at 31%:69%. B: The optical image of the cross-section
of the
same PLA/G-PVOH sheath-core fiber.
[0052] FIG. 11. The degradation of the PLA/G-PVOH fibers in water and
buffered
solutions at varying pH versus time in days. Left panel, T = 49 C, Right T =
60 C.
[0053] FIG. 12A-B. SEM images of PLA/G-PVOH fibers after 7 days in
deionized (DI)
water at 49 C (A) and 60 C (B).
[0054] FIG. 13. Photograph of glass vials containing 0.25g of Evatane, 28-
05 (left) and
Evatane 28-40 (right) in 8 ml of octane. Both resins dissolved in octane at
38 C
after 5 hours.
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DETAILED DESCRIPTION
[0055] At the
outset, it should be noted that in the development of any such actual
embodiment, numerous implementation-specific decisions must be made to achieve
the developer's specific goals, such as compliance with system related and
business
related constraints, which will vary from one implementation to another.
Moreover, it
will be appreciated that such a development effort might be complex and time
consuming but would nevertheless be a routine undertaking for those of
ordinary skill
in the art having the benefit of this disclosure. In addition, the composition
used/disclosed herein can also comprise some components other than those
cited.
[0056] In the
summary and this detailed description, each numerical value should be read
once as modified by the term "about" (unless already expressly so modified),
and then
read again as not so modified unless otherwise indicated in context. Also, in
the
summary and this detailed description, it should be understood that a
concentration
range listed or described as being useful, suitable, or the like, is intended
that any and
every concentration within the range, including the end points, is to be
considered as
having been stated. For example, "a range of from 1 to 10" is to be read as
indicating
each and every possible number along the continuum between about 1 and about
10.
Thus, even if specific data points within the range, or even no data points
within the
range, are explicitly identified or refer to only a few specific, it is to be
understood
that inventors appreciate and understand that any and all data points within
the range
are to be considered to have been specified, and that inventors possessed
knowledge
of the entire range and all points within the range.
[0057] Different
types of polymers or similar polymers with different crystallinity,
melting point, degradation kinetics and solubility can be used to form the
components
in the multicomponent fibers. Depending on the final applications (such as,
proppant
transport or bridging and plugging), there are a variety of choices of
configurations
and compositions for multicomponent composite fibers, and the fiber body can
have a
variety of regular or irregular cross-sectional shapes.
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[0058] For example, the polymer components can be arranged to form a core-
sheath
configurations shown as 1 and 2 cross section in FIG. 1, island-sea with up to
360
islands (3 and 4 cross section in FIG. 1), and segmented pie (4-64 segments)
shown as
and 6 cross-section in FIG. 1.
[0059] FIG. 2 shows the examples of side-by-side multicomponent fibers
comprising
different polymers or similar polymers with different melting points,
degradation
kinetics and physical properties.
[0060] Combinations of the above configurations are also possible.
[0061] Each component of a multicomponent fiber may occupy 10-90% of the
weight of
the entire fiber, or 25-75%, or 50-50% or any range in between. The components
can
be regular or irregular in shape or cross-section, and components can be
symmetrically or asymmetrically placed (e.g., a core can be off-center).
[0062] In all cases, the reactive filler can be in one component or the
other, or in all
components, as needed for degradation kinetics, strength and the actual
application.
Reactive fillers can comprise 0-10% or 0.2-4% of the component to which it is
added.
More can be used if needed for particular applications.
[0063] Poly(lactic acid) (PLA) with different crystallinity levels, as
examples of
degradable polyesters, are used to construct the multicomponent fibers. The
selection
of the PLA resin is based on their melting temperatures, the rate of water
penetration,
and the degradation kinetics, all of which correlate to the crystallinity of
PLA
polymers. For example, PLA with the melting point of 125-135 C is an amorphous
polymer that degrades faster than semi-crystalline PLA with the melting point
at 160-
170 C.
[0064] In Table 1, Fibers 1, 2 and 3 all have semi-crystalline PLA polymer
as the core
and amorphous PLA polymer as the sheath. In these fibers, the core provides
the
stiffness and strength, and the sheath component absorbs water and can rapidly
degrade at given temperatures. Fiber 1 has reactive fillers in the core only,
and
loading of the filler is up to 10% of the core polymer (FIG. 3). For Fiber 2,
reactive
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fillers (e.g., up to 10%) are also added into the sheath component and Fiber 3
has
reactive fillers only in the sheath component (e.g., up to 10%). The weight %
of
sheath component in Fibers 1, 2 and 3 may be around 50-90%.
[0065] The
configuration of Fibers 4, 5 and 6 is reversed with amorphous PLA as the
core and semi-crystalline PLA as the sheath, but the components are otherwise
the
same as that of Fibers 1, 2 and 3. The configuration of Fibers 4, 5 and 6
allows the
fibers to maintain stiffness and flocculation (fiber network in water to
support
proppant) for longer time and only break down at the later stage of
degradation. The
core component in Fibers 4, 5 and 6 may contain up to 10% reactive fillers, or
the
sheath up to 10%, or both. The weight % of the sheath component in Fibers 4, 5
and 6
may be around 10-50%, or be the same as above depending on the desired
characteristics.
Table 1. Examples of polymers and fillers in degrable core-sheath PLA fibers
Fiber Sheath Melt point ( C) ZnO in Core Melt point ( C) ..
ZnO in
ID polymer Sheath polymer Sheath Polymer Core
polymer Core
1 60600 125-135 no 62010 160-170 yes
2 6060D 125-135 yes 62010 160-170 yes
3 6060D 125-135 yes 62010 160-170 no
4 6201D 160-170 no 6060D 125-135 yes
62010 160-170 yes 6060D 125-135 yes
6 6201D 160-170 yes 6060D 125-135 no
[0066] Though the
above examples of multicomponent composite fibers have core-sheath
configurations, the arrangement of PLA components and the distribution of
reactive
fillers can be applied to island-sea configurations, side-by-side
configurations and
other configurations, such as braided or twisted.
[0067] Tables 2 and
3 show additional examples, where the configuration of the
components is in an island sea configuration (Table 2), or a side-by-side
configuration
(Table 3). Segmented pie configuration and combinations of configurations are
also
possible. All the PLA polymers in Tables 1, 2, 3 and 4 have a Glass Transition
Temperature (Tg) in the range of 55-60 C.
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Table 2. Examples of polymers and fillers in degradable island-sea PLA fibers
Sea Melting point Island
componen ( C) Sea ZnO in componen Melting point ( C) ZnO in
t polymer Sea t island polymer island
60600 125-135 no 6201D 160-170 yes
60600 125-135 yes 6201D 160-170 yes
60600 125-135 yes 6201D 160-170 no
6201D 160-170 no 6060D 125-135 yes
62010 160-170 yes 6060D 125-135 yes
6201D 160-170 yes 6060D 125-135 no
Table 3. Examples of polymers and fillers in degradable side-by-side PLA
fibers
ZnO in
Major side Melting point ZnO in Minor side Melting point
minor
polymer ( C) major side major side polymer ( C) minor side
side
6060D 125-135 no 62010 160-170 yes
6060D 125-135 yes 62010 160-170 yes
6060D 125-135 yes 6201D 160-170 no
6201D 160-170 no 60600 125-135 yes
6201D 160-170 yes 6060D 125-135 yes
6201D 160-170 yes 60600 125-135 no
100681 As another alternative, the degradable polymers may be used to
construct the
sheath and the water soluble polymers may be used as the core (FIG. 4A). In
this
case, the hydrophobic, degradable polymeric sheath provides a layer of
protection
from moisture for longer shelf life, and the water soluble core provides
mechanical
strength to the fibers that should help to maintain the performance properties
including proppant settling, bridging and plugging. When the fibers are
exposed to
water, the core with fast dissolution kinetics will dissolve first to result
in a hollow
degradable fiber with very thin wall (< 2 p,m) which then degrades or even
breaks
down to small particles in the down-hole high pressure environment.
[0069] In yet another approach, we take advantage of fast physical
dissolution of one
component in the multicomponent fibers, where the other component will provide
the
stiffness, physical properties and easy processing. The water soluble polymers
may
be used to form sheath, sea, or one side of the multicomponent fibers, and
degradable
polyesters may be used to form core, island or the other side of the
multicomponent
fibers (FIG. 4B). In this case, the degradable polymers as the core provide
the
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mechanical strength, stiffness, and process-ability for the multicomponent
fibers, and
the water soluble polymer as the sheath dissolves rapidly in water at ULT,
which
effectively reduces the degradable portion to only 10-50% of total weight.
[0070] In both
cases, the water soluble polymers may occupy 50-90% of the fibers in
order to take the most advantage of their fast dissolution kinetics at ULT.
For
example, the PVOH/PLA bicomponent fiber made herein takes much less time to
reach the same weight loss% at the same degradation time and temperature
compared
to the degradation of a monocomponent PLA fiber, because the degradable
polymer
with slow degradation kinetics (several weeks to degrade) only accounts for 10-
50%
of the total weight of the fibers and the water soluble polymer with fast
dissolution
kinetics (several hours to dissolve) accounts for the major component of the
multicomponent fiber.
[0071] Polyethylene
oxide, polyvinyl alcohol (GOHSENOL, GOHSENAL, ECOMATY,
and EXCEVAL from Kuraray), modified polyvinyl alcohol (Nichigo G-polymer from
Nippon Gohsei), aliphatic polyamide (NP2068 of H. B. Fuller), sulfonated
polyester
(AQ38 and AQ55, Eastman), and polyacrylic ester/acrylic or methacrylic acid
copolymers and blends thereof are examples of polymers for the water soluble
component.
[0072] Poly(lactic
acid) (PLA), poly(glycolic acid) (PGA), poly(caprolacton) (PCL),
polybutylene succinate polymers and polybutylene succinate-co-adipate polymers
and
copolymer or blends thereof are examples of polymers for the degradable
polyester
components.
[0073] The specific
choice of the water soluble polymer for constructing the
multicomponent fibers is based on the application temperatures. For example,
if the
wellbore temperature is at 38 C or lower, AQ 38 or Nichago G-polymer may be
used
as one of the components in a bicomponent fiber.
[0074] Reactive
fillers and other additives that can accelerate degradation may be placed
in the degradable polyesters to improve the degradation of the polyester, and
the
loading is up to 10% (FIG. 4C). However, placing reactive fillers in water
soluble
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polymers may provide a caustic aqueous environment that may facilitate rapid
degradation of the polyesters (FIG. 4D).
[0075] Another
approach is to construct multicomponent fibers in which the first polymer
component provides stiffness and strength, where the second polymer dissolves
in
hydrocarbons at low temperatures (Figure 5A-B). The first polymer in the
fibers will
partially degrade in water first during the stages of hydraulic fracturing,
and the
second polymer will dissolve in hydrocarbons during the production stage. The
first
degradable polymer could occupy the sheath, the sea or one side of a
bicomponent
fiber, and the hydrocarbon soluble polymer occupies the core, the island or
the other
side of a bicomponent fiber.
[0076] Polyolefins
(such as polyprolylene PP or polyethylene PE), ethylene vinyl acetate
(EVA), modified EVA and copolymers and blends thereof are good choices for the
hydrocarbon soluble polymers, and specific selection of the polymer depends on
the
application temperatures. For this purpose, the water degradable composite may
form
the sheath (core-sheath), sea (island-sea), minor side (side-by-side), and the
hydrocarbon soluble polymers form the core, island and the major side of the
multicomponent fibers.
[0077] The weight
ratio of water degradable composite and hydrocarbon soluble
polymers is in the range of 10:90 to 90:10 depending on the desired resulting
physical
properties (stiffness and tensile) of the fibers and the application
temperatures.
100781 Fillers
increase the porosity of the fibers, and can also facilitate faster
dissolution.
The loading of the fillers inside any of the fibers herein described also
depends on the
desired physical properties of the fibers (inorganic fillers reduce the
tensile strength of
the fibers). The process-ability of spinning composite fibers (fibers with
inorganic
fillers) also puts constraints on the loading of the fillers.
[0079] We expect to
use no more than 10% weight percent of fillers inside the fibers.
Some adhesion-promoting monomer or reactive functional polymers may be needed
for better compatibility between the polymer matrix and the inorganic fillers.
The
choice of adhesion-promoting monomers includes silane based adhesion promoters
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(Silquestk brand, for example), maleated or acid functionalized polymers
(DuPont
Fusabondk, and Optimk E-117), and alkyl phosphate esters (Zeleck brand, for
example). The choice of the adhesion promoters is determined by the choice of
the
fillers, and the loading of the adhesion promoters is the range of 0.5-5% of
the total
polymers.
[0080] In all the
above fiber designs, small amounts of other additives or polymers such
as compatibilizers, plasticizers, fire retardants, anti-microbials, pigments,
colorants,
lubricants, UV stabilizers, dispersants, nucleation agents, etc. that are
commonly used
in the plastic processing industry can be added to modify the fiber's
characteristics
and process capability. These additives include organic carboxylic acid,
carboxylic
acid ester, metal salts of organic carboxylic acid, multicarboxylic acid,
fatty acid
esters, metal salts of fatty acid, fatty acid esters, fatty acid ethers, fatty
acid amides,
sulfonamides, polysiloxanes, organophosphorous compound, Al(OH)3, quaternary
ammonium compounds, silver base inorganic agents, carbon black, metal oxide
pigments, dyes, silanes, titanate etc.
100811 Although the
degradation of the multicomponent fibers shown herein were
conducted in water or in buffer solutions, this application does not preclude
the use of
other external, pH adjusting additives in the solution to further accelerate
the rate of
degradation of multicomponent fibers. As an example, thus use of pH changers
to
initiate rapid degradation downhole may be used.
PLA/PLA SAMPLES
[0082] Table 4
shows the spinning conditions and Table 5 shows the composition and
tensile strength of the sheath-core bicomponent fibers that were actually
made. The
amorphous PLA 6060D occupied the sheath component that facilitated fast water
absorption and degradation, and the crystalline 6201D resin occupied the core
that
provided stiffness and strength.
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[0083] Table 4 The extruder zone temperatures for the bicomponent PLA
fibers
Zone Temperature ( C) inside extruder
Take
Total up Spinneret
Zone 1 Zone 2 Zone 3 Zone 4
throughput speed temperatur
__________________________________________________ (ghm) (m/m) e ( C
)
Bi-75S/25C, Bi- Sheath (6060D) 180 185 195 205
0.2315 960 250
50S/50C
Core (6201D) 205 220 232 245
Sheath (6060D) 180 185 195 205
Bi-505/50C-ZnO __________________________________ 0.2701 700 250
Core (6201D) 200 215 225 235
[0084] The samples
are named according to their type (e.g., Bi for bicomponent) and
sheath/core ratio (e.g., 50S/50C is 50% of each), and finally reactive filler
is indicated
at the end. Thus, Bi-75S/25C is 75% sheath surrounding a 25% core, and Bi-
50S/50C-ZnO is 50/50 sheath/core with ZnO added, in this case to the core.
[0085] The
crystallinity% of Bi-50S/50C was higher than that of Bi-75S/25C since the
percentage of the crystalline polymer in the core was higher. Consequently,
the Tg
and the tensile strength of the fibers with higher % crystallinity were also
higher. Bi-
50/50-ZnO has 4% of ZnO fillers in the core component only, and this fiber's
tensile
strength, Tg and crystallinity were lower than that of the ZnO-free Bi-
50S/50C. These
results indicate possible polymer degradation during the fiber spinning
process. FIG.
6 shows the photomicrographs of the bicomponent fibers.
Table 5. The characteristics of the bicomponent fibers
Fiber Tensile Elongation 7-9 %
crystallinity in
Sheath% Core% ZnO% in diameter strength at Break
( C) total fiber
ID (SIC ratio) (6060D) (6201D) Core (pm) (Mpa) (cy.)
Bi-75S/25C 75% 25% 0 18 1.3 261 32 61 14
62.11 11.83
Bi-50S/50C 50% 50% 0 16 1.0 313 17 75 8
63.47 21.60
Bi-50S/50C-ZnO 50% 50% 4% 25 3 169 45 87 58
59.31 18.81
[0086] The PLA
bicomponent fibers were cut to 6 mm long. A fixed amount of the fibers
was immersed in 100 ml of DI water. The bottles were kept at 60 C for 7, 14
and 21
days. After degradation, the residuals were filtered and washed with DI water
three
times before being dried at 49 C in an oven. The weight loss as a percentage
of the
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total original weight was calculated and used as the degree of degradation.
See FIG.
7 and 8.
[0087] As shown in
FIG. 7, Bi-75S/25C fiber with more amorphous PLA 6060D had
more weight loss% than the Bi-50S/50C fiber with less amorphous PLA. The
addition of 4% reactive filler, ZnO, in the core resulted in more weight loss%
for Bi-
50S/50C-ZnO compared to the similar fiber Bi-50S/50C at the same degradation
condition (FIG. 8).
[0088] We also
added a variety of additives to the water to determine their effects on
degradation. The PLA fibers were provided by NatureWorks. A fixed amount
(1.2_mg) of PLA fibers were dispersed in 100 ml of DI water. 50 mmol of water
insoluble additive was added to the mixture. The mixture was placed in the
oven at
66 C for 48h. After that time, the mixture was cooled down to room
temperature, the
residues were filtered off, washed with 6% HC1 and DI water, dried at 50 C,
and
weight determined. The results are shown in FIG. 9, where it can be seen that
all
additives increased the degree of degradation at 48 hours, especially the
combination
of ZnO and 4-dimethylaminopyridine. However, PLA containing both ZnO 4-
dimethylaminopyridine only showed slightly higher degradation compared with
PLA
containing only ZnO fillers. Although compared to ZnO, MgO is more effective
to
accelerate PLA degradation, the melt spinning of PLA fibers with MgO as a
filler
turned out be very challenge even at very low weight% of MgO (<1%). The
spinning
was interrupted frequently due to fiber breakage.
PLA/G-PVOH SAMPLES
[0089] Nichigo G-
polymerTM (referred to as G-PVOH in this patent), developed by
Nippon Gohsci, is a hydrolyzed copolymer of vinyl acetate and proprietary
comonomers. G-PVOH is an
amorphous polymer that combines ordinarily
conflicting traits of "low crystallinity" and "high hydrogen-bonding
strength," and
realizes functions of water solubility at room temperature, low melting
points, high
stretching characteristics, and a wide temperature gap between the melting
point
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(185 C) and the thermal decomposition temperature (> 220 C) which make it
possible to develop fibers and films using conventional melt extrusion
processes.
[0090] Nichigo G-polymerTM 8042P (MFI 28 0 min, Tm = 173 C, SAP value 88-
90%
mole%) or 8070P (MFI 17 g/10 mm, Tm = 170 C, SAP value 88-90% mole%) was
used to make the exemplary bicomponent PLA/G-PVOH fiber. NatureWorks
amorphous PLA 6060D resin was used to construct the sheath (< 30%), and 8042P
was used to construct the core (?70%) of the bicomponent fiber.
100911 The melt spinning of PLA/G-PVOH bicomponent fibers was conducted on
a Hills
Bicomponent Pilot Machine in the Fiber Science Lab of Nonwovens Institute. The
spinning conditions are outlined in Table 6:
[0092] Table 6: the spinning conditions of the PLA/G-PVOH bicomponent
fiber.
Zone Temperature ( C) inside extruder Total
Sheath/Core Spinning Speed
throughput
ratio Zone 1 Zone 2 Zone 3 Zone 4
temperature ( C) (m/m)
(ghm)
Sheath (6060D) 170 190 220 230
30%/70% 235 0.74 1000
Core (G-8042P) 170 185 210 230
[0093] The SEM image shows the as-spun PLA/G-PVOH fiber (FIG. 10A), and the
optical image of the cross-section of the fiber clearly indicates the big core
surrounded by a thin layer of sheath polymer (FIG. 10B). The average fiber
diameter
was 27 pm and the thickness of the sheath was 3 pm with the spinning speed set
at
1000 m/m.
[0094] The degradation of the PLA/G-PVOH bicomponent fiber was conducted in
water
at different pH (acid, DI water or base buffers) at 49 C and 60 C for 7, 14
and 21
days. The percentage of weight loss (weight loss%) was used to measure the
degradation.
[0095] FIG. 11 shows the weight loss% vs. degradation time and temperature
in various
pH aqueous solution. At both temperatures (49 C and 60 C), the PLA/G-PVOH
fibers
lost more than 70% weight after only 7 days in DI water or at different buffer
solutions (FIG. 11) and form hollow fibers with < 2 pm thin wall at 49 C (FIG.
12A)
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and the hollow fiber broke down at 60 C (FIG. 12B). The pH of the solutions,
in
contrast, had little effect on the rate of degradation. The weight loss% is
determined
by the weight% of water soluble component in the fibers.
EVA SAMPLE
[0096] One specific
example of a hydrocarbon soluble polymer is ethylene vinyl acetate.
Ethylene vinyl acetate (EVA) is the copolymer of ethylene and vinyl acetate.
Commercial grades of EVA resins have vinyl content ranging from 9 to 40% and a
melt flow index range from 0.3 to 500 dg/min. These specialty thermoplastic
polymers are inherently flexible, resilient, and tough, and can be processed
using
conventional thermoplastic or rubber handling equipment and techniques.
[0097] The melt
spinning process for fibers requires resin melt index in the range of 10 to
45 g/min (ASTM D1238, modified), and Melt Viscosity in the range of 10 to 20
(Pa
S) at 190 C temperature. The VA% (vinyl acetate content in the EVA copolymer)
impacts the flexibility and the toughness of the resin and the final products.
Higher
VA% results in more flexible and tougher products.
[0098] The
following EVA resins: DuPont Elvax 550 and Elvax 250, and Arkema
Evatanet 20-20, 33-15, 28-05 and 28-40, were chosen for the initial trial
based on
their % of vinyl acetate content and their melt index (ASTM D1238), though EVA
resins from other brands and suppliers should be equally useful.
[0099] Different
grades of EVA polymers may be blended to make homogeneous or
heterogeneous blend fibers for optimum process-ability and properties. The
choice of
the resins for EVA blends is determined by the melting point and the Ring and
Ball
Softening point of the resins. Blending of EVA resin with other resins for
better
physical properties of the resultant blend fibers is also under consideration.
Polymers
other than EVA may be blended with the EVA resin to improve the physical
properties of the fibers. The choice of polymers includes polyolefins and
polyolefin
oligomers (ethylene or propylene), wax, pitch and bitumen.
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[00100] The EVA resins also have good solubility in hydrocarbons at low
temperatures.
The solubility of the EVA resins was checked by the following experiment:
0.25g of
EVA resin completely dissolved in 8 ml of octane after 2-5 hours at 38 C. FIG.
13
shows the pictures of Evataneg 28-05 and Evatanet 28-40 resins dissolved in
octane
at 38 C. Although no actual multicomponent fibers are made yet, this result
indicates
that it is possible to make a fiber where one component is soluble in
petroleum.
[00101] The preceding description has been presented with reference to some
embodiments. Persons skilled in the art and technology to which this
disclosure
pertains will appreciate that alterations and changes in the described
structures and
methods of operation can be practiced without meaningfully departing from the
principle, and scope of this application. Accordingly, the foregoing
description
should not be read as pertaining only to the precise structures described and
shown in
the accompanying drawings, but rather should be read as consistent with and as
support for the following claims, which are to have their fullest and fairest
scope.
[00102] The statements made herein merely provide information related to the
present
disclosure and may not constitute prior art, and may describe some embodiments
illustrating the invention. In particular, the following references may
generally relate
to certain subject matters of the current application and are hereby
incorporated by
reference to the current application in their entireties for all purposes:
[00103] Zhang X. et al., 'Morphological behavior of poly(lactic acid) during
hydrolytic
degradation', Polymer Degradation and Stability 93 (2008) 1964-1970 and ref.
therein.
[00104] Tarantili P.
A., 'Swelling and hydrolytic degradation of poly(D, L-lactic acid) in
aqueous solution', Polymer Degradation and Stability 91 (2006) 614-619 and
ref.
therein.
1001051 Xanthos Q., `Nanoclay and crystallinity effects on the hydrolytic
degradation of
polylactides', Polymer Degradation and Stability 93 (2008) 1450-1459 and ref.
therein.
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[00106] Ratheesh et al., Materials Chemistry and Physics 122 (2010) 317-320
(coating on
MgO).
[00107] Meyer B. et
al., 'Partial dissociation of water leads to stable superstructures on the
surface of Zn0', Angew. Chem. Int. Ed. 2004, 43, 6642-6645.
1001081 Chrisholm et
al., 'Hydrolytic stability of sulfonated poly(butylenes terephthalate',
Polymer, 44 (2003) 1903-1910.
[00109] Guido
Grundmeier et al., 'Stabilization and acidic dissolution Mechanism of
Single-Crystalline Zn0(0001) surfaces in electrolytes studied by In-Situ AFM
Imaging and Ex-Situ LEED', Langmuir 2008, 24, 5350-5358.
1001101 Martin Muhler, et al., 'The identification of hydroxyl groups on ZnO
nanoparticles by Infrared spectroscopy', Phys. Chem. Chem. Phys., 2008, 10,
7092-
7097.
1001111 Arrigo Calzolari, et al., 'Water adsorption on Nonpolar Zn0(1010)
surface: A
microscopic understanding', J. Phys. Chem. C, 2009, 113, 2896-2902.
[00112] PCT/US11/49169, 'Mechanisms for treating subterranean formations with
embedded additives'.
[00113] U520120231690, U520120238173, U520060083917, U520100273685,
U55916678, US7858561, US7833950, U57786051, U57775278, US7748452,
U57703521, US7565929, U57380601, US7380600, U57275596.
21
