Note: Descriptions are shown in the official language in which they were submitted.
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FIBER ASSISTED RE-CROS SLINKABLE POLYMER GEL AND PREFORIVIED PARTICLE
GELS FOR FLUID LOSS AND CONFORMANCE CONTROL
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority benefit of United States
Patent Application No.
17/014,608, filed September 8, 2020.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present invention generally relates to the use of particle
gels to control fluid
channeling problems in a porous underground rock formations or reservoirs.
Description of the Prior Art
[0003] Voids, wormholes, fractures, fracture-like channels and other
abnormal openings often
exist naturally in porous underground rock formations or reservoirs or are
formed by injecting
fluid in reservoir flooding processes such as secondary and tertiary oil
recovery processes that are
used in the production of oil from hydrocarbon-containing reservoirs. The
resulting heterogeneity
in the permeability of fluids travelling through the reservoir can often cause
the injection fluids to
preferentially channel through the abnormal openings, resulting in an
inefficient and uneconomic
flooding process. In-situ gels and, more recently, preformed particle gels
(PPGs) have been used
to plug or significantly decrease the permeability of fractures or fracture-
like channels and thereby
result in a more efficient and economical flooding process. PPGs were designed
to overcome some
inherent drawbacks of the traditional in-situ gels, such as the change of
gelant composition during
injection, gelation uncertainty, and uncontrollability. Additionally, with a
larger particle size and
a higher gel strength (elastic modulus), the PPGs can be more precisely placed
into the fractures
with minimized damage to unswept hydrocarbon-rich formations.
[0004] A re-cross-linkable preformed particle gel (RPPG) has been
recently developed to
improve the performance of conventional PPGs by enabling the gel particles to
re-assemble as an
integral material after placement in the fractures. Studies showed that the re-
cross-linked RPPGs
have significant toughness and high elastic modulus that could more
effectively resist fluid flow
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in the large opening fractures, manifesting as a higher breakthrough pressure
and a higher
resistance to fluid after the breakthrough.
[0005] However, a need still exists for further improvements in the
properties and performance
of the current RPPGs First, the current RPPG products may be susceptible to
being broken through
by a fluid subsequently injected into the reservoir under sufficiently high
pressure. A desirable
solution to this problem would be to improve the elastic modulus of RPPGs to
resist these high
injection pressures. Second, when the fractures are vertical or have
abnormally high vertical
apertures, the RPPG particles may tend to preferentially precipitate into the
lower part of the
fractures or the bottom of large openings as a result of gravitational forces,
which leaves the upper
space open or less plugged due to a lower concentration or absence of particle
gels. A desirable
solution to this problem would be to improve the ability of the RPPG particles
to remain in
suspension in order to form a lattice structure within the fractures during
formation of the bulk gel.
SUMMARY OF THE INVENTION
[0006] In one embodiment, there is provided a composition useful for
controlling fluid flow.
The composition comprises a quantity of fibers and a quantity of swellable
particles comprising
cross-linkable polymer chains and/or an assembling agent.
[0007] In another embodiment, there is provided a method of forming a
gel formation in a target
zone of a subterranean environment. The method comprises introducing the above
composition
into the subterranean environment.
[0008] In another embodiment, there is provided a method of forming
the above composition.
The method comprises: (i) dispersing the quantity of fibers in a carrier fluid
and forming a
homogenous mixture; and (ii)dispersing the quantity of swellable particles in
the homogenous
mixture, thereby causing at least a portion of the quantity of swellable
particles to swell.
[0009] In another embodiment, there is provided a method of forming
the above composition.
The method comprises: (i) mixing the quantity of fibers and the quantity of
swellable particles to
form a homogenous mixture; and (ii) contacting the homogenous mixture with a
carrier fluid,
thereby causing at least a portion of the quantity of swellable particles to
swell.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Fig. 1 is a schematic drawing showing a fiber-reinforced
hydrogel in accordance with
one embodiment of the present invention;
[0011] Fig. 2 is a schematic diagram of a fracture model testing
apparatus;
[0012] Fig. 3 is a set of photographs showing particle gel placement
and movement over time
in a fracture model;
[0013] Fig. 4 is a graph showing rupture pressures and breakthrough
pressures of gel
compositions;
[0014] Fig. 5 is a set of photographs showing fluid movement through
the particle gels in the
fracture model;
[0015] Fig. 6 is a set of photographs showing particle gel
compositions with and without fiber;
[0016] Fig. 7 is a graph showing particle gel volume change over time
with and without fiber;
[0017] Fig. 8 is a graph showing particle gel volume change over time
at different fiber
concentrations;
[0018] Fig. 9 is a graph showing particle gel volume change over time
using different particles
sizes;
[0019] Fig. 10 is a graph showing particle gel volume change over
time using different fiber
lengths; and
[0020] Fig. 11 is a graph showing injection pressures using different
particle gel compositions.
DETAILED DESCRIPTION
[0021] In the embodiments described herein, fibers have been
successfully used to improve the
property and performance of PPG and RPPG (re-crosslinking and/or re-
associating) particle-
containing compositions. The compositions may include particle-containing gel
compositions that
comprise re-crosslinking, re-associating, and/or self-healing components. The
compositions
generally comprise a quantity of fibers and a quantity of swellable particles,
wherein the swellable
particles comprise cross-linkable polymer chains and/or assembling agents. In
certain
embodiments, the swellable particles may comprise polymer chains (or polymer
chain matrix)
having assembling agent(s) interspersed therein. Thus, the quantity of fibers
may be used with re-
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crosslinking particle gels and/or re-associating particles gels (i.e.,
particles that do not re-crosslink,
per se, but re-associate), such as those described herein or others known in
the art. In certain
embodiments, the particle gel compositions are selected such that the gels
reform bulk-like gel
structure and do not remain as discrete particles. The fiber may be added
during synthesis or during
swelling of the compositions. For example, in certain embodiments, a particle-
containing gel is
synthesized with the addition of fiber to provide improved plugging
efficiency, including higher
pressure resistance to fluids, as compared to conventional preformed particle
gel products. In
certain such embodiments, the fiber-embedded particle gels comprise a mixture
of any of a variety
of PPG and RPPG particles (i.e., with various monomers/polymers, cross-
linkers, initiators,
additives, etc.) and a quantity of fibers dispersed in a carrier fluid. In
certain other embodiments,
dry fibers are physically mixed with PPG or RPPG particles before addition of
a carrier fluid to
provide improved structural characteristics of the resulting PPG or RPPG
compositions upon
addition of a carrier fluid (e.g., an injection liquid) and swelling of the
particles.
[0022] As used herein, the term "fiber" refers to a natural or man-
made elongated thread-like
filament structure. In certain embodiments, the fiber comprises a natural
fiber material such as
vegetable fiber, wood fiber, animal fiber, mineral fiber, and/or biological
fiber. In additional or
alternative embodiments, the fiber comprises a man-made fiber material, such
as semi-synthetic
fiber (e.g., cellulose regenerated fibers) and synthetic fiber (e.g., metallic
fibers, carbon fibers,
silicon carbide fibers, fiberglass, mineral fibers, polymer fibers). In some
embodiments, the fiber
comprises a synthetic fiber material selected from the group consisting of
polyethylene,
polypropylene, nylons (aliphatic or semi-aromatic polyamides), and polyvinyl
alcohol. However,
it should be appreciated that any of a variety of fiber materials may be used
in accordance with
embodiments of the invention so long as the length and diameter of the fibers
allow for ready
dispersion (i.e., in the gel compositions) and/or mixing into the liquid
carrier (e.g., water) with dry
PPG or RPPG particles to form a pump-able mixture/dispersion.
[0023] In some embodiments, the fibers have an average length of
about 0.1 mm to about 100
mm, from about 0.5 mm to about 50 mm, or from about 1 mm to about 25 mm. In
certain
embodiments, the fibers have an average diameter of about 0.1m to about 1,000
pm, from about
0.5 pm to about 500 pm, or from about 1 p.m to about 100 p.m. Generally, the
fibers will have an
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aspect ratio (defined as the ratio of fiber length to diameter) of about 10 to
about 1000. In some
embodiments, the fibers comprise "short fibers" (i.e., discontinuous fibers)
generally having an
aspect ratio (defined as the ratio of fiber length to diameter) of about 10 to
about 80 or about 20 to
about 60. In other embodiments, the fibers comprise "long fibers" (i.e.,
continuous fibers)
generally having an aspect ratio of about 100 to about 1000 or about 200 to
about 500.
[0024] The swellable particles used in accordance with embodiments of
the present invention
may comprise any of a variety of PPG or RPPG receipts (including various
monomers/polymers,
cross-linkers, assembling agents, initiators, and additives). Exemplary PPG
and RPPG particle
compositions that may be used in embodiments of the present invention include
those described
in WO 2017/210486 and WO 2020/046939, each of which is incorporated herein in
its entirety.
The fiber-containing compositions in accordance with embodiments of the
present invention
generally comprise mixtures and dispersions comprising a quantity of swellable
PPG and/or RPPG
particles. The particles generally comprise polymers, crosslinkers, assembling
agents, reagents,
and/or optional additives, as described below.
[0025] In certain embodiments, the particles comprise polymerizable
monomers and/or pre-
made polymers, an assembling agent and/or a cross-linking agent, and optional
other ingredients.
In certain other embodiments, the particles are formed by polymerizing
monomers and cross-
linking agents to form a polymer matrix, drying the polymer matrix, and
grinding the dry polymer
matrix to form the swellable particles.
[0026] In other embodiments, the particles comprise a polymer formed
from one or more
starting monomers selected from the group consisting of acrylamides,
sugars/saccharides,
chloroprene, nitrile-containing compounds, sulfonates, acrylates,
methacrylate, silicates, nano-
clays and combinations of the foregoing.
[0027] In further embodiments, the particles comprise a polymer
comprising a "re-cross-
linking moiety" formulated and established by water-soluble monomers, which
can be initiated by
a free radical, cross-linkable at subterranean conditions, therein forming
covalent, ionic, or
coordination bonding. In certain embodiments, the monomer comprising a re-
cross-linking moiety
is a monomer possessing an anionic charge at neutral pH (7.0). Representative
anionic monomers
may include sodium, potassium, and ammonium salts of acrylic acid, methacrylic
acid, maleic
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acid, itaconic acid, 2-propenoic acid, 2-methyl-2-propenoic acid, other water-
soluble carboxylic
acids, or combinations thereof. In some embodiments, the monomer comprising a
re-cross-linking
moiety comprises a water-soluble carboxylic acid. In other embodiments, the
monomer comprising
a re-cross-linking moiety can be nonionic, and possess no charge at a pH
ranging from about 4 to
about 10. Representative nonionic monomers can include, for example, N-
isopropylacrylamide,
N,N-diethylacrylami de, dimethylaminopropyl acryl amide, dimethylaminopropyl
methacrylamide,
acryloyl morpholine, hydroxyethyl acrylate, hydroxypropyl acrylate,
hydroxyethyl methacrylate,
hydroxypropyl methacrylate, dimethylaminoethylacrylate, dimethylaminoethyl
methacrylate,
maleic anhydride, N-vinyl pyrrolidone, vinyl acetate, N-vinyl formamide, or
combinations thereof.
In certain embodiments, the monomers comprising a re-cross-linking moiety can
be a combination
of anionic and nonionic monomers. In one or more embodiments, the preferred
monomer for a re-
association of free gel particles moiety is an acrylamide or a derivative
thereof. In certain
embodiments, the monomers comprising a re-cross-linking moiety can comprise
sodium salts of
acrylic acid, potassium salts of acrylic acid, ammonium salts of acrylic acid,
methacrylic acid,
maleic acid, itaconic acid, 2-propenoic acid, 2-methyl-2-propenoic acid, or
combinations thereof
[0028] In certain embodiments, the particles comprise a polymer
formed from monomers
comprising an "acid-resistance moiety," which exhibits insensitivities to a pH
environment,
particularly aqueous acidic conditions. In some embodiments, a monomer
comprising an acid-
resistance moiety comprises a sulfonate (i.e., 2-acrylamido-2-methyl-1-
propanesulfonic acid
sodium salt (AMPS)), sulfate, or phosphate monomers, which contain bulky
groups, thereby
facilitating chain spacing with steric hindrance. Moreover, these monomers may
possess a low
value of pKa, such as the sulfonate group that has a pKa value of 2.3. The
representative monomers
comprising an acid-resistant moiety may include a sulfonate, sulfate, or
phosphate group; sodium
or potassium vinylsulfonate and vinyl sulfate salts like sodium or potassium
vinyl sulfates; phenyl
vinyl sulfonate salts like sodium or potassium phenyl vinyl sulfate; and/or
vinyl phosphate salts
like sodium or potassium vinyl sulfate. In some embodiments, the monomer
comprising an acid-
resistance moiety comprises a monomer exhibiting a pka of less than 4, 3.5, 3,
2.9, 2.8, 2.7, 2.6,
2.5, or 2.4. In certain embodiments, the monomer comprising an acid-resistance
moiety may
comprise a water-soluble monomer that contains cationic pendant groups, such
as
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diallyldimethylammonium chloride, (3 -(methacryloylamino) propyl) trimethyl
ammonium
chloride, (2-(methacryloyloxy) ethyl) trimethyl ammonium chloride, vinylbenzyl
trimethyl
ammonium chloride, or combinations thereof. Additionally or alternatively, in
various
embodiments, the monomers with cationic pendant groups may include
dimethylaminoethylacrylate methyl chloride quaternary salt,
dimethylaminoethylacrylate benzyl
chloride quaternary salt, dimethylaminoethylmethacrylate methyl chloride
quaternary salt, or
combinations thereof. In one or more embodiments, the monomer with an acid-
resistance moiety
may comprise 2-Acrylamido-2-methyl-1-propanesulfonic acid sodium salt (Na-
AMPS).
[0029] In certain embodiments, the particles comprise a polymer
formed from a monomer
comprising a "CO2-philic moiety," which comprises "CO2 philes." As used
herein, the term "CO2
phile" refers to a molecular entity that is attracted to CO2 molecules and has
strong interactions
with CO2 that are more thermodynamically favorable than the interactions with
polar solvents.
[0030] In some embodiments, the CO2-philic monomers may comprise
vinyl benzoate, benzyl
vinyl formate, ethyl vinyl ether, methyl vinyl ether, vinylidene fluoride,
lactic acid or lactic acid
cyclic dimmer, glycolic acid or glycolide, hexamethylcyclotrisiloxane,
1II,1II,2II,2II-
perfluorooctyl methacrylate, or combinations thereof In one or more
embodiments, the preferred
CO2-philic monomer is vinyl acetate. Studies have shown that poly(vinyl
acetate) (PVAc) has
reasonable solubility in CO2 because of its amorphous structure, low melting
point, and weak
Lewis acid base interactions between the acetate group and CO2. In certain
embodiments, the
monomer comprising the CO2-philic segment is synthesized by free-radical
polymerization in
aqueous solutions. In such embodiments, the CO2-philic monomers (e.g., vinyl
acetate) may be
water-soluble and may co-polymerize with the re-cross-linkable monomers and
acid-resistant
monomers. In various embodiments, the synthesis method of the CO2-philic
monomers is not
limited and other polymerization routines such as ionic, ring-opening, or
condensation
polymerization can also be deployed. In some embodiments, the polymerization
of the CO2-philic
monomers takes place within a different non-polar solvent, therein forming the
configuration of a
semi-inter penetrating network. In some embodiments, the CO2-philes might be
introduced by
dispersion and may be incorporated in the form of a polymer, such as polyvinyl
acetate.
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[0031]
However, in certain embodiments, the polymer does not include, and is
substantially
free of, CO2-philic moieties (CO2-philic moieties refer to molecular entities
in the polymer that is
attracted to CO2 molecules and has strong interactions with CO2 that are more
thermodynamically
favorable than the interactions with polar solvents). Specifically, in certain
embodiments, the
polymer matrix is substantially free of CO2-philic monomers such as vinyl
benzoate, benzyl vinyl
formate, ethyl vinyl ether, methyl vinyl ether, vinylidene fluoride, lactic
acid or lactic acid cyclic
dimmer, glycolic acid or glycolide, hexamethylcyclotrisiloxane, 1H,1H,2H,2H-
perfluorooctyl
methacrylate, and vinyl acetate.
[0032]
The monomers can be selected to create a homopolymer(s), a
copolymer(s), and both a
homopolymer(s) and a copolymer(s). Polymerizing can be carried out using
conventional
polymerization techniques, including those selected from the group consisting
of solution
polymerization, emulsion polymerization (including inverse emulsion
polymerization), and
suspension polymerization. It will be appreciated that this polymerization
allows one to custom
synthesize the polymer (including making desired chemical modifications). In
an alternative
embodiment, the polymer can be a commercial product or "off-the-shelf' polymer
as well, with
the assembling agent being incorporated into the polymer chain network.
[0033]
In certain embodiments, the polymer chains (backbone) of the polymer
matrix comprise
a homopolymer, which is formed from a single type of monomer. In some
embodiments, the
monomer is an amide monomer (i.e., a monomer comprising an amide functional
group). In certain
embodiments, the amide monomer is selected from the group consisting of
acrylamide,
methacrylamide, N-methylacrylamide, N-tert-butylacrylamide, N-ethylacrylamide,
N-
hydroxyethyl acrylamide, N-isopropylacrylamide, N, N-diethylacrylamide,
dimethylaminopropyl
acrylami de, dimethylaminopropyl methacrylamide, acrylamide, N-
isopropylacrylamide, N,N-
dimethyl acryl amide, N,N-di ethyl acryl ami de,
dimethylaminopropyl acrylamide,
dimethylaminopropyl methacrylamide, N-vinyl formamide. Particularly preferred
nonionic amide
monomers include acrylamide, N-methylacrylamide, N,N-dimethylacrylamide, and
methacrylamide. Advantageously, amide monomers in the polymer matrix can react
with the re-
cross-linking agent through transamidation as shown in the reaction scheme
below.
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0
\C-NH2
0 0
0 H2N 'µNH2 \c8 2NH3t
\C¨NH2
[0034] In other embodiments, the polymer chains (backbone) of the
polymer matrix comprise
a copolymer, which is formed from two or more types of monomers. In certain
such embodiments,
at least one of the two or more types of monomers comprises a monomer that can
react with the
re-cross-linking agent, such as under appropriate stimulus (e.g., high
temperature) at subterranean
conditions In some embodiments, the at least one monomer comprises a
sulfonate, sulfate, or
phosphate monomer. In other embodiments, the monomer comprises sulfonate,
sulfate, or
phosphate group(s); sodium or potassium vinylsulfonate and vinyl sulfate salts
like sodium or
potassium vinyl sulfates; phenyl vinyl sulfonate salts like sodium or
potassium phenyl vinyl
sulfate; and/or vinyl phosphate salts like sodium or potassium vinyl sulfate.
In particularly
preferred embodiments, the monomer is 2-acrylamido-2-methyl-1-propanesulfonic
acid sodium
salt (Na-AMPS).
[0035] In some embodiments, the at least one of the two or more
monomers comprises a water-
soluble monomer that contains cationic pendant groups, such as
diallyldimethylammonium
chloride, (3-(m ethacryl oyl ami no) propyl) trimethyl ammonium chloride, (2-
(m ethacryl oyl oxy)
ethyl) trimethyl ammonium chloride, and/or vinylbenzyl trimethyl ammonium
chloride. In other
embodiments, the alternative monomers with cationic pendant groups include
di methyl amin oethyl acryl ate methyl chloride quaternary salt, di m ethyl
aminoethyl acryl ate b enzyl
chloride quaternary salt, and/or dimethylaminoethylmethacrylate methyl
chloride quaternary salt.
[0036] In other embodiments, the at least one of the two or more
monomers comprises a
nonionic monomer. Representative nonionic monomers include hydroxy ethyl
acrylate,
hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate,
dimethylaminoethylacrylate (DMAEA), and dimethylaminoethyl methacrylate
(DMAEM).
Generally, C8-C22 backbones can be employed. Exemplary hydrophobic monomers
include the
higher alkyl esters such as octyl, decyl, dodecyl, tridecyl, tetradecyl,
octadecyl, etc. of ct,f3-
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ethylenically unsaturated carboxylic acids, such as acrylates and
methacrylates. Also included are
alkyl esters having 8 to 22 carbon atoms with ethylenically unsaturated
carboxylic acids such as
maleic anhydride, fumaric acid, itaconic acid and aconitic acid, alkylaryl
esters of ethylenically
unsaturated carboxylic acids such as nonyl -o-phenyl acrylate, nonyl-a-phenyl
methacrylate,
dodecyl-a-phenyl acrylate and dodecyl-a-phenyl methacrylate; N-alkyl,
ethylenically unsaturated
amides such as N-octadecyl acrylamide, N-octadecyl methacrylamide, N,N-dioctyl
acrylamide
and similar derivatives thereof; a-olefins such as 1-octene, 1-decene, 1-
dodecene and 1-
hexadecene; vinyl alkylates wherein alkyl has at least 8 carbons such as vinyl
laurate and vinyl
stearate; vinyl alkyl ethers such as dodecyl vinyl ether and hexadecyl vinyl
ether; N-vinyl amides
such as N-Vinylpyrrolidone, N-vinyl lauramide and N-vinyl stearamide; and
alkyl aromatics such
as t-butyl styrene or t-butyl phenyl.
[0037] The particles may also comprise one or more assembling
agent(s) and/or cross-linking
agent(s). 'The assembling agent(s) or cross-linking agent(s) may be selected
based on the particular
application for the particle gel composition. For example, one or more
assembling agents may be
used when a re-associating particle gel composition is desired. When present,
the assembling agent
acts as an additive (i.e., a separate chemical entity) that aids the polymer
gel mechanical response
to provide an auto-adherent, self-healing property in the polymer gel. In
certain embodiments, the
assembling agent is selected to be one that associates with the final polymer
in situ, thus producing
a gel. Additionally, the type of assembling agent can be used to control the
re-assembly time. It is
preferred that the assembling agent does not react with the above monomers
during the
manufacture of the particles. Preferably, assembling agents have positively
and/or negatively
charged groups and can be either single component or multiple components. The
most preferred
assembling agents are selected from the group consisting of polyacrylamide,
one of the multivalent
Group III-VII transition metal molecules, methylene bisacrylamide,
polyethylene glycol,
dimethacrylate, phenol-formaldehyde, diallylamine, triallyl amine, divinyl
sulfonate, diethylene
glycol diallyl aldehydes, diethyeneglycol diallyl ether, polyethyleneimine,
dichlorophenol,
benzoyl peroxide, di-tert-butyl peroxide, dibutyl hydrogen phosphite (DBHP),
C8-C22 alkanes, and
mixtures thereof. Particularly preferred assembling agents are selected from
the group consisting
of Cr, Zr, Co, and Al molecules or ions, organic compounds such as those
selected from the group
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consisting of methylene bisacrylamide, polyethylene glycol, dimethacrylate,
phenol-
formaldehyde, diallylamine, triallylamine, divinyl sulfonate, diethylene
glycol diallyl aldehydes,
diethylene glycol diallyl ether, polyethyleneimine, and combinations of the
foregoing. The
foregoing agents can be provided directly, or a source of that particular
assembling agent can be
provided. Examples of preferred sources of assembling agents include those
selected from the
group consisting of zirconium-acetate, chromium-acetate, aluminum acetate,
aluminum citrate,
cobalt acetate, zirconyl chloride, and mixtures of the foregoing.
[0038] In certain embodiments, crosslinking agent(s) may be used when
a cross-linkable or re-
cross-linkable particle gel composition is desired. As examples, the cross-
linking agent(s) may
comprise any reagent(s) that can connect the polymer chains via cross-
linkings, which take place
simultaneously with the formation of polymer chains. In various embodiments,
the cross-linking
agent is a divinyl monomer that can copolymerize with vinyl monomers and form
cross-linking
points during the propagation of polymers. As described in this section, the
cross-linking denotes
a chemical cross-linking, namely permanent, covalent bonding. Representative
cross-linkers may
include, for example, methylene bisacrylamide, diallylamine, triallylamine,
divinyl sulfone,
diethyleneglycol diallyl ether, or combinations thereof. In one or more
embodiments, the preferred
cross-linker is methylene bisacrylamide (MBA). In certain embodiments, the
cross-linking agent
comprises diacrylyl tertiary amide, diacrylylpiperazine, diallyltartardiamide,
dihydroxyethylene-
bi s-acrylamide, and bis-acrylylcystamine, trimethylolpropane trimethacrylate,
propyleneglycol
tri acryl ate, tri propyl enegly col di acryl ate, ally] m ethacryl ate, tri
ethyl en eglycol dim ethacryl ate,
tetrahydrofurfuryl methacrylate, trimethylolpropane triacrylate, or
combionations thereof. In one
or more embodiments, the cross-linking agent may comprise a multifunctional
cross-linker such
as pentaerythritol triacrylate, 1,5 pentane diol dimethacrylate,
pentaerythritol triallylether, or
combinations thereof.
[0039] In certain embodiments, the cross-linking agent may comprise
any reagent(s) that can
react with the "re-cross-linking moiety," therein generating self-healing and
discrete particle
reassociations, to thus produce a bulk gel at subterranean conditions
comprised of discrete polymer
gel particles that associate to form a gel possessing bulk gel properties.
More particularly, such
cross-linking agents are able to react with the side groups of the -re-cross-
linking moiety" and
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thereby form coordination bonding, covalent bonding, ionic bonding, and/or
physical tackifying.
In other words, the polymer matrix may comprise a plurality of cross-linkable
polymer chains and
at least a portion of the cross-linking agent(s) may be interspersed among the
cross-linkable
polymer chains. Consequently, the cross-linking agent may be capable of
associating with the
polymer chains upon exposure to a fluid capable of swelling the polymer
matrix. Such cross-
linking agents can be either a single component or multiple components, which
comprise multiple
cross-linkers together as a combination. In certain embodiments, the cross-
linking agent comprises
a chelate comprising a multivalent metal ion (e.g., Al3+, Fe3+, Cr3+, Ti4+,
Sn4 , or Zr4 ) and a ligand
such as acetates, tartrates, malonates, propionates, benzoates, and/or
citrates. The ligands may be
organic ions complexed with a multivalent metal ion via coordination bonding,
which can affect
the kinetic rate of re-cross-linking. These cross-linkers can react with
carboxyl groups or other
reactive groups that are pendant on the "re-cross-linking moiety," and thereby
a bulk gel will be
obtained in-situ. Representative cross-linking compounds can include, for
example, Cr(III)-
acetate, Cr(III)-propionate, Zr(IV)-acetate, Zr(IV)-lactate, or combinations
thereof In one or more
embodiments, the preferred cross-linking agent is Zr(IV)-acetate. In certain
embodiments, the
cross-linking agent is polymeric component such as polyethyleneimine, poly-L-
lysine, poly-c-
lysine, polyallylamine, polyvinylamine, or combinations thereof. These cross-
linkers can connect
neighbored amide groups via transamidation.
[0040] In some embodiments, the cross-linking agent may comprise a
"re-cross-linking agent,"
which refers to any latent reagent(s) that can react with the polymer matrix,
thereby generating
self-healing and discrete particle reassociations, to thus produce a bulk gel
at subterranean
conditions comprised of discrete polymer gel particles that associate to form
an entirety possessing
bulk gel properties. The re-cross-linking agent is generally embedded within
the polymer matrix
RPPG is synthesized. At higher temperature subterranean conditions, the re-
cross-linking agent is
able to react with the sidegroups of the polymer matrix, which forms covalent
bonding. In some
embodiments, the re-cross-linking agent can react with the carboxylate group
or amide group
among the matrix wherein the cross-linking take place through transamidation.
[0041] The re-cross-linking agent can be either a single component or
multiple components,
which comprise multiple cross-linkers together as a combination. The re-cross-
linking agent may
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be an oligosaccharide or polysaccharide rich in amino groups, wherein the
amino groups are at
least 75, 80, 85, 90, or 95 percent primary amines. The oligosaccharides and
polysaccharides can
be either natural raw materials or functionalized amino derivatives.
[0042] In some embodiments, the re-cross-linking agent is an aminated
alginate, that is alginic
acid functionalized with primary amine. In certain such embodiments, the
alginates are unbranched
polysaccharides comprising (or consisting of) 13-D-mannuronate (M) and a-L-
guluronate (G). In
particular embodiments, the alginates comprise sequences of M (M-blocks), G (G-
blocks), and
residues interspersed with MG sequences (MG-blocks). The alginates can be
obtained from both
algal and/or bacterial sources. Preferably, the aminated alginate is obtained
via the grafting or
Hofmann reactions. However, in alternative embodiments, an alternative pathway
to produce the
animated alignate can involve reductive amination.
[0043] In certain embodiments, the re-cross-linking agent is chitosan
or modified chitosan
functionalized with primary amine. Chitosan is a linear polymer occurring
naturally only in certain
fungi Mucoraceae and is chemically comprised of glucosamine and N-
acetylglucosamine
monomers linked through r3- (1 4) glycosidic linkages. One exemplary chitosan
modification can
be achieved via the sequential phthaloylation, nucleophilic substitution
reaction, and
dephthaloylation.
[0044] In some embodiments, the re-cross-linking agent is a dextran
amine, which is the
dextran functionalized with primary amine. Dextran is a complex branched
glucan, namely the
branched poly a-d glucosides of microbial origin having predominantly
glycosidic bonds. The
polymer main chain consists of a-1,6 glycosidic linkages between glucose
monomers, with
branches from a-1,3 linkages. This characteristic branching distinguishes a
dextran from a dextrin,
which is a straight chain glucose polymer-tethered by a-1,4 or a-1,6 linkages.
In certain
embodiments, the aminated dextran is obtained via the reductive amination
involved oxidization
and imine reduction. Alternatively, the aminated dextran is obtained by
deploying non-reductive
amination.
[0045] In certain embodiments, the re-cross-linking agent can be
aminated cellulose, that is
cellulose functionalized with primary amine. Cellulose is a polysaccharide
consisting of a linear
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chain of several hundred to many thousands of 13 (1¨>4) D-glucose units.
Preferably, the aminated
cellulose is obtained through a Staudinger reaction or reductive amination.
[0046] In other embodiments, the re-cross-linking agent is aminated
guaran, that is
functionalized with primary amine. Guaran, also known as guar gum, is a gal
actomannan
polysaccharide extracted from guar beans, which is an exo-polysaccharide
composed of the sugars
galactose and mannose. The backbone is a linear chain of 13 (1¨>4) linked
mannose residues to
which galactose residues are (1¨>6) linked at every second mannose, forming
short side-branches.
Preferably, the aminated guar gum is obtained via carboxymethylation and
coupling or amination
in basic condition with the presence of aminating agent.
[0047] In further embodiments, the re-cross-linking agent is an
aminated heparin, that is the
heparin functionalized with primary amine.
[0048] In certain embodiments, the re-cross-linking agent is a
complex form of amino
saccharide and a multivalent metal ion. rt he multivalent metal ion can be
salts of, but not limited
to, Al3+, Fe3+, Cr3+, TO+, Sn4+, or Zr4+. The ligands can be natural raw
materials or the
functionalized amino-saccharide. The ligands herein can be the oligosaccharide
or polysaccharide
that is rich in amino groups, particularly where the amino groups are
predominantly primary
amines. The ligands complexed with multivalent metal ion via coordination
bonding affect the
kinetic rate of re-cross-linking. Exemplary ligands include chitosan, aminated
chitosan, aminated
alginate, aminated dextran, aminated cellulose, aminated heparin, and aminated
guaran.
[0049] In some embodiments, the concentration of assembling agent(s)
and cross-linking
agent(s) in the particles can be used to control the gelation properties in
the final product
composition. That is, the assembling agent and/or cross-linking agent
concentration can be used
to control the re-assembled gel strength (for robust gels) or viscosities (for
weak gels). This
typically results in a preferred weight ratio of monomers to assembling/cross-
linking agent is from
about 2:1 to about 200:1, more preferably from about 5:1 to about 50:1, and
even more preferably
from about 5:1 to about 15:1. Such a ratio will typically result in monomers
present at levels of
from about 15 to about 50% by weight, preferably from about 23 to about 50% by
weight, and
more preferably from about 23 to about 30% by weight, based upon the weight of
total solids
utilized taken as 100% by weight. Furthermore, this will typically result in
the total
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assembling/cross-linking agent being present at levels of from about 0.5 to
about 6% by weight,
preferably from about 1.25 to about 6% by weight, and more preferably from
about 3.5 to about
6% by weight, based upon the weight of all ingredients utilized taken as 100%
by weight.
[0050] In certain embodiments, a polymerization initiator will also
be present during the
particle synthesis process. The initiator will be selected based on the
monomers being utilized and
the polymerization process selected, but typical initiators include those
selected from the group
consisting of persulfates (e.g., ammonium persulfate, potassium persulfate),
N,N,N',N'-
tetramethylethylenediamine, acyl peroxide, hydrogen peroxide, dialkyl
peroxides, ester peroxide,
ketone peroxide, azo compounds, and mixtures of thereof. Furthermore, the
amount of initiator
utilized will typically be from about 0.01 to about 0.2% by weight, preferably
from about 0.02 to
about 0.1% by weight, and more preferably from about 0.02 to about 0.05% by
weight, based upon
the weight of the monomers utilized taken as 100% by weight.
[0051] A polymerization accelerator can optionally be present during
the particle synthesis
process. Typical accelerators include those selected from the group consisting
of sodium
thiosulfate (STS), sodium bisulfite (SBS), sodium metabisulfite (SMS),
thiomalic acid,
nitrilotriacetic acid, glycerol, ascorbic acid, and mixtures thereof.
Furthermore, the amount of
accelerator utilized will typically be from about 0.01 to about 0.2% by
weight, preferably from
about 0.02 to about 0.1% by weight, and more preferably from about 0.02 to
about 0.05% by
weight, based upon the weight of all ingredients utilized taken as 100% by
weight.
[0052] The particles may also include one or more additives, which
can be mixed into the
system before the synthesis stage or subsequently added to the particles. In
certain embodiments,
the additives are ones that coordinate/associate with the formed polymer
(e.g., to form hydrogen
bond/ Van der Waals associations). Other additives can interpenetrate the
polymer chains, while
others can simply be mixed into the system without reaction with other
components. For instance,
the particles can be pre-treated by surfactant or a surface coating material
before mixing into
reservoir fluid.
[0053] Exemplary optional ingredients or additives include
tackifiers, plasticizers, polymers,
aromatic compounds, polysaccharides, deoxidants, adjustors of gelant (e.g.,
NH4C1, NaOH,
carbamide), clays (e.g., montmorillonite, bentonite), nanoclay, initiators,
stabilizers (e.g.,
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tetramethylethylenediamine, resorcinol, organic complexing agents, aN3),
celluloses, epoxy
resins, silica, silicon oxide, aluminum oxide, carbon nanotubes, graphene,
ethylenediaminetetraacetic acid (EDTA), and mixtures thereof. Other optional
additives include
nanoparticles (e.g., hydrophilic silica nanoparticles), oxygen scavengers
(i.e., reducing agents
which can remove the dissolved oxygen from an aqueous solution through a
gradual process of a
redox reaction), chelating agents, thickening agents, nano- or micro-fibers
(similar to or different
than those used in the dispersions described herein) and biocides.
[0054] In one or more embodiments, the particles may be prepared by
polymerizing the
monomers described herein in the presence of one or more assembling agents,
cross-linking agents,
fibers, and/or optional additives. The polymerization occurs in a solvent
system, preferably an
aqueous solvent system. In certain embodiments, the solvent system comprises
an aqueous solvent
selected from the group consisting of water and brine/saline solutions (e.g.,
NaCl, CaCl2, A1C13),
although other solvents can also be used. Regardless, the solvent system will
typically be present
at levels of from about 50 to about 70% by weight, preferably from about 65 to
about 70% by
weight, and more preferably from about 66.7 to about 70% by weight, based upon
the total weight
of all ingredients utilized taken as 100% by weight. Of course, the solids
levels would be the
balance of the foregoing percentages. During the polymerization process, the
monomers
polymerize to form a plurality of cross-linkable polymer chains and/or polymer
chains having
interspersed assembling agent(s). The resulting polymers can be one or more
homopolymer, one
or more copolymer, or a mix of homopolymers and copolymers.
[0055] Typical polymers for use in the invention include those
selected from the group
consisting of polymers or copolymers of hydrolyzed polyacrylamide,
polyacrylamide, chloroprene
rubber, nitrile rubber, hydrophilic resin sulfonate, xanthan, guar, acrylates
or methacrylates (e.g.,
lauryl methacrylate, stearyl methacrylate) silicates, acrylamides (e.g., N, N-
dimethylacrylamide),
and combinations of the foregoing.
[0056] During polymerization, the assembling agent(s), if present,
release free radicals after
being dissolved in the solvent, thus causing them to associate with the
polymer chains as they are
formed. The assembling agent and any other ingredients end up being
substantially uniformly
distributed within the entangled (but not cross-linked) polymer chain network.
Thus, all the
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compositions will be proportionally released at the same time in the reservoir
conditions (e.g.,
reservoir temperature, formation liquid pH or salinity, formation electrical
property), and the
reassembled gel quality can be better controlled.
[0057] Although an exemplary method of forming the particles is
described herein, it should
be understood that other methods of forming the particles (or variations of
the method described
herein) may be used in accordance with embodiments of the present invention.
Regardless of the
method, the resulting particles will generally be swellable and comprise cross-
linkable polymer
chains and/or assembling agents.
[0058] The resulting particles could be in four forms: turbid liquid,
emulsions, wet particles,
and dry particle gel system. The particle composition can be synthesized
either as a bulk gel and
then be dried and ground into micro-, or millimeter-sized particles, or as a
micro-particle,
submicro-particles, or nano-particles through emulsion polymerization. For
solid particles, the
particle size could be ranged from nanometer to millimeter. Typically, the
average particle size
(using the largest average dimension) of the particles is from about 10 nm to
about 10 mm,
preferably from about 800 nm to about 10 mm, more preferably from about 0.1 mm
to about 5
mm, and even more preferably from about 1 mm to about 4 mm. The preferred
weight ratio of
polymers to assembling/cross-linking agent(s) is from about 2:1 to about
200:1, more preferably
from about 5:1 to about 50:1, and even more preferably from about 5.1 to about
15.1.
[0059] Compositions comprising the quantity of fibers and the
quantity of swellable particles
may be prepared using a variety of methods in accordance with embodiments of
the present
invention. In one or more embodiments, a bulk gel composition may be prepared
having both the
fiber and particles embedded inside the gel during the synthesis process. In
certain such
embodiments, the quantity of fiber is first dispersed in the liquid carrier,
with the swellable
particles subsequently added to the dispersion. The dispersion can then be
gelatinized to form the
bulk gel composition. The embedded fiber is preferably uniformly distributed
in the gel
composition. The resulting gel composition has improved elastic modulus as
compared to RPPG
gels without fiber. This provides for improved plugging efficiency and better
flushing resistance
as compared to prior gel compositions. The fiber also provides reduced density
compared to prior
gels to assist the composition to be better placed in large openings.
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[0060] In one or more embodiments, the swellable particles may be
combined with the quantity
of dry fibers, for example a homogenous mixture of particles and fibers, and
subsequently added
to, and dispersed in, a carrier liquid prior to use. The fibers improve the
dispersion of the particles
as compared to prior particle dispersions without added fibers and form a more
complete plugging
performance in vertically oriented fractures, fractures with abnormally high
vertical aperture, or
the other large openings, to prevent gravitational convection of the particles
and poor swelling
dynamics. In certain such embodiments, the quantity of fibers is physically
mixed the quantity of
swellable particles in the presence of a carrier fluid, such a well injection
liquid or other solvent
system. The fibers are preferably uniformly dispersed in the mixture, for
example by shear
dispersion stirring.
[0061] Carrier fluids used in accordance with embodiments of the
present invention can be used
to form dispersions comprising the fibers and particles. In certain
embodiments, the carrier fluid
can also be used to cause the particles to swell, associate, and/or cross-
link, depending on the
specific application for the composition. In certain embodiments, the carrier
fluid comprises a
solvent system, preferably an aqueous solvent system. In certain embodiments,
the aqueous solvent
system comprises freshwater, brine, or other injection liquid. In certain
embodiments, the solvent
system comprises a brine solution having a salt concentration of about 0.1% to
about 25% by
weight, preferably about 0.5% to about 10% by weight, and more preferably
about 1% to about
5% by weight. In certain embodiments, the salt in the brine solution comprises
NaCl, CaCl2, and/or
AlC13).
[0062] The concentration of fibers, swellable particles, carrier
fluid, and any additives can vary
depending on the particular components used and the particular application for
the composition.
In certain embodiments, the composition comprises the quantity of fibers and
the quantity of
swell able particles at a weight ratio of about 1:1000 to about 10:1,
preferably about 1:500 to about
1:1, and more preferably about 1:100 to about 1:10 (fibers:particles).
Regardless whether the fibers
are added during gel synthesis or whether the dry fibers and particles are
mixed prior to gel
formation, in use the compositions will generally comprise (consist of, or
consist essentially of) a
quantity of fibers and a quantity of swellable particles dispersed in a
carrier liquid. In certain such
embodiments, the composition may comprise about 0.01% to about 20% by weight,
preferably
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about 0.1% to about 10% by weight, and more preferably about 0.2% to about 2%
by weight of
the quantity of fibers. In certain embodiments, higher amounts of fiber may be
used. However, for
reservoir well applications, higher levels of fiber will plug the injection
pump and thus should be
avoided. In certain embodiments, the composition may comprise about 0.1% to
about 40% by
weight, preferably about 1% to about 30% by weight, and more preferably about
5% to about 20%
by weight of the quantity of swellable particles. In certain embodiments, the
composition may
comprise about 2% to about 50% by weight, preferably about 5% to about 40% by
weight, and
more preferably about 10% to about 30% by weight of the quantity of total
solids (i.e., including
the fibers and swellable particles). The remainder of the composition will
generally comprise the
carrier fluid, such as an injection liquid or other solvent system. In certain
embodiments, the
composition comprises at least 50% by weight, preferably at least 60% by
weight, more preferably
at least 70% by weight, and even more preferably at least 80% by weight of the
carrier liquid.
[0063] In the compositions and methods described herein, the fiber
acts as a support scaffold
for the particles, which provides considerable suspension for the particles
and prevents the
particles from sedimentation. Thus, the compositions having particles and
fibers suspended therein
swells evenly and re-cross-links and/or re-associates with uniform structure
and optimum integrity.
In addition, compositions having RPPG particles with re-cross-linked polymers
and embedded
fiber have a higher elastic modulus and an improved plugging performance than
compositions
without fiber.
[0064] In use, the compositions can be dispersed by water, brine, or
other aqueous solvent or
injection liquid and pumped into formation. As noted above, the composition
may comprise
particles or gels having fibers embedded therein, or the fibers may be
separately added to RPPG
particles prior to use. For example, dry fibers may be added to RPPG particles
that are co-dispersed
into water, formation water, or brine, as an injectable phase that is pumped
into reservoirs as a
means to better control fluid flow through abnormal large opening features,
such as vertical or
inclined fractures, void conduits, and so on. The RPPG compositions act as a
barrier to fluid flow
and, upon proper placement in such a feature, will swell with water and
occlude fluid flow through
the RPPG-filled feature. The fibers within the compositions can maintain the
RPPG particles
uniformly distributed in whole large openings, with no or little settling of
the particles due to
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gravity, until the bulk gel is formed. This addresses the problem with prior
RPPG compositions
without dispersed fibers, which were do not have equal access to the water
phase of the injected
dispersion and therefore suffer non-uniform swelling with water. The fibers
maintain proper
spacing and access to all surfaces of the RPPG particles to the water phase
and promote proper,
uniform swelling and feature filling as intended by the RPPG treatments and
control of
underground water flooding operations.
[0065] During their transport through formation, all of the
components in the composition will
generally move together. After placement in the target zone, the particles
accumulate in large
fractures, channels, and/or other highly-permeable features will
proportionally release all
compositions from the particles under reservoir conditions after a designed
time, which can avoid
the problems of composition variation and/or non-uniform distribution.
[0066] Upon exposure to water, brine (e.g., aqueous NaC1, CaCl2, or
AlC13), or other solvents
and injection fluids, the particles begin to swell. It is preferred that
swelling commence within
about 0.1 seconds to about 300 seconds, and preferably within about 0.1
seconds to about 10
seconds of contact with the target fluid. The particles will swell to a size
that is at least about 20
times, preferably at least about 40 times, and more preferably at least about
100 times their initial
average particles sizes. In some embodiments, the particles will swell to a
size that is from about
times to about 200 times, preferably from about 20 times to about 200 times,
and more preferably
from about 30 times to about 100 times their initial average particles sizes.
It is preferred that these
swelling ranges be reached within a time period of from about 60 minutes to
about 240 hours,
preferably from about 60 minutes to about 300 minutes, and preferably from
about 120 minutes to
about 180 minutes of contact with the target fluid.
[0067] As the particles swell, the polymer chain network is relaxed
from its entangled state.
This relaxing exposes the assembling agent(s) and/or cross-linking agent(s),
which enables
interaction. The package can be suitable to reassociate at any temperatures
above 20 C, preferably
above 50 C (for example, with high-temperature RPPG particles). During this
swelling, the
particles associate, combine together, and form a bulk gel. That is, the
released compositions will
stick all particles together to form a thermo-stable strong gel. "Thermos-
stable" means that the
assembled gels are physically and chemically stable and will be minimally or
not at all degraded
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by reservoir environments. "Reservoir environments" refers to conditions
related to a true
petroleum ground source reservoir, including reservoir temperature, formation
liquid pH or
salinity, and formation electrical property.
[0068] In certain embodiments, the compositions may be used in
methods of altering or
controlling a fluid present in a subterranean environment, such as wells,
pipelines, pipelines, or
fractures. Generally, the method may involve introducing the composition into
a subterranean
environment, optionally via a carrier fluid such as brine or water, and
allowing the composition to
contact a particular fluid, causing the particles within the composition to
swell. In one or more
embodiments, the carrier fluid can be selected from the group consisting of
water, brine solvent
(comprising NaCl, CaCl2, and/or A1C13), and other fluids that cause the
composition to swell.
Upon contacting the fluid, an assembling agent or cross-linking agent may
associate with the
polymer chains, causing the swelling. This swelling indicates the association,
cross-linking, and/or
reassembly of the polymer chains or polymer matrix. In other words, the
swelling may cause the
particles in the composition to associate and/or cross-link, combine together,
and form a bulk gel.
In certain embodiments, the compositions may be used in CO, flooding, CO2 huff-
puff, or Water-
Alternative-Gas (WAG), CO2 storage, geotherm, pollution control, or other
hydrocarbon recovery
applications.
[0069] In one or more embodiments, the compositions of the present
invention advantageously
utilize the fibers as reinforcing agents within the compositions to provide a
stronger, particulate
plugging agent for improved underground fluid flow control. Short fibers, in
particular, added to
hydrogel materials reinforce the particles and engender added particle
strength to traditionally
weak, water swollen hydrogel polymers. The incorporation of fibers into
hydrogels does
complicate the hydrogel production technology, and creation of the particles
from synthesized bulk
gel causes recovery of the particles to be more difficult as fibers will
protrude from the drying/dried
gel particles. However, the methods described herein achieve the desired goals
of reinforcing a re-
cross-linked/re-associated hydrogel plug in underground features and supports
proper rehydration
of RPPG particles with water or brine to better and more completely fill
underground void space
conduits.
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[0070] Additional advantages of the various embodiments of the
invention will be apparent to
those skilled in the art upon review of the disclosure herein and the working
examples below. It
will be appreciated that the various embodiments described herein are not
necessarily mutually
exclusive unless otherwise indicated herein. For example, a feature described
or depicted in one
embodiment may also be included in other embodiments, but is not necessarily
included. Thus,
the present invention encompasses a variety of combinations and/or
integrations of the specific
embodiments described herein.
[0071] As used herein, the phrase "and/or," when used in a list of
two or more items, means
that any one of the listed items can be employed by itself or any combination
of two or more of
the listed items can be employed. For example, if a composition is described
as containing or
excluding components A, B, and/or C, the composition can contain or exclude A
alone; B alone;
C alone; A and B in combination; A and C in combination; B and C in
combination; or A, B, and
C in combination.
[0072] The present description also uses numerical ranges to quantify
certain parameters
relating to various embodiments of the invention. It should be understood that
when numerical
ranges are provided, such ranges are to be construed as providing literal
support for claim
limitations that only recite the lower value of the range as well as claim
limitations that only recite
the upper value of the range. For example, a disclosed numerical range of
about 10 to about 100
provides literal support for a claim reciting "greater than or equal to about
10" (with no upper
bounds) and a claim reciting "less than or equal to about 100" (with no lower
bounds).
EXAMPLES
[0073] The following examples set forth synthesis and testing of
compositions comprising
fibers and swellable particles. It is to be understood, however, that these
examples are provided by
way of illustration and nothing therein should be taken as a limitation upon
the overall scope of
the invention.
EXAMPLE 1
[0074] Polypropylene fiber with a length of 0.5 inch was mixed with 1 wt% NaC1
brine and
was stirred to form a uniform suspension mixture. Dry RPPG particles
comprising polyacrylamide
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and zirconium (IV) with a diameter 1-2 mm were swollen in the fiber dispersed
brine. The
concentrations of fiber and RPPG were 0.4 wt% and 10 wt%, respectively. The
system was stirred
for 5 minutes, when the partially swollen RPPG and fiber uniformly dispersed
in the brine. The
resulting mixture is shown schematically in Fig. 1.
[0075] Then the mixture was injected at 5 mL/min into a transparent,
non-leakage fracture
model to inspect the behavior of injection and water-plugging. The fracture
model and core
flooding setup are shown schematically in Fig. 2. The dimensions of the
fracture were 8.3 in (L) x
5.0 in (H) x 0.5 in (W). A controlled experiment without using fiber that had
all other procedures
consistent was conducted for comparison.
[0076] The 0.8 fracture volume (FV) of mixture, including partially
swollen RPPG and water,
was injection into the model in both experiments. Then the fracture model was
sealed and aged at
room temperature for four days (much longer than the re-cross-linking time)
for RPPG swelling
and re-cross-linking. 'The RPPG volume change during the shut-in time was
shown in Fig. 3, where
the red lines highlighted the gel front.
[0077] As shown in the two upper images of Fig. 3, the RPPG front was
considerably less
impacted by the gravity after being placed, manifesting as a more vertical gel
front. Additionally,
the volume of fiber assisted RPPG increased more than 1/6 of its volume after
placement, while
the RPPG without fiber only had a slight volume increase.
EXAMPLE 2
[0078] This example is a continuing of the experiments described in
Example 1. After aging,
colored brine was injected from the inlet to test the plugging performance of
placed RPPG, which
was represented by breakthrough pressure and water permeability after
breakthrough. The brine
injection pressure is shown in Fig. 4.
[0079] As shown in Fig. 4, a constant-pressure injection method was
used before reaching the
rupture pressure, at which pressure the water started to enter the RPPG-filled
fracture. The brine
was inj ected at constant pressure for a certain time and increased by a set
value when the gel pack
was not broken through. Then, the brine was injected at 2 mL/min until the
end. As shown in Fig.
4, the fiber-assisted RPPG had a higher rupture pressure, breakthrough
pressure, and constant-rate
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injection pressure, compared with the RPPG without fiber. The greater
pressures indicated an
improved performance of the fiber-assisted RPPG for resisting water flow both
before and after
breakthrough.
[0080] To demonstrate the plugging performance of RPPG more
intuitively, the flow of dyed
brine inside the transparent model is shown in Fig. 5.
[0081] In Fig. 5 (image A), the water (dyed) broke through the upper
part of gel and showed
an overriding behavior when fiber was not added. Because in this model with a
considerable
vertical aperture, the RPPG was impacted by the gravity and tended to
concentrate to the lower
space, leaving the upper space less plugged. However, as shown in Fig. 5
(image B), when the
RPPG was assisted with fiber, the gel pack was significantly more homogenous,
and therefore, the
water flowed following the shortest path between inlet and outlet. In
addition, the color of flowing
path was lighter, which suggested a narrower channel along the path. These
results visually
confirmed the plugging performance improvement of the fiber-assisted RPPG
indicated by
pressure measurement.
EXAMPLE 3
[0082] A series of tests were performed to analyze the swelling
characteristics of RPPG
compositions using different concentrations of fiber, particle sizes, and
brine compositions. First,
90g 1% NaCl was mixed with and without 0.4 wt% fiber to form homogenous
mixtures. The fiber
was a commercial SuperSweep Fiber from FortaInc. The brine was mixed with lOg
dry RPPG
(polyacrylamide/zirconium (IV)) particles 1-2 mm to form a homogenous mixture.
The mixture
was stirred for 5 minutes to simulate the blending and turbulent flow during
injection in the real
field application. As shown in Fig. 6, the gel composition comprising 0.4 wt%
fiber had a hazier
appearance compared to the composition without fiber.
[0083] The mixture was poured into the graduated cylinders and the
volume change was
inspected visually for 72 hours. As shown in Fig. 7, the particles in the
reassembled RPPG
composition without fiber settled noticeably, which resulted in an effective
volume of the particle
gel (i.e., the portion of the brine comprising suspended particles) within the
cylinder of 76-80 mL.
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In contrast, the particles in the reassembled RPPG composition with 0.4 wt%
fiber remained
suspended in the full composition, which resulted in an effective volume of
about 100 mL.
[0084] The experiment was repeated using different concentrations of
fiber in the RPPG
composition. As shown in Fig. 8, all tested compositions (0.1 wt%, 0.2 wt%,
and 0.4 wt%) showed
improved volume retention compared to the composition tested above without
fiber. However, 0.2
wt% and 0.4 wt% fiber showed superior results (100 mL volume) compared to 0.1
wt% fiber.
[0085] The experiment was repeated using 1-4 mm RPPG particles (50% 1-
2 mm, 50% 2-4
mm), 2% KC1 brine, and 0.5 wt% fiber concentration. Similar to the fiber-
containing compositions
above, the particles remained suspended in the full composition, which
resulted in an effective
volume of about 100 mL.
[0086] The experiment was repeated using 1% NaCl brine, a fiber
concentration of 0.2%, and
different particle sizes. As shown in Fig. 9, all tested compositions (0.5-1
mm, 1-2 mm, and 2-4
mm) showed improved volume retention compared to the composition tested above
without fiber.
However, the smaller particles (0.5-1 mm and 1-2 mm) showed superior results
(100 mL volume)
compared to the larger particles (2-4 mm). A higher fiber concentration is
likely needed for larger
particles to remain suspended.
[0087] The experiment was repeated using 1-2 mm RPPG particles, 1%
NaCl brine, a fiber
concentration of 0.2 wt%, and nylon fibers of varying lengths (1.3 cm, 0.65
cm, 0.43 cm). As
shown in Fig, 10, fiber length did not noticeably affect the RPPG swelling.
EXAMPLE 4
[0088] Water plugging performance was tested and compared for conventional
PPG, RPPG
(without fiber), and fiber assisted RPPG (from Example 1). The testing
apparatus was the fracture
model used in Example 1 above. The inj ectivity (as evidenced by pressure) of
each composition
is shown in Fig. 11. As shown in Table 1 below, the permeability of the fiber
assisted RPPG was
superior to the RPPG, which was superior to the convention RPPG for all flow
rates.
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Table 1.
Flow rate Conventional PPG R.PPG Fiber As:sisted
RPPG
2 ruLimin 2505.3 Ind 120.0 Ind 70.1 Ind
3 inlimin 2846.5 /lid 149.1 nici 97,8 rud
ruLlarin 3131.1 Ind 214.5 rucl 125.2 rad
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