U.S. patent application number 14/369451 was filed with the patent office on 2014-12-25 for multicomponent degradable materials and use.
The applicant listed for this patent is SCHLUMBERGER TECHNOLOGY CORPORATION. Invention is credited to Miranda Amarante, Vadim Kamil'evich Khlestkin, Huilin Tu, S. Sherry Zhu.
Application Number | 20140374106 14/369451 |
Document ID | / |
Family ID | 48698559 |
Filed Date | 2014-12-25 |
United States Patent
Application |
20140374106 |
Kind Code |
A1 |
Zhu; S. Sherry ; et
al. |
December 25, 2014 |
MULTICOMPONENT DEGRADABLE MATERIALS AND USE
Abstract
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")
(.ltoreq.60.degree. C.) in subterranean formations.
Inventors: |
Zhu; S. Sherry; (Waban,
MA) ; Tu; Huilin; (Sugar Land, TX) ;
Khlestkin; Vadim Kamil'evich; (Novosibirsk, RU) ;
Amarante; Miranda; (Somerville, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SCHLUMBERGER TECHNOLOGY CORPORATION |
Sugar Land |
TX |
US |
|
|
Family ID: |
48698559 |
Appl. No.: |
14/369451 |
Filed: |
December 21, 2012 |
PCT Filed: |
December 21, 2012 |
PCT NO: |
PCT/US2012/071147 |
371 Date: |
June 27, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61631174 |
Dec 28, 2011 |
|
|
|
Current U.S.
Class: |
166/305.1 ;
428/366; 428/373; 428/374 |
Current CPC
Class: |
D01F 8/14 20130101; Y10T
428/2929 20150115; D01F 1/10 20130101; Y10T 428/2916 20150115; D10B
2401/12 20130101; E21B 43/16 20130101; D10B 2505/00 20130101; Y10T
428/2931 20150115; D01D 5/30 20130101 |
Class at
Publication: |
166/305.1 ;
428/373; 428/374; 428/366 |
International
Class: |
D01F 8/14 20060101
D01F008/14; E21B 43/16 20060101 E21B043/16; D01F 1/10 20060101
D01F001/10 |
Claims
1. 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, or a mixture thereof; b) a water
soluble polymer or a hydrocarbon soluble polymer; and c) a reactive
filler mixed with component a, that shortens the degradation time
of said component when mixed therewith; d) wherein component a is
different than component b; and e) said multicomponent fiber having
a diameter of less than 100 micrometers, having a configuration
selected from the group consisting of sheath-core,
islands-in-the-sea, ribbon, segmented pie, side-by-side, and
combinations thereof, and said fiber being degradable in 30 days or
less at 60.degree. C.
2. The fiber of claim 1, said reactive filler being selected from
the group consisting of Ca(OH).sub.2, Mg(OH).sub.2, CaCO.sub.3,
Borax, MgO, CaO, ZnO, NiO, CuO, and Al.sub.2O.sub.3.
3. A degradable multicomponent fiber, comprising: a) a degradable
polyester; b) a water soluble polymer or a hydrocarbon soluble
polymer; c) a reactive filler that shortens the degradation time of
component a, said reactive filler being selected from the group
consisting of Ca(OH).sub.2, Mg(OH).sub.2, CaCO.sub.3, Borax, MgO,
CaO, ZnO, NiO, CuO, 4-Dimethylaminopyridine (DMAP), and
Al.sub.2O.sub.3; d) wherein component a differs from component b,
and wherein components a and b are adjacent each other in said
fiber, and wherein said fiber degrades in .ltoreq.30 days at
60.degree. C. in water.
4. The fiber of claim 3, said degradable polyester selected from
the group consisting of polylactic acid (PLA), polycarprolactone,
polyglycolic acid (PGA), polylactic-co-polyglcolic acid (PLGA), and
a mixture thereof.
5. The fiber of claim 3, said hydrocarbon soluble polymer
comprising ethylene vinyl acetate, olefin, propylene, ethylene, or
combinations thereof.
6. The fiber of claim 3, said water soluble polymer comprising
polyvinyl alcohol, modified polyvinyl alcohol, or their
mixtures.
7. A multicomponent fiber comprising a first degradable polymer
adjacent a second hydrocarbon soluble polymer, wherein said fiber
degrades in water and petroleum.
8. The fiber of claim 7, said degradable polymer comprising a
polyester, polylactic acid (PLA), polycarprolactone, polyglycolic
acid (PGA), polylactic-co-polyglcolic acid (PLGA), or a mixture
thereof.
9. The fiber of claim 7, said degradable hydrocarbon soluble
polymer comprising ethylene vinyl acetate, olefin, propylene,
ethylene, or combinations thereof.
10. The fiber of claim 7, said further comprising a reactive filler
mixed with said polyester to accelerate its degradation rate, and
said reactive filler is Ca(OH).sub.2, Mg(OH).sub.2, CaCO.sub.3,
Borax, MgO, CaO, ZnO, NiO, CuO, Al.sub.2O.sub.3, DMAP, or mixtures
thereof.
11. The fiber of claim 7, said further comprising a ZnO mixed with
a PLA.
12. A multicomponent fiber comprising an amorphous PLA adjacent a
crystalline PLA and ZnO intimately admixed with either or both,
said fiber having a diameter of less than 100 .mu.m and being
degradable in water at 60.degree. C. in 30 days or less.
13. (canceled)
14. (canceled)
15. A method of producing hydrocarbon from a subterranean
reservoir, comprising: a) injected a fluid comprising water and a
fiber of claim 1 into a subterranean reservoir comprising a
hydrocarbon; and b) producing said hydrocarbon.
Description
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")
(.ltoreq.60.degree. 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 water degradable
components. Some of the multicomponent fibers described herein lost
more than 60% weight at temperatures below 60.degree. 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.degree. 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 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.ltoreq.60.degree. 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(.epsilon.-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 naphthalate) (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(.epsilon.-caprolactones), poly(glycolic acids) (PGA),
and poly(lactic-co-glycolic acids) (PLGA). Poly(lactic acids) can
be produced either by direct condensation of lactic 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 Natureworks. 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 (Zn.sup.2+, Mg.sup.2+, 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).sub.2, Mg(OH).sub.2, CaCO.sub.3, Borax, MgO, CaO, ZnO,
NiO, CuO, Al.sub.2O.sub.3, 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 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.degree. 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 thereofIGS. 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 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).
[0029] 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) are open-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.
[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.degree. 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:
TABLE-US-00001 ABBREVIATION TERM DI Deionized water DMAP
4-Dimethylaminopyridine G-PVOH Nichigo G-polymer .TM. 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.
[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-50S/50C--ZnO; B: Bi-75S/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.degree. 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.degree.
C. in water versus time in days.
[0050] FIG. 9. Influence of additives on the degradation rate of
PLA fibers at 60.degree. C. for 48 hours. The PLA fibers were
provided by NatureWorks.
[0051] 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.degree. C., Right T=60.degree. C.
[0053] FIG. 12A-B. SEM images of PLA/G-PVOH fibers after 7 days in
deionized (DI) water at 49.degree. C. (A) and 60.degree. C.
(B).
[0054] FIG. 13. Photograph of glass vials containing 0.25 g of
Evatane.RTM. 28-05 (left) and Evatane.RTM. 28-40 (right) in 8 ml of
octane. Both resins dissolved in octane at 38.degree. C. after 5
hours.
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.
[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 5 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.degree. C. is an amorphous polymer that degrades faster
than semi-crystalline PLA with the melting point at 160-170.degree.
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 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-US-00002 TABLE 1 Examples of polymers and fillers in degrable
core-sheath PLA fibers Melt Melt point (.degree. C.) point
(.degree. C.) Fiber Sheath Sheath ZnO in Core Core ZnO in ID
polymer polymer Sheath Polymer polymer Core 1 6060D 125-135 no
6201D 160-170 yes 2 6060D 125-135 yes 6201D 160-170 yes 3 6060D
125-135 yes 6201D 160-170 no 4 6201D 160-170 no 6060D 125-135 yes 5
6201D 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 (T.sub.g) in the range of 55-60.degree.
C.
TABLE-US-00003 TABLE 2 Examples of polymers and fillers in
degradable island-sea PLA fibers Sea Melting point Island ZnO
compo- (.degree. C.) Sea ZnO in compo- Melting point (.degree. C.)
in nent polymer Sea nent island polymer island 6060D 125-135 no
6201D 160-170 yes 6060D 125-135 yes 6201D 160-170 yes 6060D 125-135
yes 6201D 160-170 no 6201D 160-170 no 6060D 125-135 yes 6201D
160-170 yes 6060D 125-135 yes 6201D 160-170 yes 6060D 125-135
no
TABLE-US-00004 TABLE 3 Examples of polymers and fillers in
degradable side-by-side PLA fibers Major Melting ZnO in Minor
Melting ZnO in side point (.degree. C.) major side point (.degree.
C.) minor polymer major side side polymer minor side side 6060D
125-135 no 6201D 160-170 yes 6060D 125-135 yes 6201D 160-170 yes
6060D 125-135 yes 6201D 160-170 no 6201D 160-170 no 6060D 125-135
yes 6201D 160-170 yes 6060D 125-135 yes 6201D 160-170 yes 6060D
125-135 no
[0068] 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 (.ltoreq.2 nm) 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 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.degree. 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
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 (FIG. 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.
[0078] 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 (Silquest.RTM. brand, for example), maleated or acid
functionalized polymers (DuPont Fusabond.RTM., and Optim.RTM.
E-117), and alkyl phosphate esters (Zelec.RTM. 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).sub.3, quaternary ammonium
compounds, silver base inorganic agents, carbon black, metal oxide
pigments, dyes, silanes, titanate etc.
[0081] 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.
TABLE-US-00005 TABLE 4 The extruder zone temperatures for the
bicomponent PLA fibers Take Zone Temperature (.degree. C.) Total up
Spinneret inside extruder throughput speed temperature Zone 1 Zone
2 Zone 3 Zone 4 (ghm) (m/m) (C.) Bi--75S/25C, Bi--50S/ Sheath
(6060D) 180 185 195 205 0.2315 960 250 50C Core (6201D) 205 220 232
245 Bi--50S/50C--ZnO Sheath (6060D) 180 185 195 205 0.2701 700 250
Core (6201D) 200 215 225 235
[0083] 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.
[0084] 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 T.sub.g 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, T.sub.g 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-US-00006 TABLE 5 The characteristics of the bicomponent
fibers Fiber Tensile Elongation Sheath % Core % ZnO % in diameter
strength at Break T.sub.g % crystallinity in ID (S/C ratio) (6060D)
(6201D) Core (.mu.m) (Mpa) (%) (.degree. C.) total fiber 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
[0085] 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.degree. 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.degree. C. in an oven. The
weight loss as a percentage of the total original weight was
calculated and used as the degree of degradation. See FIGS. 7 and
8.
[0086] 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).
[0087] 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.degree. C. for 48 h. After that time, the mixture was
cooled down to room temperature, the residues were filtered off,
washed with 6% HCl and DI water, dried at 50.degree. 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
[0088] Nichigo G-Polymer.TM. (referred to as G-PVOH in this
patent), developed by Nippon Gohsei, 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 (185.degree. C.) and the thermal
decomposition temperature (>220.degree. C.) which make it
possible to develop fibers and films using conventional melt
extrusion processes.
[0089] Nichigo G-Polymer.TM. 8042 P (MFI 28 g/10 min,
Tm=173.degree. C., SAP value 88-90% mole %) or 8070P (MFI 17 g/10
min, Tm=170.degree. 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 (.ltoreq.30%), and
8042P was used to construct the core (.gtoreq.70%) of the
bicomponent fiber.
[0090] 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:
TABLE-US-00007 TABLE 6 the spinning conditions of the PLA/G-PVOH
bicomponent fiber. Zone Temperature (.degree. C.) Total Sheath/Core
inside extruder Spinning throughput Speed ratio Zone 1 Zone 2 Zone
3 Zone 4 temperature (.degree. C.) (ghm) (m/m) Sheath (6060D)
30%/70% 170 190 220 230 235 0.74 1000 Core (G-8042P) 170 185 210
230
[0091] 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 .mu.m and the
thickness of the sheath was 3 .mu.m with the spinning speed set at
1000 m/m.
[0092] The degradation of the PLA/G-PVOH bicomponent fiber was
conducted in water at different pH (acid, DI water or base buffers)
at 49.degree. C. and 60.degree. C. for 7, 14 and 21 days. The
percentage of weight loss (weight loss %) was used to measure the
degradation.
[0093] FIG. 11 shows the weight loss % vs. degradation time and
temperature in various pH aqueous solution. At both temperatures
(49.degree. C. and 60.degree. 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 .mu.m
thin wall at 49.degree. C. (FIG. 12A) and the hollow fiber broke
down at 60.degree. 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
[0094] 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.
[0095] 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.degree. 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.
[0096] The following EVA resins: DuPont Elvax.RTM. 550 and
Elvax.RTM. 250, and Arkema Evatane.RTM. 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.
[0097] 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.
[0098] The EVA resins also have good solubility in hydrocarbons at
low temperatures. The solubility of the EVA resins was checked by
the following experiment: 0.25 g of EVA resin completely dissolved
in 8 ml of octane after 2-5 hours at 38.degree. C. FIG. 13 shows
the pictures of Evatane.RTM. 28-05 and Evatane.RTM. 28-40 resins
dissolved in octane at 38.degree. 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.
[0099] 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.
[0100] 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: [0101] Zhang X. et al., `Morphological
behavior of poly(lactic acid) during hydrolytic degradation`,
Polymer Degradation and Stability 93 (2008) 1964-1970 and ref
therein. [0102] 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. [0103]
Xanthos Q., `Nanoclay and crystallinity effects on the hydrolytic
degradation of polylactides`, Polymer Degradation and Stability 93
(2008) 1450-1459 and ref therein. [0104] Ratheesh et al., Materials
Chemistry and Physics 122 (2010) 317-320 (coating on MgO). [0105]
Meyer B. et al., `Partial dissociation of water leads to stable
superstructures on the surface of ZnO`, Angew. Chem. Int. Ed. 2004,
43, 6642-6645. [0106] Chrisholm et al., `Hydrolytic stability of
sulfonated poly(butylenes terephthalate`, Polymer, 44 (2003)
1903-1910. [0107] Guido Grundmeier et al., `Stabilization and
acidic dissolution Mechanism of Single-Crystalline ZnO(0001)
surfaces in electrolytes studied by In-Situ AFM Imaging and Ex-Situ
LEED`, Langmuir 2008, 24, 5350-5358. [0108] Martin Muhler, et al.,
`The identification of hydroxyl groups on ZnO nanoparticles by
Infrared spectroscopy`, Phys. Chem. Chem. Phys., 2008, 10,
7092-7097. [0109] Arrigo Calzolari, et al., `Water adsorption on
Nonpolar ZnO(1010) surface: A microscopic understanding`, J. Phys.
Chem. C, 2009, 113, 2896-2902. [0110] PCT/US11/49169, `Mechanisms
for treating subterranean formations with embedded additives`.
[0111] US20120231690, US20120238173, US20060083917, US20100273685,
U.S. Pat. No. 5,916,678, U.S. Pat. No. 7,858,561, U.S. Pat. No.
7,833,950, U.S. Pat. No. 7,786,051, U.S. Pat. No. 7,775,278, U.S.
Pat. No. 7,748,452, U.S. Pat. No. 7,703,521, U.S. Pat. No.
7,565,929, U.S. Pat. No. 7,380,601, U.S. Pat. No. 7,380,600, U.S.
Pat. No. 7,275,596.
* * * * *